Employing Inverted Brayton Cycle to Solve Stack Temperature Problems After Water Recovery From HAT Cycle Exhaust Gas

Abstract

By adding an induced draft fan or exhaust compressor between flue gas condenser and stack to make the turbine expand to a pressure much lower than ambient pressure, this paper actually employed inverted Brayton cycle to solve stack temperature problems after water recovery from Humid Air Turbine (HAT) cycle exhaust gas and compare the effect of different discharging methods on the system’s performance. Comparing with the methods of gas discharged directly or recuperated, this scenario can obtain the highest electrical efficiency under certain pressure ratio and turbine inlet temperature. Due to the introduction of induced draft fan, in spite of one intercooler, there are twice intercoolings during the whole compression since the flue gas condenser is equivalent to an intercooler but without additional pressure loss. So the compression work decreases. In addition, the working pressure of humidifier and its outlet water temperature are lowered for certain total pressure ratio to recover more exhaust heat. These enhance the electrical efficiency altogether. Calculation results show that the electrical efficiency is about 49% when the pressure ratio of the induced draft fan is 1.3∼1.5 and 1.5 percentage points higher than that of HAT with exhaust gas recuperated. The specific works among different discharging methods are very closely. However, water recovery is some extent difficult for HAT employing inverted Brayton cycle.