The document assesses boiler performance, identifying causes of inefficiency such as poor combustion and maintenance. It provides a detailed analysis of key parameters including steam generation capacity, equivalent evaporation, and overall boiler efficiency based on operational trials. Additionally, it outlines various heat losses and the importance of conducting a thorough heat balance for accurate efficiency testing.

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2. Assessment of a Boiler
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1. Boiler performance
• Causes of poor boiler performance
-Poor combustion
-Heat transfer surface fouling
-Poor operation and maintenance
-Deteriorating fuel and water quality
• Boiler efficiency: determine deviation from
best efficiency
• Heat balance: identify heat losses

3. A) Evaporative
capacity or
Evaporative ratio
can be expressed in terms of:
a) kg of steam/hr
b) kg of steam/kg of fuel fired
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4. But different boilers give out steam at different
temperature and pressure,
Evaporative capacity expressed in terms of mass of
water getting converted to steam doesn’t give a good
comparison
Equivalent evaporation refers to the quantity of dry
saturated steam generated per unit time from feed water
at 1000C to steam at 1000C at the saturation pressure
corresponding to 1000C.
me= ma(h-hf)/h fg (i.e. bundles of Latent
Heat)
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5. It is defined as the ratio of the heat received
by 1 kg of water at the working conditions to
that received by 1 kg of water evaporated from
and at 1000C
Fe = (h –hf)/2257 KJ
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6. Ratio of heat actually utilized in the generator
to the heat supplied by the fuel.
IS 8753: Indian Standard for Boiler
Efficiency Testing
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7. Q1) During the boiler
trial
observations were
made.
Steam generation:
Coal consumed:
Rate of steam generation:
Feed water temperature:
Total heating surface area:
Total grate area:
Calorific value of coal:
for 24 hours
following
16 bar, dry saturated.
10,000 kg
2500 kg/hr
27C
3000 m2
4m2
28000 kJ/kg
Determine:
(i) the mass of coal burnt per m2 of grate per hour
(ii) the equivalent evaporation from and at 100C per
kg of coal
(iii) the equivalent evaporation from and at
100C per m2 of total heating surface per
hour
(iv) the boiler efficiency ( Onkar 11/488)
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8.  Equivalent evaporation from and at 100C per kg of coal
=
 Coal burnt per hour=416.67 kg/hr
 Coal burnt per m2 of grate per hour = 104.17 kg/m2 grate surface per hr
 Rate of steam generated per kg of coal =5.99 = 6 kg steam/kg coal
(approx)
 Heat added to steam per kg of coal = 6 [hg at 16 bar – 4.18 x 27}=16086.84 kJ
 Latent, heat from and at 100C = 2257 kJ/kg
 Equivalent evaporation from and at 100C per kg of coal = 7.13 kg
 Equivalent evaporation from and at 100C per m2 of total surface per hour
= (7.13 x 416.67)/3000 = 0.99 Kg
 Boiler efficiency = (7.13 x2257)/28000 = 57.47 %
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10. The efficiency test does not account for:
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 Standby losses. Efficiency test is to be carried out, when the boiler is operating
under a steady load. Therefore, the combustion efficiency test does not reveal
standby losses,which occur between firing intervals
 . Blow down loss. The amount of energy wasted by blow down varies over a
wide range.
 . Soot blower steam. The amount of steam used by soot blowers is variable that
depends on the type of fuel.
 . Auxiliary equipment energy consumption. The combustion efficiency test
does not account for the energy usage by auxiliary equipments, such as burners,
fans, and pumps.

11. Assessment of a Boiler
Heat Balance
An energy flow diagram describes geographically how energy
is transformed from fuel into useful energy, heat and losses
FUEL INPUT STEAM
OUTPUT
Stochiometric
Excess Air
Un burnt
Stack Gas
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Ash and Un-burnt parts of
Fuel in Ash
Blow
Down
Convection &
Radiation

12. Assessment of a Boiler
Heat Balance
Balancing total energy entering a boiler against the energy that
leaves the boiler in different forms
Heat loss due to dry flue gas
Heat loss due to steam in fuel 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 & other unaccounted loss
12.7 %
8.1 %
1.7 %
0.3 %
2.4 %
1.0 %
100.0 %
Fuel
73.8 %
Heat in Steam
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BOILER

13. Heat utilized in making steam
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Heat taken for generation of steam per kg of fuel
burnt shall be
Qsteam = msteam (h – hw)
msteam is mass of steam generated per kg of fuel
burnt,
h is enthalpy of final steam produced
and hw is enthalpy of feed water.
Qsteam = Equivalent evaporationx 2257, kJ/kg of
fuel burnt

14. A) Heat lost to flue gases
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15. B) Heat lost due to incomplete combustion
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16. C) Heat lost in unburnt fuel:
Some portion of heat may get lost in unburnt fuel, which could be given as
Qunburnt = mubf x C
In case of solid fuels this loss cannot be completely avoided
D) Heat loss due to moisture in fuel
Moisture present in fuel shall get evaporated and superheated as fuel is
burnt. For this latent and sensible heat requirement shall be met from
heat available in boiler due to burning of fuel.
Mathematically, for unit mass of fuel burnt,
Qmoisture = mmoist (hs2 – hf2) = mmoist [hg +Cp
(tg –tsat ) - hf2 ]
= mmoist [ 2676 +Cp (tg -100) - hf2 ] (as flue gases are at atm press)
where mmoist is mass of moisture per kg of fuel burnt,
hs2 is enthalpy of final (superheated) steam produced and
hf2 is enthalpy of water at boiler furnace temperature.
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17. E) Heat lost to steam by combustion of
Hydrogen per kg of fuel
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18. F) Heat loss due to convection, radiation
and other unaccountable losses
Exact quantification of these losses is not possible, therefore
these can be estimated by the difference of total heat available
and cumulative heat loss described from A to E.
Qunaccounted = (mf x C) – (Q for generating steam + Qdry flue
+Qsteam in flue + Qincomplete + Qunburnt + Qmoisture
+QHydrogen )
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19. Heat Balance Sheet
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20. Boiler trial refers to running the boiler under test conditions for its
performance estimation.
It gives the steam generation capacity of boiler, thermal efficiency of
plant and heat balance sheet of the boiler.
Under trial the boiler is run for quite long durations so as to attain
steady state. Generally the boilers are run for 4 to 6 hours duration
for the boilers of oil fired type and coal fired types. Duration of
boiler run for attaining steady state changes from boiler to boiler.
Observations are taken after the boiler attains steady state for a
duration ranging from 10–15 minutes. Measurements are made for
fuel supply, combustion analysis, steam generation rate and its
quality/state, flue gas and their analysis, temperature and pressure at
salient locations and all other measurements as required for heat
balance sheet preparation.
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