boiler- energy conservation and auditing
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Energy Conservation and EnergyAuditing of Thermal Power Plant
In accordance with Energy Conservation Act, 2001,the Thermal Power Generating Stations have beennotified as the Designated Consumers (DCs) by thegovernment and accordingly it has become
mandatory to carry out energy audit on a regularbasis and report the energy conservation measuresadopted to Bureau of Energy Efficiency (BEE). CEA incooperation with GTZ under Indo-German Energyprogram has prepared initial guidelines for energy
auditing of Power Plants to provide common basisfor such energy audits. These should be used forimproving the energy efficiency of power plants inthe country.
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The overall aim of this measure under Indo
Germany Energy programme is to support and
prepare public and private power plant operators
for performance reporting as well as
implementation of financially attractive and
technically viable improvements of power plant
net heat rate under the provisions of the Energy
Conservation Act.
The project is being executed under two main
sub-components:
The Indo German EnergyProgramme (IGEN)
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The following outcomes are expected of the
programme:
a. Assistance in the improved efficiency of
thermal power plants
b. Establishment of mapped power plants data
bank
c. Establishment of Energy Efficiency cell at
Power Plants
d. Capacity building of the power plant
professional on power
Outcome Expected from IGEN
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Economic growth in India, being dependent on powersector, has necessitated an enormous growth in electricity
demand over the last three decades. In 1947, the totalgeneration capacity was 1360 MW, in 1991 it grew to65000 MW and as on date (CEA report 10th August 2011)the installed capacity has grown to 1,81,558 MW of whichthermal capacity being 118409 MW. Many ultra mega
projects using supercritical boilers are in various stages oferection/commissioning.The following is the break up of installed capacity as on10/8/2011.
Coal = 99503 MWGas = 17706 MWDiesel = 1200 MWThermal total = 118409 MW (65 % of total installedcapacity)
Nuclear = 4780 MW , Hydro = 38206 MW=
Power Scenario in India
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Energy Conservation and EnergyAuditing of Thermal Power Plant
Improving the energy efficiency in power plants can be
achieved by :1) Improving energy efficiency in existing plants.2) Higher size units3) Technology adoption
Since the major power generation contribution is fromthermal sector, an average increase of 1% in thethermal power plant efficiency would result in:
a. Coal savings of approx. 11 million tons per annum
b. 3% CO2 reduction per annum
c. Higher productivity from the same resource is
equivalent to capacity addition.
d. Lower generation cost per Kwh.
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Following systems in Thermal Power Stations arecovered for energy auditing.1. Coal handling plant2. Boiler3. Thermal Insulation4. Ash handling5. Water pumping6. Fans7. Turbine
8. Condenser cooling9. Compressor air system10. Motors11. Air Conditioning12. Lighting
Energy Conservation and EnergyAuditing of Thermal Power Plant
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nergy er ormance ssessmenof the Boiler
Performance of the boiler, like efficiency and
evaporation rate reduces with time, due to poorcombustion, heat transfer fouling and pooroperation and maintenance. Deterioration of fuelquality and water quality also leads to poorperformance of boiler. Efficiency testing helps us tofind how far the efficiency has drifted away from thebest efficiency. Any observed abnormal deviationscould therefore be investigated to pin point theproblem area for necessary corrective action. Hence
it is necessary to find out the current level ofefficiency for performance evaluation, which isprerequisite for energy conservation action in powerplant.
Focus should be
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Boiler
The boiler of a thermal power plant is used at highpressure and temperature required for the steamturbine that drives the electrical generator. Theboiler has furnace, steam drum, superheater coils,reheaters coils, economiser and airheaters.
The air and flue gas path equipment includeforced draught fans (FD). Induced draft fans (ID),airpreheaters (APH), furnace, fly ash collectors(electrostatic precipitators, bag filters) and the
flue gas stack. Brief schematic diagram of atypical coal fired sub critical boiler is given in thefollowing figure.
