3.Igen Ea Boiler

Guidelines for Energy Auditing of

P C Fired Boilers

Surender KumarDeputy Director,NPTI

Boiler Schematic

Water & Steam cycle

Fuel System

Air & flue gas Flow Path

Ash/ rejects Handling System

Performance Parameters

Boiler Aspects For Study

Coal quality - composition and calorific value

Coal milling aspects

Combustion and excess air

Reheaters

Heat recovery units – Economisers, air-preheaters

etc.

Insulation aspects

Operation and maintenance features which affect the energy

efficiency

Boiler blow down aspects

Soot blowing aspects

Condition & status of boiler and their internals

Feed water system aspects

Air and flue gas system aspect

Boiler Aspects For Study

Steps Involved In Boiler Energy Audit

Data collection

Observations and Analysis

Exploration for energy conservation measures

Report preparation

Data Collection

Data Collection-boiler SpecificationsParticulars Unit Details at Normal

cont. rating, NCRMake XXXXXX

Type Water Tube Single Drum

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 420

Reheater outlet temperature 0C 540

Water-economizer inlet temperature

0C 241

Water-economizer outlet temperature

0C 280

Oxygen content at Economizer outlet

% 4.23

Unit Design/NCR Actual

Make

Type

Year of Installation

Main Steam Pressure kg/cm2

Main Steam Temperature oC

Main Steam Flow tph

Steam pressure at LTSH outlet kg/cm2

Steam temperature at reheater inlet oC

Steam temperature at reheater outlet

oC

Steam pressure at reheater inlet kg/cm2

Steam pressure at reheater outlet kg/cm2

Steam temperature at LTSH out oC

Saturated steam temperature in drum

oC

Super heater platen outlet temperature

oC

Maximum pressure drop in reheater Kg/cm2

Super heater spray tph

Reheater Spray tph

Ambient temperature oC

Coal consumption tph

Data Collection-boiler Specifications

Unit Design Actual

Feed water pressure at the inlet kg/cm2

Feed water pressure at the outlet

kg/cm2

Feed water flow tph

Feed water temperature at the inlet

oC

Feed water temperature at the outlet

oC

Oxygen content in flue gas before/after economizer

%

Excess air % in flue gas before/ after economizer

%

Flue gas inlet temperature oC

Flue gas outlet temperature oC

Flue gas quantity tph

Data Collection- Economiser

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 and afterAPH

%

Flue gas inlet temperature oC

Flue gas outlet temperature oC

Flue gas quantity tph

Data Collection:Air Pre Heater

Unit Design Actual

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

ID Fan outlet oC

Data Collection-flue gas temperature profile

Unit Design Actual

Fixed Carbon %

Volatile Matter %

Moisture %

Ash %

Grindabiity index HGI

Coal calorific value-HHV Kcal/kg

Size of the coal to mill mm

Total contract fuel fired tph

Data Collection- coal parameters

Unit Design Actual

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

%

Data Collection-boiler heat balance

Unit Requirement at NCR

Actual Remarks

No of coal burners No

Primary Air Fuel tph

No of mills in operation No

Mill loading %

Air temperature at mill inlet after tempering

oC

Air – fuel mixture temperature after leaving mills

oC

Total coal fired tph

Air – Fuel Ratio

Data Collection- mills and burners performance

Type of mill ______________ Make _________

Capacity __________tph at coal ________grind Fineness ___________% through ________mesh

Motor rating ____________kWMotor voltage ________ V No of mills :__________

Running /Standby _________/________ Design coal parameter

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

Data Collection- coal mill specifications

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

Data Collection: Soot Blowers

Data Collection:Case Example of 210/500 MW Unit

Main Boiler NCR

Make

Natural Circulation, balanced draft, double pass, single drum, single re-heat, direct pulverized coal/oil firing, dry bottom type, tangential firing

Type XXXXXX (210 MW)

XXXX(500MW)

