Influence of a recuperator on the performance of the semi-closed oxy-fuel combustion combined cycle

Abstract

A recuperator was applied to the semi-closed oxy-fuel combustion combined cycle (SCOC-CC) to reduce its very high optimal design pressure ratio to a feasible level. The recuperator was installed in different locations in the heat recovery system: (1) before the entire heat recovery steam generator (HRSG) of the bottoming steam cycle and (2) before the HP evaporator of the HRSG. Component design parameters from state-of-the-art gas turbines (F and H classes) were used. A thermodynamic cooling model was used to estimate the reasonable amount of turbine coolant needed to maintain the turbine blade temperature of each stage at a feasible level. The turbine stage efficiency was corrected while considering the effect of turbine blade loading. The optimal pressure ratio ranges in terms of net system efficiency were found, and the influence of the recuperator effectiveness on the cycle performance was investigated. The optimal pressure ratio of the recuperated SCOC-CC was about 40–50, which was considerably lower than that of the simple SCOC-CC. The net efficiency of the recuperated SCOC-CC increased by as much as 0.6 and 1.3 percentage points in the F- and H-class gas turbines cases, respectively. The benefits of the recuperated cycle were discussed.