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Where is an evaporative cond enser used inpractice?

1.

Answer:

In those cases where the shortage of coolingwater is acute.

What shou ld b e the basic criteria for anefficient st eam condenser?

2.

Answers:

Maximum amount of steam condensed per unit area of available heat transfer surface.

1.

Minimum quantity of circulating coolantrequired.

2.

Minimum heat transfer surface required per kW capacity

3.

Minimum power drawn by the auxiliaries.4.Why must a vacuum be maintained in thesteam condenser?

3.

Answers:

By maintaining a vacuum in the steamcondenser, the efficiency of thesteam-power plant can be increased asgreater the vacuum in the system, greater will be the enthalpy drop of steam.Therefore, more work will be available per kg of steam condensing.

1.

Secondly, the non-condensate (air) can beremoved from the condensate-steam circuitby pull ing and maintaining a vacuum in thesteam side. Therefore, the condensate can

be used as boiler feed.

2.

What are the limitation s of a surfacecondenser?

4.

Answers:

It is very bulky and as such requires morefloor space.

1.

Its manufacturing, running andmaintenance costs are high.

2.

What shou ld b e the requirements of an idealsurface condenser used fo r steam pow er

5.

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Answers:

Uniform distribution of exhaust steamthroughout the heat transfer surface of thecondenser.

1.

Absence of condensate sub cooling.2.There should not be any leakage of air intothe condenser.

3.

There should not be any tube leakage.4.The heat transfer surface in contact withcooling water must be free from any depositas scaling reduces the efficiency of heatexchangers.

5.

What do you mean by vacuum?6.

Answer:

Vacuum means any pressure below atmosphericpressure.

How is vacuum in a condenser usuallymeasured?

7.

Answer:

It is measured by means of a Bourdon pressuregauge, which is calibrated to read the pressure inmm of mercury below atmospheric pressure.

On what factors do es the degree of vacuum ina condenser depend?

8.

Answers:

It depends on the partial pressure of steam andthe partial pressure of air in the condenser.

What is the vacuum efficiency of acondenser?

9.

Answers:

It is the ratio of the actual vacuum at the steaminlet to the maximum obtainable vacuum in a

perfect condensing plant, i.e., it is the ratio of actual vacuum to ideal vacuum.

What are the effects o f air l eakage in thecondenser?

10.

Answers:

It increases the back pressure on theturbine with the effect that there is less heatdrop and low thermal efficiency of the plant

1.

The pressure of air in the condenser lowers2.

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the partial pressure of steam, which meanssteam, will condense at a lower temperatureand that will require greater amount of cooling water.It reduces the rate of condensation of steam, because air having poor thermalconductivity impairs the overall heat transfer from the steam-air mixture.

4.

What is a st eam con denser?11.

Answers:

It is a heat exchanger wherein steam iscondensed either in direct contact withcooling water or indirect contact with coolingwater through a heat transfer mediumseparating them.

1.

That is, a steam condenser is either a directcontact or indirect contact heat exchanger.

2.

How many types of steam condensers areknown?

12.

Answers:

Jet Condensers1.- direct contact heat exchanger.Surface Condensers - indirect contact heatexchanger.

2.

What is a surface cond enser?13.

Answer:

It is a shell-and-tube heat exchanger in which

steam is condensed on the shell-side whilecooling water flows through the tubes. Thecondensate and cooling water leave the systemseparately.

How does the down-flow type surfacecondenser act?

14.

Answer:

Exhaust steam is admitted to the top of thecondenser, which is a tube-and-shell typecrossflow heat exchanger. Cooling water flowsthrough the tubes and extracts heat from thesteam, which is on the shell-side. Mter havingbeen condensed on the surface of the water tubes, steam is converted into condensate whichis discharged from the condenser bottom.

How does the central flow type surfacecondenser work?

15.