Capacity tph 700 1681

Main Steam pressure kg/cm2 154.9 177.2

Main Steam temperature

0C 540 540

CRH Pressure kg/cm2 43.09

HRH Pressure kg/cm2 40.99

CRH Temperature 0C 341.6

HRH Temperature 0C 540

Boiler efficiency % 87.3 88.1

Super heater outlet flow tph 645 1524.27

Reheater outlet flow tph 571 1372.42

Calorific value –GCV kcal/kg 3500 3750

Coal consumption tph 139 299

Data Collection: Boiler Specifications

333

540

38.7

37.2

Total combustion air

tph 791 1853

LTSH outlet temperature

0C 398

Reheater outlet temperature

0C 540 540

Water -economizer inlet temperature

0C 246 253

Water-economizer outlet temperature

0C 292 314

Pressure drop in reheater

Kg/cm2 1.5 2.1

Super heater spray

tph 3.2 0

Reheater Spray tph ---

Ambient temperature

oC 27 28

Data Collection: Boiler Specification

ECONOMISER

Feed water pressure at the inlet

kg/cm2 169 193.1

Feed water pressure at the outlet

kg/cm2 167.3 191.03

Feed water flow tph 659.4 1524.27

Feed water temperature at the inlet

oC 246 253

Feed water temperature at the outlet

oC 292 314

Oxygen content in flue gas before economizer

%

3.54 3.59

Excess air % in flue gas before economizer

% %

20 20

Flue gas inlet temperature

oC 493 356

Flue gas outlet temperature

oC 351 136

Flue gas quantityt APH I/L

tph 2032

Data Collection: Economiser

%

Air Pre Heater

Air quantity at APH outlet (primary)

tph 175 257

Tempering air tph 91 283

Air heater outlet (secondary)

tph 483 1263

Total combustion air

tph 791 1853

Air outlet temperature of APH – primary

oC 320 326

Air outlet temperature of APH– secondary

oC 324 326

Oxygen content in flue gas before APH

% 3.54 3.59

Flue gas inlet temperature

oC 351 356

Flue gas outlet temperature

oC 136 136

Flue gas quantity tph 2032

Data Collection: Air Pre Heater

Flue Gas Temperatures

Super heater platen outlet

1165 1119

RH front inlet 1008 1034

RH rear inlet 864 905

SH finish inlet 754

LTSH inlet 637 788

Economizer inlet 493 561

APH inlet 351 356

APH outlet 136 136

Data Collection Flue Gas Temperature profile

0C

0C

0C

0C

0C

0C

0C

0C

210 MW 500 MWUnit

Heat Balance 210M 500MW

Ambient temperature

oC 27 28

Excess air % 20 20

Dry gas loss % 4.77 4.64

Hydrogen loss % 5.83 5.54

Moisture in fuel loss

%

Moisture in air loss

% 0.12 0.16

Unburnt combustible loss

% 1.2 0.60

Radiation loss % 0.11 0.29

Un accounted loss % 1.11 0.40

Total Losses % 13.14

11.50

Heat Credits % 0.44 0.20

Guaranteed efficiency

% 87.28

88.10

Data Collection: Heat Balance

Recommended FW limits

Unit Feed water

Boiler Water

Hardness Nil

pH at 25oC 8.8-9.2

9.1-9.6

Oxygen – maximum ppm 0.007

Total iron- maximum

ppm 0.01

Total silica – maximum

ppm 0.02

Conductivity at 25oC

Micor s/cm 0.3 30

Hydrazine residual ppm 0.01-0.02

Total solids – maximum

ppb 15

chlorides ppm

Copper – maximum ppm 0.005

Permanganate consumption

ppm Nil

Data Collection: Recommended Boiler Water Parameters

Fuel Parameters – Ultimate Analysis

500 MW

Carbon % 37.03

Hydrogen % 2.26

Sulpuer % 0.33

Nitrogen % 0.85

Oxygen % 6.53

Total moisture % 12.0

Ash % 41.0

Gross calorific value Kcal/kg 3500 3750

Fuel Parameters – Proximate Analysis

Fixed Carbon % 24.0 28

Volatile matter % 23.0 24

Total moisture % 12.0 8

Ash % 41.0 40

Data Collection: Fuel Parameters

Unit110 MW

Average GCV of coal

Coal analysis – ultimate and proximate

Coal consumption details

Performance parameters of coal mills

Boiler efficiency

Steam parameters of main steam, reheat, super

heater, LTSH (flow, pressure and temperature)

Air – flow, temperature, pressures

Flue gas – Flow, temperature and pressure

Flue gas analysis

Coal consumption pattern

Measurements and Observations

Ambient temperature

Boiler loading

Motor electrical parameters (kW, kVA, Pf, A, V, Hz, THD)

etc.

