Babcock and Wilcox boiler is a water tube, horizontal, multitubular, external fired boiler. It covers wide range of pressures compared to fire tube boilers. It has steam generating capacity from 20,000 to 40,000 kg/h. It operates at an average 20–22 bar but it can be operated at maximum 40–42 bar. Its tubes are inclined at 5° to 15° for natural circulation. The diameter and length of tubes are designed as per requirement of pressure of steam. Baffles are arranged normally for two or three passes of combustion gas. All mounting and accessories shown in Figure 4.11 are explained later in this chapter. There is natural circulation of water. Water circulates from drum to tube and tube to drum with the help of downtake and uptake headers. To get superheated steam, the steam collected at upper space of the drum is recirculated through superheater. The hot flue gas as a result of combustion rises up and moves in the direction as directed by the baffles. Tubes get exposure of hot gas and transfer the heat to the water flowing inside the tubes. Hot water rises and reaches into the boiler drum and cold water comes down into the tubes. Water circulates due to natural circulation produced by temperature differences.
Figure 4.11 Babcock and Wilcox Boiler
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