In the present study, a coal-integrated gasification combined cycle power plant is simulated. A high-ash coal and low-ash coal are considered to compare the performance of the plant. The combined cycle is in typical commercial size with 450MW capacity. The feeds are Tabas and Illinois #6 coals which approximately contain more than 30% and 10% ash and have higher heating values of 22.7 MJ/kg and 26.8 MJ/kg, respectively. Energy and exergy analyses are done by ASPEN PLUS (R) and EES, respectively. Energy analysis shows that the overall efficiencies of power plants using high-ash and low-ash coals are 33% and 28%, respectively. The result shows that in high-ash case, 52 kg/s coal, 10 kg/s water, and 1050 kg/s air and in low-ash case, 48 kg/s coal and 820 kg/s air are required for providing mentioned power, approximately. Exergy analysis shows that maximum exergy destruction is in heat recovery steam generator unit. Investigating the emissions shows that high percent of ash in the coal composition has slight effects on the IGCC pollution. Finally, from thermodynamic viewpoint, it is concluded that the high-ash coal, like the conventional one, can be used as thermally efficient and environmentally compatible feed of IGCCs. Copyright (C) 2016 John Wiley & Sons, Ltd.