A surface condenser is a water-cooled

shell and tube heat exchanger A shell and tube heat exchanger is a class of heat exchanger designs. It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this ty ...

installed to condense exhaust

steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporizatio ...

from a

steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam tu ...

thermal power station A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a stea ...

s. These condensers are

heat exchangers A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...

which convert steam from its gaseous to its liquid state at a pressure below

atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...

. 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 (and temperature) 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.

Purpose

In thermal power plants, the purpose of a surface condenser is to

condense Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...

the exhaust steam from a steam turbine to obtain maximum

efficiency Efficiency is the often measurable ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without ...

, and also to convert the turbine exhaust steam into pure water (referred to as steam condensate) so that it may be reused in the

steam generator A Steam generator is a device used to boil water to create steam. More specifically, it may refer to: *Boiler (steam generator), a closed vessel in which water is heated under pressure *Monotube steam generator *Supercritical steam generator or Ben ...

boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central ...

as boiler feed water. The steam turbine itself is a device to convert the

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

in steam to mechanical

power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...

. 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 from the turbine represents the heat which is converted to mechanical power. Therefore, the more the conversion of heat per pound or

kilogram The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. ...

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 Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapo ...

of the exhaust steam is carried away by the cooling medium (water or air) used by the surface condenser.

Diagram of water-cooled surface condenser

The adjacent diagram depicts a typical water-cooled surface condenser as used in power stations to condense the exhaust steam from a

driving an

electrical generator In electricity generation, a generator is a device that converts motive power ( mechanical energy) or fuel-based power ( chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, ...

as well in other applications.Energy savings in steam systems
''Figure 3a, Layout of surface condenser'' (scroll to page 11 of 34 pdf pages) There are many fabrication design variations depending on the manufacturer, the size of the steam turbine, and other site-specific conditions.

Shell

The shell is the condenser's outermost body and contains the heat exchanger tubes. The shell is fabricated from

carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, coba ...

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 A sump is a low space that collects often undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers. Sump can also refer to an area in a cave ...

(often referred to as the hotwell) is provided. Condensate is pumped from the outlet or the hotwell for reuse as

boiler feedwater Boiler feedwater is an essential part of boiler operations. The feed water is put into the steam drum from a feed pump. In the steam drum the feed water is then turned into steam from the heat. After the steam is used it is then dumped to the ma ...

. For most water-cooled surface condensers, the shell is under artial

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...

during normal operating conditions.

Vacuum system

For water-cooled surface condensers, the shell's internal vacuum is most commonly supplied by and maintained by an external

steam jet ejector An injector is a system of ducting and nozzles used to direct the flow of a high-pressure fluid in such a way that a lower pressure fluid is entrained in the jet and carried through a duct to a region of higher pressure. It is a fluid-dynamic ...

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 The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section (or choke) of a pipe. The Venturi effect is named after its discoverer, the 18th century Italian physicist, Giovanni Battista ...

, which is a particular case of

Bernoulli's principle In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy. The principle is named after the Swiss mathematici ...

, applies to the operation of steam jet ejectors. Motor driven mechanical

vacuum pump A vacuum pump is a device that draws gas molecules from a sealed volume in order to leave behind a partial vacuum. The job of a vacuum pump is to generate a relative vacuum within a capacity. The first vacuum pump was invented in 1650 by Otto ...

s, such as the liquid ring type, are also popular for this service.

Tube sheets

At each end of the shell, a sheet of sufficient thickness usually made of

stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...

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 In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object. Fluid ...

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 Expansion may refer to: Arts, entertainment and media * ''L'Expansion'', a French monthly business magazine * ''Expansion'' (album), by American jazz pianist Dave Burrell, released in 2004 * ''Expansions'' (McCoy Tyner album), 1970 * ''Expansio ...

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.

Tubes

Generally the tubes are made of

, copper alloys such as brass or bronze, cupro nickel, or

titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion i ...

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 85 ft (26 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.

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 valve A butterfly valve is a valve that isolates or regulates the flow of a fluid. The closing mechanism is a disk that rotates. Principle of operation Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves ...

s, small vent pipe with hand

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...

for air venting at higher level, and hand-operated drain

at bottom to drain the waterbox for maintenance. Similarly on the outlet waterbox the cooling water connection will have large flanges,

s, vent connection also at higher level and drain connections at lower level. Similarly

thermometer A thermometer is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass 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 Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuri ...

