Multi-parameter optimization and fluid selection guidance of a two-stage organic Rankine cycle utilizing LNG cold energy and low grade heat

Abstract Two-stage ORC (Organic Rankine Cycle) is a very competitive configuration. However, most of the works have narrowed the studies within a single or just several fluids in spite of the great effect of working fluids on system performance. In this paper, 400 combinations of working fluids are investigated. The evaporation and condensation pressures of both the high and low temperature ORCs are optimized by PSO (Particle Swarm Optimization) with the objective function of maximum exergy efficiency. The results show that the effect of fluid1 on the system exergy efficiency is much greater than that of fluid2. Critical temperature is a key indicator for fluid1 selection and triple point temperature is a crucial indicator for fluid2 selection. The largest exergy destruction occurs in the condenser of cycle II. The proper solution to reduce this exergy destruction is raising the inlet temperature of LNG, rather than lowering the condensation temperature of cycle II.