Babcock and Wilcox Boiler Definition, Construction, Working, Applications, Advantages & Disadvantages have been discussed in detail, in this article.
Babcock and Wilcox Boiler is a horizontal drum axis, natural draft, natural circulation, multi-tubular, stationary, high pressure, solid fuel fired, externally fired water tube boiler, used to produce high pressure steam in ships for the function of other machineries and the production of electricity.
Babcock and Wilcox Boiler consists of the following parts
- Super heater
- Inspection Door
- Pressure Gauge
- Mud Collector
- Feed Check Valve
Details about each part of a Babcock and Wilcox Boiler:
Steam drum is a very important part of Badbock and Wilcox boiler . In steam drum one half of drum which is horizontal is filled up with water and steam remains on the other half. In steam drum separation of steam takes place.
A number of small diameter steel tubes are fitted at angle of 5 degree to 15 degree with horizontal to promote water circulation .These steel tubes are arranged in the combustion chamber in a zigzag way so that more surface area of the tube is exposed to hot gases.
- Down Take Header:
Down take header is present at the bottom end of the boiler and connects the water tubes to the rear end of the drum and it receives water from the drum.
- Up Take Header:
The drum is connected at one end to the uptake header by short tubes and at other end to the down-corner by long tubes.
Super heater is used to raise temperature of steam up-to superheat level . The boiler is fitted with a super heater tube which is placed just under the drum above the water tubes.
The fire-brick baffles, two in number are provided to deflect the hot flue gases uniformly throughout the boiler.
Inspection doors are provided for cleaning and inspection of the boiler during running and shut down condition.
The pressure gauge is used to measure the pressure of steam inside boiler. The Gauge is usually mounted on the front top shell or drum such that it should be clearly visible to the operator.
It’s primary function is to provide adequate space for fuel particles to burn completely and to cool the flue gas to a temperature at which the convective heating surfaces can be operated safely.
It is present at the bottom of down take header and used to collect mud from the water which would be then formed to steam.
Feed Check Valve
These are used to control the flow of water from feed to the pump of the boiler and further prevents the backflow of water from boiler to pump when the pressure is more than pump pressure or when the feed pump stops working.
Damper is a device which allows you to control the flow of gasses through it. It is also used to maintain the furnace pressure by controlling flow of flue gasses , or in the bypass flue line to maintain steam temperature.
Working of Babcock and Wilcox Boiler
Coal is fed to the grate through the fire door and is burnt.
Flow of Flue Gases
The hot flue gases rise upward and pass across the left-side portion of the water tubes. The baffles deflect the flue gases and hence the flue gases travel in the zig-zag manner (i.e., the hot gases are deflected by the baffles to move in the upward direction, then downward and again in the upward direction) over the water tubes and along the super heater. The flue gases finally escape to atmosphere through chimney.
That portion of water tubes which is just above the furnace is heated comparatively at a higher temperature than the rest of it. Water, its density being decreased, rises into the drum through the uptake-header. Here the steam and water are separated in the drum. Steam being lighter is collected in the upper part of the drum. The water from the drum comes down through the down –comer into the water tubes.
A continuous circulation of water from the drum to the water tubes and water tubes to the drum is thus maintained. The circulation of water is maintained by convective currents and is known as ‘natural circulation‘.
A damper is fitted to regulate the flue gas outlet and hence the draught. The boiler is fitted with necessary mountings. Pressure gauge and water level indicator are mounted on the boiler at its left end. Steam safety valve and stop valve are mounted on the top of the drum. Blow-off cock is provided for the periodical removed of mud and sediments collected in the mud box.
Advantages of Babcock and Wilcox Boiler
Following are the advantages of Babcock and Wilcox Boilers:
- Steam can be generated at very high pressures.
- Heating surface is more in comparison with the space occupied, in the case of water tube boilers.
- Steam can be raised more quickly than is possible with a fire tube boiler of large water capacity. Hence, it can be more easily used for variation of load.
- The hot gases flow almost at right angles to the direction of water flow. Hence maximum amount of heat is transferred to water.
- A good and rapid circulation of water can be made.
- Bursting of one or two tubes does not affect the boiler very much with regard to its working. Hence water tube boilers are sometimes called as safety boilers.
- The different parts of a water tube boiler can be separated. Hence it is easier to transport.
- It is suitable for use in steam power plants (because of the various advantages listed above).
Disadvantages of Babcock and Wilcox Boiler
Disadvantages of Babcock and Wilcox Boilers are:
- It is less suitable for impure and sedimentary water, as a small deposit of scale may cause the overheating and bursting of tubes. Hence, water treatment is very essential for water tube boilers.
- Maintenance cost is high.
- Failure in feed water supply even for a short period is liable to make the boiler overheated. Hence the water level must be watched very carefully during operation of a water tube boiler.
Applications of Babcock and Wilcox Boilers in Ships
Onboard ships, the following are the applications of Babcock and Wilcox Boilers:
- It is used to generate high pressure steam which is then used to generate electricity in ships and produce energy and power to drive equipment and machinery in ships.
- It is used for propulsion
- It is used along with reciprocating engines.
- It is used to drive the cargo pumps in tankers ships to transfer oil.
- Winch and windlass are also driven by steam in some ships.
- Used in accommodation heating.
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