CONDENSER AND VACUUM CONDENSER AND VACUUM DEVICESDEVICES

CONDENSERSCONDENSERS

The functions of the condenser are,The functions of the condenser are, a) To provide lowest economic heat rejectiona) To provide lowest economic heat rejection temperature of the steam, thus saving on steamtemperature of the steam, thus saving on steam required per unit of electricity.required per unit of electricity. b) To convert exhaust steam to water for reuse,b) To convert exhaust steam to water for reuse, saving on costly feed water requirement.saving on costly feed water requirement.

c) Deaeration of make up water introduced in thec) Deaeration of make up water introduced in the condenser.condenser. d) To form a d) To form a convenient point for introducingconvenient point for introducing makeupwater. makeupwater.

Types of CondensersTypes of Condensers

Condenser is basically a heat exchanger and Condenser is basically a heat exchanger and can be of two types.can be of two types.

i) Direct Contacti) Direct Contact

ii) Surface Contactii) Surface Contact

Direct Contact TypeDirect Contact Type

-- In this type, condensation of steam takes In this type, condensation of steam takes place by directly mixing exhaust steam and place by directly mixing exhaust steam and cooling water.cooling water.

- Requirement of cooling water is much less - Requirement of cooling water is much less here compared to surface type.here compared to surface type.

- But cooling water quality should be equal to - But cooling water quality should be equal to condensate quality.condensate quality.

Surface CondenserSurface Condenser - - This type is generally used for modern steam turbine This type is generally used for modern steam turbine

installations Condensation of exhaust steam takes installations Condensation of exhaust steam takes place on the outer surface of the tubes which are place on the outer surface of the tubes which are cooled by water flowing inside them.cooled by water flowing inside them.

- The condenser essentially consists of a shell which- The condenser essentially consists of a shell which encloses the steam space. encloses the steam space.

- Tubes carrying cooling water pass through the steam - Tubes carrying cooling water pass through the steam space. The tubes are supplied cooling water from inlet space. The tubes are supplied cooling water from inlet water box on one side and discharged, after taking water box on one side and discharged, after taking away heat from the steam, to the outlet water box on away heat from the steam, to the outlet water box on the other side.the other side.

Constructional features of the Constructional features of the Surface CondenserSurface Condenser

The condenser group consists of two condensers, each The condenser group consists of two condensers, each connected with exhaust part of low pressure casing. connected with exhaust part of low pressure casing. These two condensers are interconnected by a These two condensers are interconnected by a bypass branch pipe. bypass branch pipe.

The condenser is designed to create vacuum at the The condenser is designed to create vacuum at the exhaust of the steam turbine and to provide pure exhaust of the steam turbine and to provide pure condensate for reusing as feed water for the boilers. condensate for reusing as feed water for the boilers.

The tube layout of condenser is arranged to ensure The tube layout of condenser is arranged to ensure sufficient heat transfer from steam to cooling water sufficient heat transfer from steam to cooling water passing through the tubes, and at the same time the passing through the tubes, and at the same time the resistance to flow of steam is reduced to barest resistance to flow of steam is reduced to barest minimum.minimum.

Each condenser is subdivided into upper and lower parts. Each condenser is subdivided into upper and lower parts. Front water box, shell and rear water box constitute the lower Front water box, shell and rear water box constitute the lower part. part.

Two end tube plates support plates are located inside lower Two end tube plates support plates are located inside lower body of the condenserbody of the condenser

.. Front water boxes are divided into two parts to make the Front water boxes are divided into two parts to make the

condenser two pass design. End covers of water boxes are condenser two pass design. End covers of water boxes are kept detachable for facilitating repairs and replacement of kept detachable for facilitating repairs and replacement of tubes. Manholes are provided for routine maintenance and tubes. Manholes are provided for routine maintenance and visual inspection along with venting and draining visual inspection along with venting and draining arrangement for individual water boxes. Condenser tubes arrangement for individual water boxes. Condenser tubes are secured to the end tube plates by expanding and flanging are secured to the end tube plates by expanding and flanging of tube ends which provide very good sealing arrangement of tube ends which provide very good sealing arrangement against penetration of circulating water into the steam space. against penetration of circulating water into the steam space. The tubes are so arranged that there is equal distribution of The tubes are so arranged that there is equal distribution of steam on the tube nest with minimum resistance to steam steam on the tube nest with minimum resistance to steam flow. Non condensable gases are continuously sucked with flow. Non condensable gases are continuously sucked with the help of steam ejector or with similar arrangement the help of steam ejector or with similar arrangement provided in the particular design.provided in the particular design.

L.P. Heater No.1 is also located inside the upper parts of the L.P. Heater No.1 is also located inside the upper parts of the condenser. In order to allow expansion along the height, the condenser. In order to allow expansion along the height, the condenser is supported on springs specially designed to take up condenser is supported on springs specially designed to take up load.load.

