Babcock and Wilcox Boiler is a horizontal, externally fired, water tube, natural circulation boiler.
This boiler is named after the persons who discovered it. It was discovered by Herman Babcock and Stephen Wilcox in 1967.
This boiler is called natural circulation boiler because the circulation of water in the boiler is maintained by a convective current.
This boiler is used to produce high pressure steam and with this high pressure steam, power is produced in power generation industries.
The high pressure steam produced by this boiler can also be used for some other purposes.
Parts Of Babcock and Wilcox Boiler:
It has a cylindrical shell. It is made up of steel. This shell is filled with water. Nearly, 2/3 rd of the shell is filled with water. This shell contains both water and steam.
The shell is provided with two supports to remain in fixed position.
3 Water Pipes or Tubes:
Water Pipes are present below the boiler. These pipes are inclined at an angle of 15 degrees and the diameter of this pipe is nearly 10 cm. As it is inclined, so the water tubes are not completely filled with water and water and steam coexist and can be easily separated.
4 Feed Check Valve:
Feed Check Valve is used to fill the shell with water.
The damper is used to regulate air in the boiler.
The superheater is used to increase the temperature of the steam to a required level and send it to the steam stop valve pipe.
7 Super Heater Tubes:
After removing the moisture content from steam the air priming pipe sends the steam to the superheater tubes where superheater superheats the steam.
The furnace of this boiler is present outside the boiler as it is externally fired boiler. It is placed below the upper header.
Grate is present outside the boiler shell. It is generally made up of cast iron. The solid fuel (coal) is kept over this grate and burnt.
10 Fire Door:
Fire Door is used to ignite the solid fuel in the furnace.
Baffles are also known as deflectors. They are made up of fire-brick. They are used to deflect the flue gases so that they do not pass directly. Also, the area of contact and time of contact increases between the flue gases and water pipes, and hence the efficiency of the boiler increases.
Two baffles are used in this boiler.
12 Anti Priming Pipe:
The steam in the shell has moisture content. So an anti priming pipe is used to reduce the moisture content from the steam. This anti priming pipe has small holes which reduces moisture from steam.
13 Upper Header and Lower Header:
The water pipes are fixed between the upper header and lower header. These water pipes are fit on the holes of upper header and lower header. The upper header and lower header are connected to the shell via pipes.
The lower header is present at the rear end of the boiler and it receives water from the rear end of the shell and transfers to the water tubes.
The upper header is present at the front end of the boiler. Its main function is to transfer steam and water mixture to the shell.
14 Mud Box:
Below the lower header, a mud box is present. This mud box is used to collect the foreign particles or mud from the water coming from a cylindrical shell through water pipe. This mud can be removed later.
15 Man Hole:
Man Hole is an entry for a person to enter into the boiler and clean the boiler from inside or change its parts at the time of its maintenance. It is sometimes known as an inspection hole.
16 Blow Off Pipe:
Blow Off Pipe is used to remove the mud particle from the mud box and extra water from the boiler.
Mountings and Accessories
1 Pressure Gauge:
Pressure Gauge is used to check the pressure of steam inside the boiler.
2 Safety Valve:
The safety valve fuses when the pressure of steam exceeds the safety level in the boiler, the safety valve automatically releases the pressure from the boiler.
3 Water Level Indicator:
The water level indicator is used to indicate the level of the water and setam in the boiler shell. The lower part of the water level indicator is connected to the water and the upper part of it is connected to the steam.
4 Fusible Plug:
Fusible plug is used for the safety of the boiler. It fuses when the temperature of the boiler reaches above the safety level due to failure of water supply or some other reason.
5 Stop Valve:
It is used to stop the superheated steam. Steam can be released as per requirement and can be transferred to the required area.
Working of Babcock and Wilcox Boiler:
At first, the boiler shell is feed with water using feed pump. As the water is feed to the boiler shell, water starts flowing from the boiler shell to the water tubes via down take header or lower header.
After that when the water tubes are filled with water, the coal is burnt over the grate because of which hot gases are produced. These hot gases travel over the water pipes and the baffle plates will reflect the hot gases and these gases will undergo an up and down motion or zig-zag motion over the water tubes.
After passing over the water pipes the hot gases get out of the boiler through a passage.
Since the hot gases flow over the water pipes continuously, the water pipes start getting heated due to the hot gases and the water inside the water pipes starts getting heated uniformly.
When the water in water pipes gets heated, the density of the water decreases and due to this water starts flowing upwards towards the upper header.
As the water flows upward in the water pipe its density decreases continuously and we get a mixture of water and vapour in the upper header.
As the water tubes are inclined, so the water tubes are not completely filled with water and water and steam coexist in the water tubes and can be separated easily.
This mixture of water and vapour reaches the cylindrical shell from the upper header and gets collected at upper side of boiler shell. After reaching the shell, the mixture of water and vapour enters the anti priming pipe.
The anti priming pipe will minimize the moisture content of the wet steam. After that, the anti priming pipe supplies the moisture-free or dry steam to the superheater.
This steam will travel in the superheater tube and due to flue gases, it gets superheated and converts into superheated steam.
After converting into superheated steam it reaches the stop valve pipe and this stop valve pipe is connected to the stop valve where the superheated steam stops.
This stop valve can be opened or closed as per requirement and the steam can be provided to the required system.
This steam is generally sent to steam turbine to generate electricity.
Advantages of Babcock and Wilcox Boiler:
1) This boiler occupies very little area.
2) Any defect part can be easily replaced.
3) It has very high steam generation capacity from 2000 to 4000 kg/hr.
4) Inspection can be done even at the time of working.
5) This boiler can be cleaned easily.
6) It can expand and contract easily.
5) Draught loss is very less.
Draught: For those who don’t know, draught is the small difference in the pressure of outside air and pressure of gases within a furnace or chimney at grate level, which causes flow of air/hot floue gases to take place through the boiler.
1) The maintenance cost of this boiler is high.
2) It requires water treatment before operating it inside the boiler as it is not much suitable impure and sedimentary water.
3) It requires a continuous flow of water for its working. If the water supply is discontinuous even for a short period of time, this boiler gets overheated.
The main application Babcock and Wilcox boiler to produce high-pressure steam in power generation industries.
This high pressure steam produced by this boiler is used to generate electricity.