Engineering and Economic Implications of Conversion of a Simple Cycle Gas Turbine Plant to a Combined Cycle Plant

This work investigated the engineering and economic implication of converting simple cycle gas turbine power plants to combined cycle power plants using a gas turbine power plant in Rivers state as a case study. A gas turbine model which behaves like the real engine in the field was created and the performance parameters were estimated. Steam turbine plant operating on the superheat Rankine cycle fired by the exhaust gases of the gas turbine through a heat recovery steam generator was simulated and incorporated in the gas turbine cycle to form a combined cycle plant. Engineering and economic performance parameters such thermal efficiency, specific fuel consumption (SFC), heat rate (HR), payback period, net present value (NPV) and levelized cost of electricity (LCOE) of the gas turbine plant and the simulated combined cycle plant were estimated. The economic parameters were estimated for project lifetime of 20 years, discount rate of 10% and electricity price of N75 per kWh. The thermal efficiencies of the gas turbine cycle steam turbine plant and the combined cycle plant are 33.66%, 27.42% and 50.20% respectively. The SFC and HR of the three systems are 0.0616 kgs-1/MW, 10,695 kJ/kWh; 0.1254 kgs-1/MW, 13127 kJ/kWh and 0.0413 kgs-1/MW, 7171kJ/kWh respectively. The payback, the NPV and the LCOE of the gas turbine plant are 5.32yrs, $25.87 million and N69.94 per kWh respectively. The respective values of the combined cycle plant are 4.36yrs, $63.80 million and N66.64. The study shows that it is possible to obtain additional power of over 49% the installed capacity from the existing simple cycle gas turbine power plants.