In this article, you will learn about Cochran Boiler Definition, Construction, Working, Applications, Advantages and Disadvantages.
Definition of Cochran Boiler
Cochran Boiler is a fire tube boiler in which coal or gasses are used as a working fluid, to generate steam and the steam is further used for various purposes. It is a multi-tubular vertical fire tube boiler having numerous horizontal fire tubes. In the Cochran boiler the heating surface is increased by the means of fire tubes which helps in attaining greater efficiency than simple vertical boiler.
The Cochran boiler was manufactured by the Cochran & Co. The Cochran & Co. built a wide range of boilers, especially vertical boilers suitable for ancillary (Donkey) use on ships. In the year 1922 the company patented vertical tubular boilers and its accessories.
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Main Parts of Cochran Boiler
The main parts of Cochran boiler are:
- Shell: the main body of the boiler is called the shell. It is hemispherical on the top, to provide space for steam. The hemispherical top gives higher volume to area ratio which enhances the steam capacity.
- Grate: the solid fuel is stored in the grate section. It is designed in such a way that air can easily flow through it and also the ashes can fall from the grate easily. Fire is placed in this section.
- Combustion Chamber: it is the place where burning of fuel takes place. It is lined with fire bricks on the side of the shell in order to prevent overheating. Hot gasses from the flue pipes enter the fire tubes through the combustion chamber, it is connected to the furnace.
- Flue Gases: when the fuel starts to burn, it produces gases which are already heated and are used for heating the water. These gases are called flue gases.
- Fire Tubes: there are a number of fire tubes whose one end are connected with the furnace and other end is connected to the chimney. Several horizontal tubes are also provided in order to increase the heating surface by increasing the surface area.
- Fire Hole: a small hole is provided at the bottom of the combustion chamber to place fuel.
- Fire Box (Furnace): it acts as a mediator of fire tubes and combustion chamber. It is also made dome shaped so that the gases get deflected back till they are passed to the combustion chamber through the flue pipe.
- Chimney: it is provided for the flue gases to exit from the smoke box to the atmosphere.
- Man Hole: it is provided for the inspection and maintenance of the inside of the boiler shell.
- Flue Pipe: it is a passage connecting the combustion chamber with the fire box.
- Feed Check Valve: it is used to control and regulate the flow of water inside the boiler. It also restricts the backflow of water.
- Blow Off Valve: as the name suggests, it is use to blow of the settled impurities, mud and sediments present in the boiler water.
- Ash Pit: it is a chamber inside the boiler where ashes are stored, it is located below the grate.
- Smoke Box Door: it is used to clean materials deposited in the smoke box.
- Anti-Priming Pipe: at some instances water droplets come out with steam, in order to prevent the droplets from getting carried out by the steam the anti-priming pipe is used.
- Crown: it is the hemispherical dome shaped section of the boiler wherein the burning of fuel happens.
- Pressure Gauge: it is used in several places to measure the pressure of steam inside the boiler.
- Safety Valve: it helps to blow off the extra steam when steam pressure inside the boiler reaches above safety level.
- Water Level Indicator: as the name suggests, it is used to indicate the water level in the Cochran boiler.
- Fusible Plug: it is used as a kind of safety measure. If the inner temperature of the boiler crosses the limit, then for safety reasons this fusible plug melts and the water comes into the boiler furnace and extinguishes fire.
- Stop Valve: it is used to transfer steam to the desired location whenever required.
Working Principles of Cochran Boiler
The Cochran Boiler works on the same principle as other fire tube boilers. At first, the coal is place at the grate through the fire hole. Then air enters into the combustion chamber through the atmosphere and fuel is sparked through the fire hole. The flue gases then start flowing into the hemispherical dome shaped combustion chamber. These flue gases further move into the fire tubes. The steam produced gets collected into the upper side of the shell and is taken out when the required pressure is generated. The flue gases are now sent to the chimney through a firebox, where it escapes into the atmosphere. This is a continuous process and the steam generated is used in small industrial processes.
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Applications and Uses of Cochran Boiler
The various applications of the Cochran Boiler are listed below:
- Variety of processes and applications in industries
- Chemical processing divisions.
- Paper and Pulp Manufacturing Plants
- Refining Units
Besides these, Cochran boilers are frequently employed in power generation plants, where large quantities of steam(up to 500kg/s) having high pressures, approximately 16megapascals and high temperatures reaching up to 830K . they are also used widely in marine operations like on ships and are either fired directly by coal or oil fuels or otherwise used for heat recovery from the exhaust of large diesel engines.
Characteristic Features of Cochran Boiler
- In the Cochran Boiler, any type of fuel can be used, i.e. coal or oil fuel.
- The Cochran Boiler is best suitable for small capacity requirements.
- It provides 70% thermal efficiency when fired with coal and about 75% thermal efficiency when fired with oil.
- The ratio of the area of the grate to the area of the heating surface varies from 10:1 to 25:1. The heating surface area is approximately 120sq meter.
- The boiler operates under a working pressure of 7 bar and has a maximum capacity of up to 15 bar.
- The height and shell diameter of the Cochran Boiler approximately are 5.75m and 2.75m respectively.
Advantages of Cochran Boiler
- Either coal or oil type fuel can be used.
- Lower floor area is required.
- Installation process is quick and easy.
- Installation and initialization cost of the Cochran Boiler is low as compared to any other boiler.
- It is portable i.e. can be transported from one place to another easily.
- The Cochran Boiler has a higher volume to area ratio.
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Disadvantages of Cochran Boiler
- Steam generation is this boiler is low, this is one of the major disadvantages.
- The pressure handling capacity of the boiler is less.
- It is difficult to inspect and maintain.
There are various kinds of boilers which are used as per requirements. Generally, on ships the boilers are chosen such that they require lesser area, are cost effective and are easy to maintain. With the advancement in technology more energy efficient and cost efficient boilers are available in the market.
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