Instrumentation and controls in a boiler plant encompass an enormous range of
equipment from simple industrial plant to the complex in the large utility station.
The boiler control system is the means by
which the balance of energy & mass into and out of the boiler are achieved.
Inputs are fuel, combustion air, atomizing air or steam &feed water. Of these,
fuel is the major energy input. Combustion air is the major mass input, outputs
are steam, flue gas, blowdown, radiation & soot blowing.
Boiler control systems contain
several variable with interaction occurring among the control loops for fuel,
combustion air, & feedwater . The overall system generally can be treated
as a series of basic control loops connected together. for safety purposes, fuel
addition should be limited by the amount of combustion air and it may need minimum
limiting for flame stability.
Amounts of fuel and air must
be carefully regulated to keep excess air within close tolerances-especially over
the loads. This is critical to efficient boiler operation no matter what the unit
size, type of fuel fired or control system used.
Industrial boilers are subject to wide load variations and
require quick responding control to maintain constant drum level. Multiple element
feed water control can help faster and more accurate control response.