Experiment And Simulation Of VPSA Process For N₂/CH₄/CO₂Separation

With the dual pressures of energy shortage and air pollution, recycling andefficient utility of methane and carbon dioxide are of great significance. VacuumPressure Swing Adsorption (VPSA) have been pervasively applied in separation andpurification operations of large-scale gas due to its low investment, high automation,and low operating and maintenance consumption etc., where the development ofefficient adsorbent make a difference. In order to strengthen the process by increasingthe product purity and recovery as well as to save the energy consumed this papertried to investigate the separation process of gas mixture with experimentation andsimulation. The experiments are carried out to explore the best potential adsorbent andcorresponding operating conditions, based on which the simulation will be fulfilledFirstly, the adsorption capacity of the adsorbents for nitrogen; methane andcarbon dioxide are measured, and corresponding separation factors are calculated. Theadsorbent was verified in the laboratory, and the influence of recovery overhead flowrate, adsorption time, the pressures of the vacuum desorption, adsorption pressureswere investigated.Secondly, a novel vacuum pressure swing adsorption process for ternary gasseparation to get three products with twice replace steps is proposed for the separationof N2/CH4/CO2. The whole process was in detailed explanation and elaboration andwas simulated in Aspen-Adsorption. The optimal results indicated that in thetwo-replace step VPSA process, a methane purity of77.172vol%could be obtainedwith a recovery97.923%in the condition of the raw gas temperature298K, theadsorption pressure0.6MPa, and desorption pressure only-0.08MPa. Meanwhile, theconcentration fractions of CH4in the top and bottom of the column were0.224vol%and0.673vol%respectively. The advantage of this process implied by the simulationis that it can accomplish the concentrate of methane and the recovery of carbondioxide simultaneously, achieving the purpose of environment protection as well asresource reclamation.Finally, the results obtained by the experiments and simulation were verified inthe industrial practice. A demonstration plant based on the proposed two-stage VPSAprocess with a capacity of800Nm3/h was established for methane purification fromthe oil fire flooding exhaust gas. When process was in stable running, the feed (73.38vol%N2,10.65vol%CH4,15.24vol%CO2) could be separated into a product of59.05vol%CH4,8.21vol%CO2with a recovery of61.51%CH4, and the fraction ofCH4in the overhead nitrogen-rich methane was less than3vol%.