Supersonic separator is widely used in the field of natural gas processing for its advantages of compact structure, airtight environment protection and gas-liquid separation without external power, which provides a new treatment method for the efficient utilization of clean natural gas. In the actual operation, it is usually necessary to set back pressure at the outlet of the separator in order to realize the pressure energy recovery. In previous studies, the condensation and flow field changes caused by shock waves were often ignored. The existence of outlet back pressure will cause shock wave in the Laval nozzle of the supersonic separator, which will lead to the condensed droplets to evaporate and reduce the separation efficiency of the separator. Therefore, it is of great significance to determine the shock position, control the pressure ratio reasonably and avoid the secondary evaporation of droplets for improving the separation efficiency and energy saving of the supersonic separator. In this paper, one dimensional isentropic flow function method is used to calculate the shock position in Laval nozzle. Based on ICCT nucleation and Gyarmathy growth model, a numerical model for the condensation of methane - water vapor was established by using FLUENT software. The accuracy of the model was verified by the experimental data of Moses. The results show that the pressure energy recovery leads to the shock wave, which leads to the pressure and temperature rise in the nozzle, the Mach number decreases, the drop radius decreases, and the liquid mass fraction decreases rapidly. With the increase of energy recovery efficiency, the position of shock wave moves to the throat, which shortens the droplet growth space and reduces the liquefaction of Laval nozzle. When the pressure energy recovery efficiency is 68.75%, the maximum nucleation rate in the nozzle is 4.4×1020 m-3·s-1, the droplet radius decreases from 2.5×10-7 m at x = 0.364 m to 1.58×10-7 m at the outlet, and the liquid mass fraction decreases from 3.7% at x = 0.364 m to 0.84% at the outlet. The theoretical calculation is almost consistent with the numerical simulation. The theoretical calculation method can accurately predict the shock wave position in the non-equilibrium phase change. The research of this paper can provide a certain theoretical basis for improving the linear structure of the nozzle and installing the swirl blade of the supersonic separator, and provide a theoretical basis for realizing more pressure energy recovery in the supersonic separator.

Prediction of Shock Wave Position Considering Non-Equilibrium Phase Change of Wet Natural Gas in Nozzle

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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