7 - Test of a Surface Condenser

Test of a Surface Condenser Hermogenes L. Mejia Jr. Cristopher Miclat

Condenser •

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Condenser is a device in which steam is condensed to water at a pressure less than atmosphere. Condensation can be done by removing heat from exhaust steam using circulating cooling water.

Condenser •

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Condenser is a device in which steam is condensed to water at a pressure less than atmosphere. Condensation can be done by removing heat from exhaust steam using circulating cooling water.

Functions •

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To reduce the turbine exhaust pressure so as to increase the specific output and hence increase the plant efficiency and decrease the specific steam consumption. To condense the exhaust steam from the turbine and reuse it as pure feed water in the boiler. Thus only make up water is required to compensate loss of water

ADVANTAGES OF CONDENSER •

Improvement of thermal cycle efficiency

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Easy handling of the working fluid, i.e. by condensing and reuse:

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Hot-well is a water reserve

Elements of steam condensing plant •

Condenser

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Air extraction pump

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Condensate extraction pump

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Circulating cooling water pump

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Hot well

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Cooling tower

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Make up water pump

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Boiler feed pump

Composition of Surface Condenser

Tubesheets

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.

Tubes

Generally the tubes are made of stainless steel, copper alloys such as brass or bronze, copper- nickel, or titanium depending on several selection criteria The tube lengths range to about 85 ft (26 m) for modern power plants, depending on the size of the condenser

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

Hotwell a tank or reservoir in which hot water is collected before being recirculated, especially condensed steam about to be returned to a boiler

Classification of Condensers •

Jet condensers (or) mixing type

Parallel flow type (Low level)

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Counter flow type (High & Low levels)

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Ejector type

Surface condensers (or) non-mixing type •

Down flow type

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Central flow type

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Inverted type

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Regenerative type

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Evaporation type

Comparison of Jet & Surface condensers Jet Condensers •

Cooling water and steam are mixed up

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Low manufacturing cost

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Requires small floor space

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The condensate cannot be used as feed water to boiler unless it is free from impurities

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More power is required for air pump

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Less power is required for water pump

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Requires less quantity of cooling water

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The condensing plant is simple

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Less suitable for high capacity plants due to low vacuum efficiency

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Lower upkeep

Surface Condenser •

Cooling water & steam aren’t mixed up

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High manufacturing cost

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Requires large floor space

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The condensate can be used as feed water to boiler as it is not mixed with cooling water

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Less power is required for air pump

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More power is required for water pump

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Requires large quantity of cooling water

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The condensing plant is complicated

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More suitable for high capacity plants as vacuum efficiency is high.

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Higher upkeep

Jet Condensers (or) Mixing Type

-are used in small capacity units where clean fresh water is available in plenty. -In jet condensers, water is in direct contact with exhaust steam. Hence these are also called direct contact type (or) mixed type. Advantages : •

As a result of effective mixing, it requires less circulating cooling water

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Equipment is simple and occupy less space

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 Maintenance is cheap

Disadvantages : •

 Not suitable for higher capacities

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Condensate cannot be used as feed water to boiler

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Air leakages are more

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Requires larger air pump

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Less vacuum is maintained

Surface Condenser ( indirect contact type /non-mixed type)

-are used in large capacity plants. -In surface condensers, exhaust steam and water do not mix together. Advantages : •

Can be used for large capacity plants

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High vacuum can be created

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Condensate is free from impurities and can be reused as feed water to boiler Impure water can also be used as cooling medium Air leakage is comparatively less, hence less power is required to operate air pump

Disadvantages : •

Design is complicated and costly

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High maintenance cost

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Occupies more space

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Requires more circulating water

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The cooling water enters the shell at the lower half section and after traveling through the upper half section comes out through the outlet. The exhaust steam entering shell from the top flows down over the tubes and gets condensed and is finally removed by an extraction pump. Due to the fact that steam flows in a direction right angle to the direction of flow of water, it is also called cross-surface condenser.

Central flow type In this type of condenser, the suction pipe of the air extraction pump is located in the center of the tubes which results in radial flow of the steam. The better contact between the outer surface of the tubes and steam is ensured, due to large passages the pressure drop of steam is reduced

Inverted type Surface condenser

-In this type of jet condensers, steam enters at the bottom of the shell and flows upwards. -Air extraction pump is placed at the top. -The condensate flows down and removed at the bottom where condensate pump is located. Regenerative type Surface condenser

-In this type of condensers, the condensate after leaving the condenser is passed through the exhaust steam where the temperature is increased. -The condensate at high temperature can be reused as feed water to the boiler. -This increases the efficiency of the plant and minimize the fuel consumption.

Sources of air in Condenser

- Air leakage from atmosphere at the joints of the parts which are internally under a pressure less than atmosphere. - Air accompanied with steam from the boiler into which it enters dissolved with feed water - In jet condensers, a little quantity of air accompanies the injection of water in which it is dissolved Effects of air leakage in a condenser

- Lowered thermal efficiency - Increased requirement of cooling water - Reduced heat transfer - Corrosion

VACUUM AND ITS MEASUREMENT --Vacuum is sub-atmospheric pressure. It is measured as the pressure depression below atmospheric. --The term vacuum in the case of a condenser means pressure below atmospheric pressure. It is generally expressed in mm of Hg (mercury). Vacuum Efficiency - It is defined as the ratio of the actual vacuum to the maximum obtainable vacuum

Condenser Efficiency: •

It is defined as the ratio of the difference between the outlet and inlet temperatures of cooling water to its difference between the temperature corresponding to the vacuum in the condenser and inlet temperature of cooling water.

Condenser Efficiency = (∆ Tc)/((Tsat. Of the absolute pressure)-(Tic))

Example 1. The vacuum in a surface condenser is found barometer reading 760 mm of Hg. The cooling water enters the condenser 1at 15°C and leaves at 36°C. Find the condenser efficiency. Absolute pressure in the condenser = 760  – 707.5 =52.5 mmHg

52.5

= 0.07 bar

750 Saturation temperature corresponding to 0.07 bar is 39 c 36−15 condenser efficiency = = 0.875 = 87.5% 39−15