Guidelines for Energy Auditing of TPS-1

8/7/2019 Guidelines for Energy Auditing of TPS-1

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3.0 BOILER

BOILER

3.1 BACKGROUND

In a thermal power plant, boiler is used to produce steam at the high pressureand temperature required for the steam turbine that drives the electricalgenerator. The Boiler has Furnace, Steam drum, Super heater coils, Reheatercoils, Economizer and Air Pre Heaters.

The air and flue gas path equipment include Forced draft fan (FD),Induced draftfan (ID),Air pre heaters (APH),Boiler furnace, fan, fly ash collectors (Electrostaticprecipitator or bag house) and the flue gas stack. Brief schematic diagram of atypical Pulverised Coal fired subcritical Boiler is given in the Figure 3-1.

Figure 3-1: Schematic diagram of boiler

The brief specifications of a typical boiler used in210 MW plant is given in the Table 3-1.

Table 3-1 : Brief specifications of Boiler

Particulars UnitDetails at Normalcont. rating, NCR

Make

Type


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Particulars UnitDetails at Normalcont. rating, NCR

Capacity tph 627.32

Main Steam pressure kg/cm2 155

Main Steam temperature 0C 540

Boiler efficiency % 87.16

Super heater outlet flow tph 627.32

Reheater outlet flow tph 565.6

Calorific value GCV kcal/kg 4350

Coal consumption tph 106.2

Total combustion air tph 822

LTSH outlet temperature 0C 420Reheater outlet temperature 0C 540

Water-economizer inlettemperature

0C 241

Water-economizer outlettemperature

0C 280

Oxygen content at Economizeroutlet

% 4.23

In addition to the above, there are several other importantspecifications, which are discussed later.

Conducting energy audit of boiler is a very complexactivity involving several measurements andobservations; hence the study should becomprehensive and include all the aspects, pertainingto Boiler aspects Coal quality - composition andcalorific value Coal milling aspects

Combustion and excess air

a. Reheaters Heat recovery units Economisers, air preheaters, etcInsulation aspects Boiler blow down aspects Soot blowing aspectsOperation and maintenance features which affect the energy efficiency

b. Condition & status of boiler and their internalsFeed water system aspects


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Air and flue gas system aspects

c. Several others

3.2 STEPS INVOLVED IN CONDUCTING THE ENERGY AUDIT

The steps involved in conducting energy audit of boiler are:

Data collectionObservations and AnalysisExploration for energy conservation measuresReport preparation3.3 DATA COLLECTION

The first step in energy audit of boiler is to collect the design / PG testparameters pertaining to boiler, economiser, air preheaters, coal and coalmilling, soot blowing and other key associated equipments.

The following data sheets give brief specifications to be collected. It is suggestedto obtain the comprehensive technical specifications of boilers and its associatedequipment.

3.3.1 Specifications of boiler and associated equipment

3.3.1.1 Boiler Collect the detailed design specifications of the boiler. Thefollowing

Table 3-2 gives the list of specifications to be collected for energy audit study inaddition to following specific details.

Table 3-2 : Design Specifications of boiler

UnitDesign

NCR

Actual

Make

Type


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Year of Installation

Main Steam Pressure kg/cm2

Main Steam Temperature oC

UnitDesign

NCRActual

Main Steam Flow tph

Steam pressure at LTSH outlet kg/cm2

Steam temperature at reheater inlet oC

Steam temperature at reheateroutlet

oC

Steam pressure at reheater inlet kg/cm2

Steam pressure at reheater outlet kg/cm2

Steam temperature at LTSH out oC

Saturated steam temperature indrum

oC

Super heater platen outlettemperature

oC

Maximum pressure drop in reheater Kg/cm2

Super heater spray tphReheater Spray tph

Design ambient temperature oC

Coal consumption tph

Table 3-3 for economiser. Table 3-3: Specifications of economiser

1. 3.3.1.2 EconomiserCollect the specifications given in

the2. 3.3.1.3 Air preheater Collectthe design specifications given in the

Table 3-4: 4 for air

Unit Design

Actual


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Feed water pressure at the inlet kg/cm2

