If the axis of the boiler is inclined, it is known as inclined boiler. 2. According to the flow medium inside the tubes a) Fire tube b) Water tube boilers. The
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STEAM BOILERS A steam generator or a boiler is defined as a closed vessel in which water is converted into steam by burning of fuel in presence of air at desired temperature, pressure and at desired mass flow rate. Function of a boiler The steam generated is empl oyed for the following purposes Used in steam turbines to develop electrical energy Used to run steam engines In the textile industries, sugar mills or in chemical industries as a cogeneration plant Heating the buildings in cold weather Producing h ot water for hot water supply Classification of Boilers The different ways to classify the boilers are as follows 1. According to location of boiler shell axis a) Horizontal b) vertical c) Inclined boilers. When the axis of the boiler shell is horizontal the boiler is called horizontal boiler. Example : Lancashire boiler, Locomotive boiler, Babcock and Wilcox boiler etc. If the axis is vertical, the boiler is called vertical boiler Example : Cochran boiler. If the axis of the boiler is inclined, it is known as inclined boiler . 2. According to the flow medium inside the tubes a) Fire tube b) Water tube boilers. The boiler in which hot flue gases are inside the tubes and water is surrounding the tubes are called fire tube boiler s . Example : Lancashire, locomotive, Cochran and Cornish boiler s When water is inside the tubes and the hot gases are outside, the boiler is called water tube boiler. Example : Simple vertical boiler, Babcock and Wilcox boiler. 3. According to Boiler Pressure According to pressure of the ste am raised the boilers are classified as follows ;
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a) Low pressure (3.5 – 10 bar) b) Medium pressure (10 – 25 bar) c) High pressure boilers(> 25 bar) Examples Low pressure: Cochran and Cornish boiler Medium pressure: Lancashire and Locomotive boiler High pressure: Babcock and Wilcox boiler. 4. According to the draft used a) Natural draft b) Artificial draft boilers Boilers need supply of air for combustion of fuel. If the circulation of air is provided with the help of a chimney, the boiler is known as natural draft boile r . When either a force d draft fan or an induced draft fan or both are used to provide the f low of air the boiler is called artificial draft boiler . Examples Natural draft boiler: Simple vertical boiler, Lancashire boiler. Artificial draft boiler: Babcock a nd Wilcox boiler, Locomotive boiler. 5. According to Method of water circulation a) Natural circulation b) Forced circulation If the circulation of water takes place due to difference in density caused by temperature of water, the boiler is called natural circulation boiler . Whe n the circulation is done with the help of a pump the boiler is known as forced circulation boiler . Examples Natural circulation: Babcock & Wilcox boiler, Lancashire boiler Forced circulation: Velox boiler, Lamont boiler, Loffler boi ler 6. According to Furnace position a) Internally fired b) Externally fired boilers When the furnace of the boiler is inside its drum or shell, the boiler is called internally fired boiler. If the furnace is outside the drum the boiler is called externally fire d boiler. Examples Internally fired boiler: Simple vertical boiler Lancashire boiler, Cochran boiler Externally fired boiler: Babcock and Wilcox boiler
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7. According to type of fuel used a) Solid b) Liquid c) Gaseous d) Electrical e) Nuclear energy fuel boilers The boiler in which heat energy is obtained by the combus tion of solid fuel like coal or lignite is known as solid fuel boiler . A boiler using liquid or gaseo us fuel for burning is known as liquid or gaseous fuel boiler . Boilers in which electrical or nuclear energy is used for generation of heat are respectively called as electrical en ergy headed boilers and nuclear energy heated boiler. 8. According to number of Tubes a) Single – tube b) Multi – tube boiler A boiler having only one fire tube or water tube is ca lled a single tube boiler . The boiler having two or more, fire or water tubes is called multi tube boiler . Examples Single tube boiler: Cornish boiler, Vertical boiler. Multi – tube boiler: Lancashire boiler, Locomotive boiler, Babcock and Wilcox boiler. 9. According to Boiler Mobility a) Stationary b) Portable c) Marine boilers When the boiler is fixed at one location and cannot be transported easily it is known as stationary boiler. If the boiler can be moved from one locat ion to another it is known as a portable or mobile boile r . The boilers which can work on the surface of water are called marine boilers . Examples Stationary: Lancashire, Babcock and Wilcox boiler, vertical boiler Portable: Locomotive boiler. Marine: Marine boilers Specification of a Boiler Size of drum (Diamete r and length) Rate of steam generation(kg/hr) Heating surface (Square meters) Working pressure (bar) No. of tubes / drum
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Type of boiler Manufacturer of boiler Initial cost Quality of steam Repair and inspection facility Comparison between water – tube and fire tube boilers COCHRAN BOILER It is a Vertical drum axis, natural circulation, natural draft, multi tubular, low pressure, solid fuel fired fire tube boiler with internally located furnace. Constructional details: It consists of ; Shell: It is hemispherical on the top, where space is provided for steam. Crate : It is placed at the bottom of the furnace where coal is burnt. Fire box : It is also dome – shaped like the shell so that the gases can be deflected back till they are passed out through the flue pipe to the combustion chamber. Flue pipe : It is a short passage connecting the fire box with the combustion chamber. Fire tubes : A number of horizontal fire tubes are provided Combustion chamber : It is lined with fire bricks on the side of the shell to prevent overheating of the boiler. Hot gases enter the fire tubes from the flue pipe through the combustion chamber. Chimney : It is provided for the exit of the flue gases to the atmosphere from the smoke box. Man – hole : It is provided for inspection and repair of the interior of the boiler shell.
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Normal size of a Cochran boiler is given by; Shell diameter 2.75 meters and Height of the shell 6 meters. Working of the Cochran boiler: Coal is fed into the grate through the fire hole and burnt. Ash formed during burning is collected in the ash pit provided just below the grate and then it is removed manually. The host gases from the grate pass through the flue pipe to the combustion chamber. The hot gases from the combustion chamber flow through the horizontal fire tubes and transfer the heat to the water by convection. The flue gases coming out of fire tubes pass through the smoke box and are exhausted to the atmosphere through the chimney. Smoke box is provided with a door for cleaning the fire tube s and smoke box. Advantages of Cochran Boiler Low initial installation cost. It requires less floor area. Easy to operate and handle. Transportation of Cochran boiler is easy. It can use all types of fuel. Disadvantages of Cochran Boiler Low rate of steam generation. Inspection and maintenance is difficult.
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High room head is required for its installation due to the vertical design. It has limited pressure range. Applications of Cochran Boiler Variety of process applications in industries Chemical processing divisions Pulp and Paper manufacturing plants Refining units LA MONT BOILER La Mont boiler is a high pressure, forced circulation, water tube boiler with internally fired furnace. An external pump is used to circulate the water within small diameter wat er tubes of the boiler . This boiler works on basic principle of forced convection. If the water is circulating by a pump inside the tube, the heat transfer rate from gas to the water is increases. It is the basic principle of it. Working In Lamont boiler, the feed pump circulates the water in the economiser of the boiler. The economiser heats the water to some degree. From economiser, water enters into steam separating drum. From steam separating drum the mixture of water and steam is forced circulated through the radiant evaporator by an external centrifugal pump. In forced circulation, the pressure of circulation of water through the tubes is more as compared with the natural circulation.
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