Condenser in Thermal Power Plant
Q. What is condenser in thermal power plant?
Q. Why is condenser used?
Q. What is condenser in boiler?
Q. Condenser and Cooling tower work in power plant
- High pressure and temperature steam after expansion through the turbine, goes through the condenser. The use of condenser improves the efficiency of power plant by decreasing the exhaust pressure of steam below atmospheric pressure.
- Another advantage of the condenser is that condensed steam can be recovered and it provides a source of good and pure feed water to the boiler. This reduces, considerably, the water softening plant capacity. Air and non-condensable gases are also removed from the steam when it passes through the condenser.
- The quantity of water required for cooling of steam to condense in the condenser is quite large Hence, a source of water capable of supplying water throughout the year is required. Generally, water from river is taken for this purpose by means of circulating water pumps. Alter use in economizer the warm water is fed back to river.
- If sufficient supply of water is not available from river, the warm water from the condenser is cooled by cooling towers or ponds and is reused again.
- The condensers may be broadly classified as : (I) Jet condensers or contact condensers. (II) Surface condensers .
- We will study one from each type :
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| Figure A |
- Low level jet condensers (Counterhead type) : In this type of condenser, cold water from cooling ponds is drawn-up in the condenser shell due to the vacuum head created in the shell, without the use of a pump. It is therefore necessary the level of the cooling pond should not be much below the delivery pipe to the shell (Refer Figure A). The shell is arranged with two or three water trays with perforations to break-up water into small jets. The exhaust steam and any mixed air enters to lower portion of the shell and tries to ascend upon through the falling sprays. Thus the steam gets condensed and air ascends up and cools down. It is removed by a suction pump fixed for the purpose at the top. The mixture of condensate and cooling water descends down through a vertical pipe to the extraction pump and pumped to the hot well. The boiler feed pump delivers water to the boiler. The excess water overflows to the cooling pond. In this type of condenser, cooling water and condensed steam mixes, together. This type of condenser is suitable only where cheap pure water is available.
- Surface condensers : The surface steam condensers are essentially used in steam turbine power plants.
- They are classified as : (A) Single pass, two pass condensers. (B) Down flow, central flow regenerative condensers.
- Figure B. represents the section of a two pass, down flow condenser.
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| Figure B |
- It consists of a cast iron shell in circular shape. The two ends are covered by cover plates. A nest of brass tubes is fixed to the two tube plates at the ends. They are fixed by means of brass ferrules so that they can be replaced easily when required. The spaces between the tube plate and cover plates are known as water boxes.
- One of the two water boxes has a baffle partitioning. The box is in two sections : one upper half and other lower half.
- The cooling water is passed through the lower half section tubes. It comes out through the upper half section tubes. Hence, the temperature of water in the lower half section is less as compared with water in upper half section tubes.
- Exhaust steam enters the shell at the top. It flows downwards surrounding the cold water tubes. The steam first comes in contact with tubes containing comparatively hot water which has been progressively heated by the condensing steam. And it then passes down and is effectively condensed by the cold water in the tubes before being removed by the extraction pump.