Material on Steam Power Plants

7/26/2019 Material on Steam Power Plants

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THERMAL POWER PLANTS Prepared By MANOJ

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WORKING PRINCIPLE OF STEAM POWER PLANT

The main components of power plants are boiler-generating steam of more or less parameters of asteam turbine and an electrical generator having mutual shaft line with turbine that is connected to

a transformer to an electrical grid of power system.

First the coal delivered is unloaded in to the storage piles, then conveyed to the plant, crushed intopieces of approximately 1" and brought to coal silo.

From the coal silo it is sent to mill, where it is pulverized.

The forced drought (draft) fan supplies the mills with the hot air, heated in the boilers air-heater.

The hot air is mixed with the pulverized coal and forwarded through the boiler burners in to thefurnace, a chamber where fuel is burned. The burned fuel forms fire jets with temperature s over

1500oC (2730

oF ) as a might source of radiant and heat energy.

Some of the water is lightly reheated in economizer. In these tubes feed water is heated andpartially evaporated.

Then exits so called drum type boiler, where drum is used for separation of water and steam.

Steam flow go into the boiler super heater, where steam temperature and consequently heat energy

is rise. High parameter steam is brought through the main steam lines in to the turbine.

Expanding the steam works and makes the turbine rotate together with the generator coupled withthe turbine .In this mechanical energy is converted in to the electrical energy.

After the furnace and super heater, the furnace flue gas passes the economizer tubes.

The fuel gas comes in to the air heater where gas temperature reduces to 140-160oC.

The down steam the air heater, the fuel gas directed in to the stack with the help of the induced

draught fans. The precipitates, installed in this way, have to catch the dry fly ash from the gas.


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Steam and Drain System In Power Plants

Turbines:Auxiliary Steam PRDS(Pressure Desuperheating System):

Auxiliary steam system is intended to provide steam to turbine auxiliaries, during start up, lowloads and also during normal operation.

From the main steam line to turbine line , a tap-off is taken for Aux. steam PRDS. The steam istapped from main and reduced required pressure with the pressure control valve and the temparature is

reduced to the required temperature through a de-superheating station (by cooling it with spray watertaken from boiler feed pump discharge and pressure of spray water is reduced through the pressure

control valve(PCV) and flow is controlled by a temperature control valve(TCV). A safety valve (PSV) isprovided to protect the downstream system against excessive pressure rise.

The system provides the steam to the following utilities:

Turbine Gland Sealing : During start up and low loads

Steam jet ejectors : To create vaccumDeaerator :when turbine extractions is not available

Pegging Steam is used and during the startup conditions initial heating is done.Process : To use for some external purpose. (not cupulsary)

Parameters:

Flow Tone Per Hour (TPH)Temperature C

Pressure ATA

EXTRACTION STEAM:

The turbine is a single cylinder machine which offers the following extractions

Extraction I : Uncontrolled Extraction to LP Heater

Extraction II : Uncontrolled Extraction to Deaerator

Extraction III : Uncontrolled Extraction to HP Heater

Extraction I :

The steam is extracted from turbine casing and connected to LP Heater. Where the condensate canbe heated at some required parameters and send to the LP heater. The turbine extraction line is provided

with a two non return valves (QCNRV(Hydralic operated valve) & other one is flap NRV) connected at

the turbine end and a Motorised isolating valve connected at LP Heater end.

Extraction II :

The steam is extracted from turbine casing and connected to Deaerator. In the extraction line thereare two non return valves(hydraulic operated valves) at the end of the turbine. A motorized operated valve

are also provided in the extraction line at the deaerator end. When the extraction steam is not taken thendeaerator is supplied steam from auxiliary steam.


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3Extraction III :

The steam is extracted from turbine casing and connected to HP Heater. Where the condensate canbe heated at some required parameters and send to the BFP via. Boiler,So that the efficiency of boiler

increases. The turbine extraction line is provided with a two non return valves (QCNRV(Hydralicoperated valve) & other one is flap NRV) connected at the turbine end and a Motorised isolating valve

connected at HP Heater end.

The power assisted check valves are hooked up to the turbine governing system to make themclose with every trip of the turbine.

These nrv and motorized operated valve closes under interlock action when the water level

reaches High-High level set point in Heaters.

To safeguard the turbine against water ingress into turbine which may cause lot of damage toturbine we use non return valves.

The drains are mainly connected inbetween NRVs and Motorised isolating valve. During the start

up of the turbine, entire extraction steam piping up to the isolation valve is to be drained. The drain valves

are closed only after extablishing steam flow through the line.

Parameters:


Pressure ATA

EXHAUST DRAINS SYSTEMGLAND STEAM:

From the clearance between rotor and turbine glands the steam tries to escape, So inorder to sealthis glands we use gland steam (from the main steam a tap-off is taken and set at required parameters).

The purpose of the gland steam system is to seal the inner compartments against the atmosphere byadmitting the steam to front and rear glands at a pressure slightly above atmosphere.If the glands are not

sealed the air tries to enter through the glands and this may lead to loss of vaccum and thereafter vaccumcannot be established in the condenser. So, it is necessary to seal the glands.

Pressure and temperature indications are provided on the balance piston leak-off line to knownthe excessive leakages through the glands. Whenever these are exceeding the valves mentioned in first

commissioning report, the glands is to be replaced after taking shut-down.The steam is supplied through a control valve(PCV) at a constant pressure of 1.1 ata from the

Auxiliary steam header.During running of turbine the excess leakage from the turbine glands is dumped to condenser

through control valve(PCV).

GSC bypass to atmosphere is provided which will be used when GSC is taken out formaintenance.

Parameters:

Flow Tone Per Hour (TPH)

Temperature CPressure ATA


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4GLAND STEAM CONDENSER

The excess leakage from the turbine glands and the steam used for gland sealing is removed fromthe front and rear glands of the turbine and connected to the gland steam condenser where the gland steam

is condensed using condensate as cooling medium. This shall prevent steam oozing out from the glandsand heating the bearings pedestrals.Gland steam ejectors are used to create vaccum in the condenser.

VACCUM BREAKER

In case of turbine trip, vaccum is deliberately broken in the condenser by admitting air into thecondenser through a motor operated valve. This shall shorten the coasting down time of turbine.

Parameters:


Pressure ATA

EXHAUST HOOD SYSTEMIt is necessary to run the turbine in no load conditions for prolonged period. During this period,

the exhaust hood temperature rises beyond the safe limit, especially in material point of view. Hence it is

necessary to limit the temperature by spraying the condensate through nozzles (the solenoid valve) fittedin the exhaust hood. The spray water is taken from condensate extraction discharge pump. The solenoidvalve opens automatically when the temperature switch exceeds the preset value and when temperature

returns to safe limit the solenoid valve closes automatically thus stopping the spray water supply.Parameters:


Pressure ATA

TURBINE DRAINS

All drains from the turbine are connected to surge pipe arranged adjacent to the condenser whichare under high pressure and temp. The top of the surge pipe is connected to steam space and bottom to the

hotwell of the condenser. The hot drains may thus flash out in the surge pipe without endangering thecondenser tubes.

The inlet of the surge pipe must be minimum of 250mm above the max. water level in thecondenser. The HP drain lines should be connected nearer to hotwell and LP drain lines should be

connected nearer to steam space on the surge pipe.

MOTOR OPERATED GATE VALVEThe gate valve is provided in the live steam line to isolate the turbine during the shut-down period.

BY-PASS VALVE:During startup , steam is admitted steadily through the bypass valve for warming up the pipe line.

After attaining the required parameters the motor operated gate valve is opened and by pass valve is

closed.


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5WET STEAM WASHING SYSTEM:

This system is envisaged to clean unwanted salts deposited on the turbine blades. A pressuremeasurement is provided in the wheel chamber zone which helps in knowing about the salt deposited on

turbine blading during the course of turbine running.

EMERGENCY STOP VALVE:To stop the live steam entering into the turbine when a problem arises in turbine.

Governing Valve : The function of the valve is to control the steam inlet of the turbine.Balance piston leak off : It control the excess enlargement of rotor near the thrust bearings by

extracting the steam and this steam is connected to the controlledextractions.

Check valves (QCNRV) : These check valves are located on the extractions that are taken from theturbine in order to stop the back flow from the concerned equipments.

QCNRV(Quick Control Non Return Valve)Steam trap :To discharge condensate

PCV : used to control the pressureTCV : used to control the temperature.

Flow element : to measure the flow

Drains are provided in the valve block(emergency valve and governing valve) and turbine casing whichwill be opened during stratup and closed only after warming up period, these valve shall be kept openedduring the shut-down period.

