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  1. 1. ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 5, July 2012IMPROVING THE EFFICIENCY OF THERMAL EQUIPMENTS OF 210 MW TPS THROUGH THERMAL AUDIT MUDITA DUBEY1 Prof. ABHAY SHARMA 2 M.TECH IV SEM1 Dept. of Mechanical Engg.2 GGITS, Jabalpur mudita.dubey5@gmail.comABSTRACTIn the present work, energy analysis of a coal-based thermal power plant is done using the design datafrom a 210 MW thermal power plant under operation in India. The entire plant cycle is split up into threezones for the analysis: (1) main steam system, (2) steam turbine, condenser, feed pumps and the HP andLP heaters, (3) the entire analysis with boiler, turbo-generator, condenser, feed pumps, regenerativeheaters and the plant auxiliaries. It helps to find out the contributions of different parts of the planttowards energy destruction. The energy efficiency is calculated using the operating data from the plant atdifferent conditions, viz. at different loads, different condenser pressures, with and without regenerativeheaters and with different settings of the turbine governing. Effect of regeneration on energy efficiency isstudied by successively removing the high pressure regenerative heaters out of operation.. Increase in thecondenser back pressure decreases the energy efficiency. Successive withdrawal of the high pressureheaters show a gradual increment in the energy efficiency for the control volume excluding the boiler,while a decrease in energy efficiency when the whole plant including the boiler is considered. Keepingthe main steam pressure before the turbine control valves in sliding mode improves the energyefficiencies in case of part load. The boiler efficiency is calculated by the indirect method (lossescalculation method) and HP and LP heaters performance analysis has been done by the calculations. Thenet heat rate of the station is also calculated and target for the reduction to achieved the design value ofthe net station heat rate.Key words: Boiler, HP & LP heater, CEPINTRODUCTION thermal efficiency of 85%, combustion efficiency of 87%, a boiler efficiency of 80%,Boiler is defined as the heat added to the and a fuel-to-steam efficiency of 83%. Whatworking fluid expressed as a percentage of heat does these mean?in the fuel being burnt. The theoretical limit to Typically,boiler efficiency is 100% unlike in case of turbo 1) Thermal efficiency reflects how well thegenerator whose efficiency is limited by the boiler vessel transfers heat. The figurecycle efficiency. The maximum boiler efficiency usually excludes radiation andis thought of in terms of an optimum efficiency convection losses.which depends on fuel being burnt and the fact 2) Combustion efficiency typically indicatesthat waste products of combustion take away the ability of the burner to use fuelheat with them. completely without generating carbon monoxide or leaving hydrocarbonsWhen considering boiler energy savings, unburned.invariably the discussion involves the topic ofboiler efficiency. 3) Boiler efficiency could mean almost anything. Any fuel-use figure mustThe boiler suppliers and sales personnel willoften cite various numbers, like the boiler has a 371 All Rights Reserved © 2012 IJARCET
  2. 2. ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 5, July 2012 compare energy put into the boiler with • The Lower Heating Value (LHV), energy coming out. also called the Net Calorific Value (NCV) 4) "Fuel to steam efficiency" is accepted asa true input/output value. The gross calorific value (GCV) is the higher figure and assumes that all heat available form the fuel is to be recovered, including latent heat. In most equipment,Each term represents something different and this is not so the case, and the calculations ofthere is no way to tell, which boiler will use less efficiency based on gross calorific value willfuel in the same application! The trouble is that give maximum obtainable efficiencies muchthere are several norms to determine the lower than 100%, due to this irrecoverableefficiencies figures and it is practically very loss.difficult to verify these without costly test Both the gross calorific value and netprocedures. The easiest and most cost effective calorific value are equally valid, but formethod is to review the basic boiler design data comparison purposes, a particularand estimate the efficiency value on five (5) convention should be used throughout.broad elements. 