Answer:


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It is also a shell-and-tube type crossflow heatexchanger at the center of which is located thesuction of an air extraction pump, so that theentire steam moves radially inward and comes inbetter contact with the outer surface of the nest of tubes through which the cooling water flows. Thesteam condensate is extracted from the bottomby the condensate-extraction pump.

How do es the inverted type surface condenser work?

16.

Answer:

In this type of condenser, steam is admitted atthe bottom and flows upwards in cross-flow withthe cooling water flowing in the tubes. The air extraction pump draws its suction from the top of the condenser, maintaining a steady upwardcurrent of steam, which after having beencondensed on the outer surface of water tubes is

removed by the condensate extraction pump.

How does the evaporative condenser function?

17.

Answer:

Exhaust steam from the turbine is condensedinside the finned tubes as cooling water rainsdown from the top through the nozzles. A part of the cooling water in contact with the tube surfaceevaporates by drawing enthalpy from the steam,which upon losing its latent heat condenses anddischarges out as condensate.

What are the primary functio ns o f acondenser?

18.

Answers:

There are two important fu nction s of acondenser:

It reduces the back pressure upon theturbine by a considerable degree andtherefore, the work done per lb of steamduring expansion is increased

1.

The exhaust steam condensate can berecycled as boiler feedwater

2.

Why else is steam from an HRSG used?19.

Answer:

For steam injection into the gas turbine for NO xcontrol.


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What gas is used in the SCR metho d o f controlling NO x?

20.

Answer:

Air-diluted ammonia vapor is injected into the fluegas stream before it enters the catalyst unitsconsisting of honeycomb-shaped ceramicmaterial. These cells, with the ammonia vapor,convert nitrogen oxides to nitrogen and water vapor for discharge into the atmosphere.

What is a steam con denser?21.

Answers:

It is a heat exchanger wherein steam iscondensed either in direct contact withcooling water or indirect contact with coolingwater through a heat transfer mediumseparating them.

1.

That is, a steam condenser is either a directcontact or indirect contact heat exchanger.2.

How many types of steam condenser areknown?

22.

Answers:

Jet Condensers1.- direct contact heat exchanger.Surface Condensers - indirect contact heatexchanger using water.

2.

Ai r Condensers - direct contact heat

exchangers using air.

3.

What is a jet condenser?23.

Answers:

It is a direct contact heat exchanger inwhich steam to be condensed comes intodirect contact with the cooling water (coldcondensate) which is usually introduced inthe form of a spray from a jet. (Fig. 30.1)

1.

Upon contact with the cooling water, thesteam gives up its enthalpy and gets cooled

and ultimately settles as condensate.

2.

What is a surface cond enser?24.

Answer:

It is a shell-and-tube heat exchanger in whichsteam is condensed on the shell-side whilecooling water flows through the tubes. Thecondensate and cooling water leave the systemseparately.

How many types of j et condensers are25.


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known?

Answers:

Parallel flow jet type cond enser 1.- It is a kind of jet condenser in which bothexhaust steam and cooling water enter thecondenser at the top, both flow downwardand the steam condensate discharges outfrom the bottom of the condenser. (Fig.30.2)Contra flow type jet condenser - Thecooling fluid (cold condensate) and exhauststeam flow in a counter-current direction -steam goes up and cold condensate rainsdown.

2.

Ejector type jet condenser - It is one kindof jet condenser in which the mixing of

cooling water and steam takes place in aseries of combining cones and the kineticenergy of the steam is expended to drain off the condensate and cooling water from thecondenser. Cooling water is forced througha series of cones and gets mixed with steamcoming through ports. As the cooling water flows through the series of nozzles, itsuffers more and more pressure drop andat the same time its velocity graduallyincreases. Due to this pressure drop, moreand more steam is drawn through the ports,

gets intimately mixed with the cooling water jet and condenses thereafter.

3.

What is th e principle of op eration of ahigh-level-parallel-flow jet condenser?

26.

