1. Energy Audit & Efficiency Improvement of Operating Power Plants
28 July 2015
Dr. Y. P. Abbi
Senior Advisor/Energo Engineering Projects Limited,
Ex- Executive Director/BHEL, Senior Fellow/TERI, President/Energo

2. Energy Efficiency Improvement of Thermal Power Plants
It is responsibility of Operation & Maintenance Engineers/Managers of the plant
It involves systematic data collection & analysis (weekly/fortnigtly); and not once a year by an External Energy Auditor
Understand the science/technology for each equipment sub-system of the plant; and keep yourself abreast with their latest technology development
Planned improvements in stages; don’t wait for R&M
Retire old plants with Heat Rate deviation more than
20 %

3. Energy Efficiency Improvement – A Necessity
Power demand (as on date) is low (PLF); thus need for efficiency improvement for financial sustainability
Energy efficiency improvement leads to fuel cost saving and thus plant profitability
It leads to CO2 emission reduction (a national & international commitment)

4. Change Mindset for Energy Efficiency Improvement
Don’t make excuse that coal quality has become bad
We have to work with the available fuel, and achieve the best possible results
Blame no more the design defects; it is we who have to overcome/remove these
Don’t be defensive while analyzing results, or receiving suggestions from external Energy Auditors
Make PG Test results as the baseline; and make all efforts to achieve & maintain these
Important that all key instruments used in the plant are calibrated regularly and at least conform to prescribe accuracy

5. Required Accuracy of Instruments
Thermocouples
Temp. Range: 0 to 277 0C – 1.1 0C;
277 to C – 3/8 %
Pressure Transducers
0.1
Power Meter
Data Logger
0.03
Power Transducer
0.5
Flue Gas Analyzer
Ultrasonic Flow Meter
Anemometer
1.0
Infrared Thermometer
Lux Meter
RH Meter
Calibrated Test Flow Assembly
0.25

6. LET US CONSIDER THE PATTERN OF ENERGY CONSUMPTION & LOSSES IN A THERMAL POWER STATION

7. Typical Energy Losses in a Power Plant

8. Typical Energy Losses in a Boiler

9. Typical Energy Losses in Steam Cycle

10. “You cannot Manage what you cannot Measure”
(Accurately)
- Jack Welch, CEO, General Electric

11. What needs to be measured for Efficiency Improvement of a Power Plant ?
Heat rate of the plant
Heat rate of the steam turbine cycle & Boiler Efficiency
Auxiliary Power Consumption
Net heat rate of the power plant
(Monitored by CEA & BEE under PAT scheme)

12. Heat Rate of Steam cycle and the Power Plant
Heat Rate of steam cycle, HRsc = {(Enthalpy of SH steam) +(Heat added during RH) – (Sensible heat in feed water)} / (kW electricity generated), kCal/kWh Efficiency of steam cycle, ƞsc = 860 /HRsc Gross Heat Rate of the Power Plant, HRpp = HRsc / ƞBOILER , kCal / kWh Gross Calorific value of Fuel = GCV kCal /kg of fuel Specific fuel consumption = HRpp / GCV, kg/kWh Net Heat rate of the Power Plant = HRpp / (1 – APC in fraction)

13. Perform Achieve & Trade (PAT) scheme under Energy Conservation Act 2001
Applicable for all Designated Consumers (DCs)
Thermal Power Plants are also DCs
Every DC is given a target for reduction in energy consumption by end of three years
For power plants, the target will be in terms of reduction of Net Heat Rate of the Plant
Power plants who don’t achieve the target will have to buy Energy Certificates from those who have achieved more than their targets

14. Benefits from Heat Rate Improvement
Take the case of a typical 210 MW power plant and assume that it has the following operating variables: Heat rate = 2450 kCal/kWh Plant load factor = 85 % Coal GCV = 3997 kCal/kg (C = 41.7 %) Coal cost = INR 2000 /t CO2 emission per t of coal burnt = (41.07/100) x (44/12) = t The coal consumed and its cost, and CO2 emissions per year are as follows: Specific coal consumption = 2450/3997 =0.613 t/MWh Electricity produced = 210 x 0.85 x 365 x 24 = 1,563,660 MWh Contd.1

