Many customers do not know what the boiler thermal efficiency and evaporation ratio mean, here, we explain the question in detail.

a. It is the ratio of heat output to heat input of the boiler.
Boiler efficiency= Heat output / heat input *100.
=steam flow (enthalpy of steam -enthalpy of feed water) / coal flow * gcv.
For example if there is a 80mw boiler with 540 dig centigrade of main steam temperature, feed water temperature of 300 dig centigrade , coal flow 56 ton, gcv 4000 kcal/kg then the boiler efficiency will be =307(826.28-242.58)/56*4000=80%.

b. It the ratio of quantity of steam generation in kg/hr to quantity of fuel consumed in kg/hr.
Evaporation ratio = quantity of steam generation/quantity of fuel consumed.For example quantity of steam Is 310 ton/hr and fuel is 55 ton/hr then the evaporation ratio is 5.63. Evaporation ratio is also known as steam fuel ratio.A drop in evaporation ratio indicates drop in boiler efficiency.Boiler evaporation ratio depends on fuel quality. Higher calorific value of fuel having higher evaporation ratio.
Value of evaporation ratio for different types of boiler is listed as-
a) Coal fired boiler- 4.0-6.0.
b) Oil fired boiler- 13.0-14.5 .
c) Gas fired boiler- 11.0-13.

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