1Feed Water Chemistry & Control Nalco Indonesia ~ Power Industry Seminar Pullman, Central Park ~ Jakarta 13-14 June 2012 2 Agenda Key Issues Guidelines for Condensate, Feed Water, and Steam Chemistry Control Practical considerations in application and control New Technology 3 Steam Cycle age of unit Limits vary with the boiler treatment selected.3. Cation conductivity is principle measure in most plants (< 0. Different manufacturers have different limits Limits may depend on design. < 0.2.4 Key Issue #1 : Steam Turbine Requirements Steam purity specs can be stringent! Industry experts differ on specific allowed limits. but not commonly found online .15.and SO4 measurement important. Cl. < 0. < 0.8 mS/cm as cation conductivity) Na and SiO2 are more specific measures of contamination. service. 5 Critical Steam Cycle Chemistry Parameters Boiler and feedwater chemistry driven by steam purity requirements Turbine/Feedwater Cation conductivity (indirect measure) Sodium (NaOH) Silica Chloride (HCl) Sulfate (H2SO4) Organic acids . 6 Sources of Chemicals in Steam Volatile Carry Over Higher pressure = greater volatility Cu an issue at > 2400 psi (160 bar) Mechanical Carry Over Occurs in all boilers all the time Drops contain all boiler water solids Contamination via Attemperation Shortcut of feedwater to turbine Cu(OH)2 H2SO4 SiO2 NaOH Na3PO4 NaCl HCl Volatile Mechanical . Ca. Mg : SO4 salts to H2SO4 Na. Mg : HCO3 salts to H2CO3 Also removes amine and ammonia. Ca. Ca.Key Issue #2 : Cation (Acid) Conductivity Conductivity after strong acid ion exchange Neutral salts become strong acids Magnifies conductivity 3-5 times Cl- and SO4 2- Targets “De-gassed” cation conductivity uses a small boiler or N2 sparging to strip off CO2 from carbonic acid Na. Mg : Cl salts to HCl Na. but not organic acids CO2 to H2CO3 . ppb < 10 TOC. Parameter Specific Cond. membrane deaeration . mS/cm EPRI Std < 0.1 Cation Cond. ppb <3 Silica. Technically feasible – from 7 ppm to 100 ppb O2 Vacuum deaeration. mS/cm VGB Std < 0.8 Key Issue #3 : High Purity Make Up Purity Generally must be as good as feedwater. steam sparging. Cl. EPRI specifications are a good target for modern plants.2 Na. ppb < 300 < 20 Deaeration Few plants deaerate make up or condensate storage tanks. nitrogen sparging. SO4. or hot well during standby. All plants should develop unit specific guidelines.Minimizing corrosion and corrosion product transport is critical. pressure. and water quality into account.Key Issue #4 : Condensate and Feed Water Quality Condensate Cogen plants must guard against contamination from steam host Feedwater Feedwater used for attemperation must meet steam purity specs. . service. taking design. . .The LP section of most HRSGs is upstream of attemperation. and is treated as feedwater. (AVT) Feedwater purity and consistency drive treatment selection.FW heaters corrode on both shell and tube side! EPRI Guidelines are excellent targets. . but: May be difficult for older plants to meet without capital investment in system upgrades. 