15. Contd. 1
Coal consumed = 1,563,660 x = 958,524 t Coal cost = INR 958,524 x 2,000 = INR 1,917,048,000 CO2 emissions = 958,524 x = 1,443,441 t If the energy audit and modifications in O&M practices yields an improvement of heat rate by just 50 kCal/kWh, the fuel and fuel cost saved per year would be as follows: Heat rate (improved to) = 2400 kCal/kWh Specific coal consumption = 2400/3997 = t/MWh Contd. 2

16. Contd. 2
Coal consumed for generating 1,563,660 MWh of electricity = 1,563,660 x = 938,900 tonne Coal cost = 938,900 x 2000 = 1,877,800,000 INR CO2 emissions = 938,900 x = 1,413,890 t Thus, coal cost saved in one year = INR (1,917,048,000 – 1,877,800,000) = INR 39,248,000 CO2 emissions saved in one year = 1,443, ,413,890 = 29,551 t

17. Objectives of an Energy Audit or Performance Monitoring
To improve Heat Rate and reduce Auxiliary Power Consumption of the power plant
To identify energy efficiency improvement measures
To develop medium-term and long-term energy conservation measures, & work out techno-economics

18. Evaluation of efficiency of Boilers
Standards – ASME PTC 4 or BS 2885 or IS 8753
Applicable for boilers fired with oil, gas, solid fuels
Two Methods used – a) Direct Method, & b) Indirect Method
Applicable for different firing systems –Stoker, pf, FBC
Applicable for subcritical and supercritical boilers

19. Direct Method
Boiler efficiency = (Heat output/Heat input) × 100 = {Steam flow rate × (steam enthalpy – feed water enthalpy) × 100}/ (Fuel firing rate × gross calorific value) *Fuel as fired basis only

20. Calculation of Boiler Efficiency (ASME PTC 4)
Heat losses in the boiler (%)
Dry flue gas losses (sensible heat + un-burnt CO)
Loss due to hydrogen and moisture in the flue gases
Loss due to moisture in air
Un-burnt carbon losses (fly ash and bottom ash)
Loss due to sensible heat in fly ash and bottom ash
Radiation & convection losses from boiler surface
Total losses = Sum of all above
Boiler Efficiency
ŋBOILER = 100 – Total losses

21. Data required for boiler efficiency calculations
Ultimate analysis of fuel (C, H, O, N, S, H2O, ash)
GCV of fuel, kCal/kg
O2 in flue gas (% by vol.)
CO in flue gas (% by vol.)
Tg, Flue gas temperature, oC
Ambient air temp., humidity in air
Combustibles (un-burnt) in fly ash & bottom ash
Measurement of temp., press., flow should be done at multiple points in the duct

23. Recommended excess air levels
Fuel/Type of boiler
Excess air (%)
Coal PC
FBC
Stoker
Fuel oil
Bagasse
Wood
Blast furnace gas
15-20
20-25
25-35
03-15
15-30

24. Cold air leakage in an air heater

25. Cold air leakage in Air Heaters
As per ASME PTC 4.1 wAL, % leakage = {(% O2 in gas leaving the heater - % O2 in gas entering the heater)/ (21 - % O2 in gas leaving the heater)}x 90

26. Corrected flue gas temperature leaving the air heater for no leakage
tGONL = {% leakage x CpA x (tGO – tAI)/ (100 x CpG)} + tGO where CpA = Mean specific heat between temperature tAI and tGO CpG = Mean specific heat between temperature tGO and tGONL

27. Case study of Energy Audit of a 500 MW Boiler

28. Case study: Boiler efficiency evaluation for a 500 MW unit (Steam parameters t/h, 179 ata,540oC/540oC)
Coal properties
Design Actual
C (Wt %) H S N O
H2O
Ash
GCV (kCal/kg)

29. Measured data for energy audit
Boiler
O2 in flue gas (%)
Excess air (%)
CO (ppm)
Flue gas temp. (OC)
Ambient temp. (OC)
Wet bulb temp. (OC)
Air heater
O2 (%) in flue gas after eco
O2 (%) in flue gas after air heater 7.50

