Comparative study of different configurations of a novel concentrated solar polygeneration system using super-critical CO2 Brayton cycle and ORC

This paper presents the comparison study of three different schemes of a novel solar tower polygeneration (STPG) system, which integrates super-critical CO 2 (S-CO 2 ) Brayton cycle, organic Rankine cycle (ORC) driven hydrogen production block, and multi-stage flash (MSF) desalination technology to achieve collaborative production of electric power, hydrogen, oxygen and freshwater. KCl/MgCl 2 molten salt is selected as the heat transfer fluid in the solar island. By using Ebsilon software, operation, exergy, economic and environmental analyses of three different STPG system schemes are conducted. The results show that for all the three different STPG system schemes, the solar island, S-CO 2 Brayton cycle, hydrogen and freshwater production blocks can coordinatively achieve the effective operation for both short- and long-terms. Scheme 2, in which the evaporator of ORC is arranged between the high- and low-temperature recuperators of the S-CO 2 Brayton cycle, has the best exergy and economic performances. The output power and Brayton cycle efficiency of Scheme 2 are 57.7 MW and 47.7%. The hydrogen, oxygen and freshwater production rates of Scheme 2 are 73.5 kg/h, 588.0 kg/h and 316.4 t/h, respectively. The levelized costs of electricity, hydrogen and freshwater of Scheme 2 are 0.082 $/kWh, 6.02 $/kg and 1.46 $/t, and the net present value is 843.0 million USD. Assuming the STPG system is replacing 100.0% coal-fired driven production, the annual emission reductions of soot, SO 2 , CO 2 and NO x of Scheme 2 are 1330.9 t, 2287.5 t, 92,885.8 t and 2162.7 t, respectively. This work provides certain reference for design and optimization of solar tower polygeneration systems in the future.