Feed water pressure at the outlet kg/cm2

Feed water flow tph

Feed water temperature at theinlet oC

Feed water temperature at the outlet

oC

Oxygen content in flue gas beforeeconomizer %

Excess air % in flue gas beforeeconomizer %

Exhaust gas inlet temperature oC

Exhaust gas outlet temperature oC

Exhaust gas quantity tph

preheaters. Table 3-4: Specifications of air preheater (APH)

Unit Design Actual

Air quantity at APH outlet (primary) tph

Tempering air tph

Air heater outlet (secondary) tph

Total combustion air tph

Air temperature at fan outlet oC

Air outlet temperature of APH primary oC

Air outlet temperature of APH secondary oC

Oxygen content in flue gas before APH %

Excess air % in flue gas before APH

%

Exhaust gas inlet temperature oC

Exhaust gas outlet temperature oC

Exhaust gas quantity tph

Others


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Collect the parameters for exhaust gas as given in the Table 3-5:

Table 3-5: Exhaust gas temperature profile

Unit Design Actual

Temperatures oC

Super heater platen outlet oC

RH front inlet oC

RH rear inlet oC

SH finish inlet oC

LTSH inlet oC

Economizer inlet oC

APH inlet oC

APH outlet oC

ID Fan inlet oC

Collect the parameters for coal as given in the Table 3-6: 6. Table 3-6: Coalparameters

Unit Design

Fixed carbon %

Volatile matter %

Moisture %

Ash %

Grindability index HGI

Coal calorific value -HHV kcal/kg

Size of the coal to mill mm

Total contract fuel fired tph


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Collect the heat balance parameters of the boiler (as shown in Table 3-7:7).

Table 3-7: Heat balance of boiler Unit Design

Ambient temperature oC

Excess air %

Dry gas loss %

Hydrogen loss %

Moisture in fuel loss %

Moisture in air loss %

Unburnt combustible loss %

Radiation loss %

Un accounted loss %

Gross boiler efficiency on HHV %

Guaranteed efficiency %

Collect the recommended feed water limits (as shown in Table 3-8: ).

Table 3-8: Recommended feedwater & boiler water limits Unit Feed water Remarks

Hardness

PH at 25oC

Oxygen maximum ppm

Total iron- maximum ppm

Total silica maximum ppm

Conductivity at 25oC U/cm

Hydrazine residual ppm

Total solids maximum ppb

chlorides ppm

Copper maximum ppm

Oil

Permanganate consumption ppm

Others


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Collect the design specifications of mill and burner performance (asshown in Table 3-9: 9).

Table 3-9: Mills and BurnersPerformance Unit

Requirement at MCR

Actual Remarks

No of coal burners No

No of oil burners No

No of mills in operation No

Mill loading %

Air temperature at mill inletafter tempering

oC

Air fuel mixture temperatureafter leaving mills

oC

Total coal fired tph

In addition to the above collect the individual mill specifications and design coalparameters:

Mill specifications:

Type of mill :

Mak

e

:

Capacity : __________tph at coal ________grind

Fineness : ___________% through ________mesh

Motor rating :____________kW

Motor voltage :________ V

No of mills :__________

Running /Standby :_________/________

Design coal

parameter

Moisture :_____%Ash :_____%Volatile matter :_____%Fixed carbon :______%HGI :_____%


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Collect the information of soot blowers (Table 3-10: 10).

Table 3-10: Soot blowers Type number

Soot blowers for furnace

Soot blowers super heaters

Soot blowers for reheaters

Soot blowers for air preheaters

Medium of blow

Steam pressure before reduction

Steam pressure after reduction

Steam consumption

3.4 INSTRUMENTS REQUIRED

The following instruments are required for conducting the boiler energyaudit.

Power Analyser: Used for measuring electrical parameters such askW, kVA, pf, V, A and Hz Temperature Indicator & Probe Stroboscope: To measure the speed of the driven equipment and motor Slinghygrometer or digital hygrometer Anemometer

Available On line instruments at the site ( Calibrated )Digital Manometer of suitable range and appropriate probes formeasurement of pressure head and velocity head.


