Energy Audit & Efficiency Improvement of Operating Power Plants

28 July 2015

Dr. Y. P. AbbiSenior Advisor/Energo Engineering Projects Limited,Ex- Executive Director/BHEL, Senior Fellow/TERI, President/Energo

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 %

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)

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

Required Accuracy of InstrumentsInstrument Accuracy (+/- %)Thermocouples Temp. Range: 0 to 277 0C – 1.1 0C;

277 to 1260 0C – 3/8 %Pressure Transducers 0.1

Power Meter 0.1

Data Logger 0.03

Power Transducer 0.5

Flue Gas Analyzer 0.5

Ultrasonic Flow Meter 0.5

Anemometer 1.0

Infrared Thermometer 1.0

Lux Meter 1.0

RH Meter 1.0

Calibrated Test Flow Assembly 0.25

LET US CONSIDER THE PATTERN OF ENERGY CONSUMPTION & LOSSES IN ATHERMAL POWER STATION

Typical Energy Losses in aPower Plant

Typical Energy Losses in a Boiler

Typical Energy Losses in Steam Cycle

“You cannot Manage what you cannot Measure”

(Accurately)

- Jack Welch, CEO, General Electric

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)

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 fuelSpecific fuel consumption = HRpp / GCV, kg/kWhNet Heat rate of the Power Plant = HRpp / (1 – APC in fraction)

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

Benefits from Heat Rate ImprovementTake the case of a typical 210 MW power plant and assume that it has the following operating variables:Heat rate = 2450 kCal/kWhPlant load factor = 85 %Coal GCV = 3997 kCal/kg (C = 41.7 %)Coal cost = INR 2000 /tCO2 emission per t of coal burnt = (41.07/100) x (44/12) = 1.5059

tThe coal consumed and its cost, and CO2 emissions per year are as follows:Specific coal consumption = 2450/3997 =0.613 t/MWhElectricity produced = 210 x 0.85 x 365 x 24 = 1,563,660 MWh Contd.1

Contd. 1Coal consumed = 1,563,660 x 0.613 = 958,524 tCoal cost = INR 958,524 x 2,000 = INR 1,917,048,000 CO2 emissions = 958,524 x 1.5059

= 1,443,441 tIf 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/kWhSpecific coal consumption = 2400/3997 = 0.60045 t/MWh

Contd. 2

Contd. 2Coal consumed for generating1,563,660 MWh of electricity = 1,563,660 x 0.60045 = 938,900 tonneCoal cost = 938,900 x 2000 = 1,877,800,000 INRCO2 emissions = 938,900 x1.5059 = 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 = 1,443,441 - 1,413,890

= 29,551 t

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

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

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

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 gasesLoss due to moisture in airUn-burnt carbon losses (fly ash and bottom ash)Loss due to sensible heat in fly ash and bottom ashRadiation & convection losses from boiler surfaceTotal losses = Sum of all above• Boiler Efficiency ŋBOILER = 100 – Total losses

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 ashMeasurement of temp., press., flow should be done at multiple points in the duct

Recommended excess air levels

Fuel/Type of boiler• Coal PC FBC Stoker• Fuel oil• Bagasse• Wood• Blast furnace gas

Excess air (%)

• 15-20• 20-25• 25-35• 03-15• 25-35• 20-25• 15-30

Cold air leakage in an air heater

Ho t a ir for com bustion A ir from FD fans

A ir heater

Flue gas fromecono mizer

Flue gas to ID fan

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

Corrected flue gas temperature leaving the air heater for no leakage

tGONL = {% leakage x CpA x (tGO – tAI)/ (100 x CpG)} + tGO

whereCpA = Mean specific heat between temperature

tAI and tGO

CpG = Mean specific heat between temperature tGO and tGONL

Case study of Energy Audit of a 500 MW Boiler

Case study: Boiler efficiency evaluation for a 500 MW unit (Steam parameters- 1700 t/h, 179

ata,540oC/540oC)• Coal properties

Design ActualC (Wt %) 37.92 44.73H 02.33 01.99S 00.29 00.37N 00.84 00.62O 06.23 01.83H2O 12.00 14.10

Ash 40.39 36.22GCV (kCal/kg) 3500 3622

Measured data for energy audit

• BoilerO2 in flue gas (%) 4.01

Excess air (%) 23.06CO (ppm) 9.3Flue gas temp. (OC) 167.57Ambient temp. (OC) 23.9Wet bulb temp. (OC) 18.1• Air heaterO2 (%) in flue gas after eco. 4.01

