BABCOCK WILCOX BOILER
Babcock Wilcox boiler is a type of straight water tube boiler. In a water tube boiler, the water is inside the tubes and hot gases flow over the tubes.
Constructional Features of the Babcock Wilcox boiler:
- The boiler shell known as water and steam drum is made of high quantity steel. It is connected by short tubes with the uptake header or riser and by longer tubes to the down take header. The water level in the drum is slightly above the center. The water tubes are connected to the top and bottom header and are kept inclined at an angle of 15° to the horizontal.
- The furnace is arranged below the uptake header. Coal is fed to the grate through the fire door. Two firebrick baffles are arranged in such a manner that the hot gases from the grate are compelled to move in the upward and downward directions.
- The outer surface of the water tubes and half of the bottom cylindrical surface of the drum form the heating surface through which heat is transferred from the hot gases to the water.
- The front portion of the water tubes come in contact with the hot gases at higher temperature. So the water from this portion rises in the upper direction due to decreased density and passed into the drum through the uptake header. Here the steam and water are separated and the steam being lighter is collected in the upper part of the drum.
Main features of the Babcock Wilcox boiler:
1. The evaporative capacity of this boiler is high compared with other boilers (20,000 to 40,000 kg/hr). The operating pressure lies between 11.5 to 17.5 bar.
2. The draught loss is minimum compared with other boilers.
3. The defective tubes can be replaced easily.
4. The entire boiler rests over an iron structure, independent of brick work, so that the boiler may expand or contract freely. The brick walls which form the surroundings of the boiler are only to enclose the furnace and the hot gases.
Working of the Babcock Wilcox boiler:
- During the first turn of the hot gases, the gases are passed over the super-heater tubes and the steam is passed through the super-heater and becomes superheated steam.
- The steam is taken into the super-heater from the steam space of the drum through a tube as shown in the figure. The superheated steam coming out through super-heater is supplied through steam-pipe and steam stop valve to the turbine.
- When the steam is being raised from cold boiler, the super-heater is filled with water to the drum water level. This is essential to prevent the overheating of the super-heater tubes.
- The super-heater remains flooded with water until the steam reaches the working pressure. Once the rated pressure of steam is achieved in the boiler, then the water from the super-heater is drained and steam is fed to it for superheating purposes.
- A mud box is fitted to the down header as shown in the figure.
- The impurities and mud particles from the water are collected in the mud box and they are blown-off from time to time by means of a blow off valve as shown in the figure.