Jet Condenser in Thermal Power Plant
Condensers are broadly classified into two types: Jet Condensers and Surface Condensers.
CLASSIFICATION OF JET CONDENSERS:
These are also called Mixing Condensers and are further classified as
(a) Low Level Parallel Jet Condensers
(b) Low Level Counter flow Jet Condensers
(c) High Level (or Barometric) Jet Condensers
(d) Ejector Condensers
WORKING PRINCIPLE OF JET CONDENSERS :
In jet condensers exhaust steam from the prime mover and the cooling water come directly into contact. Heat exchange takes place quickly between them by direct conduction. For effective cooling, water is introduced into the condenser shell in a spray form. When steam condenses into water, the mixture of this condensate and cooling water gravitates down which is continuously withdrawn using a extraction pump. In Jet condensers recovery of condensate is not possible. For that reason, the above mixture of fluids is not reused as boiler feed water. This is the major draw back with jet condensers.
Parallel Flow Jet Condenser :
In a parallel flow jet condenser (Fig) steam as well as cooling water, both enter the shell at the top and the mixture is collected at the bottom. From here it is withdrawn into a hot well. Surplus condensate from the hot well gravitates to cooling pond as shown. Air is extracted by an air pump so as to maintain required vacuum in the condenser.
Counter Flow Jet Condenser :
In a Counter Flow Low Level Jet Condenser (Figure) steam enters at the bottom of the shell while water is admitted at the top and sprayed downwards. Steam flowing upwards comes in contact with water and gets condensed. Perforated conical plate issues jets of water which further break up in the perforated tray as shown.
Barometric (High Level) Jet Condenser :
A barometric jet condenser (Fig) is provided with a long vertical tail pipe to discharge the condensate to hot well. This gives an elevation to the unit. Hence it is also called high level jet condenser. In this condenser, there is no necessity of any pump to extract the water - condensate mixture. Cooling water is supplied by a separate pump. Air extraction pump is used to remove air and maintain proper vacuum in the condenser.
Ejector Condenser :
In ejector condenser (Fig) steam and water mix in a series of cones arranged as shown inside the shell. Water is allowed to flow from the top under a head of about 6 m through a number of coaxial converging (truncated) cones. This causes a vacuum behind and steam is drawn along with water. Air is also dragged along with steam. Therefore, in this type of condenser, no separate air extraction pump is required. As condensate flows out with KE into the hot well no pump is required for this purpose.
In case of sudden failure of water supply, there is a possibility of hot water from hot well to rush back into the condenser and then into the engine or turbine. To prevent this, a non-return valve is fitted at the entry of steam into the condenser.