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Additional pressure gauges with appropriate range of measurement andcalibrated before audit. Flue gas analysers / orsat apparatus Infraredpyrometers Pressure gauges Steam trap tester / Ultra sonic leak detectors3.5 MEASUREMENTS & OBSERVATIONS TO BE MADE

While conducting the audit, the following measurements and observations

are necessary Average GCV of coal Coal composition ultimate andproximate Coal consumption details Performance parameters of coalmills Heat rate- kcal/kWh Steam parameters of main steam, reheat,super heater, LTSH (flow,

pressure and temperature) Air flow, temperature, pressures Fluegas Flow, temperature and pressure Flue gas analysis Coalconsumption pattern Ambient temperature Boiler loading Motorelectrical parameters (kW, kVA, Pf, A, V, Hz, THD) Surfacetemperatures of insulation and boiler surfaces

Unburnt composition

While conducting the measurement or performance evaluation any

system simultaneously the following need to be notedUnit load of the plantDate & time of measurementInstruments used of measurementFrequency of the measurement

3.6 OBSERVATIONS AND ANALYSIS

3.6.1 System familiarisation and operational details


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Detailed interactions with the plant personnel have to be carried out to obtainfamiliarisation of system and its operational details. The brief details of thesystem have to be given in the report along with the specifications.

During the familiarisation, boiler, plant key performance data has to becollected pertaining to the following

Availability factora. PLFCoal consumption (tons and kg/kWh)Oil consumption in ml/kWhBoiler efficiency

b. Others

During the familiarization on power plant and its operation, plants

observation and past data should be obtained pertaining to the Past performancetrends on boiler loading, operation, PLF, efficiency Major constrain in achievingthe high PLF, load or efficiency (Input from plant personnel) Major renovationand modifications carried out in the recent past Coal quality and calorificvalues aspects Operational failures leading to in efficient operation such astube failures, constraints for efficient heaters operation, Soot blowersoperation Tripping Performance of economiser, air preheaters, LP / HP heaterfrom past records

Combustion control system practice followed Mills performance If plant has


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online and off line tools for performance evaluation of main equipment andBOP equipment then details of these tools Plant side initiatives to improvethe performance and efficiency of the boiler

The data and information collected to be consolidated and the same has to begiven in the report for reference.

For all major observations arrived at during the discussions, which affect theperformance and energy efficiency of the boiler; it is suggested to verify therecords and history.

3.6.2 Operating efficiency of the boiler

The boiler efficiency trial has to be conducted to estimate the operationalefficiency under as run conditions. The efficiency evaluation by and large followthe loss components mention in the reference standards for Boiler Testing atSite using indirect method namely, BS 845: 1987 and USA Standard is ASMEPower Test Code Steam Generating Units.

The test method employed is based on the abbreviated efficiency by the loss

method (or indirect method) test, which neglects the minor losses and heatcredits, which are covered in full text version. The major losses covered are:

Heat loss due to dry flue gas losses

a. Heat loss due to moisture in fuel

b. Heat loss due to hydrogen (moisture of burning hydrogen)

c. Heat loss due to combustibles in refuse

d. Heat loss due to radiation

e. Un accounted losses as per the contract with the Boiler Supplier

Indirect method is also called as heat loss method. The efficiency can be arrivedat, by subtracting the heat loss fractions from 100. The standards do not includeblow down loss in the efficiency determination process.

While conducting the efficiency evaluation, the following need to be ensured:

Trials are conducted at least for two hours and measurementsare to be taken every fifteen minutes Load on the boiler to beby and large constant and represent average loading andnormal operation No soot blowers are operated during theevaluation period No intermittent blow down is given A team

of 3-4 members are required for simultaneous measurementsand data collection of various parameters. These membersshould be trained/ explained prior to the test in theirassignments in measurements and observations.


