Condenser Prof

Condenser Prof. Prabha Chand CONDENSER The main purposes of the condenser are to condense the exhaust steam from the turbine for re-use 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). 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. Effect of condenser pressure on p-v t-s diagrams Main elements of condensing unit Classification of Condensers 1. Direct contact type condenser 2. Surface condenser • Direct contact type condenser: 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. SPRAY 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. BAROMETRIC 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. JET CONDENSER • A jet condenser baffles of a barometric type are replaced by cascade and to reduce the height of tail pipe, diffuser is provided. The diffuser acts on the same principle as the diverging section of a convergent nozzle in subsonic flow. SURFACE CONDENSOR TWO PASS SURFACE CONDENSERS • They are essentially shell and tube type of heat exchanger where cooling water flows through tubes and exhaust steam fed into the shell surroundings the tubes SINGLE PASS SURFACE CONDENSER • Single pass condenser is one in which cooling water flows through all the condenser tubes once from end to another 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 . 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 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. THANK YOU.

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