Condensate System In Power Plants

The condensate systeam is used to condense the steam. (This works under the principle of shell and tubeOn the shell side steam enters from the turbine ie to be condensed and on tube side waters acts as the

coolant to condense the steam. The coolant is taken from cooling water tank . The cooling water ispumped with high pressures and connected to the condenser. The pump is designed is such a way that it

should recover all the losses and pr. Drop). The condensate is drawn from the main condenser hotwell byone of the two 100% extraction pumps. In case of pump failure, the standby pump comes into existence

automatically. The pump is designed in such a way that it can recover the overall pressure drop(sjae+gsc+lp+deaerotor+losses). From the pump discharge the condensate passes through the ejector

condenser, GSC, LP and deaerator where it is employed as cooling medium. From the deaerator it isunruffled to BFP there after it is unperturbed to the HP via boiler with required pressure from the BFP.

HOT-WELL:

From the hotwell, the condensate is send to the concerned equipments as the cooling medium.Normal level in the hotwell is maintained by recirculating the minimum flow requirements to the

concerned equipments. An LCV is positioning in the hotwell. When the level exceeds the normal level,the dump control valve opens to increase the flow from the hotwell and maintains the constant level in the

hotwell.


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CONDENSATE EXTRACTION PUMPS:

The condensate is drawn from the main condenser hotwell by one of the 2 x 100% extraction

pumps. In case of pump failure, the standby pump comes into existence automatically .

a) The following shall be ensured for starting of the pump:

Suction valve is open

Hot level should not be lowMinimum recirculation valve should be fully open

When pressure at the discharge of the pump is more than a preset value, the following shall be done

Opening the discharge valve

standby condensate pump shall be switched ON automatically when level in the hotwell rises toHIGH LEVEL or the discharge pressure of pump falls below a preset valve.

pump shall trip when any of the following conditions exists:

hot well level falls below a preset very low level.

Motor protection circuit operated.

Bypass valves for cep discharge valves are provided only for initial priming of system. These valves

are kept normally closed.

AIR EJECTOR SYSTEM:

The air ejector system is used to create the vaccum in the condenser. It consists one hoggingejector and two main ejectors one in working condition and other as standby. To create vaccumduring starting in the short time, hogging ejector is used when the vaccum reaches 500-550mm of

the column and after stabilization of main ejector, hogging ejector shall be manually stopped.

Motive steam for the starting ejector & running ejector is taken from auxiliary steam header.

To create vaccum during startup in the short time, hogging ejector is put into service by first

opening the steam side valve (to create vaccum in the ejector) and then the air side valve (which is

above the atmospheric pressure ). Limit switch in the valve shall be used to ensure that the valve isopen before the ejector is put into service.

When condenser vaccum reaches 500mm hg, one of the two ejectors is brought into service byopening the respective steam side valve.

When the condenser reaches 600mm hg, starting ejector is taken out of services by first closing theair side valve and then closing steam side.

CONTROL AND INTERLOCKING FUNTIONS:

HOT-WELL LEVEL CONTROLS :

For initiating alarms, interlocks, controls and actions following are provided on the hot well.

VERY LOW LEVEL (LSLL):Two level switches in 1 out of 2 logic shall be annunciated in the control room and condensate

pump shall trip under interlock action.

LOW LEVEL (LSL):One level switch shall annunciated in the control room


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HIGH LEVEL (LSH):

One level switch shall annunciated in the control room and standby pump shall be startedautomatically.

LEVEL TRANSMITTERS (LT):

Two level transmitters to select the average level in the hot well.

HIGH HIGH LEVEL (LSHH):One level switch annunciated in the control room.

NORMAL LEVEL:This shall be used for START PREMISSIVE for condensate extraction pump.

Normal level in the hot well is maintained by hot well level controlled by positioning the excess dumpcontrol valve(LCV1) and make up control valve(LCV2). As the hot well level rises, the dump control

valve opens to increase the flow from the hot well and maintains the constant level in the hot well. Whenthe hot well level falls, the make up control valve opens to maintain the constant level in the hot well.

MINIMUM RECIRCULATION CONTROL:

Minimum recirculation control valve(LCV1) along the deaerator level control valve(LCV2) maintains a

minimum flow of condensate through CEP at all modes of operation. Two flow transmitters installedacross the flow orifice downstream of GSC in one of the two mode to feed signal to controller which

modulates minimum recirculation control valve.Here the control valves(LCV1 &LCV2) is operated by flow controller.

FEED WATER SYSTEM IN POWER PLANTS:

The feeding heating system consists of one LP heater, one Deaerator, One HP heater.

LP HEATER :The LP heater is condensing heater with an external drain cooler. The header and drain cooler are

horizontally designed. An extraction is taken from the turbine and connected to the shell side to heat thecondensate and condensate is taken from the hotwell. Normal drains of LP heater are cascated to

condenser. Afer passing through the LP heater it enters the deaerator feed storage tank via deaerator.

DEAERATOR:

Deaerator is used to remove the air bubbles in the condensate so that no oxide are formed in thecondensate. Deaerator is designed to operate under constant pressure mode Heating system bled from

turbine. During the startup conditions intial heating process is done by taking from an external source i.eauxiliary steam header at required parameters. When turbine extraction is not available, deaerator is

pegged from an external source i.e, auxiliary steam header through deaerator pegging control station. Anrv is used to stop the back flow.


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BOILER FEED PUMP

The condensate is drawn from the Deaeratorl by one of the 2 x 100% extraction pumps. In case ofpump failure, the standby pump comes into existence automatically .

a) The following shall be ensured for starting of the pump:

Suction valve is openb) When pressure at the discharge of the pump is more than a preset value, the following shall be done

Opening the discharge valve Standby condensate pump shall be switched ON automatically when discharge pressure of pump

falls below a preset valve.

Pump shall trip when any of the following conditions exists:

When Deaeratorl level falls below a preset very low level.

Motor protection circuit operated.

HP HEATER:HP heater is condensing heater with a flash tank(under high level conditions,the alternative path

provided on heater diverts the drains directly to the flash tank). The header and drain cooler arehorizontally designed. An extraction is taken from the turbine and connected to the shell side to heat the

condensate and condensate is taken from the hotwell. Normal drains of LP heater are cascated tocondenser. Afer passing through the LP heater it enters the deaerator feed storage tank via deaerator.

CONTROL AND INTERLOCKING FUNTIONS:

DEAERATOR LEVEL CONTROL :For initiating alarms, interlocks, controls and actions following are provided on the hot well.

VERY LOW LEVEL (LSLL):

Three level switches shall be annunciated in the control room and boiler feed pump shall trip underinterlock action.

LOW LEVEL (LSL):One level switch shall annunciated in the control room

HIGH LEVEL (LSH):

Highlevel in the feed storage tank shall be shall annunciated in the control room.

One level switch at 50mm above HIGH LEVEL(LSH) for deaerator overflow valveopen interlock and annunciated in the control room.

One level switch at 50mm below HIGH LEVEL(LSH) for deaerator overflow valve closesinterlock and annunciated in the control room.

LEVEL TRANSMITTERS (LT) :Two level transmitters to select the average level in the Deaerator.

HIGH HIGH LEVEL (LSHH):One level switch annunciated in the control room.

Closing the motor operated valve and then the qcnrv & nrv that are located on the steam supply

line from deaerator to turbine.


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Closing of deaerator pegging control valve(PCV) located on the steam supply line to deaerator

from auxiliary steam header.

Repeatedly opening the motor operated drain valve.

Closing the motor operated valve on incoming condensate to deaerator.

NORMAL LEVEL:This shall be used for START PREMISSIVE for Boiler Feed Pump.

Lubrication System In Power Plants

Through there are many rotating equipments in a power plant the heart of a power plant is lube oilsystem. The oil system is so designed that each bearing under consideration is supplied with oil to the

required parameters of pressure, temperature and flow and the outlet oil from all the bearings is drainedproperly back to the system so that the lubrication system shall be a closed cut lubrication system.

Oil from the Main oil tank will b pumped by the main oil pump (driven by a.c) to the bearings in

the system through coolers and filters. Thus cool and filtered oil will enter into the bearings in therequired/designed qualities at the designed pressure.

This oil will form as a wedge/hydrodynamic oil film in between and the shaft on which the shaft

rotates, thus eliminating metal to metal contact.

The oil after taking away the heat in the bearings will flow in between bearings and comes back tothe main oil tank, making the system as a closed circuit one.