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Before conducting the actual measurement for the evaluation, it issuggested to carry out a demo exercise for one set of measurement andobservation

Measurement locations: During the test, the power plant under the coordinationof energy auditor may organise the collection and analysis of samples at thefollowing locations

Flue gas analysis at air preheaters inlet / out let Temperature of flue gas at airpreheaters inlet / out let Fly ash sampling at the economiser outlet and ESPhoppers for unburnt carbon in fly ash Sample of bottom ash from hopper orscrapper Sample of raw coal from RC Feeder of the mill for proximate andultimate analysis of fuel and gross calorific value. Pulverised coal samples fromeach mill for sieve analysis. Sample of mill rejects for GCV. The following Table 3-11: gives the data sheet for measurements and observations for conducting asrun test for boiler efficiency evaluation

Table 3-11: Data sheet for boiler efficiency evaluation

Parameters Unit Design As run data

Date

Duration h

Avg. Unit load MW

% of NCR %

Frequency Hz

Coal consumption Kg/h

Ambient parameters

Dry bulb temperature OC


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Wet bulb temperature OC

Relative humidity %

Moisture content in the air Kg/kg of air

Fuel Parameters Ultimate Analysis

Carbon %

Hydrogen %

Sulpher %

Nitrogen %

Oxygen %

Total moisture %

Ash %

Gross calorific value Kcal/kg

Fuel Parameters ProximateAnalysis

Fixed Carbon %

Volatile matter %

Total moisture %

Ash %

Steam parameters

Main steam flow tph

Main steam pressure kg/cm2

Main steam temperature OC

Air/ Flue gas parameters (APHoutlet)

Oxygen content %

Carbon dioxide content %

Flue Gas Temperature at APH Outlet OC

Parameters Unit Design As run data

CO %

Excess air %


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Unburnt in Ash

Carbon content in fly ash %

Carbon content in bottom ash %

In the above data sheet, steam parameters, proximate analysis, loaddetails are given, and these are not used in the efficiency evaluation,however these are very important since these parameters required forcomparison, whether the operating parameters are at par with normaloperation.

The following can be used for estimating the losses:

a. Dry Flue gases Ldfg:

(6.11* C)+ 5.43 *S

22

Stochiometofair kg / kg ,air ric = 8.34 * (H-

8 / O )+

100 100 100

% O

2

% EA ,plied sup air Excess = *100

21-% O

2

% EA

1+ * air ricStochiomet

plied sup air Actual (fuel of kg / air of kg ),AAS =

100

quantity gas flue Dry (kg / kg ),Wd of fuel =

100

C S BA % C * BAsh FA % C * FAsh

*

+ -

%) CO 100 267 100 100

(% CO+ Wd ,quantity gas flue Dry * Cp ,heat Specific * (FGT-ABT) * 100

2

L ,losses gas flue Dry dfg% = GCV ,Fuel of CGV

b. Loss due to unburnt carbon in ash, Luca

L ,ash in carbon uburnt to due Loss uca =

kg / kcal in carbon of value Calorific * [


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(FA%C * FAsh)+]BAsh)

GCV ,fuel of GCV (BA% C *

c. Loss due to moisture in fuel, LmfM

L ,fuel in moisture in to due Loss mf= *[]584(45.0* (FGT-ABT) +* 100

100 GCV

d. Loss due to Hydrogen in fuel, Lhf

Loss L ,fuel in moisture in to due hf= * [ 584]9*H2(45.0*(FGT-ABT) +* 100

100 GCV

e. Loss due to moisture in air, Lma

AAS *MA ,air in Moisture * 45.0 * (FGT-ABT) * 100

L ,air in moisture in to due Loss =

ma

GCV

f. Loss due to carbon monoxide, Lco

% CO *C 5744*100

L ,xidecarbonmono to due Loss = *

co

% CO GCV

% CO +

2

During the flue gas analysis when CO is obtained in ppm, then losses

can be obtainedL ,monoxide carbon to due Loss

co

= *

ppm in CO * 10-6* h / kg in n consumptio fuel * 5744 28 * 100

GCV

g. Radiation and un accounted losses Consider these losses as given in the PGtest / Design documents. Alternatively, the radiation losses can be estimated bymeasuring the surface temperatures and surface areas of the boiler section.

Normally surface loss and other unaccounted losses are assumed based on the

type and size of the boiler.