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SCHEMATIC DIAGRAM OF BOILER
vWater cycle
vFuel cyclevAir & flue gas cycle
vSteam cycle
vAsh/ rejects cycle
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BOILER SPECIFICATION FOR 210 MW KWUUNIT
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FACTORS AFFECTINGPERFORMANCE OF COMBUSTION
SURFACE CONTACT AREA OF FUEL WITH AIRAIR-FUEL RATIORETENTION TIME
COMBUSTION CHAMBER TEMPERATURETURBULANCE IN COMBUSTION CHAMBERREMOVAL OF PRODUCTS OF COMBUSTION
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COMBUSTION
TIMESUFFICIENT RETENTION TIME MUST BE ALLOWED FOR THE
FUEL TO STAY INSIDE THE FURNACE TO COMPLETECOMBUSTION.TIME REQUIRED/AVAILABLE DEPENDS FUELTYPE,QUALITY,SIZEFURNACE SIZE, VELOCITY, DRAUGHT
TEMPERATURE
EFFECTS THERMAL DIFFUSION OF REACTINGMOLECULES DUE TO INCREASED VELOCITY OFMOLECULES WITH INCREASE IN TEMPERATUREINFLUENCE THE RATE OF REACTION
FACTORS AFFECTING TEMPERATUREHEAT ABSORBED BY FURNACEHEAT ABSORBED BY REACTANTS TO BRING THEM TOIGNITION TEMPERATUREHEAT ABSORBED BY NITROGEN IN AIR
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COMBUSTION
TURBULANCE
MECHANICAL AGITATION OF REACTANTS TO BRING THEMINTO PHYSICAL CONTACT
REQUIREMENT IS MORE AT FINAL STAGE OF COMBUSTION
LESSER THE TURBULANCE MORE CARBON LOSS
DEPENDS
WIND BOX TO FURNACE DIFF.PR.IN CORNER FIREDBOILERS
TERTIARY AIR IN WALL FIRED BOILERS
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Boiler Efficiency Test
Purpose of Test : The purpose of the test is
to calculate actual performance and efficiencyof the boiler and compare it with design valuesor norms. It is an indicator for tracking day today and season to season variation in efficiencyand energy efficiency improvements.
B il Effi i
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Boiler Efficiency
By boiler
efficiencyis
meant themeasure of
B il Effi i C l l ti
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There are two methods of determining boiler efficiency1.
Direct method2. Indirect or losses methodThe direct method : This method is straight forward
and consists of measuring the heat supplied to theboiler and heat added to the steam in the boiler in a
given time.Efficiency ( for non reheat unit)= (Enthalpy of steam Enthalpy of feed water)* Steam
Flow
(Quantity of coal * CV)= WS{ Cp(T-To) + L + (To t)}Mf* CV
WS = Steam flow rate Cp = Specific heat ofsteam
T = S. H Steam temperature To = Saturation
Boiler Efficiency CalculationMethods
B il Effi i
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The trouble with this method is that several of thesequantities are difficult to measure particularly coalquantity, the steam quantity and CV of coal. Theerror in measurement results in an overalltolerance of about + 1.5 % . However this methodof efficiency determination is gaining popularity of
late and used more frequently because of simplicityand advances being made in measurementtechniques.
In indirect method, the efficiency is calculated bydetermining the losses in the boiler.
For this, chemical analysis of the fuel and the flue gasanalysis are the basis of calculation.
Efficiency = 100 % - Losses
Boiler EfficiencyMethods
B il Effi i
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Boiler EfficiencyMethodsThus if losses are known, the efficiency can be derived.
An important advantage of this method is that the
errors in measurement do not make significantchanges in efficiency.
Thus if boiler efficiency is 90 % an error of 1% in directmethod will result significant changes in efficiency.
90+ 0.9 = 89.1 to 90.9In indirect method, 1 % error in measurement of losseswill result inEfficiency = 100 (10+0.1)
= 90 + 0.1 = 89.9 to 90.1Clearly, the tolerance is narrow in losses method.However because of advancement in instrumentationand easiness the direct method is also becomingpopular nowadays.
LOSSES ENCOUNTERED IN
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LOSSES ENCOUNTERED INBOILER
CONTROLLABLE
COMBUSTIBLE IN ASH LOSS
DRY GAS LOSS
CO IN FLUE GAS
MILL REJECTS LOSS LOSSES DUE TO POOR INSULATION
UN CONTROLLABLE
MOISTURE IN FUEL HYDROGEN IN FUEL
AIR MOISTURE
SENSIBLE HEAT IN ASH
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Controllable Variables Affecting BoilerPerformance
Super heater Steam Outlet Temperature Reheater Steam Outlet Temperature
Air Heater Leakage
Super heater spray Reheater Spray
High Primary airflows
Coal Mill Reject High Carbon Content in Fly Ash
High Carbon Content in Bottom Ash
Furnace Exit Gas Temperature
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Controllable Variables AffectingBoiler Performance
Economizer Exit Gas Temperature
Air heater Exit gas Temperature
Boiler air in leakage
Auxiliary Power Consumption of Fans, Mills andSoot Blowers
Excess Oxygen in Flue Gas
Cycle Losses due to Leaking Vent and Drain Valves
Soot Blowing Optimization
Mill Air In Leakage on Suction Mills
Steam Purity Problems
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AREAS/EQUIPMENTCONTRIBUTING TO VARIOUS
LOSSES IN A BOILER
COMBUSTION IN FURNACE
AIRHEATER PERFORMANCE
MILL PERFORMANCE
FANS PERFORMANCE
WATER LOSSES
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TYPICAL BOILER LOSSES
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FACTORS WHICH EFFECT BOILEREFFICIENCY (Boiler Losses)
Loss due to the heat carried away by hot fluegases.
