Boiler- Energy Conservation and Auditing

7/31/2019 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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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



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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

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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

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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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7/18/12 INCREASE IN A.H. OUTLETE

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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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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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

Boiler- Energy Conservation and Auditing

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