CFD modeling on non-equilibrium condensation process of H2S in CH4-H2S mixture expansion through supersonic nozzles

Supersonic separation is an alternative technology potentially applicable in bulk H2S removal from natural gas containing high concentration of H2S. The spontaneous condensation of H2S in the Laval nozzle is the precondition of the separation. An Eulerian-Eulerian two-phase model containing non-equilibrium condensation behavior is developed to predict the condensation characteristics of H2S in CH4-H2S binary gas during supersonic expansion. The effects of H2S feed concentration, operating parameters and nozzle geometry on the condensation process are investigated. The results show that H2S vapor nucleates at adequate level of supersaturation during the rapid expansion in supersonic nozzles. When the inlet mole fraction of H2S increases, the nucleation process occurs much earlier and more H2S can be condensed into liquid phase. Condensation process of H2S can be further enhanced by increasing the inlet pressure and decreasing the inlet temperature. The increment of expansion ratio can improve the condensation performance of supersonic nozzle as the flow is expanded further.