Surface temperatures of insulation and boiler surfaces

Other important Parameters

Unit load of the plant

Date & time of measurement

Instruments used for measurement

Frequency of the measurement


Availability factor

PLF

Coal consumption (tons and kg/kWh)

Oil consumption in ml/kWh

Boiler efficiency

Past performance trends on boiler loading, operation, PLF,

efficiency

Major constraints in achieving the high PLF, load or efficiency

(Input

from plant personnel)

Major renovation and modifications carried out in the recent

past

Coal – quality and calorific values aspects

Operational failures leading to in efficient operation such as

tube

failures, constraints for efficient heaters operation


Soot blowers operation

Tripping

Performance of economiser, air preheaters, LP / HP

heater from past records

Combustion control system – practice followed

Mills performance

If plant has online and off line tools for performance

evaluation of

main equipment and BOP equipment – then details of

these tools

Plant side initiatives to improve the performance and

efficiency of

the boiler

Measurements & Observations

Instruments Required For Boiler Auditing

Power Analyser: Used for measuring electrical

parameters such as kW, kVA, pf,V, A and Hz

Temperature Indicator & Probe

Stroboscope: To measure the speed of the driven

equipment and motor

Sling hygrometer or digital hygrometer

Anemometer

Available On line instruments at the site

( Calibrated )

Instruments Required

Digital Manometer of suitable range andappropriate probes for measurement of pressure head and velocity head

Additional pressure gauges with appropriate range of measurement and calibrated before audit

Flue gas analyzers / orsat apparatus

Infrared pyrometers

Pressure gauges

Steam trap tester / Ultra sonic leak detectors

Instruments Required

Trials are conducted at least for two hours and measurements are to be taken every fifteen minutes

Ensure during Auditing:

Load on the boiler to be by and large constant and

represent

average loading and normal operation

No soot blowers operated

No intermittent blow down

Preparedness for simultaneous data measurements

and collection of various

parameters.

Demo exercise for one set of measurement and

observation

Pre audit Checks

Flue gas analysis at air preheaters inlet / out let

Temperature of flue gas at air preheaters inlet / out let

Fly ash sampling at the economiser outlet and ESP

hoppers for

unburnt carbon in fly ash

Sample of bottom ash from hopper or scrapper

Sample of raw coal from RC Feeder of the mill for

proximate and

ultimate analysis of fuel and gross calorific value.

Pulverised coal samples from each mill for sieve

analysis.

Sample of mill rejects for GCV.

Measurement Locations

Data Analysis

Operating efficiency of the boiler:

Heat loss due to dry flue gas losses

Heat loss due to moisture in fuel

Heat loss due to hydrogen (moisture of burning hydrogen)

Heat loss due to combustibles in refuse

Heat loss due to radiation

Un accounted losses as per the contract with the Boiler Supplier

Observations & Analysis

Data SheetBoiler Efficiency Evaluation



1. Dry flue gas loss:

Theoretical Air Requirement

Actual Air Requirement

Dry Flue Gas Quantity (Wd), Kg/Kg of fuel

Dry flue Gas Loss Ldfg %

Computation of Boiler Losses

2. Loss due to unburnt carbon in ash:

)%()%(,

/

,

BAshBACFAshFACGCVfuelofGCV

kgkcalincarbonofvalueCalorific

LashincarbonunburnttodueLoss uca

GCV

ABTFGTM

LfuelinmoisturetodueLoss mf

100584)(45.0(,

3. Loss due to moisture in fuel:

4. Loss due to hydrogen in fuel:

GCV

ABTFGTH

LfuelinhydrogentodueLoss hf

100584)(45.0(

9, 2

Where H2 – kg of H2 in 1 kg of fuel


5. Loss due to moisture in air:

GCVABTFGThumidityAASLairinmoistureintodueLoss ma

100)(45.0,

Where AAS=Actual mass of air suppliedHumidity = humidity of air in kg/kg of dry air