However it can be calculated if the surface area of boiler and its surface temperature areknown as given below:

L6=

0.548 x [ (Ts / 55.55)4 (Ta / 55.55)4] + 1.957 x (Ts T )a 1.25 xsq.rt


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of [(196.85 V m + 68.9) / 68.9]

where

L6=

Radiation loss in W/m2

V m =

Wind velocity in m/s

T s =

Surface temperature (K)

T a=

Ambient temperature (K)

Once after estimating the individual components, the losses need to be

tabulated and compared with the PG test value or best achievable values.

While comparing the losses, the deviations need to be highlighted andfactors contributing for these deviations need to be arrived at.The following Table 3-12: gives the tabulation sheet for boiler efficiencyon

Table 3-12: Efficiency evaluation of the boiler

Particulars UnitDesignValue

Actualvalue

%Deviation

Remark

Date & time of the test

Load MW

Fuel GCV kcal/kg

Loss due to hydrogen infuel

Dry Flue gases, Ldfg %

Loss due to moisture inAir

Loss due to unburntcarbon in ash, Luca

%

Loss due to moisture infuel, Lmf

%

Loss due to carbon %


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Particulars UnitDesignValue

Actualvalue

%Deviation

Remark

monoxide, Lco

Radiation losses %

Unaccounted losses &manufacturers margin %

Total losses %

Boiler Efficiency %

Loss due to Hydrogen inFuel

All loss components should be thoroughly examined for the deviations,since in most of the plants, the actual GCV of the fuel and composition of

the fuel does not match with design specifications, and the above lossesneed to be corrected for the present fuel.

3.6.3 Coal Mills

The major objectives of coal mill energy audit are: To evaluate specificenergy consumption of the mills. (kWh/ton of coal) To establish air tocoal ratio of the Mills (ton of air per ton of coal) To evaluate specificcoal consumption of the unit (kg /kWh) Compare the actualconsumption with design/PG test values Suggest ways to optimiseenergy consumption To discuss on general health of equipment andreview maintenance practices which affect energy consumption.

The energy audit of coal mills has to be commenced by obtaining aoverview of system which include mills, RC feeders, PA fans, seal air fans,mill reject handling system and associated ducts, piping, valves anddampers, lubrication system, thermal insulation status of mills/PA fansducts/piping etc.

While monitoring the general health of various installations identify noticeableleakages of coal, air, oil and also to check condition of thermal insulation etc.

During the audit obtain samples of raw coal, pulverised coal, mill rejects, millgearbox oil, fly ash and bottom ash analyse for the various parameters.


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Raw Coal: GCV, ash content, volatile matter, fixed carbon, total moisture, andHGI value of coal.

Pulverised Coal: Mill fineness (% passing through 200 mesh), Running hours ofmill grinding elements with material composition of each part. Individual RCFcoal integrator readings should be compared with overall coal integrator

readings.Mill Reject Coal: Ash content and gross calorific value of mill rejects, Fly Ash,Bottom Ash and Combustibles in fly ash and bottom ash & GCV.

Mill Gear Box Oil: Viscosity, moisture, mechanical impurities and appearance oflubricating oil of mill gearboxes.

Carry out power measurements of mills, PA fans, seal air fans, etc,. In theabsence of energy meters, take readings from on-line panel instruments forcurrent, voltage, power factor etc. For LT equipment, portable instrument canbe used for power measurements.

Coal flow to also be established by dirty Pitot tube test (to be carried out on

Pulverised coal lines). This also helps to identify unbalancing/choking isoccurring in flow in the Pulverised Coal lines. The on line coal flow values ifavailable, may also to be taken by appropriate coal feeder calibration. Airflowto be established per PA fan by clean air Pitot tube method or by Aerofoil DPwhere available. Various parameters observed should be enlisted on a logsheet shown

ParticularsObservations

Mill No

Date

Time (hr)

Unit Load (MW)

Mill coal Flow(tph)

Mill Inlet Temp.

o( c)

Mill Outlet Temp.

o( c)

Mill difference.


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Pressure. (mmwc)

Air flow to mill

(tph)

PA common

header pressure

(mmwc)

Coal Flow Rate

(tph)

L

R

Mill Power (kwh)

Mill Current

(Amps)

RCF coal

integration

readings

Energy Meter

readings:

Specific power

consumption

Based on above observations, Auditor may draw Inference as followSpecific power consumption kWh per tonnage of coal handled Coalfineness and its impact on the unburnt & air to fuel ratio.