O2 (%) in flue gas after air heater 7.50

Calculation of boiler efficiency

Parameter (%) Design CalculatedDry flue gas loss 5.08 8.89Heat loss due to CO 0.00 0.00Heat loss due to moisture in air 0.12 0.12Heat loss due to moisture and Hydrogen in fuel 5.95 5.78Heat loss due to unburnt in bottom ash 0.90 0.07Heat loss due to unburnt in fly ash 0.00 0.02Sensible heat in bottom ash 0.38 0.26Sensible heat in fly ash 0.18 0.33Surface & unaccounted loss 0.67 0.10Total heat losses 12.57 15.65Boiler efficiency 87.43 84.35

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 167.57Corrected after applying leakage correction 190.0Design value 146.0

Expected improvement in boiler efficiency

From ToFlue gas temp. (OC) 190 146Excess air (%) 23.6 20.0Boiler efficiency (%) 84.35 87.18*

* This would be very close to the design value of 87.43%.

Coal and monetary savings potential through efficiency improvement

Current coal consumption (t/y) 2,632,181Saving potential throughefficiency improvement (t/y) 74,490Coal cost (INR/t) 2,000Monetary savings (INR/y)

148,980,000

Energy Audit of Steam Turbines

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

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)

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

Audited performance parameters of a 500 MW steam turbine

Parameters Flow (t/h) Pressure(bar)

Temperature(OC)

Enthalpy(kCal/kg)

Isentropic enthalpy(kCal/kg)

Main steam 1575.97 169.17 535.08 809.11 -

CRH-HPT exhaust

1450.00 46.47 343.49 731.05 721.71

HRH-IPT inlet

1450.00 42.47 530.09 838.87 -

IPT exhaust - 6.727 268.39 715.03 707.72

LPT exhaust - 0.096 - 531.02 -

Audited performance parameters of a 500 MW steam turbine (contd.)

Parameters Flow (t/h) Pressure(bar)

Temperature(OC)

Enthalpy(kCal/kg)

Isentropic enthalpy(kCal/kg)

FW at eco inlet

1580.90 210.02 249.54 259.05 -

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 -

- - - - - -

Audited performance parameters of a 500 MW steam turbine (contd.)

• Coal consumption 286.66 t/h*• Power generation 504.95 MW

* Unit control board value

Analysis of performance of steam turbine

Parameter Design@0% makeup water

Design @3% makeup water

PG test value Audited Performance

TGHR, kCal/kWh

1988.10 2023.6 1994.38 2030.74

TG efficiency, %

43.26 42.50 43.12 42.35

Boiler efficiency, %

87.43 87.43 88.90 84.35

Plant HR, kCal/kWh

2273.93 2314.54 2243.48 2407.51

Analysis of performance of steam turbine (Contd.)

Parameter Design@0% makeup water

Design @3% 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 3500 - 3622

Specific coal consumption, kg/kWh

0.650 0.661 - 0.665

Specific coal consumption, kg/kWh-UCB value

- - - 0.568

Cylinder efficiency of three turbines

Parameter PG Test AuditHPT efficiency (%) 87.24 89.32IPT efficiency (%) 91.36 94.42LPT efficiency (%) 56.33 52.29Overall efficiency (%) 43.12 42.36

Inference & Recommendations• SH spray is 2.39%, which is higher than

prescribed limit• Turbine heat rate of 2030.74 (at 0.63%

makeup water)is higher than the design value of 1988.10

• Coal consumption as calculated is higher than UCB value. Thus, Gravimetric Feeder needs re-calibration

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.

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.

Plant Auxiliaries

Performance DataofJSW Energy Plants(compiled by Centre for Science and Enviroment)

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 (2011-12) = 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

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 2010-11, 11-12, 12-13Availability = 91 %PLF = 96 %GHR = 2261 kCal/kWhGHR (design) = 2162 kCal/kWh

APC = 7.46 %CO2 emission = 0.93 t CO2/MWh

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 87.67 %

• PAT Targets (NHR)SBU I: 2515 to 2503 kCal/kWhSBU II: 2422 to 2420 kCal/kWh

Rajasthan West Power Plant, Barmer

• 2 x 120 MW, High Sulphur Lignite fired, CFBC boilers

• PAT Targets (NHR)3723 to 3559 kCal/kWh

Thank you ypa4@yahoo.co.in

abbi.yashpal@energoindia.com

Books Authored

Y P Abbi & Shashank Jain“Handbook on Energy Audit and Environment Management”, published by TERI Press, 2006

Y P Abbi“Energy Audit of Thermal Power, Combined Cycle, and cogeneration Plants”, published by TERI Press, 2012

http://bookstore.teriin.org