133.What is Over-firing and Under-firing? What parameter of the boiler will be affected much? How to overcome?

When load is increased in a boiler, as a dynamic compensation, fuel fired will be more than that required for steady state. This is called over firing. Similarly when load is decreased in a boiler fuel fired will be less than that of steady state. This condition is under firing.

The temperature pick-up in the final super heater will vary considerably. The value of change is proportional to the % of mismatch. The feed forward loop input shall be compensated suitably to over come the effect of mismatch.