EFFECTIVE UTILIZATION OF WASTE HEAT FROM DIESEL GENSET TO RUN AIR CONDITIONING PLANTR. J. Yadav1 and R. S. Verma2 Department of Mechanical Engineering, Pimpri Chichwad College of Engg., Nigdi, Pune- 411 044 Phone: 020-2715 7612 Extn. 2161, Mobile: 09823 230820, E-mail:
[email protected] 2 Department of Mechanical Engineering, Army Institute of Technology, Dighi Hills, Pune-411015 Phone: 020-2715 7612 Extn. 2161, Res:020-24210704 1 Abstract Load shedding is a common practice everywhere due to increased load on power stations. Industries depending heavily on electrical energy are the most affected ones. Industries are encouraged to have their own captive power stations. Diesel generating sets are the most common captive power stations. The exhaust gases of these gensets have a very large amount of heat (about 700 degrees Celsius at full load ), which is wasted, can be effectively exploited. Waste heat of coolant (about 120 degrees Celsius) from diesel gensets, equipped with evaporative cooling system can also be exploited. The waste heat of the exhaust & coolant so exploited can run a central air conditioning plant based on vapour absorption chiller. The present case study ( Theoretical) shows that a 30 TR vapour absorption chiller based central air conditioning plant can be run by tapping waste heat of the exhaust (14.5 TR ) and coolant heat (15.5 TR ) of 125 HP genset. The practical implementation of such vapour absorption chillers by number of companies like Thermax India Ltd. , Kaltimex, et. al. are reported. Such system with combined heating power & cooling (CHPC ) is the need of time for conservation of the energy. Keywords: Waste Heat Utilization, Vapour Absorption Chiller, Gensets, Air conditioner, CHPC (combined heating power & cooling ) Nomenclature P = Pressure t = Temperature ξ = Concentration by weight h = Specific enthalpy f = Specific rich solution circulation q = Heat transfer per unit mass D = mass of vapour distilled from generator 1. Introduction Absorption refrigeration cycle is similar to the vapor compression cycle in that it employs a volatile refrigerant , usually either ammonia or water, which alternatively vaporizes under low pressure in the evaporator by absorbing the latent heat from the material being cooled and condenses under high pressure in the condenser by surrendering the latent heat to the condensing medium. The principle difference in the absorption and vapor-compression cycles is the motivating force that circulate the refrigerant through the system and provides the necessary pressure differential between the vaporizing and condensing processes. In the absorption cycle , the vapor compressor employed the vapor compression cycle is replaced by an absorber and generator which perform all the functions performed by the compressor in the vapor compression cycle. In addition whereas the energy input required by the vapor compression cycle is supplied by the mechanical work of the compressor, the energy input in the absorption cycle is in the form of heat supplied directly to the generator. The source of the heat supplied to the generator is usually low pressure steam or hot water although in smaller systems the heat is usually supplied by the combustion of an appropriate fuel, such as natural gas, propane, or kerosene, directly in the generator or by an electric resistance heater installed in the generator. 37 State 2. Absorption System Operation: Fig. Where it is cooled and liquefied.9 mm Hg & t = 91 deg Celsius. This vapor comes in contact with weak solution coming from the generator into absorber.67 = 0.ξ diagram ) h2 = -22kJ/ kg Poor solution concentration of water ξ = 1. Here. ) ξ Li-Br2 =0. Analysis of Performance of the Vapour Absorption Chiller System ( Case Study for 125 HP Genset) Diesel genset details: 1) Rated Power Output Of Engine Considered = 125 Hp 2) Break Hp Of Engine = 3/4 X 125 = 93. illustrates evaporative cooling with the water cooled condenser.