Optimal design of a two-stage refrigeration cycle for natural gas pre-cooling in a gas refinery considering the best allocation of refrigerant

摘要

Part of the process gas cooling in a sample gas refinery is provided by a two-stage vapor compression refrigeration cycle. This cycle has been designed only based on thermodynamics' objective function with propane refrigerant. A gas-turbine is used as the compressors' driver in this sample plant. In the present study, the complete investigation of this compression refrigeration cycle with its gas turbine, as a prime mover, has been redesigned by using the genetic algorithm, and refrigerant analyses. The cycle has been modeled in MATLAB software by considering the economic, thermodynamic, and environmental objective functions. The results show that the basic redesign of the cycle, with propylene as the best refrigerant, can improve the coefficient of performance from 1.42 to 2.01 in comparison to the available cycle. It also can reduce the nitrogen oxide and carbon monoxide emission from 30.74 to 29.7 ppm and 81.0 to 71.6 ppm, respectively, and it can reduce the cost of the product from 1091.5 $ to 781.5 $ per hour. In fact, by replacing propylene refrigerant with propane and multi-objective basic redesign, all three economic, thermodynamic, and environmental functions can be improved in comparison to the available cycle.