In a 150 MW steam turbine unit operating on an enhanced Rankine cycle, steam is delivered from the boiler to the high pressure turbine at 15 MPa and 500° C. It leaves the high pressure turbine at 2 MPa before being reheated to 500°C, after which it enters a second turbine from which it is exhausted to the condenser at 10 kPa. After leaving the condenser saturated, the condensate is pumped back up to 15 MPa and 50° C to restart the cycle.
Assuming an isentropic efficiency of 80% for each expansion:
a) Sketch a T-s diagram for the cycle identifying each part of the cycle, and listing assumptions you have made;
b) Calculate the rates of heat transfer for the boiler and reheater;
c) Calculate the rate of work out (per kg of steam flow) for each turbine;
d) If the feed pump is insulated, and pumps the condensate from negligible velocity into a pipe of inside diameter 200mm, through a rise of 15m, estimate the power required to drive the pump (per kg of steam flow). Hence, calculate the mass flow rate of steam, assuming that the feed pump is driven directly from the turbine unit output with no losses.
e) Calculate the overall efficiency of the unit. Compare this to the efficiency of a Carnot cycle operating entirely inside the saturation dome, between the same maximum and minimum pressures. State why this Carnot cycle is not practical.