Modeling and Simulation of Vacuum-Pressure Swing Adsorption Process for natural gas Recovery from light Mercaptans

A dynamic simulation of Vacuum-Pressure Swing Adsorption (VPSA) process at non-isothermal and non-adiabatic conditions has been Implemented for purification of natural gas from mercaptan in a methane recovery unit (MRU). The process includes six packed columns with a two-layer bed in each consisting activated Alumina and 13X zeolite. Inlet natural gas includes 95.98% methane, 1.82 ×10−3% water vapor, 1% carbon dioxide, 1.34 ×10−2% mercaptan and 3% heavy hydrocarbons. In this process feed at high pressure and high flow rate is passing through a pressurized column consisting 26.6 adsorbent in a cyclic process consisting pressurization, adsorption, equalization, blow down, vacuum and regeneration. The results of simulation revealed that for effective evacuation of the bed from sulfur in the regeneration step a vacuum condition of 0.1 bar with the purge/ feed ratio of 0.06 with temperature of 350k is required. The simulated VPSA process was approached to the steady conditions during 7 cycles and the mercaptane content of outlet natural gas was reached from 134 to less than 10 ppmv.