It is planned to update an existing 85 MW (net) power plant which operates on Brayton cycle with the addition of a vapour power

cycle.

The original Brayton cycle in operation has the air entering the single stage compressor of the gas turbine cycle at 102.8 kPa and

283 K, where it is compressed to 1,572.84 kPa. The isentropic efficiency of the compressor is 80 %. The combustion chamber

adds heat to the air in order to set the conditions at the inlet to the gas turbine at 1,572.84 kPa and at 1,380 K. Air expands

through the turbine, which has an isentropic efficiency of 86 %, to a pressure of 102.8 kPa.

The new proposed system would add at this point an interconnecting heat exchanger, where the air can release most of its heat

contents at constant pressure and is finally discharged at 375 K. The vapour power cycle is configured in a way that steam enters

the steam turbine at 12 MPa and 413 °C, and expands to the condenser pressure of 14 kPa. Saturated liquid water enters the

pump at 14 kPa. The turbine and pump have isentropic efficiencies of 86 % and 79 %, respectively.

Assume and use variable specific heat concept for your Brayton cycle calculations!

Air

in

Compressor

5

Exhaust,

gases

Pump

Qin

Combustion

chamber

Gas cycle

Heat exchanger

Steam

cycle

7

Gas

turbine

3

Steam

turbine

4

(8)

P

TA

Qin

Gas

cycle

Steam

cycle

00

3/n(c) The mass flow rate of air:

Number

(d) The mass flow rate of steam:

Number

kg/s.

(e) The required rate of heat input in the combustion chamber:

(f) The thermal efficiency of the original gas power cycle:

(g) The net power output of new combined power cycle:

(h) The new thermal efficiency of the combined cycle:

kg/s

Number

Number

Number

Number

MW

%

MW

%

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