Energy separation and condensation effects in pressure energy recovery process of natural gas supersonic dehydration

Pressure energy recovery is one of the main advantages of a supersonic separator. However, the pressure energy recovery process can cause droplet evaporation in the divergent section, which will reduce the liquefaction efficiency of the nozzle. This paper aims to clarify the shock wave/boundary layer interaction and liquefaction efficiency of wet natural gas in the process of pressure energy recovery. A mathematical model of methane-water vapor condensation was established to study the energy separation and condensation characteristics of wet natural gas in the nozzle. The results show that shock wave/boundary layer interaction leads to the energy separation phenomenon. When pressure energy recovery efficiency is reduced from 78.6% to 57.1%, the Mach number and liquid mass fraction at the outlet of the nozzle increase from 0.368 to 0.683 and 0 to 0.73%, respectively. In addition, the counterclockwise vortex region increases, and the energy separation phenomenon becomes more obvious. In actual gas processing, the pressure energy recovery efficiency at the range of 57.1%–64.2% can effectively improve energy recovery efficiency and ensure high liquefaction efficiency of natural gas in the nozzle.