Analysis of the impact of gas turbine modifications in integrated gasification combined cycle power plants

In an IGCC (integrated gasification combined cycle) plant, the operating environment of the gas turbine (GT) deviates from the design conditions due to its integration with both the gasifier and the air separation unit (ASU). In particular, a trial to design the entire system with low GT–ASU integration would cause a decrease in the compressor surge margin and the turbine blade overheating. In this study, modification of the turbine and compressor to avoid a decrease in the surge margin and overheating was simulated, and the result was compared with the case without modification. The entire IGCC plant was modeled and the full off-design operation of the gas turbine was simulated. Under-firing and a decrease in dilution nitrogen can mitigate the two problems without component modification but inevitably cause a considerable performance penalty in the low integration degree regime. Both turbine modification (annulus area increase) and compressor modification (increase in the surge pressure ratio) enabled a continuous increase in power and efficiency with decreasing integration degree. In the very low integration degree regime, the power benefits of the two modifications were similar and considerable. A sensible power boost can be achieved if the turbine coolant modulation can be adopted instead of under-firing in modification strategies.