CIRCULATION
Circulation is the flow of water, steam or both through the tube circuits of a boiler (from boiler drum,boiler down comer, riser water walls ). Adequate circulation is necessary for all the circuits to remove the heat from the boiler furnace and cool the heating surfaces by carry the heat. Due to carry the heat from the the metal surfaces the temperature of metals remain cools within a specific limit. Sufficient circulation in provided in steam water circuit to avoid any salts deposits on the inner metallic surface of boiler. In a circuit if the fluid enters at the inlet and leaves the outlet to the next circuit it is a once through system. If part of the fluid from the outlet of the circuit is returned to the inlet of the same circuit it is a re circulation system. In a boiler the following circuits always adopt once through system. Economiser Super heaters Re heaters In these circuits the inlet pressure of the fluid effects the circulation. The water walls or evaporator circu