Design and Simulation a Cyclic Adsorption Process as the Prerefiner of a Mini LNG unit

Carbon dioxide separation from natural gas was investigated by pressure-temperature swingadsorption (PTSA) process as a mini-LNG pre-refiner unit. The process was designed with four columnsof Zeolite ۱۳X adsorbent, working in a cyclic adsorption-desorption operation at high pressure ofnatural gas. The NG feed composition was contained about ۹۳.۵% methane, ۱% Co۲, and otherhydrocarbons, with total flow rate of ۴۱۷ kg/hr, at ۶۲ bar pressure and ۲۷°C temperature. The cyclicoperation was designed in five main steps consisting adsorption at high pressure, depressurization,heating and cooling with the saturated steam stream in internal heat exchanger in a stepwise procedureand finally pressurization by small part of feed. Heating and cooling each consist of three sub-steps.The heating of the bed consists of steps of increasing the temperature to ۱۰۰, ۱۷۰ and ۲۳۰ ° C,respectively, and the cooling stage is performed at temperatures of ۱۷۰, ۱۰۰ and ۲۷ ° C, respectively.Simulation of the PTSA process was performed by ASPEN ADSORPTION software. The requiredequilibrium isotherms and kinetic data were extracted from the literatures. After simulation andapproaching to the cyclic steady-state condition, the fraction of Co۲ in NG product was reduced from۱% to ۴.۱ppmv, and the methane recovery in product was achieved about ۸۹.۸%.

Keywords:

Natural gas , Mini-LNG , carbon dioxide , zeolite ۱۳x , Design