Question

A CCGT uses natural gas of net calorific value 50.05 MJ/kg as the fuel is utilised in a gas turbine power plant fitted with a heat recovery steam generator (HRSG) in its exhaust. There is a single gas turbine, which has a net power output of 176 MW; the exhaust gas from that turbine is fed into the HRSG which in turn is used to supply steam to a steam turbine.

The operating details for the gas turbine are:

Compressor inlet pressure: 100 kPa Compressor pressure ratio: 15:1

Ambient/air inlet temperature: 300 K

Turbine entry temperature: 1400 K Turbine exhaust pressure: 120 kPa

Isentropic efficiency of the compression is 88%, and that of expansion is 92%.

The operating details for the steam side are:

Turbine entry steam pressure: 50 bar

Turbine entry steam temperature: 450 °C

Condenser pressure: 0.1 bar Pinch point temperature difference: 25 °C

Turbine isentropic efficiency is 90%; neglect the feed pump work.

a. Find mass flow rate of the natural gas to the combustion chamber,

b. mass flow rate of air in the compressor,

c. and the mass flow rate of gas in the turbine and thermal/cogeneration efficiency.

Answer 1