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For a typical coal fired boiler, the design indicates that 70% passing through 200mesh is ideal. Similarly, these values need to be obtained and compared with theactual. The following Table 3-13: can be used as data sheet for mill finenessanalysis.

Table 3-13:Coal fineness

Particulars /Mill

Passing through (%)

50 Mesh 100 Mesh 140 mesh 200 mesh

Design

Mill No #

Mill No #

Mill No #

Mill No #

Observe the mill rejects with respect to the quantity and calorific value:Tabulate the results as shown in Table 3-14:.

Table 3-14: Mill rejects

Mill NoFuel input,tph

Fuel Reject,kg/h

Millreject%

Calorificvalue of thereject

Remarks

Mill No #

Mill No #

Mill No #

Mill No #

Carryout the detailed analysis of mill rejects, compare with the other millsand coal quality. The variation in mill rejects (among the mills) could bedue to variation in performance of mill due to mill internals status, fuelhandling, etc.

3.6.4 Combustion control, excess air and cold air infiltration

While conducting the study, the following need to be verified:

Present excess air and comparison with PG test or design value


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Combustion control systems installed and status of operation, calibration systemsMonitoring and controlling mechanism for oxygen, excess air and reporting systemsin place Effect of excess air on boiler performance Excess air with respect to boilerload variation Cold air infiltration in to the system observe the present method ofmeasurement, estimation, frequency of measurement for estimating the losses andcontrol mechanisms initiated. The air infiltration also increases load on the ID fan andhinders the capacity of the boiler.

The best way to identify the cold air infiltration is to measure the oxygen profile acrossthe flue gas path.

The following data sheet (Table 3-15:) can be used for excess air and combustioncontrol system.

Table 3-15: Data sheet for estimating air infiltration

Location Parameter Oxygen Excess airFlue gastemperature

Exhaustgasquantity

Design

Economizer Actual

outlet Deviation

Remarks

Design

APH inletActual

Deviation

Remarks

Design

APH outletActual

Deviation

Remarks

ESP outlet/ID

Design

Location Parameter Oxygen Excess air Flue gastemperatur

Exhaustgas


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e quantity

fan inlet Actual

Deviation

Remarks

Design

ID fanoutlet

Actual

Deviation

Remarks

The above data sheet will help in identifying thesuitable improvement options. If there is any

increase in oxygen content then carryout thefollowing: Quantity of air in filtered (the exhaustgas quantity can be measured / estimated basedon the oxygen content) Heat losses due toinfiltration (impact on boiler efficiency)

Sources for air filtrationSuggest the measures to reduce the cold air infiltration into the

system. Typical acceptance value for a 210 MW power plant, toincrease oxygen by 3% across the APH inlet to ID fan inlet). How ever,there are very good monitoring systems are available the increase inoxygen is less than 3%. Recommend suitable monitoring system foroxygen profile in flue gas path and suggest instruments required forthe monitoring along with suggesting ideal locations for sensorsinstallation Estimate the energy saving benefits in the followingequipment by having very good cold air infiltration controllingmechanism

Improvement in boiler efficiency Improvement in APH Reductionin ID/PA and FD fan power consumption Increase in boilerloading / PLF


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3.6.5 Performance of air preheaters

Air preheater is one of the critical equipment in the boiler and its performancehas direct affect on boiler efficiency. A run test has to be carried out to assessthe performance of the air preheaters.

Air heater leakage and air heater gas side efficiency has to be carried out tocheck the performance of APH.

Air heater leakage in APH is weight of air passing from the airside to gas side ofthe air heater. This is an indicator of the condition of the air heaters seals, asthe air heater seals wear, air heater leakage increase. The increase in air heaterleakage increases the power requirements of the forced draft and induced draftfans, increasing the unit net heat rate and possibly limiting the unit capacity.

Air heater gas side efficiency is defined as the ratio of temperature drop,corrected for leakage, to the temperature head and expressed as a percentage.

