thermal+power+plant+report

8/12/2019 Thermal+Power+Plant+Report

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Introduction:

A thermal power station is apower plant in which theprime mover issteam driven. Wateris heated, turns into steam and spins asteam turbine which drives anelectrical generator.After it passes through the turbine, the steam iscondensed in acondenser;this is knownas aRankine cycle.The greatest variation in the design of thermal power stations is due to

the different fuel sources. Some prefer to use the term energy center because suchfacilities convert forms ofheatenergy into electrical energy.

Almost allcoal,nuclear,geothermal,solar thermal electric,andwaste incineration plants,as well as many natural gas power plants are thermal.Natural gas is frequentlycombustedingas turbines as well asboilers.The waste heat from a gas turbine can be used to raisesteam, in acombined cycle plant that improves overall efficiency.

Such power stations are most usually constructed on a very large scale and designed forcontinuous operation.

History:

Reciprocating steam engines have been used for mechanical power sources since the 18thCentury, with notable improvements being made byJames Watt.The very first commercialcentral electrical generating stations in New York and London, in 1882, also usedreciprocating steam engines. As generator sizes increased, eventually turbines took overdue to higher efficiency and lower cost of construction. By the 1920s any central stationlarger than a few thousand kilowatts would use a turbine prime mover.

Efficiency:

The electric efficiency of a conventional thermal power station, considered as saleableenergy produced at the plant bus bars compared with the heating value of the fuelconsumed, is typically 33 to 48% efficient, limited as all heat engines are by the laws ofthermodynamics. The rest of the energy must leave the plant in the form of heat. Thiswaste heat can be disposed of withcooling water or incooling towers.If the waste heat isinstead utilized for e.g. district heating, it is called cogeneration. An important class ofthermal power station are associated withdesalination facilities; these are typically foundin desert countries with large supplies of natural gas and in these plants, freshwaterproduction and electricity are equally important co-products.

Since the efficiency of the plant is fundamentally limited by the ratio of the absolutetemperatures of the steam at turbine input and output, efficiency improvements requireuse of higher temperature, and therefore higher pressure, steam. Historically, otherworking fluids such as mercury have been experimentally used in a mercury vapourturbine power plant, since these can attain higher temperatures than water at lowerworking pressures. However, the obvious hazards of toxicity, and poor heat transferproperties, have ruled out mercury as a working fluid.
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Steam generator or boiler:

Fig: Schematic diagram of typical coal-fired power plant steam generator highlighting the airpreheater (APH) location. (For simplicity, any radiant section tubing is not shown.)

The steam generating boiler has to produce steam at the high purity, pressure andtemperature required for the steam turbine that drives the electrical generator. Thegenerator includes the economizer, the steam drum, the chemical dosing equipment, andthe furnace with its steam generating tubes and the superheater coils. Necessary safetyvalves are located at suitable points to avoid excessive boiler pressure. The air andflue gaspath equipment include: forced draft (FD)fan,air preheater (APH), boiler furnace, induceddraft (ID) fan, fly ash collectors (electrostatic precipitator orbaghouse) and the flue gasstack.

For units over about 200 MW capacity, redundancy of key components is provided byinstalling duplicates of the FD fan, APH, fly ash collectors and ID fan with isolatingdampers. On some units of about 60 MW, two boilers per unit may instead be provided.

Boiler furnace and steam drum:

Once water inside theboiler orsteam generator,the process of adding the latent heat ofvaporization or enthalpy is underway. The boiler transfers energy to the water by thechemical reaction of burning some type of fuel.

The water enters the boiler through a section in the convection pass called theeconomizer.From the economizer it passes to the steam drum. Once the water enters thesteam drum it goes down the downcomers to the lower inlet waterwall headers. From theinlet headers the water rises through the waterwalls and is eventually turned into steamdue to the heat being generated by the burners located on the front and rear waterwalls(typically). As the water is turned into steam/vapor in the waterwalls, the steam/vaporonce again enters the steam drum. The steam/vapor is passed through a series of steamand water separators and then dryers inside thesteam drum.
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Thesteam separators and dryers remove the water droplets from the steam and the cyclethrough the waterwalls is repeated. This process is known asnatural circulation.

The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, sootblowers, water lancing and observation ports (in the furnace walls) for observation of thefurnace interior. Furnaceexplosions due to any accumulation of combustible gases after atrip-out are avoided by flushing out such gases from the combustion zone before ignitingthe coal.

The steam drum (as well as the superheater coils and headers) have air vents and drainsneeded for initial startup. The steam drum has internal devices that removes moisturefrom the wet steam entering the drum from the steam generating tubes. The dry steamthen flows into the superheater coils.

