Performance characteristics of a 200-kW organic Rankine cycle system in a steel processing plant

The main objective of this research is to design and build a 200-kW ORC system with reduced size that could be installed in a steel processing plant where space is limited. The real-time operating characteristics of the ORC system are demonstrated with actual flue gases. First, an ORC system with R245fa refrigerant was developed for a heat source temperature of 140 °C. The evaporation and condensation pressures were 2,090 kPa and 220 kPa, respectively. The net power output was 235.7 kW with a thermal efficiency of 12.9%. Using an electric heat source, the design point performance of the system is experimentally demonstrated and shows a net power output of 177.4 kW with thermal efficiency of 9.6%. The turbine isentropic efficiency and generator efficiency were 68.1% and 98.5% at a rotational speed of 14,000 rpm. Next, the ORC system was implemented by designing a dedicated heat transfer loop for a steel processing plant using data measured from a chimney. The experimental net power output is 105.8 kW with a thermal efficiency of 8.6% when the plant is operated at the highest work load. The fluctuation of the flue gas temperature is successfully suppressed with a thermal storage tank installed in the heat transfer loop. A partial-load analysis was conducted and showed that the system has the highest performance with more than 165 kW of net power output. Economic analysis of such system showed that the right sized ORC system with always working parent plant had good economics with a payback period of 9 years.