Answer:

This con denser, also called barometriccondenser, works as foll ows - The condenser is mounted on a long pipe (at least 10.34 m)called barometric leg which acts in a wayidentical to a barometer. Now if water is used in a

barometer then the barometric height would be10.34 m. If some vacuum exists in the condenser,the height of water column (h) will be less than10.34 in. Now it is possible, by using thiscondenser leg, to drain away the condensatefrom the condenser.

How many types of su rface cond ensers areknown?

27.

Answers:


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Down flo w type1.- Exhaust steam is admitted to the top of the condenser, which is a tube-and-shelltype cross flow heat exchanger. Coolingwater flows through the tubes and extractsheat from the steam which is on theshell-side. After having been condensed onthe surface of the water tubes, steam isconverted into condensate, which isdischarged from the condenser bottom.(Fig. 30.7)Central f low type - It is also a shell-and-tube type cross flow heat exchanger atthe center of which is located the suction of an air extraction pump so that the entiresteam moves radially inward and comes inbetter contact with the outer surface of thenest of tubes through which the coolingwater flows. The steam condensate isextracted from the bottom by thecondensate-extraction pump.

2.

Inverted flow type - In this type of condenser, steam is admitted at the bottomand flows upwards in cross-flow with thecooling water flowing in the tubes. The air extraction pump draws its suction from thetop of the condenser, maintaining a steadyupward current of steam, which after havingbeen condensed on the outer surface of water tubes is removed by the condensateextraction pump.

3.

Evaporative cond enser type - Exhauststeam from the turbine is condensed insidethe finned tubes as cooling water rainsdown from the top through the nozzles. Apart of the cooling water in contact with thetube surface evaporates by drawingenthalpy from the steam, which upon losingits latent heat condenses and dischargesout as condensate.

4.

Where is the evaporative con denser used inpractice?

28.

Answers:

In those cases where the shortage of coolingwater is acute.

What are the two prime function s of acondenser?

29.

Answers:

It reduces the backpressure upon theturbine by a considerable degree andtherefore, the work done per kg of steamduring expansion is increased.

1.


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The exhaust steam condensate can berecycled as boiler feedwater.

3.

What are the auxil iary equ ipment requi red for operating a steam cond enser?

30.

Answers:

Cooling water (which may be coldcondensate) circulation pump. Generally, itis a centrifugal one.

1.

Arrangement for cooling the condensate(i.e., a heat exchanger) in case thecondensate is recycled to extract heat fromthe exhaust steam.

2.

An air pump or steam ejector to remove air and other non-condensing gases from thecondenser.

3.

An extraction pump (usually centrifugal) toremove the condensate from the condenser.

4.

What shou ld b e the basic criteria for anefficient st eam condenser?

31.

Answer:

Maximum amount of steam condensed per unit area of available heat transfer surface.

1.

Minimum quantity of circulating coolantrequired.

2.

Minimum heat transfer surface required per kW capacity.

3.

Minimum power drawn by the auxiliaries.4.Why is vacuum maintained in th e steamcondenser?

32.

Answers:

By maintaining a vacuum in the steamcondenser, the efficiency of thesteam-power plant can be increased asgreater the vacuum in the system, greater will be the enthalpy drop of steam.Therefore, more work will be available per kg of steam condensing.

1.

Secondly, the non-condensate (air) can beremoved from the condensate-steam circuit

by pull ing and maintaining a vacuum in thesteam side. Therefore, the condensate canbe used as boiler feed.

2.

What are the advantages of a jet condenser over a surface cond enser?

33.

Answers:

Simplicity in design.1.Lower in manufacturing cost.2.Lower maintenance cost.3.Occupies lesser floor space.4.


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Requires lesser amount of cooling water.6.What are the advantages of a surfacecondenser over a jet cond enser?

34.

Answers:

It imparts to power generation plant ahigher thermal efficiency.

1.

The condensate can be reused as boiler feedwater.

2.

Auxiliary power requirement is less than thatof a jet condenser.

3.