This is an indicator of the internal condition of the air heater. As conditions insidethe air heater worsen (baskets wear, ash plugging, etc), the air heater gas side

efficiency decreases. This is generally accompanied by an increase in exist gastemperature and decrease in air heater outlet temperature.

Air leakage estimation: The following gives the air leakage in to the air preheaters(APH) system if the Oxygen % is measured at the entry and exit of the air preheaters(APH)

(APH the leaving gas the in % O-APH entering gas the in % O )* 100

22AL %, leakage APH=

(21-APH leaving gas the in % O )

2

Alternatively, if the CO2% is measured in the exhaust gases then the air leakageis estimated by

(APH the entering gas the in % CO-APH leaving gas the in % CO )* 100

22

AL %, leakage APH = APH leaving gas the in % CO

2

Gas side efficiency: The gas side efficiency is defined as the ratio of the temperature drop,corrected for leakage, to the temperature head and expressed aspercentage.

Temperature drop is obtained by subtracting the corrected gas outlettemperature from the inlet. Temperature head is obtained by subtractingair inlet temperature from gas inlet temperature.

The corrected gas outlet temperature is defined as the outlet gastemperature for no air leakage and is given by the following:

AL*Cpa *(Tg -Tae)


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= lTglTgnl 100*Cpg+

Tgnl Gas outlet temperature corrected for no oC

leakage

Cpa The mean specific heat between Tac and Tgl Kcal/kgoC

Tae Temperature of the air entering the APH oC

Tal Temperature of the air leaving the APH oC

Tgl Temperature of the gas leaving the APH oC

Cpa The mean specific heat between Tgl and Tgnl Kcal/kgoC

Units

Air leakage estimation and gas side efficiency estimation are importantwhile evaluating the performance of the air heater.

The measured data and estimated parameters need to be tabulated forcomparison with the design or best-run values. The following Table 3-16:gives the data sheet for filling the parameters.

Table 3-16: Data sheet for air preheaters (APH)

UnitDesign/PG test Actual

%Deviation

Remarks

Total combustion air tph

Oxygen content in flue gasbefore APH %

Excess air % in flue gasbefore APH %

Air heater leakage %

Quantity of air in filteration tph

Temperature of the airentering the APH

oC

Temperature of the airleaving the APH

oC

Air temperature at fan outlet oC

Temperature of the gasleaving the APH

oC


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Gas outlet temperaturecorrected for no leakage

oC

Note: Auditor can identify the following. Loss parameters from the aboveData of leave/ Observations 1) Increase in FD and ID fan powerconsumption 2) Air preheater performance

3.6.6 Controllable losses due to unburnt in ash

Collect the fly ash and bottom ash samples, during the efficiency testperiod for the analysis of unburnt carbon. It is also suggested to verify thepast data pertaining to

Ash quantities bottom ash and fly ash Unburnt analysis Coal used,coal mill performance parameters, unit load, etc (for the dates

pertaining to the unburnt analysis)

It is also suggested to see the trend if the plant monitors the unburntregularly by plotting the graph. For this purpose collect the historical data ofanalysis. Work out boiler efficiency and impact on coal consumption, for

every raise of 0.1% in unburnt Secondary air temperature

Use the following data sheet Table 3-17: for tabulating unburnt values.

Table 3-17: Unburnt reported values

Day / MonthUn burnt in Fly ash Un burnt in Bottom

ash

Design Actual Design Actual


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After collecting the data, it is suggested analyse for the high (if any)

and suggest suitable options to reduce the same.

3.6.7 Operation of Soot blowers

List the number and type of soot blowers installed along with theiroperating condition. The data sheet for soot blowers is given in Table 3-18: .

Table 3-18: Datasheet for soot

blowers Location

Type ofsootblower

No of sootblowers

installed

No of sootblowersunder

operation

Reasonfor nonoperation

Effect of dysfunctional operation

Furnace walls

Super heater &Reheater sidewalls

Air heaters

The dysfunctional soot blowers cause clinker build up, loss of heattransfer, leads to break downs, higher flue gas high steam temperature at

the super heater zone, higher de-super heater spray, etc.Compare the normative de superheated spray with actual spray quantity.( Table 3-19: ).

