Q. Basic requirements of a control scheme of steam generators?

The basic requirements of a control scheme are:

• Master steam pressure control by feedback to the water flow controllers on each boiler. There is one water flow controller per pass for each boiler.

• Ability to balance the steam load, as necessary, between the boilers. This should allow any combination of boilers to be taken out of service without seriously affecting the operation of the control scheme.

• Air-fuel cross-limiting on each boiler to prevent operation with excess combustibles.

• Combustion air-gas ratio control for each boiler which may easily be enhanced with excess oxygen control.

The control scheme should easily be interpreted, and have the capacity to display actual airflows, gas flows, ratios, etc. This feature is particularly important to maintain the service factor of the control scheme.