What is Cochran Boiler?
Cochran Boiler is a vertical drum axis, natural circulation, natural draft, low pressure, multi-tubular, solid fuel fired, fire tube boiler with internally fired furnace. It is the modified form of simple vertical boiler. In this boiler, the fire tubes are placed horizontally. The efficiency of this boiler is much better than the simple vertical boiler.
Main Parts and Construction
1. Shell: It has a vertical axis cylindrical drum with hemispherical dome type shell at the top.
2. Grate: It is the platform on which the solid fuel is burnt.
3. Combustion Chamber: The burning of fuel takes place in the combustion chamber.
4. Fire Tubes: Cochran boiler has multi tubular fire tubes. The hot flue gases from the combustion chamber travels to the smoke box through these fire tubes. The fire tubes helps in the exchange of heat from the hot flue gases to the water.
5. Fire Hole: It is the hole provided to fire the fuel inside the furnace.
6. Furnace: It lies at the bottom of the boiler. Furnace is the place where all the fuel is burnt. Without furnace the working of this boiler is not possible.
7. Chimney: The chimney is attached to the smoke box. It transfer smoke to the environment. The size of chimney is small as compared with other boiler.
8. Fire Brick Lining. The fire brick lining is present in the combustion chamber and helps in the combustion of the fuel.
9. Manhole: A manhole is provided for the cleaning and inspecting of the boiler from inside.
10. Flue Pipe: It is a small passage connecting the fire box and combustion chamber. The hot gases enters into combustion chamber through the flue pipe.
Other Boiler mountings and accessories attached to the this boiler are:
1. Pressure Gauge: It measures the pressure of steam inside the boiler.
2. Safety Valve: It blows off the extra steam when the steam pressure inside the boiler reaches above safety level.
3. Water level Indicator: The position of the water level in the Cochran boiler is indicated by the water level indicator.
4. Stop Valve: Stop valve is used to transfer steam to the desired location when it is required. Otherwise it stops the steam in the boiler.
5. Blow off Cock: It is used to blow off the settle down impurities, mud and sediments present in the boiler water.
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- In Cochran boiler first the fuel is inserted into the fire box and placed on the grate. The fuel is ignited through the fire hole provided at the right bottom of the boiler.
- The fuel is burnt in the fire box and due to the burning of the fuel, smoke and hot flue gases emerges out. The hot flue gases enter into the combustion chamber through flue pipes.
- From the combustion chamber hot gases enters into the fire tubes. The fire tubes are surrounded by water. The hot flue gases inside the tubes exchange the heat from the hot gases to the water. Due to the exchange of heat, the temperature of the water start increasing and it gets converted into steam. The steam produced rises upward and collected at top of the boiler in the hemispherical dome. An anti-priming pipe is installed at top of the boiler which separates the water from the steam and makes it dry steam. This dry steam is then transfer to the turbines through the steam stop valve.
- The hot flue gases and smoke after exchanging heat moves to the smoke box. From the smoke box the burnt gases and smoke is discharge to the atmosphere through the chimney.
- Burnt fuel is transferred to the ash pit. Blow off cock is preset at left bottom of the boiler and is used to blow of the impurities, mud and sediment from the boiler water.
- A fusible plug is also provided at top of the combustion chamber. When the temperature of the combustion chamber crosses the permissible level, the fusible plug melts and the water through the combustion chamber enter into the furnace of the boiler and stop the fire. In this way a big fire accident can be prevented to take place and also protects the boiler from damage.
- Various boiler mounting and accessories are attached to the boiler for its efficient working.
(i) Low initial installation cost.
(ii) It requires less floor area.
(iii) Easy to operate and handle.
(iv) Transportation of Cochran boiler is easy.
(V) It can use all types of fuel.
(i) Low rate of steam generation.
(ii) Inspection and maintenance is difficult.
(iii) High room head is required for its installation due to the vertical design.
(iv) It has limited pressure range.