The following article will guide you about how to calculate boiler efficiency by indirect method.
Definition of Boiler Efficiency:
The boiler efficiency is defined as the ratio of heat actually used for producing steam in a certain period to the heat supplied in the furnace during the same period. Both quantities being measured in the same units. The boiler efficiency also serves as an indication of the boiler performance and is obviously independent of the quality of the fuel.
The above equation does not take into account the heat lost in the unburnt fuel. The loss has to be subtracted from the denominator for more accurate results.
In this method, the efficiency can be obtained by substracting the heat loss fractions from 100.
Boiler efficiency = 100 – (L1 + L2 + L3 + L4 + L6 + L7 + L8).
Where L1 = Loss due to dry flue gas
L2 = Loss due to hydrogen in fuel
L3 = Loss due to moisture in fuel
L4 = Loss due to moisture in air
L5 = Loss due to partial combustion to CO
L6 = Losses due to radiation, convection and unaccounted
L7 = Unburnt losses in fly ash
L8 = Unburnt losses in bottom ash.
The following parameters are measured for computation of boiler efficiency:
(i) Percentage of CO2 or O2 in flue gas
(ii) Percentage of CO in flue gas
(iii) Temperature of flue gas.
(iii) Feed water
(iv) Condensate water
(v) Combustion air.
(3) Temperature Measurement:
(iii) Make up water
(iv) Condensate return
(v) Combustion air
(vii) Boiler feed water.
(4) Pressure Measurement:
(iii) Combustion air
(5) Water Condition:
(i) Total dissolved solids
(ii) pH value
(iii) Blow down rate and quantity.
Calculation of Boiler Efficiency by Indirect Method:
Boiler efficiency is estimated by the calculation of various losses in the boiler.
The fuel analysis is normally made on the basis of proximate analysis and the proximate analysis can be converted to ultimate analysis.