The weight of the condenser and its tubes is taken by the sprigs The weight of the condenser and its tubes is taken by the sprigs and through them by the condenser foundation. The weight of and through them by the condenser foundation. The weight of circulating water and the condensate along with the thrust of the circulating water and the condensate along with the thrust of the springs is transferred to the turbine foundation.springs is transferred to the turbine foundation.

Special care is taken for removal of the condensate formed as a Special care is taken for removal of the condensate formed as a result of condensation of the steam. Baffle plates are provided to result of condensation of the steam. Baffle plates are provided to guide the steam flow on the tube nest and for collecting the guide the steam flow on the tube nest and for collecting the condensate tricking from upper rows of the tubes and directing it condensate tricking from upper rows of the tubes and directing it towards the intermediate support plates for flowing down in towards the intermediate support plates for flowing down in narrow layers, leaving the passage free from steam flow.narrow layers, leaving the passage free from steam flow.

Material for Condenser TubesMaterial for Condenser Tubes

Selection of tube material depends mainly on the Selection of tube material depends mainly on the quality of cooling water and cost. Copper bearing quality of cooling water and cost. Copper bearing alloys are preferred as copper has very high heat alloys are preferred as copper has very high heat transfer coefficient. But as copper has very little transfer coefficient. But as copper has very little mechanical strength; it has to be reinforced by mechanical strength; it has to be reinforced by alloying with other metals. alloying with other metals.

Copper alloys are basically of three categoriesCopper alloys are basically of three categories i) Brass i) Brass ii) Cupro-nickel and ii) Cupro-nickel and iii) Bronzeiii) Bronze

Stainless steel tubes are also used.Stainless steel tubes are also used. They have good corrosion resistance They have good corrosion resistance

though heat transfer coefficient is quite though heat transfer coefficient is quite lower than the copper alloys.lower than the copper alloys.

Because of high cost, stainless steel is Because of high cost, stainless steel is used only where water is highly corrosive. used only where water is highly corrosive.

Some sea side power plants are using Some sea side power plants are using Titanium also despite high cost, because of Titanium also despite high cost, because of highly corrosive environment.highly corrosive environment.

Circulating/Cooling Water Circulating/Cooling Water LeakageLeakage

There are two kinds of CW leakage, internal and There are two kinds of CW leakage, internal and external. Internal leakage into the steam and external. Internal leakage into the steam and condensate space is most important of the two.condensate space is most important of the two.

Leakage of cooling water into the condenser Leakage of cooling water into the condenser steam side can have serious consequences. The steam side can have serious consequences. The CW carries impurities with it, into the condensate CW carries impurities with it, into the condensate system; the most detrimental are those containing system; the most detrimental are those containing chlorides, such as sodium chloride. Such chlorides, such as sodium chloride. Such impurities are then carried forward into the boiler.impurities are then carried forward into the boiler.

The presence of in the boiler water constitutes a The presence of in the boiler water constitutes a potential hazard, principally because acid potential hazard, principally because acid chlorides can be formed and boiler tube erosion chlorides can be formed and boiler tube erosion can result. can result.

It is therefore very important that CW leakage is It is therefore very important that CW leakage is detected promptly, source of leakage located, and detected promptly, source of leakage located, and the leak is rectified.the leak is rectified.

Fortunately, the impure water has a property Fortunately, the impure water has a property which can be utilized to detect the leak. The which can be utilized to detect the leak. The impure water conducts electricity better than the impure water conducts electricity better than the pure water and has higher conductivity. If the pure water and has higher conductivity. If the conductivity of the condensate is monitored, conductivity of the condensate is monitored, increase in conductivity will indicate CW leakage.increase in conductivity will indicate CW leakage.

Vacuum Devices/ Air Ejection Vacuum Devices/ Air Ejection SystemSystem

Condenser vacuum is a very important parameter Condenser vacuum is a very important parameter for effective and efficient working of the turbine. If for effective and efficient working of the turbine. If there is presence of air or non condensable gases there is presence of air or non condensable gases in the condenser vacuum can deteriorate resulting in the condenser vacuum can deteriorate resulting in load reduction or even tripping of the machine in in load reduction or even tripping of the machine in extreme case. Therefore an air extraction system extreme case. Therefore an air extraction system is needed to remove air and other no condensable is needed to remove air and other no condensable gases from the condenser to maintain vacuum.gases from the condenser to maintain vacuum.

Amount of air to be extracted from condenser Amount of air to be extracted from condenser during start up is quite large and the extraction during start up is quite large and the extraction should be done as rapidly as possible so as to should be done as rapidly as possible so as to allow the turbine to be started.allow the turbine to be started.

Under normal operating conditions, quantity of air Under normal operating conditions, quantity of air to be extracted is lower. It consists of air leakage to be extracted is lower. It consists of air leakage into the condenser via flanges and glands and into the condenser via flanges and glands and also of very little non condensable gases present also of very little non condensable gases present in the steam.in the steam.

To guard against excessive water vapor extraction To guard against excessive water vapor extraction along with air, the space beneath the air extraction along with air, the space beneath the air extraction baffles has been provided with its own cooling baffles has been provided with its own cooling tubes in order to condense as much water vapor tubes in order to condense as much water vapor as possible and thus preventing its removal from as possible and thus preventing its removal from the condenser.the condenser.

