Design and optimization of combined gasoline vapor recovery, cascade power and Rectisol wash for liquid natural gas cold energy utilization

The worldwide energy crisis and environmental pollution have led to an enormous demand for liquid natural gas. The recovery and application of cold energy released from the liquid natural gas vaporization process can play a significant role in solving these issues. In this study, a new configuration is proposed to realize the cascade utilization of cold energy, which includes five subsystems: gasoline vapor recovery, cascade Rankine power generation, Rectisol wash, air conditioning and liquefied air energy storage. Each subsystem is validated by the published literature of experiment and simulation, and parameters that are critical to the system are studied in depth. The genetic algorithm is then used to obtain the maximum net output power, using the working fluid composition, mass flow and fraction as optimization variables. As a result, the recovery rate of oil-gas is 95%, which meets environmental regulations for vapor recovery. When a binary zeotropic mixture (fluoromethane/carbon dioxide, 0.2247/0.7753) is selected in an actual case, the specific work and exergy efficiency of power generation are 135.16 kJ/kg and 31.57%, respectively, and 2639 kg/h of raw coal-gas can be purified to remove carbon dioxide. Under the coordination of liquefied air energy storage system coupled with an allocation algorithm, the demands and supplies of electricity and air conditioning have been matched. Therefore, the cascade utilization model provides a novel idea for cold energy recovery in natural gas stations.