Theoretical Study On Flow, Heat And Mass Transfer Of Radial Flow Adsorber

With the increasing demand for the industrial gases such as oxygen, nitrogen and argon in China, we are extremely urgent in research and development of the large-scale and high-efficiency cryogenic air separation system. In the cryogenic air separation process, the adsorption purification is crucial to ensure the safe operation; but the higher energy consumption of the purification process and the lower adsorbent utilization rate are severely restricting the development of the large-scale cryogenic air separation system. Radial flow adsorbers have been widely used in large-scale cryogenic air separation in recent years for its lower bed pressure drop, less regeneration energy and less area occupied. However, nonuniform flow distribution over the bed height usually exists in a radial flow adsorber, which will decrease the utilization of adsorbents and even result in operation safety problems. Until now, the research on flow, heat and mass transfer of radial flow adsorber is not complete. Therefore, the following researches have been done:1. In this article, a two-dimensional model is established to simulate the H2O, CO2dynamic competitive adsorption process in alumina and13X zeolite. The extended Dubinin-Astakhov equation was applied to define the adsorption equilibrium and calculate the saturated adsorption capacity of both adsorbents. A linear driving force model was used to define the mass transfer process. To solve the partial differential equations, finite volumn method was used for discretization. Couple algorithm of CFD software Fluent was applied to iterate and solve the discrete material equations, momentum equation and energy equation.2. With the above dynamic model, the distribution of concentration of H2O and CO2and its propagation with time, the temperature distribution were calculated. The results show that the H2O, CO2concentration distribution along the bed height is nonuniform. More gas flow through the top of the bed which causes the breakthrough in this area is faster than other regions in the adsorber and is partially responsible for the poor utilization of adsorbents. In addition, the structure with a diversion pipe in the center pipe was investigated compared with the original structure. The results show that when the amount of air processing is750m3/h, the adsorption amount of H2O and CO2increased by2.3%and1.2%.3. The structure parameters in a dimensionless differential equation which determines the flow characteristics of Z-flow type radial flow adsorber were dimensionless processed, and the effects of structure parameters on the flow distribution in the adsorber were investigated systematically. Meanwhile, the theoretical result of the flow distribution in an experimental radial flow adsorber was in agreement with the experimental data. The results show that reducing the axial height of adsorption bed and the diameters of adsorbent particles can significantly improve the flow distribution in the Z-flow type radial flow adsorber; While the amount of processed air has little impact on that, when the kinematic viscosity of air and other structure parameters are constant.