Water Treatment Handbook by ADIL

Water Treatment Hand BookPREFACE Aqua Designs was started with the mission of providing eco friendly solutions which will be useful for individuals, industries and also to nature. Since its inception, Aqua Designs has offered successful solutions on environmental perspective which has created a unique place in the industrial sector. The vision of MD Mr. Suthakar is to spread the message of harvesting water, reducing its usage, recycling and reuse. This vision transformed into collection of data on water and its uses and sharing this knowledge with one and all in order to make this world a lively place to live. .......... and hence this book. With best compliments from S. Suthakar Managing Director – Aqua Designs ABOUT US Aqua Designs – Offers A to Z solutions for water and waste water treatment. A one Stop Shop for all types of consultancies in water and waste water management. Aqua Designs commitment to the environment, keeps it in the forefront of product innovations, purification and recycling technologies. Aqua Designs provides water solutions for Institutions, Industry, Municipal Authorities, and Commercial and Public properties. The Company boasts of the widest range of specialty water-related products and services that are ISO 9001:2000 certified by RINA of Italy. Aqua Designs was the proud recipient of the prestigious Award for The “Best Upcoming Water Company 2006 – 2007”given by the magazine Water Digest in association with UNESCO, NDTV Profit & WES-Net India in order to acknowledge those persons and Organizations, who have contributed toward water and its industry. Aqua Designs was also the proud winner of the Awards for “Best Water Treatment Project – Industrial 2007-2008” & “Best Water R&D and Technological Breakthrough 2007-2008” instituted by Water Digest. For the year 2008-2009, Aqua Designs added one more feather in its cap. It bagged two more Awards instituted by the Water Digest for the categories Best Consultancy & Best Water Conservation IT Park showing its strength in IT Sector using MBR Technology. A proven track record of offering A – Z solutions was appreciated and the Best Consultancy Award is the proof for that. The Company has excellent marketing and sales team with a cumulative experience beyond 100 years. It is one of the major reason for Aqua Designs entering big corporate and Multi National Companies. Due to its expertise the Company is able to offer competitive Designs and proposals, which keeps the competitors at bay .This proven technology has made the company one of the front runners in this field. Aqua Designs success depends on its human resources. From Designs, Proposals, Projects, Erection and commissioning to operation and maintenance, it has proved its capability in the market which gives them a clear edge over others in the market. Aqua Designs is supported by its own State-of-the-Art Laboratory for testing water, waste water, air & stack samples both for physiochemical and microbiological parameters as per PCB norms and IS standards. We have the facility to monitor stack emissions and ambient air quality...The facility is certified under ISO 9001:2000. The Laboratory handles and supports all in house requirements; specific client needs and also offers Pilot Plant studies. Aqua Designs provides services starting from EIA to Designs to implementation of Projects to Operation & Maintenance to Supply of Specialty Chemicals to run the operations and finally to analyze the various products of the treatment using its Laboratory facility. Aqua Designs also has its own chemical manufacturing and fabrication facilities to support its growing needs in business. Aqua Designs was formed with the sole intention of suggesting eco friendly solutions for Industries and Municipalities. The vision was to provide solutions to varied sectors in par with the developed nations. Aqua Designs not only offers the concepts and design to their customers, but also stay with the customer and successfully operate the scheme for years. The customer satisfaction has lead Aqua Designs to be successful in various types of Industries ranging from Petrochemicals, Automobile, Food and Beverages, Breweries and Distilleries, Chemicals, Electronics, Power Industries etc. Aqua Designs believes only in continual improvement. It keeps offering innovative solutions to its customers. One such is the concept of Membrane Bio Reactors technology for treating the Sewage. Aqua Designs has now set a trend such that big IT Parks have started using MBR Technology. Aqua Designs is leaping forward like a giant and nothing can stop it. In the near future it aspires to be a Global leader. Aqua designs “believes in Better the Best” and this has made everything possible. CHAPTER 1 Impurities in Water................................ ................................................................ ...................... CHAPTER 2 Filters ................................................................ ................................ ........................................... CHAPTER 3 Iron Removal Filters ................................ ................................................................ ..................... CHAPTER 4 Ion Exchange ................................ ................................................................ ................................ CHAPTER 5 Softener ................................................................ ................................ ....................................... CHAPTER 6 Membrane System................................ ................................................................ ....................... CHAPTER 7 Steam Boiler ................................ ................................................................ ................................ CHAPTER 8 Cooling Water Treatment................................ ................................ ................................ ............. CHAPTER 9 Pumps ................................................................ ................................ .......................................... CHAPTER 10 Raw Water Treatment ................................ ................................................................ ................. CHAPTER 11 Industrial Waste Water Treatment ................................................................ .............................. CHAPTER 12 Chemical Cleaning................................ ................................................................ ........................ 1 8 13 17 36 40 49 62 79 84 92 97 WATER SAMPLE TEST PROCEDURES ................................................................ ........................ 107 Phenolphthalein (P) Alkalinity Test Procedure ................................ ................................ ........ 109 Total (M) Alkalinity Test Procedures ................................................................ ....................... 110 Conductivity Test Procedure ................................ ................................ ................................... 112 pH-Electrometric Method Test Procedures ................................................................ ............. 113 Total hardness Test Procedures ................................................................ .............................. 114 Sulphite testing procedure ................................ ................................ ...................................... 115 Chloride Test Procedure ................................ ................................ ................................ .......... 116 Checking Acid Solution Strength for Cleaning ................................ ................................ .......... 117 UNITS AND MEASUREMENT CONVERSION ...................................................... 118 BASICS................................................................ ................................ ..................................... 119 CHAPTER 1 01 Impurities in Water Water impurities Impurity in water technology is a relative term. For example Hardness is not considered as an impurity in drinking water but in industrial water treatment it leads to scaling of equipment and hence considered as an impurity. Common impurities in water, their effect and method of removal are as follows: Impurities Turbidity Suspended silica Effect Can clog pipelines and equipment can choke Ion exchange resin and RO membranes Indication of organic, iron etc. and can be harmful to the unit operation ahead. Can foul Ion exchange resins membranes and may be detrimental to process. Will depend upon the type of bacteria, can induce corrosion and also harmful to RO membrane. Red water, corrosion, deposit, interferes with dyeing, bleaching etc. Method of removal Coagulation, and filtration setting Color Coagulation, settling filtration, followed by activated carbon filter. Coagulation, setting, filtration, followed by activated carbon filtration. Coagulation, filtration, setting and super chlorination, UV, ozonation Aeration, coagulation, filtration, filtration through Manganese Zeolite Ion exchange, addition of acid or alkali. Ion exchange Lime Soda Organic matter Bacteria Iron pH High pH or low pH can both induce corrosion. Scaling, cruds with soap interfere with dyeing and also harmful to other process. Calcium, Magnesium (Hardness) 02 WATER TREATMENT HAND BOOK Impurities Sodium Effect Unharmful when low in concentration, increase TDS, high concentration can induce corrosion. Corrosion, foaming and carry over Method of removal Ion Exchange through cation H+ resin. Reverse Osmosis Bicarbonates, Carbonates, Alkalinity, Hydroxide (Alkalinity) Acid addition Ion Exchange by WAC Resin Split stream by hydrogen cation resin Degassification after step 2 and 3 Ion Exchange Reverse Osmosis Evaporation Electrolysis. Ion Exchange Reverse Osmosis Evaporation Electrodylasis. Ion Exchange Reverse Osmosis Sulphate Scaling if associated with Calcium, harmful in construction water. Corrosion Chloride Nitrate Normally not found in raw water. Harmful in food processes (especially baby food). Scaling and deposition on equipment. Corrosion Silica Ion Exchange Carbon Dioxide Open aeration, Degasification, and Vacuum deaeration. Aeration, filtration through Manganese Zeolite, aeration plus chlorination. Deaeration Addition of chemicals likes sodium sulphite or hydrazine. Hydrogen Sulphide Corrosion Oxygen Corrosion 03 Impurities Ammonia Effect Corrosion especially of Copper and Zinc Method of removal Aeration Hydrogenations exchange if ammonia is present in Ionic form. By adding chemicals Activated carbon Free chlorine Corrosion Definition of Terms Total Cations= TC= Ca++ + Na+ all as CaCO3 Total Anions=TA=T Alkalinity + Cl + SO4-- + NO3 all as CaCO3 Total Hardness=TH= Ca++ + Mg++ as CaCO3 Total Alkalinity=T.Alk= HCO3 - + CO3-- + OH- all as CACO3 EMA= Cl- + SO4-- + NO3- all as CaCO3 Total Acid Ions=EMA + CO2 + SiO2 all as CaCO3 Total electrolyte=TE=TC=TA Total dissolved solids=TDS=TE + SiO2 Total electrolyte: Electrolytes are strongly ionized compounds. TE is numerically equal to either TC or TA (not some of both). SiO2 and CO2 being weekly ionized are not included in total electrolyte. Leakage: Electrolyte or silica passing through the demineralizing unit due to incomplete ion exchange. Conductivity: The ability of a solution to carry current. Conductivity measurement is used to indicate the purity of water. It is measured as micro mhos or micro siemens/cm. Resistivity: Resistivity is a measurement used for ultra pure water. Its unit is megohm. Resistivity is reciprocal of conductivity Water Analysis Format The following format which has been shown is for ease of designing calculation where total cation or anion can be easily seen, matched for correction of analysis and also for designing the Ion Exchange units. Water testing laboratories normally do not give analysis for many ions in CaCO3 units; example Chloride ion, given as Chloride (mg/liter) which should be converted to CaCO3ppm units, by multiplying by 1.41. Similar other ions, which are not mentioned in CaCO3 units, should be converted to CaCO3 units. 04 WATER TREATMENT HAND BOOK Substance Symbol Example Substance Symbol Example Calcium Magnesium Ca++ Mg++ 125 105 Bicarbonates Carbonates, Hydroxides Chlorides Sulphate Nitrate HCO3CO3-OHClSO4-No3- 150 0 0 100 80 0 Sodium Potassium Na+ K+ 100 0 Total Cation TC 330 Total Anions TA 330 Total Hardness Ca + Mg 230 Alkalinity HCO3- + CO3-- + OHClSo4– No3- 150 Equivalent Mineral Acidity All the above are expressed as ppm CaCO3 Iron Fe express ed in mg/liter as Fe 0.5 Silica Carbon Dioxide 180 SiO2 Co2 20 15 Substance Turbidity Colour Total Dissolved Solids Suspend Solids Acidity/Alkalinity NTU Hazen Ppm Ppm pH Unit Example 5 NTU 5 Hazen Unit 350 ppm 20 ppm 7.3 05 Conversion Factors for conversion to Calcium Carbonate (CaCO3) Ions Symbol Ionic weight Equivalent weight To convert to CaCO3 multiply by CATIONS Aluminum Ammonium Barium Calcium Copper Hydrogen Iron (Ferrous) Iron (Ferric) Magnesium Manganese Potassium Sodium Al+++ Nh4 + Ba ++ Ca+ Cu++ H+ Fe++ 27.0 18.0 137.4 40.1 63.6 1.0 55.85 9.0 18.0 68.7 20.0 31.8 1.0 27.8 5.56 2.78 .728 2.49 1.57 50.0 1.80 Fe+++ Mg++ Mn++ K+ Na+ 55.85 24.3 54.9 39.1 23.0 18.6 12.2 27.5 39.1 23.0 2.69 4.10 1.82 1.28 2.17 06 WATER TREATMENT HAND BOOK Ions Symbol Ionic weight Equivalent weight To convert to CaCO3 multiply by ANIONS Bicarbonate Bisulphate Bisulphite Carbonate Chloride Fluoride Hydroxide Nitrate Phosphate (monovalent) Phosphate (divalent) Phosphate (trivalent) Sulphate Sulphide Hc03HSO4HSO3 Co3– ClFOHNo3H2PO461.0 97.1 81.1 60.0 35.5 19.0 17.0 62.0 97.0 61.0 97.1 81.1 30.0 35.5 19.0 17.0 62.0 97.0 0.82 0.515 0.617 1.67 1.41 2.63 2.94 0.807 0.516 HOP4– 96.0 48.0 1.04 Po4— 95.0 31.7 1.58 So4– S– 96.1 32.1 48.0 16.0 1.04 3.12 Sulphite So3– 80.1 40.0 1.25 07 CHAPTER 2 08 WATER TREATMENT HAND BOOK Filters Basic Operation of Filter The basic operation of Pressure Filter, Dual Media Filter and Activated Carbon and iron removal filters is same. All Units operate in down flow mode, where the water enters from the top, percolates through the media and treated water is collected from the bottom. Sequence of Operation u Service: The water to be filtered enters from the top of the shell, percolates downward through the media and is drawn off from the bottom. u Backwash: The water enters from the bottom of the vessel, passes through the media and is drained from the top. This is called BACKWASH and it is done to carry the dirt accumulated on the top. Generally back washing is done once in every 24 hrs or when the pressure drop exceeds 8 psi. (0.5 kg/cm2). Rinse : The water enters from the top passed through the media and is drained off from the bottom. Dirty Water Raw Water Filter Media Collecting System Treated Water Filter Media Collecting System Raw Water Backwash Note When activated carbon is installed in a vessel, it should be soaked for 12 to 24 hours to remove trapped air and back washed to remove fines and stratify the bed. A necessary maintenance item, periodic back washing removes solids trapped in the carbon bed, as well as fine carbon particles. Since the dechlorination reaction oxidizes the carbon surface, which slowly breaks down the carbon structure, back washing is especially important in de-chlorination applications. Frequency is determined by the solids content of the feed water. Tests on activated carbon dechlorination systems indicate that regular back washing of carbon beds helps preserve the dechlorination and filtering efficiency. By back washing regularly and expanding the carbon by at least 30 percent, fouling or binding of the carbon bed does not occur. 09 CAUTION Wet activated carbon removes oxygen from air. In closed or partially closed containers and vessels, oxygen depletion may reach hazardous levels. If workers must enter a vessel containing activated carbon, appropriate sampling and work procedures for potentially low-oxygen spaces should be followed as required by salutatory requirements. Thumb rules for designing a filter Calculate area of vessel by required volumetric flow rate and the velocity as mentioned in the following table. Area (m2) = Volumetric Flow Rate (m3/hr)/ Velocity (m/hr) (1) Based on above calculated area calculate diameter of the vessel by the following formulae: Diameter (m) = [Area (m2)/ 0.785] ½ (2) Parameters Sand Filters 7.5 – 12 0.45 - 0.6 (fine sand) 1.6 max 2650 Dual Media Filters 12-20 0.65 - 0.76 (Anthracite) 1.85 1600 Activated Carbon 15-20 0.35 - 0.5 Velocity (m3/m2/hr) Effective size of Media (mm) Uniform coefficient Density (kg/m3) <2(115 typical) Other requirements Parameters Loss of head Length of run between cleaning Method of cleaning Amount of wash water Time for back washing Time for air scouring 0.03 M for clean bed to .2 to 3 M final 12 to 24 hours or when the pressure drop across the bed reaches 0.5 Kg/cm2 Back washing at rate of 36 M/Hr or 24 m/hr with air scouring at 36 M/hr at 0.35 to 0.5 kg/Cm2 pressure 1 to 4 % 10 to 20 minutes 2 to 5 minutes 10 WATER TREATMENT HAND BOOK Important points on Filter: u Normally, pressure sand filter is used to filter suspended solids upto 30 ppm and dual filter for 50-55 ppm and water with higher suspended solids would require coagulation. Output quality of water from Pressure Sand Filter is 25 to 50 microns. u Normally, velocity for Sand velocity is taken for water treatment / residential filter are taken from 7.5 to 18 M3/M2/hr; for institutional filters 20 to 30 u M3/M2/hr. For recirculation of water like swimming pool velocities can be taken greater than 35 M3/M2/hr for low turbidity application u velocity will induce higher head loss through the bed and Higher frequency of backwash will increase.Back washing of filter should always be carried out using clean water. u Whenever air scouring is provided, it should be done before back washing step. u strainers are provided at bottom, pebbles and gravels need Where not be put. Quantity of Media Quantity of media is Calculated in Cubic Meters (M3) and then converted to Kgs The depth for various media is Sand/ Anthracite 540 mm Crushed Gravels 100 mm Pebbles (1/2 to1/4) 100 mm Media Height Pebbles (1 to1/2) 100 mm Pebbles (11/2 to 1/4) 160 mm Volume = Area* (depth/1000) Trouble Shooting of Filters PROBLEM Turbidity Breakthrough Loss of media CAUSE Change in Raw water Broken Laterals High backwash flow REMEDY Analyze water Backwash Change the laterals or rectify. Control Backwash Give Backwash If backwash does not solve problem give extended backwash Change Filter media if Step 1 & 2 does not work Air Scour & Give extended backwash Check pretreatment if any Decrease Velocity Change Media if nothing of above works. High Pressure Drop across Bed Media Dirty Mud Ball Formation Change in Raw Water Quality 11 Filter Details u velocity is at 36 M / Hr at pressure is 0.5 Kg / cm2 Blower u minimum service Velocity is 7.5 M/ Hr u service Velocity is 9.0 M/Hr Normal u Maximum service Velocity is 7.5 M/ Hr u Backwash velocity For Air scour type 24 M/Hr u Backwash velocity For Non Air scour type 24 M/Hr u of Media is 2600gm/cc Density Model Diameter in mm Bed Area in M2 Height on straight (HOS)in M HVT Height on straight (HOS) in M for Air scour type Bed Depth in Meters Service Flow (mini) M3/Hr Service Flow Normal) M3/Hr Service Flow (Maxi) M3/Hr BW Flow M3/Hr For Air Scouring type 500 0.20 600 0.28 800 0.51 1000 1200 1400 1600 0.79 1.13 1.54 2.01 1800 2000 2200 2.54 3.14 3.80 1500 1500 1500 1500 1500 1500 1500 15 00 1500 1500 1400 1400 1400 1400 1400 1400 1400 1400 1400 1400 1 1 1 1 1 1 1 1 1 1.5 2.1 3.83 5.93 8.48 11.5 15.08 19.05 23.55 28.50 1.8 2.52 4.59 7.11 10. 17 13. 86 18. 09 22. 86 28. 26 34. 20 2.0 2.8 5.1 7.9 11.3 15.4 20.1 31.4 25.4 38.0 4.8 6.72 12. 24 18. 96 27. 12 36. 96 48. 24 60. 96 75. 36 91. 