Frequent changes to the boiler fuel firing system destabilize 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 over all efficiency. Same is the case when the burner switches from high fire to low fire.
Frequent changes to fuel firing system thus destabilize combustion, resulting in higher fuel consumption. By rule of thumb, the maximum acceptable stack gas temperature is 30oC over the steam temperature. Also every 20oC deviation from optimum flue gas temperatures increases the fuel consumption by 1%. These losses are typical for plants with frequent fluctuation in steam load.
For new establishments selecting the right capacity boiler, bearing in mind the load fluctuations typical to a sector, is important. Right boiler capacity selection in the first place eliminates these operational losses.
In case of existing establishments, by analyzing the plant load pattern, it is possible to make adjustments to the boiler so as to minimize the losses.