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THERMAL POWER STATION PDF

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Thermal electric power generation is one of the major methods. A thermal power station works on the principle that heat is released by. Page |1 INTRODUCTION: A thermal power plant converts heat energy of coal into electrical energy. coal is burnt in a boiler which converts water into steam. plants, turbines different heads, plant capacity as a base load and peak load station, power plant auxiliaries. MODULE-II (10 HOURS). Thermal Power: Overall .


Thermal Power Station Pdf

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seas, the cover photo shows. Ireland's West Offaly Power Station, which was delivered as a full- fledged coal-fired thermal power plant. The design has cleared. PDF | On Jul 11, , Zheng-Fei Hu and others published Thermal Power Plants. PDF | The performance analysis of Egbin Power Plant in terms of efficiency and reliability is herein presented. The Station consists of six units of steam turbines.

As steam moves through the system and loses pressure and thermal energy, it expands in volume, requiring increasing diameter and longer blades at each succeeding stage to extract the remaining energy.

It is so heavy that it must be kept turning slowly even when shut down at 3 rpm so that the shaft will not bow even slightly and become unbalanced.

This is so important that it is one of only six functions of blackout emergency power batteries on site. The other five being emergency lighting , communication , station alarms, generator hydrogen seal system, and turbogenerator lube oil. The hot reheat steam is conducted to the intermediate pressure turbine, where it falls in both temperature and pressure and exits directly to the long-bladed low-pressure turbines and finally exits to the condenser.

There is generally no permanent magnet , thus preventing black starts.

The rotor spins in a sealed chamber cooled with hydrogen gas, selected because it has the highest known heat transfer coefficient of any gas and for its low viscosity , which reduces windage losses. This system requires special handling during startup, with air in the chamber first displaced by carbon dioxide before filling with hydrogen.

This ensures that a highly explosive hydrogen— oxygen environment is not created. The desired frequency affects the design of large turbines, since they are highly optimized for one particular speed. The electricity flows to a distribution yard where transformers increase the voltage for transmission to its destination.

The steam turbine-driven generators have auxiliary systems enabling them to work satisfactorily and safely. The steam turbine generator, being rotating equipment, generally has a heavy, large-diameter shaft.

The shaft therefore requires not only supports but also has to be kept in position while running. To minimize the frictional resistance to the rotation, the shaft has a number of bearings.

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The bearing shells, in which the shaft rotates, are lined with a low-friction material like Babbitt metal. Oil lubrication is provided to further reduce the friction between shaft and bearing surface and to limit the heat generated. Stack gas path and cleanup[ edit ] See also: Flue-gas emissions from fossil-fuel combustion and Flue-gas desulfurization As the combustion flue gas exits the boiler it is routed through a rotating flat basket of metal mesh which picks up heat and returns it to incoming fresh air as the basket rotates.

This is called the air preheater. The gas exiting the boiler is laden with fly ash , which are tiny spherical ash particles. The flue gas contains nitrogen along with combustion products carbon dioxide , sulfur dioxide , and nitrogen oxides. The fly ash is removed by fabric bag filters in baghouses or electrostatic precipitators. Once removed, the fly ash byproduct can sometimes be used in the manufacturing of concrete.

This cleaning up of flue gases, however, only occurs in plants that are fitted with the appropriate technology. Still, the majority of coal-fired power stations in the world do not have these facilities. Japan has been using flue gas cleaning technology for over 30 years and the US has been doing the same for over 25 years. China is now beginning to grapple with the pollution caused by coal-fired power stations.

Where required by law, the sulfur and nitrogen oxide pollutants are removed by stack gas scrubbers which use a pulverized limestone or other alkaline wet slurry to remove those pollutants from the exit stack gas. Other devices use catalysts to remove nitrous oxide compounds from the flue-gas stream. The tallest flue-gas stack in the world is In the United States and a number of other countries, atmospheric dispersion modeling [19] studies are required to determine the flue-gas stack height needed to comply with the local air pollution regulations.