10 Key Issue #5 : Control of Dissolved Oxygen EPRI research and field study led to reduction in O2 target From < 20 ppb at CPD to < 10 ppb at CPD For all treatment programs Required for corrosion control Overfeed of passivator is not a good option Too strong of a reducing environment contributes to FAC Excess hydrazine and carbohydrazide produce ammonia Excess organic passivators can add to TOC. organic acids EPRI recommends / Nalco concurs: Limit air inleakage – have active detection and repair program Deaerate make up Nitrogen cap hotwell for standby . iron is the focus of performance CORROSION leads to IRON IRON leads to DEPOSITION DEPOSITION leads to CORROSION (again) & OVERHEAT .11 Corrosion ~ Iron ~ Deposition ~ Corrosion For high purity boiler systems. 12 Corrosion ~ Iron ~ Deposition ~ Corrosion NaOH Magnetite Steam Out NaOH NaOH Water In Fe3O4 porous deposit NaOH . 13 Chemically Influenced BTFs 2001 survey results 1997 survey results Organizations having chemically influenced BTFs 81% 61% •Hydrogen damage 57% 37% •Acid phosphate corrosion 25% 17% •Corrosion fatigue 45% 43% •Pitting 40% 7% •Stress corrosion cracking 28% 18% •Caustic Gouging 11% 11% Source: 2002 EPRI Study. “ Priorities for Corrosion R&D” 13 . 14 Boiler Tube.Hydrogen Damage 14 . Less protective cupric oxide surfaces have 30 times the Cu release! .Key Issue #6 : Metal Passivation Passivation: Iron oxides to magnetite (reducing environment) .4Cu2O + 3H2O + 2N2 + CO2 Or magnetite / hematite mix (neutral or oxidizing environment) Copper oxides to cuprous form (Cu2O) .Passivation Reactions: Carbohydrazide 12 Fe2O3 + (N2H3)2CO --.8Fe3O4 = 3H2O + 2N2 + CO2 8CuO + (N2H3)2CO --.Cuprous oxide will oxidize to cupric within 10 hours in O2 environment! .Passivation Reactions: Hydrazine N2H4 + 6Fe2O3 4Fe3O4 + N2 + 2H2O N2H4 + 4CuO 2Cu2O + N2 + 2H2O . . Phosphate Continuum and Caustic Treatment. Cycle chemistry Guidelines for Fossil Plants. 2004.Iron Oxide Passive Layer ~ Reducing Environment Source: EPRI. 17 Iron Oxide Passive Layer ~ Neutral-Oxidizing Environment Source: EPRI. . Cycle chemistry Guidelines for Fossil Plants. 2004. Phosphate Continuum and Caustic Treatment. Key Issue #7 : Flow Accelerated Corrosion Over half of utilities report FAC Two failure mechanisms – single-phase and two-phase Occurs in - Condensate and Feedwater Piping around BFP Piping to Economizer Inlet Header Economizer Inlet Header Tubes Deaerators Heater Shells and Drains Steam Turbine Exhaust LP Evaporators Second-most common failure mechanism . What is FAC ? Dissolving of protective magnetite layer (Fe3O4) Influenced by several factors: Velocity Flow geometry Two phase flow Temperature pH Oxygen concentration Overfeed of Passivators Metallurgy that contribute to magnetite solubility . Factors Affecting FAC .Temperature Extremely temperature dependent: Occurs in HRSG IP & HP Economizer tubes & headers. Tendency for FAC Moderate Range Severe Range Moderate Range Temperature Deg C 80 150 150 180 180 230 Deg F 176 302 302 356 356 446 Saturation Pressure psia 7 70 70 146 146 409 . Occurs in cold re-heat return lines. and in LP evaporators & drums. FW heater drip lines. Factors Affecting FAC – pH . . 2004. Cycle chemistry Guidelines for Fossil Plants. Phosphate Continuum and Caustic Treatment.Factors Affecting FAC ~ Oxidizing & Reducing Environment Source: EPRI. Monitor feedwater ORP.Pay attention to amine distribution ratio in multi-pressure HRSGs Avoid a highly reducing environment! .Need proper sample points! .Higher end of range is better! .Cycling units: do not feed high levels of reducing agent to compensate for high O2 at start up.FAC Solution Material upgrade to 1 or 2% chrome Maintain pH in proper range with ammonia