Condenser in Power Plant

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CONDENSER IN POWER PLANT

Introduction:

Steam Condenser: It is a device or an appliance in whichsteam condenses and heat released by steam isabsorbed by water.

Classification of Condensers

1. Jet condensers2. Surface condenser

Jet Condensers : The exhaust steam and water come indirect contact with each other and temperature of thecondensate is the same as that of cooling water leavingthe condenser. The cooling water is usually sprayed into

the exhaust steam to cause, rapid condensation.Surface Condensers : The exhaust steam and water donot come into direct contact. The steam passes over theouter surface of tubes through which a supply of coolingwater is maintained.

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PARALLEL-FIOW TYPE OF JET CONDENSER :

The exhaust steam and cooling water find their entry atthe top of the condenser and then flow downwards andcondensate and water are finally collected at thebottom.

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Fig. Parallel flow type condenser

COUNTER-FLOW TYPEJET CONDENSER:

The steam and cooling water enter the condenser fromopposite directions. Generally, the exhaust steam

travels in upward direction and meets the cooling water

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which flows downwards.

Fig. Low level counter flow type condenser

LOW LEVEL JET CONDENSER (COUNTER-FLOW

TYPE JET CONDENSER)Figure Shows, L, M and N are the perforated trays whichbreak up water into jets. The steam moving upwardscomes in contact with water and gets condensed. Thecondensate and water mixture is sent to the hot well bymeans of an extraction pump and the air is removed byan air suction pump provided at the top of thecondenser.

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HIGH LEVEL JET CONDENSER (COUNTER-FLOWTYPE JET CONDENSER)

It is also called barometric condenser. In this type theshell is placed at a height about 10.363 meters abovehot well and thus the necessity of providing anextraction pump can be obviated. However provision of own injection pump has to be made if water underpressure is not available.

Fig. High level counter flow type condenser

EJECTOR CONDENSER FLOW TYPE JETCONDENSER:

Here the exhaust steam and cooling water mix in hollowtruncated cones. Due to this decreased pressureexhaust steam along with associated air is drawnthrough the truncated cones and finally lead todiverging cone. In the diverging cone, a portion of

kinetic energy gets converted into pressure energy

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which is more than the atmospheric so that condensateconsisting of condensed steam, cooling water and air isdischarged into the hot well. The exhaust steam inlet is

provided with a non-return valve which does not allowthe water from hot well to rush back to the engine incase a failure of cooling water supply to condenser.

Fig. Ejector flow type condenser

SURFACE CONDENSERS

DOWN-FLOW TYPE:

The cooling water enters the shell at the lower half

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section and after traveling through the upper half section comes out through the outlet. The exhauststeam entering shell from the top flows down over the

tubes and gets condensed and is finally removed by anextraction pump. Due to the fact that steam flows in adirection right angle to the direction of flow of water, itis also called cross-surface condenser.

CENTRAL FLOW TYPE:

In this type of condenser, the suction pipe of the air

extraction pump is located in the centre of the tubeswhich results in radial flow of the steam. The better7


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contact between the outer surface of the tubes andsteam is ensured, due to large passages the pressuredrop of steam is reduced.

Fig. Shows Central flow type

INVERTED FLOW TYPE:

This type of condenser has the air suction at the top,the steam after entering at the bottom rises up andthen again flows down to the bottom of the condenser,

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by following a path near the outer surface of thecondenser. The condensate extraction pump is at thebottom.

REGENERATIVE TYPE:

This type is applied to condensers adopting aregenerative method of heating of the condensate. Afterleaving the tube nest, the condensate is passed throughthe entering exhaust steam from the steam engine orturbine thus raising the temperature of the condensate,for use as feed water for the boiler.

EVAPORATIVE TYPE:

The principle of this condenser is that when a limited

quantity of water is available, its quantity needed tocondense the steam can be reduced by causing thecirculating water to evaporate under a small partialpressure.

