BOILERS

BOILERSBOILERSBOILERSUses of BoilersTo generate steam to drive turbines to generate electricity.Steam used for air conditioning systems.Steam used for driving steam engines.Steam used for boilers to run ships using super heated steam.Steam used for auto clave's, portable heat /hot water for buildings.Classification of BoilersBoilers can be classified as follows:According to geometric orientation of boiler:According to relative position of water and hot gases:According to location of furnace:According to method of water circulation:According to working pressure:According to mobility of boiler:According to number of tubes in the boiler: According to geometric orientation of boilerIf the axis of boiler is horizontal then it is called horizontal boiler. Example:- Lancashire boiler, Locomotive boiler.If the axis of boiler is vertical then it is called vertical boiler.Example:- Cochran boiler.If the axis of boiler is inclined then it is called inclined boiler.

According to relative position of water and hot gasesFire tube boilers:- If the hot gases of combustion from the furnace pass through the tubes and water is surrounding the tubes is called fire tube boilers.Example:- Cochran, Lancashire, Locomotive. Water tube boiler:- If the water passes through the tubes and hot gases surrounding the tubes is called water tube boiler. Example:- Babcock and Wilcox boiler.

According to location of furnaceExternally fired boilers:- In this boiler the furnace is placed outside the boiler shell. Generally water tube boilers are externally fired.Example:- Babcock and Wilcox boiler.Internally fired boilers:- In this boiler the furnace is placed inside the boiler shell. Generally fire tube boilers are internally fired.Example:- Lancashire, Cochran boiler.According to method of water circulation Natural circulation boilers:- In this boiler, water flow take place naturally, by density difference of water. The flow of water and steam are set up due to density difference resulting from difference in temperature.Example:- Lancashire, Babcock and Wilcox boiler.Forced circulation boilers:- In this boiler, water flow takes place by a pump.Example:- Benson boiler, La- mont boiler, Velox boiler.According to working pressureHigh pressure boiler:- The working pressure of this boiler is higher than 25 bar.Example:- Babcock and Wilcox boiler.Medium pressure boiler:- The range of working pressure of this boiler is between 10 bar to 25 bar.Example:- Lancashire boiler, Locomotive boiler.Low pressure boiler:- The range of working pressure is between 3.5 to 10 bar. Example:- Cochran and Cornish boiler.According to mobility of boilerStationary boiler:- This boiler cannot be moved easily from one place to another place. This are used in power generation or process heating in industries. Example:- Lancashire, Babcock and Wilcox boiler.

Mobile boiler:- It is portable boiler and can be easily moved. This is used in marine and locomotive.Example:- Locomotive boiler.According to numbers of tubes in the boilerSingle tube boiler:- This boiler having only one fire or water tube for circulation of hot gases or water.Example:- Cornish boiler.Multi-tube boiler:- This boiler having two or more fire or water tubes for the circulation of hot gases or water. Example:- Locomotive, Cochran, Lancashire, Babcock and Wilcox boiler. Fire Tube Boiler

Water Tube Boiler

Comparison between Fire tube boiler and Water tube boilerFire Tube BoilerHot gases are inside the tube and water is outside.Operating Pressure limited to 25 bar.Rate of steam generation is lower.Not suitable for large power plant.Chance of explosion is less due to low pressure.Floor space requirement is more.Cost is less.Required less skill for efficient and economic working.For producing process steam.There is no problem of scale deposition and less problem of overheating and bursting.Water Tube BoilerWater is inside the tube and hot gases outside.Can work under as high pressure as more than 125 bar.Rate of steam generation is higher.Suitable for large power plant.Chance of explosion is higher due to high pressure.Floor space requirement is less.Cost is more.Required more skill and careful attention for efficient and economic working.For producing steam for power generation as well as process heating.Small deposition of scale will cause overheating and bursting of the tubes.

COCHRAN BOILERCochran boiler is modification of simple vertical boiler.

Working of Cochran Boiler

Advantages of Cochran BoilerIt is compact and portable boiler therefore minimum floor area is required.Initial cost of boiler is less.It can be moved and set up readily in different locations.Quick and easy installation.Any type of fuel can be used.(coal or oil)Disadvantages of Cochran BoilerSteam raising capacity is less due to vertical design.Water along with steam may enter the steam pipe under heavy loads due to small steam space.Efficiency is poor in smaller size.LANCASHIRE BOILERLancashire is one of the most commonly used stationary boiler.

Working of Lancashire Boiler

Advantages of Lancashire BoilerDue to three passes of flue gases, the heating surface area per unit volume of boiler is large.The fluctuations in load can be easily met by this boiler due to large reservoir.Easy operation, low maintenance costs, easy to clean and inspect.By use of economizer and super heater, maximum heat of flue gases is utilized, so efficiency of boiler can be increased. Disadvantages of Lancashire BoilerMaximum working pressure is limited to 16 bars.Due to brick work, more floor area is required.Response of pressure build up is less.The furnace is inside the tubes therefore the grate area is restricted.BABCOCK AND WILCOX BOILERThis boiler is used in stationary and marine engine. This is exclusively used when pressure above 10 bar and steam generating capacity more than 7000 kg/hr. is required.

Working of Babcock and Wilcox Boiler

Advantages of Babcock and Wilcox BoilerThe steam generation capacity of the boiler is very high, about 2000 to 40,000 kg/hr.Replacement of defective tubes is easy.The draught losses as compared to other boilers is minimum.It is used in power station for generation large quantity of steam.Boiler is required less space area compared to fire tube boilers, and offers greater operational safety.