Less amount of air is carried to the boiler.4.What are the limitation s of a surfacecondenser?

35.

Answers:

It is very bulky and as such requires morefloor space.

1.

Its manufacturing, running and

maintenance costs are high.

2.

What shou ld b e the requirements of an idealsurface condenser used fo r steam pow er plants?

36.

Answers:

Uniform distribution of exhaust steamthroughout the heat transfer surface of thecondenser.

1.

Absence of condensate subcooling.2.There should not be any leakage of air into

the condenser.

3.

There should not be any tube leakage.4.The heat transfer surface in contact withcooling water must be free from any depositas scaling reduces the efficiency of heatexchangers.

5.

What do you mean by vacuum?37.

Answer:

Vacuum means any pressure below atmosphericpressure.

How is vacuum in a condenser usuallymeasured?

38.

Answers:

It is measured by means of a Bourdon pressuregauge, which is calibrated to read the pressure inmm of mercury below atmospheric pressure.

If the gauge pressure of a condenser is 630mm of Hg, what will be the absolute pressure

39.


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in the condenser?

Answer:

It means the pressure in the condenser is 630mm below atmospheric pressure. Theatmospheric pressure is 760 mm of Hg, theabsolute pressure in the condenser.

On what factors do es the degree of vacuum ina condenser depend?

40.

Answer:

It depends on the partial pressure of steam andthe partial pressure of air in the condenser.

How could air enter the condenser?41.

Answers:

With the boiler feedwater as dissolvedgases.

1.

Flange leakage.2.Cooling water (for jet condenser) containinga certain amount of dissolved air in it.

3.

What are the effects o f air l eakage in thecondenser?

42.

Answers:

It increases the backpressure on the turbinewith the effect that there is less heat dropand low thermal efficiency of the plant.

1.

The pressure of air in the condenser lowersthe partial pressure of steam, which meanssteam, will condense at a lower temperatureand that will require greater amount of cooling water.

2.

It reduces the rate of condensation of steam, because air having poor thermalconductivity impairs the overall heat transfer from the steam-air mixture.

3.

What basic governor t roubles are apt tooccur?

43.

Answers:

Hunting-alternate speeding and slowing of the engine, which means that the governor is too sensitive to load changes.

1.

Sticking-failure to control speed, allowingthe engine to run away or slow down-whichmeans that the governor is not sensitive toload changes or parts are binding or worn.

2.

What is a governor safety stop?44.


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Answers:

On throttling-type governors, the safety stop is aweighted arm that needs the support of agovernor belt. If the belt breaks, the idler armdrops and shuts the steam supply valve to theengine. On Corliss units, the flyballs fall to thelowest position and knock off the safety cams; thecams disengage the catch blocks on the steamintake valves so that no steam is admitted to theengine.

Why is con densation or excessive carryover dangerous to reciprocating engin es?

45.

Answer:

Because water is non-compressible. If anexcessive amount of water gets into the cylinder,it will wreck the engine.

Why should a steam or moistu re separator beinst alled in the steam lin e next to a steamturbine?

46.

Answer:

All multistage turbines, low-pressure turbines,and turbines operating at high pressure withsaturated steam should have a moistureseparator in order to prevent rapid blade wear from water erosion.

Under what cond itions may a relief valve notbe required on the exhaust end of a tu rbine?

47.

Answer:

If the manufacturer has provided that the turbineshells are constructed for full-inlet steampressure for the entire length of the shell. It isabsolutely essential to have a relief valve toprotect the shell in the event an exhaust valve isclosed and high-pressure steam is admitted tothe shell on the front end of the machine.Explosions have occurred when this happened.

What are some condit ion s that may prevent aturbin e from developi ng ful l power?

48.

Answers:

The machine is overloaded.1.The initial steam pressure and temperatureare not up to design conditions.

2.

The exhaust pressure is too high.3.The governor is set too low.4.The steam strainer is clogged.5.


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Turbine nozzles are clogged with deposits.8.Internal wear on nozzles and blades.9.

