STEAM CONDENSERS

Definition

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

A condenser is basically steam to water exchanger in which heat from exhaust steam is transferred to circulating cooling water

Function

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 condensers in steam power plant

1) High pressure ratio provides larger enthalpy drop

2) Work output per kg of steam increases and hence specific steam consumption decreases

3) Condensate can be reused as hot feed water to the boiler. This reduces the time of evaporation and hence fuel economy

4) No feed water treatment is required and hence reduces the cost of the plant

5) The formation of deposits in the boiler surface can be prevented with the use of condensate instead of feed water from outer sources

Elements of steam condensing plant1) Condenser

2) Air extraction pump

3) Condensate extraction pump

4) Circulating cooling water pump

5) Hot well

6) Cooling tower

7) Make up water pump

8) Boiler feed pump

Elements of steam condensing plant

Classification of condensers

1) Jet condensers (or) mixing typea) Parallel flow type (Low level)b) Counter flow type (High & Low levels)c) Ejector type

2) Surface condensers (or) non-mixing typea) Down flow typeb) Central flow typec) Inverted typed) Regenerative typee) Evaporation type

Jet Condenser Vs Surface CondenserJet Condensers

(Direct Contact type/Mixed type)Surface Condensers

(Indirect Contact type/Non-Mixed type)

Comparison of jet & surface condensersJet Condensers Surface Condensers

1) Cooling water and steam are mixed up

2) Low manufacturing cost

3) Requires small floor space

4) The condensate cannot be used as feed

water to boiler unless it is free from

impurities

5) More power is required for air pump

6) Less power is required for water pump

7) Requires less quantity of cooling water

8) The condensing plant is simple

9) Less suitable for high capacity plants

due to low vacuum efficiency

10)Lower upkeep

1) Cooling water & steam aren’t mixed up

2) High manufacturing cost

3) Requires large floor space

4) The condensate can be used as feed

water to boiler as it is not mixed with

cooling water

5) Less power is required for air pump

6) More power is required for water pump

7) Requires large quantity of cooling

water

8) The condensing plant is complicated

9) More suitable for high capacity plants

as vacuum efficiency is high

10)Higher upkeep

Jet condensers

Jet condensers 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 & disadvantages of Jet condensers

1) As a result of effective mixing, it requires less circulating

cooling water

2) Equipment is simple and occupy less space

3) Maintenance is cheap

Advantages

Disadvantages 1) Not suitable for higher capacities

2) Condensate cannot be used as feed water to boiler

3) Air leakages are more

4) Requires larger air pump

5) Less vacuum is maintained

Surface condensers

Surface condensers are used in large

capacity plants

In surface condensers, exhaust steam and

water do not mix together. Hence they are

also called indirect contact type (or) non-

mixed type

Advantages & disadvantages of surface condensers

1) Can be used for large capacity plants2) High vacuum can be created3) Condensate is free from impurities and can be reused as

feed water to boiler4) Impure water can also be used as cooling medium5) Air leakage is comparatively less, hence less power is

required to operate air pump

Advantages

Disadvantages 1) Design is complicated and costly2) High maintenance cost3) Occupies more space4) Requires more circulating water

Parallel flow low level Jet condenser

Counter flow low level Jet condenser

High level Jet condenser

Ejector type Jet condenser

Down flow Surface condenser

Central flow Surface condenser

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

The condensers used in a regenerative method of heating

the condensate are called regenerative type condensers.

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 minimise

the fuel consumption.

Evaporative Surface condenser

Sources of air in Condenser

1) Air leakage from atmosphere at the joints of the parts which are internally under a pressure less than atmosphere

2) Air accompanied with steam from the boiler into which it enters dissolved with feed water

3) 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

1) Lowered thermal efficiency

2) Increased requirement of cooling water

3) Reduced heat transfer

4) Corrosion

Methods of obtaining maximum vacuum

1) Air pump

2) Steam air ejector

3) De-aerated feed water

4) Air tight joints

Vacuum Measurement

Vacuum Efficiency

It is defined as the ratio of actual vacuum to the maximum obtainable vacuum.

steamof pressure Absolute

- Pressure

Barometer

Vacuum Actual= efficiency Vacuum

vacuum obtainable

Maximumvacuum Actual = efficiency Vacuum

Condenser EfficiencyIt is defined as the ratio of difference

between the outlet and inlet temperatures of cooling water to the difference between the temperature corresponding to the vacuum in the condenser and inlet temperature of cooling water

watercooling of etemperatur Inlet -

vacuum to ingcorrespond

eTemperatur watercooling of

etemperatur in Rise

= efficiency Condenser

Edward’s Air Pump

Two Stage Air Ejector