Locomotive Boiler

Characteristic of boiler:

1. Horizontal Boiler
2. Multi tube Boiler
3. Straight tube Boiler
4. Fired tube Boiler
5. Single Boiler
6. Coal fired Boiler
7. Natural draft Boiler
8. Mobile Boiler
9. Low pressure Boiler
10. Internally fired Boiler
11. Natural Circulation Boiler 

 

Boiler Mountings

Various boiler mountings are as under:
1) Pressure gauge
2) Water Level Indicator
3) Fusible plug
4)Safety Valve
i) Lever Safety Valve
ii) Spring Loaded safety Valve
5) Steam stop valve
6) Feed check valve
7) Blow off cock

1. Pressure gauge

 

Function: 
1.To record the steam pressure at which the steam is generated in the boiler.
2. A Bordon pressure gauge in its simplest form consists of elliptical elastic tube bent into an arc of a circle
3. This bent up tube is called as BOURDON’S tube.
4. One end of tube gauge is fixed and connected to the steam space in the boiler.
The other end is connected to a sector through a link.





2) Water Level Indicator


• The function of water level indicator is to indicate the level of water in the boiler constantly.
• It is also called water gauge.
• Normally two water level indicators are fitted at the front end of every boiler.

3) Fusible plug
• Function: To extinguish fire in the event of water level in the boiler shell falling below certain specified limit.
• It protects fire tubes from burning when the level of the water in the water shell falls abnormally low and the fire tube or
crown plate which is normally submerged in the water, gets exposed to steam space which may not be able to keep it
cool.
• It is installed below boiler's water level.
• When the water level in the shell falls below the top of the plug, the steam cannot keep it cool and the fusible metal
melts due to over heating. Thus the copper plug drops down and is held within the gunmetal body by the ribs. Thus the steam space gets
communicated to the firebox and extinguishes the fire. Thus damage to fire box which could burn up is avoided.
• By removing the gun metal plug and copper plug the fusible plug can be put in position again by interposing the fusible
metal usually lead or a metal alloy.

4)Safety Valve                                  
Function : The function of safety valve is to release the excess steam when the pressure of steam inside the boiler exceeds
the rated pressure.
There are 4 types of safety valves:
i) Lever Safety Valve
The disadvantage of this valve is that it admits of being tempered with, and the effect of
a small addition to the weight is magnified considerably in its action on the value.
ii) Spring Loaded safety Valve
• For locomotives and marine engines both the lever and dead weight types are unsuitable for obvious reasons,
and the valve must be spring loaded, as such valve is unaffected by vibration or deviation from the vertical.
• Disadvantage :
One disadvantage of this valve is that the load on the valve increases as the valve lifts, so that pressure required
just to lift the valve is less than that required to open it fully.
iii)Dead Weight Safety Valve
• It is mainly used for low pressures, low capacity, stationary boilers of the Cornish and Lancashire types.
• Merits:
1)Simplicity of design
2)Gives quite a satisfactory performance during operation.
3)It cannot be easily tempered from the pressure adjustment view.
• Demerits:
1)Unsuitable for use on any boiler where extensive vibration and movement are experienced( e.g. locomotive and marine work).
2)It is not suitable for high pressure boilers because a large amount of weight is required to balance the steam pressure.
iv) High steam and low water safety valve
• It serves the following purposes.
(i) The steam automatically escapes out when the level of water falls below a certain level.
(ii) It automatically discharges the excess steam when the pressure of the steam rises above a certain pressure.
Use : It is generally used on Lancashire or Cornish boiler.
It cannot used in mobile boilers.

5) Steam stop valve
• A valve is a device that regulates the flow of a fluid (gases, fluidized solids, slurries, or liquids) by opening,
closing, or partially obstructing various passageways.
• Function: to shut off or regulate the flow of steam from the boiler to the steam pipe or steam from the steam
pipe to the engine.
• When the hand wheel is turned, the spindle which is screwed through the nut is raised or lowered depending
upon the sense of rotation of wheel. The passage for flow of steam is set on opening of the valve.

6) Feed check valve
Function: The function of a feed check valve is to control the supply of water
to the boiler and to prevent the escaping of water from the boiler when the pump pressure is less or pump is stopped.
i) To allow the feed water to pass into the boiler.
ii) To prevent the back flow of water from the boiler in the event of the failure of the feed pump.
The feed check valve is fitted in the water space of the boiler slightly below the normal level of the water.
 
                                                           7) Blow off cock
• Function: To drain out the water from the boiler for internal cleaning, inspection, repair or other purposes.
• It may discharge a portion of water when the boiler is in operation to blow out mud, scale or sediments, periodically.
• It is fitted on the boiler shell directly or to a short branch pipe at the lowest part of the water space.






8) Manhole and mud box: 
Manhole provides opening for cleaning, inspection and maintenance
purpose. Mud box is a collection chamber (as shown in Babcock and Wilcox boiler) for collecting the Mud.

Classification of boilers

1. Horizontal, Vertical or Inclined Boiler.

-If the axis of the boiler is horizontal, the boiler is called horizontal, 

-If the axis is vertical, it is called vertical boiler and 

-If the axis is inclined it is called as inclined boiler.

2. Fire Tube and Water Tube

-In the fire boilers, the hot gases are inside the tubes and the water surrounds the tubes.
Examples: Cochran, Lancashire and Locomotive boilers.
-In the water tube boilers, the water is inside the tubes and hot gases surround them.
Examples: Babcock and Wilcox,
 Yarrow boiler etc.

3. Externally fired and internally fired

-The boiler is known as externally fired if the fire is outside the shell.
Examples: Babcock and Wilcox boiler boiler
-In case of internally fired boilers, the furnace is located inside the shell.
Examples: Cochran, Lancashire boiler etc.