Since a highly reliable and continuous lubricatin of the bearings is of the utmost importance,sufficient redundancy is provided in the lubricating system. In case of any problem with Main oil pump/Auxiliary oil pump will take over and in case auxiliary oil pump also develops problem. Emergency oil

pump (run by dc) will come into operation. However emergency oil pump operation is only to ensureproper lubrication during the coasting down period. If Emergency oil pump also fails., which is last

possible than oil from over head oil tank will be supplied to the bearings for coasting down period.

In certain cases when rotor are heavy jacking oil is provided . It ensure that during startup to liftthe rotor rating metal to metal contact. The jacking oil pump will stop as soon as the film is formed.

Jacking oil is required for all the cases. It will be used where the bearings specific pressure is high

MAIN OIL TANK The oil tank is located on the ground.

The oil tank serves for storing the oil volume required for governing and lubricating system. Itallows the impurities to be deposited at the bottom of the tank along with the oils sludge. A

gradient is provided at the bottom of the tank to enable the impurities to be collected for easydrain-off. Baffle plates are provided to give a longer time in the tank, so that the entrapped air is

effectively released. Level gauge and level transmitter indicate the level in the tank.

The oil vapor extraction tanks mounted on the oil tank top plate evacuate oil vapors accumulated

in the oil tank. The exhaust is led to safe location outside the hall.


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The oil tank is provided with connection for oil centrifusion. The oil centrifuge inlet connection

provided in the oil tank is of loop configuration in order to prevent entering of the oil. Tank in caseof leakage in the oil purification circuit. The top of the loop is in line with minimum oil level in

the oil tank. If the oil level in the tank falls below min. level, flow to centrifuge circuit isinterrupted as air enters into the loop through the hole provided at the top of the loop. The low and

high levels, are annunciated in the control room. When ever the level falls below minimum oillevel, the level shall be raised to normal operating level by adding clarified oil. Mostly we use

servo prime 46 as the lubricating oil.

LUBE OIL PUMPThe lube oil pump is a single stage centrifugal pump driven by A.C motor. The delivers the total

oil required for governing and lubricating oil system. The oil which flows through the governing system isknown as leak oil and the oil which flows through the coolers side is known as lube oil. Tap-off for

governing circuit is taken immediately after pump discharge. For lubricating purpose, oil is taken downstream the oil cooler after suitable pressure reduction using an adjustable throttle.

MAIN OIL PUMP AND AUXILIARY PUMPS

The main oil pump is invariably ac motor driven centrifugal pumps to ensure maximum reliability

.It may also provide high pressure oil for the relay system at a pressure of 150kg/cm2. By raisingall the oils to this pressure, the lubricating oil being drain off through a reduction valve. Although

this method is often adopted because of its simplicity and because the relays automaticallyclose the stop valve, if the lubricating oil supply falls it is wasted of pumping energy.

The quantity of oil used makes it economically to incorporate a centrifugal pump driven directly to

the bearings. It is self priming and requires oil ejector to over come the suction head both when startingand during running a governing hydraulic systems is used. The pumps may be mounted directly in the

main oil tank with their inlets submerged below the oil level thus obviating the need for an oil ejector.

Note:

The auxiliary pump is automatically brought into operation by a relay when the oil pressure fallsbelow a certain value.

A check valve in the pump discharge ensures safety of the pump against reverse rotation when thepump is kept as stand by.

If the pump discharge pressure falls below 6.5kg/cm2, the stand by pump will be started throughpressure switch.

If the stand by pump also fails, the turbine will be tripped set at 0.8kg/cm2.

EMERGENCY OIL PUMPS

During coasting down of turbine, when lube oil pump is not available, lubricating oil is provided

by emergency oil pump. The emergency oil pump is driven by D.C. motor.The E.O.P. will cut in automatically by lube oil pressure switch set at 0.7kg/cm2. In order to ensurepositive supply of oil to the bearings, this pump is connected directly to the lube oil with out going

through cooler and filter.


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JACKING OIL PUMP

A positive displacement pump unit provides the supply of high-pressure oil to the bottom side ofthe individual shaft journal, an oil pump unit is provided. The pump is driven by A.C motor and from the

pump the lifting oil passes to the various bearings and from the bearings the oil returns to the drain header.

When a turbine is started up the shaft journal are in contact with the white metal of the bearingsdue to the weight of the rotor. The low pressure of the lubricating oil supply when the set is stationary is

insufficient to stop the metal to metal contact between journal and bearing shells. So the starting andstopping in the presence of metal to metal contact would result in increase to wear of the white metal

surface. So in order to prevent the metal to metal contact between journal and bearings shells duringstartup and shutdown, an oil pocket machine into the bottom shell of the journal bearing is supplied with

oil under high pressure. This lifts the shafting the shafting system slightly and it floats on a film of the oil.Only a small volume of oil is needed to perform the lifting of the shaft.

The lifting oil pressures required are set individually with the throttling valves at each bearing. Pressure

gauges provided down stream of these throttles shall be referred for setting the throttle position.

The check valves fitted between the throttling valves and the bearings prevent oil from the bearings

flowing back into the jacking oil system when the turbine is running and jacking oil system has beenshutdown.

OIL COOLERS:Twin coolers shall be provide and shall be piped in a parallel arrangement using a continuous flow

transfer valve.The main factor of the cooler is to freeze the water and an oil-bypass line around the coolerbeing included to regulate the oil supply temperature. To regulate lube oil temperature the control valves

are provided to by-pass around the cooler. The control valve shall be sized to handle all oil flow passingthrough the cooler with a pressure drop equal to or less than the pressure drop in the cooler. The coolers

are usually mounted vertically for easy removal of the tubbiest and water passing upwards through thetubes ensures complete flooding at all times. Oil enters at the top and passes across the tubes in a zigzag

manner, guided by the fins. The oil and water passes are arranged in counter flow. The arrangementreduces the amount of sludge precipitation. In the cooler as the hot oil entering the cooler does not strike

the coldest part of the cooler tube.In the coolers the efficiency of a centrifugal pump may be of the order of 55% and the remaining

45% of the pump input energy generates heat in the oil. The oil absorbs a large amount of heat from thebearing friction and shaft conduction. To remove this heat the oil is passed through coolers which reduces

the temperature to that required for the bearings.

Both the water side and the oil side of the cooler shall be self-venting and self-draining or shall becompletely drainable.

Each cooler are divided into three types, They are: Water cooled

Shell and tube

Air cooledA removable bundle design is required for shell and tube coolers. Removable bundle coolers are

constructed with a removable channel cover.

Note:

To prevent the oil from being contaminated if coolers fails, the oil side operating pressure shall be higherthan the water side operating pressure.


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SPECIFICATION:

OIL FILTER:Twin full flow filters with replaceable elements or cartridges with filtration of 10microns nominal

or finer shall supplied. The filter shall be located down stream of the coolers and shall be piped in aparallel arrangement using a continuous flow transfer valve. Filter cases and heads shall be suitable for

operation at the maximum discharge pressure. The filter shall not be equipped with relief valves are othervalves which can cause by-pass of unfiltered oil around the filter elements.

The pressure drop for clean filtered elements are cartridges shall not exceed 15% of the total allowabledirty pressure drop at an operating temperature of 38C.

FEATURES:

Oil flow from the outside inward towards the centre of the filter element.

Adequate support of the filter elements to prevent them from rupturing or to prevent unfilteredoil from bypassing the elements and reaching the equipment.

Minimum exposure of non stainless steel filter casing surface to the oil down stream of the filter

elements.

Adequate support and maintainable alignment of staged filter cartridges.

Proper sealing at the ends of the cartridges, including cartridges to casing sealing and sealingbetween stacked cartridges.

The ability to completely drain oil from the filter housing while avoiding contamination of the

downstream side with unfiltered oil during replacement of the filter elements.

Consideration of the use of guard elements to capture debris in case of filter element deteriorationor failure.

OVER HEAD OIL TANK:

When E.O.P. also fails, as a last resort to protect bearings, an over head oil tank is provided. Thetank is kept at an elevation of 6.5m to provide lubricating oil by gravity.

The tank is filled using lube oil pump during initial startup. Overflowing oil through flow glass

indicates the oil filling completion. Once the tank is full, the inlet valve is closed and a small amount of oilis allowed to continuously over flow through the tank.


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EQUIPMENT-LAYOUT

In a power plant station the equipment are arranged as shown in the figure.In the 15MW TG power plant the length of TG hall is 47000 mm and TG hall span is 27000mm.

The ground floor elevation is 0.0m.

The mezzanine floor elevation is 4.0m.

The operating floor elevation is 9.0m.

