Closed cycle gas turbine

Closed cycle gas turbine:
-Working fluid air or other gas is circulated continuously inside the machine
- Working fluid does not come in contact with the atmospheric air or fuel
-Heat to working fluid is given externally by the burning of the fuel that is why it is external combustion engine
-Turbine exhaust rejects heat in a cooler
Advantage of closed cycle gas turbine:
-Due to externally fired, cheaper fuel such as coal can be used
-Products of combustion is not in directly contact with turbine blades, hence fouling and heat transfer from the surface of the blade can be avoided
-Part load efficiency is improved by changing the pressure ratio and varying the quantity of working fluid keeping as cycle temperature constant and at constant speed
-High operating pressure causes low specific volume for the working fluid reducing the size of machines, heat exchangers and piping
-Heat transfer coefficients are higher which reduces the heat exchanger size
Disadvantage of closed cycle gas turbine:
-more complicated and costly system
-Air heaters alone represent over 30% of total mass and cost
-system is not sufficiently strong to resist high pressure