Table 3-19: Comparison of actual and normative spray consumption

Unit loadSteamflow, tph

Steamtemperature, C

Attemperationspray, tph

% ofAttemperationof steam flow

Remarks

At NCR - MW

At actual load. MW

If the actual super heater spray is more than normal, then this willaffect the unit performance and heat rate. Identify causes fordisfunctioning of soot blowers of each zone and possible remedies.Check the following: Soot blower piping. Poppet valves servicing.Functioning of rotary and traverse motor. Positioning of split camassembly, shifting of nozzle position.


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Retract limit switches.

Sleeves condition.Positioning of concentricity of swivel tube in respect of wallOther parameters which affect the performance f soot blowers

During the study, observe for these causes due to dysfunctional soot blowers.

3.6.8 Water Treatment

Water quality influences the performance of the boiler internals, observe the presentwater treatment parameters pertaining to

Type and rated capacity, operating capacity of the internal and external treatmentmethods

Water quality parameters design vs comparison

Control of blow down Present instrumentation, its condition and operationalstatus Condensate polishing unit

The higher the boiler operating pressure, the greater will be the sensitivity toimpurities. It is suggested to check the following given in Table 3-20: .

Table 3-20: Feed water and condensate parameters

ParticularsFeed water Condensate

Design Actual Design Actual

Hardness

PH at 25oC

Oxygen maximum ppm

Total iron- maximum ppm

Total silica maximum ppm

Conductivity at 25oC U/cm

Hydrazine residual ppm

Total solids maximum ppb

chlorides ppm

Copper maximum ppm


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Others

Check scope for improving the control systems.

3.6.9 Visual survey and insulation survey of the boiler system

It is suggested to make a visual survey and measurements of the ducting

and insulation system for Insulation status (measure the surface temperaturewith the aid of surface thermocouple / infrared pyrometer or by usingthermal imaging cameras) Physical condition of insulation Identification oflocations where action is required to improve the insulation (provide withdetailed techno-economics) Improvement options

Procedure for conducting the energy audit of insulation is given separately.

3.6.10 Exploration of energy conservation possibilities

While conducting the energy audit of the boilers, the following need to beexplored in detail to arrive at appropriate energy conservation measures

Boilers Steam and water parameters (flow, pressure and temperature) Airand gas parameters (flow, pressure and temperature) Burners operationPrimary and secondary air ratios and temperatures Air infiltration in to boilersUnburnt loss reduction Combustion control boiler excess air, O2Measurement inaccuracy or unbalance, Dry flue gas losses Insulation Airinfiltration to flue gases Blow down and its control Water quality & its controlCoal quality and performance of coal mills Super heater and reheaterperformance Super heater temperature, slagging of furnace water walls andtubes, Fouling on the pendant and horizontal convection tubes, soot blowersperformance Boiler control systems Limitation on Performance of associatedequipments (pumps, fans, heaters, soot blowers, mills, etc) affecting boilerloading and efficiency Loading on ID, FD and PA fans Operation of dampers

/inlet guide vanes / speed controllers of fans Fouling of boiler heating surfacesInstallation of energy saving retrofits DM water consumption

Air preheatersAir InfiltrationGas side efficiency

Performance of air preheaters


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EconomiserPressure dropPerformance

3.6.11 Key observations and Analysis

This forms the major component of energy audit system the details should givenin details pertaining to the section mentioned in the earlier sections:

Detailed observations and their description pertaining to the following,which include, Energy consumption pattern (fuel consumption, specificconsumption, heat rate, plant load factor, operating hours, efficiency,energy metering and monitoring aspects) Boiler loading pattern and unitload Major O&M aspects affecting the boilers Boiler efficiency and heatbalance, loss components

Combustion and control

a. Water and steam quality & control aspects

b. Soot blowers

c. Insulation aspects

Economiser Air preheaters Air infiltration Mills and performance aspects Fuelquality aspects Burner operation and performance Recent modifications carriedout Observation on visual survey Make up water aspects Blow down aspectsSince energy audit is case specific activity hence, In addition to the above therewill be several other components, which affect the energy efficiency. The auditshould also cover these points


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Documents

Guidelines for Energy Auditing of TPS-1