Research On The Variable Mass Flow In A Radial Flow Adsorber For Pressure Swing Adsorption Of Oxygen Generation

Radial flow adsorber is an important technical approach for large-scale pressure swing adsorption(PSA)oxygen generation device.It has been widely used with advantages of good expansibility of oxygen generation rate and small pressure drop of the bed.In comparison to the axial flow adsorber,the internal variable mass flow is more complicate in radial flow adsorber regarding the air distribution holes of inflow and outflow as well as the adsorption and desorption of adsorbents.In addition,internal flow characteristics under different gas flow patterns are different.Therefore,flow characteristics under various gas flow patterns in variable mass flow for the PSA radial flow adsorber are worthy of research and discussion.In this paper,the numerical model and experimental research work were carried out,along with the following conclusions.The experimental investigation was carried out in a two-tower PSA radial flow adsorber system.The effects of Z type of centripetal flow,Z type of centrifugal flow,?type of centripetal flow,?type of centrifugal flow were investigated.The results show that in different cyclic periods for pressurization,adsorption,depressurization and purge,the axial static pressure of the radial flow adsorber outer-channel are not change significantly in Z type of centripetal flow and II type of centripetal flow,while those for the Z type of centrifugal flow and ?type of centrifugal flow are change obviously.The axial static pressure drop of Z type of centrifugal flow in radial flow adsorber outer-channel are 45Pa,100Pa,119Pa and 30Pa,and the axial pressure drop of?type of centrifugal flow in radial flow adsorber outer-channel are 40Pa,80Pa,80Pa and 20Pa,respectively.The greater the pressure drop,the worse the effect of flow distribution.It shows that the radial flow adsorber of centripetal flow is better than centrifugal flow,which is more applicable to PSA oxygen generation.A mathematical model was established to simulate the variable mass flow in the radial flow adsorber in 4 types of gas flow patterns for PSA oxygen generation.The theoretical and experimental data are in good agreement.The mathematical model has been used to study the characteristics of variable mass flow in air distribution holes of inflow and outflow as well as adsorption and desorption.It can adapt to the different cyclic of PSA process for pressurization,adsorption,depressurization and purge.The simulation results are dependent on the pressure variation rather than empirical formula or semi-empirical formula,with the considerations of the axial and radial gradient distribution,the radial wall porosity,the heating effect and the gas compressibility.The flow characteristics of the variable mass flow in 4 types of gas flow patterns were also studied.The results show that during the step of adsorption,there is a greater change in velocity located at the mass transfer zone,while in other three steps the changes in velocity are approximately linear along the bed.During the step of depressurization,there is a higher velocity in the bed,blasting the adsorbent and causing the adsorbents attrition and pulverization.Therefore,it is necessary to control the rate of depressurization.During the adsorption stage,there is a clear pressure wave crest in the radial flow adsorber,where the adsorption source has important effects on the variable mass flow and should not be neglected.During the adsorption stage,the maximum radial non-uniformity of velocity near the central-channel of centripetal flow and centrifugal flow are 4.0 and 6.0,respectively.The results show that the radial centripetal flow performs is better than the radial centrifugal flow.During the purge stage,the axial pressure drop of Z type of centripetal flow and the?type of centripetal flow are 104 Pa and 54 Pa,respectively,indicative of higher applicability for the?type compared to the Z type.The influences of the structural parameters such as the outer-channel width,the opening ratio of central-channel and outer-channel on the variable mass flow were analyzed.The results show that the best outer-channel width of Z type and?type are 11 mm and 5 mm,respectively.The greater opening ratio of central-channel of Z type and?type are all 5%,and the opening ratio of outer-channel has a little influence.Comparing the effects of structural parameter variations under 4 types of gas flow patterns of the PSA radial flow adsorber on the radial non-uniformity of velocity,Mf,the importance follows the order of:the opening ratio of central-channel>the outer-channel width>the opening ratio of outer-channel.Values of Mf for the 4 flow patterns at optimal conditions(outer-channel width and opening ratio of central-channel)are compared,resulting in the order of:Mf of?type of centripetal flow<Mf of Z type of centripetal flow<Mf of?type of centrifugal flow<Mf of Z type of centrifugal flow.The?type of centripetal flow with the best result of variable mass flow uniformity in a radial flow,with the outer-channel width of 5 mm and the opening ratio of central-channel of 5%,is found to applicable to the variable mass flow in the radial flow adsorber for PSA of oxygen generation.The results of this study can provide references for the further research of the flow characteristics of the variable mass flow in a radial flow adsorber and the optimization of the radial flow adsorber structure for PSA of oxygen generation.