2 12 WATER TREATMENT HAND BOOK CHAPTER 3 13 Iron Removal Filters Many water supplies contain quantities of iron & manganese that may be detrimental to number of domestic and industrial use if not removed. Iron & manganese removal is very important pretreatment step in Ion Exchange & R.O. treatment. umanganese exists in water in the following forms Iron & u Insoluble iron & manganese u iron & manganese Soluble u iron & manganese Organic u Combination of all three Depending on the type of iron present in water different treatment methods are adopted. S.No Type of impurity Insoluble iron & manganese Removal method No oxidation required. Simple Coagulation in solid contact Unit followed by filtration Oxidation by air, chlorine & filtration Lime / Lime soda softening Ion Exchange Coagulation by alum, settling Manganese zeolite 1 2 Soluble iron & manganese 3 4 Organic bound iron Combination of three above Manganese Zeolite (manganese Greensand) Manganese zeolite is a natural green sand coated with manganese oxide that removes Iron & manganese from solution. The greensand is processed by treating with manganous sulfate and then with potassium permanganate. This results in the higher Oxides of manganese in and on the green sand granules. The resultant greensand is a manganese zeolite with following characteristics. Parameter Colour Density Effective size Uniformity coefficient Mesh size Attrition loss per annum % Bed Depth (minimum) Freeboard Service flow rate Backwash flow rate Black 1360Kg/M3 0.30- 0.35 mm 1.6 16—60 2—4 % 700 mm of greensand and 300mm of anthracite 50% of bed depth 5 –12 M3/hr/M2 20—25 M3/hr/M2 14 WATER TREATMENT HAND BOOK Removal process Manganese zeolite process is used in conjunction with above process when the concentration is more or as a standalone process if the concentrations of Fe & Mn are low. There are two methods, which is normally employed for removal of Fe & Mn by Manganese zeolite. u Batch process (intermediate Regeneration) u Continuous KMnO4 feed system Batch process (intermediate Regeneration) The regenerative batch process uses Manganese zeolite both as oxidizing source and also as filter media. After the zeolite is saturated with metal ions, it is regenerated with KMnO4 (potassium per manganate). This process has its limitation. Batch process is employed when the concentration of iron & manganese is small (i.e. < 2 PPM) and also if the flowrate required is not very high. (Flow rate limited to about 5-6M/Hr) The capacity of manganese zeolite is (0.09lbs iron or manganese / Cu Ft) And the regeneration is done by 0.5 % KMnO4. The amount of KMnO4 required is about (0.18lbs of KMnO4 / Cu Ft of media). Backwashing at 20-25 M3/Hr /M2 is done once in 24 hours or when the pressure drop across the bed reaches to 7-8 psi, whichever is earlier. Continuous KMnO4 feed system: Batch process is still used but is being replaced quite rapidly by continuous feed system. In this process KMnO4 solution is added before the pressure filter that contains dual media and manganese zeolite. The Anthracite on the top of Manganese zeolite acts as a filter and removes the iron & manganese oxidized by permanganate. MnO2 oxidizes the residual ions that are not oxidized by permanganate. MnO2 also removes excess KMnO4. When the bed gets saturated with metal oxides, it is backwashed to remove all particulate matters. Reaction times Permanganate is fed as 1-2 % solution directly to the inlet line. Contact time for oxidation is about 20—60 seconds; hence it is fed 20 '(50-60 mm) upstream from the zeolite bed Alkali is added to low pH water for optimum removal but utmost care should be taken during alkali addition due to precipitation problem KMnO4 is used either in conjunction with chlorine or alone. KMnO4 dosage differs depending on whether it is used alone or with chlorine. 15 Dosage of KMnO4 With chlorine 1 mg/liter ofCl2 / 1ppm of Fe KMnO4 mg/liter = (0.2mg/literKMnO4 for 1ppm of Fe) + (2 mg/liter of KMnO4 for 1ppm Of Mn) + (5mg/liter of KMnO4 for1ppm of H2S) Without Chlorine KMnO4 mg/liter = (1.mg/literKMnO4 for 1ppm of Fe) + (2 mg/liter of KMnO4 for 1ppm Of Mn) + (5mg/liter of KMnO4 for 1ppm ofH2S) Birm Birm is another type of manganese dioxide. It is a silicon dioxide core that has been coated with manganese dioxide. This makes Birm much lighter than its ore counterpart, less than 400gms/liter. The benefit of this type of product is that it can be backwashed at a flowrate of 0.8Kg. / Liter. Birm does require dissolved oxygen in the water for the precipitation of iron, where the manganese dioxide ore does not. Birm relies on its ability to act as a catalyst between iron and oxygen. It has a limited amount of MnO2 available, so it does not have the ability to supply oxygen through a redox reaction. The oxygen content should be, at least, equivalent to 15% of the total iron content. If the oxygen content is less than 15%, aeration is required. Birm is recommended on levels of iron less than 10 ppm. It can be utilized on higher concentrations, but the frequency of regeneration (backwashing) becomes excessive. Birm has a capacity of approximately 900 -1100 grams/Cu meter. It can treat up to 3 cubic meters of water containing 10 ppm Fe as CaCO3. Birm should not be used on waters that have oil or hydrogen sulfide, and the organic matter should not exceed 5 ppm. As with any product, consult the manufacturer for operational guidelines. (Sybron Chemicals). 16 WATER TREATMENT HAND BOOK CHAPTER 4 17 Ion Exchange Ion Exchange Load Calculation Let us take the following examples Feed water analysis as ppm CaCO3 Cations Calcium Magnesium Sodium Potassium Iron Total Unit as ppm CaCO3 210 40 120 5 0 375 Total 375 Anions Bicarbonate Chloride Sulphate Nitrate 200 70 85 20 Free CO2 - 15, Silica – 5 Ion Exchange load w.r.t different unit operation Unit Operation Softening Dealkaization Strongly acid Cation(TC) Weakly Basic Anion Strongly acid Cation after dealkalization Strongly Basic Anion after WBA Strongly Basic Anion Strongly Basic Anion after Degassing Strongly basic Anion after degassing and WBA Ion Exchange Load Total Hardness (Ca +Mg) HCO3 Total Cations (Ca+Mg+Na+K) EMA (SO4+Cl+NO3) Total Cations – Carbonate Hardness Total Anions – EMA Total Anions (Cl+SO4+NO3+SiO2) (Alkalinity + CO2) Total Anion – (T.Alk + EMA ) +SiO2 Concentration (as ppm CaCO3) 250 200 375 175 175 225 375 185 (assuming 5 ppm leakage of CO2) 10 ppm (assuming 5 ppm leakage ) 18 WATER TREATMENT HAND BOOK Ion Exchange load w.r.t different unit operation utotal cations to total cations to total Anions. They should be equal. Match (Error of +_ 5% can be considered) u the table for calculating the Resin Quantity. The Ion Exchange Refer to load can be taken as mentioned in the table. Ion Exchange Resin Quantity (liters) = [Flow (m3/hr)* Ion Exchange load(ppm)* Time] / Ex.capacity of Resin (gms/liter) Sizing consideration for Ion Exchange System Parameters Velocity* Bed Depth Cation 15-20 M/hr Anion 15-20 M/hr Mixed bed 30-44 M/hr Degassifier 50-70 M/hr 2400-3600 1000-2000 mm mm 60-100% 900-2000 mm 900-2000mm Free Board * 60-100% 60-100% Type of Hub/radial Hub/radial Hub/radial Rasching rings Internal Strain on plate Strain on plate Strain on plate Pall rings Approximate regenerate Level and operating Capacity Parameters Regeneration level gm/L Cation Regeneration level gm/L ANION EC for CATION gm CaCO3/L EC for ANION gm CaCO3/L 110 54 50 35 25 WAC 110 SAC 80 55 80 80 WBA SBA Type 1 SBA Type 2 MB 80 80 40 20 Design parameters Parameters Regenerant flowrate Total rinse Unit M3/Hr/M3 BV WAC 4 5 1.5 6 16 SAC 4.8 5 1.5 9 16 WBA SBA Type 1 SBA Type 2 2.1 5 1.5 6 8 4 5 1.5 6 8 4 5 1.5 6 8 Displacement BV Rinse Backwash M3/Hr/M2 velocity Fast Rinse M3/Hr/M3 19 4 % NaOH contains 41.75 gms NaOH per liter 50 % NaOH contains 763 gms NaOH per liter 99% NaOH contains 803 gms NaOH per liter 4 % HCl contains 40.72 gms HCl per liter 32 % HCl contains 479.2 gms HCl per liter Ion exchange systems Following different schemes of DM / Ion exchange systems are possible depending upon the application and the outlet water quality required Note: u parameters on the quality of water required in various Detailed industries is given in Chapter 9. u SA – Strong Acid Resin (H+) u SA*- Strong Acid Resin (Na+) u WB – Weak Base Anion Resin u D – Degasser u SB – Strong Base Anion Resin u WC – Weak Acid Cation Resin u MB – Mixed bed (mixture of Strong Acid Cation Resin (H+) and u base anion resin (OH-) strong # Type Of DM/ Ion Exchange Systems Application Removal of silica, removal of CO2 is not required Where CO2 and silica removal is required, low alkalinity water Where CO2 content is high, i.e. high alkalinity water Outlet Water Quality Conductivity < 50 micro mhos 1 SA WB 2 SA SB Conductivity < 30 micro mhos, silica < 0.5 ppm Conductivity < 30 micro mhos, silica < 0.5 ppm 3 SA D SB 4 SA D WB SB EMA and alkalinity Conductivity < high in raw water 30 micro mhos, silica < 0.5 ppm 20 WATER TREATMENT HAND BOOK 5 WC SA D WB SB High EMA and high alkalinity in raw water Hardness > =1 Alkalinity Softening, where only hardness to be removed Conductivity < 30 micro mhos, silica < 0.5 ppm 6 SA* Hardness less than 5 ppm as CaCO3 7 WC D Dealkalization when only temporary hardness is present Dealkalization alkalinity with permanent hardness 8 SA* SA D 9 MB1 10 MB1 MB2 Low conductivity water required MB is installed after SBA When ultrapure water is required for pharmaceutical or electronic industries 10 % of the influent alkalinity TDS reduction upto alkalinity removal 10 % of the influent alkalinity TDS reduction alkalinity removal Conductivity < 1 micro mhos, silica < 0.002 ppm Conductivity < 0.02 micro mhos, resistivity 14-18 mega ohms silica < 0.002 ppm Service Raw Water is passed through ion exchange unit till the required quality of water is being produced. This is known as service cycle. When the resin stops producing desired quality water, the Resin is said to be exhausted and will have to be regenerated. Service flow can be down flow (top to bottom) or upflow (bottom to top). Regeneration The restoration of resin back to its original form is called Regeneration. Depending upon the resin, regeneration is usually done by using acid, alkali or common salt. These chemicals are known as regenerant. Sequence of Regeneration for down flow unit is :1. Backwash 2. Chemical injection 3. Displacement (slow rinse) 4. Fast rinse or Final rinse In the up flow unit upward wash is only done for a minute or so. 21 Operation of Ion Exchange unit Downflow Coflow Regeneration 2 Backwash Chemical Injection 3 4 1 2 3 4 5 Raw water Backwash outlet Chemical Injection inlet Power water for ejector Drain for chemical and final rinse Regeneration Tank 1 5 Slow Rinse 3 Fast Rinse 1 4 5 5 22 WATER TREATMENT HAND BOOK Upflow Countercurrent Regeneration Chemical Injection Slow Rinse Regenerant Flow 4 3 5 Power Water Drain 3 Power Water 5 Drain 2 Final Rinse 2 6 6 Final Rinse Raw water or feed water Raw water or feed water 1 Final Rinse 1 23 Typical Regeneration Efficiencies for different type of resins Resin Type / Configuration Regeneration System Co-current HCl Counter-current HCl Co-current H2SO4 Counter-current H2SO4 Typical Regeneration Efficiencies (%) 200-250 120-150 250-300 150-200 105-115 105-115 Co-current Counter current Co-current Counter-current 250-300 140-220 150-200 125-140 120-150 Strong Acid Cation Weak Acid Cation Weak Acid Cation + Strong Acid Cation Strong Base Anion Type 1 Strong Base Anion Type 2 Weak Base Anion Typical Regeneration level ranges for single resin column Regenerant System Regenerant Level g/liter Co-current Regeneration Hcl H2SO4 NaOH 60 - 80 60 - 80 60 - 80 Typical operating capacity mg/liter 40 – 60 45 – 65 30 – 40 Counter current Regeneration Hcl H2SO4 NaOH 60 - 80 60 - 80 60 - 80 50 – 70 55 – 75 55 – 75 24 WATER TREATMENT HAND BOOK Design Guide lines for Operating and Designing Resin System Parameter Swelling Strong Acid Cation Na → H Weak Acid Cation H → Ca Strong Base Anion Cl → OH Weak Base Anion Free base → Cl Bed Depth Minimum Cocurrent single Resin Counter current Single Resin Backwash Flow Rate SAC Resin WAC Resin SBA Resin WBA Resin Flow Rates Service/Fast Rinse Co-current Regeneration Counter- current Regeneration Total Rinse Requirements SAC Resin WAC Resin SBA Resin 750 mm 1000 mm Guideline 5-8 % 15-20 % 15-25 % 15-25 % 10-25 M/hr 10-20 m/hr 5-15 M/hr 3-10M/Hr 5-60M/hr 1-10 M/hr 5-20M/hr 2-6 3-6 3-6 2-4 Bed Bed Bed Bed Volumes Volume Volume Volume Note:- These are only for help. Actual data should be obtained from the resin manufacturer. Most resins have similar data. Degasser The forced-draft degasifier blows an air stream countercurrent to the water flow. The undesirable gas escapes through the vent on the top of the aerator. A disadvantage to this process is that the water is saturated with oxygen after aeration. 25 Packing Data Ring Size mm Number of rings in 1 M3 of random packing Free Volume M3/M3 Packing Surface Area M2/M3 Hydraulic radius of passage Equivalent Diameter of Packing D=4r Mass of 1 M3 of rings Kg 25 X 25 X 3 35 X 35 X4 50 X 50 X4 53200 0.74 204 0.00363 0.01452 532 20200 0.74 140 0.00555 0.02220 505 6000 0.785 87.5 0.00900 0.0360 530 Ceramic Raschig ring – There are 145 pieces of raschig ring per liter. The ring size is 38 mm X 38 mm and weighs about 6 kg. 26 WATER TREATMENT HAND BOOK Degassifier Height and Raschig rings Heights Inlet CO2 ppm 500 Outlet CO2 ppm 8 5 2 8 5 2 8 5 2 8 5 2 8 5 2 8 5 2 Degassifier Heights Meters 4.26 4.90 5.49 3.65 4.26 4.90 3.65 3.65 4.26 3.04 3.65 4.26 2.43 3.04 3.65 2.43 3.04 3.65 Raschig rings Heights Meters 2.90 3.20 3.96 2.29 2.59 3.35 2.00 2.43 3.04 1.67 2.13 2.89 1.21 1.67 2.43 1.21 1.37 2.13 200 150 100 50 35 Degassifier Flow & Area (velocity taken is 60 m3/h/m2) Degassifier Cross Sectional Internal Diameter Required air flow 3 Flow M3/Hour Area in M2 Of degasser in mm rate in M /Hour 0.083 75 5 325 7.5 0.125 112.5 400 10 12.5 15 17.5 20 22.5 25 27.5 30 35 40 45 50 0.167 0.208 0.250 0.291 0.333 0.375 0.416 0.458 0.500 0.583 0.667 0.750 0.833 460 512 560 600 650 691 728 764 800 862 925 977 1030 150 187.5 225 262.5 300 337.5 375 412.5 450 525 600 675 750 27 Failure to produce specified quality of water The failure to produce specified quality treated water will depend upon the specific Ion Exchange unit. The causes for deteriorating water quality from each Ion Exchanged bed are given in the tabulated form. Quality of water can also deteriorate due to resin fouling. Various types of foulants which can contaminate the Ion Exchange resin. Defects 1.Change in Raw water Composition Causes Increase in TDS % change in Na/TC or Alk/TA Flow meter not working or out of calibration Conductivity meter not working or working inaccurately Insufficient chemical Weak regenerant (less Chemical or too much dilution water) Poor distribution of regenerant Ejector not functioning or Chemical going very slowly Remedies Obtain new water analysis and Set water meter to new capacity. Calculate new capacity to the increased load. Check, rectify or replace Check power to conductivity meter Calibrate meter Cell dirty, Replanitinize. Check and follow proper regeneration Check and rectify. Faulty internal distributor or broken strainer on top in pack bed system.Insufficient power water flow at required pressure to ejector Check rubber lining above ejector, check for chokage in ejector, air lock in vessel or if every thing is ok change faulty ejector. Reduce Backwash flow rate. Dechlorinate. Check performance of ACF Unit. If no ACF unit is there, use reducing agent (like sodium sulphite). Check & Rectify. Do not exceed specification Check for resin in effluent or resin or in resin trap.. Change strainer Rectify bottom distributor. This happens sometime during injection. Take care Service cycle Exceeding Specification Faulty regeneration Loss of ion exchange Resin High Backwash in Downflow system Chemical attack by Oxidizing agent like chlorine Excessive high pressure flow rate Broken Strainers in Upflow system/ Upset supporting bed or damaged underdrain. Air sucking through ejector in Pack bed system 28 WATER TREATMENT HAND BOOK Fouling of Ion Exchange material Oxidized iron or manganese in raw water(Normally effects cation)Excessive turbidity in raw 1 Air, chlorine or other oxidizing agent can oxidize iron and manganese Pretreatment with any of the above Cleaning by Hcl for cation or by Brine for Anion Channeling or short Circuiting Excessive turbidity in raw water Excessive Resin fines Resin degraded Excessive high flow rates or operating pressure Cross Contamination of Resin in Mix bed See fouling of resins Short circuiting for possible cause Resin Dirty See fouling of resins Short circuiting for possible cause Resin Dirty High Pressure drop across resin bed See in Fouling of Resin Use Clean regenerant chemical, Use DM water for dilution Inspect pipeline clean and remove obstruction. Replace pipe with good rubber lining or rectify Open valve fully (except control valve) Clean strainers (For removal of resin) 1. See Pump Trouble Shooting for solution Restricted flow Obstructions in pipelines p u m p Ve s s e l s e t c ., Damaged Rubber lining Valves not properly opened Strainer clogged due to dirt and resin fines Pump not delivering 1. See pump trouble shooting chart for cause Excessive Rinsing Organic Fouling of Anion Ion Exchange Resin Brine Treatment. For extreme Condition Sodium hypochlorite dosing, Should be done under supervision 29 Improper Regeneration Increased Concen-tration of sulphuric acid in cation regeneration Regen-erant dosage too low or too weak Inadequate backwash Damage underdrain or internal distributor See method of Regeneration Use correct method of regeneration Give extended backwash (30 minutes or more) to clean the resin bed. Replace or Rectify Have storage system and operate at higher flow or use recycle system.Minimum linear velocity should not fall below 2 M3/Hr /M2 Replace Note :- Valve Leakage can give wrong reading in instruments & water analysis Low service flow rate Very slow service rate increases leakage from unit (will reflect on anion unit ) Valve leakage Defective Valve Nominal aging of Resin Cation Life – 5 to 10 years Anion Resin – 3 to 5 years 3 to 5 % per annum 1 Replace old resin Attrition Loss 1 Top up resin lost Water should not be totally drained after rinsing. The level of water should always be above resin bed Air mixing should be done for minimum of ten minutes Check air requirement & blower capacity Inadequate mixing of Resin. Applies to Mixed Bed only Improper Drain down Air Mixing time too short Not Enough air Problem of middle collector in mixed bed Can be caused by leakage of cation Resin Improper dilution of regenerant Broken collector Add Cation Resin to make up Loss or add inert resin Check Change 30 WATER TREATMENT HAND BOOK Indian standard grade for the commonly used regeneration chemicals Hydrochloric Acid -Sulphuric Acid -Sodium Hydroxide -IS 1021 (Pure Grade - Flakes) Sodium Carbonate -Sodium Sulphite -Sodium chloride -Alum -IS 265 IS 266 IS 252 (Tech/Rayon Grade 46% lye) IS IS IS IS 251 247 297 260 (Tech (Tech (Tech (Tech Grade) Grade) Grade) Grade) Recommended impurity level for Hydrochloric Acid Impurity Fe Other metals(total) Organic Matter H2SO4 as SO3 Oxidants(HNO3,Cl2) Suspended matter as turbidity Inhibitors Maximum level 0.01% 10 ppm 0.01 % 0.4 % 5 ppm 0 none Concentration and density of HCl solution Percent 1 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 Sp.Gravity 1.0032 1.0082 1.0181 1.0279 1.0376 1.0474 1.0574 1.0675 1.0776 1.0878 1.0980 1.1083 1.1187 1.1290 1.1392 1.1493 1.1593 1.1691 1.1789 Grams/Liter 10.03 20.16 40.72 61.67 83.01 104.7 126.9 149.5 172.4 195.8 219.6 243.8 268.5 293.5 319.5 344.8 371.0 397.5 424.4 31 Recommended impurity level for Sodium Hydroxide Impurity Maximum level 0.6% NaCl 30 ppm NaClO3 0.75% Na2CO3 Fe 10 ppm 5 ppm Heavy metals(Total) 50 ppm SiO2 Na2SO4 0.2 % Concentration and density of NaOH solution Percent 1 2 3 4 5 6 7 8 9 10 16 20 26 30 36 40 46 50 Sp.Gravity 1.0095 1.0207 1.0318 1.0428 1.0538 1.0648 1.0758 1.0869 1.0979 1.1089 1.1751 1.2191 1.2848 1.3279 1.3900 1.4300 1.4873 1.5253 Grams/Liter 10.10 20.41 30.95 41.71 52.69 63.89 75.31 86.95 98.81 110.9 188.0 243.8 334.0 398.4 500.4 572.0 684.2 762.7 Recommended impurity level for Sodium Chloride Impurity Sulphate Magnesium and Calcium Maximum level 0.6% 30 ppm Concentration and density of NaCl solution Specific Gravity 1.005 1.012 1.027 1.041 1.056 1.071 1.086 1.101 1.116 1.132 1.148 1.164 1.180 1.197 Percent 1 2 4 6 8 10 12 14 16 18 20 22 24 26 Grams/Liter 10.05 20.25 41.07 62.47 84.47 107.1 130.2 154.1 178.5 203.7 229.5 256.0 283.2 311.2 32 WATER TREATMENT HAND BOOK Concentration and density of H2SO4 solution Percent 1 1.5 2 3 4 5 10 15 20 30 40 50 98 100 Sp.Gravity 1.005 1.008 1.012 1.018 1.025 1.032 1.066 1.109 1.140 1.219 1.303 1.395 1.906 1.944 Grams/Liter 10.05 15.12 20.24 30.54 41.00 51.60 106 166.1 228 365.7 521.2 697.5 1799 1831 Common conversion factors for ion exchange calculation To convert from Kgr/ft3 as CaCO3 Kgr/ft3 as CaCO3 Kgr/ft3 as CaCO3 g CaCO3/litre g CaO/litre To g CaO/Litre g CaCO3/Litre eq/litre Kgr/ft3 (as CaCO3) Kgr/ft3 (as CaCO3) Multiply by 1.28 2.29 0.0458 0.436 0.780 Flow Rate To convert from U.S. gpm/ft3 U.S. gpm/ft2 U.S. gpm BV/min To BV/hr M/hr M3/hr U.S. gpm/ft3 Multiply by 8.02 2.45 0.227 7.446 Other Parameters Parameter Pressure drop Regenerant concentration Density Rinse requirement To convert from PSI/ft PSI/ft Ibs/ft3 Ibs/ft3 U.S. gal/ft3 To MH2O/M of Resin G/cm2/M g/litre g/litre BV Multiply by 2.30 230 16.0 16.0 0.134 33 1 gallon of water weighs 8.33 pounds 1 Cubic foot of water weighs 62.4 pounds 1 cubic centimeter of water weighs 1 gram 1 liter of water weighs 1 kilogram 1 cubic meter of water weighs 1 metric ton 1 metric ton = 2240 lb. Water analysis conversion factor Substance Calcium Magnesium Sodium Potassium Iron (ferrous) Iron (ferric) Aluminium Barium Strontium Atomic /molecular weight 40.0 24.3 23.0 39.1 55.8 55.8 27.0 137.4 