30. Calculation of boiler efficiency
Parameter (%) Design Calculated
Dry flue gas loss
Heat loss due to CO
Heat loss due to moisture in air
Heat loss due to moisture and
Hydrogen in fuel
Heat loss due to unburnt in bottom ash
Heat loss due to unburnt in fly ash
Sensible heat in bottom ash
Sensible heat in fly ash
Surface & unaccounted loss
Total heat losses
Boiler efficiency

31. Analysis of boiler efficiency test results
Flue gas losses are higher than design
Excess air level is 23.6 % (recommended value is 20 %)
Flue gas temperature (OC)
Measured
Corrected after applying
leakage correction
Design value

32. Expected improvement in boiler efficiency
From To Flue gas temp. (OC) Excess air (%) Boiler efficiency (%) * * This would be very close to the design value of 87.43%.

33. Coal and monetary savings potential through efficiency improvement
Current coal consumption (t/y) 2,632,181 Saving potential through efficiency improvement (t/y) 74,490 Coal cost (INR/t) 2,000 Monetary savings (INR/y) 148,980,000

34. Energy Audit of Steam Turbines

36. Energy audit of steam turbines (Data required)
Steam flow, temperature and pressure conditions at the entry to the HP turbine
Cold reheat steam temperature and pressure
Temperature and pressure of hot reheat steam at the inlet of IP turbine
Temperature and pressure of IP exhaust steam
LPT exhaust pressure
Extraction temperature and pressure of steam of all the extractions (6 in case of 500 MW and 5 in case of 210 MW)
Super heater and reheater spray conditions (quantity, pressure and temperature)
Feed water condition at the economiser inlet (quantity, pressure and temperature)
Make up water quantity
Coal consumption and power generation

37. Analysis of steam turbine data
TG heat rate (HR)
= (Heat input to turbine)/Power generated
Heat input to turbine = {Heat in main steam + Heat picked up in reheat + Heat in make-up water + Heat picked up in super heater (SH) spray + Heat in reheater (RH) spray – Heat in feed water}
Heat picked up in reheat = {HRH flow x (Enthalpy of HRH Steam – Enthalpy of CRH steam)}
Heat picked up in SH spray = {SH spray quantity x (Enthalpy of SH spray – Enthalpy of feed water at economiser inlet)}
HRH flow = CRH flow = {MS flow – Extraction-6 quantity – Gland steam leakages}
 Assumed as 1.5% of the MS flow to turbine
Extraction-6 quantity = { FW flow through HPH-6 (enthalpy in – enthalpy out)} / (enthalpy of steam in – enthalpy of steam out)

38. Analysis of steam turbine data (Contd.)
 TG efficiency = 860/TGHR
Plant heat rate = (TGHR/Boiler efficiency)x100
Steam rate (SR) in kgs/kWh is steam input to the turbine (kgs) to actual power output from the turbine (kWh)
Specific coal consumption (SCC) in kgs/kWh is overall plant heat rate (kCal/kWh) to the GCV of coal (kCal/kg) on as-fired basis.
Cylinder efficiency (HP/IP)= (actual enthalpy drop / isentropic enthalpy drop)x 100
=(steam inlet enthalpy – steam outlet enthalpy)/(steam inlet enthalpy – Isentropic enthalpy)x 100

39. Audited performance parameters of a 500 MW steam turbine
Flow (t/h)
Pressure
(bar)
Temperature
(OC)
Enthalpy
(kCal/kg)
Isentropic enthalpy
Main steam
169.17
535.08
809.11 -
CRH-HPT exhaust
46.47
343.49
731.05
721.71
HRH-IPT inlet
42.47
530.09
838.87
IPT exhaust
6.727
268.39
715.03
707.72
LPT exhaust
0.096
531.02

40. Audited performance parameters of a 500 MW steam turbine (contd.)
Flow (t/h)
Pressure
(bar)
Temperature
(OC)
Enthalpy
(kCal/kg)
Isentropic enthalpy
FW at eco inlet
210.02
249.54
259.05 -
SH spray
35.17
195.31
314.50
337.81
RH spray
2.49
115.56
183.94
187.65
Make-up water
9.74
25.00
25.04

41. Audited performance parameters of a 500 MW steam turbine (contd.)
Coal consumption t/h*
Power generation MW
* Unit control board value

