Locomotive Boiler: Steam Generation and Key Components

1.Lancashire fire tube boiler:- A.introduction:❖ lancashire boiler is a horizental type and statoonary fire tube boiler. ❖This boiler generates low-pressure stream and it is a natural circulation boiler. ❖ This boiler was invented in the year 1844,by william fairbairn. ❖ It has high thermal effciency of about 80 to 90 percent. B.construction 1.pressure gauge:-The function of the pressure gauge is to indicate the pressure of the stream incide the boiler. 2.safety valve:-The safety valve is used to blow off the stream when the pressure of the steam inside the boiler exceeds theworking pressure. 3.stream stop valve:-The function of a steam stop valve is to stop and allows the flow of steam from the boiler to the steam pipe. 4.feed check valve:-It stop and allows the flow of water inside the boiler. 5.water level indicator:-it indicates the level of water in the boiler. It is placed in front of the bolier. 6.Blow off valve :- Its function is to remove the sediments or mud periodically that is collected at the botton of the boiler. 7. Manhole:- The hole is provided on the boiler so that a man can easily enter inside the boiler for the cleaning and repairing purpose. 8. Fire door:- This is used to ignite the present fuel inside or outside the boiler. 9. Fusible plug:- It is used to extinguish the fire inside the boiler when the water level inside the boiler falls to an unsafe level and prevent an explosion. It also prevents the damage that may happen due to the explosion. 10. Ash pit:- The Ash-pit used to collect the ash of the burnt fuel 11. Economizer:- An economizer is a mechanical device that is used as a heat exchanger in the steam power plant. It is used to pre-heat the fluid or water by taking the residual heat from the combustion products( flue gases). It is installed to increase the efficiency of the boiler. 12. Super heater:- The main purpose of the superheater is to increase the temperature of the saturated steam without any change in the pressure. 13. Air pre-heater:- Air preheater is also a mechanical device that abstracts the heat from the flue gases and transfers it to the air(atmosphere). C. Working Principle:❖ This Lancashire boiler works on the basic principle of the heat exchange. ❖ The heat is transfer from flue gases to the water through convection. ❖ It is basically a shell and tube type heat exchanger in which the flue gases flow through the tubes and the water flows through a shell. ❖ It is a natural circulation boiler that uses the natural current to flow the water inside the boiler. D. Applications:❖ Lancashire Boiler can be used in several filed like. ❖ It is used in industries like paper industries, textile industries, sugar industries, tire industries, etc ❖ The Lancashire boiler is used to drive steam turbines, locomotives, marines, etc. 2. Locomotive Boiler:A.Introduction:❖ It is a device that is used to create steam from water by using heat energy. ❖ Also, you can see an artificial steam jet draught is present in this type of boiler for increasing the heat transfer rate. ❖ The Locomotive ❖ It is a horizontal drum axis multi-tube boiler. ❖ The main function of it is to generate high steam rate because of that we see the grate area of this type of boiler is quite big also it has a number of fire tubes for improving the steam producing rate. ❖ As the name suggests it is a locomotive boiler means it is movable so that we don't need to fit chimney in it, the flow of air over the stack removed the flue gases due to the pressure difference between the grate and the outside. ❖ This type of boiler is capable of producing a high steam rate and hence it is used for railway locomotive engines and in marines. ❖ In this type of boiler, the stack is used instead of a chimney and burnt gas or flue gasses are removed by this stack. B.Construction:Construction or Main Parts The construction or main parts of a locomotive boiler are: 1. Fire hole:- It is a hole provided at the rear end of the boiler. The solid fuel is inserted and ignited into the furnace through this hole. 2. Fire box:- It is a box in which the burning of the fuel takes place. 3. Fire brick arch:- It is a brick arch placed inclined over the grate. It prevents the entry of the ash, dust and burnt fuel particles into the fire tubes. It provides a way to the hot flue gases to travel a definite path before entering into the fire tubes of the boiler. 4. Grate:- Grate is a platform on which the solid fuel is kept and burnt 5. Boiler tubes:- They are the fire tubes through which the hot flue gases pass and exchange the heat with the surrounding water. 6. Blast pipe:- It is a pipe provided above the steam engine. The exhaust steam passes through this blast pipe. It is used to create an artificial draft that pushes the smoke out through the chimney and creates suction for the hot flue gases. The suction created allows the hot flue gases to move forward through the fire tubes. 7. Steam pipe:- It is a pipe through which the steam passes. We have two steam pipes; one is the main steam pipe present in between the superheater header and dome. And the second one is that which connects the superheater exit end to the steam engine. 