or amines . . consider control of passivator to ORP Monitor with soluble iron tests before and after suspect areas .Do not allow excess feed of reducing agents! . contributing to cation conductivity Ammonia counter ion neutralizes the acids Many feel okay to continue use Organic Passivators .Produces CO2 on breakdown. Excess carbohydrazide will produce ammonia.Some breakdown to organic acids.Most believe should not use Carbohydrazide . .Most believe carbohydrazide is okay to use . .No alkaline counter ion .Key Issue #8 : Use of Organic Amines & Passivators EPRI & VGB recommend Ammonia and Hydrazine Stuttgart Conference on Organics – June 2005 Co-Sponsored by EPRI and PowerPlant Chemistry Organic Amines - Used safely for many years No factual evidence of contribution to turbine corrosion Some breakdown to organic acids. contributing to cation conductivity .08 mS/cm cation conductivity from the CO2.CO2 not believed to cause any significant corrosion in steam cycle .Estimate that 20 ppb Carbohydrazide contributes 10 ppb CO2. and creates 0. Organic Amine & Passivator – CO2 Myth CO2 is not solid so it won’t be deposited in the LP blade and creating localized acidic condition It is required ~ 200 ppb of CO2 to drop the pH of pure water from 6.0 At low pressure.5 to < 6. V/L of CO2 is quite the same with Ammonia and higher than neutralizing amines. There are some literatures from independent parties that clearly explained that CO2 won’t depress pH of initial condensation in the level that we commonly found boiler operation (<2 mS/cm) and when the alkalizing agent is exist (Robert Svoboda and Alstom) . It is mean all of CO2 will be neutralizing by proper dosing of ammonia/amines. which contributes 0.08 mS/cm cation conductivity (But 0 degassed cation conductivity) O II NH2-NH-C-NH-NH2 CARBOHYDRAZIDE .Nalco 1250 (ELIMIN-OX) • Active Content : CARBOHYDRAZIDE (CHZ) • ALL VOLATILE & NON-SOLIDS Contribution in Steam Cycle • It is used as a METAL PASSIVATOR • Much SAFER than HYDRAZINE • NOT A SUSPECT CARCINOGEN • Slight increase in cation conductivity from CO2 20 ppb CHz contributes 10 ppb CO2. it is very simple to check @ BFW sample.MECHANISM REACTION of ELIMIN-OX At LOW Temp.or 0. (T 1350C) 1 ppm Elimin-Ox 29 ppb (.029 ppm) CO2 & NO IMPACT to STEAM & CONDENSATE corrosivity Practically. as residual of 10 – 30 ppb (as N2H4) ~ local (site) BFW sampling w/t T > 1800C . Increasing Passivation Passivation Better than Blank at All Temperatures * Blank Carbohydrazide Methlyethylketoxime * 150 200 * * 250 300 350 400 Temperature (oF) 28 . Increasing Passivation Passivation Better than Blank at High Temperatures * Blank Hydrazine Erythorbic Acid * * 150 * 200 250 300 350 400 Temperature (oF) 29 . Increasing Passivation Passivation Equal to Blank * Blank Sulfite DEHA Hydroquinone * * 150 200 * 250 300 350 400 Temperature (oF) 30 . Feedwater Iron Reduction in 1500 psig boiler with ELIMIN-OX 31 . Feedwater Copper Reduction in 1500 psig boiler with ELIMIN-OX 32 . salts of lactic and glycolic acid. ammonia Carbohydrazide (N2H3)2CO 13. light alcohols. ammonia. ammonia. low molecular weight species. acetic acid. carbon dioxide 33 . ammonia. carbon dioxide Erythorbic Acid C 6H 8O 6 40. nitrogen.Reaction and/or Breakdown Products Chemical/Formula Hydrazine N2H4 %C (wt.2 Methylethylketone. dialkylamines.) Reaction and/or Breakdown Products 0 Nitrogen. nitrate.5 