Why is it necessary to open casing drains anddrains on the steam line goin g to th e turbinewhen a turbine is t o b e started?.

49.

Answers:

To avoid slugging nozzles and blades inside theturbine with condensate on start-up; this canbreak these components from impact. The bladeswere designed to handle steam, not water.

What three metho ds are used to restorecasing surfaces that are excessively eroded?

50.

Answers:

Metal-spraying.1.Welding.2.Insertion of filler strips or patch plates. The

manufacturer should be consulted on themetallurgy involved so that the best methodcan be selected.

3.

What is steam rate as appli ed to tu rbo-generators?

51.

Answer:

The steam rate is the pounds of steam that mustbe supplied per kilowatt-hour of generator outputat the steam turbine inlet.

What is the most prevalent so urce of water indu ction into a steam turbo-generator?52.

Answer:

Leaking water tubes in feedwater heaters, whichhave steam on the shell side supplied fromturbine extraction lines. The water at higher pressure can flow back into the turbine becausethe extraction steam is at a lower pressure. Checkvalves are needed on the steam extraction line toprevent the back-flow of water into the turbine.

What is a regenerative cycle?53.

Answer:

In the regenerative cycle, feedwater is passedthrough a series of feed-water heaters and isheated by steam extracted from stages of asteam turbine. This raises the feedwater to near the temperature of boiler water, thus increasingthe thermal efficiency of the cycle.

What is th e re-heating cycl e?54.


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Answer:

In the re-heating cycle, superheated steam isexpanded in a high-pressure turbine and thenreturned to the boiler's re-heater to raise thetemperature of the steam to the inlet temperature,usually to around 537°C; it is then returned to theturbine to be expanded through intermediate-pressure turbines. In some cases, the steam isagain returned for re-heating in the boiler andthen expanded in the lower-pressure sections of the turbine. The main purpose of re-heating thesteam on large turbo-generators is to avoidcondensation in the lower-pressure sections of the turbine, which can rapidly cause bladeerosion problems from wet steam.

What do es the Willans lin e show?55.

Answer:

The Willians line is a plot of throttle flow versusthe load, usually expressed in kilowatts; generallyit is a straight line except for low and high loads.The Willians line is used to show steam rates atdifferent loads on the turbine.

What are the two basic types of t urbi nes?56.

Answer:

Impulse type.1.Reaction type.2.

What is th e operating princip le of an impulseturbine?

57.

Answer:

The basic idea of an impulse turbine is that a jetof steam from a fixed nozzle pushes against therotor blades and impels them forward. Thevelocity of the steam is about twice as fast as thevelocity of the blades. Only turbines utilizing fixednozzles are classified as impulse turbines.

What is the operating princip le of a reaction

turbine?58.

Answer:

A reaction turbine u tilizes a jet of steam that f lowsfrom a nozzle on the rotor. Actually, the steam isdirected into the moving blades by fixed bladesdesigned to expand the steam. The result is asmall increase in velocity over that of the movingblades. These blades form a wall of movingnozzles that further expand the steam. The steamflow is partially reversed by the moving blades,


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producing a reaction on the blades. Since thepressure drop is small across each row of nozzles (blades), the speed is comparatively low.Therefore, more rows of moving blades areneeded than in an impulse turbine.

What are topp ing and superposed turbines?59.

Answer:

Topping and superposed turbines archigh-pressure, non-condensing units that can beadded to an older, moderate-pressure plant.Topping turbines receive high-pressure steamfrom new high-pressure boilers. The exhauststeam of the new turbine has the same pressureas the old boilers and is used to supply the oldturbines.

What is an extraction turbine?60.

Answer:In an extraction turbine, steam is withdrawn fromone or more stages, at one or more pressures, for heating, plant process, or feedwater heater needs. They are often called "bleeder turbines."

What is a radial-flow turbine?61.