87.6 Equivalent Weight 20 12.25 23.0 39.1 27.9 18.6 9.0 68.7 43.8 To CaCO3 43.8 4.12 2.17 1.28 1.79 2.69 5.56 0.73 1.14 Anions Substance Bicarbonate Carbonate Chloride Sulphate Nitrate Phosphate Sulphide Co2 Silica Atomic / molecular weight 61.0 60.0 35.5 95.1 62.0 95.0 32.1 44.0 60.1 Equivalent Weight 61.0 60.0 35.5 48.0 62.0 31.7 16.0 44 60.1 To CaCO3 0.82 0.83 1.41 1.04 0.81 1.58 3.13 1.14 0.83 34 WATER TREATMENT HAND BOOK Set-Points for Brine regeneration to remove organic fouling Parameter Units Subsequent First Salt Caustic Caustic Regeneration Regeneration Regeneration 32 112 32 Quantity of Regenerant Regenerant Strength Gm/liter % 3.5 15 5 Quantity of dilute Regenerant Grams /liter 912 745.6 640 Volume of Regenerant Liter/liter of resin 0.9246 0.6968 0.6432 Flow Rate of Regenerant M3/Hr/M3 of resin 2.8 1.6 1.92 Time for Regeneration Minutes 20 25 20 Flow Rate of Rinse Water M3/Hr/M3 of resin 1.6 4 1.6 Time for Rinsing Minutes 10 15 10 35 CHAPTER 5 36 WATER TREATMENT HAND BOOK Softener (Basic ion exchange process) Thumb rules of designing a Softener STEP 1 – To select resin quantity (liters) for a particular hardness (ppm) for a particular output (m3) per regeneration per hour based on regeneration level 160 gm/liter, ion exchange capacity = 55, TDS limit = 1500 ppm, refer TABLE 1 Resin Quantity = Load (ppm as CaCO3) * Flow * time Ex. Capacity For example Load = Hardness = 100 ppm as CaCO3 Flow = 5M3 /hr Time = (Service cycle) = 12 hrs. Ex. Capacity = 60 gm as CaCO3 = 100 liters Resin Quantity = 100 * 5 * 12 60 Note: Na / TC and TDS and correction factor should be applied. Actual Resin Quantity = 60 * correction due Na/TC factor * Correction due to TH factor = 60 * 0.96 * 0.97 = 56 (approximately) Hence Ion Exchange load for designing a softener is 56. These calculations are based on Ion Exchange resin and will vary from manufacturer to manufacturer resin. STEP 2 – To select vessel model for a selected resin quantity, approx. flow rates based on linear velocity- min (8 M3/M2/hr) and max (25 M3/M2/hr), and free board 5-100 %, refer TABLE 2 Important points on Softener Regeneration level, hardness leakage desired and correction factors can be found from resin supplier's graph. Suggested vessel selection chart for softeners TABLE 1: STEP 1 – To select resin quantity ( liters) for a particular hardness (ppm) for a particular output(m3) per regeneration per hour based on regeneration level 160 gm/liter, ion exchange capacity = 55, TDS limit=1500 ppm) Output b/w Regen-eration (OBR M3) 5 10 Resin Qty in liters for various hardness Hardness Hardness = 150 = 250 ppm ppm 13.5 27.0 22.5 45.0 Hardness = 350 ppm 31.5 63.0 Hardness = 500 ppm 45.0 90.0 Hardness Hardness Hardness = 650 = 800 = 1000 ppm ppm ppm 58.5 117.0 72.0 144.0 90.0 180.0 37 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 39.0 52.5 66.0 79.5 91.5 105.0 118.5 132.0 144.0 157.2 171.0 184.5 198.0 210.0 223.0 237.0 250.5 262.5 65.0 87.5 110.0 132.5 152.5 175.0 197.5 220.0 240.0 262.0 285.0 307.5 330.0 350.0 372.0 395.0 417.5 437.5 91.0 122.5 154.0 111.3 213.5 245.0 276.5 308.0 336.0 366.8 399.0 430.5 462.0 490.0 521.0 553.0 584.5 612.5 135 180 225 270 315 360 405 450 495 540 585 630 675 720 765 810 855 900 175.5 234.0 292.5 351.0 409.5 468.0 526.5 585.0 643.5 702.0 760.5 819.0 877.5 936.0 994.5 1053.0 1111.5 1170.5 216.0 288.0 360.0 432.0 504.0 576.0 648.0 720.0 792.0 864.0 936.0 1008.0 1080.0 1152.0 1224.0 1296.0 1368.0 1440.0 270.0 360.0 450.0 540.0 630.0 720.0 810.0 900.0 990.0 1080.0 1170.0 1260.0 13500 1440.0 1530.0 1620.0 1710.0 1800.0 TABLE 2: STEP 2 – To select vessel model for a selected resin quantity, approx. flow rates based on linear velocity min=8 m3/m2/hr and max=25 m3/m2/hr, and free board 5-30 % Vessel Resin Approx. Free Resin Flow Rate Board Model Qty Qty Capacity Min-max (%) (liters) (liters) (liters) LPH 6 x 32 160-500 8% (14.6 liters) 13.5 160-500 20 % 6 x 35 (16. l liters) 6 x 35 33 % (18.0) 9% 7 x 40 (24.5 ltrs) 7 x 44 (27.1 ltrs) 70 704-2,200 50 % 80 704-2,200 33 % 60 584-1,825 30 % 160-500 584-1,825 12 % Approx. Flow Rate Min-max LPH Vessel Free Board Model Capacity (%) (liters) 10x54 (63.8 ltrs) 12x48 (78.5 ltrs) 12x48 (78.5 ltrs) 13x54 (106 ltrs) 13x54 (106 ltrs) 13x54 (106 ltrs) 13x54 (106 ltrs) 14x65 (150 ltrs) 415-1,295 6 % 212-663 22.5 212-663 20 % 276-865 27.0 8x40 16 % (31.4 ltrs) 8x44 29 % (34.9 ltrs) 90 100 704-2,200 18 % 704-2,200 6 % 822-2,570 50 % 276-865 9x35 350-1,093 26 % (33.9 ltrs) 38 WATER TREATMENT HAND BOOK 31.5 350-1,093 8% 9x35 (33.9 ltrs) 10x35 (40.1 ltrs) 10x40 (46.5 ltrs) 10x35 (40.1 ltrs) 10x40 (46.5 ltrs) 10x44 (51.7 ltrs) 10x40 (46.5 ltrs) 10x44 (51.7 ltrs) 10x47 (55.0 ltrs) 10x54 (63.8 ltrs) >100 <140 >140 <180 >180 <240 8222,570 1,0003,140 1,4004,370 ~ 14x65 (150 ltrs) 16x65 (182 ltrs) 18x65 (250 ltrs) 415-1,295 27 % ~ 415-1,295 48 % ~ 39 415-1,295 3% >240 <300 >300 <430 >430 <650 >650 <950 >950 <1250 1,9006,000 2,3007,300 3,70011,600 5,40016,800 9,40029,448 ~ ~ 21x62 (310 ltrs) 24x62 (450 ltrs) 30x72 (710 ltr) 36x72 (1020 ltr) 48x72 (1840 ltr) 63x64 (2500 ltr) 415-1,295 19 % 415-1,295 33 % ~ 45 415-1,295 3% ~ 415-1,295 15 % ~ 415-1,295 415-1,295 22 % 42 % > 1250 16,000<1700 50,240 ~ 39 CHAPTER 6 40 WATER TREATMENT HAND BOOK Membrane System Conventional and membrane process solutions to common water problems Constituent of concern Conventional process Membrane process Coagulation/flocculation Turbidity Suspended solids Media filtration Microfiltration Biological contamination Disinfection Color Activated carbon Ultrafiltration Odor Cl, + media filtration Volatile organics aeration Hardness Sulfates Manganese Iron Heavy metals Total dissolved solids Nitrate Lime softening ion exchange Nanofiltration Oxidation, filtration Ion exchange Coagulation/flocculation Distillation Ion exchange Reverse osmosis Electrodialysis Pretreatment water quality for membrane processes Spiral CA Suspended matter Turbidity NTU SDI Ionic content Iron, mg/L (ferrous) Manganese mg/L Silica mg/L(w/o) in concentrate Chemical Feed Residual Chlorine ppm Scale inhibitor mg/l in concentrate Acidification pH Maximum feed temperature oC Maximum LSI with Scale inhibitor <1.0 <4.0 <2.0 <0.5 <160 <1.0 <4.0 <2.0 <0.5 <160 <5 <15 <0.1 <0.1 <saturation in feed Spiral PA EDR <1.0 12-18 5.5-6.0 ND 12-18 4-10 ND As required As required 40 Note 45 +2.45-+2.8 43 2.1 41 Note:- Type of Membrane PA = polyamide, CA = Cellulose Acetate and EDR = Electrodialysis Reversal CA membranes work in Narrow pH range 5.5-6.0 and require acidification to prevent hydrolysis. Therefore, the Langelier Saturation Index of the existing concentrate tends to be low enough and scale inhibitor for calcium carbonate scale is not required. Troubleshooting Guide CHECK Pressure drop between feed and reject. Pressure drop between feed and permeate Permeate conductivity VERIFY Has not increased by more than 15%. EFFECT More than 15% indicates fouling of feed path and membrane surface. Requires cleaning More indicates fouling of membrane surface. Requires cleaning. More indicates fouling of membrane surface. Requires cleaning. More can cause membrane damage or sulfate scaling. Less can cause carbonate scaling or metal oxide fouling. Has not increased by more than 15%. Has not increased by more than 15%. Acid dosing Is within recommended value. Instruments Reading Verify by calibration and carry out of lab check of the parameters the instrument is monitoring. The pH controller generally controls acid dosing pumps. The pH controller should be calibrated periodically and tripping of dosing pump to the set point should be checked. Wrong operation False sense of security that everything is OK. pH meter calibration & control More or less acid dosing than required.Effect of this has already been mentioned earlier. 42 WATER TREATMENT HAND BOOK O ring Probing with ¼ 'plastic tube and by measuring how far it has been inserted. Failure can lead to increase salt passage, increase permeate flow. Decrease pressure drop. If fully closed, 100% recovery will result and cause membrane damage due to precipitation of inorganic salt. Brine valve Should not be closed fully. Foulants & Their Impact Foulants Metal Oxide Colloidal Fouling Scaling Biological Fouling Organic Fouling Oxidant(Cl2) Abrasion (carbon,Silt) O-ring or glue leaks Recovery too high Possible Location 1St Stage 1St Stage Last Stage Any Stage Pressure drop Normal to increased Normal to increased Increased Normal to increased Normal Normal to increased Decreased Normal to decreased Decreased Permeate Flow Decreased Decreased Salt Passage Normal to increased Normal to increased Increased Normal to increased Decreased to increase Increased Increased Increased Increased Decreased Decreased All Stages 1St Stage (Most Severe) 1st Stage Random Decreased Increased Increased Normal to increased Normal to Decreased All stages 43 Cleaning of RO Membrane RO membranes get fouled with suspended solids contained in the feedwater or with sparingly soluble salts, as minerals are concentrated. Pretreatment is done to reduce the fouling potential of feedwater but inspite of that fouling occurs over a period of time. Symptom of fouling 1. Decrease in Product flow. 2. Increase in salt passage. 3. Increase in differential pressure 4. Deterioration in permeate quality 5. Increase in the differential pressure across the RO stage. Indications that the system requires cleaning 1. A 10 to 15 % decline in normalized Product flow. 2. A 10 % increase in salt passage. 3. 15 % increase in differential pressure. Types of Foulants 1. Inorganic fouling – Like Calcium Scales or Metal Oxides 2. Organic Fouling – Example Humic Acid 3. Particulate Deposition or colloidal fouling –Particulate matter 4. Biofouling Types of Membrane Cleaning Solutions The number of formulation for cleaning solutions is varied but we are mentioning only the common type of cleaners used for most common fouling problems. Foulant Inorganic Salts Metal Oxides (Iron) Inorganic Colloids (silt) Biofilms Cleaning Chemicals 0.2 % HCl 0.5 % Phosphoric Acid 2.0 % Citric Acid 0.5 % Phosphoric Acid 1.0 % Sodium Hydrosulphite 0.1%Sodium Hydroxide,30 oC 0.025 % Sodium Dodecylsulphate 0.1 % NaOH, 30 oC 0.1 % NaOH, 30 oC 1 % Sodium salt of ETDA and 0.1 % NaOH 0.025 % Sodium Dodecylsulphate 0.1 % NaOH 30 oC 0.1% sodium triphosphate 1.0 % Sodium salt of ETDA Remarks Organics 44 WATER TREATMENT HAND BOOK Flux The throughput of a pressure-driven membrane filtration system expressed as flow per unit of membrane area (e.g., gallons per square foot per day (gfd) or liters per hour per square meter (Lmh). Type of Water Municipal wastewater (sewerage) Treated River or Canal water Surface Water (lakes/Reservoir) Deep Wells (low turbidity) RO Permeate Water Surface seawater Beach well seawater System Operating Water Flux (gpd/ft2) & (M3/M2.d) 8-12 - or 8-14 – or 8-14 – or 14-18- or 20-30 –or 7-10 - or 7-10 - or 0.33-0.49 0.33-0.57 0.33-0.57 0.33-0.73 0.81-1.22 0.29 –0.40 0.29 –0.40 If the water quality is better, higher flux that can be used without causing excessive fouling. Number of Elements: When the flux has been set and the element area (a function of the specific membrane selected) is known, the required number of elements can be calculated: Number of elements =Permeate Flow (LPD)/(LMH)*Active Membrane area (M2) Recovery Rate = (Permeate Flow rate / Feed flow rate)*100 Osmotic pressure Osmotic pressure can be defined as the pressure and potential energy difference that exists between two solutions on either side of a semipermeable membrane. A rule of thumb for osmosis is that 1 psi of osmotic pressure is caused by every 100 ppm (mg/l) difference in total dissolved solids concentration (TDS). Selection of Feed pumps Feed pumps should be selected on the basis of high efficiency. Variable frequency drives now are commonplace in brackish water RO Plants. These frequency drives should also be selected on similar basis. Typical feed pump energy requirements for brackish water RO plants range from 0.5 to 2 kWh/M3 and for seawater it is less than 3 kWh/M3 with the use of energy recovery device. Scaling of Membrane Process Scaling is predicted by Langelier Saturation Index (LSI) or at a higher ionic strength the Stiff & Davis Index predicts the scaling tendency more accurately. 45 u If pH >pHs (or pHsd) then water is saturated with calcium carbonate. u If pH <pHs (or pHsd) then water is unsaturated. u A positive value of index indicates tendency towards scaling. u With the scale inhibitors available nowadays an LSI <+2.4 can be easily controlled. u Circulating a muriatic acid solution can easily redissolve carbonate scale. Lowering the pH during operation can also dissolve it. u In predicting the solubility limits of sulphate two points are important.u a) Modern RO membranes reject divalent ions very well. Therefore it is reasonable to assume a zero percent salt passage when calculating the concentrating factor CF. u b) Compounds are more soluble in the concentrate than in feed water. The solubility product constant Ksp of each compound increases with ionic strength. u As a rule of thumb, the scale inhibitor dosages for RO systems are calculated as concentrations in the concentrate of 12 –18 Mg/liter. This value is then converted to a feed water dosage using the CF for design recovery and assuming zero percent salt passage. To predict the product and concentrate composition and volume: uare four important pieces of information needed to predict There the product and concentrate composition and volume: u Recovery rate, (Ret): -The recovery rate is limited by the concentration of sparingly soluble salts in the feed water. Lowering the pH and adding anti-scalants can increase the potential recovery rate. The other determining factor is the configuration of the membrane system. Each element can recover approximately 10 percent of the feed flow as product. Generally, 50 percent recovery is assumed for a 6-element vessel. u Rejection rate: -Manufacturers lists a rejection rate for chloride and one for sulfate or other divalent ions for NF membranes. For greater accuracy, use a weighted average based on the feed water composition. For instance, if the feed water has a ratio of 3: 1 monovalent to multi-valent ions and the rejection rates are 90 percent for chloride and 99.5 percent for sulfate, the weighted average rejection rate would be Rejection = (0.75*0.9)+(0.25*0.995) / (0.75+0.25) =0.924 If the goal is to minimize concentrate volume, choose a membrane with a very high rejection. However, if the goal is to minimize concentrate TDS, choose a membrane that will produce the target water quality. NF membranes are sufficient in many cases. 46 WATER TREATMENT HAND BOOK u Feed water-dissolved solids concentration, C, in mg/L. u delivery water concentration after blending, C, in mg/L. Target u Accurate product and concentrate concentration prediction calculations that take concentration polarization into consideration can get quite complex, but do no provide that much more accuracy in a first pass cost estimate. Product concentration, Cp in mg/L: Cp= Cf (1-Rejection) / Recovery Concentrate concentration Cc in mg/L Cc =Cf* Rejection / (1-Recovery) The maximum amount of blend water that can be mixed with the membrane product and still achieve the target water quality is calculated as follows, assuming filtered feed water is used for the blend water: Qb = Qt (Ct- Cp) / (Cf-Cp) Where Qb is the maximum blend volume in m3/day, Q, is the target volume in m3/day, and Ct is the target dissolved solids concentration in mg/L. If there is a component of the blend water that is more limiting than the total dissolved solids, there are two options. Either plan to remove that component from the blend water or use the concentration of that component in the blend water for Cf and the estimated remaining concentration of it in the membrane product water for Cp. As an example, consider the following situation: Cf = 900 mg/L with 0.5 mg/L manganese Rejection = 0.95 Recovery = 0.85 Ct = 300 mg/L with less than 0.05 mg/L manganese Cp = 900*(l-0.95)/0.85 = 56 mg/L Cb = (300-56)/ (900-56) = 0.29 or 29 percent blending with feed water. When the manganese concentration is considered as the limiting component: Cf = 0.5 mg/L manganese Rejection = 0.95 Recovery = 0.85 Ct = Less than 0.05 mg/L manganese Cp = 0.05*(l-0.95) / 0.85 = 0.03 mg/L Cb = (0.05-0.03) / (0.5-0.03) = 0.04 or 4 percent blending with feed water. 47 If the blend water is filtered with greensand or the manganese is removed in some other way, the higher level of blending is possible, otherwise not. However it is decided, once the blend volume has been established, the membrane process feed, product, and concentrate flows are set (all in m3/day): Qp = Qt- Qb Qf = Qp / Recovery Qc = Qp (1-Recovery) / (Recovery) Pump Horsepower for RO Using the following assumptions: Feed water is being pumped from a tank of approximately the same height as the membrane skid, 10 meters of pipe Pipe is a 10 cm (4 in.) in diameter for 20cm (8-in.) modules and 5 cm (2 in.) for 10 cm (4 in.) module. Horsepower (Hp) without energy recovery Hp = hg+0.5v2+p*Qf*1000/(746*Ef) Horsepower (Hp) with energy recovery Hp = (hg+0.5v2+p)(1-Er)*Qf*1000/746 Where h is height difference between top of tank and membrane inlet in m, g is gravitational constant, 9.81 m/s2 v is velocity = Q / pipe area, m/s, Qf = membrane feed flow, m3/sec, 1000 = mass of one m3 of water in kg, 746 = conversion factor from J/s to hp, Ef= combined Efficiency of Pump and Motor E recovery = energy recovery in decimal, 0.20 - 0.30 depending on concentrate pressure. 48 WATER TREATMENT HAND BOOK CHAPTER 7 49 Steam Boiler Steam Boiler System The principal components of a steam boiler system include a steam boiler, condensate return tank, condensate pump, deaerator, feedwater pump, steam traps, low water flame cut-off controller, chemical feeder, and make-up water treatment equipment. However, depending on the size of the system and the end use of the steam, other components may include a converter or heating coils, unit heater, steam sparger, jacketed steam cooker, and/or steam sterilizer List of Problems Caused by Impurities in Water Impurity(Chemical Formula) Alkalinity (HCO3-, CO3 2- and CaCO3) Hardness (calcium and magnesium salts, CaCO3) Iron (Fe3+and Fe2+) Problems Carryover of feedwater into steam,produce CO2 in steam leading to formation of carbonic acid (acid attack) Primary source of scale in heat exchange equipment Causes boiler and water line deposits Corrosion of water lines, boiler, return lines, heat exchanger equipment,etc. (oxygen attack) Corrosion occurs when pH drops below 8.5 Corrosion Scale in boilers and cooling water systems Common Chemical Treatment Methods Neutralizing amines, filming amines, combination of both, and lime-soda. Lime softening, phosphate, chelates and polymers Phosphate, chelates and polymers Oxygen scavengers, filming amines and deaeration pH can be lowered by addition of acids and increased by addition of alkalis Chlorination Scale in boilers and cooling water systems Oxygen (O2) pH Hydrogen Sulfide (H2S) Chlorination 50 WATER TREATMENT HAND BOOK Troubleshooting Water system for Boiler Condition Possible Cause Improper functioning of Water softener Infiltration of raw water at converters. Action Regenerate/repair water softener. Take condensate samples at all steam converters to pinpoint place of infiltration. Make necessary repair. Check deaerator press /temp.Check deaerator valve to ensure the most effective opening. Repair feedwater pump seal. Replenish test reagents. Repair or adjust chemical feed pump. Clean or replace chemical feedline. Make sure the chemical you are using is what you want. Increase chemical dosage. Inspect boiler and condensate piping system for any indication of leaks. Make sure drain valves on condensate receiving tanks are closed. Check boiler blowdown valves to ensure 100% shut-off. Check continuous blowdown valves setting. Check water softener. See action for “Hardness in boiler feed water.” Select phosphate based on the needed Po4 percent to ensure the highest quality for the hardness content. Hardness in Boiler feed Water Dissolved oxygen in Feedwater exceeds the recommended range. Deaerator malfunction. Feedwater pump sucking air at the seal. Insufficient sodium sulfite residual. Testing reagent shelf life expired. Chemical feed pump inoperative or out of adjustment. Restriction in the chemical feedline. Mistake in chemical identification. Inadequate amount of treatment chemical. Makeup water increase due to lead in the system (boiler section or condensate). Consistently low Chemical residual in system(General). Low phosphate residual. Increased hardness in feedwater. Wrong type/choice of phosphate. 