292267006-Steam-Condenser typesppt .pptx

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1. Steam Condenser

2. CONDENSER The main purposes of the condenser are to condense the exhaust steam from the turbine for reuse in the cycle and to maximize turbine efficiency by maintaining proper vacuum. As the operating pressure of the condenser is lowered (vacuum is increased), the enthalpy drop of the expanding steam in the turbine will also increase. This will increase the amount of available work from the turbine (electrical output). By lowering the condenser operating pressure, the following will occur: • Increased turbine output • Increased plant efficiency • Reduced steam flow (for a given plant output) It is therefore very advantageous to operate the condenser at the lowest possible pressure (highest vacuum).

3. FUNCTION OF CONDENSER Function of the condenser is to create a vacuum by condensing steam, Removing dissolved non condensable gases from the condensate. Conserving the condensate for re-use as the feed water supply to the steam generator. Providing a leak-tight barrier between the high grade condensate contained within the shell and the untreated cooling water. Providing a leak-tight barrier against air ingress, preventing excess back pressure on the turbine. Serving as a drain receptacle, receiving vapor and condensate from various other plant heat exchangers, steam dumps, and turbine bleed-offs.

4. Classification of Condensers

5. Classification of Condensers 1. Jet condensers 2. Surface condenser Jet Condensers:  The exhaust steam and water come in direct contact with each other and temperature of the condensate is the same as that of cooling water leaving the condenser. The cooling water is usually sprayed into the exhaust steam to cause, rapid condensation. 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 cooling water is maintained.

6. PARALLEL-FIOW TYPE OF JET CONDENSER: The exhaust steam and cooling water find their entry at the top of the condenser and then flow downwards and condensate and water are finally collected at the bottom.

7. LOW LEVEL JET CONDENSER (COUNTER-FLOW TYPE JET CONDENSER): The steam and cooling water enter the condenser from opposite directions. Generally, the exhaust steam travels in upward direction and meets the cooling water which flows downwards.

8. HIGH LEVEL JET CONDENSER (COUNTER-FLOW TYPE JET CONDENSER) It is also called barometric condenser. In this type the shell is placed at a height about 10.363 meters above hot well and thus the necessity of providing an extraction pump can be obviated. However provision of own injection pump has to be made if water under pressure is not available.

9. EJECTOR FLOW TYPE JET CONDENSER Here the exhaust steam and cooling water mix in hollow truncated cones. Due to this decreased pressure exhaust steam along with associated air is drawn through the truncated cones and finally lead to diverging cone. In the diverging cone, a portion of kinetic energy gets converted into pressure energy which is more than the atmospheric so that condensate consisting of condensed steam, cooling water and air is discharged into the hot well. The exhaust steam inlet is provided with a non-return valve which does not allow the water from hot well to rush back to the engine in case a failure of cooling water supply to condenser.

10. SURFACE CONDENSOR

11. SURFACE CONDENSERS DOWN-FLOW TYPE: The cooling water enters the shell at the lower half section and after traveling through the upper half section comes out through the outlet. The exhaust steam entering shell from the top flows down over the tubes and gets condensed and is finally removed by an extraction pump. Due to the fact that steam flows in a direction right angle to the direction of flow of water, it is also called cross-surface condenser.

12. SURFACE CONDENSERS CENTRAL FLOW TYPE: In this type of condenser, the suction pipe of the air extraction pump is located in the centre of the tubes which results in radial flow of the steam. The better contact between the outer surface of the tubes and steam is ensured, due to large passages the pressure drop of steam is reduced.

13. SURFACE CONDENSERS INVERTED FLOW TYPE: This type of condenser has the air suction at the top, the steam after entering at the bottom rises up and then again flows down to the bottom of the condenser, by following a path near the outer surface of the condenser. The condensate extraction pump is at the bottom.

14. SURFACE CONDENSERS EVAPORATIVE TYPE: The principle of this condenser is that when a limited quantity of water is available, its quantity needed to condense the steam can be reduced by causing the circulating water to evaporate under a small partial pressure. The exhaust steam enters at the top through gilled pipes. The water pump sprays water on the pipes and descending water condenses the steam. The water which is not evaporated falls into the open tank (cooling pond) under the condenser from which it can be drawn by circulating water pump and used over again. The evaporative condenser is placed in open air and finds its application in small size plants.