Answer:

In a radial-flow turbine, steam flows outward fromthe shaft to the casing. The unit is usually areaction unit, having both fixed and movingblades. They are used for special jobs and aremore common to European manufacturers, suchas Sta-Laval (now ABB).

What is a stage in a steam turbine?62.

Answer:

In an impulse turbine, the stage is a set of moving blades behind the nozzle. In a reactionturbine, each row of blades is called a "stage." A

single Curtis stage may consist of two or morerows of moving blades.

What is a diaphragm?63.

Answer:

Partitions between pressure stages in a turbine'scasing are called diaphragms. They hold thevane-shaped nozzles and seals between thestages. Usually labyrinth-type seals are used.One-half of the diaphragm is fitted into the top of


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the casing, the other half into the bottom.

What are four types of turb ine seals?64.

Answers:

Carbon rings fitted in segments around theshaft and held together by garter or retainer springs.

1.

Labyrinth mated with shaft serration’s or shaft seal strips.

2.

Water seals where a shaft runner acts as apump to create a ring of water around theshaft. Use only treated water to avoid shaftpitting.

3.

Stuffing box using woven or soft packingrings that are compressed with a gland toprevent leakage along the shaft.

4.

In whi ch turbi ne is tip leakage a problem?65.

Answer:

Tip leakage is a problem in reaction turbines.Here, each vane forms a nozzle; steam must flowthrough the moving nozzle to the fixed nozzle.Steam escaping across the tips of the bladesrepresents a loss of work. Therefore, tip seals areused prevent this.

What are two types of cl earance in a turbine?66.

Answer:

Radial1.- clearance at the tips of the rotor andcasing.

Axial - the fore-and-aft clearance, at thesides of the rotor and the casing.

2.

What are four types of thrust hearings?67.

Answer:

Babbitt-faced collar bearings.1.Tilting pivotal pads.2.Tapered land bearings.3.Rolling-contact (roller or ball) bearings.4.

What is th e function of a thrust bearing?68.

Answer:

Thrust bearings keep the rotor in its correct axialposition.

What is a balance piston?69.

Answer:

Reaction turbines have axial thrust because


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pressure on the entering side is greater thanpressure on the leaving side of each stage. Tocounteract this force, steam is admitted to adummy (balance) piston chamber at thelow-pressure end of the rotor. Some designersalso use a balance piston on impulse turbinesthat have a high thrust. Instead of piston, sealstrips are also used to duplicate a piston'scounter force.

What is a combination th rust and radialbearing?

70.

Answer:

This unit has the ends of the babbitt bearingextended radially over the end of the shell.Collars on the rotor face these thrust pads, andthe journal is supported in the bearing betweenthe thrust collars.

What is a tapered-land th rust bearing ?71.

Answer:

The babbitt face of a tapered-land thrust bearinghas a series of fixed pads divided by radial slots.The leading edge of each sector is tapered,allowing an oil wedge to build up and carry thethrust between the collar and pad.

What is impo rtant to remember about radialbearings?

72.

Answer:

A turbine rotor is supported by two radialbearings, one on each end of the steam cylinder.These bearings must be accurately aligned tomaintain the close clearance between the shaftand the shaft seals, and between the rotor andthe casing. If excessive bearing wear lowers thehe rotor, great harm can be done to the turbine.

What is gl and-sealing steam?73.

Answer:

It is the low-pressure steam that is led to asealing gland. The steam seals the gland, whichmay be either a carbon ring or labyrinth typeagainst air at the vacuum end of the shaft.

What is the functio n of a gland drain?74.

Answer:

The function of a gland drain is to draw of water


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from sealing-gland cavities created by thecondensation of sealing steam.

What is an air ejector?75.

Answer:

An air ejector is a steam siphon that removesnon-condensable gases from the condenser.

How many go vernors are needed fo r safeturbin e operation? Why?

76.

