Cochran boiler – This is the best vertical, multi-tubular fire tube boiler. It consists of a number of horizontal tubes, called flue tubes, that fit into a vertical cylindrical shell with a hemispherical top.
Working of Cochran boiler
Cochran boiler is a fire tube boiler. the fuel is inserted into the boiler through the grate. The fuel is burnt inside the fire box and channeled into the combustion chamber.
Then the smoke or the fire passes through the tube provided inside the boiler around which the water is present so that the water can absorbed the heat from the fire tube and converted into steam.
The smoke flow the smoke box and gets out through the chimney around the shell of the boiler a brick liner is provided which does not allow to dissipate the heat from the combustion chamber.
The brick liner is made of a refractive material. The steam which is generated is accumulated or is obtained inside the hemispherical shell. A water level indicator is provided to check the amount water.
Pressure gauge is provided to check the intensity of internal pressure inside the shell. Stop valve is use to decrease the internal pressure whenever it crosses the pressure limit. A man hole is provided for maintains of boiler.
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Classification of steam generator or boiler
definition of boiler – Boiler is a device use to generate steam. This generated steam is supplied or turbines to produce electricity. The generated steam can also be used for process work and heating purpose in mills, sugar factories. Boiler is also know as steam generator.
In cochran boiler there are 7 types of classification of boilers :
(1) According to the contents in the tube
According to the contents in the tube steam boilers are of 2 types (1) Fire Tube or Smoke Tube Boiler (2) Water Tube Boiler.
If hot flue gasses the boiler furnace, flows through the tubes and water surrounds these tubes, the boiler is know as a fire tube boiler. Examples are Cochran boilers, Cornish boilers.
If water flows through tubes, which are surround by fire or hot flue gases from a boiler furnace, the boiler is know as a water tube boiler. So examples are Babcock Wilcox, Stirling etc.
(2) According to the position of the furnace
According to the position of the furnace, this boiler is classified as (1) internal fired boiler (2) external fired boiler. The furnace area (the space in which the fuel combustion takes place) is provided inside the boiler shell.
Therefore it is completely surrounded by a surface cooled by water. Most fine tube steam boilers are fined internally. So examples of internally ignited boilers are Lancashire, locomotive boilers.
If the furnace is arrange outside the boiling water zone, the boiler is know as an external fired boiler. Example Babcock and Wilcox Boilers.
(3) According to the axis of the shell
According to the axis of the shell it is of two types (1) vertical boilers and (2) horizontal boilers. So in case of vertical steam boiler the axis of the shell is vertical. Example Cochrane boiler.
And the axis of the shell is horizontal in the case of horizontal steam boilers, for example Lancashire, Locomotive and Babcock & Wilcox.
(4) According to the number of tubes
According to the number of tubes, it is of two types that is (1) Single tube boiler and other is (2) Multitube boiler. In case of single tube boiler there is only one fire tube or water tube.
Hence simple vertical boilers, Cornish boilers are single tube as they have only one flue tube. But in case of multitube boilers having two or more fire tubes or water tubes, Cochrane, Babcock, Wilcox and locomotive boilers are multitube boilers.
(5) According to the method of circulation of water and steam
According to the method of circulation of water and steam, they are classified as (1) natural circulation boilers (2) forced circulation boilers.
If the circulation of water in a boiler is due to convection currents generate by heat, the boiler is refer to as a natural circulation boiler. So example are Babcock and Wilcox boilers.
But in the case of forced circulation boilers, there is a forced circulation of water by a centrifugal pump driven by some external power. Examples of forced circulation boilers are lamont, benson boiler.
(6) According to the use
According to the use, it is of two types (1) stationary boilers (2) mobile boilers. If the boiler is use only in one place then they are called stationary boilers.
So this type of boiler is use in power plants and industrial works. For Example Lancashire boiler. Mobile steam boilers are those that move from one place to another, So these are boiler locomotives and marine boilers.
(7) According to the source of heat
According to the source of heat it is of three types and that is (1) Combustion of solid fuel (2) Combustion of liquid fuel (3) Combustion of gaseous fuel.
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Mounting and accessories are also the main function in cochran boiler, so let’s see what is mounting and accessories.
Mounting of boiler
In cochran boiler the boiler mounting are those mechanical appearances which are essential for operating a boiler smoothly, softly and safely know as mounting.
So there are different types of boiler mountings.
- Pressure gauge
- Water level indicator
- Fusible plug
- Steam stop valve ( Stop valve )
- Safety Valve
- Blow off cock
- Feed check valve
(i) Pressure gauge
It is present in front of the boiler. The function of pressure gauge it indicates the gauge pressure of steam with in the boiler.
(ii) Water level indicator
It is also present in front of the boiler and generally present two in number. So it indicates the level of water present in the boiler. And it is shows the instantaneous level of water that is present inside the steam boiler. Which is necessary for its proper working.
(iii) Fusible plug
It is present to the crown plate of the furnace or firebox. Its function is to extinguish fire in the furnace when the water level in the boiler falls to an unsafe limit. This avoids the explosion that may takes place because of the overheating of the furnace plate.
(iv) Steam stop valve ( Stop valve )
It is usually present on the highest part of the boiler with the help of a flange. So the main function of the steam stop valve is
- To control the flow of steam from the boiler to the main steam pipe.
- To completely shut off the steam supply when required.
(v) Safety valve
Safety valve are attached to the steam boiler chest. It prevent the boiler pressure from rising above its normal working pressure by automatically opening when the boiler pressure exceeds the normal working pressure.
(vi) Blow of cock
It is present at the bottom of the boiler drum. The function of a blow off cock is to remove periodically the sediments or dust or unwanted particles deposited at the bottom of the boiler while the boiler is in operation.
(vii) Feed check valve
It is non-return valve and fitted to a screwed spindle to regulate the lift. It is to control the flow of water from the feed pump to the boiler and to prevent they back flow of water from the boiler to the form when the pump pressure is less than they boiler pressure.
Accessories of boiler
The boiler accessories are the integral parts of the boiler they are use in the boiler to improve its efficiency. Boiler accessories are
- Economiser
- Super heater
- Steam separator
- Steam trap
- Feed pump
- Air preheater
(i) Economiser
It is use to heat the feed water by the utilization of heat from the hot fuel gases before it leaves the chimney. A economiser improves the economy of the steam boilers.
(ii) Super heater
A super heater is an important accessory use in the boiler. So Its main function is to increase the temperature of saturated steam without raising its pressure.
(iii) Steam separator
A steam separator is fitted before the steam turbine to separate water particles from steam.
(iv) Steam trap
It is the automatically to drain a way the water collected in the steam pipe.
(v) Feed pump
The function of feed pump is to feed the water into the boiler through the form.
(vi) Air preheater
Air preheater is the device to increase the temperature of air before enters into the furnace.
For types of friction.
From the above discussion we learn how cochran boiler work and their main function and hope you like this theme, Thank you.