A natural gas oxy-fuel semiclosed combined cycle for zero CO_2 emissions: a thermodynamic optimization

摘要

This article presents an optimization study of a semiclosed combined cycle for CO_2 capture, based on the combined cycle (CC) gas turbine side, where the produced water is extracted by condensation; its results are compared with those from the classic open CC. In this study, besides the overall pressure ratio (OPR) influence on the global efficiency, the influence of gas composition is also presented showing that it can change significantly the optimum OPR. Additionally, the sensitivity of the global efficiency to the maximum gas turbine temperature T_(4t), gas turbine components efficiency and cooling bleeds, and the representative parameters of components technology level, are included. The optimum OPR shows that this type of cycle is not out of the current technology. The influence of gas composition on components performance maps is not considered, only some considerations on maps scaling. Also, starting from a baseline concept, some alternatives have been studied looking for a global efficiency improvement; the cooling down of the gas turbine entry conditions and the use of N_2 from the air separation unit as high-pressure turbine cooling, by means of the efficiency sensitivity to the blade cooling, are considered. Finally, it also provides efficiency close to the classic open CC and inside the efficiency of related cycles.