Answer:

Two independent governors are needed for safeturbine operation. One is an overspeed or emergency trip that shuts off the steam at 10percent above running speed (maximum speed).The second, or main governor, usually controlsspeed at a constant rate; however, many

applications have variable speed control.How i s a flyball go vernor u sed wit h ahydraulic control?

77.

Answer:

As the turbine speeds up, the weights are movedoutward by centrifugal force, causing linkage toopen a pilot valve that admits and releases oil oneither side of a piston or on one side of a spring-loaded piston. The movement of the pistoncontrols the steam valves.

What is a multi -port governor valve? Why is itused?

78.

Answer:

In large turbines, a valve controls steam flow togroups of nozzles. The number of open valvescontrols the number of nozzles in use accordingto the load. A bar-lift or cam arrangementoperated by the governor opens and closes thesevalves in sequence. Such a device is a multi-port

valve. Using nozzles at full steam pressure ismore efficient than throttling the steam.

What is meant b y criti cal speed?79.

Answer:

It is the speed at which the machine vibratesmost violently. It is due to many causes, such asimbalance or harmonic vibrations set up by theentire machine. To minimize damage, the turbineshould be hurried through the known critical


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speed as rapidly as possible. (Caution, be surethe vibration is caused by critical speed and notby some other trouble).

How is oil pressure maintained when startingor stop ping a medium-sized tu rbine?

80.

Answer:

An auxiliary pump is provided to maintain oilpressure. Some auxiliary pumps are turned by ahand crank; others are motor-driven. This pumpis used when the integral pump is running tooslowly to provide pressure, as when starting or securing a medium-sized turbine.

Why is it poo r practice to allow turbine oil t obecome too coo l?

81.

Answer:

If a turbine oil is allowed to become too cold,condensation of atmospheric moisture takesplace in the oil and starts rust on the polishedsurfaces of the journal bearings. Condensedmoisture my interfere with lubrication.

Steam blowing from a turbine gland iswasteful. Why else should it be avoided?

82.

Answer:

It should be avoided because the steam usuallyblows into the bearing, destroying the lubricationoil in the main bearing. Steam blowing from aturbine gland also creates condensate, causingundue moisture in plant equipment.

Besides lubrication, which are two functi onsof lubricating oi l in some turbin es?

83.

Answer:

In large units, lube oil cools the bearings bycarrying off heat to the oil coolers. Lube oil insome turbines also acts as a hydraulic fluid to

operate the governor speed-control system.

What is meant b y the water rite of a turbine?84.

Answer:

It is th e amount o f water (steam) used by theturbin e in poun ds per horsepower per hour or kilowatts per hour.

85.

What are five types of condensers?86.

Answer:


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Surface (shell-and-tube).1.Jet condenser.2.Barometric condenser.3.

Air-cooled condenser.4.Evaporative condenser.5.

Why is t here a relief valve on a turbin e

casing?

87.

Answer:

The turbine casing is fitted with spring-loadedrelief valves to prevent damage by excessivesteam pressure at the low-pressure end if theexhaust valve is closed accidentally. Somecasings on smaller turbines are fitted with asentinel valve, which serves only to warn theoperator of over-pressure of the exhaust end. Aspring-loaded relic valve is needed to relieve high

pressure.

Why must steam turbin es be warmed upgradually?

88.

Answer:

Although it is probable that a turbine can, if itsshaft is straight, be started from a cold conditionwithout warming up, such operation does notcontribute to continued successful operation of the unit. The temperature strains set up in thecasings and rotors by such rapid heating have aharmful effect. The turbine, in larger unitsespecially should be warmed slowly byrecommended warm-up ramp rates because of close clearances.

What shoul d you lost vacuum while o peratinga cond ensing turbin e plant?

89.

Answer:

If vacuum is lost shut down immediately. Thecondenser cannot stand steam pressure, thecondenser tubes may leak from excessivetemperature. Excessive pressure will alsodamage the shell, the exhaust and thelow-pressure parts of the turbine.

What are the main causes of tu rbin evibration?

90.

