Swirl intensity as a control mechanism for methane purification in supersonic gas separators

Supersonic gas separator is proposed for methane purification. One-dimensional analysis is performed to examine the design aspects associated with the converging-diverging nozzle and the liquid separation chamber. The results indicate that at low swirl intensities, the separation chamber length is about 100 times of the nozzle throat. Increasing the swirl intensity would lower this length sharply and it will be less than 10 for swirl intensity of unity which is equivalent to a swirl angle of 45 degrees. In addition, a sensitivity analysis of the separator performance to the inlet conditions like the temperature, pressure, and composition of the mixture is carried out. It is observed that increasing the inlet temperature will reduce the condensation rate and separation performance, while an increase in the inlet pressure and methane mole fraction will boost the flow condensation rate. Further, changes in the inlet condition will affect the critical droplets diameter and required separation length. In this regard, the separation length will increase with decreasing inlet temperature and increasing inlet pressure and methane mole fraction. The results reveal that the operation envelope of the supersonic separator is more sensitive to the variations in the inlet flow temperature where high swirl intensity is required at low inlet temperature in order to maintain the separation chamber length. Finally, the results support that, for a fixed geometry of the supersonic gas separator, in order to maintain the performance, single or combined variations in the inlet conditions can be compensated by changing the swirl intensity within a reasonable envelope.