3) Fuel Specification: The fuel specified has a1) Boiler Stack Temperature: Boiler stack dramatic effect on efficiency. With gaseous temperature is the temperature of the fuels having higher the hydrogen content, combustion gases leaving the boiler. This the more water vapor is formed during temperature represents the major portion of combustion. The result is energy loss as the the energy not converted to usable output. vapor absorbs energy in the boiler and The higher the temperature, the less energy lowers the efficiency of the equipment. transferred to output and the lower the boiler efficiency. When stack temperature is The specification used to calculate evaluated, it is important to determine if the efficiency must be based on the fuel to be value is proven. For example, if a boiler runs used at the installation. As a rule, typical on natural gas with a stack temperature of natural gas has a hydrogen/-carbon (H/C) 350°F, the maximum theoretical efficiency ratio of 0.31. If an H/C ratio of 0.25 is used of the unit is 83.5%. For the boiler to for calculating efficiency, the value operate at 84% efficiency, the stack increases from 82.5% to 83.8%. temperature must be less than 350°F. 4) Excess Air Levels: Excess air is supplied to the boiler beyond what is required for complete combustion primarily to ensure2) Heat Content of Fuel: The efficiency complete combustion and to allow for calculation requires knowledge of the normal variations in combustion. A certain calorific value of the fuel (heat content), its amount of excess air is provided to the carbon to hydrogen ratio, and whether the burner as a safety factor for sufficient water produced is lost as steam or is combustion air. condensed, and whether the latent heat (heat required to turn water into steam) is 5) Ambient Air temperature and Relative recovered. Disagreements exist on what is Humidity: Ambient conditions have a considered an "energy input". Unfortunately dramatic effect on boiler efficiency. Most any fuel has two widely published energy efficiency calculations use an ambient contents. They are: temperature of 80°F and a relative humidity of 30%. Efficiency changes more than 0.5% • The Higher Heating Value (HHV), for every 20°F change in ambient also called Gross Calorific temperature. Changes in air humidity would Value (GCV) have similar effects; the more the humidity, the lower will be the efficiency. 372 All Rights Reserved © 2012 IJARCET
  3. 3. ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 5, July 2012 Fig :-Steam cycle for 210 mwOperating efficiency of the boiler: Operating efficiency of the Turbine:The test method employed is based on the After evaluating the turbine heat rate andabbreviated efficiency by the loss method (or efficiency, check for the deviation from theindirect method) test, which neglects the minor design and identify the factors contributing forlosses and heat credits, which are covered in full the deviations. The major factors to be lookedtext version. The major losses covered are: into are:  Heat loss due to dry flue gas losses  Main steam and reheat steam inlet parameters  Heat loss due to moisture in fuel  Turbine exhaust steam parameters  Heat loss due to hydrogen (moisture of burning hydrogen)  Re-heater and super heater spray  Heat loss due to combustibles in refuse  Passing of high energy draining  Heat loss due to radiation  Loading on the turbine  Un accounted losses as per the contract  Boiler loading and boiler performance with the Boiler Supplier  Operations and maintenance constraintsIndirect method is also called as heat lossmethod. The efficiency can be arrived at, by COMBUSTION PROCESSES have been, aresubtracting the heat loss fractions from 100. The and will be for the near future, the primestandards do not include blow-down loss in the generator of energy in our civilization, which isefficiency determination process burning fossil fuels at an ever-increasing rate. The processes must be managed well for the sake of the environment and the sustainability of 373 All Rights Reserved © 2012 IJARCET