ξ diagram ) h1 = -50 kJ/ kg Rich solution concentration of water ξ = 1. So the absorber is cooled by circulating water. The liquid refrigerant then passes through expansion valve and into the evaporator where it absorbs heat and vaporizes. Saturated condition state at P = 71.63 = 0. ) Flash chamber & absorber pressure P o = 6. In this case condensation of the vapor formed in the overhead tank occurs in the heat exchanger cooled by a secondary water circuit.0. When the solution is heated. the advantage is taken from the high latent heat of vaporization of water by allowing it to evaporate in the cylinder jackets.67 ( from h. The absorption refrigeration uses a strong solution of refrigerant vapor in water (mostly ammonia in water) i. the refrigerant vapour is driven out of the solution from generator and it goes to the condenser.63 h4 = -140 kJ/ kg . Working of Evaporative Cooling System In this system. t = 45 deg Celsius and ξ Li-Br2 = 0. It is readily absorbed releasing latent heat of condensation.9 mm Hg ( At 45 deg Celsius. e.9 mm Hg & t = 105 deg Celsius. Condenser temperature = 45 deg Celsius. Strong solution rich in ammonia is pumped to the generator where heat is supplied from external source. ) ξ Li-Br2 =0. Saturated condition state at P = 71. 3. the engine will be cooled because of the evaporation of the water in the cylinder jacket into steam. The pump circulates the cooling water to the engine and the heated water from the engine is delivered to tank thereby the circulation is maintained. If the steam is formed at pressure above atmospheric the temperature will be above the normal permissible temperature The fig. and the water returns to by gravity.63 ( from h.372 Advances in Energy Research (AER – 2006) 2.75 kW 4) Heat Lost To Coolant (Latent Heat) = 75 kW Vapour absorption chiller details : Operating conditions : for a water-lithium bromide chilled-water plant for air-conditioning are as follows : Generator temperature = 105 deg Celsius. placed in the generator. 4.75 kW 3) Heat Lost Along with Exhaust = 93.33 State 4.54 mm Hg ( At 5 deg Celsius. Chilled-water temperature = 5 deg Celsius.ξ Li-Br2 =1 .ξ Li-Br2 =1 . Temperature of solution entering generator = 95 deg Celsius.0.( saturated ) Thermodynamic calculations: Condenser & generator pressure P k = 71. The refrigerant vapor then passes through suction line to absorber. ) (A) Thermodynamic Conditions State 1. Absorber temperature = 45 deg Celsius. shows schematic arrangement of absorption system. h = ( 2501 + 1. h6 =4. State 5.4 kJ / kg State 8. At these conditions it represents a superheated state.54 mm Hg pressures.75 (-22 + 50) = 3189 kJ / kg of vapour.75 kg / kg of vapor f -1 = 15. It is that water vapour at 71.9 mm Hg pressure and 105 deg Celsius temp.88t ) kJ / kg Using the latter procedure h = 2501 + 1.54 mm Hg & t = 5 deg Celsius ( saturated vapour ) h8 = 2501 + 1.4 = 2321.88( 5 ) = 2510 kJ / kg (B ) Refrigerating effect: qo = h8 – h7 = 2510 – 188. State 7. State 4a.75 kg / kg of vapor State 3.Effective Utilization of Waste Heat from Diesel Genset to Run Air Conditioning Plant 373 The enthalpy is read against temperature and composition. P = 6.6 kJ / kg. Coefficient of performance.33 = 16.6 / 3189 = 0.75 = = -118 kJ / kg. Energy balance of liquid-liquid heat exchanger Specific solution circulation rates f ( h1 – h4) = ( f -1 ) ( h2 – h3 ) hence h3 = h2 .75 ( -50 + 140 ) /15. The enthalpy of water vapour above the reference state of saturated water at 0 deg Celsius can be found either from steam tables or from the empirical relation.37 – 0.54 mm Hg & t = 5 deg Celsius ( liquid + water ) h7 = h6 = 188. It may be noted that point 4 represents a sub cooled state at 6. Assume the same as 4 Specific solution circulation rates f = 1 – 0.22 + 16. COP ≈ q o / qb = 2321.4 kJ / kg.728 . P = 6.