Geothermal plants need no boiler since they use naturally occurring steam sources. Heatexchangers may be used where the geothermal steam is very corrosive or containsexcessive suspended solids. Nuclear plants also boil water to raise steam, either directly

passing the working steam through the reactor or else using an intermediate heatexchanger.

Fuel preparation system:

In coal-fired power stations, the raw feed coal from the coal storage area is first crushedinto small pieces and then conveyed to the coal feed hoppers at the boilers. The coal isnextpulverized into a very fine powder. The pulverizers may beball mills,rotating drumgrinders,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 becomingunpumpable. The oil is usually heated to about 100C before being pumped through thefurnace fuel oil spray nozzles.

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

Air path:

External fans are provided to give sufficient air for combustion. The forced draft fan takesair from the atmosphere and, first warming it in the air preheater for better combustion,injects it via the air nozzles on the furnace wall.

The induced draft fan assists the FD fan by drawing out combustible gases from thefurnace, maintaining a slightly negative pressure in the furnace to avoid backfiringthrough any opening. At the furnace outlet, and before the furnace gases are handled bythe ID fan, fine dust carried by the outlet gases is removed to avoid atmospheric pollution.
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This is an environmental limitation prescribed by law, and additionally minimizes erosionof the ID fan.

Auxiliary systems:

Fly ash collection:

Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabricbag filters (or sometimes both) located at the outlet of the furnace and before the induceddraft fan. The fly ash is periodically removed from the collection hoppers below theprecipitators or bag filters. Generally, the fly ash is pneumatically transported to storagesilos for subsequent transport by trucks or railroad cars.

Bottom ash collection and disposal:

At the bottom of every boiler, a hopper has been provided for collection of thebottom ashfrom the bottom of the furnace. This hopper is always filled with water to quench the ashand clinkers falling down from the furnace. Some arrangement is included to crush theclinkers and for conveying the crushed clinkers and bottom ash to a storage site.

Boiler make-up water treatment plant and storage:

Since there is continuous withdrawal of steam and continuous return ofcondensate to theboiler, losses due to blow-down and leakages have to be made up for so as to maintain thedesired water level in the boiler steam drum. For this, continuous make-up water is addedto the boiler water system. The impurities in the raw water input to the plant generallyconsist ofcalcium andmagnesium salts which imparthardness to the water. Hardness in

the make-up water to the boiler will form deposits on the tube water surfaces which willlead to overheating and failure of the tubes. Thus, the salts have to be removed from thewater and that is done by a water demineralising treatment plant (DM). A DM plantgenerally consists of cation, anion and mixed bed exchangers. The final water from thisprocess consists essentially of hydrogen ions and hydroxide ions which is the chemicalcomposition of pure water. The DM water, being very pure, becomes highly corrosive onceit absorbs oxygen from the atmosphere because of its very high affinity for oxygenabsorption.

The capacity of the DM plant is dictated by the type and quantity of salts in the raw waterinput. 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 continuouslywithdrawn for boiler make-up. The storage tank for DM water is made from materials notaffected by corrosive water, such as PVC. The piping and valves are generally of stainlesssteel. Sometimes, a steam blanketing arrangement or stainless steel doughnut float isprovided on top of the water in the tank to avoid contact with atmospheric air. DM watermake-up is generally added at the steam space of thesurface condenser (i.e., the vacuumside). This arrangement not only sprays the water but also DM water gets deaerated, withthe dissolved gases being removed by the ejector of the condenser itself.
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Steam turbine-driven electric generator:

The steam turbine-driven generators have auxiliary systems enabling them to worksatisfactorily and safely. The steam turbine generator being rotating equipment generallyhas a heavy, large diameter shaft. The shaft therefore requires not only supports but alsohas to be kept in position while running. To minimise the frictional resistance to the

rotation, the shaft has a number ofbearings.The bearing shells, in which the shaft rotates,are lined with a low friction material like Babbitt metal. Oil lubrication is provided tofurther reduce the friction between shaft and bearing surface and to limit the heatgenerated.

Barring gear:

Barring gear (or "turning gear") is the mechanism provided to rotate the turbinegenerator shaft at a very low speed after unit stoppages. Once the unit is "tripped" (i.e., thesteam inlet valve is closed), the turbine coasts down towards standstill. When it stopscompletely, 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 toconcentrate in the top half of the casing, making the top half portion of the shaft hotterthan 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 tocause damaging vibrations to the entire steam turbine generator unit when it is restarted.The shaft is therefore automatically turned at low speed (about one revolution perminute) by the barring gear until it has cooled sufficiently to permit a complete stop.