4. Forced circulation and Natural Circulation

-In forced circulation type of boilers, the circulation of water is done by a
forced pump.
Examples: Lamont, Benson Boiler etc.
-In natural circulation type of boilers, circulation of water in the boiler takes
place due to natural convention currents produced by the application of
heat.
Examples: Lancashire, Babcock and Wilcox boiler etc.

5. Higher Pressure and Low Pressure Boilers
-The boiler which produce steam at pressures of 80 bar and above are
called high pressure boilers.
Examples: Babcock and Wilcox, Benson Boiler etc.
-The boilers which produce steam at pressure below 80 bar are called low
pressure boilers.
Examples: Cochran, Cornish, Lancashire and Locomotive boiler etc.

6. Stationary and Portable

-Stationary boilers are used for power plant steam, for central station utility
power plants, for plant process steam etc.
-Mobile boilers or portable boilers include locomotive type, and other small
units for temporary use at sites.

7. Single Tube and Multi Tube Boiler

The fire tube boilers are classified as 

-single tube and 

-multi-tube boilers,
depending upon whether the fire tube is one or more than one.
Examples: Cornish, simple vertical boiler are the single tube boiler and rest
of  the boilers are multi-tube boiler.


8. According to passes
-single pass
-Multi pass

Parts of boiler

Shell: The shell of the boiler is the main container usually of cylindrical shape which contains water and steam.

Furnace: A furnace is another important part of the boiler. This may be a grate to burn coal or a burner to atomize and burn liquid fuel. Suitable area and volume should be provided of efficient combustion.

Water flow path: The water flow path is the path followed of absorption of heat from hot gases and conversion into steam. The water should be free from dissolved material in order to reduce the scaling of the heating surface.

Gas flow path: The hot gas path either in fire tube or in water tube should be arranged in such a way that maximum heat of hot gases should be transferred to the water for steam generation. The boiler efficiency mainly depends upon the gas flow path.

Steam path: In most of the boiler, the steam is taken out preferable at the top of the shell to avoid water partials being carried with the steam. To reduce the water particles carried by the steam, it mountings, water level indicator.

Fittings: The valves and gauges which are necessary for the safety of the boiler are blow-off-cock and fusible plug are some of the mountings.

Accessories: Some equipment like economizer, air pre heater and super heater are attached to the boiler to improve its overall efficiency. The economizer and air pre heater are used to extract maximum heat from the flue gases and superheater is used to increase the temperature of steam above saturation temperature. 

Definition of boiler:

It is a closed vessel in which the heat produced by the combustion of fuel is transformed to water for its conversion into steam at the desired temperature and pressure.

Babcock and Wilcox boiler

Babcock and Wilcox is a water-tube boiler is an example of horizontal inclined tube boiler it also a High Pressure Boiler.

Characteristic:

1. Horizontal Boiler
2. Muli tube Boiler
3. Water tube Boiler
4. Straight tube Boiler
5. Externally Boiler
6. Multi tube Boiler
7. Natural draft Boiler
8. Natural circulation Boiler
9. Coal fired Boiler
10. Stationary Boiler
11. Low & Medium pressure Boiler

Construction: Babcock and Wilcox boiler with longitudinal drum. It consists of a drum connected to a series of front end and rear end header by short riser tubes. To these headers are connected a series of inclined water tubes of solid drawn mild steel. The angle of inclination of the water tubes to the horizontal is about 15° or more.

Working: The fire door the fuel is supplied to grate where it is burnt. The hot gases are forced to move upwards between the tubes by baffle plates provided. The water from the drum flows through the inclined tubes via down take header and goes back into the shell in the form of water and steam via uptake header. The steam gets collected in the steam space of the drum. The steam then enters through the antipriming pipe and flows in the superheater tubes where it is further heated and is finally taken out through the main stop valve and supplied to the Steam turbine or Steam engine when needed.

The pressure of steam in case of cross drum boiler may be as high as 100 bar and steaming capacity upto 27000 kg/h.At the lowest point of the boiler is provided a mud collector to remove the mud particles through a blow-dawn-cock.
Advantages:

1. It uses both solid as well as liquid fuel for burning.
2. The drought losses as compared to other boiler in minimum.
3. As compared to other boiler the evaporation capacity is high.
4. The circulation of water is natural.
5. The defective tubes can be replaced easily.
6. It is used in power stations for generation large quantity of steam.
   

Cochran boiler

Characteristics: 

1. Vertical Boiler
2. Multi tube Boiler
3. straight tube Boiler 
4. low pressure Boiler
5. Coal fired Boiler  
6. Single tube Boiler
7. Natural draft Boiler
8. Natural circulation Boiler
9. Stationary Boiler
10. internally fired Boiler    
11. Water tube Boiler

Working: The fuel is burnt on the grate and ash is collected and disposed of from ash pit. The gases of combustion produced by burning of fuel enter the combustion chamber through the flue tube and strike against fire brick lining which directs them to pass through number of horizontal tubes, being surrounded by water. After which the gases escape to the atmosphere through smoke box and chimney.

Construction: Cochran boiler consists of a cylindrical shell with a dome shaped top where the space is provided for steam. The furnace is one piece construction and is seamless. Its crown has a hemispherical shape and thus provides maximum volume of space.
Advantages:

• The minimum floor area is required.
• Cost of construction is low.
• it can be moved and stet up take it to different location.
• Boiler has self contained furnace . No brick work setting is neccessary.
• Any type of flue can be used.

Disadvantages:

• Steam raising capacity is less due to vertical design.
• Difficult in cleaning and inspection due to vertical design.
• The capacity and pressure are limited.
• The boiler requires high head room.