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HEAT RATE MONITORING

an overview

presented bysoumyajit

mukherjee

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H E A T R A T E

h e a t r a t e

It is a measure of how efficiently thechemical energy contained in the fuelis converted into electrical energy

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The heat rate of a power plant is theamount of chemical energy, in the fuel,that must be supplied to produce oneunit of electrical energy.

Heat rate is expressed inkcal/kWhr

HR = (input in kcal) / (output inkWhr)

= (input in kcal) / (output in kcal/860)

= 860 X (input / output)= 860 / efficiency

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UNIT HEATRATE

Ratio of heat input to the boiler (all forms ofchemical energy supplied ) and the grosselectrical generation

NET UNIT HEATRATE

Ratio of heat input to the boiler and the netelectrical generationi.e., auxiliary power is tobe subtracted from gross electrical energy

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REFERENCE UNIT HEAT

RATE

This is the heat rate the unit is capable ofobtaining, based on the initial designconfiguration. It is usually derived from theturbo generator and boiler performanceguarantee or acceptance test results

GROSS TURBINE CYCLE HEAT RATE

Gross Turbine Cycle heat rate includes onlyheat input to the turbine cycle. It is theratio of total heat input to the turbine cycle

and the gross generator output

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GROSS TURBINE HR

UNIT HEAT RATE =-------------------------------BOILER EFFICIENCY

For SIPATturbine design HR = 1944.4 kcal/kWhr

boiler design efficiency =85.58%

design unit heat rate=2272kcal/kWhr

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UNIT = TURBINE X BOILER

860 860

---------------- = --------------------- X BOILER

UNIT HR TURBINE HR

1 1---------------- = ----------------------- X BOILER

UNIT HR TURBINE HR

TURBINE HEAT RATEUNIT HEAT RATE = ---------------------------------------

BOILER EFFICIENCY

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REASONS FOR HEAT RATE DEVIATION

The initial design

Ambient conditions

Load Factor

The fuel that is supplied

How well the plant is operated and

maintained

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HEAT RATE MONITORING is focusedon identifying heat rate gaps and then

identifying and implementing corrective actions

to eliminate the efficiency loss. In this

approach, heat rate deviations from

expected or design levels are identified and

quantified.

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BOILER CYCLE

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AIR PRE HEATER PERFORMANCE

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AIR PRE HEATER PERFORMANCE INDICES

Air-in-Leakage

Gas Side Efficiency

X - ratio

Flue gas temperature drop

Air side temperature rise

Gas & Air side pressure drops

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AIR PRE HEATER LEAKAGE

Increase in Air heater leakage can leadto

Reduced Air heater efficiency Increased fan power consumption

Higher gas velocities that affect ESPperformance

Loss of fan margins leading toinefficient operation and at timesrestricting unit loading

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AH Leakage is quantified as

(CO2 ge CO2gl) x 0.9 x 100CO2 gl

(O2 gl O2 ge) x 0.9 x 100

(21 - O2 gl)

CO2ge = percent CO2 in gas entering airheater

CO2gl = percent CO2 in gas leaving air heaterO2ge = percent O 2 in gas entering air heater

O2gl = percent O 2 in gas leaving air heater

Expected leakage 8.5 to 9.0 %

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Possible causes of increased leakage

axial and radial seal mechanical damage orwear

sector plate mechanical damage or warping

rotor eccentricity

excessive air to gas side differential pressure.

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AIR PRE HEATER GAS SIDEEFFICIENCY (GSE)

GSE = Tge Tgnl x 100

Tge Tae

Tae = Temperature of air entering air heater

Tge = Temperature of gas entering air heater

Tgnl = gas out temp corrected for no leakage

Expected gas side efficiency 68.8 %

Gas side efficiency is an indicator of thermalperformanceof the air heater and depends onthe internal condition of the air heater.

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AIR PRE HEATER X-RATIO

Tge TgnlX-ratio = ----------------------

Tao Tae

Expected X- ratio 0.75

A lower than design X-ratio indicates excessivegas weight through the air heater or that airflowis bypassing the air heater. A lower than design

X-ratio leads to higher than design gas outlettemperature & can be used as an indication ofexcessive tempering air to the mills or excessiveboiler air-in-leakage.

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DRY FLUE GASLOSS

It is the heat carried away by theflue gas from the stack. 20 degree

C increase in exit gas temperaturecould lead to 1% reduction in boiler

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PARAMETERS AFFECTING DRY FLUEGAS LOSS

Flue gas exit temperature at APH outlet

Mass flow rate of flue gas

Specific heat of flue gas

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REASONS FOR HIGH FLUE GASTEMPERATURE AT APH OUTLET

APH inlet flue gas temp. high

Change in X-ratio

Poor gas side efficiency of APH (Basketcondition)

Secondary combustion

More use of tempering air

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MEASURES TO REDUCE DRY FLUEGAS LOSS :

Boiler operation at optimum excess air

Ensuring cleanliness of boiler surfaces with adequate

soot blowing

Good combustion of fuel

Reduction of tempering air to mills

Reduction in air-in-leakage in the boiler

Cleaning of air heater surfaces and proper heating

elements / surface area

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UNBURNT CARBON LOSS

Factors influencing Unburnt carbon loss includes thefollowings:

PF fineness (Worn Pulveriser component, Classifier

adjustment incorrect) Primary Air Flow

Furnace size

Coal FC/VM ratio, coal reactivity

Burners healthiness

Insufficient excess air in combustion zone

SADC performance

Design unburnt carbon loss 1.5 %

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TURBINECYCLE

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CONDENSER BACK PRESSURE

Usually one of the largest heat rate deviationsat a plant

Condenser performance problems can generallybe grouped into : circulating water flow problems air in-leakage/air removal problems poor heat transfer (fouling) problems

condenser inlet circulating water temperature

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P4

P3

P2

P1

VOLUME

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LOW CIRCULATING WATER FLOWLow Circulating water flow may be due to:

Circulating Water System/Equipment Problems

Plugging

Low Water box Level

AIR IN-LEAKAGE/AIR REMOVALPROBLEMSBesides raising backpressure, air in-leakage/removal problems

allow oxygen to accumulate inside the turbine cycle. Because

oxygen is a universal corrosive agent, this provides a

mechanism for corrosion that can result in serious degradation

problems in the feed water and boiler systems. High levels of

dissolved oxygen in the condensate leaving the condenser are

expected in the case of air in-leakage/removal problems.

