Steam condenser is a device in which the exhaust steam from steam turbine is condensed by means of cooling water. The main purpose of a steam condenser in turbine is to maintain a low back pressure on the exhaust side of the steam turbine. After releasing from nozzles, the steam has to expand to a great extent for converting available energy into it to usable mechanical work. So, if the steam after doing its, work, does not get condensed, it will not give required space to other steam behind it, to expand to its required volume.
Condensation of steam in a closed system, creates an empty place by reduction of volume of the low pressure steam. It is found that, 1 Kg of dry steam at 1.033 kg/cm2 absolute pressure has a volume of 1.673 m3 when it is condensed into water at 100oC in a steam condenser, its volume becomes 0.001044 m3.
The volume of steam would be thus 1/1644 parts of the space inside the vessel, and the pressure would fall to 0.2 kg/cm2 absolute pressure. This means, pressure in the exhaust of the turbine falls to 0.2 kg/cm2 from 1.033 kg/cm2.
Elements of Steam Condenser
A steam condensing plant or simply steam condenser consists of
- Condenser chamber – where steam gets condensed.
- Cooling water supply – which provides cold water to condense steam by heat exchanging.
- Wet Air pumps – They collect condensed steam, the air and un-condensed water vapour and gases from condenser.
- Hot well in which the condensed steam is collected and from it steam boiler feed water may be taken if required.
Types of Steam Condenser
In a steam condenser, steam is always condensed with help of cooling water, but the techniques are different for different condensers. Depending upon condensation techniques, there are mainly two types of steam condensers. They are mainly
Jet Steam Condenser
Here cooling water is sprayed on the exhaust steam. This is very fast process of condensing steam. But here cooling water and condensed steam are mixed up which can not be separated.
Surface Steam Condenser
Here, cooling water and exhaust steam are separated by a barrier and condensation is done by heat exchanging through this barrier wall. Cooling water is passed through numbers of water tubes and exhaust steam passes over the outer surface of the tube. The heat of steam is absorbed by the water inside the tube through the wall of the tube.
Again in some cases, steam is passed through an array of steam tubes, cooling water is sprayed over the steam tube and condensed steam comes out from the outlet of the tubes.
Surface steam condensing is slower process than Jet Steam condensing, but the main advantage of surface steam condensing is that, the condensed steam is not thrown to waste but is returned to steam boiler through feed water system.
Comparison between Jet Condenser and Surface Condenser
|Jet Condenser||Surface Condenser|
|The process is faster||The process is slower|
|The process is simpler||The process is complex|
|The process is cheaper||The process is costlier|
|The process is used sufficient boiler feed water is available||The process is used where sufficient boiler feed water is not available and the condensed steam is reused as boiler feed water.|
|The process is installed where cooling water is easily and cheaply made suitable for boiler feed.||The process is suitable where cooling water can not be easily made suitable for boiler feeding|
|In Jet condenser, the condensed steam, air, cooling water and uncondensed vapour and other gases are mixed up and can not be easily separated.||In surface condenser, the condensed steam is totally free from cooling water hence can be reused easily as boiler feed water.|