Surface condenser

Surface condenser: 

Surface condenser - Kaushik sanghani . - Mo. +919909401178 Gujarat, India. applications of surface condensers and Requirement of surface condenser

GOVERNMENT POLYTECHNICH : 

GOVERNMENT POLYTECHNICH NEAR AJI DEM CHOWKI BHAVAGAR ROA,RAJKOT FULL NAME ENROLLMENT NO SUBJECT TOPIC OF SUBJECT Tarun chavda 096200319022 Thermal Engineering Surface condenser

INTRODUCTION: 

INTRODUCTION Surface condenser is the commonly used term for a water-cooled shell and tube heat exchanger installed on the exhaust steam from a steam turbine in thermal power stations . [1][2][3] These condensers are heat exchangers which convert steam from its gaseous to its liquid state at a pressure below atmospheric pressure . Where cooling water is in short supply, an air-cooled condenser is often used. An air-cooled condenser is however significantly more expensive and cannot achieve as low a steam turbine exhaust pressure as a water cooled surface condenser. Surface condensers are also used in applications and industries other than the condensing of steam turbine exhaust in power plants.

Slide 4: 

Diagram of water-cooled surface condenser

Why is it required? : 

Why is it required? The steam turbine itself is a device to convert the heat in steam to mechanical power . The difference between the heat of steam per unit mass at the inlet to the turbine and the heat of steam per unit mass at the outlet to the turbine represents the heat which is converted to mechanical power. Therefore, the more the conversion of heat per pound or kilogram of steam to mechanical power in the turbine, the better is its efficiency. By condensing the exhaust steam of a turbine at a pressure below atmospheric pressure, the steam pressure drop between the inlet and exhaust of the turbine is increased, which increases the amount of heat available for conversion to mechanical power. Most of the heat liberated due to condensation of the exhaust steam is carried away by the cooling medium (water or air) used by the surface condenser.

Types of parts: 

Types of parts Shell The shell is the condenser's outermost body and contains the heat exchanger tubes. The shell is fabricated from carbon steel plates and is stiffened as needed to provide rigidity for the shell. When required by the selected design, intermediate plates are installed to serve as baffle plates that provide the desired flow path of the condensing steam. The plates also provide support that help prevent sagging of long tube lengths. At the bottom of the shell, where the condensate collects, an outlet is installed. In some designs, a sump (often referred to as the hotwell ) is provided. Condensate is pumped from the outlet or the hotwell for reuse as boiler feedwater . For most water-cooled surface condensers, the shell is under vacuum during normal operating conditions.

Slide 10: 

Vacuum system Diagram of a typical modern injector or ejector. For a steam ejector , the motive fluid is steam. For water-cooled surface condensers, the shell's internal vacuum is most commonly supplied by and maintained by an external steam jet ejector system. Such an ejector system uses steam as the motive fluid to remove any non- condensible gases that may be present in the surface condenser. The Venturi effect , which is a particular case of Bernoulli's principle , applies to the operation of steam jet ejectors. Motor driven mechanical vacuum pumps , such as the liquid ring type, are also popular for this service .

Slide 11: 

Tube sheets At each end of the shell, a sheet of sufficient thickness usually made of stainless steel is provided, with holes for the tubes to be inserted and rolled. The inlet end of each tube is also bellmouthed for streamlined entry of water. This is to avoid eddies at the inlet of each tube giving rise to erosion, and to reduce flow friction. Some makers also recommend plastic inserts at the entry of tubes to avoid eddies eroding the inlet end. In smaller units some manufacturers use ferrules to seal the tube ends instead of rolling. To take care of length wise expansion of tubes some designs have expansion joint between the shell and the tube sheet allowing the latter to move longitudinally. In smaller units some sag is given to the tubes to take care of tube expansion with both end water boxes fixed rigidly to the shell.

Slide 12: 

Tubes Generally the tubes are made of stainless steel , copper alloys such as brass or bronze, cupro nickel , or titanium depending on several selection criteria. The use of copper bearing alloys such as brass or cupro nickel is rare in new plants, due to environmental concerns of toxic copper alloys. Also depending on the steam cycle water treatment for the boiler, it may be desirable to avoid tube materials containing copper. Titanium condenser tubes are usually the best technical choice, however the use of titanium condenser tubes has been virtually eliminated by the sharp increases in the costs for this material. The tube lengths range to about 55 ft (17 m) for modern power plants, depending on the size of the condenser. The size chosen is based on transportability from the manufacturers’ site and ease of erection at the installation site. The outer diameter of condenser tubes typically ranges from 3/4 inch to 1-1/4 inch, based on condenser cooling water friction considerations and overall condenser size.

Slide 13: 

Waterboxes The tube sheet at each end with tube ends rolled, for each end of the condenser is closed by a fabricated box cover known as a waterbox , with flanged connection to the tube sheet or condenser shell. The waterbox is usually provided with man holes on hinged covers to allow inspection and cleaning. These waterboxes on inlet side will also have flanged connections for cooling water inlet butterfly valves , small vent pipe with hand valve for air venting at higher level, and hand operated drain valve at bottom to drain the waterbox for maintenance. Similarly on the outlet waterbox the cooling water connection will have large flanges, butterfly valves , vent connection also at higher level and drain connections at lower level. Similarly thermometer pockets are located at inlet and outlet pipes for local measurements of cooling water temperature. In smaller units, some manufacturers make the condenser shell as well as waterboxes of cast iron .

Slide 14: 

Protection from corrosion Cathodic protection is typically employed to overcome this problem. Sacrificial anodes of zinc (being cheapest) plates are mounted at suitable places inside the water boxes. These zinc plates will get corroded first being in the lowest range of anodes. Hence these zinc anodes require periodic inspection and replacements. This involves comparatively less down time. The water boxes made of steel plates are also protected inside by epoxy paint. Cross-sectional schematic diagram of a power plant condenser for condensing exhaust steam from a steam turbine . This condenser is single-pass on both the tube and shell sides with a large opening at the top for the exhaust steam to enter and a hotwell at the bottom where condensate water drips down to and collects. Circulating water for cooling is shown in light greenish color and condensate is light blue. Note also that the springs at the condenser support pads or the expansion joint at the turbine exhaust are designed in for thermal expansion and a normal installation includes either one or the other, not both like in this diagram.

Picture of surface condenser: 

Picture of surface condenser

applications of surface condensers: 

applications of surface condensers Vacuum refrigeration Vacuum evaporation Ocean Thermal Energy (OTEC) Replacing barometric condensers in steam-driven ejector systems Geothermal energy recovery Desalination systems