What is the need of condensing the steam vapor after it comes out turbine? Why can't it be directly sent to boiler in vapor form without condensing?

then the vapor  change to water at maximum degree

because the pump can not delivery the vapor so condensing the vapor

if the vapor not condensing we have problem with the impeller of pump (low pressure & Cavitation    

ll the heating does is cause a phase change and add energy, not produce the pressure needed to run the turbine. Boiling water into steam doesn't raise its pressure unless it's confined, and that's not how turbine-based engines work. In a continuous-flow process in a power plant where steam is constantly produced in the boiler and spun through a turbine, the steam can't be at any higher pressure than the feed water supply. If it did, how could the feed water get into the boiler? Thus, the fluid entering the boiler must be high pressure to start with -- ie pumped or compressed.

Say 1 kg of Steam after total work-done in Last stage Turbine blade enters inside the Condenser accrues X volume. Now Cold water coming in condenser condenses the steam into water, now 1 kg of water accuser X/1800 volume. That means because of state changes from steam to condense-water 1800 times volume decreases.  

So if we send Steam coming from Turbine directly to boiler then all heat exchanger size will be much much larger than it's original size.

Generally in Steam-water circuit there are different water pumps like CEP( Condensate Extraction Pump), Boiler feed Pump,Feed water pump ets. So we cant use Steam in water pumps, otherwise Cavitation   will occur in BFP.

Pipe diameter will also increase very much.

The whole thing will be totally un-economical.

it should be water then pass through the feeding pump to increase its  pressure .