To study the constructional features of BABCOCK and WILCOX BOILER | BME Lab Manual

To study the constructional features of BABCOCK and WILCOX BOILER

OBJECT

To study the constructional features of BABCOCK and WILCOX BOILER.

APPARATUS

A model of BABCOCK and WILCOX BOILER.

INTRODUCTION

It is horizontal, stationary multi-water tube boiler.

CONCLUSION

It consists of a large cylindrical shell made of steel plates. There is large number of parallel tubes inclined at an angle of 5^O – 15^O to the horizontal. The upper ends of the tubes are enclosed in a chamber known as UPTAKE HEADER while the lower ends of the tubes are enclosed in another chamber called DOWNTAKE HEADER. There is an arrangement for the grate below the uptake header. Below the grate there is an ash pit. Where the ash produced by the combustion of the coal is collected. There are FIRE BRICK BAFFLES for reflecting the hot gases. These baffles are arranged in such a way that the hot gases may pass in SINE WAVE form. First the hot gases rise upward and then go down and then rise up again and finally escape to the chimney. Thus these hot gases conduct maximum amount of heat to the water available inside the tubes as maximum surface area of the tubes is exposed to them. At the lower end of the down take header there is a blow off cock fitted for the removal of impurities of water from time to time. There is a super heater fitted for super heating the steam, which increases the efficiency of the boiler. The outer surface of the inclined 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 various fittings of this boiler are:

1. Feed Check Valve

2. Pressure gauge

3. Water Level Indicator

4. Safety valve

5. Steam Stop Valve

6. Blow off Cock

7. Fusible Plug

8. Super Heater

These are used in the boiler to increase the temperature of steam above its saturation temperature. Passing the steam through a small set of inclined tubes and hot gases over them does this. Super heated steam is absolutely essential for power generation.

Figure of BABCOCK and WILCOX BOILER

WORKING

Water is fed into the boiler shell through the feed check valve. It goes into the cylindrical horizontal tube and inclined tubes. The water level gauge indicates the level of water. Coal is added to the grate and fired. Water in the upper portion of the tubes get heated first and rises up due to decreased density and passes into the drum when steam and water are separated. Now cold water from the down take header comes to take the place. In this way natural circulation of water is carried on by keeping the tubes inclined to an angle of about 15^O to the horizontal. During the first turn of the super heater becomes super heated steam. Now the super heated steam coming out through the super heater is supplied through the steam stop valve. The damper controls the rate of burning and thereby the steam generation. A chain passing through a set of pulleys operates the damper.

At the end of the down take header, a mud box is connected from where impurities can be removed. As shown in the sketch, the boiler is provided with two INSPECTION DOORS, Compared to the fire tube boiler, evaporative capacity, the pressure of steam and thermal efficiency of the boiler will be higher. It is suitable for small size thermal power plants and other industrial units.