15. CONDENSER OPERATION The main heat transfer mechanisms in a surface condenser are the condensing of saturated steam on the outside of the tubes and the heating of the circulating water inside the tubes. Thus for a given circulating water flow rate, the water inlet temperature to the condenser determines the operating pressure of the condenser. As this temperature is decreased, the condenser pressure will also decrease. As described above, this decrease in the pressure will increase the plant output and efficiency. Due to the fact that a surface condenser operates under vacuum, non condensable gases will migrate towards the condenser. The non condensable gases consist of mostly air that has leaked into the cycle from components that are operating below atmospheric pressure (like the condenser). These gases can also result from caused by the decomposition of water into oxygen and hydrogen by thermal or chemical reactions. These gases must be vented from the condenser .

16. SOURCES OF AIR IN LEAKAGE IN A CONDENSER:  • Atmospheric relief valves or vacuum breakers • Rupture disks • Drains that pass through the condenser • Turbine seals • Turbine instrumentation lines • Turbine/condenser expansion joint • Tube sheet to shell joints • Air-removal suction components • Penetrations • Condenser instrumentation, sight glasses, etc. • Low-pressure feed water heaters, associated piping, valves and instruments • Valve stems, piping flanges, orifice flanges • Manhole • Shell welds • Condensate pump seals

17. REASON FOR REMOVING AIR/GAS The gases will increase the operating pressure of the condenser. Since the total pressure of the condenser will be the sum of partial pressures of the steam and the gases, as more gas is leaked into the system, the condenser pressure will rise. This rise in pressure will decrease the turbine output and efficiency. The gases will blanket the outer surface of the tubes. This will severely decrease the heat transfer of the steam to the circulating water. Again, the pressure in the condenser will increase. The corrosiveness of the condensate in the condenser increases as the oxygen content increases. Oxygen causes corrosion, mostly in the steam generator. Thus, these gases must be removed in order to extend the life of cycle components. 

18. COOLING TOWERS

19. COOLING TOWER The cooling towers are used in many applications in engineering. The main application are in power plants and refrigeration plants. Its function is to cool the hot water from the condenser by exposing it to the atmospheric air, so that the cold water may be used again for circulation. The cooling towers are used in steam power plants where there is a limited supply of cooling water. It is placed at a certain height (at about 9 metres from the ground level). The hot water falls down in radial sprays from a height and the atmospheric air enters from the base of tower. The partial evaporation of water takes place which reduces the temperature of circulating water. This cooled water is collected in the pond at the base of the tower and pumped into the condenser.

20. Factors Affecting the cooling of water in a cooling tower Size and height of cooling tower, Arrangement of plates in cooling tower, Velocity of air entering the cooling tower, Temperature of air, Humidity of air, and Accessibility of air to all parts of cooling tower.

21. Types of Cooling Towers 1. According to the type of draught a) Natural draught cooling towers b) Mechanical Draught Cooling Towers  i )Forced draught cooling towers, and ii)Induced draught cooling towers 2. According to the material used a)Timber cooling tower b) Concrete ( ferro -concrete, multideck concrete hyperbolic) cooling towers, and c) Steel duct type cooling tower

22. a)Natural draught cooling tower In a natural draught cooling tower, as shown in fig., the circulation of air is produced by the pressure difference of air inside and outside the cooling tower. In this type of tower, the hot water from the condenser is pumped to the troughs and nozzles situated near the bottom.

23. b)Mechanical Draught Cooling Towers  In these towers the draught of air for cooling the tower is produced mechanically by means of propeller fans. These towers are usually built in cells or units, the capacity depending upon the number of cells used.

24. i )Forced draught cooling tower In Forced draught cooling tower, as shown in fig, the circulation of air is produced by means of fans placed at the base of the tower.

25. ii)Induced draught cooling tower In an Induced draught cooling tower, as shown in fig, the circulation of air is provided by means of fans placed at the top of the tower.

26. 2. According to the material used a)Timber cooling tower are rarely used due to the following disadvantages: ( i ) Short life (ii) High maintenance charges (iii)Limited cooling capacity (iv) Design generally does not facilitate proper circulation of air. b) Concrete ( ferro -concrete, multideck concrete hyperbolic) cooling towers, has the following advantages : Large capacity (ii) Improved draught and air circulation (iii) Increased stability under pressure (iv) Low maintenance. c)Steel duct type cooling tower are rarely used in case of modern power plant due to their small capacity.