Condenser:

Fig: Diagram of a typical water-cooled surface condenser.
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The surface condenser is a shell and tube heat exchanger in which cooling water iscirculated through the tubes. The exhaust steam from the low pressure turbine enters theshell where it is cooled and converted to condensate (water) by flowing over the tubes asshown in the adjacent diagram. Such condensers use steam ejectors or rotary motor-drivenexhausters for continuous removal of air and gases from the steam side to maintainvacuum.

For best efficiency, the temperature in the condenser must be kept as low as practical inorder to achieve the lowest possible pressure in the condensing steam. Since thecondenser temperature can almost always be kept significantly below 100oC where thevapor pressure of water is much less than atmospheric pressure, the condenser generallyworks under vacuum. Thus leaks of non-condensable air into the closed loop must beprevented. Plants operating in hot climates may have to reduce output if their source ofcondenser cooling water becomes warmer; unfortunately this usually coincides withperiods of high electrical demand forair conditioning.

The condenser generally uses either circulating cooling water from a cooling tower to

reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.

Feed water heater:

Fig: ARankine cycle with a two-stagesteam turbine and a single feedwater heater.
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In the case of a conventional steam-electric power plant utilizing a drum boiler, thesurface condenser removes the latent heat of vaporization from the steam as it changesstates from vapour to liquid. The heat content (btu) in the steam is referred to asEnthalpy.The condensate pump then pumps the condensate water through afeed water heater.Thefeed water heating equipment then raises the temperature of the water by utilizingextraction steam from various stages of the turbine.

Preheating the feed water reduces the irreversibilities involved in steam generation andtherefore improves the thermodynamic efficiency of the system. This reduces plantoperating costs and also helps to avoid thermal shock to the boiler metal when the feedwater is introduced back into the steam cycle.

Superheater:

As the steam is conditioned by the drying equipment inside the drum, it is piped from theupper drum area into an elaborate set up of tubing in different areas of the boiler. Theareas known as superheater and reheater. The steam vapor picks up energy and its

temperature is now superheated above the saturation temperature. The superheatedsteam is then piped through the main steam lines to the valves of the high pressureturbine.

Deaerator:

Fig: Diagram of boiler feed water deaerator (with vertical, domed aeration section and horizontal

water storage section.
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A steam generating boiler requires that the boiler feed water should be devoid of air andother dissolved gases, particularly corrosive ones, in order to avoidcorrosion of the metal.

Generally, power stations use a deaerator to provide for the removal of air and otherdissolved gases from the boiler feed water. A deaerator typically includes a vertical,domed deaeration section mounted on top of a horizontal cylindrical vessel which servesas the deaerated boiler feed water storage tank.

There are many different designs for a deaerator and the designs will vary from onemanufacturer to another. The adjacent diagram depicts a typical conventional trayeddeaerator. If operated properly, most deaerator manufacturers will guarantee that oxygenin the deaerated water will not exceed 7 ppb by weight (0.005 cm/L).

Auxiliary systems:

Oil system:

An auxiliary oil system pump is used to supply oil at the start-up of the steam turbinegenerator. It supplies the hydraulic oil system required for steam turbine's main inletsteam stop valve, the governing control valves, the bearing and seal oil systems, therelevant hydraulic relays and other mechanisms.

At a preset speed of the turbine during start-ups, a pump driven by the turbine main shafttakes over the functions of the auxiliary system.

Generator heat dissipation:

The electricity generator requires cooling to dissipate the heat that it generates. Whilesmall units may be cooled by air drawn through filters at the inlet, larger units generallyrequire special cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, isused because it has the highest knownheat transfer coefficient of any gas and for its lowviscosity which reduces windage losses. This system requires special handling duringstart-up, with air in the chamber first displaced by carbon dioxide before filling withhydrogen. This ensures that the highly flammable hydrogen does not mix withoxygen inthe air.

The hydrogen pressure inside the casing is maintained slightly higher than atmosphericpressure 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 areinstalled 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 about22kV and water is conductive, an insulating barrier such as Teflon is used to interconnectthe water line and the generator high voltage windings. Demineralized water of lowconductivity is used.
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Generator high voltage system:

The generator voltage ranges from 11 kV in smaller units to 22 kV in larger units. Thegenerator high voltage leads are normally large aluminum channels because of their highcurrent as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminum bus ducts and are supported on suitable insulators. The generator

high voltage channels are connected to step-up transformers for connecting to a highvoltageelectrical substation (of the order of 110 kV or 220 kV) for further transmission bythe local power grid.

The necessary protection and metering devices are included for the high voltage leads.Thus, the steam turbine generator and the transformer form one unit. In smaller units,generating at 11 kV, a breaker is provided to connect it to a common 11 kV bus system.