The de-aerator floor elevation is 14.0m.

GROUND FLOOR: -

In the floor the following equipments are placed. They are

BFPS.

CEPS.

Boiler house.

Oil tank.

Oil coolers.

Oil filters.

Oil pumps.

Oil Centrifuse. Condensers.

Flash tank.

Generator air cooler elements.

NGR.

MEZZANINE FLOOR: -It is the floor lie in between the ground floor & operating floor. The following

equipments were kept on this floor.

Steam jet air ejector.

Gland steam condenser.

HP heater (Horizontal). LP heater (Horizontal).

OPERATING FLOOR: -

This is above the mezzanine & ground floors.The following equipments were placed on the TG deck at operating floor elevation.

Turbine.

Gearbox.

Generator.

The control room is adjacent to TG hall were turbine control panel, generator control panel areplaced. Above control room the de-aerator is placed on the de-aerator floor.

While placing the equipment care is to be taken that sufficient walk around space is available.At the time of operation or maintenance this is very much required for all equipments. The

equipments are arranged in logical manner so that when the piping is done there is no back trackingor criss crossing of pipes.

The tube removal of equipments shell is also marked in the equipment layout so that no pipingor equipment come in that space earmarked for maintenance. All the equipments shall be kept on

a pedestal.The equipment layout for 15MW STG is enclosed.


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PUMP: -

In general pump may be defined as a mechanical device which when interposed in apipe line, converts the mechanical energy into hydraulic energy and transfers the same to the

liquid through the pipe line, there by increasing the energy of the flowing fluid.

EXTRACTION PUMPS: -The most important function in extraction pump design is the avoidance

of the excess of oxygen into the condensate system .This can be carried out in a number of ways ,they are

Two stage extraction pumps

Two stage extraction pump with internal bearing .

Three stage extraction pump alternative arrangements.

In Two stage design the gland at the left hand side adjacent to the first stage impeller is

under vacuum ,when the pump is in service .The gland is therefore scaled by leading a condensatesupply to it from the second stage discharge pipe ,care must be taken to ensure that the gland

connections to the stand by pump are isolated from the pump in operation . This results in a somewhatcomplicated small board piping system with the necessary operational requirements of changing

over the sealing connections when bringing the stand by pump into service. The water being rotated

by the action of the shaft when the pump is in use, forming a helix . The air then leaks into thepump between the water streams which form the helix.

One partial solution is to fit an internal bearing at the suction end of thePump. But this bearing must be water lubricated and may ,therefore ,be damaged by suspended

matter. The vertical spindle arrangement is particularly vulnerable to this damage during thecommissioning or after the overhaul period.

Probably the best arrangement , where the hydraulic characteristics allow is

to mount the first stage impeller on the shaft between two impellers running in parallel on a two stagedesign and in series for a three stage duty. The arrangement is slightly more expensive ,but it does

ensure positive pressure on the pump glands.Recently we used reentry type extraction pumps. The extractions pumps become integrated

with the generator coolers and auxiliary cooler system .This limits maximum design pressureneeded for the auxiliary coolers.

FEED PUMP:-The feed pump is a pump which is used to deliver feed water to the boiler. It is a

desirable that the quantity of water supplied should be at least equal to that evaporated andsupplied to the engine. Two types of pumps which are commonly used as feed pumps are

1.Reciprocating pump

2.Rotory pumpThe reciprocating pump consists of a pump cylinder and a piston. Inside the cylinder

reciprocates a piston which displaces water.


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15The reciprocating pump may be of two types. They are

1.SINGLE ACTING PUMP:

In a single acting pump , the water is displaced by one side of the pistononly and so the water is discharged in alternate strokes.

2.DOUBLE ACTING PUMP:

In a double acting pump, the water is discharged in each stroke ofthe piston, since the wateris displaced by both the sides of the piston.

The reciprocating feed pumps are continuously run by steam from the the same boiler towhich water is to be fed.

In a double direct acting steam pump, there are two single steam cylinders placed side by

side. Slide valves distribute the steam in each cylinder

The slide valve in each cylinder steam chest is operated by the crosshead on the pistonrod of the opposite cylinder, through, an arrangement of rods and rocker arms. The feed pumpis generally double acting. On each side of the pump plunger there are suction and

discharge valves. The pumps work alternately and consequently continuous flow of water ismaintained double feed pump is commonly employed for medium size boilers.

Rotary feed pumps are of centrifugal type and are commonly run either by a small steamturbine or by an electro motor. A rotary pump consists of a casing and a rotating elementknown as impeller, which is fitted over a shaft. It utilizes the centrifugal force of the rotating

impeller for pumping the liquid from one place to the other.

BOILER FEED PUMP: -Boiler feed pumps are used for pumping hot feed water from de aerators to boilers

of thermal power stations and constitutes one of the most essential equipment for uninterruptedpower supply. Every increasing steam parameters in modern power stations have resulted in

fast development of boiler feed pumps and today these pumps are highly sophisticated equipmentin thermal power stations.The function of the feed pump is to deliver feed water from de aerator

to the boiler drum at a required pressure and temperature. The water with the given operatingtemperature flows from the de aerator to the pump continuously it passes through suction branch

into the intake spiral and from there it is desired in to the first impeller. After leaving theimpeller it passes through the diffuser where the kinetic energy is converted into potential

energy. Then it flows over to the guide vanes to the inlet of the next impeller eye. This processis separated from one stage to another till it passes through the last impeller and the end

diffuser. Thus the feed water at outlet of the last stage attains the required discharge head.About 50% of the feed water is taken off from the space behind the last impeller for automatic

balancing axial thrust produced. The feed water passes through the balancing device and comes,into the space behind the balancing disc. Water is taken from space to the suction or to the feed

water tank.


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16

ELEMENTS OF BOILER FEED PUMP: -

The boiler feed pumps at highly sophisticated equipment in thermal power stationsand in fact represent the heart of a power station. Very high technical skill sophisticated

materials and rigid quality control are employed in the production of these pumps. Thesepumps operate at high rotational speed and therefore require very accurate balancing. The pump

is of robust construction and does not require any warm up.The pump consists of:

1.Casing2.Shaft

3.Shaft sleeves4.Impeller

5.Diffuser6.Ring sections

7.Suction cover8.Discharge cover

9.Stuffing box assembly10.Balance drum

11.Pump half coupling

12.Bearings and housings.

BOILER FEED BOOSTER PUMP: -

For efficient and reliable operation of the boiler feed pump, even under adverse suctionconditions and constrained layouts without provision for adequate net positive suction

head , it is often pressed to provide a booster pump to boost the suction head to the requiredlevels.

HEAT EXCHANGERS: -

A heat exchanger is any device used for effecting the process of heatexchange between two fluids that are at different temperatures. A heat exchanger in which two fluids

exchange heat by coming in to direct contact is called a direct contact heat exchanger. Example of thistype are open feed water heaters, de super heaters and jet condensers. The wall may be simple

plane wall or a tube or a complex configuration involving fins, baffles and multiple passes of tubes.These units are called surface heat exchangers, are more commonly used because they can be

constructed with large heat heat transfer surfaces in a relatively small volume and are suitable forheating cooling, evaporating or condensing applications.A periodic flow type of heat exchanger is called a

regenerator. In this type of heat exchanger, the same space is alternately occupied by the hot and coldgases between which heat is exchanged. Regenerators find their application in pre heaters for steam

power plants, blast furnaces, oxygen producers etc.

TYPES OF HEAT EXCHANGERS:-

Heat exchangers may be classified in several ways. One classification isaccording to the fluid flow arrangement or the relative direction of the hot and cold fluids. The fluidsmay be separated by a plane wall but more commonly by a concentric tube(double pipe)

arrangement. If both the fluids move in the same direction, the arrangement is called aparallel flow type. In the counter flow arrangement, the fluids move in parallel but in opposite

directions. In a double pipe heat exchanger, either the hot or cold fluid occupies the annular space andthe other fluids moves through the inner pipe. Since both fluids streams traverse the exchanger only

once, this arrangement is called single pass heat exchanger.


17/40


17Another flow configuration is one in which the fluids move at right angles to each other

through the heat exchanger. This type of arrangement is called a cross flow type. When large quantitiesof heat are to be transferred, the heat area requirement of the exchanger also becomes large. In this case

multiple pass arrangements can be used.

