In this paper, the influence of co-firing natural gas and biogas on part-load performance of a natural gas combined cycle (NGCC) plant is investigated from thermodynamics perspective. Simulations of the plant, of which design fuel is natural gas, are developed. Performance of the plant fueled by natural gas is determined as a benchmark. Part-load performance of the plant running with different mixtures of natural gas and biogas is calculated and compared with the benchmark. Results show that co-firing mixed fuel leads a reduction in energy utilization efficiency at low gas turbine load, and leads an increase at high gas turbine load. When the gas turbine is fueled by mixed fuel, exergy efficiency decreases at every condition, and the most reduction is around 6% from benchmark. It is not efficient to use biogas at low power load from both energy and exergy efficiency perspectives for the plant in this study.
Keywords biofuel, natural gas combined cycle, combined heat and power, part-load operation