Other systems:

Monitoring and alarm system:

Most of the power plant operational controls are automatic. However, at times, manualintervention may be required. Thus, the plant is provided with monitors and alarmsystems that alert the plant operators when certain operating parameters are seriouslydeviating from their normal range.

Battery supplied emergency lighting and communication:

A central battery system consisting oflead acid cell units is provided to supply emergencyelectric power, when needed, to essential items such as the power plant's control systems,

communication systems, turbine lube oil pumps, and emergency lighting. This is essentialfor a safe, damage-free shutdown of the units in an emergency situation.

Transport of coal fuel to site and to storage:

Most thermal stations use coal as the main fuel. Raw coal is transported fromcoal mines toa power station site by trucks,barges,bulk cargo ships or railway cars. Generally, whenshipped by railways, the coal cars are sent as a full train of cars. The coal received at sitemay be of different sizes. The railway cars are unloaded at site by rotary dumpers or sidetilt dumpers to tip over onto conveyor belts below. The coal is generally conveyed to

crushers which crush the coal to about inch (6 mm) size. The crushed coal is then sentby belt conveyors to a storage pile. Normally, the crushed coal is compacted by bulldozers,as compacting of highly volatile coal avoids spontaneous ignition.

The crushed coal is conveyed from the storage pile to silos or hoppers at the boilers byanother belt conveyor system.
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Boiler or Steam generator:

A boiler or steam generator is a device used to create steam by applying heat energy towater. Although the definitions are somewhat flexible, it can be said that older steamgenerators were commonly termed boilers and worked at low to medium pressure(1300 psi/0.06920.684 bar; 6.8952,068.427 kPa), but at pressures above this it is

more usual to speak of a steam generator.

A boiler or steam generator is used wherever a source of steam is required. The form andsize depends on the application: mobile steam engines such as steam locomotives,portable engines and steam-powered road vehicles typically use a smaller boiler thatforms an integral part of the vehicle;stationary steam engines,industrial installations andpower stations will usually have a larger separate steam generating facility connected tothe point-of-use by piping. A notable exception is the steam-poweredfireless locomotive,where separately-generated steam is transferred to a receiver (tank) on the locomotive.

The steam generator or boiler is an integral component of a steam engine when

considered as aprime mover;however it needs be treated separately, as to some extent avariety of generator types can be combined with a variety of engine units. A boilerincorporates afirebox orfurnace in order to burn the fuel and generateheat;the heat isinitially transferred to water to make steam;this produces saturated steam atebullitiontemperature saturated steam which can vary according to the pressure above the boilingwater. The higher the furnace temperature, the faster the steam production. The saturatedsteam thus produced can then either be used immediately to produce power via aturbineand alternator,or else may be furthersuperheated to a higher temperature; this notablyreduces suspended water content making a given volume of steam produce more workand creates a greater temperature gradient in order to counter tendency tocondensationdue to pressure and heat drop resulting from work plus contact with the cooler walls of

the steam passages and cylinders and wire-drawing effect from strangulation at theregulator. Any remaining heat in the combustion gases can then either be evacuated ormade to pass through aneconomizer,the role of which is to warm thefeed water before itreaches the boiler.

Boiler types:

1.According to the contents in the tube.i. Fire tube boiler.

ii. Water tube boiler.2.According to the position of the furnace.i. Internally fired boiler.

ii. Externally fired boiler.3.According to the axis of the shell.

i. Vertical axis.ii. Horizontal axis.
http://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Heat_energyhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Pounds_per_square_inchhttp://en.wikipedia.org/wiki/Bar_%28unit%29http://en.wikipedia.org/wiki/Pascal_%28unit%29http://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Steam_locomotivehttp://en.wikipedia.org/wiki/Portable_enginehttp://en.wikipedia.org/wiki/Traction_enginehttp://en.wikipedia.org/wiki/Stationary_steam_enginehttp://en.wikipedia.org/wiki/Fireless_locomotivehttp://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Prime_mover_%28locomotive%29http://en.wikipedia.org/wiki/Fireboxhttp://en.wikipedia.org/wiki/Furnacehttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Saturated_steamhttp://en.wikipedia.org/wiki/Boilinghttp://en.wikipedia.org/wiki/Turbogeneratorhttp://en.wikipedia.org/wiki/Turbogeneratorhttp://en.wikipedia.org/wiki/Superheaterhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/w/index.php?title=Combustion_gas&action=edit&redlink=1http://en.wikipedia.org/wiki/Economiserhttp://en.wikipedia.org/wiki/Feed_waterhttp://en.wikipedia.org/wiki/Feed_waterhttp://en.wikipedia.org/wiki/Economiserhttp://en.wikipedia.org/w/index.php?title=Combustion_gas&action=edit&redlink=1http://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Superheaterhttp://en.wikipedia.org/wiki/Turbogeneratorhttp://en.wikipedia.org/wiki/Turbogeneratorhttp://en.wikipedia.org/wiki/Boilinghttp://en.wikipedia.org/wiki/Saturated_steamhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Furnacehttp://en.wikipedia.org/wiki/Fireboxhttp://en.wikipedia.org/wiki/Prime_mover_%28locomotive%29http://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Fireless_locomotivehttp://en.wikipedia.org/wiki/Stationary_steam_enginehttp://en.wikipedia.org/wiki/Traction_enginehttp://en.wikipedia.org/wiki/Portable_enginehttp://en.wikipedia.org/wiki/Steam_locomotivehttp://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Pascal_%28unit%29http://en.wikipedia.org/wiki/Bar_%28unit%29http://en.wikipedia.org/wiki/Pounds_per_square_inchhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Heat_energyhttp://en.wikipedia.org/wiki/Steam