42. Analysis of performance of steam turbine
Parameter
makeup water
makeup water
PG test value
Audited Performance
TGHR, kCal/kWh
2023.6
TG efficiency, %
43.26
42.50
43.12
42.35
Boiler efficiency, %
87.43
88.90
84.35
Plant HR, kCal/kWh

43. Analysis of performance of steam turbine (Contd.)
Parameter
makeup water
makeup water
PG test value
Audited Performance
Overall plant efficiency, %
37.82
37.16
38.33
35.72
Steam rate, kg/kWh -
3.12
GCV of coal, kCal/kg
3500
3622
Specific coal consumption, kg/kWh
0.650
0.661
0.665
Specific coal consumption, kg/kWh-UCB value
0.568

44. Cylinder efficiency of three turbines
Parameter PG Test Audit HPT efficiency (%) IPT efficiency (%) LPT efficiency (%) Overall efficiency (%)

45. Inference & Recommendations
SH spray is 2.39%, which is higher than prescribed limit
Turbine heat rate of (at 0.63% makeup water)is higher than the design value of
Coal consumption as calculated is higher than UCB value. Thus, Gravimetric Feeder needs re-calibration

46. Inference & Recommendations (Contd. 1)
HPT & IPT efficiencies are better than the PG test level. This leads to lesser enthalpy drop in LP cylinder, and thus LP cylinder efficiency is lower.
SH spray causes less feed water flow through the water walls (once-thru boiler) and thus affects its performance.
RH spray causes less bleed steam flow to the FW heaters and thus loss of efficiency.
RH spray also lowers the cycle efficiency as the steam formed by spray water in reheater bypasses the HP cylinder, and thus affects the efficiency.

47. Inference & Recommendations (Contd. 2)
Overall performance of turbine can be improved by reducing the SH and RH sprays by suitably tilting downwards the burners.
Maintain recommended condensate levels in FW heaters. With this no heat transfer areas are immersed in the drain condensate.
Overall plant efficiency is a function of efficiencies of both boiler and steam turbine. In this case, the improving boiler efficiency can make a major contribution.

48. Plant Auxiliaries

51. Performance Data of JSW Energy Plants (compiled by Centre for Science and Enviroment)

52. JSW Energy Ltd., Ratnagiri
4 x 300 MW; Sub-critical; Imported coal –based; sea water cooling; Supplied by Shanghai Electric Co.; Commissioned in 2010 (units # 1,2) & 2011 (units # 3,4)
Sp. Coal consumption = 0.49 kg/kWh
Sp. CO2 emission = 1.03 t CO2/MWh
Plant availability ( ) = 89 %
PLF = 71.8 %
APC = 8.53 %
GHR = 2418 kCal/kWh
(12.4 % higher than design)
NHR =2673 kCal/kWh
Not included in PAT scheme

53. JSW Energy Ltd., Thoranagullu
SBU I: 2 x 130 MW with Corax Gas & Imported Coal (BHEL) + SBU II: 2 x 300 MW with Imported Coal (Shanghai Electric)= 860 MW
During , 11-12, 12-13
Availability = 91 %
PLF = 96 %
GHR = 2261 kCal/kWh
GHR (design) = 2162 kCal/kWh
APC = 7.46 %
CO2 emission = 0.93 t CO2/MWh

54. Continued Avg. Steam Cycle HR = 1978 kCal/kWh
Design Steam Cycle HR = 1930 kCal/kWh
Boiler efficiency = 88.3 %
Design boiler efficiency = 89.3 %
CWP efficiency
SBU I 68% (Low)
SBU II %
PAT Targets (NHR)
SBU I: to 2503 kCal/kWh
SBU II: 2422 to 2420 kCal/kWh

55. Rajasthan West Power Plant, Barmer
2 x 120 MW, High Sulphur Lignite fired, CFBC boilers
PAT Targets (NHR)
3723 to 3559 kCal/kWh

56. Thank you ypa4@yahoo. co. in abbi. yashpal@energoindia
Thank you Books Authored Y P Abbi & Shashank Jain “Handbook on Energy Audit and Environment Management”, published by TERI Press, Y P Abbi “Energy Audit of Thermal Power, Combined Cycle, and cogeneration Plants”, published by TERI Press,