water-cooled surface condenser

The adjacent a typical water-cooled surface condenser used in power stations to condense exhaust steam from steam turbines driving electrical generators, among other applications.There are many variations in manufacturing designs depending on the manufacturer, size of the turbine, and other site-specific conditions.

Shell

The shell is the outermost body of the condenser and contains the heat exchanger tubes.The shell is made of carbon steel plate, reinforced as necessary to provide rigidity to the shell.When required by the selected design,intermediate plates are installed as baffles to provide the required flow path for condensing steam.These plates also provide support to help prevent long tube lengths from sagging.At the bottom of the housing, where condensation collects, an outlet is installed.In some designs, a sump (often called a heat well) is provided.Condensate is drawn from the outlet or hot well to be reused as boiler feed water.For most water-cooled surface condensers, the enclosure is under vacuum under normal operating conditions.

Vacuum system 

For water-cooled surface condensers, the internal vacuum of the enclosure is usually provided and maintained by an external steam ejector system.This ejector system uses steam as the motive fluid to remove any non-condensable gases that may be present in the surface condenser.The Venturi effect is a special case of Bernoulli's principle that applies to the operation of steam ejectors.Motor-driven mechanical vacuum pumps, such as liquid ring types, are also popular.

Tube sheets

At each end of the casing, a sheet of sufficient thickness, usually of stainless steel, is provided, with holes for inserting and coiling the tubes.The inlet end of each tube is also flared for streamlined water intake.This is to avoid corrosion caused by eddy currents at the inlet of each tube and to reduce flow friction. Some manufacturers also recommend inserting plastic at the inlet of the tube to avoid vortex erosion of the inlet end.In smaller installations, some manufacturers use ferrules to seal the tube ends instead of rolling them.To handle longitudinal expansion of the tubes, some designs have expansion joints between the shell and the tubesheet, allowing the latter to move longitudinally.In smaller units the tube has some sag to handle tube expansion and the tanks at both ends are securely fastened to the housing.

Tubes

Typically, tubes are made of stainless steel, copper alloys such as brass or bronze, nickel copper or titanium, depending on various selection criteria.Copper bearing alloys such as brass or copper-nickel alloys are rarely used in new plants due to environmental concerns with toxic copper alloys.Also, depending on the boiler's steam cycle water treatment, it may be necessary to avoid the use of copper-containing tubing.Titanium condenser tubes are usually the best technical choice, but due to the dramatic increase in the cost of this material, the use of titanium condenser tubes has virtually been eliminated.Tube lengths in modern power plants range from about 85 feet (26 m), depending on the size of the condenser.The size chosen depends on the transportability at the manufacturer's site and the ease of installation at the installation site.Condenser tubes are typically 3/4" to 1-1/4" outside diameter depending on condenser cooling water friction factors and overall condenser size.

Waterboxes

The tube sheets at each end have tube ends rolled up, and each end of the condenser is closed by a fabricated tank cover called a tank, which is flanged to the tube sheet or condenser shell. Cisterns usually have manholes in the hinged lids for easy inspection and cleaning.These tanks on the inlet side will also have flanged connections for cooling water inlet butterfly valves, a small exhaust pipe with a manual valve for higher levels of air discharge, and a manual drain valve at the bottom to drain the tank for maintenance. Similarly, on the outlet tank, the cooling water connections will have large flanges, butterfly valves, upper level exhaust connections and lower level drain connections.Likewise, thermometer pockets are located at the water inlet and outlet pipes for local measurement of cooling water temperature.In smaller units, some manufacturers make the condenser housing as well as the cast iron tank.