  4. 4. ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 5, July 2012civilization. The principles of combustion are more air (carrying about 21 percent oxygen bycommon to heaters, boilers and other forms of volume) is passed through the burner than isindustrial combustion, e.g. in furnaces and kilns. chemically required for complete combustion.In this sense, the term “boiler” is This excess air speeds up the mixing of fuel andinterchangeable with “heater” throughout air. On one hand, this process ensures that nearlythis text (unless stated otherwise). Conventional all the fuel receives the oxygen it needs forfuels consist mainly of two elements – carbon combustion before it is chilled belowand hydrogen. During combustion, they combine combustion temperatures by contact with heatwith oxygen to produce heat. The fuel value lies exchange surfaces. It also prevents fuel that isin the carbon and hydrogen content. not burned completely from exploding withinNon-fossil fuels, such as biomass and alcohol, the boiler. On the other hand, excess air wastesalso contain oxygen in their molecular energy by carrying heat up the stack. A fine linestructures. Ideally, combustion breaks down the exists between combustion efficiency and safetymolecular structure of the fuel; the carbon in ensuring that as little excess air as possible isoxidizes to carbon dioxide (CO2) and the supplied to the burner. Boiler owners andhydrogen to water vapour (H2O). But an operators will want to know if their operationsincomplete process creates undesirable and are efficient. As the objective is to increase thedangerous products. To ensure complete energy efficiency of boilers, reviewing thecombustion, even modern equipment with many causes of heat loss in boiler operations may befeatures must operate with excess air. That is, useful. Fig:-Excess air on boiler efficiencyHEAT LOSSES :In such systems, many of thelosses listed in the code do not apply. And other Alternatively,systems are small enough for their losses to berolled into an “unaccounted for” category, for Efficiency (E) % 5 100 2 losses, wherewhich a value can be assumed. A simplified losses can be calculated according tomethod for quantifying boiler efficiency uses the ASMEthis equation: power test code. Since this code uses Imperial units, it isEfficiency (E) % 5 (Output 4 Input) 3 100, necessary to convert temperatures to degreeswhere: Output 5 Input 2 Losses Fahrenheit (°F) and heating units to British 374 All Rights Reserved © 2012 IJARCET
  5. 5. ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 5, July 2012thermal units per pound (Btu/lb.), which can bedone with the following conversion formulas: The following four significant types of energy losses apply to natural gas and heating fuel °F 5 (1.8 3 °C) 1 32 systems Btu/lb. 5 0.4299 3 kJ/kgDry flue gas loss (LDG) Heat is lost in the 584 = Latent heat corresponding to partial“dry” products of combustion, which carry only pressure of water vapoursensible heat since no change of state wasinvolved. These products are carbon dioxide Percentage loss = 8.26&8.26%(CO2), carbon monoxide (CO), oxygen (O2),nitrogen (N2) and sulphur dioxide (SO2). Moisture in combustion air: Moisture enteringConcentrations of SO2 and CO are normally in the boiler with the fuel leaves as a superheatedthe parts-per-million (ppm) range so, from the vapour. This moisture loss is made up of theviewpoint of heat loss, they can be ignored. sensible heat to bring the moisture to boilingCalculate the dry flue gas loss (LDG) using the point, the latent heat of evaporation of thefollowing formula: moisture, and the superheat required to bring this steam to the temperature of the exhaust gas.L1 =m x Cp x (Tf - Ta ) x 100 This loss can be calculated with the following GCV of fuel formulaWhere,L1 = % Heat loss due to dry flue gasm = Mass of dry flue gas in kg/kg of fuel L3= M x {584 + Cp (Tf . Ta)}X 100 = Combustion products from fuel: CO2 + GCV of fuelSO2 + Nitrogen in fuel + whereNitrogen in the actual mass of air supplied + O2 M = kg moisture in fuel on 1 kg basisin flue gas. Cp = Specific heat of superheated steam in(H2O/Water vapour in the flue gas should not be kCal/kg°Cconsidered) Tf = Flue gas temperature in °C = 867.62&1184.8 kJ/kg of Ta = Ambient temperature in °Ccoal 584 = Latent heat corresponding to partial Percentage loss = 5.08&6.862% pressure of water vapour Percentage loss = 0.101&.099%Wet flue gas: The combustion of hydrogencauses a heat loss because the product ofcombustion is water. This water is converted tosteam and this carries away heat in the form of Heat loss due to unburnt in fly ash (%).its latent heat. L4 = Total ash collected / kg of fuel burnt x G.C.V of fly ash x 100 GCV of fuelL2=9 x H2 x {2442 + Cp (Tf . Ta )} x 100 GCV of fuel Heat loss due to unburnt in bottom ash (%)Where L5 = Total ash collected per kg of fuel burnt xH2 = kg of hydrogen present in fuel on 1 kg G.C.V of bottom ash x 100basis GCV of fuelCp = Specific heat of superheated steam in kCal/kg °C Heat loss due to radiation and convection:Tf = Flue gas temperature in °C The other heat losses from a boiler consist of theTa = Ambient temperature in °C loss of heat by radiation and convection from 375 All Rights Reserved © 2012 IJARCET
