Off-design performance analysis of gas turbines

This work deals with the off-design performance analysis of gas turbines. Two gas turbine power stations in Rivers state, Nigeria were used as case studies. Ambient temperature-induced off-design calculations were carried out. This is because no gas turbine operates at its design point in the field and ambient temperature is one of the parameters that changes more frequently in gas turbine operation. Off-design performance models were developed to estimate the power output, thermal efficiency and the exhaust gas temperature at different ambient temperature values. Input data were obtained from the two gas turbine operations and engine adaptation results from previous researches. The power output and the thermal efficiency drops with increase in ambient temperature while the exhaust gas temperature increases with increase in ambient temperature. On the average, power output drops by 1.13 MW when ambient temperature increases by 10 ◦C for the first gas turbine power plant and the value obtained for the second gas turbine power plant which is smaller is 0.473 showing that the power drop is dependent on the power output of the plant. For the same range of ambient temperature increase, thermal efficiency drops by 0.637 % and 0.583 % respectively for the two power plants. Larger drop in power output as well as thermal efficiency occurs at the lower temperature values. The exhaust gas temperature increases with ambient temperature almost uniformly with average value of 1.29 K and 1.21 K respectively for 1◦C increase in ambient temperature. The simulated results closely matched the results obtained from the field at different ambient temperatures. The results of this work will guide power plant operators in economic analysis by estimating the power output beforehand.