The exhaust steam enters at the top through gilled

pipes. The water pump sprays water on the pipes anddescending water condenses the steam. The waterwhich is not evaporated falls into the open tank (coolingpond) under the condenser from which it can be drawnby circulating water pump and used over again. Theevaporative condenser is placed in open air and finds itsapplication in small size plants.

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Fig. Evaporative type

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Evaporative condensers:In evaporative condensers, both air and water are usedto extract heat from the condensing refrigerant. Figure22.7 shows the schematic of an evaporative condenser.Evaporative condensers combine the features of acooling tower and water-cooled condenser in a singleunit. In these condensers , the water is sprayed from toppart on a bank of tubes carrying the refrigerant and airis induced upwards. There is a thin water film aroundthe condenser tubes from which evaporative coolingtakes place. The heat transfer coefficient for

evaporative cooling is very large. Hence, therefrigeration system can be operated at low condensingtemperatures (about 11 to 13 K above the wet bulbtemperature of air). The water spray countercurrent tothe airflow acts as cooling tower. The role of air isprimarily to increase the rate of evaporation of water.

The required air flow rates are in the range of 350 to500 m 3 /h per TR of refrigeration capacity.

Evaporative condensers are used in medium to largecapacity systems. These are normally cheapercompared to water cooled condensers, which require aseparate cooling tower. Evaporative condensers areused in places where water is scarce. Since water isused in a closed loop, only a small part of the waterevaporates. Make-up water is supplied to take care of the evaporative loss. The water consumption is typicallyvery low, about 5 percent of an equivalent water cooledcondenser with a cooling tower. However, sincecondenser has to be kept outside, this type of condenser requires a longer length of refrigerant tubing,which calls for larger refrigerant inventory and higherpressure drops. Since the condenser is kept outside, toprevent the water from freezing, when outsidetemperatures are very low, a heater is placed in thewater tank. When outside temperatures are very low it

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is possible to switch-off the water pump and run onlythe blowers, so that the condenser acts as an air cooledcondenser.

Another simple form of condenser used normally inolder type cold storages is called as atmosphericcondenser. The principle of the atmospheric condenseris similar to evaporative condenser, with a differencethat the air flow over the condenser takes place bynatural means as no fans or blowers are used. A spraysystem sprays water over condenser tubes. Heattransfer outside the tubes takes by both sensiblecooling and evaporation, as a result the external heattransfer coefficient is relatively large. The condenserpipes are normally large, and they can be eitherhorizontal or vertical. Though these condensers areeffective and economical they are being replaced withother types of condensers due to the problems such asalgae formation on condenser tubes, uncertainty due toexternal air circulation etc.

Effect of air and non-condensable:This is usually a problem with high boiling point refrigerants such as

R 11, R 113 and R718 (water), which operate under vacuum leading toair leakage into the system. In addition, some air may be left behind

before the system is evacuated and charged with refrigerant. If somenon-condensable gases or air enters the system, it will collect in thecondenser where they affect performance in two ways:1. Condensation takes place at saturation pressure corresponding tocondenser pressure, which will be the partial pressure of refrigerant inmixture of refrigerant and air in this case. The air will have its partial

pressure proportional to its amount in the condenser. The total pressurewill be the sum of these two partial pressures, which will be high andthe compressor has to work against this pressure ratio hence the work requirement will increase.

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2 . Non-condensable gases do not diffuse throughout the condenser asthe refrigerant condenses. They cling to the tubes and reduce the

precious heat transfer area. The reduction in heat transfer area causesthe temperature difference between cold water and refrigerant toincrease. This raises the condenser temperature and the corresponding

pressure thereby reducing the COP.