FEED WATER HEATING EQUIPMENT:-Feed water heating is accomplished in one string for the low pressure heating, while

in two strings for the high pressure heating in order to improve the reliability of operation.Such joints in the construction of the high pressure feed water heater as between the tube and

baffle and between the water box and shell etc is setup by welding to assure prevention of leakage.The main condensate in most of the power plants returns to the steam generator as feed water. Some

makeup water may be added to replace in the cycle. In a few plants the boiler feed water may be 100%makeup, in this case the plant turbines exhaust at backpressures above atmospheric to supply steam for

other purpose. Feed water is heated by bleeding steam to heaters as in a regenerative cycle from the mainturbine, or by using exhaust steam from auxiliary drive turbine, or by byproducts steam from processes.

Feed water heaters may be classified as follows:1. Open (or) contact heaters.

2. Tray type

3.

Jet type.4. Closed (or) surface heaters.

Heated feed water enables steam generators to produce more Kg of steam and avoids severe thermalstressing by cold water entering a hot drum. Pre heating feed water also causes scale forming dissolved

salts to precipitates outside the boiler and removes dissolved O2 &CO2 which corrode boiler material.

OPEN HEATERS:-

1) Tray type: -The construction of an open heater employs a shell of rolled steel plates welded along thelongitudinal steam. Dished steel ends are joined to the shell at two ends through welding. In the tray type

heater the upper half of the shell contains two tray sections and the spray distributor, while the lower halfis mostly empty and serves as storage for heated water. Above the shell is placed a vent condenser. Feed

water after passing through the vent condenser flows into the spray distributor from where it cascades overthe staggered trays, Exhaust steam from auxiliaries or low pressure steam from a suitable point in the

turbine is passed into the heater, entering into opposite the tray sections and flowing upward counter to thedirection of water, through the heating section. The flow of two liquids through the heater, thus results in

thorough mixing up so that heat of steam is transferred to water, the steam itself also being condensed O2,CO2 & NH3are also removed by this type of heaters.

In addition to the heating of feed water, the contact type heater is oftenconstruction for de aerating action. The only difference between the simple heater and a de aerating open

heater is in the addition of a suction of air removing trays below the heating trays. After the water has

been heated in heating section, it is made to pass over the air separating trays, which provide a completeseparation of air and water, Waterthen flows down while air and non-condensable gasses together with water vapour pass to the top of the

shell and from there to the vent condenser. The vent condenser is a small surface condenser of U-type.The vapour went to the atmosphere. The interior of the shell of de aerating as also the trays is made of

corrosion resistance material such as stainless steel.


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18

JET TYPE OPEN HEATERS:-In this type of de aerating contact heater spring loaded spray valves

atomize the feed water coming from the vent condenser spray it up words against the baffle. The low

pressure steam enters a conical steam jacket fitted in the upper part of shell, and is allowed toexpanding the same direction as the water spray, mixes with water and mixture falls down to the

lower part of the shell which serves as the storage. The non-condensing gases travel upwards as inthe tray type heater and are passed on the vent condenser. It is mainly used in marine where tray

type heaters do not work well due to the pitching & rolling of the vessel. They can handle watercontaining scaling impurities and are lighter in weight. These heaters do not work well at low

pressures special at sub atmospheric pressure.

CLOSED(OR)SURFACE FEED HEATERS:-These heaters usually have shell and tube construction and may be made

horizontal and vertical. The construction of a closed heater and a surface condenser are identical exceptthat the heater is design for higher temperatures and pressures and has greater than the condenser .

It consists of a shell which has a welded longitudinal steam. To each end of the shell

is welded a steel flange for fitting the covers , and top and bottom connections are provided for

inlet of steam and exit of condensate . A baffle plate is provided below the steam inlet to spreadthe steam evenly over the tubes. The water tubes are admiralty brass or other suitable material arestretched between two end sheets of muntz metal or soft steel ,one of these being fixed and the

other floating to take up extraction strain in tubes, The floating tube sheet is covered with a headcover bolted on to it and prevents the leakage of water into space.

The heater may have single pass or the water box may be divided to give pass basin. A pair ofair pockets provided at bottom of the shell permits the with drawn of air.

The flow of steam and water through the heater is usually counter to each other low pressureheaters may use the steam under vacuum high pressure heaters at pressure above 40 bars. Steam

and water need not beat the same pressure and one pump may push water through several heatersin series. Water pressure may be as high as 250 bars. For good performance heaters must be

drained and vented.

L .P. HEATERS:-These heaters are usually constructed of mild steel tube plates and shells

with tubes of 90/10 cupronickel or admiralty brass expanded into the tube plate for a depthof approximately 1 1/2inch. The usual procedure when testing for leaks in L.P heater tube nests

is by filling the steam space with water and applying a pressure not in excess of the designpressure of the body when leaking expansions and tubes are readily shown up.

When leaking tube expansions exits a further light rolling is usually necessaryto stop the leakage , unless the severity of the leak is sufficient to erode the tube plate ,in

which case plugging may be necessary leaking tubes are normally plugged off when the

incidence of failure is slight , but there is an obvious limit to this procedure. The location of theleaking tube in the tube plate is of some consequence with u-tube heaters .


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19

H.P HEATERS:-

It is similar to L .P . heaters. The essential difference is that the tubes must withstand the full pressure of the feed pumps However if a booster pump is employed upstream

of the heater, the feed pump pressure can be reduced.The tubes may be of 70/30 cupronickel , with some iron alloyed ,and the shells of

forged steel. The water box is bolted down with bolts drilled down the axis to facilitate electricbolt heating .The bolt heating is done by passing current through carbon rods in the central

holes of the bolts .This method of bolt tightening ensures tight, joints even at the high pressureand temperature en counted in the last one (or) two heaters which receive super heated steam

from the high pressure stages of turbine.H.P heaters too are equipped with gauge glasses steam and water spring loaded relief

valves as well as body air vents .The body air vents and vents on the incoming and out goingfeed pumps are led to an open turn dish to enable observation of air release ,thence to a drain

tank ,and finally to a separates flash box ,and onto the condenser.

DE- AERATOR HEATER:-It was a conventional practice of designing the de-aerator , so that the storage tank

has a capacity sufficient enough to contain the feed water for about 15 min running at a rated

output.Reduced capacity of the storage tank has been found successful in realization of

uniform temperature distribution of the feed water in the tank,prevention of flashing in the

suction pipe of the feed water pump as well as economization of the frame work of thebuilding ,resulting from reduced weight of the tank. The distillate pump is to be operated only

for filling up the boiler drum and not to make up the de aerator when the units in operation.

In a de-aerating heater entering water spills over trays (or) sprays through nozzlesto make it present a maximum surface, for heat transfer to the atmosphere of steam filling

the heater. This also removes all dissolved O2in excess of 0.03 ml per 1 from the water .A unitthat reduces the O2 to 0.005 ml is a de-aerator.

Adding Na2So3 to the feed water or boiler reduces any remaining dissolved O2 to atolerable minimum. De- aeration may takes place at any pressure or vacuum. Heating releases the

gas from the water in minute bubbles that tend to stray entrained. These can removed byagitation (or) stirring the water turbulently. The de-aerating heater and de-aerator mix steam and

water to heat the water to saturation temperature, they also agitate the boiling water to removeentrained gases and vent them to atmosphere .The most heaters have a storage tank below with

controls to add make up water as needed to maintain feed water flow. The heating steam maybe main turbine feed steam (or) may

be from other sources.

OTHER EQUIPMENTS:-

Other equipments required for steam power plant are: Gland steam condenser.

Glands & Sealing systems.

generator.

Drains.

Drain flash tank.

Safety valves.

Steam nozzles


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GLANDS& SEALING SYSTEMS:-

Glands and sealing systems are used on turbines to prevent(or) reduce the leakage of steam (or)air between rotating and stationery components that have a

pressure difference across them.. e .g. where the turbine shaft is extended through the cylinder endwalls to the atmosphere . When the cylinder pressure is higher than atmosphere will be a

general steam leakage outwards whilst if the cylinder contains steam below atmosphere pressurethere will be leakage of air inwards and a sealing system must be used to prevent the air

from entering the cylinder and the condenser.As most of the steam leakage from glands does not pass through the turbine stages , a

loss of power output is involved and every effort is made to reduce this power loss by anefficient arrangement of seals and glands. Three types of glands and seals are in general use on

steam turbines , the carbon ring gland and the water seals. The first two glands act as restrictorsto steam and air leakage ,whilst the water seal will prevent all leakage of steam and air.

Pump glands are generally of the mechanical type .Clean water flushing is providedto reduce the heavy wear that would otherwise occur on startup after a lengthy shutdown.

Conventional soft packing glands are used on the older smaller cooling water pump design.