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4.According to the number of tubes.i. Single tube boilers.

ii. Multitubular boilers.5.According to the method of circulation of water and steam.

i. Natural circulation boilers.ii.

Forced circular boilers.6.According to the use.

i. Stationary boilers.ii. Mobile boilers.

Combustion:

The source of heat for a boiler is combustion of any of several fuels, such aswood,coal,oil,or natural gas. Nuclear fission is also used as a heat source for generating steam. Heatrecovery steam generators (HRSGs) use the heat rejected from other processes such asgasturbines.

Solid fuel firing:

In order to improve the burning characteristics of the fire, air needs to be suppliedthrough the grate, or more importantly above the fire. Most boilers now depend onmechanical draft equipment rather than naturaldraught.This is because natural draughtis subject to outside air conditions and temperature of flue gases leaving the furnace, aswell as chimney height. All these factors make effective draught hard to attain andtherefore make mechanical draught equipment much more economical. There are threetypes of mechanical draught:

1. Induced draught: This is obtained one of three ways, the first being the "stackeffect" of a heated chimney, in which the flue gas is less dense than the ambient airsurrounding the boiler. The denser column of ambient air forces combustion airinto and through the boiler. The second method is through use of a steam jet. Thesteam jet or ejector oriented in the direction of flue gas flow induces flue gases intothe stack and allows for a greater flue gas velocity increasing the overall draught inthe furnace. This method was common on steam driven locomotives which couldnot have tall chimneys. The third method is by simply using an induced draught fan(ID fan) which sucks flue gases out of the furnace and up the stack. Almost allinduced draught furnaces have a negative pressure.

2.

Forced draught:draught is obtained by forcing air into the furnace by means of afan (FD fan) and ductwork. Air is often passed through an air heater; which, as thename suggests, heats the air going into the furnace in order to increase the overallefficiency of the boiler. Dampers are used to control the quantity of air admitted tothe furnace. Forced draught furnaces usually have a positive pressure.

3. Balanced draught:Balanced draught is obtained through use of both induced andforced draft. This is more common with larger boilers where the flue gases have totravel a long distance through many boiler passes. The induced draft fan works in
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conjunction with the forced draft fan allowing the furnace pressure to bemaintained slightly below atmospheric.

Water treatment:

Feed water for boilers needs to be as pure as possible with a minimum of suspended

solids and dissolved impurities which cause corrosion, foaming and water carryover.Various chemical treatments have been employed over the years, the most successfulbeing Porta treatment. This contains a foam modifier that acts as a filtering blanket on thesurface of the water that considerably purifiessteam quality.

Boiler safety:

Many steam engines possess boilers that arepressure vessels that contain a great deal ofpotential energy.Steam explosions can and have caused great loss of life in the past. Whilevariations in standards may exist in different countries, stringent legal, testing, trainingand certification is applied to try to minimise or prevent such occurrences.

Failure modes include:

overpressurisation of the boiler insufficient water in the boiler causing overheating and vessel failure pressure vessel failure of the boiler due to inadequate construction or

maintenance.

