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Definition A boiler or steam generator is a device used to create steam by applying heat energy to water Although the definitions are somewhat flexible, it can be said that older steam generators were commonly termed boilers worked at low to medium pressure (1–300 psi /0.069–20.684 bar ; 6.895–2,068.427 kPa ) but, at pressures above this, it is more usual to speak of a steam generator .

Requirements of an efficient boiler:

Requirements of an efficient boiler It should generate maximum amount of steam at a required pressure and temperature and quality with minimum fuel consumption. It should be light in weight and should not occupy large space. It should conform to safety regulations. It should have low initial cost, installation cost and maintenance cost. It should be able to cope with fluctuating demands of steam supply. All parts and components should be easily accessible for inspection and repair.

Fuel :


Principal Parts of a Boiler :

Principal Parts of a Boiler Furnace –Energy Conversion Heating Surfaces –Absorption of Heat from the Furnace Steam/Water Separators –Separate Water from Steam. Feed water Supply –Provides the Water as the working medium for conversion to steam. Draft Equipment –Fans for supplying air for combustion and removal of fuel gas. Fuel Supply –Provides the energy source. Control Equipment –Controlling Start, Operation, Shutdown and Safe tripping of Plant

Boiler Mountings and Accessories:

Boiler Mountings and Accessories Fitting and devices which are necessary for the safety and control are knows as boiler mountings Fitting or devices which are provided to increase the efficiency of the boiler and help in the smooth working of the plant are knows as boiler accessories.

Boiler Mountings and Accessories Frequently used :

Boiler Mountings and Accessories Frequently used Safety Valve Water level indicators Bottom blow down valves Continuous blow down valve Hand holes Seperators Low- water cutoff Surface blow down line Circulating pump Feed water check valve or clack valve Desuper heater tubes or bundles Chemical injection line

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Safety valve : It is used to relieve pressure and prevent possible explosion of a boiler Water level indicators: They show the operator the level of fluid in the boiler, also known as a sight glass, water gauge or water column is provided. Bottom blow down valves: They provide a means for removing solid particulates that condense and lay on the bottom of a boiler. As the name implies, this valve is usually located directly on the bottom of the boiler, and is occasionally opened to use the pressure in the boiler to push these particulates out. Continuous blow down valve: This allows a small quantity of water to escape continuously. Its purpose is to prevent the water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause water droplets to be carried over with the steam - a condition known as priming .

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Hand holes: They are steel plates installed in openings in "header" to allow for inspections & installation of tubes and inspection of internal surfaces. Seperators : Steam drums internals, series of screen, scrubber & cans (cyclone separators). Low- water cutoff: It is a float switch that is used to turn off the burner or shut off fuel to the boiler to prevent it from running once the water goes below a certain point. If a boiler is "dry-fired" (burned without water in it) it can cause rupture or catastrophic failure. Surface blow down line: It provides a means for removing foam or other light weight non- condensible substances that tend to float on top of the water inside the boiler. Circulating pump : It is designed to circulate water back to the boiler after it has expelled some of its heat.

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Feed water check valve or clack valve : A non return stop valve in the feed water line. This may be fitted to the side of the boiler, just below the water level, or to the top of the boiler. A top-mounted check valve is called a top feed and is intended to reduce the nuisance of limescale . It does not prevent limescale formation but causes the limescale to be precipitated in a powdery form which is easily washed out of the boiler. Desuper heater tubes or bundles : A series of tubes or bundle of tubes, in the water drum but sometime in the steam drums that De-super heated steam. This is for equipment that doesn't need dry steam. Chemical injection line : A connection to add chemicals for controlling feed water pH

Boiler accessories   :

Boiler accessories Air preheater : Waste heat recovery device in which the air to on its way to the furnace is heated utilizing the heat of exhaust gases. Economizer: It is used to recover heat from exhausts gases & This heat is used to raise the temperature of feed water supplied to the boiler. Steam super heater: It is used to super heat the steam generated by boiler. Feed pump: It is used to raise the pressure of water and force it into the boiler. Injector: It is used to feed water in boilers.