Benzoquinone. water. ketones. carbon dioxide Hydroquinone C6H4(OH)2 65. carbon dioxide Diethylhydroxylamine (CH3CH2)2 NOH 53. nitrous oxide.9 Acetaldehyde. nitrite Methylethylketoxime (CH3)(CH3CH2)C=NOH 55. hydroxylamine.3 Hydrazine. nitrogen.9 Dihydroascorbic acid. water. rabbits (24 hr) Primary dermal irritation .5/110) Mild irritant (0.33/110) Irritating (26. (Most suppliers ship as a corrosive liquid) 34 .0) Severe irritant (7.23/8.0) May be corrosive.0/8.rabbits Non-irritating (0.rabbits >2000 mg/kg 420 mg/kg Primary eye irritation .Comparison of Acute Toxicology of ELIMIN-OX and 35% Hydrazine Study Performed ELIMIN-OX 35% Hydrazine Acute oral LD50 rats >5000 mg/kg 370 mg/kg Acute dermal LD50 . 35 References of Nalco 1250/Elimin-Ox . organic acids may drop the pH in initial condensation zone & cause corrosion in steam turbine Low V/L Amine is a better choice than NH4OH to neutralizeI organic acids in this particular area Species Relative V/L Destination Carbonic Acid High Final condensation Acetic & Formic Acid Low Early stage of condensation Ammonia High Final condensation Low or high Early & final stage of condensation Amines (initial condensation) .Steam & Condensate Equipment Steam Turbine – Advantages of Amines If not neutralized. 3 mS/cm lower than amine available in the market) Containing low V/L amine that will increase the pH in early condensation zones in the LP turbine. feedwater heaters and extended steam distribution system Low V/L amine will also improve pH in the LP section of multi pressure HRSG and minimize potential of FAC Increase the pH with relatively same dosage with 19% NH3 Has higher boiling point.Nalco 5711 Minimum contribution of cation conductivity. Safer to handle. Freeport Indonesia . Deliver <0.2 mS/cm cation conductivity in system with no contamination (0. and produces fewer odor Reference : PT. easier to pump without off gassing.1-0. 6 8.5 9.9 9.3 9.0 9. pH in pure water 15 14 19% NH3 13 1800 Amine Product. mg/L 12 11 CA-300C 10 356 9 8 5711 7 6 5 4 3 2 1 8.4 9.2 Condensate / FW pH 9.1 9.6 .N5711 Dosage vs Ammonia Amine Product Concentration vs.8 8.7 8. Condensate, FW, and Steam Guidelines EPRI Guidelines Industrial PC(L) PC(H) Caustic Treat AVT(O) AVT(R) OT 9.0–9.6 8.8-9.2 9.2–9.6 9.0-9.3 9.2–9.6 9.0-9.3 9.2–9.6 9.0-9.3 9.2–9.6 9.2–9.6 9.0-9.3 D 9.0–9.6 O 8.0-8.5 Cat Cond, mS/cm < 0.3 < 0.2 < 0.3 < 0.2 < 0.2 < 0.2 < 0.15 Na, Cl, SO4 ppb <5 <2 <3 <2 <2 <2 <2 Silica, ppb < 20 < 10 < 10 < 10 < 10 < 10 < 10 Fe, ppb @EI < 10 <2 <2 <2 < 2 (1) <2 < 2 (0.5) Cu, ppb @EI < 10 <2 <2 <2 <2 <2 <2 Oxygen, ppb @CPD < 20 < 10 < 10 < 10 Parameter pH (all steel) (Cu alloys) Oxygen, ppb @EI Reducing Agent ORP, mV @DA In < 10 < 10 < 5 (< 2) D 30-50 O 30 150 yes no yes no +/- 50 -300 to 350 100 to 150 Condensate, FW, and Steam Guidelines NALCO Guide for Implementation Industrial PC(L) PC(H) Caustic Treat AVT(O) AVT(R) OT 9.0–9.6 8.8-9.2 9.2–9.6 9.0-9.3 9.2–9.6 9.0-9.3 9.2–9.6 9.0-9.3 9.2–9.6 9.2–9.6 9.0-9.3 D 9.0–9.6 O 8.0-8.5 < 0.3 < 0.6 < 0.2 < 0.4 < 0.3 < 0.6 < 0.2 < 0.4 < 0.2 < 0.4 < 0.2 < 0.4 < 0.15 Na, Cl, SO4 ppb <5 <2 <3 <2 <2 <2 <2 Silica, ppb < 20 < 10 < 10 < 10 < 10 < 10 < 10 Fe, ppb @EI < 10 <2 <2 <2 <2 <2 <2 Cu, ppb @EI < 10 <2 <2 <2 <2 <2 <2 Oxygen, ppb @CPD < 20 < 10 < 10 < 10 Parameter pH (all steel) (Cu alloys) Cat Cond, mS/cm W/ organic amine Oxygen, ppb @EI Reducing Agent ORP, mV @DA In < 10 < 10 <5 D 30-50 O 30 150 yes Yes, if cycling yes no +/- 50 -250 to 350 100 to 150 The Nalco Latest Technology to Monitor/Control Corrosion Tendency of Feedwater Systems What is ORP ? H2 Reduction of Oxygen (CATHODE) Corrosion = REDOX Reactions REDOX Reactions Electron Flow Electron Flow = ORP (Oxidation Reduction Potential) ORP = bulk FW corrosivity Precipitation of Red Oxide Fe2O3 o O2 O H RED OXIDE o - BLACK OXIDE o MAGNETITE o o MAGNETITE Fe3O4 Precipitation of Black Oxide (CATHODE) FeOH++ + Fe(OH)+2 Oxidation and Hydrolysis o H++FeOH+ Evolution of Hydrogen (CATHODE) Hydrolysis of Dissolved Iron lowers pH Fe+2 Acid Pit Solution with Lower Oxygen Content eFe Oxidation of Iron ANODE ORP indicates the potential of bulk water to corrode ORP provide the best way to control BFW corrosion stress 42 Corrosion and corrosion product transport varies significantly in condensate and feedwater systems. Inc. and AT ORP are trademarks of Nalco Company. the logo. Chemtrac is a trademark of Chemtrac Systems. Corrosion varies with: Metallurgy Flow velocity (FAC) Temperature pH Dissolved oxygen Conductivity Stability of oxide layer / passivation Corrosion product transport varies with: Load / flow velocity Expansion / contraction Vibration Monitor corrosion stress with At Temperature ORP (AT ORP) Cycling Base Load Monitor corrosion product transport with Chemtrac Particle Monitor Nalco. Two Shifting . 3D TRASAR. commercial production from 2008. Nalco is the first to develop a practical AT ORP system. 1.can be more corrosive Greatly improves sensitivity and response. ORP and Oxidation / Reduction Potential are used in this presentation to have the same meaning as Redox Potential. Over 50 AT ORP units currently installed in Power plants globally. Development of AT ORP has been an industry goal. . Developed by Dr. Peter Hicks of Nalco. Work began in 1992. etc. AT ORP is measurement of ORP at the temperature and pressure of the condensate / feedwater system. More oxidizing . pH. Allows AT ORP to be used for feedback control. dissolved solids. Potential difference between measuring and reference electrodes More reducing – can be more passive ORP is influenced by temperature. O2.43 ORP1 and At Temperature ORP (AT ORP) ORP correlates to the corrosion stress of the aqueous environment + 0 RT ORP is measured on a cooled sample at room temperature. Appendix B. such as in the boiler.” .” “The future direction should be to develop the technology to measure ORP in-situ in feedwater. where components are actually in contact with high temperature water. and more importantly. and to extend the mixed-potential model for use at the elevated temperatures. the reducing power of the feedwater in mixed-metallurgy feedwater systems. “Thus ORP should be used to control the oxidizing power of the feedwater in allferrous systems or. Jan 2004.44 EPRI Cycle Chemistry Guidelines for Fossil Plants: Phosphate Continuum and Caustic Treatment. To control chemical feed to maintain the system within an AT ORP control specification range.Reducing or oxidizing agent . To make corrosion events visible. On-line in real time. To respond with appropriate magnitude and sensitivity for feedback control. To allow the plant to correlate corrosion stress to plant operational and chemistry changes. Nalco Europe AT ORP Control Equipment .Feed on demand and eliminate over or