  6. 6. ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 5, July 2012the boiler casting into the surrounding boiler combustion air and the amount of air suppliedhouse. per unit mass of coal burned must be known. L7 = AAS x humidity factor x Cp x (Tf . Ta ) xNormally surface loss and other unaccounted 100losses is assumed based on the type and size GCV of fuelof the boiler as given below WhereFor industrial fire tube / packaged boiler =1.5 to 2.5% AAS = Actual mass of air supplied per kg ofFor industrial watertube boiler = 2 to 3% fuelFor power station boiler = 0.4 to 1% Humidity factor = kg of water/kg of dry air Cp = Specific heat of superheated steam inL6 = 0.548 x [ (Ts / 55.55)4 . (Ta / 55.55)4] + kCal/kg°C1.957 x (Ts . Ta)1.25 x sq.rt of Tf = Flue gas temperature in °C [(196.85 Vm + 68.9) / 68.9] Ta = Ambient temperature in °C (dry bulb)where PERFORMANCE OF AIR PREHEATERSL6 = Radiation loss in W/m2Vm = Wind velocity in m/s Gas side efficiency: The gas side efficiency isTs = Surface temperature (K) defined as the ratio of the temperature drop,Ta = Ambient temperature (K) corrected for leakage, to the temperature head and expressed as percentage.Heat loss due to moisture present in airVapour in the form of humidity in the incoming Temperature drop is obtained by subtracting theair, is superheated as it passes through the boiler. corrected gas outlet temperature from the inlet.Since this heat passes up the stack, it must beincluded as a boiler loss.To relate this loss to the Temperature head is obtained by subtracting airmass of coal burned, the moisture content of the inlet temperature from gas inlet temperature.CONCLUSION AND ENERGY and to improve the performance of HP and LPCONSERVATION OPPORTUNITIES Heater to maintain the design feed water temperature in the two unit of 210 mwThe improvement in the efficiency of the boiler increasing the efficiency of the boiler byby the plugging air-leakage in the air-pre heater improving the performance of mill, air-pre 376 All Rights Reserved © 2012 IJARCET
  7. 7. ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 5, July 2012heater and bringing down the excess air level to c. Charging of APRDS from CRH line insteadthe design value and also improve the of MS line: -APRDS charging from cold reheatperformance of HP and LP Heater by calculating (CRH) is always more beneficial than from MSits effectiveness. In the condensate extraction line charging.pump the discharge pressures of CEPs are verymuch higher than the pressure required to take d. Isolation of steam line which is not in use:condensate from hot well and pass through - It is not advisable to keep steam lineheaters and deliver to de-aerator Installing VFD unnecessary charge if steam is not utilized sinceon CEP can reduce power consumption by 757 there energy loss occurred due to radiation. ForkW total in the CEP systems of all units. example deareator extraction can be charged from turbine Extraction/CRH or from APRDS.1. Air & flue gas cycle:- In normal running APRDS Extraction is not used so same can be kept isolated. a. Optimizing excess air ratio: - It reduces FDfan & ID fan loading. e. Replacement of BFP cartridge: - BFP draws more current If Cartridge is wore out, causingb. Replacement of oversize FD and PA fan: - short circuit of feed water Flow inside the pump.Many thermal power plants have oversize fan It affects pump performance. Hence cartridgecausing huge difference between design & replacement is necessary.operating point leads to lower efficiency. Hencefan efficiency can be improved by replacing f. Attending passing recirculation valve ofcorrect size of fan. If replacement is not BFP: - BFP Power consumption Increases duepossible, Use of HT VFD for PA & ID fan can to passing of R/C valve. It requires correctivebe the solution. action.c. Attending the air & flue gas leakages: - g. Installation of HT VFD for CEP: - CEPLeakages in air & flue gas path increases fan capacity is underutilized and also there isloading. Use of Thermo vision monitoring can pressure loss occurs across Deareator levelbe adopted to identify leakages in flue gas path. control valve. There is large scope of energyAir preheater performance is one crucial factor saving which can be accomplished by use of HTin leakage contribution. If APH leakage exceeds VFD for CEP or impeller value then it requires corrective action. 