Question

In a gas turbine generating station the overall compression ratio is 12/1, performed in three stages with pressure ratios of 2.5/1, 2.4/1, and 2/1 respectively. The air inlet temperature to the plant is 25 ℃ and intercooling between the stages reduces the temperature to 40 ℃. The HP turbine drives the HP and intermediate-pressure compressor stages; the LP turbine drives the LP compressor and the generator. The gases leaving the LP turbine passed through the heat exchanger which heats the air leaving the HP compressor. The temperature at inlet to the HP turbine is 650 ℃, and reheating between the turbine stages raises the temperature to 650 ℃. The gases leaves the heat exchanger at a temperature of 200 ℃. The isentropic efficiency of each compressor stage in 0.83, and isentropic efficiencies of HP and LP turbines are 0.85 and 0.88 respectively. Take the mechanical efficiency of each shaft as 0.98. The air mass flow is 140 kg/s. Neglecting the pressure losses and changes in kinetic energy, and taking the specific heat of water as 4.19 kJ/kg.K, and take Cp and γ for air to be 1.005 kJ/kg.K and 1.4 respectively. calculate. (a) The power output in kilowatts; [2 marks] (b) The cycle efficiency; [2 marks] (c) The flow of cooling water required for the intercoolers when the rise in water temperature must not exceeded 40 K; [2 marks] (d) The thermal ratio of heat exchanger [2 marks] (e) Draw the T-s diagram [2 marks]

Answer 1