22-01-2013, 12:19 PM
DESIGN OF CONDENSER
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Introduction of Condenser:
The Work done in any heat engine is directly proportional to the temp. Range of the working
fluid in the engine, OR For greater amount of expansion of working fluid, greater will be the
work done. In case of steam engines, the lower limit of expansion (or exhaust) may be
decreased below the atmospheric pressure. This is done by exhausting the steam into a
closed vessel called condenser. In condenser exhaust steam is condensed & vacuum is
maintained in it.
Steam condenser is an appliance in which the steam exhausted from a steam engine is
condensed. Condenser is installed such that the exhaust steam from a Steam Engine is
delivered into it. In the condenser, the heat is removed from the exhausted steam in form of
latent heat by means of cooling water which absorbs this latent heat. The exhaust steam after
losing its latent heat changes its state into water, which is termed as Condensate and this
process, is called as condensation.
In effect a Condenser is a heat exchanger wherein the exhaust steam of a Steam Engine is
condensed either in direct or indirect contact with cooling water through a heat transfer
medium separating them.
In short the purpose of the condenser in a vapor compression cycle is to accept the hot, highpressure
gas from the compressor and cool it to remove first the superheat and then the latent
heat, so that the refrigerant will condense back to a liquid. In addition, the liquid is usually
slightly sub cooled. In nearly all cases, the cooling medium will be air or water.
Functions of a Condenser:
By designing the turbine to exhaust into a condenser which maintains a pressure lower than
atmospheric there are three important advantages to be gained.
Saving in steam:
o There is a big reduction in the amount of steam required to generate each unit of electricity
by using a condenser. In a turbine without a condenser the lowest pressure to which the
steam can be expanded is that of the atmosphere. It can be said that in this case the back
pressure against which the steam is exhausted is atmospheric pressure.Atmospheric pressure
is equivalent to the pressure which would support a column of mercury approximately 760
mm high.
o If the last stages of the turbine were under vacuum, and the back pressure reduced by a
condenser to 68 mbar, then the steam would be able to continue its expansion down to 68
mbar. During this expansion each pound of steam is capable of doing a great deal more
work. For example, in a 62 bar turbine with a back pressure 51mbar, the steam does nearly
30% of its work as it expands below atmospheric pressure. Thus the use of a condenser
brings considerable saving.
Conservation of pure feed water:
o Very large quantities of steam pass though a turbine, for example, a 660 MW machine on
full load uses some 532 kg/sec. It would, of course, be not only very wasteful but almost
impracticable to allow this vast amount of steam to be exhausted to atmosphere. By using a
condenser the exhaust steam is converted back to hot water which is removed from the
condenser for continuous use in the power station heat cycle.
Operation of condenser:
Before starting up, the system should be checked for correct piping and proper control and
safety devices.
The following procedure is generally applicable to all types of condensers:
Start the moderate temperature fluid and operate vents to remove trapped air.
Gradually start the extreme temperature fluid, allowing the exchanger to adjust its
temperature slowly. Operate the vents.
When shutting down, stop the extreme temperature fluid first, and then operate the vents.
Avoid thermal shock due to rapidly altering the flow of either stream, unless the unit is
specifically designed to withstand this type of service.
Be sure all condensate is drained from the steam units before admitting steam to avoid water
hammer.
When the exchanger has reached operating conditions, check all bolted connections for
tightness.
Record operating pressures and temperature for future reference. Loss of capacity and
increase of pressure drop will indicated the progress of fouling.