Performance improvement of the bottoming steam Rankine cycle (SRC) and organic Rankine cycle (ORC) systems for a triple combined system using gas turbine (GT) as topping cycle

Abstract

In the present study, performance improvement of SRC and ORC systems used as a bottoming system in a GT based triple combined system was evaluated for varying turbine inlet temperature and pressure. In the first step, SRC was parametrically optimized for a varying pressure (from 10 bar to 100 bar) and temperature (from saturated steam temperature to 480 °C). In the second step, a parametric optimization is performed to comprehensively evaluate the effects of acetone, R113, R141b, R152a, R245fa and R365mfc on thermodynamic performances of ORC (Organic Rankine Cycle) with the increasing turbine inlet pressure and temperature. Along with the optimization, the ORC turbine inlet pressure was heightened from 7.5 bar to the critical pressures of the working fluids with the increments of 2.5 bar. The ORC turbine inlet temperature was varied between saturation temperature and the maximum working temperature of selected working fluids. Finally, energy and exergy efficiencies of the overall triple combined system (GT-SRC-ORC) was calculated by depending on pressure, temperature and working fluids. As a result, the best working fluids among the selected fluids was found as R141b. Maximum net thermal efficiency, exergy efficiency and a net power of the ORC with R141b were calculated as 22.6%, 64.76% and 780.35 kW at 40 bar and 225 °C, respectively. Net thermal and exergy efficiency of the overall system (GT-SRC-ORC) with R141b was found 47.65%, 67.35%, respectively. By this way, the waste heat recovery corresponding to 734.57 kg/h natural gas which is equivalent to 2203.73 kg-CO2/h emissions was carried out.