Technique Research Of Supersonic Swirling Separator

Natural gas dehydration and heavy hydrocarbon separation are two important processes in surface operations of gas filed. Traditional low-temperature separation has been proven to be inefficient and require high capital and operating cost. It is difficult to prevent freezing by heating wet gas and consumes amount of anti-hydrate agent. In order to solve those problems, a new gas conditioning process—supersonic swirling separator has been developed.Based on the theory of gas dynamics, thermodynamics and fluid dynamics, the paper analyses the basic working principle of supersonic separator and set up the mechanic models of compressible gas flow in cyclone generator, blades, Laval nozzle, stabilizing tube, diffuser. By using CFD software-FLUENT, the paper studies the distributions of velocity, temperature and pressure in generator blades, nozzle, diffuser and the whole separator. By comparison and analysis of different blade design methods, the paper presents the optimum design method for the separator. Subsonic convergent section of Laval nozzle is designed according to double cubic curve method, throat is designed as a smooth circular arc, and supersonic divergent section is designed according to Foelsch method. The stream from this type of nozzle has preferable uniformity of velocity, less energy loss and designed Mach number after boundary-layer correction.According to the swirling separation efficiency in the blade section, 75.2% of water and 73.2% of heavy hydrocarbon can be separated according to simulated computation. Hydrate formation will not occur because the maximum residence time of liquid droplets from the nozzle outlet to the diffuser outlet is about 9.6 milliseconds due to relatively slow hydrate-crystal growth. So the supersonic swirling separator can prevent freezing without anti-hydrate agent. As is shown by the simulation of Hysys, when the outlet pressure is 4MPa the dew point of hydrocarbon decreases to -27.83℃while hydrate formation temperature is 11.7℃. The paper studies the distributions of the velocity, the temperature and the pressure in the swirling separator by simulation and analysis. The shock wave is controlled near the diffuser inlet. The shock wave dissipates the kinetic energy of the fluid stream, increases the swirl ratio and the swirling separating efficiency, which is the key factor to design the separator. The pressure recovery ratio is controlled between 40% and 47%, the separator can be in normal operation.