Mechanism of Combustion Air Supplied into Steam Boiler

There are some mechanisms of combustion air will be supplied into steam boiler:

§         Natural Draft

If the height of stack is higher from sea level, so pressure above stack will be lower than one atmosphere. So a steam boiler’s exit pressure being less than the steam boiler furnace pressure. Pressure tends to move from higher space to lower space. Beside that difference temperature between the outside air and inside flue gas also creating suction in the furnace of steam boiler. Parameter of height stack, pressure, and temperature can generate natural draught.

§         Forced  Draft

Force draught is created by Force Draft (FD) Fan blowing air which taken from atmosphere to the furnace.  FD Fan can force air to furnace until the pressure will be positive.

§         Induced Draft

Induced draught is created by Induced Draft (ID) Fan located at the steam boiler outlet which sucks air from the furnace and discharge them at the stack exit. Steam boiler is maintained in negative pressure to prevent flames leaking out and make certain steam boiler is operated safely with avoid fire of insulation and casing.

§         Balanced Draft

Balanced draught is created by employ FD Fan and ID Fan together. In Balance draft operation, the furnace pressure is maintained near to the atmospheric pressure. FD Fan force air to make combustion take place, in turn ID Fan pull flue gas (product of combustion) from steam boiler through to stack.