In this article, you learn what is Cochran boiler? And its parts, working principles, applications, advantages, and disadvantages of Cochran boiler.
What is Cochran Boiler?
The Cochran boiler is a vertical, multi-tube boiler generally used for small-capacity steam generation. The Cochran boiler is made in different sizes of evaporative capacities ranging from 150 to 3000 kg per hour and working pressure of up to 15 bar.
The Cochran boiler consists of an external cylindrical shell and a firebox. The shell and firebox are both hemispherical. The hemispherical crown of the boiler shell gives maximum space and strength to withstand the pressure of steam inside the boiler. The hemispherical crown of the firebox is also advantageous for resisting intense heat.
The firebox and a combustion chamber are attached through a short pipe. The flue gases from the combustion chamber flow to the smokebox through a number of tubes. The gases from the smokebox escape to the atmosphere through the chimney. The combustion chamber is lined with firebricks to withstand intense heat.
A manhole near the top of the crown on the shell is provided for cleaning. At the bottom of the firebox, there is a grate, and the coal is fed in through the fire hole, which is kept closed by a fire door.
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Parts of a Cochran Boiler
The following are the main parts of a Cochran Boiler:
- Boiler shell
- Combustion chamber
- Fire door
- Fire tubes
- Fire hole
- Flue pipe
- Ash pit
- Flue gases
- Flue pipe
#1 Boiler Shell
It is made up of steel plates bent into a cylindrical form and riveted or welded together. The ends of the shell are closed by means of endplates. A boiler shell should have enough capacity to include water and steam.
#2 Combustion Chamber
The combustion chamber is the space, usually below the boiler shell, meant for burning fuel to generate steam from the water contained in the shell.
The grate is a platform, in a combustion chamber, upon which fuel is burnt. The grate generally consists of cast iron bars that are spaced apart so that air (required for combustion) can pass through them. The surface area of the grate, over which the fire takes place, is called the grate surface.
#4 Fire Door
It is a door that allows for the combustion of a boiler or furnace, or the inspection of the fire, through which the boiler or furnace is fired.
It is the space, above the grate and below the boiler shell, in which the fuel is actually burnt. The furnace is also called a firebox.
#6 Fire Tubes
It is a horizontal tube placed between the combustion chamber. The flue gases from the combustion chamber flow to the smokebox through a number of fire tubes. These fire pipes help exchange heat from hot flue gases to water.
#7 Fire Hole
The fire hole is provided at the bottom of the combustion chamber to fire the fuel inside the furnace.
A chimney is provided at the top of the boiler connected to the smokebox. The exhaust gases coming out of fire tubes pass through a smokebox and escape to the atmosphere through a chimney.
#9 Man Hole
A manhole is provided for the cleaning, repairing, and inspecting of the boiler shell.
#10 Flue Pipe
The firebox and the combustion chamber are connected through a short pipe called flue pipe. The hot flue gases from the grate insert into the combustion chamber through the flue pipe.
#11 Ash Pit
Ash pits are chambers built beneath grates in steam boiler furnaces to collect ash from the fire above. Additionally, the ash pit serves as an air supply chamber via the grate. To provide plenty of air space, there must be enough height between the ash pit’s bottom floor and the grate.
#12 Flues Gases
When fuel combustion in the combustion chamber begins, a gas with a specific temperature is produced, and this temperature rises as more fuel burns in the combustion chamber.
As flue gases reach a certain temperature, the water around them begins to heat up and continues to do so until it becomes extremely hot. These gases are referred to as flue gases.
#13 Flue Pipe
The flue pipe’s primary function is transporting hot flue gases from the grate to the combustion chamber. It connects the grate and the combustion chamber.
The smokebox is primarily used to store and discharge smoke into the chimney during the operation of the Cochran boiler. To protect the steel from acid, hot char, and rainwater damage, it is made of riveted or welded steel plate, and the floor is lined with concrete.
Working of Cochran Boiler
Coal is supplied into the grate through a fire hole and burnt. Ash formed during burning is collected in the ash-pit provided just below the grate, and then it is removed manually.
The hot gases from the grate pass through the combustion chamber to the horizontal fire tubes and transfer the heat to the water by convection. The exhaust gases from fire tubes pass through the smokebox and escape to the atmosphere through a chimney.
The smokebox is provided with a door for cleaning the fire tunes and smokebox. The working pressure and steam capacity of the Cochran boiler are 6.5 bar and 3500 kg/hr, respectively.
Cochran Boiler Mountings and Accessories
Following are the Important mounting of Cochran boiler:
- Water level indicator
- Pressure gauge
- Safety valve
- Stop valve
- Blow off valve
- Feed check valve
- Fusible Plug
1. Water Level Indicator
The water level indicator is an important fitting, which indicates the water level inside the boiler. It is a safety device, upon which the safe working of the boiler depends.
2. Pressure Gauge
The pressure gauge is used to measure the pressure of the steam inside the steam boiler. The pressure gauge is fixed in front of a steam boiler.
3. Safety Valve
The safety valve is an instrument attached to the steam boiler to prevent explosions due to the excessive internal pressure of steam. Thus, a safety valve ensures the safety of a boiler from being damaged due to excessive steam pressure.
4. Stop Valve
The function of a stop valve is to control flow within the boiler and to stop it completely when required.
5. Blow off Valve
The function of a blow-off valve is to periodically remove the sediments deposited at the bottom of the boiler while the boiler is in operation and to empty the boiler. At the same time, it is being cleaned or inspected.
6. Feed Check Valve
The function of a feed check valve is to control the flow of water from the feed pump to the boiler and to prevent the backflow of water from the boiler to the pump when the pump pressure is less than the boiler pressure or when the feed pump ceases to work.
7. Fusible Plug
The function of the fusible plug is to put off the fire in the furnace of the boiler when the water level falls below an unsafe level and thus avoid the explosion, which may take place due to overheating of the tubes and the shell.
Applications of Cochran Boiler
The following are the applications of the Cochran boiler:
- These types of boilers are used in various industries to perform process applications.
- Cochran boilers are also employed in chemical processing divisions.
- They are also installed in pulp and paper manufacturing plants.
- Most of the time, they are applied to refining units.
- They are often employed in power generation plants where large amounts of steam must be produced.
Advantages and Disadvantages of Cochran Boiler
- Low initial installation cost.
- It requires less floor area.
- Easy to operate and handle.
- Transportation of Cochran boiler is easy.
- It can use all types of fuel.
- Low rate of steam generation.
- Inspection and maintenance are difficult.
- A high room head is needed for its installation due to the vertical design.
- It has a limited pressure range.
Features of Cochran Boiler
- The Cochran boiler has a 75 percent efficiency.
- It has a maximum pressure of 15 bar and a working pressure of 7 bar.
- The Cochran boiler has a heating surface area of 120 square meters.
- The Cochran boiler has a height and shell diameter of 5.75 and 2.75 meters, respectively.
In the Cochran boiler, coal is put into the furnace through a fire hole. The air then enters the combustion chamber through the atmosphere and the fuel exits the fire hole. Heat is exchanged from the flue gases in the fire tubes to the water.
Cochrane boilers are employed in power generation plants where there is a large volume of steam with a pressure higher than about 500 kg/s. 160 bar and higher temperatures reach 550o C. Most of the time, they are employed in refining units.
As you know Cochran boiler is a vertical, multi-tube boiler commonly used for small-capacity steam production. It is low in cost and easy to operate and handle. This boiler uses any fuel.
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