Under normal operating conditions, quantity of air Under normal operating conditions, quantity of air to be extracted is lower. It consists of air leakage to be extracted is lower. It consists of air leakage into the condenser via flanges and glands and into the condenser via flanges and glands and also of very little non condensable gases present also of very little non condensable gases present in the steam.in the steam.

To guard against excessive water vapor extraction To guard against excessive water vapor extraction along with air, the space beneath the air extraction along with air, the space beneath the air extraction baffles has been provided with its own cooling baffles has been provided with its own cooling tubes in order to condense as much water vapor tubes in order to condense as much water vapor as possible and thus preventing its removal from as possible and thus preventing its removal from the condenser.the condenser.

Types of Air Extraction SystemsTypes of Air Extraction Systems

There are two major systems for extraction There are two major systems for extraction

of air from the condenser viz. of air from the condenser viz.

a) Air Ejectorsa) Air Ejectors

b) Air Pumpsb) Air Pumps

Air EjectorsAir EjectorsThe operating medium of the air ejector can be The operating medium of the air ejector can be

either high pressure gas or liquid .In thermal either high pressure gas or liquid .In thermal power stations, steam of low parameter (Approx power stations, steam of low parameter (Approx 4.5Kg/cm2,250deg.C) is used for the air ejector. 4.5Kg/cm2,250deg.C) is used for the air ejector. The operating principle is simple- steam is passed The operating principle is simple- steam is passed through a nozzle and the pressure energy through a nozzle and the pressure energy converted velocity energy. High velocity fluid converted velocity energy. High velocity fluid aspirates air and other non condensable gases aspirates air and other non condensable gases from the condenser and moves into the diffuser from the condenser and moves into the diffuser which reconverts the velocity energy into pressure which reconverts the velocity energy into pressure energy. energy.

The pressurized mixture of steam and air is The pressurized mixture of steam and air is exhausted, either directly to atmosphere or exhausted, either directly to atmosphere or through coolers to recover the steam in the form of through coolers to recover the steam in the form of the condensatethe condensate

Air PumpsAir PumpsAir pumps allow greater flexibility as it is not Air pumps allow greater flexibility as it is not

dependent on the boiler for raising vacuum. Air dependent on the boiler for raising vacuum. Air pumps on a separate water circuit and there is no pumps on a separate water circuit and there is no risk of the concentration of soluble uncondensable risk of the concentration of soluble uncondensable gases in the condensate. Air pump can deal with gases in the condensate. Air pump can deal with both starting and normal conditions and therefore both starting and normal conditions and therefore separate starting equipment is unnecessary.separate starting equipment is unnecessary.

Air pumps are basically of three types viz. Air pumps are basically of three types viz.

a) Rotary a) Rotary

b) Liquid Ring b) Liquid Ring

c) Hydraulic c) Hydraulic

Rotary PumpRotary Pump: -: - When this pump rotates, water is drawn through the guide When this pump rotates, water is drawn through the guide nozzle and is broken into slugs by the impellor blades. nozzle and is broken into slugs by the impellor blades.

These slugsof water pass the discharge nozzle, aspirate the air and effectively These slugsof water pass the discharge nozzle, aspirate the air and effectively seal the pockets of air as they pass through the diffuser. From the diffuser, seal the pockets of air as they pass through the diffuser. From the diffuser, the air non-condensable gases are taken to sealing water tank. the air non-condensable gases are taken to sealing water tank.

The swirling motion imparted to the mixture by the tangential entry, assists The swirling motion imparted to the mixture by the tangential entry, assists separation of water and gases.separation of water and gases.

The gases are released to atmosphere through a vent in the top of the tank. The gases are released to atmosphere through a vent in the top of the tank.

The sealing water is recirculated to the tank.The sealing water is recirculated to the tank.

Liquid Ring Type: -Liquid Ring Type: - This is essentially a centrifugal This is essentially a centrifugal pump. A multiblade rotor revolves within an pump. A multiblade rotor revolves within an elliptical casing which is partially filled with water. elliptical casing which is partially filled with water.

The rotating impeller throws the liquid outwards The rotating impeller throws the liquid outwards resulting in a solid ring of liquid revolving in the resulting in a solid ring of liquid revolving in the casing at the same speed as the rotor but casing at the same speed as the rotor but following the shape of the casing. following the shape of the casing.

This causes the liquid to enter and recede from the This causes the liquid to enter and recede from the inter blade spaces on the impeller. inter blade spaces on the impeller.

The provision of inlet and outlet parts enables this The provision of inlet and outlet parts enables this pumping section to be used for sucking in and of pumping section to be used for sucking in and of the gases from the condenser.the gases from the condenser.

Hydraulic Air Pump: Hydraulic Air Pump: - It is a water - It is a water operated ejector using a motor driven operated ejector using a motor driven recirculating lift pump and a simple recirculating lift pump and a simple spillover system.spillover system.

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