Thermoeconomic analysis & optimization of the combined supercritical CO2 (carbon dioxide) recompression Brayton/organic Rankine cycle

Abstract

Exergoeconomic analysis is reported for a new combined SCRB/ORC (supercritical CO2 recompression Brayton/organic Rankine cycle) in which the waste heat from SCRBC (supercritical CO2 recompression Brayton cycle) is utilized by an organic Rankine cycle (ORC) for generating electricity. The analysis is also performed for the SCRBC for comparison purposes. Considering eight different working fluids for the ORC, thermodynamic and exergoeconomic models are developed for the cycles through applying mass and energy conservations, exergy balance and exergy cost equations to systems' components. Influences on the SCRB/ORC and SCRBC performances are investigated of the pinch point temperature difference in pre-cooler1 and in condenser, the compressor pressure ratio and the ORC turbine inlet temperature. Using the EES (Engineering Equation Solver) software, the SCRB/ORC performance is optimized thermodynamically and economically. It is concluded that the exergy efficiency of SCRB/ORC is higher than that of the SCRBC by up to 11.7% and that, the total product unit cost of SCRB/ORC is lower than that of the SCRBC by up to 5.7%. The results also indicate that the highest exergy efficiency and the lowest product unit cost for the SCRB/ORC are obtained when Isobutane and RC318 are considered as the ORC working fluid, respectively.