Research On Adsorption Performance Of Vertical Radial Flow Adsorber Used In Air Separation Unit

Dual-bed adsorber consisting of activated alumina and molecular sieve is one of the most important equipment used in cryogenic air separation unit for feed air prepurification. Energy consumption of air purification system accounts for about16%of the overall energy consumption of the air separation plant, therefore, it is quite important to study the adsorption performance. Compared with horizontal adsorber, vertical radial flow adsorber generally occupies much less space and can be maintained conveniently. Besides, airflow resistance through the adsorbent bed is much smaller. At present, radial flow adsorber has been widely applied especially in large-scale air separation unit. This paper first reviewed the development process of radial flow adsorber as well as temperature swing adsorption technology in both domestic and abroad. A dynamic mathematical model of vertical radial flow adsorber was built, aiming at predicting the dual-bed adsorption performance and achieving optimal design of the adsorber. And following researches have been done:1. In this article, a one-dimensional mathematical model was established to describe the radial flow adsorption process. The extended Langmuir 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 difference method was used for discretization. Newton decomposition method was applied to iterate and solve the nonlinear equations.2. With the above dynamic model, the distribution of temperature along the adsorbent bed and concentration of the adsorbate gases was calculated. Compared with single layer bed, dual-bed packed with activated alumina and molecular sieve shows a better performance. Calculation results showed that there was an interaction in the adsorption process between water vapor and carbon dioxide. As the strongly adsorbed component, water vapor would inhibit the adsorption of carbon dioxide after it appearing in the layer of molecular sieve, resulting in a roll-up phenomenon in the concentration curve. Under the premise of the total thickness of the adsorption bed maintaining the same, an appropriate thickness ratio of the two adsorbents guarantees penetration of alumina and molecular sieve simultaneously, making full use of the dual-bed adsorption and extending service life of the equipment.3. The mathematical model of the radial flow adsorber regeneration process was built. The internal temperature and concentration distribution of the regeneration gas was calculated. Performance analysis of the prepurification system was discussed by comparing the influence of process parameters such as temperature and flow rate. Energy consumption of the regeneration process was calculated and energy saving method was provided.