Boiler type D is the boiler which has arrangement of drum, tubes and pipe with form D. Boiler type D has two drums; steam drum and water drum. Water flows from steam drum through convection bank tubes which connect steam drum and water drum (or can be called as mud drum). Convection wall tubes receive heat transfer from the combustion process by convection. Thus convection wall tubes also act as economizer.
Baffle is used in the convection wall tubes to arrange flue gas flow longer than without baffle, so the heat will be received by tubes higher and finally increase efficiency of boiler. After flow through convection wall tubes, the temperature of water will be higher. Water from water drum or mud drum will flow through water wall tubes to perform evaporation process. Water wall tubes receive heat transfer by radiation and convection. For more detail configuration see Figure 1 below.
In water wall tubes, water is heated and converted into steam then steam will be distributed to steam drum. Separation process between steam and water occur in steam drum. Steam can be separated from water by use cyclone, baffle or centrifugal mechanism.
In boiler type D, placement of burner is depending on fuel type. For liquid fuel such as oil, burner will be located on the wall of boiler. For solid fuel such as coal, combustion process will carry out in the floor of boiler with horizontal position or make an angle with floor and the fuel is distributed by conveyor.