Thermoeconomic Analysis of Gas Turbine Cogeneration Plant—a Case Study

In a process plant where there is a simultaneous demand for power and process heat, cogeneration is an effective method of utilizing the fuel energy. In the present paper an energy and exergy analysis of a 20 MW gas turbine (GT) cogeneration topping cycle plant with supplementary fuel firing to meet the process heat requirements at full and half load operating conditions has been presented. The energy and exergy values at different locations of the plant are depicted in the form of Sankey and Grassmann diagrams. The plant performance has been evaluated on the basis of fuel utilization efficiency, power-heat ratio and second law efficiency. Technoeconomic aspects of the plant have also been estimated on the basis of the fuel-saving ratio and the pay-back period. The fuel-saving ratio for the full and half load conditions is found to be 0.35 and 0.25 respectively. Analysis shows that exergy losses in the combustion chamber of the GT and the heat recovery steam generator (HRSG) furnace are significant. Further, the pay-back period estimated at the full load operating condition is about 5 years.