Frequent changes to the boiler fuel firing system destabilises combustion, resulting in higher fuel consumption. This leads to poor
boiler efficiencies and higher fuel bills
Most boilers operate on a
combustion control scheme where,
for variation in combustion, air flow is
varied first followed by fuel flow. This
is called a “cross limiting” control
scheme. Thus when the boiler fuel
firing is changed from low fire to high
fire, the burner first increases the air
flow and then the fuel flow. During this
period greater heat is carried away
with the air to the stack reducing the
overall efficiency. Same is the case
when the burner switches from high
fire to low fire.
Frequent changes to fuel firing
system thus destabilise combustion,
resulting in higher fuel consumption.
By rule of thumb, the maximum
acceptable flue gas temperature is
30 C over the steam temperature.
o Also every 20 C deviation from
optimum flue gas temperature
increases the fuel consumption by
1%. These losses are typical for
plants with frequent fluctuation in
For new establishments selecting the
right capacity boiler, it is important to
bear in mind the load fluctuations
typical to a sector. Right boiler
capacity selection in the first place
eliminates operational losses.
In case of existing establishments, by
analysing the plant load pattern, it is
possible to make adjustments to the
boiler so as to minimise the losses.