The United States also requires the height of a flue-gas stack to comply with what is known as the " good engineering practice " GEP stack height. Fly ash collection[ edit ] Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters or sometimes both located at the outlet of the furnace and before the induced draft fan.

The fly ash is periodically removed from the collection hoppers below the precipitators or bag filters. Generally, the fly ash is pneumatically transported to storage silos for subsequent transport by trucks or railroad cars. Bottom ash collection and disposal[ edit ] At the bottom of the furnace, there is a hopper for collection of bottom ash.

This hopper is kept filled with water to quench the ash and clinkers falling down from the furnace. Arrangements are included to crush the clinkers and convey the crushed clinkers and bottom ash to a storage site. Ash extractors are used to discharge ash from municipal solid waste—fired boilers.

Auxiliary systems[ edit ] Boiler make-up water treatment plant and storage[ edit ] Since there is continuous withdrawal of steam and continuous return of condensate to the boiler, losses due to blowdown and leakages have to be made up to maintain a desired water level in the boiler steam drum. For this, continuous make-up water is added to the boiler water system. Impurities in the raw water input to the plant generally consist of calcium and magnesium salts which impart hardness to the water.

Hardness in the make-up water to the boiler will form deposits on the tube water surfaces which will lead to overheating and failure of the tubes. Thus, the salts have to be removed from the water, and that is done by a water demineralising treatment plant DM. A DM plant generally consists of cation, anion, and mixed bed exchangers. Any ions in the final water from this process consist essentially of hydrogen ions and hydroxide ions, which recombine to form pure water.

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Very pure DM water becomes highly corrosive once it absorbs oxygen from the atmosphere because of its very high affinity for oxygen. The capacity of the DM plant is dictated by the type and quantity of salts in the raw water input. However, some storage is essential as the DM plant may be down for maintenance. For this purpose, a storage tank is installed from which DM water is continuously withdrawn for boiler make-up.

The piping and valves are generally of stainless steel. Sometimes, a steam blanketing arrangement or stainless steel doughnut float is provided on top of the water in the tank to avoid contact with air.

DM water make-up is generally added at the steam space of the surface condenser i. This arrangement not only sprays the water but also DM water gets deaerated, with the dissolved gases being removed by a de-aerator through an ejector attached to the condenser.

Fuel preparation system[ edit ] Conveyor system for moving coal visible at far left into a power station. In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into small pieces and then conveyed to the coal feed hoppers at the boilers.

The coal is next pulverized into a very fine powder. The pulverizers may be ball mills , rotating drum grinders , or other types of grinders. Some power stations burn fuel oil rather than coal. The oil must kept warm above its pour point in the fuel oil storage tanks to prevent the oil from congealing and becoming unpumpable.

Boilers in some power stations use processed natural gas as their main fuel. Other power stations may use processed natural gas as auxiliary fuel in the event that their main fuel supply coal or oil is interrupted. In such cases, separate gas burners are provided on the boiler furnaces.

Barring gear[ edit ] Barring gear or "turning gear" is the mechanism provided to rotate the turbine generator shaft at a very low speed after unit stoppages.

Once the unit is "tripped" i. When it stops completely, there is a tendency for the turbine shaft to deflect or bend if allowed to remain in one position too long. This is because the heat inside the turbine casing tends to concentrate in the top half of the casing, making the top half portion of the shaft hotter than the bottom half. The shaft therefore could warp or bend by millionths of inches. This small shaft deflection, only detectable by eccentricity meters, would be enough to cause damaging vibrations to the entire steam turbine generator unit when it is restarted.

The shaft is therefore automatically turned at low speed about one percent rated speed by the barring gear until it has cooled sufficiently to permit a complete stop. Oil system[ edit ] An auxiliary oil system pump is used to supply oil at the start-up of the steam turbine generator. It supplies the hydraulic oil system required for steam turbine's main inlet steam stop valve, the governing control valves, the bearing and seal oil systems, the relevant hydraulic relays and other mechanisms.

At a preset speed of the turbine during start-ups, a pump driven by the turbine main shaft takes over the functions of the auxiliary system. Generator cooling[ edit ] While small generators may be cooled by air drawn through filters at the inlet, larger units generally require special cooling arrangements.

