Assessment of boiler performance

ENERGY PERFORMANCE
ASSESSMENT OF BOILERS
ASHISH KUMAR JAIN

Performance Terms and Definitions
Heat output
Heat Input
Boiler Efficiency,  =
Heat in steam output (kCals)
Heat in Fuel Input (kCals)
Quantity of Steam Generation
Quantity of fuel Consumption
Evaporation Ratio =
The efficiency of a boiler is expressed as the % of useful heat
available from the total energy available by burning the fuel.
This is expressed on the basis of gross calorific value (GCV) .

Standards
British standards, BS845: 1987
This describes the methods and conditions under which a boiler
should be tested.Boiler should be operated under steady load
conditions (generally full load) for a period of one hour before taking
reading
ASME Standard: PTC-4-1 Power Test Code for Steam Generating
Units
q Part One: Direct method (also called as Input -output method)
q Part Two: Indirect method (also called as Heat loss method)
IS 8753: Indian Standard for Boiler Efficiency Testing
All standards do not include blow down as a loss in the efficiency
determination process.

Direct Method Testing
Boiler
Fuel Input 100%
+ Air
SteamOutput
Efficiency = Heat addition to Steam x 100
Gross Heat in Fuel
Flue
Gas
Water
100
valuecalorificGrossxratefiringFuel
enthalpy)waterfeedenthalpy(steamxrateflowSteam
xEfficiencyBoiler



Indirect Method Testing
Boiler Flue gas sample
Steam Output
Efficiency = 100 – (1+2+3+4+5+6+7+8) (by Indirect Method)
Air
Fuel Input, 100%
1. Dry Flue gas loss
2. H2 loss
3. Moisture in fuel
4. Moisture in air
5. CO loss
7. Fly ash loss
6. Surface loss
8. Bottom ash loss
Water
Blow down

Instruments used for Boiler Performance
Assessment.
Instrument Type Measurements
Flue gas
analyzer
Portable or fixed % CO2 , O2 and CO
Temperature
indicator
Thermocouple,
liquid in glass
Fuel temperature, flue gas
temperature, combustion
air temperature, boiler
surface temperature,
steam temperature
Draft gauge Manometer,
differential
pressure
Amount of draft used or
available
TDS meter Conductivity Boiler water TDS, feed
water TDS, make-up water
TDS.
Flow meter As applicable Steam flow, water flow,
fuel flow, air flow

1.Technical specification of boiler
1 Boiler ID code and Make
2 Year of Make
3 Boiler capacity rating
4 Type of Boiler
5 Type of fuel used
6 Maximum fuel flow rate
7 Efficiency by GCV
8 Steam generation pressure &superheat temperature
9 Heat transfer area in m2
10 Is there any waste heat recovery device installed
11 Type of draft
12 Chimney height in metre

2 - Fuel analysis details
Fuel Fired
GCV of fuel
Specific gravity of fuel (Liquid)
Bulk density of fuel (Solid)
Proximate Analysis Date of Test:
1 Fixed carbon %
2 Volatile matter %
3 Ash %
4 Moisture %

Ultimate Analysis Date of Test:
Carbon %
Hydrogen %
Sulphur %
Nitrogen %
Ash %
Moisture %
Oxygen %
Water Analysis Date of Test:
Feed water TDS ppm
Blow down TDS ppm
PH of feed water
PH of blow down
Flue gas Analysis Date of Test:
CO2 %
O2 %
CO %
Flue gas temperature OC

S
.
N
o
T
i
m
e
Ambient air Fuel Feed water Steam Flue gas
analysis
Surface
Temp of
boiler, oC
Dry
bulb
Temp,
oC
Wet
Bulb
Temp,
oC
Flow
Rate,
kg/hr
T
e
m
p
o
C
Flow
rate,
m3/hr
T
e
m
p
o
C
Flo
w
rat
e,
m3
/hr
Pr
ess
ur
e
kg
/c
m2
g
T
e
m
p
o
C
O
2
%
C
O
2
%
C
O
%
T
e
m
p
0
C
1
.
2
.
3
.
4
.
5
.
6
.
7
.
8
.
4. Format sheet for boiler efficiency testing
Date: ………………… Boiler Code No. …………………
Boiler Supervisor Energy Manager Energy Auditor

Fuel firing rate = 5599.17 kg/hr
Steam generation rate = 21937.5 kg/hr
Steam pressure = 43 kg/cm2
(g)
Steam temperature = 377 o
C
Feed water temperature = 96 o
C
%CO2 in Flue gas = 14
%CO in flue gas = 0.55
Average flue gas temperature = 190 o
C
Ambient temperature = 31 o
C
Humidity in ambient air = 0.0204 kg / kg dry air
Surface temperature of boiler = 70 o
C
Wind velocity around the boiler = 3.5 m/s
Total surface area of boiler = 90 m2
GCV of Bottom ash = 800 kCal/kg
GCV of fly ash = 452.5 kCal/kg
Ratio of bottom ash to fly ash = 90:10
Fuel Analysis (in %)
Ash content in fuel = 8.63
Moisture in coal = 31.6
Carbon content = 41.65
Hydrogen content = 2.0413
Nitrogen content = 1.6
Oxygen content = 14.48
GCV of Coal = 3501 kCal/kg
The data collected are
for a boiler using coal
as the fuel.
Find out the boiler
efficiency by indirect
method.