Essential boiler fittings:

Safety valve Pressure measurement Blowdown Valves Main steam Stop Valve Feedcheck valves Fusible Plug Water gauge Low-Water Alarm Low Water Fuel Cut-out Inspector's Test Pressure Gauge Attachment Name Plate Registration Plate Feedwater pump

Steam accessories:

Main steam stop valve Steam traps Main steam stop/Check valve used on multiple boiler installations.
http://en.wikipedia.org/wiki/Feed_waterhttp://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/w/index.php?title=Foaming&action=edit&redlink=1http://en.wikipedia.org/wiki/Carryover_with_steamhttp://en.wikipedia.org/wiki/Steam_qualityhttp://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Potential_energyhttp://en.wikipedia.org/wiki/Steam_explosionhttp://en.wikipedia.org/wiki/Safety_valvehttp://en.wikipedia.org/wiki/Pressure_gaugehttp://en.wikipedia.org/wiki/Check_valvehttp://en.wikipedia.org/wiki/Water_gaugehttp://en.wikipedia.org/wiki/Feedwater_pumphttp://en.wikipedia.org/wiki/Steam_traphttp://en.wikipedia.org/wiki/Steam_traphttp://en.wikipedia.org/wiki/Feedwater_pumphttp://en.wikipedia.org/wiki/Water_gaugehttp://en.wikipedia.org/wiki/Check_valvehttp://en.wikipedia.org/wiki/Pressure_gaugehttp://en.wikipedia.org/wiki/Safety_valvehttp://en.wikipedia.org/wiki/Steam_explosionhttp://en.wikipedia.org/wiki/Potential_energyhttp://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Steam_qualityhttp://en.wikipedia.org/wiki/Carryover_with_steamhttp://en.wikipedia.org/w/index.php?title=Foaming&action=edit&redlink=1http://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/wiki/Feed_water


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Combustion accessories:

Fuel oil system. Gas system. Coal system. Automatic combustion systems.

Steam turbine:

Introduction:

A steam turbine is a prime mover in which rotary motion is obtained by the gradual

change of momentum of the steam. In steam turbine, the force exerted on the blades is due

to the velocity of steam. This is due to the fact that the curved blades by changing the

direction of steam receive a force or impulse. The dynamical pressure of steam rotates the

vanes, buckets or blades directly. The turbine blades curved in such a way that the steam

directed upon them enters without shock, though there is always some loss of energy bythe friction upon the surface of blades. The basic principle of operation of a steam turbine

is the generation of high velocity steam jet by the expansion of high pressure steam and

then conversion of kinetic energy, so obtained into mechanical work on rotor blades.

Classification of steam turbine:

The steam turbines may be classified into the following types:

1.According to the mode steam actioni. Impulse turbine and

ii. Reaction turbine.2.According to the direction of steam flow

i. Axial flow turbine andii. Radial flow turbine.

3.According to the exhaust condition of steami. Condensing turbine and

ii. Non-condensing turbine.4.According to the pressure of turbine

i. High pressure turbine.ii. Medium pressure turbine and

iii. Low pressure.5.According to the number of stages

i. Single stage andii. Multi-stage turbine.
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Impulse turbine:

An impulse turbine, as the name indicates, is a turbine which runs by the impulse of steam

jet. In this turbine, the steam is first made to flow through a nozzle, then the steam jet

impinges on the turbine blades. The action of the jet of steam, impinging on the blades, is

said to be an impulse and the rotation of the rotor is due to the impulsive forces of the

steam jets. The steam impinges on the buckets with kinetic energy. De-Level turbine is thesimplest type of impulse turbine.

Reaction turbine:

In a reaction turbine, the steam enters the wheel under pressure and flows over the

blades. The steam while gliding, propels the blades and make them to move, as a matter

fact, the turbine runner is rotated by the reactive forces of steam jets. The backward

motion of the blades is similar to the recoil of gun. The steam glides over the moving vanes

with pressure and kinetic energy. The steam flows first through guide mechanism and

then through the moving blades. It may be noted that an absolute reaction turbine israrely used in actual practice.


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Impulse Turbine Stage:

As the steam passes through a nozzle from a high pressure pipeline to a lower pressureregion, the velocity of the steam increases as the thermal energy is converted to kineticenergy. The velocity of the flow depends upon the difference in pressures between thehigh pressure and the low pressure regions. The weight rate of flow depends upon the

velocity and the cross sectional area of the nozzle throat. This is illustrated in figure 1-2below. The decrease in thermal energy as the steam passes through the nozzle equals theincrease in kinetic energy, which is proportional to the square of the velocity.

KE = WV / 2gWhere KE = kinetic energy in ft lbW = weight of the steam in lbV = velocity of the steam in ft/secg = 32 ft /sec

If an obstruction, such as a turbine blade, is placed in the path of the flowing steam, the

steam will exert a force, or an "impulse" on the blade in an amount equal to the weightrate of flow and the velocity of the steam. As the blade moves due to this force, work isperformed on the blade in an amount equal to the force times the distance the blademoves due to this force. If the blade is one of a series of such blades connected to a rotor,the rotor will spin as the continuous flow of steam impinges on each successive blade.Such a device would constitute a simple form of a turbine called an impulse turbine. Thisaction is illustrated in figures 1-2 and 1-3 below.


