The boilers is comprised of two basic systems. One system is the steam water system also called the waterside of the boiler. In waterside, water is introduced and heated by transference through the water tubes, converted to steam, and leaves the system as steam.
Boilers must maintain a chemical balance. The manner in which this is done can interact with the feedwater control system. The amount of blowdown must be considered in the feedwater control scheme, especially if the blowdown is continous. Often the blowdown flow is divided by concentration ratio times the feedwater flow. Continous blowdown is the common method for controlling the chemical concentration. On large boilers this may be done automatically by measuring the water conductifity to control the blowdown rate. The blowdown rate may also be achieved combining the conductifity with ratio control of blowdown, ratioing blowdown to feedwater flow. In utility plants, conductifity is usually measured and blowdown is achieved manually. This required on a periodic basis or when the conductifity gets too high.
Conductifity is measured in micro mhos which is equal to the reciprocal of 1 mechanical ohm (resistance). The other boiler system is fuel air-flue gas system, also referred to as the fireside of the boiler. This system provides the heat that transferred to the water. The inputs to this system are the fuel and air required to burn the fuel. The fuel and air chamber is also referred to as the windbox. The outputs are the flue gas and ash.