51 Low sulfite residual. Chemicals feed pump inoperative. An increase of oxygen content in feedwater. Improper sampling or testing technique. Check sulfite feed system and make necessary adjustment/repair. Check deaerator operation and make necessary adjustment/repair. Increase sodium sulfite feed rate. “Collecting Water Samples. Test for sulfite first. Stir sample smoothly. Increase blowdown rate. Adjust the surface blow down valve. Analyze boiler water to determine treatment chemical residual and make adjustments. Reduce the total dissolved solids in the boiler by blowdown. Make sure water level is not too high. Reduce amine injection, but maintain the recommended pH. Take condensate samples at all steam converters and test for hardness and TDS to find the point of infiltration. Make necessary repair. Analyze the condensate for iron/copper content. Ensure amine treatment is reaching all points in the condensate system. Total dissolved solids exceed the recommended range. Insufficient boiler blowdown. Excessive chemical addition. High total dissolved solids in condensate. Boiler water carryover with the steam. Too much amine injected. Infiltration of raw water at converters. Active corrosion occurring in the system. Boilers Boilers use varying amounts of water to produce steam or hot water, depending on their size. They require make up water to compensate for uncollected condensate or to replace blow down water. These units have a tendency to develop leaks as they age. 52 WATER TREATMENT HAND BOOK Water Efficiency Opportunities: 1. Install a condensate return system – A condensate returns system reuses condensate water as make-up water. This can save up to 50-70 percent of the water used and can save energy as well. Locate and repair leaks – Boilers can develop leaks in steam traps and the distribution system. Escaping steam wastes both water and energy. Limit blow down – Adjust blow down limits to near the minimum required to properly flush the system and maintain desired water quality. Establish an effective corrosion and scale program –Regularly inspect boiler water and fire tubes. Reducing scale by chemical treatment or mechanical removal will increase heat transfer and energy efficiency and will reduce the amount of blow down necessary to maintain water quality. 2. 3. 4. 5. Install automatic controls to treat boiler make up water. Eliminate systems that mix condensate with cool fresh water for blow down to the sewer. Water Treatment Recommendation 1.The make-up water treatment to these systems depends on the boiler pressure and the end use of the steam. 2.The make-up should preferably be softened for low pressure steam boiler. 3.The make-up must be softened & dealkalized for steam boiler systems when the total alkalinity concentration in the make-up is high (i.e., systems where the boiler is blown down to control alkalinity rather than TDS). 4. In boiler system where silica controls the blowdown, the make up water should be demineralized. 1.Sodium sulphite must be added at a point after mechanical deaeration such that a residual sulphite concentration of 30-60 ppm (50 – 100 ppm Na2SO3) is maintained in the boiler water. 2.It does not matter if the sulphite concentration is more but it should not be less than 30 ppm SO3 or 50 ppm Na2SO3. 3.The sulphite-oxygen reaction may be catalyzed by adding 5 ml of cobaltous chloride solution per 100 g of sodium sulphite. 1. If the pH of the boiler water is less than 10.5, caustic must be added to the boiler. 2. If the pH of the boiler water is greater than 11.5, the blowdown rate must be increased and the caustic addition must be decreased—the boiler water pH level must be 10.5-11.5 pH. A B C 53 D 1. If the boiler water total alkalinity concentration is greater than 700 ppmCaCO3, then the blowdown rate must be increased and the caustic or trisodium phosphate addition must be decreased. 2. The boiler water total alkalinity concentration must be less than 700 ppm CaCO3; 1. If the boiler water hydroxide alkalinity concentration is less than 150 ppm CaCO3, caustic or tri-sodium phosphate must be added to the boiler water. 2. Alternately, if the boiler water hydroxide alkalinity concentration is greater than 300 ppm CaCO3, the blowdown rate must be increased and the caustic or tri-sodium phosphate addition must be decreased—the boiler water hydroxide alkalinity must be 150-300 ppm CaCO3 1. If the phosphate is added upstream of the boiler feed pumps, hexameta phosphate must be used since tri-sodium phosphate would precipitate hardness salts, thus increasing the wear on pump seals. Hexameta phosphate on the other hand keeps hardness in solution until it reaches the boiler, at which point the alkalinity and increased temperature there converts it to trisodium phosphate; 2. If the phosphate is added directly to the boiler water, either hexameta or tri-sodium phosphate may be used; 3. If the phosphate is being consumed more rapidly than trisodium phosphate is being added (i.e.,hardness in leakage into the system), hexameta phosphate should be used at least temporarily because it has a higher phosphate concentration and thus a higher capacity for hardness than tri-sodium phosphate; 4. When hexameta phosphate is used, its conversion to trisodium phosphate in the boiler effectively reduces the OH alkalinity concentration and the pH level of the boiler water; 1. If the pH level of the condensate return is less than 8.5, a neutralizing amine such as morpholine must be added to the feedwater after the make-up location. 2. If the pH level of the condensate return is greater than 9.5, the amine addition must be decreased the condensate return pH level must be 8.5-9.5. 3. If problems persist in achieving proper pH levels in the condensate return system, seek the advice of the water treatment consultant. If there is no condensate return, amine must not be added In conjunction with the above controls and regulation of boiler blowdown, the boiler water neutralized total dissolved solids must be controlled within the limits of 1500-3000 ppm (or 2000-4000 micromhos/cm). E F G H Note:- For Details See Boiler Water Treatment Manual. 54 WATER TREATMENT HAND BOOK Note Hydrazine Sulphate oxygen scavenging should only be used with drum type boilers. Drum boilers have blowdown facilities. TDS levels should be monitored more rigorously when using hydrazine sulphate as an oxygen scavenger, since TDS levels may increase with the formation of ferrous sulphate. The venting is not sufficient. Increase venting by opening the manually operating vent valve. Excessive oxygen content in deaerator effluent The steam pressure reducing valve not working properly. Check valve for free operation. Check water and, if possible, steam flow rates vs. design. Trays or scrubber and inlet valves are designed for specific flow ranges. Temperature in storage tank does not correspond within 5 º F of saturation temperature of the steam Spray nozzle not working. There could be deposit or sediment on the nozzle on the spring broken or seat. Leaking stuffing boxes of pump upstream of deaerator can be the cause Repair stuffing box or seal with deaerated water. Excessive consumption of oxygen scavenger Trays collapsed-possibly from interrupted steam supply or sudden supply of cold water causing a vacuum. Condensate may be too hot. Water entering the deaerating heater must usually be cooled if the temperature. 55 Chemical dosage Oxygen scavenger Sodium sulphite 7.88 ppm of sodium sulphite is required to remove 1ppm of dissolved oxygen. This requirement is for pure sodium sulphite. 93 % pure sodium sulphite will require 10 ppm of sodium sulphite per ppm of oxygen. The amount of catalyst required is 0.25 % Hydrazine Theoretically 1 ppm of Hydrazine reacts with 1 ppm of dissolved oxygen. In practice of 1.5 to 2 ppm is used for 1 ppm of dissolved oxygen Amine Requirement Amount of amine required for maintaining pH of 8.0 in water containing 10 ppm CO2 Morpholine –37 ppm: - It has a specific gravity of 1.002 and has a pH of 9.7 for 100-ppm solution Cyclohexylamine –15 ppm: - It has a specific gravity of 0.86 and has a pH of 10.7 for 100-ppm solution Suggested dosage of Sodium sulphite & Hydrazine Dosage of Sodium sulphite Boiler pressure (Kg/Cm2) 14.00 21.00 31.00 42.00 52.00 64.00 70.00 105.00 Ppm Na2SO3. 80-90 60-70 45-60 30-45 25-30 15-20 Not recommended Not recommended Recommended Hydrazine Residual Drum pressure (Kg/Cm2) 63.00 70.00 105.00 175.00 210.00 Residual Hydrazine in ppm. 0.1-0.15 0.1-0.15 0.05-0.10 0.02-0.03 0.01-0.02 56 WATER TREATMENT HAND BOOK Type of Amine Ammonia Cyclohexylamine Conditions Co2 Absent Co2 Absent CO2 Present Amount needed 0.2 ppm to give pH 9.0 1 ppm to give pH 9.0 2.3 parts per part of CO2 to give pH 8.1 (corresponds to bicarbonate) 2.0 parts per part of CO2 to give pH 7.4 1.4 ppm per ppm of Co2 to give pH of 7.0 Notes Cyclohexylamine is not for use in systems having a feedwater alkalinity more than 75 ppm These system lengths are for classification only and are not absolute. For example a medium length system may have more of the characteristics of a long system if lines are poorly insulated or because of bad design. Amine Limits Amine Cyclohexylamine DEAE Hydrazine Morpholine Octadecylamine Limitation Not to exceed 10 ppm in steam. Not to exceed 10 ppm in steam. Zero in steam Not to exceed 10 ppm in steam. Not to exceed 3 ppm in steam. Note:- These should not come in contact with food products and hence any steam in contact with milk and other such products should not have amine. 57 Limits on Boiler water conditions for an effective treatment program Boiler MaxiPressure -mum psig(kg/ TDS (ppm) cm2) 1-15 6000 (1.05) 16-149 (1.12-10.5) 4000 150-299 4000 (10.5-20) 300-449 3500 (20-30) 450-599 3000 (31-40) 600-749 2500 (41-52) 750 2000 (>52) Maxim um Con ductivity ( mho) 9000 6000 6000 5250 4500 3750 3000 Maxi-mum Silica (ppm) 200 200 150 90 40 30 20 Range Sulfite (ppm SO3) 30-60 30-60 30-60 20-40 20-40 15-30 15-30 Range Phosph ate(pp mPO4) 30-60 30-60 30-60 30-60 30-60 30-60 30-60 Range Alkalini ty(ppm CaCO3) 300-500 220-500 220-500 180-450 170-425 170-425 170-425 *Lign osulphon ate (ppm) 70-100 70-100 70-100 70-100 60-90 50-80 40-90 NOTE Ortho-Phosphate Hydroxyl Alkalinity (Causticity) Sodium Lignosulfonate (as tannic acid) Range BIS Standard for Feed water and Boiler Water 1st Standard (10392-1982) Chemical requirements for feed water and boiler for low and medium pressure boilers: Feed Water: Parameters Total Hardness pH Value Dissolved Oxygen Silica Upto20Kg /cm2 <10 21 Kg/cm2 - 39Kg/cm2 <1.0 40Kg/cm2 - 59Kg/cm2 <0.5 Unit ppm as CaCO3 8.5-9.5 0.1 8.5-9.5 0.02 5 8.5-9.5 0.01 0.5 As ppm As ppm SiO2 58 WATER TREATMENT HAND BOOK Boiler water Upto20 Kg/cm2 Not Detectable 700 21 Kg/cm2to 39 Kg/cm2 Not Detectable 500 40Kg/cm2 59Kg/cm2 Not Detectable 300 As ppm CaCO3 As ppm CaCO3 Parameters Total Hardness Total Alkalinity Caustic alkalinity pH Value Residual Sodium Sulphite Residual Hydrazine Ratio Na2SO4 /Caustic Al kalinity (NaOH) Ratio Na2SO4/ Totallkalinity (as NaOH) Phosphate Total Dissolved Solids Unit 350 11.0 to 12.0 30 to 50 0.1 to 1.0 Above 2.5 Above 0.4 20 to 40 3500 <0.4 of Caustic Alkalinity 200 11.0 to 12.0 20 to 30 0.1 to 0.5 Above 2.5 Above 0.4 15 to 30 2500 <0.4 of Caustic Alkalinity 60 10.5 to 11.0 -- ppm as Na2SO3 ppm as N2H4 0.05 to 0.3 Above 2.5 Above 0.4 5 to 20 1500 ppm as PO4 ppm Silica 15 As ppm SiO2 59 ASME Guidelines for Water Quality in Modern Industrial Water Tube Boilers for Reliable Continuous Operation Boiler Feed Water Drum Pressure (psi) (kg/cm2) 0-300 (0-20) 301-450 (21-30) 451-600 (31-42) 601-750 (43 –52) 751-900 (53-63) 901-1000 (64-70) Iron (ppm Fe) Copper (ppm Cu) Total Hardness (ppm CaCO3) 0.300 0.300 0.200 0.200 0.100 0.050 0.0 0.0 Silica (ppm SiO2) Boiler Water Specific Total Conductance Alkalin (micro mh ity**(ppm os/cm)(unn CaCO3) eutralized) 700* 600* 500* 400* 300* 200* 0*** 0*** 7000 6000 5000 4000 3000 2000 150 100 0.100 0.050 0.030 0.025 0.020 0.020 0.050 0.025 0.020 0.020 0.015 0.015 0.010 0.010 150 90 40 30 20 8 2 1 1001-1500 0.010 (71-105) 1001-1500 0.010 (71-105) ABMA Standard Boiler Water Concentrations for Minimizing Carryover Drum Pressure (psig) 0-300 301-450 451-600 601-750 751-900 901-1000 1001-1500 1501-2000 Total Silica*(ppm SiO2) 150 90 40 30 20 8 2 1 Boiler Water Conductance Specific** (micromhos Alkalinity (ppm CaCO3) /cm) 700 7000 600 6000 500 5000 400 5000 300 3000 200 2000 0 150 0 100 This value will limit the silica content of the steam to 0.25 ppm as a function of selective. 60 WATER TREATMENT HAND BOOK Boiler Water Limits Boiler Pressure psig 0 to 300 301 to 450 451 to 600 601 to 750 751 to 900 901 to 1000 1001 to 1500 1501 to 2000 Over 2000 TDS 3500 3000 2500 2000 1500 1250 1000 750 500 Alkalinity 700 600 500 400 300 250 200 150 100 Suspended Solids 300 250 150 100 60 40 20 10 5 Silica* 125 90 50 35 20 8.0 2.5 1.0 0.5 Silica Levels Allowed in Boiler Water Boiler Pressure (psi) 0-15 16-149 150-299 300-449 450-599 40 600-749 Allowable Silica (as ppm SiO2) 150 150 150 90 30 750 20 61 CHAPTER 8 62 WATER TREATMENT HAND BOOK Cooling Water Treatment Description of Process Cooling towers are heat exchangers that are used to dissipate large heat loads to the atmosphere. They are used in a variety of settings, including process cooling, power generation cycles, and air conditioning cycles. All cooling towers that are used to remove heat from an industrial process or chemical reaction are referred to as industrial process cooling towers (IPCT). Cooling towers used for heating, ventilation, and air conditioning (HVAC), are referred to as comfort cooling towers (CCT). Cooling towers are classified as either wet towers or dry towers. Dry towers use a radiator like cooling unit instead of water evaporation. Objective for Cooling Water Treatment The following four basic objectives for Cooling Water Treatment are 1. Minimize problems from corrosion, scale, deposition, and growth to obtain maximum efficiency. 2. Implementation and control must be "do-able" with a minimum input of labor and money. 3. Cost effective as possible considering the total water system capital and operating costs. 4. Must be environmentally acceptable. Factors important for cooling System Following steps are necessary to optimize the cycle of concentration (COC) for a cooling tower and evaluate cooling water requirement or replacement 1. 2. Evaluate the cooling system Determine the water quality constituents sand concentration limits for cooling system protection 3. Evaluate water treatment requirements 4. Choosing monitoring and maintenance requirement Create a plan to change chemistry or flow rates, if problem occurs. 63 Equipment Cooling tower Piping for cold water Material of construction Wood, Plastic, Metal and fiber glass Mild steel (MS), PVC, Stainless steel (SS) and fiber glass Copper, copper alloy, SS, & galvanized steel tubes Mild steel Water lines may be of copper Heat exchangers(Chillers, Jacketed vessel, etc) Covers of Heat exchangers & Support plates Type of Material GI Pipes Effect of impurity Corrosion (white rust) at High TDS and pH above 8.5 or less than 6.5 Corrosion due to chloride, Chloride above 200 ppm can create problem in Ss304 when deposit forming conditions exist but if no deposit forming surface can withstand around 1000 ppm Cl. 316 SS can withstand about 5000 ppm Cl even with deposit forming surface Highly corrosive due to solids and also due to acidic or basic conditions Oxygen also corrosive to mild steel Corrosion to ammonia Natural decay. Can get chemically attacked. Corrosion resistant. Biomass can get built up on plastic film Stainless steel Mild steel Copper & Copper alloys Wood Plastic 64 WATER TREATMENT HAND BOOK Cooling Tower Maintenance Schedule Daily/Weekly 1.Test water sample for proper concentration of dissolved solids. Adjust bleed water flow as needed. 2.Measure the water treat-ment chemical residual in the circulating water. Maintain the residual recommended by your water treatment specialist. 3.Check the strainer on the bottom of the collection basin and clean it if necessary. 4.Operate the make-up water float switch manually to ensure proper operation. 5.Inspect all moving parts such as drive shafts,pulleys, and belts. 6.Check for excessive vibration in motors, fans, and pumps. 7.Manually test the vibration limit switch by jarring it. 8.Look for oil leaks in gearboxes. 9.Check for structural deterioration, loose connectors, water leaks, and openings in the casing. 10.During periods of cold weather, check winterization equipment. Make sure any ice accumulation is within acceptable limits. Periodic 1.Check the distribution spray nozzles to ensure even distribution over the fill. 2.Check the distribution basin for corrosion,leaks, and sediment. 3.Operate flow control valves through their range of travel and re-set for even water flow through the fill. 4.Remove any sludge from the collection basin and check for corrosion that could develop into leaks. 5.Check the drift elimina tors, air intake louvers, and fill for scale build-up. Clean as needed. 6.Look for damaged or out- of-place fill elements. 7.Inspect motor supports, fan lades, and other mechanical parts for excessive wear or cracks. 8.Lubricate bearings and bushings. Check the level of oil in the gearbox. Add oil as needed. 9.Adjust belts and pulleys. 10.Make sure there is proper clearance between the fan blades and the shroud. 11.Check for excessive vertical or rotational replay in the gearbox output shaft to the fan. Annual 1.Check the casing basin,and piping for corrosion and decay.Without proper mainte -nance,cooling towers may suffer from corrosion and wood decay. Welded repairs are especially susceptible to corrosion. The protective zinc coating on galva -nized steel towers is burned off during the welding process. Prime and paint any welded repairs with a corrosion resistant coating. 2.Leaks in the cooling tower casing may allow air to bypass the fill. All cracks, holes, gaps, and door access panels should be properly sealed.Remove dust, scale, and algae from the fill, basin, and distribution spray nozzles to maintain proper water flow. 65 Cooling Tower Inspection Process Generally, the cooling tower structure and system should be inspected every six months in temperate climates. In more tropical and desert climates the interval should be more frequent, in accordance with equipment manufacturer and engineering recommendations. A list of items that need to be inspected is shown below: u Wooden structural members: - Look for rotten and broken boards, loose hardware and excessive fungal growth. The plenum area after the drift eliminators is the most likely to suffer wood rot, since biocides added to the water do not reach this area. Pay particular attention to structural members in this area. u structural members: - Check concrete supports and Other members for excessive weathering and cracking. Look for metal corrosion. On fiberglass ductwork and piping, check for cracking and splitting. u distribution throughout the tower should be uniform. Check Water piping for leaks. u Fans should be free of excessive vibration. Check mounts for deterioration and looseness. Examine blade leading edges for fouling, corrosion and dirt buildup. Check the fan stack for integrity, shape and stack-to-blade clearance. u for broken fill, debris in the fill, scale on fill water outlet. Inspect u debris and plant growth in the drift eliminator. Make sure the Look for eliminator is not broken or missing altogether. u for alga growth, scale and plugged nozzles in the hot water bay Check (cross flow towers). Nozzles should be checked monthly during the cooling season. u all observations on the Operator Checklist. This should include Record gearbox oil levels, oil additions (frequent refills could be a sign of bearing wear or leaks), water data, chemical inventories and hot water bay observations. Cooling Water Monitoring u to keep the water log sheet records up to date. Maintain a Be sure record of necessary components, control ranges, control capabilities (especially for calcium, pH, alkalinity, biocide, chemical feeds, conductivity, possible phosphate content.) Follow water treatment procedures closely. u Periodically check the water appearance for turbidity and foam. u wet surfaces for evidence of slime, algae or scale. Do the same Inspect for submerged surfaces. Use a corrosion coupon to monitor system corrosion rates where potential corrosion problems are indicated. u chemical additions for visible and uniform flow and proper Monitor rate. 66 WATER TREATMENT HAND BOOK u Heat exchangers can also be monitored for heat transfer performance to give an early warning of water treatment deficiencies. Small side stream test heat exchangers are available commercially for monitoring cooling water site fouling. Biological growth can rapidly cause systems to get fouled. Slime appearing on a submerged coupon is a good indicator that there is a problem. Submerged coupons, which are found in the cooling tower reservoir, indicate growth in less accessible areas of the cooling tower. Treatment Chlorination Filtration Sulphuric acid Inhibitors