Effects of cooling and heating sources properties and working fluid selection on cryogenic organic Rankine cycle for LNG cold energy utilization

Cryogenic organic Rankine cycle (ORC) is considered as one of the most attractive solutions to utilize LNG cold energy for power generation. However, its thermodynamic performance is affected by cooling and heating sources and working fluid selection significantly. Thus, it is crucial to quantify the effects of these factors on cryogenic ORC performance. In this work, we proposed a single-stage cryogenic ORC system to utilize LNG cold energy for sustainable power generation. The effects of LNG vaporization pressure, seawater temperature, minimum temperature approach (MTA), and working fluid selection on cryogenic ORC performance were explored quantitatively. The proposed system adopting different single working fluids and binary working fluids was optimized by particle swarm optimization algorithm to maximize specific net power output (SNPO) with respective to different cooling and heating source properties. The results indicated that the LNG vaporization pressure had the most significant influence on ORC performance. Moreover, R1270 exhibited the highest SNPO (89.34 kJ/kg) and exergy efficiency (18.96%), while C2H6 showed the highest thermal efficiency (14.51%). The overall performance was improved significantly by using R1270 and C2H6 (30% and 70%) as binary mixture working fluid at 4000 kPa LNG vaporization pressure. However, performance intensification was marginal for a higher LNG vaporization pressure. These results revealed that binary working fluids were not always superior to single working fluids. Hence, this study provided valuable insights on choosing proper working fluids and optimizing design parameters for cryogenic ORC at different operation conditions.