Simulation Research On Pressure Swing Adsorption Cycle Of Air Separation For Oxygen

Pressure Swing Adsorption(PSA) was widely used because of its strong applicability, high reliability, low cost, high efficiency, environmental friendliness, etc. The FLUENT software was selected to simulate the two-bed Skarstrom PSA cycle of air separation for oxygen. Program was defined to express the mass, heat and momentum transfer in the gas-solid two-phase adsorption process. The distribution of oxygen concentration, gas temperature, gas flow rate and bed pressure drop in the process were simulated. Meanwhile, the influence of particle diameter on the performance of PSA separation was studied in order to provide guidance for practical production. The main research contents are as follows:Based on the principle of PSA air separation, the mass transfer model and the equilibrium adsorption model were combined with the porous media model by the User-Defined Function in FLUENT. And the solid phase energy equation was added by using the function of User-Defined Scalar. Then a gas-solid two-phase PSA coupling model was established to reflect the mass, heat and momentum transfer during gas solid two phases.The grid independence was assessed by simulating model of seven kinds of different grid numbers. And the model with 50854 grid number was proved satisfying the requirements. In order to verify the correctness of the model, the simulation and experiment results of the average mole fraction of oxygen in outlet were contrasted and the error was about 2%.Based on the gas-solid two-phase PSA model, the Skarstrom cycle with two beds and four steps was simulated to achieve mole fraction of oxygen in gas phase, component concentrations in the solid phase and temperature of two phases at the end of four steps for different cycles. The results show that, in the first cycle, the mole fraction of oxygen could reach 58.7%. The concentration of oxygen and nitrogen in solid phase were 0.12mol/kg and 1.19mol/kg respectively, and the recovery rate of oxygen was 32.55%. With cycle number increasing, the mole fraction and recovery rate of oxygen rose continuously. The process reached steady state in the sixth cycle. At this point, the maximum mole fraction of oxygen was 99% and the recovery rate of oxygen was 53.35%.Using the gas-solid two-phase PSA model, the effects of the adsorbent particle diameters on the concentration and recovery of oxygen were studied. The models with the particle diameters of 0.8mm, 1.6mm, 2.4mm, 3.2mm and 4.0mm were simulated when ratio of Purge was 0.5. It was found that under the same conditions the larger the particle diameter was, the worse the bed flow effect, unable to effectively resist bed inlet gas jet, resulting in bed being penetrated easily and reducing oxygen purity greatly. The smaller the particle diameter was, the larger the bed pressure drop was, weakening the effect of adsorption as well. The adsorbent particle diameter of 1.6mm showed the best performance.