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In order to obtain the maximum amount of work from the steam, all of its kinetic energymust be converted to work. In other words, the steam must leave the blade with zeroabsolute velocity. Assuming a frictionless blade, the velocity of the steam relative to theblade must be the same entering as leaving, but reversed in direction. Also, the bladevelocity must be one half of the entering steam velocity. (Refer to figure 1-3). There areactually two different forces acting on the blade. The first is the force of the steam jetstriking the blade, as described. The second is the reactive force due to the change indirection of the steam flow between the entrance and exit from the blade. In actualturbines, it is impractical to utilize the full advantage of complete reversal of the steam. Ina conventional impulse stage, the blades project radially from the wheel and the nozzlesare placed so that the steam flow is at an angle to the plane of rotation. (Shown in figure 1-4).


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The pressure and velocity changes taking place are shown in figure 1-4. The only pressuredrop occurs in the nozzle. The pressure entering the blades is the same as that leaving theblades.

Force Vector Diagram for Impulse Stage:

Now consider the force vector diagram of following figure. A mass of steam entering a rowof moving blades with a relative velocity V2 will have a momentum which will exert animpulse force F1 in the direction V2. The same mass of steam leaving the row of movingblades with a relative velocity V3will exert a reactive force F2on the blade opposite to thedirection of V3. If V2 is equal to V3in magnitude, assuming no friction between the steamand the blade, and if the blade entrance angle () is equal to the blade exit angle (), thecomponents T1and T2will be equal and opposite, and the resultant will produce zero axialthrust on the turbine wheel. In actual design, angle () is made slightly larger than angle() to account for friction between steam and blade.

T1 F1

R1

R2 T2

F2


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Model Steam Turbine

In this activity we will demonstrate how different energy sources can be used to spin aturbine. Remember that the sole purpose of spinning a turbine at a power plant is to rotatean electrical generator. The turbine in this activity is not strong enough to operate anelectrical generator; however, we can still experience how the force of steam is used to

make a turbine spin. We will also be constructing a device that produces steam in amanner similar to that used at a steam-driven power plant. We will recall from the theorythat the actual steam production technology at a power plant is extremely sophisticatedand produces steam at very high pressures. However, this activity works well enough toget the point across.

Steam turbines have come very much to the fore during recent years, especially formarine propulsion. In principle they are far simpler than cylinder engines, steam beingmerely directed at a suitable angle on to specially shaped vanes attached to a revolvingdrum and shaft. In the Parsons type of turbine the steam expands as it passes throughsuccessive rings of blades, the diameter of which rings, as well as the length and number of

the blades, increases towards the exhaust end of the casing, so that the increasing velocityof the expanding steam may be taken full advantage of. The De Laval turbine includes but asingle ring of vanes, against which the steam issues through nozzles so shaped as to allowthe steam to expand somewhat and its molecules to be moving at enormous velocitybefore reaching the vanes. A De Laval wheel revolves at terrific speeds, the limit being tensof thousands of turns per minute for the smallest engines. The greatest efficiency isobtained, theoretically, when the vane velocity is half that of the steam, the latter, afterpassing round the curved inside surfaces of the vanes, being robbed of all its energy andspeed. The turbines to be described work on the De-Laval principle, which has beenselected as the easier for the beginner to follow.

A Very Simple Turbine:

We will begin with a very simple contrivance, shown in Figure. As a "power plant" it isconfessedly useless, but the making of it affords amusement and instruction. For the boilerselect a circular pipe, of diameter 4 inches, so as to give plenty of heating surface, and atleast 6 inches deep, to ensure a good steam space and moderately dry steam, welded bothside to make it water tight. A shallow boiler may "prime" badly, if reasonably full, and flingout a lot of water with the steam. Clean the metal round the joints, and drill three holes onthe upper portion, one for water inlet, one for steam outlet and last one is for mountingpressure gauze, two half an inch in diameter and one inches in diameter. For the turbineblades take a piece of thin sheet GI; flatten it out. Then scratch a series of marks on thesheet and turn it to seven numbers of pieces of equal dimensions and make a slight bendfrom the two nearest edges to make them in the form of curved shape. And directlywelded them in equal distance on the circumference of the turbine hub. Turbine hub andshaft are made up of stainless steel with two numbers of ball bearings and the wholeassembly is supported on stand. A check valve is fitted on steam outlet to control the flowsof steam through the pipelines and turbine. Pipeline is made up of mild steel, half an inchin diameter. Nozzle is fitted in the pipe line. A rigid frame made up of mild steel is made tosupport the whole establishment.


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VANE NOZZLE OUTLET PIPE LINE

P.G.

C.V. W.I.