[ f ( h1 – h4) / ( f -1 ) ] = -22 – 16.1868 ( 45 ) = 188. Saturated water at 45 deg Celsius.33 / 0. Heat added in the generator per unit mass of vapour distilled qb = h5 – h2 + f (h2 – h1 ) = 2698 .88( 105 ) = 2698 kJ / kg State 6. The conventional method is to recover the waste heat through individual recovery equipment to cater to Heating/ Cooling requirements.75 x 93.) Table 1: Cooling Potential based on Engine rating ENGINE RATING [ Kw ] 300 500 1000 1500 2000 COOLING CAPACITY on Exhaust + Jacket Water [ USRT ]* 100-110 175-200 300-350 425-500 525-600 *Indicative and may vary as per Engine waste heat parameters Figure 1: Sankey Diagram for IC Engine with & without heat recovery (Source:Thermax India Ltd.) Commercial Data Available from Industries for Co-Generation The commercial data available from various industries shows clearly that engine gensets normally have about 40 % overall electrical efficiency. such as Caterpillar. D = [ 145 kJ / s ] / [3189 kJ / kg of vapour ] D = 145 / 3189 kg of vapour/ s Cooling effect = D x qo = 145 / 3189 x 2321.56 kW = 105.6 k J/ s = 105.374 Advances in Energy Research (AER – 2006) (C ) Water vapour distilled. Deutz . commercial/ industrial users are shifting towards self.. With increased natural gas availability and ever widening demand supply gap for power.56 / 3. Industries are utilizing the tri-generation systems which utilizes the waste heat from the engine Exhaust directly along with the jacket water to generate Chilled/ Hot water to cater to the Air-conditioning / Process cooling / Heating requirements. & Cummins etc. Heat available for vapor generation from cooling system of Diesel Genset = 75 kW.generation to meet their ever increasing power needs.75 = 70 kW.516 = 30 TR . Total heat available for vapour generation = 70 + 75 = 145 kW. With CHPC Systems the overall efficiency is doubled to 80 % The data for different capacity of diesel genset engines of different manufacturer is easily available. Man B & W. Following table shows cooling potential based on engine rating. D: Heat available for vapor generation from exhaust system of Diesel Genset = 0. Pune) . the balance 60 % is wasted to the atmosphere.( Data from Thermax India Ltd. Supermarkets Software Parks Shopping malls/Multiplexes. Thus energy generated can be used as an option to the electrical board. Thus CHPC system provide an impressive operating savings. with the use of CHPC systems following will be the advantages • • • • Peak Electric power reduction High Efficiency of 80 % Power Reliability & Quality Significant emission reduction By taking into above considerations following will be the Best application areas for implementation of trigeneration • • • • • • • Hospitals Hotel High Schools. Potential of Cogeneration and Application Areas As Diesel Engines are the leading prime mover in the world in the range upto 5 MWe.Effective Utilization of Waste Heat from Diesel Genset to Run Air Conditioning Plant 375 Figure 2: Laout of heat recovery System 6. The energy cost may reduce approximately by 35 %. . Process industries Conclusion The theoretical analysis shows such an air-conditioning plant would take the load of 30 TR. Naturally the organization will opt to use the in-house generated energy for the round the clock availability and its cost-effective performance with 80 % efficiency which in turn give lower energy cost. K.Tata McGraw-Hill. P. Ltd. 2. Aroa. References 1. . ( 2001) “ Principles of Refrigeration” . Roy J. Ganesan.Scitech Publishing ( I ) Pvt. Dossat. V. This certainly will help in reducing the present problem of load shedding. Ramalingam . 3. ( 2001 ) “ Internal Combustion Engines” . New Delhi. C.K. “Internal Combustion Engines”.376 Advances in Energy Research (AER – 2006) The implementation of CHPC will surely help in lowering the fuel and electricity consumption in the industry. New Delhi. We hope to inspire others to study the possibility of such co-generation / Tri-generation. “ Refrigeration & Air-conditioning” . 4.Tata McGraw-Hill. Pearson Education Asia.