3. Fuel & ash Cycle:-2. Steam, Feed water and condensate cycle:-a. BFP scoop operation in three element mode a. Optimized ball loading in Ball tube mill: -instead of DP mode: - In three element mode Excessive ball loading increases mill power.throttling losses across FRS valve reduces leads Hence ball loading is to be Optimized dependingto reduction in BFP power. upon coal fineness report.b. Optimization of level set point in LP & HP b. Use of Wash Coal or Blending with A-heater: - Heater drip level affects TTD & DCA grade coal: - F-grade coal has high ash content.of heater which finally affect feed water O/L Overall performance can be improved by usingtemp. Hence it requires setting of drip level set Wash coal or blending of F-grade coal with A-point correctly. grade coal instead of only using F- grade coal. 377 All Rights Reserved © 2012 IJARCET
  8. 8. ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 5, July 2012c. Avoiding idle running of conveyors & of compression air dryer use heat generated incrusher in CHP compression cycle, thus reduces sp. Power consumption.d. Use of Dry ash Evacuation instead of WETdeashing System: - Dry deashing system c. Use of screw compressor insteadconsumes less power & also minimizes waste reciprocating compressor: - Sp. Powerreduction. consumption of screw compressor is less than reciprocating air compressor leads to reduce aux.e. Optimize coal mill maintenance:-Mill power consumption.corrective/preventive maintenance is to beoptimized depending parameter like- running References:-hrs, mill fineness, bottom ash unburnt particle,degree of reject pipe chocking etc. The Energy and Resources Institute. 2009. TERI Energy Data Directory and Yearbook. New4. ECW & ACW system:- Delhi, India: The Energy and Resources Institute.a. Isolating ECW supply of standbyauxiliaries: - Many times standby coolers are Tongia, R. 2003. The Political Economy ofkept charged from ECW side. Also Standby Indian Power Sector Reforms. Program onequipment’s auxiliaries like Lube oil system Energy and Sustainable Development workingkept running for reliability. We can isolate paper no. 4. Stanford University.Standby cooler from ECW system & switching Khanna, Madhu, Kusum Mundra, and Amanof standby auxiliaries, doing trade off between Ullah. 1999. Parametric and Semi-Parametricreturn & reliability. Estimation of the Effect of Firm Attributes on Efficiency: The Electricity Generating Industryb. Improving condenser performance by in India. The Journal of International Trade &condenser tube cleaning & use of highly Economic Development: An International andefficient debris filter: - Tube cleaning by bullet Comparative Review 8(4): 419–30.shot method increases condenser performance,condenser tube cleaning is necessary which is to Khanna, M., and N.D. Rao. 2009. Supply and Demand of Electricity in the Developing carried out in overhaul. Also highly advanced Annual Review of Resource Economics 1: 567–debris filter contribute condenser performance. 95. Khanna, M., and D. Zilberman. 1999. Barriers toc. Application of special coating on CW pump Energy-Efficiency in Electricity Generation inimpeller: - It improves pump impeller profile India. Energy Journal 20(1): 25–41.condition, increasing pump performance. 2001. Adoption of Energy Efficient5. Compressed air system:- Technologies and Carbon Abatement: The Electricity Generating Sector in India. Energya. Optimizing discharge air pressure by Economics 23(6): 637–58.tuning loading/unloading cycle: - It helpful toreduce sp. Power consumption. Knittel, Christopher R. 2002. Alternative Regulatory Methods and Firm Efficiency:b. Use of heat of compression air dryer Stochastic Frontier Evidence from the U.S.instead of electrically heated air dryer: - Heat 378 All Rights Reserved © 2012 IJARCET
  9. 9. ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering & Technology Volume 1, Issue 5, July 2012Electricity Industry. The Review of Economics Maruyama, N., and M.J. Eckelman. 2009. Long-and Statistics 84(3): 530–40. Term Trends of Electric Efficiencies in Electricity Generation in Developing Countries. Energy Policy 37(5): 1678–86. 379 All Rights Reserved © 2012 IJARCET