Antiscalant Antifoulant Fouling in cooling system Reasons of Fouling If fouling is not controlled, it will result in heavy deposits inside Silt introduced by the makeup water cooling water tubes, resulting in Dirt from air reduced tube diameter. Reaction of residues from chemical treatment Fouling is controlled by filtration and by chemicals and oxidation by Microbiological debris chlorine and or ozone Products produced by corrosion such as hydroxides and insoluble salts Selection of capacity of side stream filter % reduction of undissolved solids Select 80 % Time desired for reduction in hours = t= 48 hours maximum select maximum in 48 hours Blowdown = b in M3/hrs b=100 M3/Hrs V= total volume of cooling system M3 6000 Filtration rate F= v/t Loge[(100)/(100-%reduction)]-b Microorganism Bacteria, algae and fungi present in cooling water decreases the efficiency of heat transfer in cooling tower and condensers. Chlorine is the most widely used chemical in industry as oxidizing agent for destruction and dissolution of microorganism Chlorine is only effective when pH is between 6 to 7 Cooling water pH %of HOCl for effective oxidation 6 97 7 76 8 24 9 3 At pH 7 in CW system every 1 ppm Cl2 dosed only 0.76 ppm is used as oxidizing agent for control of microorganism General guidelines for chlorine dosing of reasonably good water Cooling Water System Estimated Chlorine dosage 67 Cooling Water System Once Through inland Lake /river/seawater Recirculation cooling water system Makeup water for CW circulation water Estimated Chlorine dosage Continuous dosing of 1-2 ppm + shock dosing of 3-5 ppm for 15 minutes after every 8 hour cycle Continuous 1-2 ppm. Shock dose of 3-5 ppm Continuous 1-2 ppm. Calculation of H2SO4 Dosing System CW circulation rate Makeup water percentage M Alkalinity to be maintained ppm M.Alkalinity in Makeup water ppm Cycle of concentration Quantum of M.Alkalinity ppm CWR=34000 P=2 M=150 A=140 C=2 (CWR*P/100 *Q) /1000 Acid dosing =34000* Required AH 0.02*130/ 1000=88.4 kgs at 98 % Dosage Quantity at 30oC H2SO4 % Sp.Gr Dosing D=AH/ Sp.Gr =88.4/ 1.826 =48.4 lph Q=[(A*C)-M]=[(140*2) -150]=130 98 1.826 68 WATER TREATMENT HAND BOOK Impact of Water quality Parameters on Cooling Systems Water Quality Parameters Impact on System Scaling Calcium scaling more troublesome because of inverse solubility of some calcium salts) Magnesium salt problematic whenn silica levels high. Can be corrosive. Useful in predicting Calcium carbonate scale potential Difficult to remove silica deposit Apart from makeup water, SS can also be present as corrosion and deposit by products. Can be cause of Under deposit corrosion by adhering to bio film. Ideal nutrient for Micro organism, Highly corrosive to copper, Reduces chlorine effectiveness as Disinfectant Problem when in high concentration (Ca>1000 ppm) & (PO4 >20 ppm) Calcium Phosphate deposit Corrosive at higher concentration For SS 300 ppm considered corrosive but for other metals >1000 ppm considered corrosive Forms undesirable foulants with Phosphate.Deactivates specialized polymers used to inhibit calcium phosphate scaling. Indication of Bio growth Good at low levels but can contribute to deposit at higher level Manure for microorganism Galvanized Corrosion Pretreatment like coagulation and clarification Side stream filtration Treatment Hardness (Ca +Mg ) Softening by external treatment Antiscalant Descaling if scaling has taken place Dealkalization Alkalinity mainly due bicarbonate Silica TSS Ammonia Bromine better disinfectant in presence of Ammonia Air stripping Close monitoring of Blowdown. Proper use of dispersant Phosphate Chloride Iron BOD Zinc Organism Heavy Metal Oxidizing Biocide 69 Non Oxidizing Biocides Material 1 Methylenebisthiocya-nate Tetrahydro 3,5Dimethyl2H-1-3,52 Thiadiazone-2Thione Na Dimethyl– Dithio3 carbamate DibromoNitrilo4 Propion-amide (Chloro) 5 Methylisothiazolin one Glutaral 6 dehyde % Formula Form active SCNCH2SCN Min Dose ppm Max Dose ppm Feed Time Min pH Max pH SS 10 25 50 1/wk 6 8 C5H10 N2S2 Sol 24 30 60 1/wk 6.5 14 C3H6NS2 Na Sol 30 20 40 1/wk 7 14 C3H2N2 OBr Sol 20 6 15 1/wk 6 8 C4H4NOS Cl & C4H5NOS O=CH (CH2)3 CH=O Sol 1.15 25 50 1/wk 6 9.5 Sol 45 25 100 1/wk 6 14 AlkylBenzylRC6H5 7 Dimethyl Ammonium (CH3)3 NCl Chloride Dioctyl(C6H17)2 Dimethyl (CH3)2 8 Ammonium NCl Chlorite Sol 9.4 30 120 1/wk 6 14 Sol 50 30 120 1/wk 6 14 SS-suspension & Sol=Solution (Source –Technical Data sheet of Vulcan Chemicals). 70 WATER TREATMENT HAND BOOK Oxidizing Biocides: Material Formula Form % FAC Residual Requirements Min Dose ppm Chlorine Dioxide ClO2 sol Max Dose ppm 0.5 C 5 9 Feed Type Min pH Max pH – 0.2 Chlorine Calcium Hypochlorite Sodium Hypochlorite (I) Sodium Hypochlorite(D) Lithium Hypochl orite Trichloro Isocyanuric acid Sodium Dichloro Isocyanuric acid Bromo, Chloro, Dimethyl Hydantion Sodium Bromide“Chlorine” Cl2 Ca (OCl)2 gas 100 0.5 1.0 C 6 7.5 solid 65 0.5 1.0 C 6 7.5 NaOCl solution 12 0.5 1.0 C 6 7.5 NaOCl solution 5 0.5 1.0 C 6 7.5 LiOCl solid 35 0.5 1.0 C 6 7.5 (CON Cl)3 solid 89 0.5 1.0 C 6 7.5 (CON)3 Cl2 Na solid 56 0.5 1.0 C 6 7.5 C5H6N2 O2ClBr solid –– 38% as NaBr 0.2 0.5 C 7 10 NaBr varies 2.0 4.0 C 7 10 71 Diagnostic Indicators for Cooling Systems Indicator Metals: Copper>0.25 mg/l Iron>1.0 mg/l Zinc>0.5 mg/l OR Measured corrosion rates Copper>0.2MPY Mild steel piping>3 MPY Mild steel Hex tubing> 0.5 MPY Galvanized steel>4 MPY Additives: Chlorine > 0.5 mg/l Ozone >0.2 mg/l Possible Problem High corrosion rate Inadequate chemical dosage control Use of conditioning chemicals containing copper or zinc Possible Solution Improve corrosion protection through use of an additive or by other means Improve additive dosage control and/or monitoring Eliminate use of additives containing copper or zinc Consider replacing copper components or piping Reduce or stabilize additive dosage Improve monitoring Install an automatic conductivity probe controlled oxidizing agent feed system. Raise pH Implement pH control Check dosage of low-pH additives Reduce recirculation rate Increase line size Replace copper elements with non metallic parts or other non copper parts Investigate: System settings Chemical dosing rates Blow down system operation Overuse of these oxidizing chemicals leads to high corrosion rates Carbon dioxide> 5 mg/l pH < 7.0 Copper oxide protection is inhibited Inadequate pH control Water velocity: > 3 feet/sec @ >150ºF > 5 feet/sec @ 120ºF > 8 feet/sec @ <90ºF Leaks or system failure High rate of corrosion of copper piping;could cause leaks or system failure Conductivity outside the manufacturer's recommended range System operation not optimized Possible misuse of additives Improper blowdown rate The heat load to the system has greatly increased. Possible massive system leak. The water consumption rate has increased greatly. Check if additional heat load has been added on the system today. Check the system for leaks. Inspect sanitary sewer and storm sewer manholes on site for unusually high flows. 72 WATER TREATMENT HAND BOOK Cooling water distribution headers in all plants are generally of carbon steel without any protective lining. In some places Hume pipe are also used to severe corrosion. Coolers and condensers (tube Bundles) Fertilizers – Stainless steel and carbon steel Oil refineries – general admiralty brass but in some cases combination of admiralty brass and carbon steel Petrochemicals- Combination of 90-10 Copper Nickel, admiralty brass, SS and carbon steel LPG Plants- mainly carbon steel Acrylic Fiber Plants – Stainless steel, Copper –Nickel and carbon steel Chilling and refrigeration - 90-10 copper Nickel, Copper / SS Air compressor & Nitrogen Plants – Admiralty Brass Power plants – Copper-Nickel /Copper /SS Control limits for various cooling water treatments Table1 SHMP + Zn Characteristics 1 2 3 4 5 6 7 8 9 pH MO Alkalinity Ca Hardness Total hardness Chloride as Cl Sulphate as SO4 Silica as SiO2 TSS Unit Mg/L Mg/L Mg/L Mg/L Mg/L Mg/L Mg/L Mg/L 200-300 300-500 200-300 800-1000 75-100 20-30 (30-50) SHMP+CrO4+Zn Normal Maximum Normal Maximum 6.3 6.8 *1 6.5-7.0 7.0 *1 300 500 300 *2 200-300 300-500 200-300 800-1000 75-100 20-30 300 500 300*2 1000 100 30 1000 100 30 (50) *3 Organo Phosphate Mg/L (HEDP) as PO4 10 Total Inorganic Phosphate as PO4 Mg/L 11 Chromate as CrO4 Mg/L Mg/L Mg/L Mg/L 15-20 –– 3-5 5-10 25*4 –– 5*4 10 10-15 20-25 2-3 –– 15*4 30*4 3*4 –– 12 Zinc Sulphate as Zn Polymeric 13 dispersant TDS 14 1200-1500 1500 1500-2000 2000 *1-MO Alkalinity will find its own level based on pH to be maintained. *2- In case of stainless steel exchangers, chloride levels will be low depending on design. *3- With polymeric dispersant *4 Actual inhibitors levels depend on operating conditions 73 Table2 Zn+O-PO4+ Polymer Characte ristics 1 2 3 4 5 6 7 8 pH MO Alkalinity Ca Hardness Total hardness Chloride as Cl Sulphate as SO4 Silica as SiO2 TSS Organo Phos phate(HEDP) as PO4 Unit Mg/L Mg/L Mg/L Mg/L Mg/L Mg/L Mg/L Mg/L 300400 600800 200-300 8001000 75-100 30-50 Normal 7.5–8.0 Maxi mum 8.0 Zn +HEDP Normal Maxi mum Zn +HEDP + SHMP (max) Nor Maxi mal mum *1 *1 *1 400 800 300*1 1200 125 50 300-400 600-800 200-300 800-100 75-100 20-30 (30-50)*3 400 800 300*2 1200 125 30 (50)*3 300-400 600-800 200-300 8001000 75-100 400 800 300*2 1200 125 20-30 30 (30-50)*3 (50)*3 9 Mg/L – – 8-10*4 10*4 4-6*4 4-6*4 Total Inorga 10 nic Phosp-hate as PO4 Orthophos 11 phate as PO4 12 Zinc Sulphate as Zn Polymeric 13 dispersant 14 TDS Mg/L – – – – 6-8*4 8*4 Mg/L Mg/L Mg/L Mg/L 8-10*4 1-1.5 20-30 15002000 15*4 1.5 50 2000 – 2-3 5-10 15002000 – 3 10 2000 – 1.5-2 15-20 15002000 – 2 20 *1-MO Alkalinity will find its own level based on pH to be maintained. *2- In case of stainless steel exchangers, chloride levels will be low depending on design. *3- With polymeric dispersant *4 Actual inhibitors levels depend on operating conditions 74 WATER TREATMENT HAND BOOK Puckorius Scaling Index The Langelier Saturation Index and Ryznar Stability Index were originally developed to identify scaling (calcium carbonate) and corrosion tendencies of water in supply piping. These indexes, which are still in wide use today, are considered very conservative. Most scaling and corrosion conditions identified by these indexes can typically be controlled by specialty chemicals. Their usefulness is therefore limited, but because of their common use, the following calculation procedure is provided The Puckorius Scaling Index modifies the Ryznar Stability Index by calculating the pH of the bulk water, and thus, more accurately predicts scaling conditions. LSI = (measured pH) - (pHs). A positive value indicates scale; a negative value, no scale. RSI = (2 pHs) - (measured pH). A value below 6 means scale; above 6, no scale. Calculating pH of saturation (pHs). The pH of saturation (pHs) can be determined from the relationship between various characteristics of water. The following factors and formula are used in determining the pHs: (1) Factors Needed to Calculate pHs: A = Total Dissolved Solids (ppm), table B-1 B = Temperature (oF), table B-2 C = Calcium Hardness (ppm as CaCO3), table B-3 D = Total Alkalinity (ppm as CaCO3), table B-4 (2) pHs = 9.30 + A + B - (C + D) Calculation of Calcium Carbonate Saturation Index Factor "A" FOR Total dissolved Solids Total Solid Mg /liter 50 100 600 1000 2000 3000 4000 5000 Value of “A” 0.07 0.1 0.18 0.2 0.22 0.24 0.25 0.26 o Factor "B" FOR Temperature F 32-34 36-42 44-48 50-56 58-62 64-70 72-80 82-88 90-98 100-110 112-122 124-132 134-146 148-160 162-178 o C 0-1 2-6 7-9 10-13 14-17 18-21 2.1 28-31 32-37 38-43 44-50 51-55 56-64 65-71 72-81 Value of “B” 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 75 Factors "C" for Calcium Hardness (as ppm CaCO3)* Zero to 1000 ppm Calcium Hardness Value of “C” As CaCO3 10-11 12-13 14-17 18-22 23-27 28-34 35-43 44-55 56-69 70-87 88-110 111-138 139-174 175-220 221-270 271-340 341-430 440-550 551-690 691-870 871-1000 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Calcium Hardness Value of “C” As CaCO3 10-11 12-13 14-17 18-22 23-27 28-34 35-43 44-55 56-69 70-87 88-110 111-138 139-174 175-220 221-270 271-340 341-430 440-550 551-690 691-870 871-1000 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.+ 3.0 76 WATER TREATMENT HAND BOOK Equilibrium pH Value (pHeq) determined from Total Alkalinity Alkalinity ppm hundreds 0 100 200 300 400 500 600 700 800 900 0 –– Alkalinity, ppm CaCO3, tens 10 20 30 40 50 60 70 80 7.33 7.84 8.15 8.32 8.47 8.59 8.68 8.78 8.85 8.92 90 7.44 7.88 8.15 8.34 8.48 8.60 8.70 8.79 8.86 8.93 6.00 6.45 6.70 6.89 7.03 7.14 7.24 7.77 7.81 8.08 8.10 8.29 8.30 8.44 8.46 8.57 8.58 8.67 8.67 8.76 8.77 8.84 8.85 8.91 8.92 7.47 7.53 7.59 7.64 7.68 7.73 7.91 7.94 7.97 8.00 8.03 8.05 8.17 8.19 8.21 8.23 8.25 8.27 8.35 8.37 8.38 8.40 8.41 8.43 8.49 8.51 8.52 8.53 8.54 8.56 8.61 8.62 8.63 8.64 8.65 8.66 8.71 8.72 8.73 8.74 8.74 8.75 8.79 8.80 8.81 8.82 8.82 8.83 8.87 8.88 8.89 8.89 8.90 8.90 Example 1 Water from a cooling tower has a TDS of 1,000 ppm, calcium hardness of 500 ppm (as CaCO3), total alkalinity of 100 ppm (as CaCO3) and measured pH of 8.2. The hottest temperature on the waterside of the heat exchanger is 120oF. pHs = 9.30 + A + B - (C + D) pHs = 9.30 + 0.20 + 1.57 - (2.30+2.00) = 6.77 Example 2 Water from a cooling tower has a total alkalinity of 100 ppm (as CaCO3) and a measured pH of 8.2 (same as example 1). From table 5, the pHeq is 7.47. PSI = (2pHs) - (pHeq) = 2 (6.77) - 7.47 = 13.54 - 7.47 = 6.07 RSI = (2pHs) - (measured pH) = 13.54 8.2 = 5.34 LSI = (measured pH) - (pHs) = 8.2 6.77 = +1.43 The pHeq may also be calculated as follows: pH eq = 1.485 log TA + 4.54 where TA denotes total alkalinity. 77 Scaling Indices versus conditions LSI 3.0 2.0 1.0 0.5 0.2 0.0 -0.2 -0.5 -1.0 -2.0 -3.0 PSI/RSI 3.0 4.0 5.0 5.5 5.8 6.0 6.5 7.0 8.0 9.0 10.0 Condition Extremely severe scaling Very severe scaling Severe scaling Moderate scaling Slight scaling Stable water, no scaling, no tendency to dissolve scale No scaling, very slight tendency to dissolve scale No scaling, slight tendency to dissolve scale No scaling, moderate tendency to dissolve scale No scaling, strong tendency to dissolve scale No scaling, very strong tendency to dissolve scale Selection of capacity for side stream Filter for cooling tower F=V/t loge [(100) / (100-% reduction)]-b % of reduction of undissolved solids (select 80 %) t= time desired for reduction in hours (select maximum of 48 hours) b= blowdown rate in m3/hr V= total volume of cooling system in M3 Example for V=6000 M3, t=48 hours and b=100 M3/Hr F=100 M3/H 78 WATER TREATMENT HAND BOOK CHAPTER 9 79 Pumps Introduction Pumps play a vital role in any water treatment system. Pump moves liquid from one place to another. Hence selection of pump is very critical in all water treatment system. Here we are giving general guideline, which will help, in discussing with the pump manufacturer or supplier. Types of Pump The three types of pump most commonly employed are Centrifugal, Rotary and Reciprocating. Each class of pump is further divided into. Pump Class Type Volute Diffuser Regenerative turbine Vertical Turbine Mixed Axial Flow Axial flow (Propeller) Gear Vane Cam & Piston Screw Lobe Shuttle Block Direct acting Power(including Crank & Flywheel) Diaphragm Piston Simplex Duplex Triplex Single stage and Multistage. See manual on pumps Centrifugal Rotary Reciprocating Characteristics of different types of pumps Characteristics Discharge Flow Usual Maximum suction lift (Meters) Centrifugal Steady 4.6 Clean, clear dirty abrasive and liquids with high solid content. Low to high Rotary steady 6.7 Viscous, Nonabrasive Reciprocating steady 6.7 Liquid handled Clean and clear Discharge Pressure range Medium Low to high 80 WATER TREATMENT HAND BOOK Usual capacity range How increased head affects capacity Power input How decreased head affects capacity Power input Smallest to largest available Decrease Depends on specific speed Increase Small to medium None Increase Relatively small Decrease and None for duplex and triplex Increase Increases marginally None Depends on specific speed Decrease Decrease Liter/sec Average efficiency Total head in meters 5 7 10 20 30 50 70 100 200 300 500 1 34 2 44 3 50 5 58 10 66 20 72 30 75 50 78 100 81 200 83 0.15 0.20 0.29 0.58 0.87 1.44 2.02 2.88 5.77 8.65 14.4 1.23 0.31 0.45 0.89 1.34 2.23 3.12 4.46 8.92 13.4 22.3 0.30 0.41 0.59 1.18 1.77 2.94 4.12 5.88 11.8 17.7 29.4 0.43 0.59 0.85 1.69 2.54 4.23 5.92 8.45 16.9 25.4 42.3 0.75 1.04 1.49 2.97 4.46 7.43 10.4 14.9 29.7 44.6 74.3 1.47 1.91 2.73 5.45 8.18 13.6 19.1 27.3 54.5 81.8 136 1.96 2.75 3.92 7.84 11.8 19.6 27.5 39.2 78.4 118 196 3.15 4.4 6.3 12.6 18.9 31.5 44.0 63.0 126 189 315 6.05 8.48 12.1 24.2 36.3 60.5 84.8 121 242 363 605 11.8 16.6 23.6 47.3 71.0 118 166 236 473 710 1180 81 Basic guideline for selecting Pump 1. 2. Sketch the proposed piping layout. Base the sketch on actual job condition. Single line diagram can be used Determine the required capacity of pump. The required capacity is the flow rate, which has to be handled at a particular pressure. Once the flow rate has been determined a suitable factor of safety is applied. In any case it should not be less than 10 % Compute the total head on pump Analyze the liquid conditions. Obtain complete data on liquid to be pumped. Select the class and type as given in the table Evaluate the pump chosen for installation. Check specific speed, impeller type and operating efficiency. 3. 4. 5. 6. Formulas required for pump Calculation Specific speed of impeller Nq=3.65*n*Q ½ / H ¾, Where n= speed in rpm H= head in meters, Q= discharge in Cubic meter /sec This calculation allows comparison of all types of rotodyanmic pump on equal footing. Pressure and Specific Gravity Pressure developed by pump is proportional to specific gravity of liquid. P=H, Where Y is the specific gravity H in meters = Pressure in absolute atmosphere/ Sp.Gravity H in Feet = Pressure psi/Sp. Power Absorbed by pump Power = *Q*H /C1*n, Where Y is Sp.Gravity Q –Discharge rate (capacity) in Cubic meter /sec H= head in Meter C1 = 75 for power in Metric HP = 76.04 for power in British HP = 101.98 for power in Kw =1000 kgf/M3 at 4C Motor, brake, and water horsepower can be calculated as follows: Mhp = Brake horsepower / Motor efficiency Bhp = Water horsepower / pump efficiency Whp = head (ft) x flow (gpm) /3960 To better understand the performance and operating characteristics of pumps, operators should become familiar with the pump curve that is supplied by the manufacturer for each pump. 82 WATER TREATMENT HAND BOOK Pump curves usually show three curves on one sheet: u The head-capacity curve shows the discharge in gallons per minute (gpm) the pump will deliver against various heads when operated at the proper speed. This curve shows that as the head increases, the discharge decreases, until there is no further discharge. Conversely, as head decreases, flow increases. u The second curve, also plotted against flow, shows the efficiency at which the pump operates at various points on the head capacity curve. This curve shows that no pump is 100% efficient, due to internal friction losses. The highest efficiency that can be hoped for is around 85%. Efficiency can be expected to decrease with age and wear. u curve, the brake horsepower curve, shows power consumed The third plotted against flow. If we know the total head at which the pump is operating, we can use the curve to find the gallons pumped. The power required by the pump, as well as the pump efficiency, can also be read from the curve for any set of conditions. This curve shows that it usually takes more horsepower to pump more water: the lower the flow, the lower the horsepower required, and the higher the flow, the higher the horsepower required. 83 CHAPTER 10 84 WATER TREATMENT HAND BOOK Raw Water Treatment Objectives The objectives of a public water supply water system are to provide safe and aesthetically appealing water to the customers without interruption and at a reasonable cost- an adequate quantity of water at sufficient pressure for fire protection and industrial water for manufacturing. Selection of Water Treatment Processes Selection of a suitable water treatment process for a given utility is always a complex and diverse task. Conditions are likely to be different for different water utility. Adoption of an appropriate water treatment process by a water utility is influenced by the necessity to meet the regulatory guidelines, the desire of the utility and its customers to meet other water quality standards and objectives and the need to provide water service at the lowest reasonable cost. A water treatment plant should be designed considering the fact that it should supply continuous and safe water to the customers regardless of the raw water characteristics and the environmental conditions. Hence, the selection of treatment process is important in the plant design. The ultimate plant design has a system that is proven to be simple, effective, reliable, durable and costeffective. The design of water treatment plant starts with the preliminary studies that include: 1. Design period; 2. Water supply areas – identifying the areas to be served; 3. Population – estimating the present and future population; 4. Estimating maximum daily water demand; 5. Evaluation and selection of the water source; 6. Size of the treatment plant; 7. Location of the treatment plant site; and 8. Financing. The selection of package treatment plants and special proprietary devices or processes should be based on proper consideration of: Raw water condition and demand variability; 1. Operation and maintenance; 2. Servicing, repairs or replacement; and Operational flexibility. 