A Bi-Drum Boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Flue gasses of burned fuel inside the furnance heats water in the steam generating tubes. . Here, saturated steam is drawn off the top of the drum.
For superheated steam, the steam will re-enter the furnace through a superheater to become superheated. Superheated steam is a dry gas and therefore used to drive turbines, since water droplets can severely damage turbine blades.
Cool water at the bottom of the steam drum returns to the feedwater drum via downcomer tubes, where it pre-heats the feedwater supply. The feedwater is supplied to the steam drum and the downcomers supply water to the bottom of the waterwalls. Exhaust gases are also used to pre-heat the air blown into the furnace and warm the feedwater supply to increase economy of the boiler.
Bi-Drum Boiler comes in -
1. Single Drum Water Tube Boiler
2. Bi-Drum Water Tube Boiler