Performance assessment of steam Rankine cycle and sCO2 Brayton cycle for waste heat recovery in a cement plant: A comparative study for supercritical fluids

Summary The main objective of this study is to investigate the feasibility of a waste heat recovery (WHR) closed Brayton cycle (BC) working with supercritical carbon dioxide (sCO2). For this aim, an actual WHR steam Rankine cycle (RC) in a cement plant was evaluated thermodynamically. After, a sCO2‐BC was theoretically adapted to the actual WHR system for the performance assessment. Both systems were analyzed comparatively in terms of energy and exergy. According to the results, the sCO2‐BC showed higher performance than the actual steam RC with a net electricity generation of 9363 kW where it was calculated as 8275 kW for the actual cycle. In addition, the energy efficiencies were found to be 27.6% and 24.18% where the exergy efficiencies were calculated as 58.22% and 51.39% for sCO2‐BC and steam RC, respectively. In the following part of the study, the closed BC was examined for different supercritical working fluids, namely, CO2, pentafluoroethane (R125), fluoromethane (R41), and sulfur hexafluoride (SF6). Parametrical analyses were conducted to determine the effects of the system parameters such as turbine inlet temperature, compressor inlet temperature, and pressure ratio on the cycle performance. The simulation results of the comparative study showed that, among the supercritical fluids, the CO2 demonstrated a higher performance for the closed BC with an energy efficiency of 27.9% followed by R41, SF6, and R125. As a result, the utilization of sCO2‐BC for WHR can be sustainably adapted and extended for environmentally friendly energy generation. A closed BC working with CO2 is investigated using the data of an actual waste heat recovery steam RC in a cement plant. The power generation rates are determined as 8275 kW and 9363 kW while the efficiencies are found to be 24.18% and 27.6% for the actual RC and the adapted BC, respectively. According to the comparative analyses of closed BC for different supercritical fluids, the best working fluid is determined to be CO2 followed by R41, SF6, and R125.