This chapter investigates the Joule–Thomson effect and optimal foreign droplet parameters in using a supersonic separator for high-pressure natural gas dehydration and analyzes the effects of different swirl strengths on separation efficiency and energy conversion. Additionally, an economic analysis of the pre-dehydration process using supersonic separators is conducted. The effect of inlet pressure is critical; as the inlet pressure rises from 6 to 120 bar, the centrifugal acceleration increases by 27.8%, and the temperature drop caused by the Joule–Thomson effect increases from 5.3 to 29.4 K. The optimum diameter of inlet foreign droplets increases from 1.6 to 3.3 μm, and the droplet concentration increases from 0.0011 to 0.0026 kg/s, maximizing the dehydration efficiency to 81.75%. Notably, normal swirl strength achieves the maximum separation performance, with a water vapor removal rate 18.03% higher than that of strong swirl strength. The temperature drop shows maximum deviations of 20.70 and 12.51% compared to weak and strong swirl strengths. The impact of swirl strength on entropy generation shows a gradually increasing trend as the inlet pressure rises. Meanwhile, the ERDS, LCS, IRIB, and TRIB each had different effects on the flow behaviors, separation performance, and pressure energy loss of the supersonic separator. Especially the first parameter, the swirl strength and centrifugal acceleration decay to 0.044 and 2.41 × 104 m s−2 as it increases. At the same time, the droplet removal rate significantly improves, but the separation performance does not increase indefinitely due to the shock waves. The dehydration efficiency first increases to 95.09% at Er = 1.5 and then decreases; the dew-point depression also expands to 25.28 K and then drops, and the corresponding pressure loss rises to 0.47 and then falls. Using supersonic separators in the pre-dehydration process results in a substantial cost reduction of $6,691,060 over a 20-year period.