(a) Dry flue gas loss, and (b) Wet flue gas loss(lossdue to moisture in fuel and due to moisture formed by
combustion of H2 in fuel) Moisture in combustion air loss Unburnt carbon loss Carbon in ash loss Unburnt gas loss Due to incomplete combustion of
carbon Excess air loss. Radiation loss and unaccounted losses. Blow- down and leakages.
Dry Flue gas Losses : This is the heat loss in in the dry
component of the gases, as these are discharged from
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Boiler Efficiency Typical Example
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Boiler Efficiency Typical ExampleMaintaining efficiency : The best way to analyze the problemof maintaining efficiency is to examine the major losses inefficiency, what effects them, and what can be done to
control them.A typical heat balance for a pulverized coal fired utility boilerwould be :Dry gas loss5.16 %Loss due to hydrogen and moisture in the fuel 4.36 %Loss due to unburned combustible 0.50 %Loss due to radiation 0.30%
Loss due to moisture in air 0.13%Manufacturers margin and unaccounted loss 1.50 %Overall efficiency88.05 %
Minor losses are usually lumped into one percentage figure
B il Effi i
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Boiler Efficiency
Monitoring Efficiency: Continuous monitoring offlue temperature and flue gas oxygen content by
regularly calibrated recorder or indicator and byperiodic checks on combustibles in the refuse willindicate if original efficiencies are being maintained.If conditions vary from the established performancebase, corrective adjustments or maintenance stepsshould be taken.High exit-gas temperatures and high draft losseswith normal excess air indicates dirty heatabsorbing surfaces and need for soot blowing.
High excess air normally increases exit gastemperatures and draft losses and indicate the needfor adjustment to the fuel-air ratio. The high excessair may, however, be caused by excessive casingleaks, cooling air, or air heater leaks.High combustible in the refuse indicates a need for
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m Boiler efficiency varies with type of fuel.
m Oil / Coal being best and lowest with gas.
m Coal properties directly affect the efficiency of
the boilerm Moisture in coal decreases boiler efficiency.
m Efficiency of boiler will change if the fuel firedis not as per the design (High FGET in Tatasunit 5 boiler is due to high moisture and highvolatile matters in coal).
BoilerEfficiency
Boiler Losses
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Boiler Losses
STACKLOSS
Heat carried
Boiler Losses
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HEAT CARRIED AWAY BY MOISTUREHeat absorbed by the moisture in flue gasesconstitutes a loss because, water vapour is notcondensed in the boiler and thus substantial amountof latent heat (Approx..540 Kcal / kg at atmosphericpressure) is lost.There are two sources of moisture in flue gases viz.
Moisture in fuel. Combustion product of hydrogen content in fuel.SOURCE OF MOISTURE IN FLUE GASES Moisture in fuels such as coal and gas. Fuels containing high hydrogen Such as naturalgas generate Large amount of water vapourWhen burned. 2H2 + O2 2H2Oi.e . 1 kg of hydrogen, when burnt, produces 9kg of
water vapour .
Boiler Losses
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INCOMPLETE COMBUSTION
Incomplete combustion means partial burning of fuel.Part of the fuel may remain unburned or carbon in fuelmay burn partially to form carbon monoxide.
Causes of incomplete combustion are: Inadequate air. Improper distribution of air. Fuel not properly pulverized oratomized.
Low furnace temperatures. Moisture in fuel. Low secondary air temperatures.
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WHY INCOMPLETE COMBUSTION IS A LOSS
Unburned fuel is obviously a loss because it releases noenergy, but
is paid for. Partially burned carbon releases much less energy thanwhen burnt
fully.
2C + O2 2CO + 4,400 BTU.C + O2 CO2 + 14,600 BTU.
