Steam boiler has main function to convert water to high quality steam. The steam is then supplied into turbine generator. Before supplied into turbine generator, steam should apply the requirement for both pressure and temperature. Condenser is used in power plant to make back pressure and temperature of steam from turbine generator is lower and then converts steam into condensate.
Condenser can be classified into two types: contact condenser and surface condenser. Condenser with contact type is no longer used in power plant, because its working principle is making contact each other between condensing water and steam. Therefore, possibility of steam getting contamination from condensing water is highly occuring. So the condensate is not suitable for the requirement of steam boiler feedwater, it will be high disadvantage for designer or owner.
Condenser with type surface has different working principle from contact condenser type. It never making contact between steams and condensing water, so the purity of condensate is maintained from contamination of condensing water. The working principle of this condenser is similar with economizer, steam from turbine generator pass through around the tubes (outside tubes or can be called the shell side) and condensing water flow in the inside tubes.
The shell condenser is not designed for under pressure but for vacuum pressure. So the relief valve is placed on the condenser to release pressure to the atmosphere if higher than vacuum.