85 Water Treatment Processes Aeration Aeration is the process of bringing water and air into close contact in order to remove dissolved gases, such as carbon dioxide, and to oxidize dissolved metals such as iron. It can also be used to remove volatile organic chemicals (VOC) in the water. Aeration is often the first major process at the treatment plant. During aeration, constituents are removed or modified before they can interfere with the treatment processes. Examples of aeration processes include diffused mechanical nozzle spraying, multiple tray cascading and packed power type. Coagulation The first step destabilizes the particle's charges. Coagulants with charges opposite those of the suspended solids are added to the water to neutralize the negative charges on dispersed non-settlable solids such as clay and colorproducing organic substances. Once the charge is neutralized, the small-suspended particles are capable of sticking together. The slightly larger particles formed through this process and called microflocs, are not visible to the naked eye. The water surrounding the newly formed microflocs should be clear. If it is not, all the particles' charges have not been neutralized, and coagulation has not been carried to completion. More coagulant may need to be added. Flocculation Following the first step of coagulation, a second process called flocculation occurs. Flocculation, a gentle mixing stage, increases the particle size from submicroscopic microfloc to visible suspended particles. The microflocs are brought into contact with each other through the process of slow mixing. Collisions of the microfloc particles cause them to bond to produce larger, visible flocs called pinflocs. The floc size continues to build through additional collisions and interaction with inorganic polymers formed by the coagulant or with organic polymers added. Macroflocs are formed. High molecular weight polymers, called coagulant aids, may be added during this step to help bridge, bind, and strengthen the floc, add weight, and increase settling rate. Once the floc has reached it optimum size and strength, the water is ready for the sedimentation process. 86 WATER TREATMENT HAND BOOK Sedimentation Sedimentation basins are used to settle out the floc before going to the filters. Some type of sludge collection device should be used to remove sludge from the bottom of the basin. Filtration Removal of suspended solids by filtration plays an important role in the natural treatment of groundwater as it percolates through the soil. It is also a major part of most water treatment. Groundwater that has been softened or treated through iron and manganese removal will require filtration to remove floc created by coagulation or oxidation processes. Since surface water sources are subject to run-off and do not undergo natural particles and impurities. Iron and manganese in water also promote the growth of iron bacteria, a group of organisms that obtains its energy for growth from the chemical reaction that occurs when iron and manganese mix with dissolved oxygen. These bacteria form thick slime growths on the walls of the piping system and on well screens. Such shines are rust-colored from the iron and black-colored from the manganese. Variations in flow can cause these slime growths to come loose, resulting in dirty water in the system. Disinfection The object of disinfection is to kill disease-causing organisms present in the water. With regard to water treatment, disinfection refers to the destruction of most intestinal or fecal bacteria. Sometimes disinfection is not complete. Some viruses and especially some protozoa, such as Giardia or cryptosporidium, could survive the disinfection process. The only method of complete protection is to sterilize the water by boiling it for a period of 15 to 20 minutes The methods of disinfection practical in public water supplies are chlorination, ozonation, use of ultra-violet light, and over-liming. Potassium permanganate, iodine, bromine, and silver are also used, but less frequently. Chlorination is so widely used that the term disinfection and chlorination are almost the same in waterworks practice. Coarse Screen Coarse screens, often termed bar screens or racks, and must be provided to intercept large, suspended or floating material. Such screens or racks are made of l/2-inch to 3/4-inch metal bars spaced to provide 1- to 3-inch openings. Fine Screen Surface waters require screens or strainers for removal of material too small to be intercepted by the coarse rack, These may be basket-type, in-line strainers, manually or hydraulically cleaned by back washing or of the traveling type, which are cleaned by water jets. Fine screen, clear openings should be approximately 3/8 inch. 87 Design Parameters for Water Treatment Processes Aeration Forced or induced draft aeration devices should be designed to ensure even water distribution, adequate counter currents of air and proper external exhausting. As a guide, the loading should be within the range of 0.7 to 3.4 L/s per m² of total tray area (0.8 to 4 gpm/ft.) and 5 or more trays used with separations not less than 150 mm (6 inches). Where pressure aeration is proposed for oxidation purposes, consideration should be given to compressed air quality and mixing, the scaling potential of the water and subsequent air release. Aerators should have a bypass and provisions should be made for inspection and cleaning of the devices. Exhaust gases should be vented outside the building. Coagulation To achieve proper coagulation, high intensity rapid mixing is considered necessary. It is recommended that rapid mixing be accomplished by either an in- line-mixing device or mixing in a separate process tank. Typical energy gradients (G values) would be in the range of 1000 sec-1. It is recommended that some flexibility be provided in rapid mix design if possible. Flocculation The design of flocculation systems should allow for low velocities and avoidance of rapid acceleration to ensure maintenance of a good floc. When designing a flocculation process, selection of the mode of mixing and determination of the physical relations and characteristics of the flocculation tanks and clarifiers (sedimentation tanks) are among the first decisions to be made; either hydraulic mixing or mechanical mixing may be chosen. Where sedimentation follows flocculation, the retention time for floc formation should be at least 30 minutes. Sedimentation This process is designed to remove a majority of the settleable solids by gravitational settling, thereby maximizing the downstream unit processes such as filtration. The factors that influence sedimentation efficiency include: Surface overflow rate (also known as surface loading rate); Inlet and outlet arrangements; type of sedimentation tank; Raw water characteristics and local climate conditions. There are three main configurations for sedimentation tanks: horizontal rectangular basins; upflow sedimentation tanks; and upflow clarifiers with sludge blanket. 88 WATER TREATMENT HAND BOOK Design Data Typical Design Values Equipment Design Parameter Unit Remarks Design should have provision for disposing Debris removed by screens Coarse Screen Coarse Screen 0.05–0.08 Meter /sec Fine Screen Aeration Velocity Tray type Water velocity Air requirement Tray spacing Area required Cascade Type Head Area Flow velocity Spray Type Head Nozzle diameter Nozzle spacing Nozzle discharge Basin are Spray pressure 0.4 –0.8 0.8-1.5 7.5 30-75 50-160 1.0-3.0 85-105 0.3 1.2-9 2.5-4.0 0.6-3.6 5-10 105-320 about 70 Meter /sec m3/m2/min m3/m3 water cm m2/m3.s meter m2/m3.s m/s meter cm meter liter/sec m2/m3.s kPa Coagulation Rapid Mix Detention time Velocity gradient Gt Slow Mix Detention time Velocity gradient Gt 0.2-5 700-1000 3X104 –6X104 0.2-5 15-60 1X104 –15X104 Min S-1 Flocculation 89 Sedime-ntation Rectangular Tanks Surface overflow rate: Detention time: Water depth: Width/Length Weir loading: Upflow Clarifiers Surface overflow rate: Detention(settling) time: Water depth: Weir loading: Upflow velocity Sludge Blanket Clarifiers Surface overflow rate: Detention (settling) time: Weir loading: Upflow velocity: Flocculation time 0.8 – 2.5 1.5 – 3 3–5 > 1/5 < 11 1.3 – 1.9 1–3 3–5 7 <3 1– 3 1–2 7 - 15 < 0.6 20 Meter/Hr Hour Meter M3/Hr.M Meter/Hr Hour Meter M3/Hr.M m/h Meter/Hr Hour M3/Hr.M m/h minutes Rapid sand filter Filtration Rate Backwash rate Air scour Filtration system Minimum filtration cycle Filter media depths Dual Media Silica Anthracite Pressure Filters Filtration rate 120-140 37-50 37-73 24 >24(600) >200 >450 <15 M3/M2.day M3/M2.Hr M3/M2.Hr Hour Inches (mm) mm mm M/hour Taste & Odour Control Aeration as described before. KMnO 4 Dosage PAC dosage Chlorine Dose Chlorine residual Ozone dose Fluoride Dose 0.5-2.5 0.5-5 Mg/liter Mg/liter PAC is Powdered activated carbon. The dosage of PAC can at times go upto 50 mg/L Disinfe-ction 1-5 0.5-1 1-5 0.7-1.2 Mg/liter Mg/liter Mg/liter Mg/liter Fluoride 90 WATER TREATMENT HAND BOOK Membrane Processes Microfiltration (MF) Pore size Pressure Ultrafiltration (UF) Pore size Pressure Nanofiltration (NF) Pore size Pressure Reverse osmosis (RO) Pore size Pressure 0.1– 0.2 0.7 – 1.4 (10 – 20) 0.003 – 0.01 0.7 – 7.8 (10-40) 0.001 – 0.005 5.3 – 10.6 (150) m kg/cm2 psig m mm kg/cm2 psig m mm kg/cm2 psig <1 nm > > 14 (200) kg/cm2(psi) Distribution Velocity in mains Pressure 1-2 138-1000 M/sec kPa Detention Parameters for Sedimentation coagulants in Water treatment Type of Treatment Overflow Rate M3/M2/day 20-30 28-40 Detention Time hours 2-8 2-8 for various Channel Loadings M3/M/Day 150-220 200-275 Alum coagulation Iron coagulation Lime-soda coagulation 28-45 4-8 200-275 91 CHAPTER 11 92 WATER TREATMENT HAND BOOK Industrial Waste Water Treatment Industrial Pretreatment Processes The treatment of industrial wastewater involves the same processes as those used in the treatment of civil water. However, because of specific compositions, the systems tend to vary. The chemical-physical type processes are especially important for the removal of inorganic matter. The basic processes used are Wastewater Unit operation Unit Operation Screening Comminution Flow equalization Sedimentation Flotation Granular –medium Filtration Precipitation Adsorption Disinfection Dechlorination Other Chemical Processes Activated sludge Process Aerated Lagoon Trickling Filters RBC Pond Stabilization Anaerobic digestion Biological nutrient removal Physical Chemical Biological Physical u Screening is removal of coarse solids by use of a straining device. u Sedimentation is gravity settling of pollutants out of the wastewater. u Flotation is the use of small gas bubbles injected into the wastewater, which causes pollutant particles in the wastewater to rise to the surface for subsequent removal. Air stripping is removal of volatile and semi-volatile organic u compounds from wastewater by use of airflow. 93 Chemical Neutralization is adjustment of alkalinity and acidity to the same u concentration (pH 7). Precipitation is addition of chemicals to wastewater to change the u chemical composition of pollutants so that the newly formed compounds settle out during sedimentation. Coagulation is use of chemicals to cause pollutants to agglomerate u and subsequently settle out during sedimentation. Adsorption is use of a chemical, which causes certain pollutants to u adhere to the surface of that chemical. Disinfection is use of a chemical (or other method such as ultraviolet u radiation) to selectively destroy disease-causing organisms. (Sterilization is the destruction of all organisms.) Breakpoint chlorination is the addition of chlorine to the level that u chloramines will be oxidized to nitrous oxide and nitrogen, and chlorine will be reduced to chloride ions. Biological Air activated sludge is an aerobic process in which bacteria consume u organic matter, nitrogen and oxygen from the wastewater and grow new bacteria. The bacteria are suspended in the aeration tank by the mixing action of the air blown into the wastewater. This is shown schematically in Figure 1. There are many derivations of the activated sludge process, several of which are described in this section. High purity oxygen activated sludge is an aerobic process very similar u to air activated sludge except that pure oxygen rather than air is injected into the wastewater. Aerated u pond/lagoon is an aerobic process very similar to air activated sludge. Mechanical aerators are generally used to either inject air into the wastewater or to cause violent agitation of the wastewater and air in order to achieve oxygen transfer to the wastewater. As in air activated sludge, the bacteria grow while suspended in the wastewater. Trickling u filter is a fixed film aerobic process. A tank containing media with a high surface to volume ratio is constructed. Wastewater is discharged at the top of the tank and percolates (trickles) down the media. Bacteria grow on the media utilizing organic matter and nitrogen from the wastewater. Rotating u biological contactor (RBC) is a fixed film aerobic process similar to the trickling filter process except that the media is supported horizontally across a tank of wastewater. The media upon whom the bacteria grow is continuously rotated so that it is alternately in the wastewater and the air. Oxidation ditch is an aerobic process similar to the activated sludge u process. Physically, however, an oxidation ditch is ring-shaped and is equipped with mechanical aeration devices. 94 WATER TREATMENT HAND BOOK Pollutant Bio-Chemical Oxygen Demand (BOD) Pretreatment Processes Activated Sludge Trickling filter or RBC Aerated lagoon Oxidation ditch Sedimentation Screening Flotation Chemical precipitation Nitrification/denitrification Air stripping Breakpoint chlorination Chemical precipitation Biological treatment Air stripping Biological treatment Chemical precipitation Evaporation Membrane process Coagulation Flotation Biological treatment Membrane process Air stripping Biological treatment Carbon adsorption Chemical disinfection UV radiation ozonation Total Suspended Solids (TSS) Nitrogen Phosphorus Heavy metals Fats, Oil and Grease (FOG) Volatile Organic Compounds Pathogens 95 Pretreatment Process Physical Screening Sedimentation Centrifugation Air stripping Chemical Neutralization Precipitation Coagulation Adsorption Items to Look for in the Field for Efficient Operation No blinding or clogging of screens, no excessive build-up of material on the screen Low flow rate, no short circuiting of flow, no floating sludge, scum removal if appropriate No scaling of packing and piping, or freezing problems at low temperatures pH monitoring, automated chemical feed, adequate mixing Automated chemical feed system, adequate mixing & contact timer Automated chemical feed system, adequate mixing & contact timer Efficient means of regeneration is key to performance Automated chemical feed system, adequate mixing & contact timer Disinfection Biological Activated sludge Fine bubble aeration, even distribution of air and mixing, dissolved oxygen concentration monitoring, air flow turndown capability, no bulking/floating sludge Method for positive air circulation, even & periodic dousing of filter media Steady shaft rotation Trickling filter Rotating biological contactor (RBC) 96 WATER TREATMENT HAND BOOK CHAPTER 12 97 Chemical Cleaning General Guidance Chemical cleaning of water systems can be divided into two classifications: preoperational and remedial. Pre-operational cleaning is performed to prepare the water-contacted metal surfaces to receive chemical treatment, which provides protection from scale, corrosion, and microbiological growth. Remedial cleaning is performed to restore water systems that have been fouled with scale, corrosion products, and microbiological growth due to inadequate or ineffective water treatment. Cleaning, particularly remedial cleaning is often performed by outside contractors familiar with cleaning procedures, techniques, and safety. It should be noted that if the water system is significantly scaled, the chemical treatment program was obviously inadequate and was not properly designed, set-up, controlled, or applied. After cleaning has been completed, the chemical treatment program and QC program must be improved so the same problem does not recur. Use of a well-designed QA program would have produced identification and notification of potential and developing problems before they became serious. Pre-operational cleaning is often performed by contractors responsible for the fabrication of the water system before turning it over to the military installation. Water system operations personnel must assess the effectiveness of any cleaning process that has been performed. Pre-Operational Cleaning Pre-operational cleaning can be performed on all new systems or pieces of equipment installed in any existing system, including new boiler tubes or new chiller copper tube bundles. New piping and coils will usually be contaminated with materials such as mill scale, rust, oil, and grease resulting from the fabrication, storage, and installation of the equipment. Pre-operational cleaning is performed to remove these materials and prepare metal surfaces to receive corrosion protection from chemical treatment. Pre-operational cleaning agents that are used include detergents, wetting agents, rust removers, and dispersants. These cleaning agents have a pH in the range of 9 to 11. Water systems containing piping or components constructed of galvanized steel and aluminum should not be subjected to procedures that require high pH (greater than 8.5) because this would contribute to initiating corrosion of these surfaces. The requirement for performing a pre-operational cleaning process is usually written into the specification for new construction of a water system that must be performed by a mechanical contractor. The mechanical contractor is required to perform the work as directed in the specifications. However, if the specifications are not appropriate for the specific system, including consideration of all system metallurgy, the cleaning process may contribute to corrosion to mild steel, galvanized steel, copper, or aluminum, or it may result in incomplete cleaning of dirty and corroded metal surfaces. A qualified inspector should review the specifications or qualified independent consultant to ensure that cleaning agents and procedures have been specified appropriately. 98 WATER TREATMENT HAND BOOK Remedial Cleaning Remedial cleaning is performed to restore a water system that is fouled with scale, corrosion products, or microbiological biomass due to inadequate or ineffective waters treatment. The problem could have resulted from using improper chemical technology, failure to maintain treatment levels within control parameters or the failure of pre- treatment equipment. The cleaning agents used for remedial cleaning usually include acids, chelants, neutralizing agents, and specialty cleaning chemicals. Safety and Environmental Issues Remedial cleaning may pose safety issues for personnel handling acids, caustics, and various chemicals. There could also be environmental concerns associated with chemical disposal. Inexperienced personnel should not perform the chemical cleaning of an industrial water system. Contracting Cleaning Services For some cleaning jobs, such as large boilers and cooling towers, it may be advisable to engage a service company specializing in chemical cleaning. If the cleaning service is contracted, it is vital that adequate lines of communication be established, and that safety procedures employed by the service company comply with military regulations. An orientation meeting should be scheduled between military installation personnel and the service company representatives. At that time, the scope of the work can be defined, proper procedures initiated, and the nature of the hazards described thoroughly. The use of proprietary cleaning chemicals or chemical formulations may be involved; disclosure of the use and nature of these chemicals should be made at the orientation meeting. Military policies and restrictions can also be explained. Reasons for Cleaning Maintenance of an effective water treatment program is essential to minimize scale and corrosion problems in industrial water systems; however, scale and deposits that form will require remedial cleaning (descaling). If not removed, these scale and water-caused deposits may impact the safety of operations personnel, interfere with heat transfer, and cause excessive damage to, or destruction of, the water-using equipment. Cleaning is not appropriate for the removal of deposits when corrosion of the system has advanced to the point where a large number of leaks may result from the removal of the deposits. Types of Deposits The deposits that occur in water systems can be inorganic mineral salts and corrosion products or organic (oily) or biological in nature. Deposits range in composition from very dense crystalline structures, to very porous and loosely bound materials, to gelatinous slimes. Most of the deposits formed from water constituents consist of corrosion products such as iron and copper oxides, mineral scales, or mixtures of these materials. 