8. Superheater:- It superheats the steam to the desired temperature before entering into the cylinder of the steam engine. 9. Smoke box:- According to its name, it is a box in which the smoke of the burnt fuel after passing through the fire tubes gets collected. From there it is exhausted in the environment by the chimney. 10.Super heater element pipes:- These are the pipes of superheater through which the steam travels and gets superheated. 11.Dome:- It is present at the top and contains the regulator for regulating the steam produced through the steam pipe. 12.Regulator valve:- It is a valve that regulates the steam through the main steam pipe for superheating. 13.Superheater header:- It is the head of the super heater which accepts the steam from the steam pipe. 14.Chimney:- It is used to throw out the exhaust smoke and gases to the environment. The length of the chimney is very small in this boiler. 15. Safety valve:- It is used to maintain the safe working steam pressure in the locomotive boiler. It blows off steam when the pressure of the steam increases above safety level and prevents blasting of the boiler. C. working principle:❖ In the locomotive boiler, first, the solid fuel (coal) is inserted on the grate and is ignited from the fire hole. ❖ The burning of the fuel starts and it creates hot flue gases. ❖ A fire brick arch is provided that makes the flow of hot flue gases to a definite path before entering into the long tubes (fire tubes). ❖ It also prevents the entry of burnt solid fuel particles into the tubes. ❖ The hot flue gases pass through the long fire tubes and heat the water surrounding them. ❖ Due to the heating, the water gets converted into saturated steam and gets collected at the top. ❖ The saturated steam from the dome enters into the main steam pipe through the regulator valve. ❖ The steam travels in the main steam pipe and reaches to the super heater header. ❖ Form header, the steam enters into super heater element pipes ❖ Here it is superheated and then the superheated steam enters into the steam pipe of the smoke box. ❖ The steam from the super heater goes to the cylinder containing piston. ❖ The superheated steam made the piston moves within the cylinder. ❖ The piston is connected to the wheels of the steam engine and the wheels start rotating. The exhaust steam from the cylinder enters into the blast pipe. ❖ The burnt gases and smoke after passing through the fire tubes enter into the smokebox. ❖ The exhaust steam coming out from the blast pipe pushes the smoke out of the boiler through the chimney. ❖ Here the smoke cannot escape out from the boiler on its own, so artificial draft is created by exhaust steam coming out from the steam engine. ❖ This artificial draft created pushes the smoke out of the smokebox and creates suction for the hot flue gases. D.Applications:❖ Locomotive boilers are mostly used in railways and marines. ❖ The efficiency of this boiler is very less. ❖ It cannot work in heavy-load conditions because this leads to the overheating of the boiler and finally gets damage. ❖ They are also used in traction engines, steam rollers, portable steam engines, and some other steam road vehicles. 3. Cochran Boiler:A. Introduction:❖ Cochran Boiler is a multi-tubular vertical fire tube boiler having a number of horizontal fire tubes. ❖ The efficiency of this boiler is much better than the simple vertical boiler. ❖ It is the modification of a simple vertical boiler where the heating surface has been increased by means of a number of fire tubes. B. Construction:1.Shell:- The main body of the boiler is known as a shell. It is hemispherical on the top, where space is provided for steam. - This hemispherical top gives a higher volume to area ratio which increases the steam capacity. 2. Grate:- In the grate section, solid fuel is stored, it is designed so well that air can easily flow through it, and also the ashes fall from the grate quite easily. In this section, the fire is placed. 3. 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. The combustion chamber is connected to the furnace 4. Fire Tubes:- There are various fire tubes whose one end is connected to the furnace and other to the chimney. Sevaral horizontal fire tubes are provided to increased the heating surface. 5. Fire Box (Furnace):- It works as a mediator of fire tubes and combustion chamber. 6. Fire Hole:- The small hole is provided at the bottom of the combustion chamber to place fuel is known as a fire hole. 7. Ash Pit:- It is a chamber inside a boiler where ashes are stored. 8. Man Hole:- It is provided for the inspection and repair of the interior of the boiler shell. 9. Flue Pipe:- It is a short passage connecting the firebox with the combustion chamber. 10. Fire Brick Lining:- It is a special type of brick ling use in Cochran Boiler to reduce the convection of heat from the outer surface of the boiler. Fire Brick is generally made of fire clay. 11. Feed Check Valve:- It is used to control the flow of water inside the boiler, it also helps to restrict the backflow of water. 