AIR JET EJECTORS: -The operating medium of an air ejector can be either high pressure gas or liquid. This is passed

through a nozzle and the pressure energy is converted into velocity energy. The high velocity fluid

aspirates the air and non condensable gases and the mixture is projected into a diffuser whichreconverts the velocity energy into pressure energy. Steam is a suitable operating medium and is

used in the steam jet air ejector.The steam consumption is controlled by the compression ratio of the and this factor influences

the decision to adopt either single or multiple stage ejectors for a particular condition. To meet therequirements when raising vacuum a starting ejector is provided. This is a high capacity high steam

consumption ejector, of single stage and with out an after condenser.A main air ejector with stand by unit is usually provided for normal operation. The heat in

the operating system is partially recovered in the condensate which flows through the inter and aftercoolers.

If an installation is to operate with a direct cooling system, as is provided by the sea orriver, vacuum as high as 29.2 in HG would be expected during the winter months. A two stage

ejector is generally only capable o f maintaining a vacuum of 29.0 in HG even at zero flow ,butthree stage ejector will hold up to 29.4 in HG and would there fore be used.

Further advantage here is that for a comparable duty the three stage ejector shows a slight savingin steam consumption over the two stage ejector.

GENERATOR:-

Generator is used to produce electricity. The turbine and generator are connected

by a shaft. In the generator the field system will always be the rotating member and is calledthe rotor while the armature assembly, comprising armature winding and magnetic iron corewill be stationary and is called the stator. In the generator the mechanical energy obtained in the

turbine is converted into electrical energy. Generator air cooler is used in order to cool thegenerator.


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21

GEAR BOX:-

The use of very large circulating water pumps with low rotational speeds hasnecessitated the use of an intermediate gearbox .How speed motors of the size required are

very expensive and it is economically justifiable to sacrifice 1 to 2% in efficiency byintroducing a step down gearbox between pump and motor. The gear ratio can be set to allow a

motor with an economic running speed to be selected. In practice a 4000 h. p .c pump unitrunning at 200 rev/min will require a 5:1 step down gear box ,permitting the use of a 1000

rev/min motor. The gear boxes may be of 2 basic types ,either parallel shaft offset(or) co axial.

LUBRICATION SYSTEMS:-

Oil is required by the bearing in order to provide a continuous oil wedge onwhich the shaft revolves , this requires only a small quantity of oil .

However shaft conductivity , surface friction and turbulance set up in the oil producesconsiderable,amount of heat and in order to keep the bearing temperature constant at the desired

level a further quantity of oil is required to remove this heat.Oil is supplied to the bearing at a pressure from 5 to 25 lb/in

2gauge. This pressure is

required to ensure that the pressure in the upper part of the bearing does not below atmosphere ,in

which case discontinuities in the oil film would form .On the other hand if the pressure is toohigh the oil be sprayed out from the end of the bearing at a high velocity &will become finallyatomized. In the conditions the oil may easily escape from the bearing house. The temperature of

oil must be kept within certain limits. If the oil temperature entering the bearing is too low , insufficient bearing lubrication will occur due to high velocity of the oil , whilst if the oil

temperature on leaving the bearings too high, this will lead to deterioration of oil due to highrates of oxidation.

This temperature of oil leaving the bearing is limited to 1600F .So that the maximum

temperature with the bearings not more than 1600F and required leaving temperature is achieved

by adjusting the supply of oil to each bearing .

OIL PUMPS:-Types of oil pumps;

1. Main oil pump2. Auxiliary oil pump

3. Jacking oil pump4. Emergency oil pump

MAIN OIL PUMP:-

The main oil pump is invariably driven from the turbine shaft, either directlyor through gears , to ensure maximum reliability .It may also provide high pressure oil for the

relay system at a pressure of from 50 to 2000 lb/in2usually by raising all the oil to this

pressure , the lubricating oil being drain off through a reduction valve .Although this method isoften adopted because of its simplicity and because the relays automatically close the stopvalve, if the lubricating oil supply falls it is wasted of pumping energy. Some turbines use a

double gear pump having high and low pressure outputs, but on large turbines it may beadvantageous to employ to separate pumps.

The normal type of pump used on turbines has been the gear pump. This requires nopriming and provides positive oil displacement but must be driven from the shaft through reduction gear at

about 400 RPM. The pump has two or three meshing gears.


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22On large turbines the quantity of oil used makes it economically to incorporate a centrifugal

pump driven directly from turbine shaft. It is not self priming and requires oil ejector to over come thesuction head both when starting and during running. When a separate governing hydraulic systems is used

the oil lubricating system may be simplified by the adoption of ac motor driven centrifugal pumps. Thepumps may be mounted directly in the main oil tank with their inlets submerged below the oil level thus

obviating the need for an oil ejector.

AUXILLIARY PUMP:-It is used for starting, stopping, and emergencies. It is sometimes driven by a

steam turbine, but for some years the tendency has been to use a motor driven auxiliary pump feed withsupply. The auxiliary pump is automatically brought into operation by a relay when the oil pressure falls

below a certain value.

EMERGENCY OIL PUMP:-It is invariably provided as a stand by the auxiliary pump. In the event of

a fault interrupting the normal station or unit supply the d. c. pump which is fed from the station batterycircuits in, thus ensuring the safety of the bearing whilst the turbine is brought to rest.

JACKING OIL PUMP:-Supply of very high pressure oil provided by a small capacity positive

displacement. Jacking oil is fed into the base of the bearings in sufficient quantity to establish each oil

film on which the heavy rotors may float at very low speed of rotation, when the normal oil wedge wouldnot be formed. The presence of jacking oil film whilst the machine reduces the torque required by the

turbine motor and prevent the metal to metal contact damaging the bearings.

OIL VALVES:-As the pumps are constant speed types, a uniform quantity oil will be delivered. Surplus

oil must be blend continuously and this process through the spring loaded relief valves generally groundtogether in a valve box. Filled to both the main and

Auxiliary pumps are relief valves which limit the delivery pressure each pump is fitted with a non returnvalve in the discharge valve branch which prevents oil flowing back through the idle pump units.

OIL COOLERS: -

The efficiency of a centrifugal pump may be of the order of 55% and the remaining45% of the pump input energy generates heat in the oil. The oil absorbs a large amount of heat from the

bearing friction and shaft conduction. To remove this heat the oil is passed through coolers which reducesthe temperature to that required for the bearings.

Coolers are designed to have the maximum surface area for heat transfer compatible with smallpressure drop between entrance and exit.

STRAINERS:-These are used for removing the dust particles. It consists of cylindrical wire mesh are

interposed between the returning drains and drain tank. In addition ,filters of the duplex (or) auto dean

types are usually inter posed. In the pump delivery pipe to protect the bearing and relay system fromforeign particles. These filters can be cleaned while in service.


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23

STEAM CONDENSER: -A steam condenser is a device or an appliance in which steam condenses and

heat released by steam is absorbed by water. It serves the following purposes;

1) It maintains a very low back pressure on the exhaust side of the piston of the steam engine or turbine

,in available heat energy for converting into mechanical work. The shaded are in the given fig. Showsthe increase in work obtained by fitting a condenser to non-condensing engine. The thermal efficiency

of a condensing unit is higher than that of non-condensing unit for ,the same available steam.

2) It supplies to the boiler pure and hot feed water as the condensed steam which isdischarged from the condenser and collected in a hot well can be used as feed water

for the boiler..Organs of a steam condensing plant .

A steam condensing plant mainly consists of the following organs / elements :1) condenser (to condensate the steam)

2) supply of cooling (or injector)water3)wet air pump(to remove the condensed steam ,the air &uncondensed water vapour and gases from

the condenser ; separate pumps may be used to deal with air and condensate).

4) Hot well (where the condensate can be discharged and from which the boiler feed water is taken ).5) Arrangement for re cooling the cooling water incase surface condenser is employed.

CLASSIFICATION OF CONDENSERS: -

1. Jet condensers2. Surface condenser

In Jet condensers ,the exhaust steam and water come in direct contact with eachother and temperature of the condensate is the same as that of cooling water leavingthe condenser. The cooling water is usually sprayed into the exhaust steam to cause

rapid condensation.

In surface condensers , the exhaust steam and water do not come into direct contact.The steam passes over the outer surface of tubes through which a supply of coolingwater is maintained .There may be single pass or double pass. In a single pass condenser

, the water flows in one direction ,only through all the tubes ,while in two passcondenser the water flows in one direction through the tubes and returns through the

remainder.A Jet condenser is simpler and cheaper than a surface condenser .It should be installed

when the cooling water is cheaply and easily made suitable for boiler feed or when a cheap source

of the boiler and feed water is available is not thrown as a waste but returned to the boiler.

