Condenser (heat transfer)

A capacitor in process engineering is the physical condensation.

This refers to the skipping of a substance from the gaseous to the liquid state.

Capacitors are used in heat engines and refrigeration plants for the liquefaction of the exhaust steam or the vapor refrigerant. This allows in these systems a closed loop process.

As defined in the German translation of the European standard EN 378 part 1 of the condenser in refrigeration equipment is called a condenser to create a linguistic differentiation from electrical capacitor.

History

With the invention of the capacitor by James Watt first steam engines were built, which had a relatively low energy consumption. A capacitor is therefore a crucial element for the efficient operation of steam engines and steam turbines, and its introduction is considered a milestone of the history of technology.

James Watt used his machines for the simple design of the injection capacitor. In a separate vessel downstream of the vapor outlet of the machine, cold water is injected. The vapor liquefies and leaves an almost complete vacuum. This vacuum allows an improved utilization of the inherent thermal energy in the steam to generate kinetic energy. Injection capacitors are still used today; but they have become very rare, as they can provide no useful condensate for feeding the boiler because of the entry of solutes.

Types

Water-cooled condenser

Compared with the injection of capacitors Watt water-cooled surface condensers are used in the form of the tube bundle heat exchanger or plate today.

Here, the cold cooling water is passed through pipes in the exhaust steam, and the exhaust steam is condensed on the outside of the opposite side to the cooling pipes. The number of tubes in a condenser can be very large; so are in the capacitors of a large nuclear power plant up to 20,000 of 10 m length. For the tubes have a nominal diameter of 15 mm to 30 mm is typical. Within the condenser, the cooling water is heated to 8-10 ° C during operation of the steam turbine. A typical nuclear power plant includes a steam turbine, up to six such capacitors, which are flowed through in each case having up to 7 cubic meters cooling water per second. Such a capacitor to transmit a thermal output up to 700 megawatts from the exhaust steam of the turbine to the cooling water. This can be achieved under vacuum capacitor depends mainly on the inlet temperature of the cooling water and the quality of the heat transfer in the individual tubes and may fall to below 40 mbar in very favorable cases.

In compression refrigeration systems is the " condenser " placed after the compressor or behind the expeller and the rectification of absorption chillers. The superheated refrigerant is passed through the condenser is liquefied by heat transfer to a cooling medium.

A special feature of this surface condensers is the presence of so-called steam streets. This refers to gaps in the tubing through which the turbine exhaust can easily flow into the tube bundle. Are the streets tubes at the edges of the steam streets. They have a greater wall thickness compared to normal tubes in the condenser, as they are exposed to a particular degree the impingement of the incoming high velocity wet steam. In addition, accumulates in the condenser, the air gets into the steam system by seals and nichtentgastes feed water. Particularly prone in this respect is the labyrinth seal of the turbine shaft. The transported air from the steam concentrated preferably in Lüftkühlerbereich and is constantly sucked from there with a vacuum pump.

In general, capacitors are cooled by water, which is taken from the environment and its pollution as fouling can compromise the function of the capacitor. Even a thin layer of dirt in the pipes of the capacitor has a significant impact on the overall efficiency of a steam power plant. Therefore, the water is cleaned before using a filtering process; the fine dirt in the pipes during operation, eliminating special sponge rubber balls, which are introduced with the Taprogge process in the cooling water and removed with large screens again.

The cooling water for the condensation is, if possible, directly from a river or water and recycled. To limit the amounts of cooling water and the temperature of the returned cooling water, it is in turn cooled in recooling stations (e.g., open cooling tower or dry coolers ) again.

Air-cooled condensers and condenser

If the location of the power plant cooling water was not available, so an air condenser is used (german air cooled condenser ) instead of a water-cooled condenser.

The air-cooled condenser or condenser consisting of a tube register, through which a stream of air is performed by free or forced convection. Free convection is, however, only used in small refrigeration systems (refrigerators ). Typically axial fans are used, the stationary (so-called table radiator ) are arranged or horizontally. The tubes of the condenser are provided on the air side with ribs for the transfer of heat to increase the effective area. The fin blades are usually made of aluminum sheet. To optimize variable speed fan motors are used, which are controlled by the condenser pressure.

Air condensers were used, among other things for steam locomotives to reduce their consumption of feed water ( see condensation locomotive ). Here also favored the wind as natural ventilation cooling.

Evaporative

The evaporative condenser having a housing, in which a pipe register is introduced, which receives the refrigerant. From above, water is injected into the housing. Below the housing a radial fan are installed, which support the housing in countercurrent to the water flowing air. There is a lively exchange of heat between the pipe surface, the ascending air stream and the down sparkling water drops. The air is largely saturated with water vapor. Above the evaporative condenser rises to an air - mist mixture. For the deposition and distribution of liquid drops internals are included in the condenser, which mostly consist of plastics moldings.