What Is Boiler?
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.
Boilers can be classified as follows:
1. According to the flow of water and hot gases – fire tube (or smoke tube) and water tube boilers.
In fire tube boilers, hot gases pass through tubes which are surrounded with water. Examples: Vertical, Cochran, Lancashire and Locomotive boilers. There may be single tube as in case of Lancashire boiler or there may be a bank of tubes as in a locomotive boiler.
In water tube boilers, water circulates through a large number of tubes and hot gases pass around them. Eg., bobcock & Wilcox boiler.
2. According to the axis of the shell – vertical and horizontal boilers.
3. According to location or position of the furnace. Externally and internally fired boilers.
In internally fired boilers, the furnace forms an integral part of the boilers structure. The vertical tubular, locomotive and the scotch marine boilers are well known examples.
Externally fired boilers have a separate furnace built outside the boiler shell and usually below it. The horizontal return tube (HRT) boiler is probably the most widely known example of this type.
4. According to the application – stationery and mobile boilers. A stationary boilers is one of which is installed permanently on a land installation.
A marine boiler is a mobile boiler meant for ocean cargo and passenger ships with an inherent fast steaming capacity.
5. According to steam pressure – low, medium and high pressure boilers.
1.Simple Vertical Boiler:
The image shows the simplest form of an internally fired vertical fire-tube boiler. It does not require heavy foundation and requires very small floor area.
The fuel (coal) is fed into the grate through the fire hole and is burnt. The ashpit placed below the grate collect the ashes of the burning fuel.
The combustion gas flows from the furnace, passes around the cross tubes and escapes to the atmosphere through the chimney.
Water goes by natural circulation due to convection currents, from the lower end of the cross tube and comes out from the higher end.
The combustion gas flows from the furnace, passes around the cross tubes and escapes to the atmosphere through the chimney.
Water goes by natural circulation due to convection currents, from the lower end of the cross tube and comes out from the higher end.
2. High Pressure Boiler:
A boiler which generates steam at a pressure of 85 kgf/sq.cm or above is termed as a“high pressure boiler”. The present tendency is towards the use of high pressure boilers in power plants. The modern high pressure boilers used for power generation have capacities of 40 to 1600 tonnes/hr of superheated steam with a pressure upto 210 kgf/sq.cm and a temperature of about 650’C. One of the largest modern steam power plants in the world is in japan with a steam capacity of 1600 Tonnes/hr. In India, the trombay power plant has a steam generating capacity of 550 tonnes/hr, Ramagundampower power plant with 320 tonnes/hr and bokaro plant with 160 tonnes/hr.
Water tube boilers are generally preferred for high pressure and high output whereas fire tube boilers for low pressure and low output.
Water tube boilers are generally preferred for high pressure and high output whereas fire tube boilers for low pressure and low output.
Types of high pressure boilers
- La-Mont Boiler
- Loeffler Boiler
- Benson Boiler
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