HEAT RATE AUDIT INTHERMAL POWER PLANTSHIVAJI CHOUDHURY
The New ScenarioIn the new competitive scenario, powerstations must face: • To Reduce the generating costs. • To Maintain high availability, efficiencyand operational flexibility. • To Meet strict environmentalconditions. • To Manage and extend the equipmentlife, including systems modernization.
The Generation Cost The variable overall cost =(The PlantAvailability Factor ,Station Heat Rate ,Specific Fuel Oil Consumption , AuxiliaryEnergy Consumption ). The Variable Cost, decides thecompetitiveness of the electric units in agenerating pool.
The Generation Cost Reduction The kWh fuel cost = 70 % approxthe variable overall cost . The Fuel cost components: Thestation Heat Rate (kcal/kWh). To reduce the variable cost throughthe heat rate improvement.
Heat rate Heat rate is the heat input (fuel)required per unit of power generated(kcal/kWh), for specific fuel beingfired and specific site conditions. Station heat rate =Turbine cycle heat rate=-------------------------- x100Boiler efficiency %
Objective• To point out the causesand location of efficiency losses.• Improve stationheat rate.
LOSSES IN THERMAL POWER PLANT 1.Boiler losses 2.Turbine losses 3.Condensate/feed water system losses. 4.Circulating water system losses. 5.Steam conditions 6.Electrical auxiliary losses 7.Steam auxiliary losses 8.Fuel handing 9.Heat losses 10.Cycle isolation 11. Impact of parameter deviation on HEAT RATE 12.D M water Makeup
1.1.Moisture losses High moisture in air Tube leaks Coal quality
1.2.Dry losses Boiler casing air leakage Air pre heater leakage Incorrect fuel air ratio Fouled heat transfer surfaces
1.3.Incomplete Combustion Coal quality Increased in ash contain Increased in carbon contain Decreased Coal mill fineness Classifier vanes improperly adjusted Ring/roller wear Classifier vane wear Burner tips plugged/eroded Burner damper settings Incorrect fuel air ratio. Hi oxygen at boiler out
2.Turbine losses Symptoms HP/IP/LP section efficiency Causes 2.1.Mechanical damage Metallurgical defects Maintenance practices 2.2.Flow area decrease Mechanical blockage Blade deposits 2.3.Flow area bypass 2.4.Flow area increase
2.3. Flow area bypass H P Turbine inlet bushing leakage Main steam valve leakage H P gland seal leakage IP steam /intercept valve leakage I P Turbine inlet bushing leakage
2.4. Flow area increase Spill strip or packing leakage. Rubbing Thermal stress Erosion of turbine stages. Solid particle erosion of nozzle block. Condenser leaks Poor water chemistry Blade mechanism damage.
Leaking steam notcontribution to powergeneration (in RED)2.5.Cross section of turbine –showingefficiency loss due to leakage
3.Condensate / F W systemlosses Symptoms Low feed water temp Causes HP/LP heaters out of service CEP/BFP efficiency Shaft rub Impeller wear Flow resistance path increase LP/HP heaters (high TTD/DCA) Excessive tube plugged FW heater out/bypass FW heater level low/high
4.Circulating water losses Symptoms High back pressure Causes Number of CW pump in operation Air binding of condenser tubes Excessive air in leakage Inadequate air removal capacity Fouled condenser tubes Microfouling Plugged condenser tubes Air binding water box Low circulating water flow Increased CW system resistance Decreased CW pump performance Excessive condenser tube plugged
5.Steam condition Firing conditions High super heater spray flow High re heater spray flow Inadequate heat transfer surface
6.Electrical auxiliary losses Symptoms Station load Causes Precipitator (ESP) performance Ash deposit Excessive rapping High ash in coal Fan (ID,FD,PA ) Change in fan efficiency AHP chocking Pump (BFP,CEP,CW ) Change in pump efficiency LP/HP Feedwater heater tube plugged Coal Mill performance Classifier setting incorrect Coal quality
7.Seam Auxiliary Losses Excessive soot blowing Decreased in BFP Turbine efficiency Low inlet steam temperature Excessive steam flow through vacuumpump/ejector Steam trap/vent leaking Excessive usage of steam coil
8.Fuel Handling Spillage from the belt/transport Measurement inaccuracies Coal pile erosion Wind erosion Water erosion Coal pile fire
9. Heat Losses Insulation on duct, pipe , turbine etc . No insulation Insulation damages Poor insulation Cladding missing /loose Steam leakage. Leakage to blow down tank. Leakage through vents, drains.
