Condensers

In the name of God

CondensersArash Vali esfahani (87109294)

Mechanical School ofSharif University of Technology

Fall 2012

Classification of condensers

Direct contact type, where the cooling water and steam directly meet and come out as asingle stream. They are classified in to three categories.• Spray condenser• Barometric condenser• Jet condenser

Spray condenser

Classification of condensersSurface condensers (indirect contact type) where there is no mixing of cooling water andsteam. It is shell and tube type heat exchanger. The heat released upon condensation istransferred to circulating cooling water through the walls of the tube. They are classified in to categories:

Down flow Surface condensers Central flow

Inverted type Regenerative surface condensers. Evaporative condensers

Classification of condensers

Air-cooled condencers * natural convection* induced convection

Water-cooled condecers* Tube-in-Tube (double pipe)* Shell-and-Coil* Shell-and-Tube

Evaporative condencers

Water-cooled Surface Condenser

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 providerigidity for the shell. Based on design considerations, intermediate plates areinstalled to serve as baffle plates that provide the desired flow path of thecondensing steam. These plates also provide support that help prevent sagging oflong tube lengths.At the bottom of the shell, where the condensate collects, an outlet is installed. Insome designs, a sump (often referred to as the hot well) is provided. Condensate ispumped from the outlet of the hot well for reuse as boiler feed water.For most water-cooled surface condensers, the shell is under vacuum during normaloperating conditions.

Surface Condenser

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 copperbearing alloys such as brass or cupro nickel is rare in new plants, due to environmentalconcerns of toxic copper alloys. Also depending on the steam cycle water treatment for theboiler, it may be desirable to avoid tube materials containing copper. Titanium condensertubes are usually the best technical choice, however, it is very expensive. The tube lengthsrange to about 55 ft (15 m) for modern power plants, depending on the size of thecondenser. The size chosen is based on transportability from the manufacturers’ site andease of erection at the installation site. The outer diameter of condenser tubes typicallyranges from 3/4 inch (19 mm) to 1-1/4 inch (13 mm), based on condenser cooling waterfabrication considerations and overall condenser size.

Surface Condenser

Water boxes

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 water box, with flanged connection to the tube sheet or condenser shell. The water box is usually provided with man holes on hinged covers to allow inspection and cleaning.

These water boxes 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 water box for maintenance. Similarly on the outlet water box the cooling water connection will have large flanges, butterfly valves, vent connection also at higher level and drain connection at lower level.

Surface CondenserVacuum SystemFor most water-cooled surface condensers, the shell is under vacuum during normal operating conditions.The shell’s internal vacuum is most commonly created 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 particular case of Bernoulli’s principle, applies to the operation of steam jet ejectors.

Surface Condenser

Evaporative Condenser

Cooling TowersThe primary task of a cooling towers is toreject heat into the atmosphere. It represents a relatively inexpensive and dependable means of removing low-grade heat from cooling water. Hot water from heat exchanges is sent to the cooling tower.Cooling towers fall into two main categories :(a) Natural draft(b) Mechanical draft

Cooling Towers Natural DraftNatural draft towers use very large concrete chimney to introduce air through the media. Due to the large size of these towers, they are generally used for water flow rates above 45,000 m3/hr. These types of towers are used only by utility power stations.

Mechanical DraftMechanical draft towers utilise large fans to force or such air though circulated water. The water falls downward over fill surface, which help increase the contact time between the water and the air – this helps maximise heat transfer between the two. Cooling rates of mechanical draft towers depends upon their fan diameter and speed of operation. Since, the mechanical draft cooling towers are much widely used, more detailed discussion of the same follows.

Mechanical Draft TowersMechanical draft towers are available in the following airflow arrangements :(a) Counter flows induced draft(b) Counter flow forced draft(c) Cross flow induced draft

In the counter flow induced draft design, hot water enters at the top, while the air is introduced at the bottom and exists at the top. Both forced and induced draft fans are used.In cross flow induced draft towers, the water enters at the top and passes over the fill. The air, however, is introduced at the side either on one side (single-flow tower) or opposite sides (double-flow tower). An induced draft fan draws the air across the wetted fill and expels it through the top of structure.

CrossflowAdvantages of the crossflow design: Gravity water distribution allows smaller pumps and maintenance while in use. Non-pressurized spray simplifies variable flow. Typically lower initial and long-term cost, mostly due to pump requirements.

Disadvantages of the crossflow design: More prone to freezing than counterflow designs. Variable flow is useless in some conditions.

CounterflowAdvantages of the counterflow design: Spray water distribution makes the tower more freeze-resistant. Breakup of water in spray makes heat transfer more efficient.

Disadvantages of the counterflow design: Typically higher initial and long-term cost, primarily due to pump

requirements. Difficult to use variable water flow, as spray characteristics may be

negatively affected.

Mechanical Draft Towers Normal capacities range from approximately 10 tons,

2.5 m3/hr flow to several thousand tons and m3/hr. Towers can be either factory built or field erected – for example concrete towers are only field erected.

Cooling Towers fills Fill

Most towers employ fills (made of plastic or wood) to facilitate heat transfer by maximising water and air contact. Fill can either be splash or film type. With splash fill, water falls over successive layers of horizontal splash bars, continuously breaking into smaller droplets, while also wetting the fill surface. Plastic splash fill promotes better heat transfer than the wood splash fill. Film fill consists of thin, closely spaced plastic surfaces over which the water spreads, forming a thin film in contact with the air. These surfaces may be flat, corrugated, honeycombed or other patterns. The film type of fill is the more efficient and provides same heat transfer in a smaller volume than the splash fill.

Cooling Towers fills

Cooling Tower componentsCold Water BasinLouversGenerally, cross-flow towers have inlet louvers. The purpose of louvers is to equaliser air flow into the fill and retain the water within the tower. Many counter flow tower designs do not require louvers.

Air InletFansNozzlesThese provide the water sprays to wet the fill. Uniform water distribution at the top of the fill is essential to achieve proper wetting of the entire fill surface. Nozzles can either be fixed in place and have either round or square spray patterns or can be part of a rotating assembly as found in some circular cross-section towers.

Cooling Towers(

Cooling Towers

Tower Materials In the early days of cooling tower manufacturer, towers were

constructed primarily of wood. Wooden components included the frame, casing, louvers, fill and often the cold water basin. If the basin was not of wood, it likely was of concrete.

Today, tower manufacturers fabricate towers and tower components from a variety of materials. Often several materials are used to enhance corrosion resistance, reduce maintenance and promote reliability and long service life. Galvanised steel, various grades of stainless steel, glass fibre and concrete are widely used in tower construction as well as aluminium and various types of plastics for some components. Wood towers are still available, but they have glass fibre rather than wood panels (casing) over the wood framework. The inlet air louvers may be glass fibre, the fill may be plastic, and the cold water basins may be steel. Larger towers sometimes are made of concrete. Many towers – casings and basins – are constructed of galvanised steel or where a corrosive atmosphere is a problem, stainless steel. Sometimes a galvanised tower has a stainless steel basin. Glass fibre is also widely used for cooling tower casings and basins, giving long life and protection from the harmful effects of many chemicals.