## 1 Introduction  
Large-scale PSA oxygen generation systems have attracted considerable attention in recent years due to the low cost [1] and increasing demand for industrial gases. In China, the pressure swing adsorption (PSA) oxygen generation scale has reached 40,700 Nm\({}^{3}\) h\({}^{-1}\) in the coal chemical industry. Due to the huge gas flow used in large-scale oxygen generation plants, diameters larger than 4-5 m are generally required in conventional axial-flow adsorbers, which exceed economical shipment limits. Such axial-flow adsorbers also have inherently large void volume percentages in the upper and lower head spaces, and difficulties in flow distribution, leading to negative impacts on oxygen generation [2]. The high gas flow rate results in a high superficial velocity across the bed, creates an unwanted pressure drop typically comprising 10-15% of the total power consumption [3], and contributes to great efficiency loss. In contrast, radial-flow adsorbers have advantages of small pressure gradient at the feed end, better adsorbent utilization during the inward feed step, and have a more effective desorption and purge step [4; 5]. Vertical radial-flow adsorbers are widely used in the purification process of large-scale cryogenic air separation systems [6; 7] and also used on the large scale of PSAoxygen production [3]. [PERSON] et al. [8] mentioned that, \"As competitive pressures are driving companies to operate their PSA units with high superficial velocities and short mass-transfer zones, radial bed designs are becoming more and more popular.\"  
[PERSON] et al. [9] used the full energy conservation equation to derive the mathematical model of the fluid flow in a radial-flow reactor, and verified the model by experiment. It was found that the axial distribution of the fluid along the bed depends on the static of the two sides of the bed. [PERSON] et al. [10] showed that the radial-flow direction (center or centrifugation) had an effect on the reaction conversion rate. [PERSON] and [PERSON] [11] showed that a uniform distribution of gas flow in the radial-flow bed has a more significant effect on the reaction conversion rate. [PERSON] et al. [12] investigated the flow distribution in a radial-flow bed reactor using electrical resistance tomography and CFD, and showed the radial velocity gradient of the fluid flowing from the inlet end to the center increased gradually. [PERSON] et al. [13] pointed out that the narrow flow path that forms in the radial-flow adsorption bed can improve the uneven distribution of fluids. [PERSON] [14] proposed a non-uniform distribution of openings in the inner and outer cylinders to improve the uniform distribution of airflow. [PERSON] et al. [15] studied the flow distribution of four radial-flow react beds and found that the centrifugal-\(\pi\)-flow configuration is the superior configuration for the radial flow reactor. [PERSON] et al. [16] found that the centrifugal-\(\pi\)-flow configuration had the most uniform axial flow over other configurations. [PERSON] et al. [17] concluded that the centripetal \(\pi\)-type flow gives better flow distribution than other types of flow on a specific type of air filter incorporating an annular bed of activated carbons. [PERSON] and [PERSON] [18] investigated the properties of the fluids in flow channels of a three-layer radial-flow reactor. [PERSON] et al. [19] analyzed the pressure drop in a Z-flow type radial-flow adsorber and derived a differential equation to determine the ideal cross-sectional radii. [PERSON] et al. [20] found an optimized axial flow reactor had about 99.4% lower pressure drop in comparison to the conventional configuration. [PERSON] et al. [21] have studied the effect of the structure of a radial-flow adsorber on gas distribution. Previous works on radial-flow adsorbers mainly focus on gas flow distribution and chemical reaction efficiency. There are limited studies on PSA oxygen generation. [PERSON] et al.