HUB

SHAFT

HEAT*

SUPPORT

C.V. = Check Valve

W.I. = Water Inlet

P.G. = Pressure Gauge

Fig: Steam Turbine Model

*Note: Heat is supplied with the aid of electric heater of 1000W

BOILER


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Model of steam turbine:

Main components:

Boiler: The boiler is made from a mild steel circular pipe, of diameter 4 inches, so as to

give plenty of heating surface, 6mm thickness and at least 6 inches deep, to ensure a good

steam space and moderately dry steam, welded both sides (upper and lower) to make it

water tight. A shallow boiler may "prime" badly, if reasonably full, and fling out a lot of

water with the steam. Clean the metal round the joints, and drill three holes on the upper

portion, one for water inlet, one for steam outlet and last one is for mounting pressure

gauze, two half an inch in diameter and one inches in diameter. One socket of inches

in diameter is fixed by welding joint, two numbers of half inches socket are also welded

with upper portion of boiler. Boiler is filled with water in such a manner that space for

steam must be there above the water surface. Water is heated by electric heater of 1000W.

Heater is fitted below the boiler and supply heat at a constant rate. Formation of Dry

steam is occurred just above the water surface. Boiler must be sustain heat and steampressure due to safety reason. For that precaution must be followed.

Steam outlet pipe: Simple mild steel pipe of half inches in diameter is used as a steam

outlet pipe. It is connected with check valve. Nozzle is fitted with this pipe to increase the

velocity of the steam by decreasing the pressure. Steam outlet pipe must be sustain the

steam pressure.

Check valve: Check valve is fitted between the outlet pipe and the socket. It is used to

check the flow of steam or in other words to control the flow of steam. It is made up of

brass material due to safety reason. It is fitted just above the boiler shell and manuallyoperated. We can control the flow of steam by revolving the wheel of valve.

Pressure gauge: A Bourdon type pressure gauge is fitted on the boiler to know the

steam pressure inside the boiler. Pressure gauge is one of the important mounting.

Pressure gauge must be fitted on every boiler due to safety reason or in other words to

minimum the risk or hazards. Pressure gauge shows reading in both C.G.S. system and

F.P.S. system (in both kg/cm2 and psi).

Nozzle: Nozzle is a device which is used to increase the velocity of fluid by decreasing

pressure. Convergent-divergent nozzle is commonly used for this purpose. We constructthis nozzle from a mild steel bar of half inches diameter. Drilled a 3mm hole through the

center. On the outside end, enlarge this hole to 5mm to a depth of 200mm. Nozzle is fitted

with outlet pipe so that the steam may expand and gain velocity as it approaches the

blade.


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Turbine wheel: Turbine wheel consists of shaft, hub and blades. Hub is made up of

stainless steel and blades are welded on the circumference of the hub in equal distance.

Shaft is fitted in the hub and rotates along its axis with the aid of steam force. Shaft is made

up of mild steel material. To decrease the friction between the shaft and inner surface of

the hub two ball bearings are fitted between them.

Components of turbine wheel:

1. Shaft.2. Hub.3. Bearings.4. Blades or vanes.

Blades: Seven numbers of vanes are fitted on the hub of the turbine. Constructionprocedures of making blades are to mark out a piece of GI sheet to form seven rectangles,2.5 inches by 6 inches. Cut very carefully according to the marking line. In the edge of a

piece of hard wood 1 inch thick file a notch 3/8 inch wide and 1/8 inch deep with a 1/2-inch circular file and procurea metal bar which fits the groove loosely. Each blade is laid inturn over the groove, and the bar is applied lengthwise on it and driven down with amallet, to give the blade the curvature of the groove. When all the blades have been madeand shaped, weld them on the circumference of the hub. True up the long edges of theblades with a file, and bring them off to a sharp edge, removing the metal from the convexside.

Frame: A rigid frame is made from 1x1 inch MS angle to support the wholearrangement. Frame must have enough strength to give proper support.


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Conclusion:

In this activity we will demonstrate how different energy sources can be used to spin a

turbine. Since this activity is a simple demonstration, the full scientific method outline is

not called for here. The turbine in this activity is not strong enough to operate an electrical

generator; however, we can still experience how the force of steam is used to make a

turbine spin. We will also be constructing a device that produces steam in a mannersimilar to that used at a steam-driven power plant. We will recall from the theory that the

actual steam production technology at a power plant is extremely sophisticated and

produces steam at very high pressures. However, this activity works well enough to get

the point across. Our main motto is to make a working model of steam turbine which may

be in use for demonstration purpose.

Bibliography:

Steam Turbine and Steam Power Plant--by R. Yadav

A text book of Thermal Engineering--by R.S. Khurmi

& J. K. Gupta

thermal+power+plant+report

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