under feed. .45 Advanced Monitoring: At Temperature ORP Oxidation / Reduction Potential (ORP) can now be measured and controlled in condensate and feedwater systems: At system temperature and pressure. higher generation .46 Why is it important? AT ORP can help the plant to maintain a more consistent oxidation state on the metal surfaces. Reduce condensate / feedwater system corrosion Extend feedwater heater life Reduce FAC in LP section of HRSGs Reduce corrosion product deposition in boilers Reduce boiler tube failures Reduce boiler start up chemistry holds Reduce frequency and duration of boiler chemical cleaning Prevent turbine efficiency loss from deposition of corrosion products (Cu. Fe) Lower heat rate. 47 AT ORP Monitoring and Control Equipment Control PLC. Communications AT ORP Electrode Optional Sample Conditioning EPBRE (External Pressure Balanced Reference Electrode) . Ag/AgCl Reference Electrode Sensor design limits 133 bar. but before feedwater pump.48 AT ORP Electrodes: Pt measuring electrode. 260 oC Sample: 250-500 ml/min Typical install is after condensate heating. Installation (prioritized) Deaerator inlet or LP drum inlet Condensate after chemical feed LP drum or other point of interest Existing sample may be routed through AT ORP and then to: Sample panel instruments Sample conditioning and Particle Monitor or drain . • • On-line monitoring makes visible Particle monitor helps to: – – – – Correlate crud bursts to specific events. Correlate to metal passivation over time. – Usually invisible. Correlate particle counts to AT ORP. chemical. . or hydraulic shock to the system.49 Advanced Monitoring : Chemtrac® Particle Monitor • Corrosion product released in “crud bursts”. as not monitored on line. – Occur every time there’s a thermal. Correlate particle counts to ppb iron levels. Introducing: Nalco Corrosion Stress Monitor . Nalco Corrosion Stress Monitoring (NCSM) with @T ORP Technology . What Types of System Stresses NCSM can address ? Mechanical Dearator Performance Pump Leaks Operational Load changes Startup and shutdown Condensate flow Makeup flow Process leaks Temperature Chemical Dissolved oxygen (All) Oxygen scavenger/ passivator dosage pH Condensate treatment recycle NCSM . What Types of Corrosion NCSM can Minimize ? Oxygen Pitting Corrosion Flow Accelerated Corrosion (FAC) . NCMS is superior to conventional measurements Feature Response Time Sensitivity Accuracy Precision Dosage Control Corrosion Control NCSM Scavenger Residual Corrosion DO Monitor Monitor DO Test V. High High High Slow Med Med Med Slow Med Med Med Med Med High High Slow Poor Poor Poor Slow Low Low Low High Poor Poor Poor Poor Poor High Poor Poor Med Poor Poor RT ORP . Fast V. NCSM Respond to Small Increase of Dissolved Oxygen . NCSM Responds Air In Leakage in Condensate Pump . NCSM Responds to Small Changes of pH/Amine Feed Problem . 2 probes each One Particle Monitor per boiler. w/ 2 sensors Nalco analytical support program Nalco service / consulting support program .Nalco Corrosion Stress Monitoring (NCSM) 3DTfB for Power Nalco 3DT Corrosion Stress Monitoring (NCSM) Package One @ T ORP controller per boiler. NCSM with Nalco 3D TRASAR Platform Technology Measure Response Detects Communicate . NCSM with Nalco 3D TRASAR Platform Technology Measure Detects Control Your Boiler Response 24/7 from Anywhere …. Communicate . Thank You .