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POWER PLANT ENGINEERING

NME:801

Presented byMD GULFARAZ ALAMAssistant professorJETGI Barabanki

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Unit II Steam power plant

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General layout of steam power plant

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Power plant boilers Boilers

Water tube Fire tube

Babcock Wilcox

Benson boiler

Critical pressure

Cochran boiler

Lancashire

boiler

Locomotive boiler

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Super critical boilers.In all modern power plants, high pressure boilers (> 100

bar) are universally used. These high pressure boiler is known supercritical boiler.

Types of super critical boilers are as follows.La Mont boilerBenson boilerLoeffler boiler

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La Mont boiler

A forced circulation boiler was first introduced in 1925 by La Mont. The arrangement of water circulation and different components are shown in Fig.

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Loeffler boilerThe major difficulty experienced in Benson boiler is the

deposition of salt and sediment on the inner surfaces of the water tubes.

The difficulty was solved in Loeffler boiler by preventing the flow of water into the boiler tubes.

Most of the steam is generated outside from the feed water using part of the superheated steam coming out from the boiler.

This boiler can carry higher salt concentration than any other type and is more compact than

indirectly heated boilers having natural circulation.

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Boilers mountings and accessoriesMounting:- Boiler mountings are used to run a boiler in a

safe way ex: safety valve, Water level indicators etc.accessories:-Boiler accessories are used to improve the

efficiency of a boiler ex: economizer, air pre-heater etc

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Coal handling Coal delivery equipment is one of the major components of

plant cost. The various steps involved in coal handling are as follows,

Coal Deliver

yUnloadi

ngTransfe

rOutdoor Storage

Covered

Storage

In Plant Handlin

g

Weighing&Measuring

Furnace

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pulverizers and coal burners A pulverized coal burner should satisfy the following

requirements: It should mix the coal and primary air thoroughly and should bring

this mixture before it enters the furnace in contact with additional air known as secondary air to create sufficient turbulence.

It should deliver and air to the furnace in right proportions and should maintain stable ignition of coal air mixture and control flame shape and travel in the furnace.

Coal air mixture should move away from the burner at a rate equal to flame front travel in

order to avoid flash back into the burner.

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Fluidized bed combustion Burning of pulverised coal has some problems such as particle size of coal used in pulverised firing is limited to 70-100 microns.

the generation of high temp. about (1650 C) in the furnace creates number of problems like slag formation on super heater.

Fluidized Bed combustion system can burn any fuel including low grade coals (even containing 70% ash), oil, gas or municipal waste.

tubes

Air

Flue gases

steam

Fuel anddolomite

water

Distributer plate

tubes

ash

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Ash handling systemA large quantity of ash is, produced in steam power plants

using coal. Ash produced in about 10 to 20% of the total coal burnt in the furnace.

It is desirable to quench the ash before handling due to following reasons:

1. Quenching reduces the temperature of ash.2. It reduces the corrosive action of ash.3. Ash forms clinkers by fusing in large lumps and by

quenching clinkers will disintegrate.4. Quenching reduces the dust accompanying the ash.

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The commonly used ash handling systems (i) Hydraulic system(ii) pneumatic system(iii) Mechanical system.

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Dust collection system In coal fed furnaces the

products of combustion contain particles of solid matter floating in suspension.

This may be smoke or dust. In spreader stokers and

pulverised coal fired furnaces the coal is burnt in suspension and due to this dust in the form of fly ash is produced. The size of dust particles is designated in microns (1 μ =0.001 mm).

The disposal smoke to the atmosphere is not desirable due to the following reasons

A smoky atmosphere is less healthful than smoke free air.

Smoke is produced due to incomplete combustion of coal.

In a smoky atmosphere lower standards of cleanliness are prevalent.

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condenser and cooling towers and cooling ponds Condenser:- A closed vessel in which steam is condensed

by abstracting the heat and where the pressure is maintained below atmospheric pressure is known as a condenser.

Steam condenser are of two types:1. Surface condenser. 2. Jet condenser.

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Types of condenserSurface type Jet type In surface condensers there is

no direct contact between the steam and cooling water and the condensate can be re-used in the boiler.

In such condenser even impure water can be used for cooling purpose whereas the cooling water must be pure in jet condensers.

In jet condensers the exhaust steam and cooling water come in direct contact with each other.

The temperature of cooling water and the condensate is same when leaving the condensers.

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Governing of turbine Governing of steam turbine means to regulate the supply

of steam to the turbine in order to maintain speed of rotation sensibly constant under varying load conditions.

(i) Bypass governing. (ii) Nozzle control governing. (iii) Throttle governing.

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Regeneration and reheatingRegeneration Re heating In regeneration cycle, the heat

energy from the exhaust flue gases is transferred to the compressed air before it enters the combustion chamber.

In reheat cycle, the combustion gases are not expanded in one turbine only but in two turbines.

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Operation and maintenance of steam power plant Application of control power illuminates all the malfunctions lights. Operate ‘Reset switch’ to reset malfunctions circuits: By doing so,

malfunction lights go off and all control devices assume the condition for starting.

Operate “Start” switch to initiate starting sequence. By doing this, lube oil pump and cooling fan start. If there are separate switch for these, operate these.

When lube oil reaches a preset pressure, the starter is energized and cranking of the engine begins.

With the cranking of starting of starter, the engine and exhausts ducts are purged of any combustible gases that might be present.

During the cranking cycle, the fuel boost pump is used and operated to increase fuel pressure.

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Heat balance and Efficiencythis is a useful method to watch the performance of the

diesel power plant.Among all the heat supplied to an engine only part of it is

converted into useful work.The heat balance of an engine depends on a number of

factors among which loads are primary importance.Quantity of cooling water and its outlet and inlet

temperatures.

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Site selection of a steam power plant These are the factors effecting the selection of power

plantAvailability of water.Distance from populated area.Distance from load center.Accessibility to site.Waste disposal.