Classification of boilers :

Classification of boilers

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Tube contents Fire tube boiler Hot gases pass through the tubes and water surrounds them. transferred Heat from the gases to water, which is then converted to steam. Water tube boilers Water flows inside the tubes and the hot gases flow outside the tubes. Classification of Boilers Examples: Cochran, Lancashire, Cornish, Locomotive boilers Examples: Babcock and Wilcox boiler, Stirling boiler

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Fire Tube Boilers Water Tube Boilers Hot gases pass through the tubes Hot gases pass outside the tubes Needs stronger outer shell to contain steam pressure Does not need stronger outer shell Fire tubes boilers are more difficult to accessible for cleaning, inspection and repairs. Water tubes boilers are more readily accessible for cleaning, inspection and repairs Large volume of steam generate . Small volume of steam generate . Examples: Cochran, Lancashire, Cornish, Locomotive boilers Examples: Babcock and Wilcox boiler, Stirling boiler

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Method of F iring Internally fired: Furnace region is provided inside the boiler shell and is completely surrounded by water-cooled surfaces. E.g., Lancashire, Locomotive. Externally fired: Furnace region is provided outside. E.g., Babcock and Wilcox boiler Pressure of Steam Low pressure boiler : Steam pressure below 80 bars. Examples: Cochran, Cornish, Lancashire, locomotive boilers High pressure boiler: Pressure above 80 bars. Examples: Babcock and Wilcox, Lamont

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Circulation of Water Natural circulation : Circulation of water in the boiler takes place by natural convection current produced by the application of heat. Examples : Lancashire, Locomotive, Babcock and Wilcox boilers Forced circulation: Lancashire boiler - Two large fire tubes Cornish boiler - Single large fire tube Cochran boiler Locomotive boiler - Many small tubes Babcock Wilcox water tube boiler

Industrial Boilers:

Industrial Boilers Water Tube Boilers Fire Tube Boilers Fire Box Boilers Process boilers Power boilers High pressure boilers Heating boilers Low pressure boilers Haycock and wagon top boilers Cylindrical fire-tube boiler Multi-tube boilers Lancashire boiler Cornish boiler Cochran boiler Locomotive boiler Babcock Wilcox boiler

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It is well design of a Vertical multitubular fire tube boiler Improvement over the simple vertical boiler as it provides greater heating surface. Total heating surface area is about 10-25 times the grate area Efficiency 70-75% Ranges from 1m dia.X2m high,evaporation 20kg/hr to 3m dia X6m high,evaporation 3000kg/hr. Cochran Boiler

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Is horizontal smoke tube boiler size range from a shell 2m diaX6m long to 3m diaX10m long Working pressure range are up to 20kgf/cm2 Ratio of heating surface to grate area is 24-30 Efficiency is about 56% without economizer and 75% with economizer. Similar to Cornish boiler in Lancashire Boiler two flue tubes but in Cornish boiler only one flue tubes are there. Lancashire Boiler

Lancashire Boiler contd……:

Lancashire Boiler contd ……

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Babcock and Wilcox water tube Boiler Water tube boiler having lager pressure ranges and larger sizes. Three main parts, steam and water drum, water tubes and furnace. Designed by the American firm of Babcock and Wilcox , this type has a single drum, with feed water drawn from the bottom of the drum into a header that supplies inclined water-tubes. The water tubes supply steam back into the top of the drum. Furnaces are located below the tubes and drum.

Application :

Application Steam boilers are used where steam and hot steam is needed. Hence, steam boilers are used as generators to produce electricity in the energy business. Besides many different application areas in the industry for example in heating systems or for cement production, steam boilers are used in agriculture as well for soil steaming .


References Dr. Vishal V. Pande ,Dr. Avinash R.Tekade & Prof. K.V. Shastri , Pharmaceutical Engineering, Boilers, Tech-Max Publication, Pune , First Edition, July-2011, 5-1 to 5-6.

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