Corrosion

On the cooling water side of the condenser: The tubes, the tube sheets and the water boxes may be made up of materials having different compositions and are always in contact with circulating water. This water, depending on its chemical composition, will act as an

electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon ...

between the metallic composition of tubes and water boxes. This will give rise to electrolytic

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...

which will start from more anodic materials first. ''Sea water based condensers,'' in particular when sea water has added chemical

pollutants A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...

, have the worst corrosion characteristics. River water with

are also undesirable for condenser cooling water. The corrosive effect of sea or river water has to be tolerated and remedial methods have to be adopted. One method is the use of

sodium hypochlorite Sodium hypochlorite (commonly known in a dilute solution as bleach) is an inorganic chemical compound with the formula NaOCl (or NaClO), comprising a sodium cation () and a hypochlorite anion (or ). It may also be viewed as the sodium s ...

, or

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

, to ensure there is no marine growth on the pipes or the tubes. This practice must be strictly regulated to make sure the circulating water returning to the sea or river source is not affected. On the steam (shell) side of the condenser: The concentration of undissolved gases is high over air zone tubes. Therefore, these tubes are exposed to higher corrosion rates. Some times these tubes are affected by stress corrosion cracking, if original stress is not fully relieved during manufacture. To overcome these effects of corrosion some manufacturers provide higher corrosive resistant tubes in this area.

Effects of corrosion

As the tube ends get corroded there is the possibility of cooling water leakage to the steam side contaminating the condensed steam or condensate, which is harmful to

s. The other parts of water boxes may also get affected in the long run requiring repairs or replacements involving long duration shut-downs.

Protection from corrosion

Cathodic protection Cathodic protection (CP; ) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded "sacrifi ...

is typically employed to overcome this problem.

Sacrificial anode A galvanic anode, or sacrificial anode, is the main component of a galvanic cathodic protection system used to protect buried or submerged metal structures from corrosion. They are made from a metal alloy with a more "active" voltage (more n ...

s of

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

(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 replacement. This involves comparatively less down time. The water boxes made of steel plates are also protected inside by epoxy paint.

Effects of tube side fouling

As one might expect, with millions of gallons of circulating water flowing through the condenser tubing from seawater or fresh water, anything that is contained within the water flowing through the tubes can ultimately end up on either the condenser tubesheet (discussed previously) or within the tubing itself. Tube-side fouling for surface condensers falls into five main categories; particulate fouling like silt and sediment, biofouling like slime and

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular po ...

s, scaling and crystallization such as calcium carbonate, macrofouling which can include anything from

zebra mussel The zebra mussel (''Dreissena polymorpha'') is a small freshwater mussel. The species originates from the lakes of southern Russia and Ukraine, but has been accidentally introduced to numerous other areas and has become an invasive species in ma ...

s that can grow on the tubesheet, to wood or other debris that blocks the tubing, and finally, corrosion products (discussed previously). Depending on the extent of the fouling, the impact can be quite severe on the condenser's ability to condense the exhaust steam coming from the turbine. As fouling builds up within the tubing, an insulating effect is created and the heat-transfer characteristics of the tubes are diminished, often requiring the turbine to be slowed to a point where the condenser can handle the exhaust steam produced. Typically, this can be quite costly to power plants in the form of reduced output, increase fuel consumption and increased CO₂ emissions. This "derating" of the turbine to accommodate the condenser's fouled or blocked tubing is an indication that the plant needs to clean the tubing in order to return to the turbine's

nameplate capacity Nameplate capacity, also known as the rated capacity, nominal capacity, installed capacity, or maximum effect, is the intended full-load sustained output of a facility such as a power station,

. A variety of methods for cleaning are available, including online and offline options, depending on the plant's site-specific conditions.

Other applications of surface condensers

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

Testing

National and international test codes are used to standardize the procedures and definitions used in testing large condensers. In the U.S.,

ASME The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing ...

publishes several performance test codes on condensers and heat exchangers. These include ASME PTC 12.2-2010, Steam Surface Condensers, and PTC 30.1-2007, Air cooled Steam Condensers.

References

{{Steam engine configurations, state=collapsed Power station technology Heat exchangers Energy conversion Steam power de:Kondensator (Verfahrenstechnik) hr:Parni kondenzator ja:復水器 pl:Skraplacz pt:Condensador de superfície ru:Конденсатор (теплотехника) sv:Kondensor uk:Пароконденсатор