ASH HANDLING SYSTEMS:-

A huge quantity of ash is produce in central stations, sometimesbeing as much as 10 to 20% of the total quantity of coal burnt in a day. Hundreds of tonnsof ash may have to be handled every day in large power stations.

Handle of ash includes Its removal from the furnace.Loading on the conveyers and delivery to the fill or dump from where it can be disposed off by

sale.


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The commonly used equipment for ash handling are

bucket elevator

bucket conveyor

belt conveyor

pneumatic conveyor

hydraulic equipment

rail costThe modern ash handle systems are

mechanical system

hydraulic system

pneumatic system

steam jet system

DRAUGHT: -

The small pressure difference which causes a flow of gas to take place is termed asdraught. The function of it is to force air to the fire and to carry away the gaseous products

are combustion.The draught may be classified as

Forced draught

Induced draught

Balanced draught

Steam jet draught

FORCED DRAUGHT:-This draught is produced by a fan. In this draught system a fan is installed

near or at the base of the boiler to forced the air through the cool bed and other passagesthrough the furnace, flues, air pre heater & economizer.

INDUCED DRAUGHT:-

In this system a fan is located at or near the base of the chimney. Thepressure over the bed is reduced below that of the atmosphere . By creating a partial vacuum

in furnace and flues , the products of combustion are drawn from the main flue and they passof the chimney.

BALANCED DRAUGHT:-

It is a combination of the forced and induced systems. In this system,the forced draught fan over comes the resistance in the air pre heater and chain grate stoker

while the induced draught fan over comes draught losses through boiler, economizer, air pre

heater and connecting flues.

STEAM JET DRAUGHT:-

This system produces the artificial draught. It may be of forced orinduced type depending upon where the steam jet to produce draught is located.


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AIR - PREHEATER:-

The function of air pre heater is to increase the temperature of air before itenters the furnace. It is generally placed after the economizer. So the flue gases pass through

the economiser and then to the air pre heater.An air pre heater consists of plates or tubes with hot gases on one side and

air on the other. It pre heats the air to be supplied to the furnace. Pre heated air accelerates thecombustion and facilitate the burning of coal.

Degree of pre heating depends on type of fuel

type of fuel burning equipment

rating at which the boiler and furnace are operated

FUEL OIL STORAGE & HANDLING SYSTEM:-

Oil fuels are costly to store not only because of the capital cost of fuel lying in to the

store, but because the tanks necessary to hold the oil are expansive. Tank which need a piledfoundation are about 40% more expensive than those which do not.

Fuel oils are delivered at temperature which give good handle ability and this presents someadvantage to the customer when the turn over of his stock is rapid. For exit is very useful incold weather to have gas diesel oil delivered at about ambient temperature because the user

does not usually providence heating for his equipment. B S classed fuel can be stored and firedat ambient temperature but provision could be advantage be made to see that the temperature does

not fall below 00C this can be effected by a small tank out flow heater, since it is the fuel handle system

which requires protection against extreme cold. Residual fuel oils should be stored and handled at

temperatures well above their pour points.It is necessary to provide trace heating logging for all pipe lines, filters and valves etc.

handle residual fuel oils. It is particularly important that pressure gauges and other instrumentsusing the fuel oil as a control fluid should be either heated or filled with a suitable buffer fluid

such as gas oil. The heating may be effected by means of steam or hot water or it may be electrical.Even after the boiler fuel ring main circulating oil is pre heated to atomizing temperature There can

be sufficient cooling in branches to burners which are shut down to make lagging and trace heatingnecessary.

The oil in store should never be raised in temperature to its closed flash point temperature

because this would increase the fire hazards


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26

STEAM GENERATOR: -

It is the part of the steam heat engine in which the chemical energy of afuels liberated and is partially transferred from the products of the combustion to the working

substance of the cycle is properly called the steam generator. The transfer of energy in the steamgenerator should be accomplished with a minimum of loss both in quality and availability.

The basic components of a steam generator are fuel burning equipment,heater, air heater surface and steam re super heating surface may also be add as

thermodynamic need and economic justification dictate .The ASME test code for stationary steamgenerating units defines steam generator heating surface as follows. If that portion of the

surface of the heat transfer apparatus exposed onthe one side to the gas(or)refractory being cooled and on the other to the fluid being heated,

measured on the side receiving heat. In the boiler in which vaporizationof the working substance takes place. Feed water enters the boiler at a temperature equal to or less

than saturation temperature at boiler pressure and after being, heatedto saturation temperature, it is vaporized super heated steam cannot be formed in the boiler because

of the immediate presence of saturated water with which the steam tends to be in equilibrium.

In this steam water mixtures must pass from the risers to cyclone by the

separating force of gravity. The steam free water is desired down ward to thedrum and dry steam passes upward to the steam outlets. Scrabbers are used to remove the lasttraces of moisture.


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PIPING SYSTEMS

GENERAL: The design of the steam plant piping will be in accordance with the ASME. Gas piping will

be in accordance with ASME.

OTHER CODESAlberta Safety Codes Acts and Codes of Practice

NEPA Codes (National Electrical Protection Association)NFC - NFPA Codes (National Fire Code / National Fire Protection Association)

CSA Standards (Canadian Standards Association)MSS Standard Practices (Manufacturers Standardization Society.)

API (American Petroleum Institute)ASTM (American Society for Testing and Materials)

PIPING MATERIAL SELECTION:

Material is selected based on:-Characteristics of operating fluid

For condensate, steam and water applications based on operating temperature material can be Carbon

Steel (CS), Alloy Steel (AS), or Stainless Steel (SS) .For corrosive fluids stainless steel is normally preferred.For brackish and sea water CS piping with rubber or FRP lining is used.

DESIGN TEMPERATURE:-

Up to 4120c carbon steel (A 106 Gr B) can be used.From 4120c to 5100c A 335 Grade P11 material is used.

From 5100c to 5900c A 335 Grade P22 material is used.From 5400c to 6350c P91 material is used.

AIR JET EJECTORS:

The operating medium of an air ejector can be either high pressure gas or liquid.This is passed through a nozzle and the pressure energy is converted into velocity energy. The high

velocity fluid aspirates the air and non condensable gases and the mixture is projected into a diffuserwhich reconverts the velocity energy into pressure energy. Steam is a suitable operating medium and

is used in the steam jet air ejector. The steam consumption is controlled by the compression ratio of the airand this factor influences the decision to adopt either single or multiple stage ejectors for a particular

condition. To meet the requirements when raising vacuum a starting ejector is provided. This is a highcapacity high steam consumption ejector, of single stage and with out an after condenser.

A main air ejector with stand by unit is usually provided for normal operation. The heat in theoperating system is partially recovered in the condensate which flows through the inter and after

coolers.

If an installation is to operate with a direct cooling system, as is Provided by the sea or river,vacuum as high as 29.2 in HG would be expected during the winter months. A two stage ejector isgenerally only capable o f maintaining a vacuum of 29.0 in HG even at zero flow ,but three stage

ejector will hold up to 29.4 in HG and would there fore be used. Further advantage here is that for acomparable duty the three stage ejector shows a slight saving in steam consumption over the two stage

ejector.


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EXTRACTION PUMPS:

The most important function in extraction pump design is the avoidance of the excess of oxygeninto the condensate system .This can be carried out in a number of ways , they are

Two stage extraction pumpsTwo stage extraction pump with internal bearing .

Three stage extraction pump alternative arrangements.

In Two stage design the gland at the left hand side adjacent to the first stage impeller is undervacuum ,when the pump is in service .The gland is therefore scaled by leading a condensate supply

to it from the second stage discharge pipe ,care must be taken to ensure that the gland connectionsto the stand by pump are isolated from the pump in operation . This results in a somewhat

complicated small board piping system with the necessary operational requirements of changingover the sealing connections when bringing the stand by pump into service. The water being rotated

by the action of the shaft when the pump is in use, forming a helix . The air then leaks into thepump between the water streams which form the helix.

One partial solution is to fit an internal bearing at the suction end of the Pump. But thisbearing must be water lubricated and may ,therefore ,be damaged by suspended matter. The

vertical spindle arrangement is particularly vulnerable to this damage during the commissioning or

after the overhaul period.Probably the best arrangement , where the hydraulic characteristics allow is to mount the first

stage impeller on the shaft between two impellers running in parallel on a two stage design and in

series for a three stage duty. The arrangement is slightly more expensive ,but it does ensure positivepressure on the pump glands.