99 Waterside Deposits Located in Heat Exchangers Water deposits located in heat exchangers are usually carbonate-based scales, while steamside deposits may be a mixture of metallic oxides and organic residuals from lubricating oil, particularly where reciprocating-type engines are used. In steam systems, the oxides are usually iron and copper, resulting from aggressive condensate. Microbiological deposits may form in cooling systems from bacterial or algae growths, or from decomposition products of various microorganisms. Boiler Deposits Boiler deposits may take various forms. In low-pressure boilers using a relatively hard feedwater, deposits are essentially calcium and magnesium, silicates, sulfates, carbonates, phosphates and hydroxides, plus some organics. Deposits may also contain considerable amounts of silica, iron, and copper. These deposits can be spongy or porous or relatively hard and glasslike. Deposits of the latter characteristic occur where silica is present in appreciable quantities in the boiler water. Deposits in medium-pressure to high-pressure boiler systems usually are mixtures of iron and copper oxides and phosphates. Dense deposits may tend to form in high-heat transfer areas. Considerable quantities of sludge-type accumulations may be found in downcomers, mud drums, waterwall headers, crossover tubes, and areas of low water circulation in the boiler. Remedial Cleaning Procedure Cleaning procedure information and procedures presented in this Chapter are general in nature and must be modified to fit specific applications. Because contractors perform most cleanings, these procedures are provided only for general information. Cleaning Methods There are two methods generally adopted for cleaning 1. Mechanical 2. Chemical Mechanical Methods Mechanical methods are the oldest techniques used for removing deposits. To perform an adequate mechanical-type cleaning, the equipment to be cleaned may need to be partially or entirely dismantled. Even when equipment is dismantled, some areas may be extremely difficult to reach and clean. Chemical cleaning has largely replaced mechanical process equipment cleaning as the most satisfactory method of removing deposits; however, mechanical methods such as wire brushing, tumbling, scraping, and abrasive blasting with sand and grit are still employed in special applications. Chemical Methods In this method acid or alkali is generally used for cleaning. At times there are other chemicals which are also used for cleaning. 100 WATER TREATMENT HAND BOOK Cleaning Agents Cleaning agents may be broadly classified as being acid, alkaline, organic, or solvent cleaners. There is no general or universal cleaner that removes all deposits. The selection of a solvent or cleaning agent is based on the material's ability to remove or dissolve the deposit, as well as on cost considerations, safety hazards, and the effect of the cleaning material on the metals involved. General Guidance and Procedures for Preparing Cleaning Solutions General guidance and procedures for preparing cleaning solutions of inhibited hydrochloric (muriatic) acid and inhibited sulfamic acids are provided in paragraphs below. Inhibited acid contains special chemical inhibitors that prevent the acid cleaner from attacking the base metal while allowing the acid to remove the unwanted corrosion product or scale deposit. Hydrochloric (Muriatic) Acid Inhibited hydrochloric (muriatic) acid in strengths of 5 to 20% is very effective for removing calcium scale and iron oxide; however, for most applications, a 10% solution is adequate. The following formulation is for a 10% hydrochloric acid solution. It can be used for removing scale consisting primarily of carbonates with lesser amounts of phosphates, sulfates, and silicates. This type of scale is typically found in a steam boiler system containing copper alloys that has been treated with a phosphate-based program. Depending on the specific descaling application, some of these ingredients can be omitted from the formulation. Example Procedure for 10% Solution The following is an example procedure that can be used to make 3785 liters (1000 gallons) of a 10% solution: 1. Add 1079 liters (285 gallons) concentrated (36% strength) hydrochloric acid, American Society for Testing and Materials (ASTM) E 1146, Specification for Muriatic Acid (Technical Grade Hydrochloric Acid), to approximately 2271 liters (600 gallons) of water. 2. Add the proper amount of a corrosion inhibitor, Military Specification MIL-I17433, Inhibitor, Hydrochloric Acid, Descaling and Pickling, recommended by the manufacturer to the diluted acid solution. The inhibitor must be compatible with hydrochloric acid and must not precipitate under any condition during the cleaning operation. 3. In a separate tank containing about 284 liters (75 gallons) of water: 4. Add 39 kilograms (85 pounds) of the chemical (1,3) diethylthiourea to complex any copper and keep it from depositing. Do not use the diethylthiourea as the corrosion inhibitor required in paragraph 92.2.1(step 2) above. 5. Add 55 kilograms (120 pounds) of ammonium bifluoride, technical grade, to help dissolve certain iron and silica scales. 6. Add 3.79 liters (1 gallon) of wetting agent, Add the dissolved diethylthiourea, ammonium bifluoride, and wetting agent to the diluted acid solution. Add sufficient water to obtain 3785 liters (1000 gallons). 101 Carbonate Deposits. Carbonate deposits dissolve rapidly in hydrochloric acid, with evolution of free carbon dioxide. The escaping carbon dioxide tends to create some circulation or agitation of the acid, which ensures the continual contact of fresh acid with the scale. Once the carbonate has been dissolved from a mixed deposit, a loose, porous structure may be left behind. This residual material can be effectively removed from the equipment either mechanically or by washing with highpressure water. Phosphate Deposits The removal of phosphate deposits can usually be accomplished by using hydrochloric acid; however, phosphate deposits have a tendency to dissolve rather slowly. To minimize the total cleaning time, a temperature of 49 to 60 °C (120 to 140 °F) is usually necessary to remove a predominantly phosphate scale. Metallic Oxides Most metallic oxides found in deposits can be removed with hydrochloric acid. The rate of dissolution is a function of temperature and solution velocity. If copper oxides are present on steel surfaces, special precautions are needed to prevent copper metal plate-out on the steel. Silica and Sulfate Scale Heavy silica and sulfate scale is almost impossible to remove with hydrochloric acid. Special chemicals and procedures are required to remove this scale. Hydrochloric Acid Limitations Hydrochloric acid is not used to clean stainless steel because the chloride ion in the acid solution may cause pitting or stress corrosion cracking. Hydrochloric acid is not used for removing scale from galvanized steel surfaces since the galvanizing will corrode. Aluminum is not cleaned using hydrochloric acid. Sulfamic Acid Sulfamic acid is an odorless, white, crystalline solid organic acid that is readily soluble in water. An inhibited sulfamic acid compound, in a dry powder form, is available. A 5 to 20% solution (2 to 9 kilograms to approximately 38 liters of water [5 to 20 pounds to approximately 10 gallons of water]) is used for removing scale from metal surfaces. The following information pertaining to sulfamic acid should be considered. u ?Carbonate deposits are dissolved in sulfamic acid in a similar manner as in hydrochloric acid. All the common sulfamate salts (including calcium) are very soluble in water. u powder form of sulfamic acid is safer to handle than a liquid The dry solution of hydrochloric acid; however, aqueous solutions of sulfamic acid are much slower in action and require heating to remove scale. The sulfamic acid solution is heated to a temperature in the range of 54 to 71 oC (130 to 160 oF) to obtain the same fast cleaning time that is achieved by using hydrochloric acid at room temperature. Sulfamic acid is more effective on sulfate scale than hydrochloric acid. 102 WATER TREATMENT HAND BOOK u Inhibited sulfamic acid, used at temperatures up to 43 oC (110 oF), will not corrode galvanized steel. Its use is recommended for removing scale in cooling towers, evaporative condensers, and other equipment containing galvanized steel. In general, sulfamic acid can be applied to equipment while it is operating but should be drained from the system after a few hours, and the concentration of the normally used corrosion inhibitor should be increased several-fold to protect the metal surfaces. u ?Commercially prepared descaling compounds consisting of concentrated or diluted inhibited acid (containing 7 to 28% of the acid and inhibitor) may be purchased under various trade names at prices 4 to 30 times the cost of the ingredients themselves if purchased as generic chemicals. u ?Advertisements of some of these products may contain claims that the acid does not attack cotton clothing and skin. These claims are usually based on a very dilute solution of the acid that causes a minimal attack on clothes and skin; however, the cost of the cleaning process may be increased because a higher quantity of dilute product may be needed. Be aware that handling acid in any strength must be performed with considerable care, caution, and adherence to safety procedures. u of diluted acid is expensive; therefore, concentrated acid of The cost government specifications should be purchased and diluted to usable strengths. The necessary corrosion inhibitors can be added to the dilute acid solution. Users of small quantities of acid cleaners (possibly less than 38 liters [10 gallons] of diluted acid per year) may not be able to justify purchasing undiluted acid and spending the time, cost, and effort to prepare the cleaning solution. Cleaning Preparation u to be cleaned must be isolated from other parts of the system. The unit For systems that cannot be isolated by the closing of valves, isolation may be accomplished using rubber blankets, wooden bulkheads with seals, inflatable nylon or rubber bags, rubber sponge-covered plugs, or blind flanges and steel plates with rubber seals. u whether to clean using a soaking process or by circulating the Decide cleaning solution. In either case, temporary piping or hose lines will be required to connect the cleaning solution mixing tanks or trucks to the unit, with return lines to tanks or drains. Proper precautions and adequate provisions must be made to protect equipment, isolate control lines, replace liquid level sight glasses with expendable materials, and provide suitable points for checking temperatures. u The entire cleaning procedure/process must be developed in detail before starting chemical cleaning operations. Factors to be considered include: the methods for controlling temperatures; the means of mixing, heating, and circulating the chemical solution; proper venting of dangerous gases from equipment to a safe area. 103 Methods for Removing Scale Removing scale may be accomplished by circulating the inhibited acid solution through the equipment or by soaking the equipment in a tank of inhibited acid. Before starting any descaling process, check the acid to make sure it is properly inhibited. You may check the acid by placing a mild steel coupon into a beaker containing the prepared, diluted acid. You should notice no reaction around the coupon. If you observe a reaction generating hydrogen gas bubbles around the coupon, add more inhibitor. Recirculating Cleaning Process for Boilers The following example is an appropriate procedure for cleaning small boilers or other systems using a hot recirculating inhibited acid solution: 1. Fill the boiler or system with preheated (71 to 77 oC [160 to 170 oF]) dilutes inhibited acid solution. 2. Allow the dilute inhibited acid solution to remain in place for 8 hours. Circulate the acid solution for approximately 15 minutes each hour at a rate of about 3.15 liters per second (50 gallons per minute) to ensure good mixing. 3. Keep the temperature of the acid solution preheated at 71 to 77 oC (160 to 170 oF). Measure and record the temperature at least once every 30 minutes. 4. Check and record the acid strength at least every hour 5. Drain the system by forcing the acid solution out using 276 to 345 kilopascals (40 to 50 pounds per square inch gauge) nitrogen; follow Specification A-A-59503, Nitrogen, Technical, Class 1. If leaks develop when the system is under nitrogen pressure, you must use an alternate method for removing the acid, such as pumping. 6. Fill the boiler with preheated (65 to 71 oC [150 to 160 oF]) water and soak at this temperature for 15 minutes. 7. Drain under nitrogen pressure of 276 to 345 kilopascals (40 to 50 pounds per square inch gauge). 8. Prepare this mild, acid-rinse solution: Add 7.57 liters (2 gallons) of hydrochloric acid (ASTM E 1146 or IS 226) for each 3785 liters (1000 gallons) of water. Also add corrosion inhibitor, in the amount recommended by the manufacturer. 9. Fill the boiler with the preheated (71 to 77 oC [160 to 170 oF]) mild acidrinse solution and soak for 30 minutes. 10. Drain the mild acid-rinse solution under nitrogen pressure at 276 to 345 kilopascals (40 to 50 pounds per square inch gauge). Maintain a positive pressure of nitrogen in the boiler to prevent outside air from leaking inside. 11. Fill the boiler with the passivating solution preheated to 65 to 71 oC (150 to 160 oF), circulate for 10 minutes, and hold in the boiler at 65 to 71 oC for an additional 30 minutes. Drain and rinse boiler until the pH of the rinse water is pH 8 to 10. 104 WATER TREATMENT HAND BOOK Circulating Method without Heat The steps below describe a typical process for descaling smaller equipment, such as enclosed vessels or hot water heater coils, without heating the inhibited acid solution: 1. Note that an acid cleaning assembly may consist of a small cart on which is mounted a pump and an 18.9- to 189-liter (5- to 50-gallon) steel or polyethylene tank with a bottom outlet to the pump. 2. Install sill cocks at the bottom of the water inlet of the heat exchanger and the top of the water outlet so that a return line can be connected directly from the acid pump and from the heat exchanger to the acid tank. 3. Prepare an inhibited acid cleaning solution 4. Pump the acid solution into the heat exchanger through the hose connection. Continue circulation until the reaction is complete, as indicated by foam subsidence or acid depletion. 5. If the scale is not completely removed, check the acid strength in the system If the acid strength is less than 3%, add fresh acid solution and continue circulation until the remaining scale is removed. Usually an hour of circulation is adequate. 6. Drain the heat exchanger. 7. Neutralize remaining acid by circulating a 1-% sodium carbonate (soda ash) solution {about 3.6 kilograms per 38 liters (8 pounds per 100 gallons)}for about 10 minutes. 8. Rinse thoroughly with water until the pH of the rinse water is pH 8 to 10. Fill and Soak Method Prepare an inhibited dilute acid solution in a container of suitable size. Depending on the item to be cleaned and the types of scale involved, you may want to place an agitator (mixer) in the tank or install a pump outside the tank to circulate the acid solution. A method to heat the acid may be required, such as a steam coil. All equipment must be explosion-proof and acid-resistant. 3. Immerse the item to be cleaned in the dilute acid solution. Continue soaking until the reaction is complete as indicated by foam subsidence or acid depletion. 4. If the scale is not completely removed, check the acid strength. If it is less than 3%, add additional acid and continue soaking the items until the remaining scale is dissolved. Usually 1 to 2 hours of soaking is adequate. 5. Remove item from tank. 6. To neutralize remaining acid, immerse the item in a 1% sodium carbonate (soda ash) solution (about 3.6 kilograms per 38 liters [8 pounds per 100 gallons]) for 2 to 3 minutes. Rinse the item thoroughly with water. 1. 2. 105 Checking Acid Solution Strength The initial strength of the dilute inhibited acid will vary from 5 to 20%, although 10% is typical. The strength of the acid decreases since acid is consumed in dissolving the scale. The strength of the acid solution should be measured periodically during a cleaning operation. When the acid strength falls below 3%, the solution may be discarded since most of its scale-dissolving capability will have been used. Use the following procedure to check the acid strength: Apparatus: 1. 2. 3. 4. 5. 1. 2. 1. 2. 3. 4. 5. Burette, 25 milliliters (0.8 ounce) automatic (for sodium hydroxide solution) Bottle, with dropper, 50 milliliters (2 ounces) (for phenolphthalein indicator solution) Graduated cylinder, 10 milliliters (0.3 ounce) Casserole, porcelain, heavy duty, 210-milliliter (7.1-ounce) capacity Stirring rod Sodium hydroxide solution, 1.0 normality (N) Phenolphthalein indicator solution, 0.5% Measure 10 milliliters of acid solution accurately in the graduated cylinder. Pour into the casserole. Add 2 to 4 drops of phenolphthalein indicator solution to the casserole and stir. Fill the automatic burette with the 1.0 N sodium hydroxide solution; allow the excess to drain back into the bottle. While stirring the acid solution constantly, add sodium hydroxide solution from the burette to the casserole until color changes to a permanent faint pink. This is the endpoint. Read the burette to the nearest 0.1-milliliter (0.003-ounce). Reagents: Method: Results: For hydrochloric acid: Percent hydrochloric acid = milliliter of 1.0 N sodium hydroxide x 0.36. For sulfamic acid: Percent sulfamic acid = milliliter of 1.0 N sodium hydroxide x 0.97 106 WATER TREATMENT HAND BOOK WATER SAMPLE TEST PROCEDURES 107 WATER SAMPLE TEST PROCEDURES Purpose of Testing Testing of industrial water is done to determine the amount of treatment chemicals in the water so that dosage levels can be properly regulated. These tests are the only known means of having reliable operations, as far as the water is concerned. Testing Techniques Accurate test results depend on following good basic laboratory procedures and techniques. 1. Water analyses require certain chemical apparatus. These are scientific instruments and are to be treated as such. The apparatus should be HANDLED WITH CARE! It is necessary to keep everything in GOOD ORDER at all times. Have a place for everything and everything in its place! Be sure all bottles are properly labeled and avoid mixing bottles! All bottles should be tightly closed. Keep any reserve stock of solutions and reagents in cool, dark place. All equipment and apparatus should be kept CLEAN! Unless this is done, the tests will not be reliable and errors will be introduced. Thoroughly rinse and dry all glassware immediately after use. If color apparatus are employed, do not expose to heat or to direct sunlight. If any liquid is spilled on any of the equipment or apparatus, wipe off at once and dry. MEASURE CAREFULLY! The apparatus are precision instruments that are capable of very fine measurements. The results will be “off” if improper amounts of samples are taken, if incorrect volumes of solution are added, if the burette is not read correctly, of if the methods prescribed on the following pages are not performed exactly as written. The SUSPENDED MATTER OR SLUDGE will generally settle to the bottom if the sample is allowed to stand before testing. The clear water can then be used for the tests, making it unnecessary to filter (except for specific tests). Theoretically, all water analyses should be made at 77oF (25oC); however, no appreciable error will be introduced if the test is made between 68 and 86oF (20 to 30oC). In general, the shorter the time between the collection and the analysis of the sample, the more reliable will be the results. 