Air LeakageAs both the exhaust of the steam turbine and the condenser areoperating under a substantial vacuum, air is bound to leak into the

system. This leakage occurs through the gland seals on the steamturbine and through minute holes in the piping connectionsassociated with the surface condenser itself. Over a period of years,Heat Exchange Institute has determined the normal quantity of air that should leak through properly designed turbines and pipingsystems, and these are specified in their "Standards for SurfaceCondensers ." Manufacturers have similarly standardized their ejector sets so that several standard sizes are available for specific air

which are the only moving parts in a surface condenser system should be supplied in duplicate. Power plant practice usually requires twin air Ejector sets, one a standby, but for air conditioning installations, asingle set is sufficient.

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Materials of ConstructionMaterials used in construction of steam surface condensers.Use of copper alloy tube sheets in steam surface condensers with theAccompanying requirement that tube sheets be bolted to the shell byMeans of collar bolts is a carryover from marine practice. There is

No reason why a steel tube sheet cannot be used, in view of the factThat the refrigeration condenser just upstream of the steam condenser Uses this type of construction. When a steel tube sheet is used,The specification should indicate that it may be welded to the shell.

Copper based alloy(ASTM B 111,B543)

Stainless steel (ASTM A268, B268, A249,14


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A213, A269)

Titanium( ASTM B 338 Gr 1&2)

Carbon steel (ASTM A 179,A214)

REASON FOR REMOVING AIR/GAS:

The gases will increase the operating pressure of the condenser. This rise in pressure will decreasethe turbine output and efficiency.

The gases will blanket the outer surface of thetubes. This will severely decrease the heat transferof the steam to the circulating water. Again, thepressure in the condenser will increase.

The corrosiveness of the condensate in thecondenser increases as the oxygen contentincreases. Oxygen causes corrosion, mostly in thesteam generator. Thus, these gases must beremoved in order to extend the life of cycle

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components.

EFFECT OF AIR INGRESS:For maximum thermal efficiency, corresponding toa minimum back pressure, a vacuum is maintainedin the condenser. However, this vacuumencourages air in- leakage.

Thus, to keep the concentration of non-condensable gases as low as possible, the

condenser system must be leak tight, together withany part of the condensate system that is undervacuum. Failure to prevent or remove the non-condensable gases may cause serious corrosion inthe system, lower heat transfer properties, and/orincrease plant heat rate due to the back pressurerise associated with a high in leakage.

The cost of excess back pressure in terms of additional fuel or increased heat rate.

CONDENSER TUBE CLEANING :Macro-fouling (accumulation of debris), not onlyreduces the cooling water flow rate through thetubes it can cause tube corrosion and tubeerosion failures.

Micro-fouling (biological growth) and scalingreduces the heat transfer coefficient and couldcause under deposit corrosion resulting inpremature tube failures.

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Various tube cleaning options are available toreduce or eliminate the micro/macro fouling andscaling.

off-line

on-line methods. (Sponge balls or brushesmay be automatically recirculated through thecondenser).

Cycle Isolation:Generating plants often suffer from powerlosses/heat rate due to leakages through valves tocondenser.

Check incoming drain lines, feedwater heater highlevel dumps, minimum flow valves, and steam trapsfor leakage or improper operation which could addunexpected heat load to the condenser.

To minimize leakages through valves tocondenser , Select all control valves (e gemergency drain of heaters) to condenser withleakage class v and Select all isolating /drain valveto condenser with leakage class MSS SP 61.

REFERENCE

The TEXT book of POWER PLANT

ENGINEERING by R.K Rajput .17


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Wikipedia

Refrigeration and Air conditioning by P.L.

Balloney, Khanna Publishers.

Refrigeration and Air conditioning by C.P.

Arora, Tata McGraw Hill.

EXPERTS COMMENTS

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THANK

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CONCLUSION As from this we know all the functions of

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different types of steam condenser that areused in Thermal Power plant. We know how

Jet Condenser works and how a steam

condenser works. And also we know differentchallenges found in a power plant related tocondensers. From this we know all about theuses and function of steam condenser inthermal power plant.

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Condenser in Power Plant