Answers:

Unbalanced parts.1.Poor alignment of parts.2.


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Loose parts.9.Rubbing parts.10.Lubrication troubles.11.steam troubles.12.Foundation troubles.13.Cracked or excessively worn parts.14.

What is the purpose of a turning gear?91.

Answer:

Heat must be prevented from warping the rotorsof large turbines or high-temperature turbines of 400°C or more. When the turbine is being shutdown, a motor-driven turning gear is engaged tothe turbine to rotate the spindle and allowuniform cooling.

What does he term "ramp" rate mean?92.

Answer:

Ramp rate is used in bringing a turbine up tooperating temperature and is the degrees Celsiusrise per hour that metal surfaces are exposed towhen bringing a machine to rated conditions.Manufacturers specify ramp rates or their machines in order to avoid thermal stresses.Thermocouples are used in measuring metaltemperatures.

What is the dif ference between partial and fu llarc admission?

93.

Answer:

In multi-valve turbine inlets, partial arc ad missionallows the steam to enter per valve opening in asequential manner, so as load is increased, morevalves open to admit steam. This can causeuneven heating on the high-pressure annulus asthe valves are individually opened with loadincrease. In full-arc admission, all regulatingvalves open but only at a percentage of their fullopening. With load increase, they all open morefully. This provides more uniform heating aroundthe high-pressure part of the turbine. Mostmodern controls start with full-arc and switch topartial arc to reduce throttling losses through thevalves.

What are some common trou bles in su rface-condenser operation ?

94.

Answer:

The greatest headache to the operator is loss of vacuum caused by air leaking into the surfacecondenser through the joints or packing glands.


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Another trouble spot is cooling water leaking intothe steam space through the ends of the tubes or through tiny holes in the tubes. The tubes mayalso become plugged with mud, shells, debris,slime or algae, thus cutt ing down on the coolingwater supply. Corrosion may be uniform, or it mayoccur in small holes or pits.

Where would you look f or a fault i f the air ejector di dn't raise enoug h vacuum?

95.

Answers:

In this case, the trouble is usually in thenozzle. You will probably find that thenozzle is eroded.

1.

The strainer protecting the nozzle isclogged.

2.

The steam pressure to the nozzle is too low.3.How wou ld you sto p air from leaking in to acondenser?

96.

Answer:

First find the leak by passing a flame over thesuspected part while the condenser is under vacuum. Leaks in the flange joints or porouscastings can be stopped with asphalt paint or shellac.

Do you stop cool ing water flow thro ugh asteam cond enser as soon as the turbi ne isstopped?

97.

Answer:

You should keep the cooling water circulating for about 15 minutes (also see the manufacturer’srecommendation) or more so that the condenser has a chance to cool down gradually and evenly.Be sure to have cooling water flowing through thecondenser before starting up in order to preventsteam from entering the condenser unless it iscooled. Overheating cause severe leaks andother headaches.

How wo uld you sto p a leaky tube in acondenser that was contaminating the feedwater?

98.

Answer:

To stop leaky tube from contaminating thefeedwater, shut down, remove the water-boxcovers, and fill the steam space with water. Byobserving tube ends, you can find the leaky tube.

An alternate method is to pressurize (30 kPa) the


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steam space with air. Then flood the water boxesto the top inspection plate and observe any air bubbles. Once you have found the leaky tube or tubes, drive a tape bronze plug (well-coated withwhite lead) into each end of the tube to cut it outservice. This allows you to use the condenser since the tubes need not be renewed until about10 percent of the tubes are plugged.

Why must co ndensate be subjected to salinitytests where brackish cooling water used?

99.

Answer:

Condensate may leak from thecooling-water side to the steam side of condenser and contaminate the feedwater,thus causing scale to form in the boilers,brackish cooling water may leak into thesteam space from cracked or porous tubesor ruin around the joints at the end of the

tube ends, etc. By taking salinity readingsof the condensate, leaks may be foundbefore they can do any harm.

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