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AIR INGRESSIf air suction depression is more than design

then it is an indication of air ingress problem.Common causes for air leakage include:

Inadequate turbine shaft sealing (low seal

steam or water pressure) Vacuum breaker leaks

Air leaking in expansion joints

Leakage through various components under

vacuum Leakage around pressure relief diaphragm

Seal steam pressure at the shaft seals

For AIR REMOVAL problems check healthinessof the vacuum pumps

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HEAT TRANSFER (FOULING)

PROBLEMSFouling problems are difficult to diagnose since

they share many of the symptoms of low flow

problems. Thus, fouling is often diagnosed byeliminating other possible causes of highbackpressure or by a positive response to somesort of cleaning process.

Increasing terminal temperature difference(TTD) indicates heat transfer impairment.

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HIGH CIRCULATING WATERTEMPERATURE

If the circulating water temperature ishigher than normal, considerationshould be given to placing additional

cooling tower fans in service.Moreover cooling tower performance isto be monitored.

check cooling tower effectiveness isclose to the design effectiveness.

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HIGH HEAT LOAD

Condenser backpressure varies with heat loading. While

this may notseem like a problem, unanticipated heat loads can givethe appearance of high backpressure for a given unitload.

Check :

feed water heater emergency drains are not open /passing

condensate low flow recirculation valve remains open athigher loads

MAL drains and all other drains to flash tanks are notopened when not required

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FINAL FEED WATERTEMPERATURE

Lower final feed water temperature thandesign value will definitely affect theheat rate of the unit.

LP/HP heaters performance are to bemonitored.

Steam temperature entering heater

Drip outlet temperature

Inlet feed water temperature Outlet feed water temperature ( check this is

same with the inlet feed water temperature ofthe next higher heater)

Steam pressure in heater shell

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MAKEUP

Makeup is the quantity of water that islost from the cycle during operation.

The heat rate deviation for makeup is an

approximation, as the location in thecycle of each loss is not known,therefore the exact heat rate deviationis not known.

Typically, an assumption is made thatthe loss is from the boiler drum, half atsaturated liquid condition and half atsaturated vapour.

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TURBINE EFFICIENCY

It is more common to periodically test the

turbines (usually at valves wide open) and tocompare that efficiency to the expected VWOefficiency, and to assume that the heat ratedeviation is constant over the load range.

The actual deviation can be due to variousfactors, depending on the cause of theefficiency loss. If the steam path is worn orrough, the exhaust temperature increases, so

less energy per kilogram of steam flow isconverted to mechanical work. In the HP turbinethis loss is partially offset because less energywill be required to be added in the reheater.

This small gain can also be lost if the amount ofreheat attemperation gets increased.

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AUXILIARY STEAM USAGE

Several auxiliary equipment present in the

plants that are supplied with steam. The steamthat is used may be main steam, from a turbineextraction, from the CRH, or some otherlocation. Regardless of the source of the steam,

its use comes at some price.

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MAIN STEAM PRESSURE BEFORE ESV

MAIN STEAM TEMPERATURE BEFORE ESV

HOT REHEAT STEAM TEMPERATUREBEFORE IV

REHEAT ATTEMPERATION

SUPERHEAT ATTEMPERATION

UNIT AUXILIARY POWER

UNACCOUNTABLE LOSS

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Parameters Deviations Loss of HeatRate in Kcal/Kwh

Additional CoalPer month (MT)

Additional CoalCost per month(Lakhs)

Vacuum 5 mmHg 10 405 2.46

Partial Load 5% reduction 9.98 404.2 2.46

Low FW TemperatureOne HP Heaterout for 24 Hrs.

24 972 5.91

FW Temp. at ECO.inlet

1 C 0.8 32.40 0.20

Increase in MUWconsumption

1%( 6.71 T/Hr.)

15.19 615.20 3.74

Drop in MS Temp. 1 C 0.92 37.26 0.23

Drop in HRH Temp. 1 C 0.69 27.95 0.17

Increase in RH Spray 5 T/Hr. 3.21 130.01 0.79

Rise in CWTemperature

1 C 7.51 304.16 1.85

Drop in MS Pressure 1 Ksc. 1.36 55.08 0.33

Rise in Flue gas exittemp.

1 C 1.54 62.37 0.38

R d ti i h t t lt i l

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Reduction in heat rate results in severalbenefits:

The amount of money spent for fuel will bereduced. This lowers the cost of generation ofelectricity.

The amount of emissions to the environment

will be reduced. Reduces the amount ofgreenhouse gas that is produced.

Less fuel burned means less ash to be disposedof, and less particulate matter go out of the

stack.

Less wear and tear on equipment such aspulverizers, coalpipes and nozzles, CHPequipments.

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THANKYOU

its a VIBRANT PROFFESSIONAL CIRCLE

presentation

presented bysoumyajitmukherjee