GCV1005744

%CO%COC%CO

L,xidecarbonmonotodueLoss2

co

GCV100

574428h/kginnconsumptiofuel10ppminCO

L,monoxidecarbontodueLoss

6

co

6. Loss due to CO in flue gas:


Efficiency evaluation of Boiler

Particulars

Unit

DesignValue

Actual value

% Deviation

Remark

Date & time of the test

Load MW

Fuel GCV kcal/kg

Loss due to hydrogen in fuel

%

Loss due to Dry Flue gases, Ldfg

%

Loss due to moisture inAir

%

Loss due to unburnt carbon in ash, Luca

%

Loss due to moisture in fuel, Lmf

%

Loss due to carbon monoxide, Lco monoxide

%

Radiation losses %

Unaccounted losses &manufacturers margin

%

Total losses %

Boiler Efficiency %

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 unburnts in residue

Heat loss due to moisture in air

Heat loss due to radiation & other unaccounted loss

5.5%

4.2%

1%

0.3%

1%

1%

87%

100%Heat fromFuel

BoilerHeat Balance

Energy Audit- Coal Milling System

Objectives of energy audit :

To evaluate specific energy consumption

(kWh/ton of coal)

To establish air to coal ratio of the mills (ton of

air per ton of coal)

To evaluate specific coal consumption of the

unit (kg /kWh)

Compare the actual consumption with

design/pg test values

Suggest ways to optimise energy consumption


Overview of system includes mills, RC feeders, PA fans, seal air fans,mill reject handling system and associated ducts, piping, valves and dampers, lubrication system, thermal insulation status of mills/pa fans ducts/piping etc.

Samples of raw coal, pulverised coal, mill rejects,mill gearbox oil, fly ash and bottom ash


Raw Coal: GCV, ash content, volatile matter, fixed carbon, total

moisture,and HGI value of coal. Pulverised Coal:

Mill fineness (% passing through 200 mesh), Running hours of mill grinding elements with material composition of each part, Individual RCF coal integrator readings be compared with overall coal integrator readings.

Mill Reject Coal: Ash content and gross calorific value of mill rejects,

FlyAsh, Bottom Ash and Combustibles in fly ash and bottom ash & GCV.

Mill Gear Box Oil: Viscosity, moisture, mechanical impurities and

appearance of lubricating oil of mill gearboxes.


Energy Audit- Coal Milling SystemObservations

Energy Audit- Coal Milling SystemCoal fineness

Mill rejects

COMBUSTION CONTROL, EXCESS AIR AND COLD AIR INGRESS

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

Present excess air and comparison with PG test or design value

Combustion control systems installed and status of operation,

calibration systems

Monitoring and controlling mechanism for oxygen, excess air and reporting systems in place

Effect of excess air on boiler performance

Excess air with respect to boiler load variation

Cold air infiltration in to the system – observe the present method of measurement, estimation, frequency of measurement for estimating the losses and control mechanisms initiated.

PERFORMANCE OF AIR PREHEATERS

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

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

leakage is estimated by


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 as percentage.

Temperature drop is obtained by subtracting the corrected gas outlet temperature from the inlet. Temperature head is obtained by subtracting air inlet temperature from gas inlet temperature.


Theoretical

Total air = PA+ SA+ Seal air tph

EXPLORATION OF ENERGY CONSERVATION OPPORTUNITIES

Boilers: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 boilers

Unburnt loss reduction

Combustion control – boiler excess air, O2 Measurement inaccuracy or unbalance

Dry flue gas loss

Insulation

Air infiltration to flue gases

Water quality, Blow down and its control

Stack Temperature Boiler Soot Deposits, High Excess Air , Air inleakages before

the combustion chamber, Low Feed Water Temperature , Passing dampers and poor air heater seals , Higher elevation burners in service, Improper combustion…

Incomplete Combustion Poor milling i.e. Course grinding, Poor air/fuel distribution to

burners, Low combustion air temperature, Low primary air temperature, Primary air velocity being very high/very low, Lack of adequate fuel/air mixing…..