As is evident partial burning of carbon generates carbonmonoxide, a toxic gas and releases much less heat and
thus constitutes a huge loss.
B il L
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Boiler Losses
Loss due to excess air :Quantity of air supplied over and above theminimum required amount of theoreticallydetermined air (stoichometric) is called excess air.Certain quantity of excess air needs to besupplied, because it is practically not possible for
every molecule of fuel to come in contact withevery molecule of oxygen supplied in the limitedtime the mixture remains in boiler with no excessair, resulting in improper combustion andconsequent losses.However, too much excess air increases theamount of flue gases. Since, the temperature ofexit gas temperature is nearly constant , increasein flue gas flow means increase in stack loss.
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LOSS DUE TO HIGH EXCESS OXYGEN
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INCREASE OF EXCESS OXYGEN%
0 1 2 3 4 5
10
20
30
40
5
0
60
MO
NETO
RYL
OS
S/D
AY
IN
Rs .
THOU
SAND
S
LOSS DUE TO HIGH EXCESS OXYGEN
1% INCREASE IN EXCESS OXYGEN WILL LEAD TO AN ANNUALLOSS OF
LOSS DUE TO HIGH F G TEMP AT A H
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0 5 1
0
1
5
2
0
MONIT
ORY
LOS
S
PER
DAY
IN
Rs.
THO
USA
NDS
LOSS DUE TO HIGH F.G. TEMP.AT A.H.OUTLET
INCREASE IN
F.G.TEMP. AT
A.H. OUTLETBY 100C
WILL LEAD TO
AN ANNUAL
LOSS OFRs.1CRORE
FOR A 210 MW
UNIT
504
540353
025201
5105
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Boiler Performance Monitoring
Flue Gas Exit Temperature (FGET)
Reasons
m Water wall , superheater & Reheater surfacesslagging
m Fouling in air preheater
m Low coal mill outlet temperaturem High moisture and volatile matter in coal
m Low Coal calorific value
m Air leak in furnace
m High excess air
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Boiler Performance Monitoring
Excess air & Air flow
(Actionable)m Excess air set point changed
with load changes.m Carbon in ash monitored daily.m
Secondary air dampers, Fuel LOSSES
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LOSSESDry Gas Loss
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COMPUTATION OF BOILER LOSSES
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COMPUTATION OF BOILER LOSSES
2. Loss due to unburnt carbon in ash:
[ ])%()%(,
/
,
BAshBACFAshFACGCVfuelofGCV
kgkcalincarbonofvalueCalorific
LashincarbonunburnttodueLoss uca
+
=
3. Loss due to moisture in fuel:
4. Loss due to hydrogen in fuel:
Where H2 kg of H2 in 1 kg of fuel
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COMPUTATION OF BOILER LOSSES
5. Loss due to moisture in air:
Where AAS=Actual mass of air suppliedHumidity = humidity of air in kg/kg of dry air
6. Loss due to CO in flue gas:
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TYPICAL BOILER HEATBALANCE
BOILER
Boiler Efficiency (Heat in Steam)
Heat loss due to dry flue gas
Dry Flue Gas LossHeat loss due to wet flue gas
Heat loss due to moisture in fuel
Heat loss due to unburnts in residue
Heat loss due to moisture in air
Heat loss due to radiation & otherunaccounted loss
5.5%
4.2%
1%
0.3%
1%
1%
87%
100%HeatfromFuel
EXPLORATION OF ENERGY CONSERVATION
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OPPORTUNITIESBoilers:Steam and water parameters ( flow, pressure and
temperature )
Air and gas parameters ( flow, pressure and temperature ) Burners operation Primary and secondary air ratios and temperatures Air infiltration in to boilersAir infiltration to flue gases Unburnt loss reduction Combustion control boiler excess air, O2 Measurement
inaccuracy Dry flue gas loss InsulationWater quality, Blow down and its control
EXPLORATION OF ENERGY CONSERVATION
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OPPORTUNITIESCoal quality and performance of coal mills Super heater and reheater performance Super heater temperature, slagging of furnace water walls andtubes Fouling on the pendant and horizontal convection tubes, sootblowers performance Boiler control systems Limitation on Performance of associated equipments (pumps,fans, heaters, soot blowers, mills, etc) affecting boiler loading andefficiency Loading on ID, FD and PA fans
Operation of dampers /inlet guide vanes / speed controllers offans Fouling of boiler heating surfaces Installation of energy saving retrofits DM water consumption
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