Comparison and Optimization of Mid-low Temperature Cogeneration Systems for Flue Gas in Iron and Steel Plants

Three generation systems, namely, steam Rankine cycle (SRC), organic Rankine cycle (ORC), and steam-organic combined Rankine cycle (S-ORC), were simulated using the Engineering Equation Solver (EES) to efficiently utilize flue gas emissions from 200 to 450 °C in iron and steel plants. Based on the simulation results for thermal efficiency, exergy efficiency, and power generation, the performances of the three power generation systems were compared and analyzed. To further utilize waste heat from the turbine exhaust steam of the ORC system, cascade ORC (CORC) was designed for heat sources above 300 °C. Based on a comprehensive performance comparison, the application of the ORC using R141 b is preferable for 200 to 300 °C flue gas. For 300 to 450 °C flue gas, CORC is an alternative technology to improve the efficiency and quality of waste heat utilization. For flue gas above 450 °C, S-ORC can achieve higher efficiency and power generation than conventional SRC, with a relatively small negative pressure and high dryness of the turbine outlet steam. Hence, S-ORC can be considered as a substitute for SRC.