Recently we used reentry type extraction pumps. The extractions pumps become integratedwith the generator coolers and auxiliary cooler system .This limits maximum design pressure

needed for the auxiliary coolers.

FEED WATER HEATING EQUIPMENT:-

Feed water heating is accomplished in one string for the low pressure heating, while in two strings forthe high pressure heating in order to improve the reliability of operation.

Such joints in the construction of the high pressure feed water heater as between the tube andbaffle and between the water box and shell etc is setup by welding to assure prevention of leakage.

The main condensate in most of the power plants returns to the steam generator as feed water. Somemakeup water may be added to replace in the cycle. In a few plants the boiler feed water may be 100%

makeup, in this case the plant turbines exhaust at back pressures above atmospheric to supply steam forother purpose. Feed water is heated by bleeding steam to heaters as in a regenerative cycle from the main

turbine, or by using exhaust steam from auxiliary drive turbine, or by byproducts steam from processes.Feed water heaters may be classified as follows:

Open (or) contact heaters.

Tray typeJet type.closed (or) surface heaters.

Heated feed water enables steam generators to produce more Kg of steam and avoids severe thermalstressing by cold water entering a hot drum. Pre heating feed water also causes scale forming dissolved

salts to precipitates outside the boiler and removes dissolved O2 &CO2 which corrode boiler material.


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OPEN HEATERS:-

1) Tray type: -The construction of an open heater employs a shell of rolled steel plates welded along thelongitudinal steam. Dished steel ends are joined to the shell at two ends through welding. In the tray type

heater the upper half of the shell contains two tray sections and the spray distributer, while the lower halfis mostly empty and serves as a storage for heated water. Above the shell is placed a vent condenser. Feed

water after passing through the vent condenser flows into the spray distributer from where it cascadesover the staggard trays, Exhaust steam from auxiliaries or low pressure steam from a suitable point in the

turbine is passed into the heater, entering into opposite the tray sections and flowing upward counter to thedirection of water, through the heating section. The flow of two liquids through the heater, thus results in

thorough mixing up so that heat of steam is transferred to water , the steam itself also being condensedO2,CO2 & NH3 are also removed by this type of heaters.

In addition to the heating of feed water , the contact type heater is often construction for deaerating action. The only difference between the simple heater and a de aerating open heater is in the

addition of a suction of air removing trays below the heating trays. After the water has been heated inheating section, it is made to pass over the air separating trays which provide a complete separation

of air and water, Waterthen flows down while air and non-condensable gasses together with water vapour pass to the top of the

shell and from there to the vent condenser . The vent condenser is a small surface condenser of U-type.

The vapour went to the atmosphere. The interior of the shell of de aerating as also the trays is made ofcorrosion resistance material such as stainless steel.

JET TYPE OPEN HEATERS:-In this type of de aerating contact heater spring loaded spray valves atomize the feed water

coming from the vent condenser spray it up words against the baffle. The low pressure steam entersa conical steam jacket fitted in the upper part of shell, and is allowed to expanding the same

direction as the water spray, mixes with water and mixture falls down to the lower part of the shellwhich serves as the storage. The non-condensing gases travel upwards as in the tray type heater

and are passed on the vent condenser. It is mainly used in marine where tray type heaters do notwork well due to the pitching & rolling of the vessel. They can handle water containing scaling

impurities and are lighter in weight. These heaters do not work well at low pressures special atsub atmospheric pressure.

CLOSED(OR)SURFACE FEED HEATERS:-

These heaters usually have shell and tube construction and may be made horizontaland vertical. The construction of a closed heater and a surface condenser are identical except that the

heater is design for higher temperaturesand pressures and has greater than the condenser .

It consists of a shell which has a welded longitudinal steam. To each end of the shellis welded a steel flange for fitting the covers , and top and bottom connections are provided for

inlet of steam and exit of condensate . A baffle plate is provided below the steam inlet to spread

the steam evenly over the tubes. The water tubes are admiralty brass or other suitable material arestretched between two end sheets of muntz metal or soft steel ,one of these being fixed and theother floating to take up extraction strain in tubes, The floating tube sheet is covered with a head

cover bolted on to it and prevents the leakage of water into space.The heater may have single pass or the water box may be divided to give pass basin. A pair of

air pockets provided at bottom of the shell permits the with drawn of air.The flow of steam and water through the heater is usually counter to each other low pressure

heaters may use the steam under vacuum high pressure heaters at pressure above 40 bars. Steamand water need not beat the same pressure and one pump may push water through several heaters


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30in series. Water pressure may be as high as 250 bars. For good performance heaters must be

drained and vented.

L .P. HEATERS:- These heaters are usually constructed of mild steel tube plates and shellswith tubes of 90/10 cupronickel or admiralty brass expanded into the tube plate for a depth

of approximately 1 1/2inch. The usual procedure when testing for leaks in L.P heater tube nestsis by filling the steam space with water and applying a pressure not in excess of the design

pressure of the body when leaking expansions and tubes are readily shown up.When leaking tube expansions exits a further light rolling is usually necessary

to stop the leakage , unless the severity of the leak is sufficient to erode the tube plate ,inwhich case plugging may be necessary leaking tubes are normally plugged off when the

incidence of failure is slight , but there is an obvious limit to this procedure. The location of theleaking tube in the tube plate is of some consequence with u-tube heaters

H.P HEATERS:-It is similar to L .P . heaters. The essential difference is that the tubes must

with stand the full pressure of the feed pumps However if a booster pump is employedupstream of the heater, the feed pump pressure can be reduced.

The tubes may be of 70/30 cupronickel , with some iron alloyed ,and the shells of

forged steel. The water box is bolted down with bolts drilled down the axis to facilitate electricbolt heating .The bolt heating is done by passing current through carbon rods in the centralholes of the bolts .This method of bolt tightening ensures tight, joints even at the high pressure

and temperature en counted in the last one (or) two heaters which receive super heated steamfrom the high pressure stages of turbine.

H.P heaters too are equipped with gauge glasses steam and water spring loaded reliefvalves as well as body air vents .The body air vents and vents on the incoming and out going

feed pumps are led to an open turn dish to enable observation of air release ,thence to a draintank ,and finally to a separates flash box ,and onto the condenser.

DE- AERATOR HEATER:-

It was a conventional practice of designing the de-aerator , so that the storage tank has acapacity sufficient enough to contain the feed water for about 15 min running at a rated output.

Reduced capacity of the storage tank has been found successful in realization of uniformtemperature distribution of the feed water in the tank,

prevention of flashing in the suction pipe of the feed water pump as well as economizationof the frame work of the building ,resulting from reduced weight of the tank. The distillate

pump is to be operated only for filling up the boiler drum and not to make up the de aeratorwhen the units in operation.

In a de-aerating heater entering water spills over trays (or) spraysthrough nozzles to make it present a maximum surface, for heat transfer to the

atmosphere of steam filling the heater. This also removes all dissolved O2 in excess of 0.03 ml

per 1 from the water .A unit that reduces the O2 to 0.005 ml is a de-aerator.

Adding Na2 So3 to the feed water or boiler reduces any remaining dissolved O2 to

a tolerable minimum. De- aeration may takes place at any pressure or vacuum. Heating releasesthe gas from the water in minute bubbles that tend to stray entrained. These can removed by

agitation (or) stirring the water turbulently. The de-aerating heater and de-aerator mix steam andwater to heat the water to saturation temperature, they also agitate the boiling water to remove

entrained gases and vent them to atmosphere .The most heaters have a storage tank below with


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31controls to add make up water as needed to maintain feed water flow. The heating steam

may be main turbine feed steam (or) maybe from other sources.

OTHER EQUIPMENT:Other equipments required for steam power plant are;Gland steam condenser.

Glands & Sealing systems.Generator.

Drains.Drain flash tank.

Safety valves.Steam nozzles

GLANDS& SEALING SYSTEMS:-Glands and sealing systems are used on turbines to prevent (or) reduce the leakage

of steam (or)air between rotating and stationery components that have a pressure difference across

them.. e .g. where the turbine shaft is extended through the cylinder end walls to the atmosphere .When the cylinder pressure is higher than atmosphere will be a general steam leakage outwardswhilst if the cylinder contains steam below atmosphere pressure there will be leakage of air

inwards and a sealing system must be used to prevent the air from entering the cylinder andthe condenser.

As most of the steam leakage from glands does not pass through the turbine stages , aloss of power output is involved and every effort is made to reduce this power loss by an

efficient arrangement of seals and glands. Three types of glands and seals are in general use onsteam turbines , the carbon ring gland and the water seals. The first two glands act as restric

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Material on Steam Power Plants