Hydrogen gas cooling, in an oil-sealed casing, is used because it has the highest known heat transfer coefficient of any gas and for its low viscosity which reduces windage losses.

This system requires special handling during start-up, with air in the generator enclosure first displaced by carbon dioxide before filling with hydrogen.

This ensures that the highly flammable hydrogen does not mix with oxygen in the air. The hydrogen pressure inside the casing is maintained slightly higher than atmospheric pressure to avoid outside air ingress. The hydrogen must be sealed against outward leakage where the shaft emerges from the casing. Mechanical seals around the shaft are installed with a very small annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to prevent the hydrogen gas leakage to atmosphere.

The generator also uses water cooling. Since the generator coils are at a potential of about 22 kV , an insulating barrier such as Teflon is used to interconnect the water line and the generator high-voltage windings. Demineralized water of low conductivity is used. Generator high-voltage system[ edit ] The generator voltage for modern utility-connected generators ranges from 11 kV in smaller units to 30 kV in larger units.

The generator high-voltage leads are normally large aluminium channels because of their high current as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminium bus ducts and are supported on suitable insulators. The generator high-voltage leads are connected to step-up transformers for connecting to a high-voltage electrical substation usually in the range of kV to kV for further transmission by the local power grid.

The necessary protection and metering devices are included for the high-voltage leads. Natural Draft cooling tower 2. Forced Draft cooling tower 3. Induced Draft cooling tower 4. Balanced Draft cooling tower Fan or draught system In a boiler it is essential to supply a controlled amount of air to the furnace for effective combustion of fuel and to evacuate hot gases formed in the furnace through the various heat transfer area of the boiler.

This can be done by using a chimney or mechanical device such as fans which acts as pump. When the gas within the stack is hot, its specific weight will be less than the cool air outside; therefore the unit pressure at the base of stack resulting from weight of the column of hot gas within the stack will be less than the column of extreme cool air. The difference in the pressure will cause a flow of gas through opening in base of stack. Also the chimney is form of nozzle, so the pressure at top is very small and gases flow from high pressure to low pressure at the top.

This fan forces the atmospheric air through the boiler furnace and pushes out the hot gases from the furnace through superheater, reheater, economiser and air heater to stacks. Induced draught: — Here a fan called ID fan is provided at the outlet of boiler, that is, just before the chimney. This fan sucks hot gases from the furnace through the superheaters, economiser, reheater and discharges gas into the chimney. This results in the furnace pressure lower than atmosphere and affects the flow of air from outside to the furnace.

The FD fan is utilized to draw control quantity of air from atmosphere and force the same into furnace. The ID fan sucks the product of combustion from furnace and discharges into chimney.

Thermal power station

The point where draught is zero is called balancing point. Ash handling system The disposal of ash from a large capacity power station is of same importance as ash is produced in large quantities. Ash handling is a major problem. The ash is collected directly through the ash outlet door from the boiler into the container from manually.

The precipitator has plate banks A-F which are insulated from each other between which the flue gases are made to pass. The dust particles are ionized and attracted by charged electrodes. The electrodes are maintained at 60KV. Hammering is done to the plates so that fly ash comes down and collect at the bottom.The largest reciprocating engine-generator sets ever built were completed in for the Manhattan Elevated Railway.

The expansion of the steam turbine produces mechanical power which drives the Excitation Generator Alternator coupled to the turbine.

49 Main Transformer. 50 Aux. Transformer.

Very pure DM water becomes highly corrosive once it absorbs oxygen from the atmosphere because of its very high affinity for oxygen. The two from the transformer are insulated, and the third one is bare.

The turbo-set, boiler and tanks containing sufficient fuel for days' service, and the auxiliary starting set, are accommodated in a gallery about ft. Thus, the steam turbine generator and the transformer form one unit. Steam control valve. Air-cooled condensers typically operate at a higher temperature than water-cooled versions. This arrangement not only sprays the water but also DM water gets deaerated, with the dissolved gases being removed by a de-aerator through an ejector attached to the condenser.

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