10.Cycle isolation Leakage from recirculation valves of BFP/CEP. Leakage through bypass valves. Leakage to condenser through high energydrains. Leakage to condenser through emergencycontrol valves of feed water heaters. Check high energy drains after every startup.Provide Thermocouple in High energy Drains,To detect passing of drain valve.
11.Impact of parameter deviation on HEATRATE (210 MW ,KWU Turbine )-operatorcontrollable parameters.SN PARTICULAR UNIT DESIGNPARAMETERSINCREASE in HEATRATE DUE TODEVIATION fromdesign parameters(IN KCAL/KWH)MULTIPLICATIONFACTOR1 PARTIAL LOADING MW 210 24.7 PER 20 MW 1.2352 MS PRESS KG/CM2 150 25.5 PER 20KG/CM21.2753 MS TEMP AT HPT INLET DEG C 535 7.5 PER 10 DEG C 0.754 HRH TEMP AT IPT INLET DEG 535 6.6 PER PER 10DEG C0.665 CONDENSER VACUUM mmHg 660 23.4 PER 10 mmHg2.346 FEED WATER TEMP DEG C 241 16 PER 20 DEG C 0.87 RH ATTEMP FLOW T/HR 0 6.4 PER 10 T/HR 0.648 OXYGEN % IN FLUE GASES % 3 8 PER 1% 8•�From above it is clear that, to achieve minimum heat rate,keep the operating parameters as close to the design parameters.
12.DM Water makeup Boiler tube leaks Excess deaerator venting to atmosphere Excess continuous blowdown Excess steam lost through condenserventing Valve packing leaks Pump seal leaks Steam leaks to atmosphere
Normative station heat rate • Existing Coal based Stations – 210 MW – 2500 Cal/kWh – 500 MW – 2425 Cal/kWh – In respect of 500 MW and above units where the boilerfeed pumps are electrically operated, the station heatrate shall be 40 Cal/kWh lower than the station heat rateindicated above. • New Coal based Stations – 1.065 x Design heat rate. – Prescribed maximum permissible design heat rate todiscourage procurement of inefficient machines
Heat Rate Monitoring Daily Heat Rate Calculation by deviationmethod & Identification Of Heat Rate Losses Monthly Performance Test (as per ASMEPTC/BS/DIN PG test Method ) Boiler Efficiency Air -Preheater performance Economizer Performance Turbine Heat Rate HP-LP-IP Cylinder Efficiency Heaters & condenser Turbine cycle rate rate
Maximum Turbine Cycle Heat RateNote – Prescribed maximum permissible heatrate to discourage procurement of inefficient machines
Example of 210 MW Operating efficiency of unit is 37.5 %. Unit heat rate is 2305 Kcal/kwhr To produce 860 Kcal ( heat equivalent toone kwhr) ,2305 kcal heat has to suppliedto boiler. Losses in the boiler- 266 kcal Losses in turbine generator- 1179 kcal Total losses-(266 +1179)= 1445 kcal Total heat input to boiler= (1445 + 860)kcalLOSSESProducesOne kwhr
Power plant efficiency Sub critical - 34% Super critical- 37% Ultra super critical 41%
Section wise losses in a particularthermal power plant
Major Reasons for Higher GrossHeat Rate in India 1. Low combustion efficiency lead to high carbon loss. 2. High force outages due to failure of boiler tubes. 3. Poor performance of milling system. 4. Lack of Maintenance planning and spare planning 5. Low turbine cylinder efficiency 6. High dry gas losses due to high unwanted excess air 7. Poor sealing and heat transfer in air pre-heaters 8. Low condenser vacuum. 9. High air ingress in the boiler and high heat loss due to poorinsulation 10. Poor Performance of ESP lead to failure of ID fan and lowavailability. 11. High cooling water inlet temperature due to poorperformance of Cooling Tower. 12. Non availability of quantity and quality coal. 13. High auxiliary power consumption . 14. Obsolete C&I system . 15. Poor quality critical valves lead to passing and poor control
Conclusion Only Improvements in the stationHeat Rate, Specific Fuel OilConsumption and Auxiliary EnergyConsumption can makegenerating units competitive.
Less Emissions As the heat rate decreases (heat rateimproves), the amount of fuel for thesame generation also goes down. Ofcourse with less fuel burned, emissions(green house gases) are lowered.
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