2. 3. 4. 5. When the water sample color interferes with the analysis, it may be necessary to filter the sample through activated charcoal, except for the sulfite and nitrite tests. 108 WATER TREATMENT HAND BOOK Phenolphthalein (P) Alkalinity Test Procedure APPARATUS: Graduated Cylinder, 50 ml, Plastic Bottle, w/Dropper (for Phenolphthalein Indicator) 2 oz Casserole, Porcelain, Heavy Duty, 200 ml Capacity Stirring Rod, Plastic REAGENTS: Standard Sulfuric Acid Solution, N/50 Phenolphthalein Indicator Solution, 1 percent METHOD: Measure the amount of water to be tested in the graduated cylinder. The amount should be based on the expected results of the test according to the following: u the casserole. Pour into u Add 6 drops of Phenolphthalein Indicator Solution to the casserole and stir. If the water does not change to a red color, there is no phenolphthalein alkalinity present and the “P” reading is reported as “zero.” If the water does change to red color, “P” alkalinity is present and the test should be continued. u the rubber bulb to force the Standard Sulfuric Acid Solution Squeeze from the bottle to fill the burette just above the zero mark; then allow the excess to drain back automatically into the bottle. ustirring the water constantly, add Standard Sulfuric Acid slowly While from the burette to the casserole until the red color disappears and the water resumes the original color of the sample before the Phenolphthalein Indicator Solution was added. This is the end point. Read the burette to the nearest 0.1-ml. u RESULTS: The P alkalinity (ppm as CaCO3) is calculated as follows: P alkalinity (ppm as CaCO3) = (ml acid) x (factor) P Alkalinity Expected, As CaCO3 Less than 100 More than 100 Sample Size 50ml 20ml Factor 20 50 EXAMPLE: 4.3 ml of N/50 sulfuric acid were required to change the color of a 50 ml sample of water from red to colorless: P alkalinity = 4.3 x 20 = 86 ppm as CaC 109 Total (M) Alkalinity Test Procedures APPARATUS: Burette, 10 ml, Automatic (for N/50 Sulfuric Acid) (item 1001) Graduated Cylinder, 50 ml, Plastic (item 1004) Bottle, w/Dropper (for Mixed Indicator) 2 oz (item 1005) Casserole, Porcelain, Heavy Duty, 200 ml Capacity (item 1003) Stirring Rod, Plastic (item 1006) REAGENTS: Standard Sulfuric Acid Solution, N/50 (item 2001) Mixed Indicator Solution, (item 2036) METHOD: Measure the amount of water to be tested in the graduated cylinder. The amount should be based on the expected results of the tests according to the following: u the casserole. Pour into u drops of Mixed Indicator Solution to the casserole and stir. If Add 10 the water changes to a light pink color, free mineral acid is present. There is no mixed indicator alkalinity, and the “M” reading is reported as “zero.” If the water changes to a green or blue color, “M” alkalinity is present and the test should be continued. u the rubber bulb to force the Standard Sulfuric Acid Solution Squeeze to fill the burette to just above the zero mark; then allow the excess to drain back automatically into the bottle. u stirring the water constantly, add Standard Sulfuric Acid While Solution slowly from the burette to the casserole until the green or blue color changes to light pink. This is the end point. Read the burette to the nearest 0.1-ml. M Alkalinity Expected, As CaCO3 Less than 100 More than 100 Sample Size 50ml 20ml Factor 20 50 RESULTS: The M alkalinity (ppm as CaCO3) is calculated as follows: M alkalinity (ppm as CaCO3) = (ml acid) x (factor) 110 WATER TREATMENT HAND BOOK EXAMPLE: 5.9 ml of N/50 sulfuric acid were required to change the color of a 50 ml sample of water from green to light pink: M alkalinity = 5.9 x 20 = 118 ppm as CaCO3 NOTES: uend point color is difficult to see, repeat the entire test using 15 If the drops of Mixed Indicator Solution. u Just before the end point is reached, the green or blue color fades to a light blue color and then becomes light pink. The end point is the first appearance of a permanent pink color. Value of P & M Alkalinity P= Zero Bicarbonate Alkalinity M Carbonate Alkalinity Nil Hydroxide Alkalinity Nil Total Alkalinity M P< 1/2M M-2P 2P Nil M P=1/2M Nil 2P Nil M P>1/2M Nil 2(M-P) 2P – M M 111 Conductivity Test Procedure Apparatus Conductivity Meter & cell In general, there are two types of conductivity meters. One has an electrode that is put into a cell containing the water to be tested. The other has a small cup mounted on the meter into which the water to be tested is poured. Either type of meter may be automatically temperature compensated, or the meter may require a temperature correction. The meter may indicate TDS or conductivity as micromhos, but either measurement represents the same characteristic of the water sample. Where the meter is designed to give either measurement, it is important to always use the same measurement to avoid an error. Thermometer Beaker Graduated cylinder Procedure Determine the cell constant if necessary, either directly with a standard potassium chloride solution (say 0.002N) or by comparison with a cell the constant of which is known accurately. (In the later case, the concentration and nature of the electrolytes in the liquid which is used for the comparison should be the same and should be similar respectively to those of the liquids with which the cell is likely to be used in practice. Use some of the samples to washout the conductivity cell thoroughly. Fill the conductivity cell with the sample. Measure the conductivity in accordance with the instruction of the instrument manufacturer. Results Depending upon the type of meter used, the results are read as either conductivity in micromhos or TDS in ppm. The relationship between these measurements when these procedures are used is as follows: TDS, ppm = 0.66 x Conductivity, micromhos Conductivity, micromhos = 1.5 x TDS, ppm. 112 WATER TREATMENT HAND BOOK pH-Electrometric Method Test Procedures Apparatus pH Meter, Complete Beaker, 150 ml, Heavy Duty Plastic (3 each) Wash Bottle, 500 ml, Heavy Duty Plastic Reagents Standard pH Buffer Solution, pH-4 Standard pH Buffer Solution, pH-7 Standard pH Buffer Solution, pH-10 METHOD: Carefully follow the procedures provided with the pH meter. They should be similar to the following: u meter from “standby” to “on” position. Turn the u Standardize instrument by immersing the electrode(s) into two different Standard pH buffer Solutions in the test beaker as follows: (a.) Place electrode(s) in pH-7 Buffer Solution and adjust the meter to read pH-7.(b). Place electrode(s) in the second pH Buffer Solution, either the pH-4 or pH-10, depending on the suspected range of the unknown sample to be tested, and adjust the meter to the same pH. u electrode(s) and thoroughly wash with distilled or condensate Remove water. u Immerse the electrode(s) in the water sample and turn the meter to “test” or “pH” position and read meter. uthe electrodes with distilled or condensate water and turn the Rinse instrument to the “standby” position. Do not turn off. Notes: unot in use, keep the glass electrodes soaking in a pH-4 Buffer When Solution. u not in use, keep the plastic cap on the reference electrode. When Some reference electrodes must be kept full of electrolyte. Follow the instrument instructions on this. 113 Total hardness Test Procedures Introduction Hardness is defined as the sum of the calcium and magnesium ions in water expressed in milligrams per liter (or ppm) as calcium carbonate. Hardness tests should be done on softeners to make sure they are functioning and deaerator water to make sure no contamination is occurring. This test is based on the determination of the total calcium and magnesium content of simple by titration with a sequestering agent in the presence of organic dye sensitive to calcium and magnesium ions. The red to blue color change endpoint is observed when all calcium and magnesium ions are sequestered. Hardness tests should be conducted on water softeners and condensate but not on boiler water as elevated iron concentrations can lead to chemical interference and poor test results. Reagent required Hardness Reagent 0.01 M Hardness Buffer Hardness Indicator Powder Procedure u Rinse the graduated cylinder and beaker or a test tube with the sample to be tested. Fill the graduated cylinder to 50 mL and add this water to the beaker or a test tube u If hardness is expected to be greater than 100 take a 50 ml sample and if less than 100 then the sample can be of 20 ml u Add 5 drops of Hardness Buffer to the beaker using the plastic pipette. Swirl to mix. u spoon of Hardness Indicator Powder. Swirl to dissolve Add 1 completely. The sample will turn red if hardness is present. If the sample is blue, the hardness level is completed to be zero. u If the sample colour is purple or red, add standard hardness titrating solution slowly from the burette to the beaker until the purple or red colour changes to blue. This is the end point. Read to nearest 0.1 ml Calculation u50 mL sample, ppm Hardness as CaCO3 = mL of Hardness For a Reagent X 20. u20 mL sample, ppm Hardness as CaCO3 = mL of Hardness For a Reagent X 50. 114 WATER TREATMENT HAND BOOK Sulphite testing procedure Introduction Sulfite is used in boiler feedwater conditioning to prevent oxygen pitting by the removal of dissolved oxygen. It is necessary to maintain an excess sulfite level to ensure rapid and complete oxygen removal. This test is based on the reaction of sulfite with iodine in acidic solution. The iodide-iodate titrant generates iodine in the acidic solution. This iodine is consumed in a reaction with excess sulfite. At the endpoint, excess iodine combines with the indicator to form a blue colour. Reagents required Iodide-Iodate Reagent N/40 Acid Starch Indicator Powder Phenolphthalein Indicator Procedure u Rinse the graduated cylinder and beaker or a test tube with the sample to be tested. Fill the graduated cylinder to 50 mL and add this water to the beaker or a test tube u If sulphite is expected to be greater than 100ppm take a 50-ml sample and if less than 100 ppm then the sample can be of 20 ml u drops of Phenolphthalein Indicator to the beaker using the Add 1 plastic pipette. Swirl to mix. usample remains colourless proceed with step 5. If the sample If the turns pink add Acid Starch indicator Powder one, 1gram at a time until the sample becomes colorless. Swirl to mix between each addition of indicator. u Titration Burette to the zero mark with Iodide-Iodate Reagent Fill the N/40. Add the reagent slowly to the Erlenmeyer flask with constant stirring. Continue to titrate until a permanent blue color develops in the sample. Read the titrated volume from the burette. Calculation For a 50 mL sample, Ppm sulphite as CaCO3 = mL of Iodide-Iodate Reagent X 20. For a 20 mL sample, Ppm sulphite as CaCO3 = mL of Iodide-Iodate Reagent X 50. 115 Chloride Test Procedure Apparatus: Burette, 10 ml Automatic (for Mercuric Nitrate Solution) Graduated Cylinder, 50 ml, Plastic Casserole, Porcelain, Heavy Duty, 200 ml Capacity Stirring Rod, Plastic Bottle, w/Dropper, 2 oz (for Chloride Indicator Solution) Reagents Standard Mercuric Nitrate Solution, 0.0141 N Chloride Indicator Solution Standard Sulfuric Acid Solution, N/50 Procedure u the amount of water to be tested in the graduated cylinder. Measure The amount should be based on the expected results of the tests according to the following: u the casserole. Pour into u ml of Chloride Indicator Solution to the water in the casserole Add 1.0 and stir for 10 seconds. The color of the water should be a green-blue color at this point. u standard Sulfuric Acid Solution a drop at a time until the water Add the turns from greenblue to yellow. u Squeeze the rubber bulb to force the Standard Mercuric Nitrate Solution from the bottle to fill the burette just above the zero mark; then allow the excess to drain back automatically into the bottle. While stirring the sample constantly, add Standard Mercuric Nitrite Solution slowly from the burette to the casserole until a definite purple color appears. This is the end point.(The solution will turn from green-blue to blue a few drops from the end point.) Read the burette to the nearest 0.1-ml. Results The Chloride, in ppm C1, is calculated as follows: Chloride, ppm C1 = (ml of Mercuric Nitrate – 0.2) x factor. Example 11.2 ml of 0.0141 N Mercuric Nitrate Solution was required to change the color of a 50-ml sample of water from a green-blue to purple. Chloride = (11.2 – 0.2) x 20 = 220 ppm) Chloride Expected as Cl Less than 20 ppm More than 20 ppm Sample Size 50ml 20ml Factor 10 20 116 WATER TREATMENT HAND BOOK Checking Acid Solution Strength for Cleaning The initial strength of the dilute inhibited acid will vary from 5 to 20%, although 10% is typical. Since the acid is consumed by dissolving the scale, the strength of the acid decreases. The strength of the acid solution should be measured periodically during a cleaning operation. When the acid strength falls below 3%, the solution may be discarded since most of its scale-dissolving capability will have been used. Use the following procedure to check the acid strength: Apparatus: Burette, 25 milliliters (0.8 ounce) automatic (for sodium hydroxide solution) Bottle, with dropper, 50 milliliters (2 ounces) (for phenolphthalein indicator solution) Graduated cylinder, 10 milliliters (0.3 ounce) Casserole, porcelain, heavy duty, 210-milliliter (7.1-ounce) capacity Stirring rod Reagents: Sodium hydroxide solution, 1.0 normality (N) Phenolphthalein indicator solution, 0.5% Method: u 10 milliliters of acid solution accurately in the graduated Measure cylinder. u the casserole. Pour into uto 4 drops of phenolphthalein indicator solution to the casserole Add 2 and stir. u automatic burette with the 1.0 N sodium hydroxide solution; Fill the allow the excess to drain back into the bottle. u stirring the acid solution constantly, add sodium hydroxide While solution from the burette to the casserole until color changes to a permanent faint pink. This is the endpoint. Read the burette to the nearest 0.1-milliliter (0.003-ounce). Results: For hydrochloric acid: Percent hydrochloric acid = milliliter of 1.0 N sodium hydroxide x 0.36 For sulfamic acid: Percent sulfamic acid = milliliter of 1.0 N sodium hydroxide x 0.97 117 Units and Measurement conversion 118 WATER TREATMENT HAND BOOK BASICS Length 1 m = 39. 37 " | in = 3,281 ' | feet 1 in | " = 25.40 mm = 2,540·10-2 m 1 ft | ' = 304. 8 mm = 0.3048 m Area 1 m² = 10.76 ft² = 1550 in² 1 ft² = 9,290·10-2 m² 1 in² = 6,452·10-4 m² Volume 1 m³ = 6,102·104 in³ 1 m³ = 35.31 cf | ft³ = 264.2 US Gallon 1 cf | ft³ = 2,832·10-2 m³ = 28.32 Liter | dm³ 1 in³ = 1,639·105m³ = 1,639·10-2 Liter | dm³ 1 US Gallon = 3,785·10-3 m³ = 3,785 Liter | dm³ 1 UK Gallon = 4,546·10-3 m³ = 4,546 Liter | dm 1 mn3 Air=38.04 SCF Air=1.292 kg Air 1 SCF Air =2,629·10-2 mn 3 Air=3,397·10-2 kg Air Density 1 kg/m³ = 6.243·10-2 lb/ft³ 1 lb/ft³ = 16.02 kg/m³ Mass 1 kg = 2.205 lb | lbs 1 lb | lbs = 0.4536 kg Velocity 1 m/s = 3.281 ft/s 1 m/s = 196.9 ft/min | FPM 1 FPM = 5.080·10-3 m/s 1 ft/sec. = 0.3048 m/s Volume Flow 1 m³/h = 0.5885 CFM | ft³/min 1 CFM = 1.699 m³/h 1 SCFM = 1.577 mn 3/h Air (only) Mass Flow 1 kg/h = 2.205 lb/h 1 lb/h = 0.4536 kg/h 119 Pressure 1 bar = 14.50 psi 1 bar = 100.0 kPa 1 bar = 0.9869 Atm. 1 mbar = 0.7501 mm Hg | Torr 1 mbar = 10.20 mm WG 1 mbar = 100.0 Pa 1 psi | lbf/in² = 6,895·10-2 bar 1 psi | lbf/in² = 6,804·10-2 Atm. 1 psi | lbf/in² = 6,895 kPa Kinematic Viscosity 1 Pa·s = 1.000 cP 1 Pa·s = 0. 6720 lb/ (ft·s) 1 cP = 1,000·10-3 Pa·s | Ns/m² 1 cP = 1,000·10-3 kg/ (m·s) 1 lb/ (ft·s) = 1.488 Pa·s 1 lb/ (ft·s) = 1488 cP | mPa·s Temperature °C | Celsius = 5 · (°F – 32) / 9 °F | Fahrenheit = 32 + 9 · °C / 5 Heat Content & Energy 1 kJ | KN·m = 0.9478 Btu 1 kJ | KN·m = 0.2388 Kcal 1 Btu = 1.055 kJ 1 Btu = 0.2520 Kcal 1 kcal = 4,187 kJ 1 kcal = 3.968 Btu 1 kWh = 859.8 Kcal Heat Load | Power 1 kW = 3412 Btu/h 1 kW = 859.8 Kcal/h 1 Btu/h = 2,931·10-4 kW 1 Btu/h = 0.2520 Kcal/h 1 kcal/h = 1,163·10-3 kW 1 kcal/h = 3.968 Btu/h 1 Boiler HP = 9.81 kW Specific Heat 1 kJ/ (kg·K) = 0.2388 Btu/ (lb·°F) 1 kJ/ (kg·K) = 0.2388 kcal/ (kg·°C) 1 Btu/ (lb·°F) = 4,187 kJ/ (kg·K) 1 kcal/ (kg·°C) = 4,187 kJ/ (kg·K) 120 WATER TREATMENT HAND BOOK Common conversion factors for ion exchange calculation Capacity To Convert Kgr/ft3 (as CaCO3) Kgr/ft3 (as CaCO3) Kgr/ft3 (as CaCO3) g CaCO3/litre g CaO/litre To g CaO/Litre g CaCO3/Litre eq/litre Kgr/ft3 (as CaCO3) Kgr/ft3 (as CaCO3) Multiply by 1.28 2.29 0.0458 0.436 0.780 Flow Rate To Convert U.S.gpm/ft3 U.S.gpm/ft2 U.S gpm BV/min To BV/hr M/hr M3/hr U.S. gpm/ft3 Multiply by 8.02 2.45 0.227 7.46 Pressure drop To Convert PSI/ft To MH2O/M of Resin G/cm/M Multiply by 2.30 230 Density To Convert Lbs/ft3 To gm/litre Multiply by 16.0 Rinse requirement To Convert U.S. gal/ft3 To BV Multiply by 0.134 121 Water Equivalents One U.S. gallon One U.S. gallon One U.S. gallon One U.S. gallon One U.S. gallon One U.S. gallon water One cubic foot One cubic foot of water One litre/second One cubic meter per hour One kgr / sq. cm One Pound/1000 gel One inch/minute rise rate One cubic meter One cubic meter One cubic meter - 0.1337 cubic foot 231 cubic inches 0.833 British Imp gallons 3.785 Liters 3785 cubic cm (Milliliters) 8.33 Pounds (Lb) 7.48 U.S. gallons 62.43 Pounds 15.9 (US) gal/Min 4.4 (US) gal/min 14.2 pounds/sq. inch 120 parts per million 0.625 gpm/sq.ft 1000 liter 264.2 U.S gallons 220 British Imp gallons Parts per hund-red thous and pts/ 100000 Grains per U.S. gallons grs/U.S gal Grains per British Imp gallon grs/Im gal Kilogr ains per cubic foot Kgr/ cu.ft Water Analysis Conver-sion table Parts per million (ppm) Milli-grams per liter mg/L Grams per Liter gms/L 1 Part per million (1 ppm) 1 milli gram per litre (1mg /litre) 1 gram per litre(1m /litre) 1 Parts per hundred thousand 1pt /100 0000) 1 1 .001 .1 .0583 .07 .0004 1 1 .001 .1 .0583 .07 .0004 1000 1000 1 100 58.3 70 .435 10 10 .01 1 .583 .7 .00436 122 WATER TREATMENT HAND BOOK Water Analysis Conversion Table for Units Employed: Equivalents Water Analysis Conver-sion table Parts per million (ppm) Milli-grams per liter mg/L Grams per Liter gms/L Parts per hund-red thous and pts/ 100000 Grains per U.S. gallons grs/U.S gal Grains per British Imp gallon grs/Im gal Kilogr ains per cubic foot Kgr/ cu.ft 1 Grain per U.S gallon(1 gr/U.S gal) 1 Grain per British Imp gal-lon (1 gr /Imp gal) 1 Kilograin per cubic foot (1 kgr /cu.ft) 1 Parts per million (1 ppm) 1 Part per hundred thousand (1 pt /100000) 1 Grain per US gallon (1 gpg) 1 English or Clark degree 1 French Degrees (1.French) 1 German Degrees (1 German) 17.1 17.1 .017 1.71 1 1.2 .0075 14.3 14.3 .014 1.43 .833 1 .0052 2294 2294 2.294 229.4 134 161 1 1 0.1 .0583 .07 .1 .0560 .020 10 1 0.583 0.7 1 0.560 .20 17.1 1.71 1 1.2 1.71 0.958 .343 14.3 1.43 .833 1 1.43 0.800 .286 10 1 .583 .7 1 0.560 .20 17.9 1.79 1.04 1.24 1.79 1 .357 123 Indian standard grade for the commonly used regeneration chemicals Regeneration Chemicals Hydrochloric Acid Sulphuric Acid Sodium Hydroxide Sodium Carbonate Sodium Sulphite Sodium chloride Alum IS 265 IS 266 IS Number IS 252 (Tech/Rayon Grade 46% lyes) IS1021 (Pure Grade - Flakes) Is251 (Tech Grade) Is251 (Tech Grade) IS 297 (Tech Grade) Is260 (Tech Grade) 124 WATER TREATMENT HAND BOOK Brief List of Reference Betz Handbook Demineralization by Ion exchange – S. Applebaum – Academic press Reverse osmosis by Zahid Amjad – Van Nostrand Reinhold (NY) Membrane Manual –Dow Chemical Company Army Engineering Publications- Public bulletin No. 420-49-05 CIBO Energy efficiency handbook WARE Boiler book on-line “Chemical Treatment of Cooling Water in Industrial Plants”by Timothy Keister (Basic Principals and Technology) ProChemTech International, Inc. Brockway, Pennsylvania Glegg handbook Water and Wastewater by Hammer and Hammer Dorfner, K., Ion Exchangers, Properties and Applications, Ann Arbor Science, Ann Arbor, Michigan, 972 Kunin, R., Ion Exchange Resins, Robert E. Krieger Publ. Co., Huntington, N.Y., 1957 Nachod, F. C. and Schubert, J., editors, Ion Exchange technology, Academic Press, New York, N.Y., 1957 Water treatment technology program Report no 29 Pure water handbook by osmonics "Pretreatment of Industrial Wastes," Manual of Practice No. FD-3 Public Works Technical Bulletin 420-49-21 Boiler water treatment lessons learned Public Works Technical Bulletin 420-49-22 Cooling water treatment lessons learned (Published by the U.S. Army Installation Support Center) International site for Spirax Sarco Industrial Water Treatment Primer TYNDALL AFB, FL 32403-6001 Sedifilt.com Web site of N.E.M Business Solutions Website of Portland water bureau How to Manage Cooling Tower Water Quality by Ken Mortensen in RSES journal _5-03pd And many more 125 Aqua Designs India Limited Off 200 Feet Road, Kolathur, Chennai - 600 099, India Phone Fax Email Web : +91 44 37171717 : +91 44 37171737 : [email protected] : www.aquadesigns.in