Integration of a cryogenic ASU within an IGCC process with simultaneous optimization and energy targeting

Abstract

The effect of oxygen purity on the thermal efficiency of an enriched-oxygen-fed integrated gasification carbon cycle (IGCC) was studied. A simultaneous process optimization with heat integration framework is proposed and used for the study. Rigorous models were used to represent the cryogenic air separation unit (ASU), gasifier and combined cycle. It was found that the thermal efficiency was highest (41.3–42.3%) within a range of 35–85 mol% O2, with the optimum at 45.5 mol% O2. Furthermore, injection of the nitrogen-rich vapor distillate from the high-pressure column of the ASU to the gas turbine was found to be the optimal nitrogen integration scheme compared to no nitrogen integration or using vapor distillate from the low-pressure column. In the optimized solution, heat integration results showed that pre-heating of the gasifier's oxygen feed occurs at the pinch and steam turbine inlet pressure values were 165, 28.6 and 4.9 bar.