Boiler efficiency by indirect method
Step – 1 Find theoretical air
requirement
Theoretical air required for
complete combustion
= [(11.43 x C) + {34.5 x (H2 – O2/8)} + (4.32 x S)] /
100 kg/kg of coal
= [(11.43 x 41.65) + {34.5 x (2.0413 – 14.48/8)} +
(4.32 x 0)] / 100
= 4.84 kg / kg of coal

Step – 2 Find theoretical CO2 %
% CO2 at theoretical condition
( CO2 )t
=
Moles of C
Moles of N2 + Moles of C
Where,
Moles of N2 =
4.84 x 77/100 0.016
+ = 0.1332
28 28
Where moles of C = 0.4165/12 = 0.0347
( CO2 )t =
0.0347
0.1332 + 0.0347
= 20.67

Step – 3 To find Excess air
supplied
Actual CO2 measured in flue gas = 14.0%
% Excess air supplied (EA) = 7900 x [ ( CO2)t – (CO2)a]
(CO2)a x [100 – (CO2)t ]
= 7900 x [20.67 – 14 ]
14a x [100 – 20.67]
= 47.44 %

Step – 4 to find actual mass of air supplied
Actual mass of air supplied = {1 + EA/100} x theoretical air
= {1 + 47.44/100} x 4.84
= 7.13 kg/kg of coal
Step –5 to find actual mass of dry flue gas
Mass of dry flue gas consists of Mass of CO2 +Mass of N2 content in the fuel+ Mass
of N2 in the combustion air supplied + Mass of
oxygen in combustion air supplied
Mass of dry flue gas =
0.4165 x 44 7.13 x 77 (7.13-4.84) x 23
+ 0.016 + +
12 100 100
= 7.562 kg / kg of coal

Step – 6 to find all losses
1. % Heat loss in dry flue gas (L1) = m x cp x (Tf – Ta )
x 100
GCV of fuel
=
7.562 x 0.23 x (190 – 31)
x 100
3501
L1 = 7.89 %

2. % Heat loss due to formation
of water from H2 in fuel (L2)
= 9 x H2 x {584 + Cp (Tf – Ta )}
x 100
GCV of fuel
=
9 x .02041 x {584 + 0.45(190-31)}
x 100
3501
L2 = 3.44 %
3. % Heat loss due to moisture in
fuel (L3)
=
M x {584 + Cp ( Tf – Ta )}
X 100
GCV of fuel
=
0.316 x {584 + 0.45 ( 190 – 31) }
x 100
3501
L3 = 5.91 %

4. % Heat loss due to moisture in
air (L4)
=
AAS x humidity x Cp x (Tf – Ta ) x 100
GCV of fuel
=
7.13 x 0.0204 x 0.45 x (190 – 31) x 100
3501
L4 = 0.29 %
5. % Heat loss due to partial
conversion of C to CO (L5)
=
%CO x %C 5744
x x 100
% CO + (% CO2)a GCV of fuel
=
0.55 x 0.4165 5744
x x 100
0.55 + 14 3501
L5 = 2.58 %

6. Heat loss due to radiation and
convection (L6)
= 0.548 x [ (343/55.55)4
– (304/55.55)4
] + 1.957 x
(343 - 304)1.25
x sq.rt of [(196.85 x 3.5 + 68.9) /
68.9]
= 633.3 w/m2
= 633.3 x 0.86
= 544.64 kCal / m2
Total radiation and convection
loss per hour
= 544.64 x 90
= 49017.6 kCal
% radiation and convection loss = 49017.6 x 100
3501 x 5591.17
L6 = 0.25 %

7. % Heat loss due to unburnt in fly ash
% Ash in coal = 8.63
Ratio of bottom ash to fly ash = 90:10
GCV of fly ash = 452.5 kCal/kg
Amount of fly ash in 1 kg of coal = 0.1 x 0.0863
= 0.00863 kg
Heat loss in fly ash = 0.00863 x 452.5
= 3.905 kCal / kg of coal
% heat loss in fly ash = 3.905 x 100 / 3501
L7 = 0.11 %
8. % Heat loss due to unburnt in fly ash
GCV of bottom ash = 800 kCal/kg
Amount of bottom ash in 1 kg of
coal
= 0.9 x 0.0863
= 0.077 kg
Heat loss in bottom ash = 0.077 x 800
= 62.136 kCal/kg of coal
% Heat loss in bottom ash = 62.136 x 100 / 3501
L8 = 1.77 %

Boiler efficiency by indirect
method
= 100 – (L1+ L2+ L3+ L4+ L5+ L6+ L7+ L8)
= 100-(7.89 + 3.44+ 5.91+ 0.29+ 2.58+ 0.25+
0.11+1.77)
= 100-22.24
= 77.76 %
Summary of Heat Balance for Coal Fired Boiler
Input/Output Parameter kCal / kg of
coal
% loss
Heat Input = 3501 100
Losses in boiler
1. Dry flue gas, L1 = 276.23 7.89
2. Loss due to hydrogen in fuel, L2 = 120.43 3.44
3. Loss due to moisture in fuel, L3 = 206.91 5.91
4. Loss due to moisture in air, L4 = 10.15 0.29
5. Partial combustion of C to CO, L5 = 90.32 2.58
6. Surface heat losses, L6 = 8.75 0.25
7. Loss due to Unburnt in fly ash, L7 = 3.85 0.11
8. Loss due to Unburnt in bottom ash,
L8
= 61.97 1.77
Boiler Efficiency = 100 – (L1 + L2+ L3+ L4+ L5+ L6+ L7+ L8) = 77.76 %

Factors Affecting Boiler
Performance
• Periodical cleaning of boilers
• Periodical soot blowing
• Proper water treatment programme and blow down
control
• Draft control
• Excess air control
• Percentage loading of boiler
• Steam generation pressure and temperature
• Boiler insulation
• Quality of fuel

Assessment of boiler performance

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