A surface condenser is a heat exchanger used in thermal power plants to convert steam into liquid. It consists of a shell with tubes through which cooling water flows, and vacuum pressure is important for efficiency. The design can have multiple tube bundles or separate sections for maintenance.
A surface condenser is a type of heat exchanger often used to condense steam under vacuum as part of a thermal power plant. The shell-and-tube condenser converts steam from its gaseous phase into liquid as part of a thermodynamic cycle that includes a steam generator, pump, and turbine. The steam condenses on the outer surface of the pipes through which the cooling water passes. The water can come from a closed loop system or from an open system to an external source. The configuration of a surface condenser is indicated by the number of passes, the system subdivision and the shape of the shell.
The thermodynamic cycle using a surface condenser incorporates a generator in which water is heated to create high pressure steam. The steam pressure drives a turbine to produce energy. The system passes the steam exhaust into the surface condenser at a lower pressure. The condenser converts the vapor back into liquid. A pump returns the condensed water to the steam generator so that the cycle can repeat itself.
The physical form of the condenser is a shell with a bundle of tubes running through it. Cooling water flows through the pipes. Heat transfer occurs when the cooling water absorbs heat from the steam through the surface of the pipes. The heat loss causes the steam to turn into liquid water, known as condensate, and fall to the bottom of the condenser. The cooling water can be recycled in a closed loop or it can be taken from an external source such as a lake or river and discharged after passing through the condenser.
Vacuum pressure is important to system efficiency. The shell of the surface condenser is kept under vacuum maintaining the temperature at a point low enough that the vapor pressure of the water is lower than the ambient pressure. This lowered level helps increase the pressure drop across the turbine, thus improving output. Vacuum pressure tends to draw non-condensable gases, such as air, into the condenser. These gases must be removed to avoid a reduction in efficiency caused by the non-condensable gases which surround the pipes and which interfere with the heat exchange. Removal is also necessary to prevent corrosion due to the presence of oxygen in the system.
The design of the unit may have the cooling water pass through the tubes once, or it may have multiple bundles of tubes so that the water flows from one end of the enclosure to the other two or more times, or passes . A split surface condenser will have separate sections and tube bundles so that one part of the unit can be shut down for maintenance while another part is still running. An undivided unit with a single shell and tube must be completely shut down for any maintenance or problems. Surface condenser shells can have rectangular or cylindrical shapes depending on the location of the equipment and the capacity of the system.
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