12. Chimney:- It is provided for the exit of flue gases to the atmosphere from the smokebox. 13. Blow Off Valve:- It is used to blow off the settle down impurities, mud, and sediment present in the boiler water. 14. Smoke Box Door:- It is used to clean the smoke box deposits materials. 15. Pressure Gauge:- It measures the pressure of steam inside the boiler. 16. Safety Valve:- It blows off the extra steam when the steam pressure inside the boiler reaches above safety level. 17. Anti Priming Pipe:- Sometimes water droplets come out with the steam, so to prevent the droplets from carried out by the steam the Anti Priming Pipe is used. 18. Crown:- It is hemispherical dome-shaped section of a boiler, where burning of fuel happens. 19. Fusible Plug:- It is one type of safety measure. If the inside temperature of the boiler cross the limit, then for safety purpose this Fusible Plug melts and the water comes into the boiler furnace and extinguish the fire. 20. Water Level Indicator:- The position of the water level in the Cochran boiler is indicated by the water level indicator. 21. Stop Valve:- Stop valve is used to transfer steam to the desired location when it is required. Otherwise, it stops the steam in the boiler 22. Water Level Gauge:- It glass tube fitted out side of the boiler to check the water level inside the boiler. C.Working Principle:❖ The Cochran boiler works as same as other fire tube boiler. ❖ First, The coal is placed at the grate through the fire hole. ❖ Then the air is entering into the combustion chamber through the atmosphere and fuel is sparked through fire hole. ❖ The flue gases now send to the chimney through a firebox where it leaves into the atmosphere. ❖ Heat is exchanged from flue gases to the water into the fire tubes. ❖ The steam produce collected into the upper side of the shell and taken out by when the required pressure generated. D. Applications:The application of Cochran boiler are:❖ Variety of process applications industries. ❖ Chemical processing divisions. ❖ Pulp and Paper manufacturing plants. ❖ Refining units. 4. Benson Boiler:A. Introduction :❖ Benson Boiler is a high pressure, drum less, supercritical, water tube steam boiler with forced circulation. ❖ The bubbles do not form because at supercritical pressure the density of water and steam becomes the same. ❖ As the latent heat of water reduces to zero the water directly changes into steam without the formation of bubbles. ❖ It was Mark Benson who first proposed the idea to compress the water at supercritical pressure before heating into the boiler and due to this the latent heat of water reduces to zero. ❖ This boiler was invented in the year 1922 by Mark Benson. ❖ This boiler is a supercritical boiler in which the feed water is compressed to a supercritical pressure and this prevents the formation of bubbles in the water tube surface. B. Construction :The main parts of Benson boiler are: 1. Air Preheater:- It preheats the air before entering into the furnace. The preheated air the burning efficiency of the fuel. 2. Convection Evaporator:- It evaporates the superheated water and converts them into steam. It does so by the convection mode of heat transfer to the water from the hot flue gases. 3. Convection Super heater:- It superheats the steam to the desired temperature (nearly 650 degree Celsius). 4. Furnace:- It is the place where the fuel is burnt. 5. Feed Pump:- It is used to supply the water inside the boiler at supercritical pressure of 225 bars. 6. Economiser:- It heats the water to a certain temperature. 7. Radiant Super heater:- It is superheater that heats the water with radiation produced by the burnt fuel. It raises the temperature to supercritical temperature. C. Working Principle:❖ It works on the principle that the pressure of the water is increased to the supercritical pressure (i.e. above the critical pressure of 225 bar). ❖ When the pressure of water is increased to the supercritical level, the latent heat of water becomes Zero and due to this, it directly changes into steam without boiling. And this prevents the formation of bubbles at the tube surface. ❖ In Benson Boiler, the feed pump increases the pressure of the water to the supercritical pressure, and then it enters into the economiser. ❖ From economiser, the water passes to the radiant heater. Here the water receives the heat through radiation and partly gets converted into steam. ❖ The temperature raises almost to the supercritical temperature. ❖ After that mixture of steam and water enters into convective evaporator where it is completely converted into steam and may superheated to some degree. ❖ Finally it is passed through the superheater to obtained the desired superheated steam. ❖ This superheated steam is then used by turbines or engines to produce electricity. D.Applications:❖ This supercritical boiler is used in different industries to generate steam for the production of electricity or mechanical power. ❖ The average operating pressure, temperature and capacity of benson boiler is 650 degree Celsius, 250 bar and 135 tonnes/h.