Energy and exergy assessment and a competitive study of a two-stage ORC for recovering SFGC waste heat and LNG cold energy

Abstract

In this paper, three functional modes of a new designed geothermal power plant are investigated, simulated, and analyzed. The single flash geothermal cycle (SFGC) is the first mode. The second mode is a SFGC with two-stage ORC recovery, and the third mode is an SFGC with two-stage ORC recovery and LNG cryogenic energy. Adding a two-stage ORC recovery and LNG refrigeration exergy cycle aims to improve the thermal efficiency and exergy efficiency of the basic SFGC system as well as use LNG's cold energy prior to entering urban consumption networks. For the two-stage recovery cycle, the ORC's working fluids also included R227ea/R116 and R124/R125. In order to analyze the proposed system, the equations of the first law and the second law of thermodynamics are used. Assuming a two-stage ORC and LNG recovery mode, the energy efficiency of the SFGC will increase from 0.2023 to 0.3863 when using R227ea and R116 working fluids, and from 0.4016 to 0.4066 when using R124 and R125 working fluids.