STEAM CONDENSERS

A closed vessel in which steam is condensed by abstracting the heat and where the pressure is

maintained below atmospheric pressure is known as a condenser

Thermal efficiency of a closed cycle power developing system using steam as working fluid and working on
Carnot cycle is given by an expression (T1 – T2)/T1. This expression of efficiency shows that the efficiency
increases with an increase in temperature T1 and decrease in temperature T2 if the exhaust of the steam takes
place below atmospheric pressure. Low exhaust pressure is necessary to obtain low exhaust temperature. But
the steam cannot be exhausted to the atmosphere if it is expanded in the engine or turbine to a pressure lower
than the atmospheric pressure. Under this condition, the steam is exhausted into a vessel known as condenser
where the pressure is maintained below the atmosphere by continuously condensing the steam by means of
circulating cold water at atmospheric temperature.

The Steam condenser are of two types:

1. Surface condenser. 2. Jet condensers

 SURFACE CONDENSERS :

In surface condensers there is no direct contact between the steam and cooling water and the condensate
can be re-used in the boiler. In such condenser even impure water can be used for cooling purpose whereas
the cooling water must be pure in jet condensers. Although the capital cost and the space needed is more
in surface condensers but it is justified by the saving in running cost and increase in efficiency of plant
achieved by using this condenser. Depending upon the position of condensate extraction pump, flow of
condensate and arrangement of tubes the surface condensers may be classified as follows:

(i) Down flow Condenser : In this type condenser(Fig 1) , Steam enters at the top and flows downward. The
water flowing through the tubes in one direction lower half comes out in the opposite direction in the upper
half.

1. Down Flow type 2. Central Flow type 3. Evaporation Type

 (ii) Central flow Condenser.: In this condenser(Fig 2), the steam passages are all around the periphery of
the shell. Air is pumped away from the centre of the condenser. The condensate moves radially towards
the centre of tube nest. Some of the exhaust steams while moving towards the centre meets the
undercooled condensate and pre-heats it thus reducing undercooling.

(iii) Evaporation Condenser: In this condenser(Fig 3), steam to be condensed is passed through a series of

tubes and the cooling waterfalls over these tubes in the form of spray. A steam of air flows over the tubes
to increase evaporation of cooling water, which further increases the condensation of steam.

Requirements Of A Modern Surface Condenser

The requirements of ideal surface condenser used for power plants are as follows:

 The steam entering the condenser should be evenly distributed over the whole cooling surface of the
condenser vessel with minimum pressure loss.
 The amount of cooling water being circulated in the condenser should be so regulated that the
temperature of cooling water leaving the condenser is equivalent to saturation temperature of steam
corresponding to steam pressure in the condenser. This will help in preventing under cooling of
condensate.
 The deposition of dirt on the outer surface of tubes should be prevented. Passing the cooling water
through the tubes and allowing the steam to flow over the tubes achieve this.
 There should be no air leakage into the condenser because presence of air destroys the vacuum in the
condenser and thus reduces the work obtained per kg of steam. If there is leakage of air into the
condenser air extraction pump should be used to remove air as rapidly as possible.

Advantages of a Surface Condenser

The various advantages of a surface condenser are as follows:
1. The condensate can be used as boiler feed water.

2. Cooling water of even poor quality can be used because the cooling water does not come in direct
contact with steam.

3. High vacuum (about 73.5 cm of Hg) can be obtained in the surface condenser. This increases the
thermal efficiency of the plant.

Disadvantages of a Surface Condenser :

The various disadvantages of' the surface condenser are as follows:
1. The capital cost is more.
2. The maintenance cost and running cost of this condenser is high.
3. It is bulky and requires more space.
 JET CONDENSERS

In jet condensers the exhaust steam and cooling water come in direct contact with each other. The
temperature of cooling water and the condensate is same when leaving the condensers.

Elements of the jet condenser are as follows:

1. Nozzles or distributors for the condensing water.

2. Steam inlet.

3. Mixing chambers: They may be either (a) parallel flow type OR (b) counter flow type depending on
whether the steam and water move in the same direction before condensation or whether the flows are
opposite.

4. Hot well.

 Types of Jet Condensers

 Low level jet condensers (Parallel flow type) : . In this condenser (Fig. 1.13) water is sprayed through
jets and it mixes with steam. The air is removed at the top by an air pump. In counter flow type of
condenser the cooling water flows in the downward direction and the steam to be condensed moves
upward.

Fig 1 Fig 2 Fig 3

 High level or Barometric condenser : Fig. 2 shows a high-level jet condenser. The condenser shell is
placed at a height of 10.33 m (barometric height) above the hot well. As compared to low level jet
condenser. This condenser does not flood the engine if the water extraction pump fails. A separate air
pump is used to remove the air.
 Ejector Condenser : In this condenser (Fig 3) cold water is discharged under a head of about 5 to 6 m
through a series of convergent nozzles. The steam and air enter the condenser through a non-return
valve. Mixing with water condenses steam. Pressure energy is partly convert into kinetic energy at the
converging cones. In the diverging come the kinetic energy is partly converted into pressure energy and
a pressure higher than atmospheric pressure is achieved so as to discharge the condensate to the hot
well.