Evaporation ratio of
boiler reduces with time, due to poor combustion, poor operation and
maintenance and heat transfer fouling.
Deterioration of fuel quality and water quality also leads
to poor performance of boiler. Hence for performance
test it is necessary to find out current evaporation ratio of boiler. Any observed
abnormal deviations could therefore be investigated to pin point the problem
area for necessary correction action.
Evaporation Ratio
= Quantity of steam generation/ Quantity of fuel consumption
Boiler evaporation
ratio also known as steam to fuel
ratio.
Boiler evaporation ratio monitoring is best for any boiler
when its own performance is compared on day to day basis as a performance
indicator. A drop in boiler evaporation ratio indicates a drop in boiler
efficiency.
Values of evaporation ratio for different type of fuels are
as below:
Coal Fired Boiler - 4.0 to
6.0
Oil fired Boiler - 13.0
to 14.5
Gas fired Boiler -
11.0 to 13.0
Boiler evaporation ratio depends on fuel quality or fuel
calorific value. Higher calorific value fuel getting higher evaporation ratio.
Boiler evaporation ratio is unit less as it is ratio.
EXAMPLE (Natural Gas
fired Boiler):
If quantity of steam generated by natural gas fired boiler
is 4000 Kg/hr and quantity of natural gas consumed by boiler is 330 Kg/hr.
Then evaporation ratio of Boiler
= Quantity of steam
generated by boiler in Kg/hr/ Quantity of Fuel consumed by boiler in Kg/hr
=4000 Kg/hr/330 Kg/hr
Evaporation ratio of
NG fired Boiler = 12.12
EXAMPLE (Coal fired
Boiler):
If quantity of steam generated by natural gas fired boiler
is 6000 Kg/hr and quantity of coal consumed by boiler is 1200 Kg/hr.
Then evaporation ratio of Boiler
= Quantity of steam
generated by boiler in Kg/hr/ Quantity of Fuel consumed by boiler in Kg/hr
=6000 Kg/hr/1200 Kg/hr
Evaporation Ratio of
coal fired boiler = 5.0
EXAMPLE (Oil fired
Boiler):
If quantity of steam generated by natural gas fired boiler
is 10000 Kg/hr and quantity of oil consumed by boiler is 710 Kg/hr.
Then evaporation ratio of Boiler
= Quantity of steam
generated by boiler in Kg/hr/ Quantity of Fuel consumed by boiler in Kg/hr
=10000 Kg/hr/710 Kg/hr
Evaporation Ratio of
oil fired boiler = 14.08