Abstract
About 20% ~ 50% energy is released to environment in the form of waste heat. The waste heat below 250℃ is difficult to recover due to its low thermal energy, but it has large amount and low fuel cost. ORC systems can efficiently convert this low temperature waste heat to electricity. Recently, due to the better heat transfer and low environmental impacts, S-CO2 Rankine cycle has shown pretty good potential in this field. A comparative study of S-CO2 Rankine cycle with R134a and R245fa ORC under 100℃ and 150℃ heat source is included in this study. Considering the pressure effect on performance and costs, the parameter settings for S-CO2 Rankine cycle are targeted on maximum power output. S-CO2 has better temperature matching with heat source so it can utilize heat source energy more efficiently. Besides, the high fluid density of S-CO2 can greatly reduce power unit size. Despite that the net power output per unit mass of working fluid in S-CO2 Rankine cycle is lower than that in ORCs, we can increase the mass flow rate of CO2 to improve the power output because of the very low fluid cost of CO2 compared to organic fluids. In order to realize the competence of S-CO2 Rankine cycle in real market, a comparative study with ORCs from Han Power is also included. Heat source temperature between 90℃~150℃ and inlet pressure of expander under 140 bar are recommended for S-CO2 Rankine cycle. But to commercialize S-CO2 Rankine cycle system, further studies and experiments on real equipment cost and component size are required.