Reliable prediction of condensation rates for purification of natural gas via supersonic separators

Supersonic separators can provide efficient and simultaneous separation and purification of natural gases from various impurities (e.g. water vapor and hydrogen sulfide). Reliable prediction of the liquid droplet growth inside Laval nozzle is essential for accurate simulation of the condensation process inside 3S unit. All previous researches have been focused on estimation of the liquid droplet growth for pure fluids (e.g. steam) and cannot be extended to binary or multi-component systems. The current article provides a new theoretical approach based on mass transfer rate calculations to predict the liquid droplet growth inside a Laval nozzle for binary mixtures. The current model can be also used to simulate the multi-component systems when no appreciable interaction exists between the condensed phases. The new model predictions are initially validated successfully with the experimental data borrowed from the literature. Afterwards, several natural gas processes are simulated inside Laval nozzles of various 3S units. The simulation results indicate that the 3S unit is able to successfully reduce both water vapor and hydrogen sulfide content of natural gas to their permissible values (7lb/MMSCF and 4 ppm, respectively) for all cases.