Question

A 5 MW gas turbine generating set operates with two compressor stages with intercooling between stages; the overall pressure ratio is 9/1. A high pressure (HP) turbine is used to drive the compressors. A low pressure (LP) turbine drives the generator (which generates the 5 MW). The temperature of the gases at the entry to the HP turbine is 650 °C and the gases are reheated to 650 °C after expansion in the first turbine (before entering the second turbine). The exhaust gases leaving the LP turbine are passed through a heat exchanger to heat the air leaving the HP stage compressor (before they enter the combustion chamber). The compressors have equal pressure ratios and intercooling is complete between stages. The air inlet temperature to the unit is 15 °C. The isentropic efficiency of each compressor stage is 0.8 and the isentropic efficiency of each turbine stage is 0.85. In the heat-recovery heat exchanger, the exhaust from the low pressure turbine is heating the exhaust from the high pressure compressor to 420 °C, before the LP turbine exhaust is vented and the HP compressor exhaust (now exiting the heat recovery heat exchanger) is sent to the combustion chamber (to be heated to 650 °C). The heat exchangers (the intercooler, heat recovery heat exchanger and the combustion chambers) all operate at constant pressure. Pressure losses and changes in kinetic and potential energies can be neglected.

a)Draw a diagram of this cycle.

b)Calculate the cycle efficiency.

c)Determine the mass flow rate through the process.

Answer 1

For air take Cp=1.005kJ/kg.K and ?=1.4 and for the gases in the combustion chamber and in the turbines and HE take Cp=1.15kJ/kg.K and ?=1.3,

Note- One important factors such as thermal ration for heat exchanger is not given so i am assuming it as 0.7,