Working of the Cochran boiler:
Today in this articles we are discussed about the Cochran boiler , how to Cochran boiler is worked , and about its mounting and accessories , great features of Cochran boiler and its advantage and disadvantage . Cochran boiler is used for the small steam requirements in industries . where small space and less installation cost required for that requirement these boilers are best suited .
For start up of Cochran boiler Coal is feed into the grate bar through the fire box hole and and fuel starting burning. during burning of fuel ash is collected into the ashpit provided just below the grate and then ash is removed manually from the ash pit.
Hot gases from the combustion chamber enters into the fire tubes.. The hot flue gases inside the tubes exchange the heat from the hot gases to the water with the help of convection method which are surrounded by water. Due to the heat transfer method heat travels through hot to cold medium so that, 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 crown 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.
After combustion and combustion gases heat are absorbed by the water for steam generation purpose so that the remaining hot flue gases and smoke moves to the smoke box. From the smoke box the waste burnt gases and smoke is discharge to the atmosphere through the chimney.
Blow off cock is provided at left bottom of the boiler and it is used to blow of the impurities, mud and sediment from the boiler water. Which is settle down the bottom of the boiler .
A fusible plug is also provided at top of the combustion chamber it is used for the safety purpose of the boiler . fusible plug is made of low melting point fusible metal like aluminum , zinc etc. When the temperature of the combustion chamber reaches the beyond the safe working limit l, the fusible plug melts due to high temperature 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.
Different type of mounting and accessories are fitted on the Cochran boiler. these are follows ;-
Steam Stop Valve: boiler Steam step stop valve regulates the steam flow during the operation and the emergency situation..The steam from the boiler first enters into an ant-priming pipe where most of the water particles associated with steam are removed. After that the steam goes for the process like in steam turbine for electricity generation or for dry purpose in the cotton industries.
Feed Check Valve: The high pressure feed water is supplied to the boiler through this valve against the boiler pressure . Feed check valve opens towards the boiler only and feeds the water to the boiler. If the feed water pressure is less than the boiler steam pressure then this valve remains closed and prevents the back flow of steam through the valve with this advantage its called the feed check valve .
Fusible Plug: fusible plug is very important mounting of the Cochran boiler when the water level in the boiler falls below the safe working level, so that the boiler wall shell and tubes will be overheated due the unavailability of the water And if this is continued, the tubes may get damaged, as the water cover will be removed. It can be prevented by stopping the burning of fuel on the grate. When the temperature of the shell increases above a particular level, the fusible plug, which is mounted over the grate, melts and forms an opening. The high-pressure steam pushes the remaining water through this hole on the grate and stop the fuel burning immediately.
Blow-off Cock: The blow-off cock is installed at the bottom of the boiler .The water supplied to the boiler always has impurities like mud, sand and, salt. Due to heating of water, they get deposited at the bottom of the boiler and if they are not removed, they are accumulated at the bottom of the boiler and reduces its capacity and heat transfer rates. Also the salt content in water can goes on increasing as a result of evaporation of water. These deposited salts are removed with the blow-off cock mounting. and is operated only when the boiler is running. When the blow-off cock is opened during the boiler operation, the high-pressure steam pushes the water and the collected waste material at the bottom is sent out. Blowing some water out also reduces the concentration of the salt. The blow-off cock is usually operated for few minutes after every 5 to 6 hours of boiler working. Blow-off cock helps to keep the boiler clean.
Pressure Gauge: Pressure gauge indicates the correct pressure of the steam in the boiler
Water Level Indicator: Water level indicator indicate the correct water level in the boiler The water level in the boiler should not fall below a critical level otherwise the boiler will be overheated and the tubes may damage due to the shortage of water or starvation .
Safety Valve: The function of the safety valve is blow off excess pressure when the pressure is increased beyond the safe working limit . When the pressure increases above design pressure, the valve opens and discharges the steam to the atmosphere. When this pressure falls just below design pressure, the valve closes automatically. Generally spring loaded safety valve is used for this purpose .
Features of Cochran boiler are listed below:-
1. In Cochran boiler are multi-fuel fired boiler in this type of boiler we can brun coal , wood , saw dust , wood chips many more fuel we can easily .
2. Cochran boiler is best suitable for small capacity requirements.
3. Cochran boiler gives about 70% thermal efficiency with coal firing and about 75% thermal efficiency with oil firing.
4. In Cochran boiler ratio of grate area to the heating surface area varies from 10: 1 to 25:
Advantages and disadvantages of Cochran boiler:-
Advantages of Cochran boiler
1. Low floor area required for the boiler installation
2. Low initialization cost.
3. It is easy to operate.
4.Less manpower requirement for the operation.
5. It is easy to transport from one place to another.
6. It has higher volume to area ratio.
Disadvantages of Cochran boiler
1.Low steam generation rate
2.Low heating surface
3.Limited pressure handles capacity.
4.It is difficult to inspect and maintenance because of narrow space inside for entering
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