Dry flue gas loss. Air in-leakage through man holes, peep holes,

bottom seals, air heater seal leakage, uneven distribution of secondary air, inaccurate samples/analysis.

Poor automatic boiler SADC, burner tilting, O2 control….

Radiation and convection heat loss. Casing radiation, sensible heat in refuse, bottom

water seal operation, not much controllable but better maintenance of casing insulation can minimize the loss.


Blowdown.

1 % of blow down carries a 0.17% heat added, in the boiler, 0.25% heat is required to make up accounts to 0.42% so blow down to be adhered to the chemist requirement.

Scaling and soot losses.

Super heated steam with high enthalpy is used. 1% of steam may be required, contains 0.62% heat

content, to make up the loss another 0.25% heat to be added to feed water resulting total heat loss of 0.87%.

Frequency of soot blowing must be carefully planned.

Auxiliary power consumption.


Saving Analysis with improvement in efficiency

Fuel Saving S% = (ɳnew- ɳasis)*100/ ɳnew

Annual energy savings

Annual cost savings

ηas is = the actual system efficiency CMWh = Fuel costs in Rs/MWh where MWh1 refers to energy in the fuelPLF = plant load factor as a fraction

Case Study:

1. Optimization of Excess Air 2. Optimization of PA to SA

Optimization of Excess Air

Parameter Design measured

Excess air at boiler exit % 19.0 23.6

Excess air at APH exit % 28.0 55.6

FG temp. at APH exit 0c 146.0 167.6

Dry Flue gas loss % 5.08 8.89

Heat loss due to CO % 0 0

Heat loss due to moisture in air % 0.12 0.18

Heat loss due to moisture and H2 in fuel % 5.95 5.78

Heat loss due to unburnt in ash % 0.90 0.09

Sensible heat loss in ash % 0.56 0.59

Surface and unaccounted losses % 0.17 0.10

Design margin % 0.5

Total heat losses %(corrected) 12.57 14.93

Thermal efficiency % 87.43 85.07

ObservationExcess Air and cold air Ingress also causes ID fan loadingExcess FG temp. at APH

Efficiency Evaluation of 500 MW unit

Causes & ActionsWorn out seals and heat Transfer elements-AttendedLeakage through peep/port holes-AttendedSoot formation on the heat transfer area- S B done

Results2.83% effciciency impr. inReduction Coal consumption By 74490 T/ARs.63.09 saving (Rs. 847 /T)

Optimization of PA to SA

Type Unit PAF A PAF B FD A FD B

Capacity M3/sec

55 55 58.4 58.4

Total design head

mmwc

1212 1212 450 450

Fan Speed rpm 1480 1480 1480 1480Fan regulation type

Inlet damper control

Inlet damper control

Blade pitch control

Blade pitch control

Fan motor rating

kw 900 900 400 400

Operating parametersAir Flow M3/

sec65.27 56.34 24.8 68.0

Power consumption

kw 920 907 78 185

System Efficiency

% 78.6 67.0 66.5 77.5

Ratio of PA 56.7(40)

43.3(60}

Observation (120MW unit)Higher PA to SA ratio

Result

Adjustment of ratio, power consumption reduced from 2090 kw to 1760 kw

Saving of Rs. 3.22 M/A, cosidering 7500 hrs/year and Rs. 1.30 per kwh

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 unburnts in residue

Heat loss due to moisture in air

Heat loss due to radiation & other unaccounted loss

5.5%

4.2%

1%

0.3%

1%

1%

87%

100%Heat fromFuel

BoilerHeat Balance

3.Igen Ea Boiler

Documents

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energy efficiency boiler

soot blowersdata collection

mw unitdata collection

mlkwh boiler efficiency

heat balance data collection

temperature air flow