Adsorption dynamics of water in layered bed for air‐drying tsa process

Abstract

Ž. The thermal swing adsorption TSA process is most commonly used to prevent the air contamination from organic solvents of low concentration and to dehumidify gases. Specifically, the air drying by the TSA process is one of the major commercial gas separation processes.Since the regeneration step in the TSA cycle requires time enough to heat and cool the bed, it is often the time-limiting step in the TSA cycle. In the design and economic assessment of the TSA process, one is principally interested in energy consumption involved with regeneration time, purge gas requirements, and heat load. The equilibrium theory has been widely used to obtain exact solutions from coupled mass and energy balances. In this case, due to the assumption of instantaneous mass-and heat-transfer rates, the predicted concentration and temperature profiles were sharper than the Ž experimental results Kumar and Dissinger, 1986; Schork and . Fair, 1988 . However, in the numerical method, the mass and energy balances are solved with the equations describing the mass-and heat-transfer rates. Although this approach has a limit resulting from computational difficulty, it has become a general method to solve the coupled differential equations. Ž . Basmadjian et al. 1975 studied the hot nitrogen regeneration of carbon dioxide in the activated carbon bed by using Ž . an adiabatic model. Carter and Husain 1974 have carried out both experiment and simulation of the adsorption breakthrough of carbon dioxide and water with helium as a carrier gas in a fixed bed. They found that a surface or capillary flow of adsorbate occurs in the adsorbed phase transport in addition to macropore diffusion. Also, the adsorption and desorption of ethane and propane mixtures on activated carbon by using a nonisothermal model with Flory-Huggins solution Ž . theory FH-VSM and a rate model considering Knudsen and Ž . surface diffusions in parallel Huang and Fair, 1988 . Davis Ž . and LeVan 1987 showed that adiabatic fixed-bed adsorption cycles with adsorption, heating, and cooling steps were analyzed by using simple wave theory.Although the air-drying TSA process is commonly used in industry, there has been little fundamental research to imCorrespondence concerning this article should be addressed to C.-H. Lee. prove an understanding of the process. Moreover, an extensive literature on adsorber analysis has been published, but relatively few theoretical analyses have been done on regen-Ž . eration Yang, 1987;Ruthven et al., 1994 . However, it is usually the regeneration step that determines the economic success of the TSA process, because it consumes a huge amount of energy for regeneration. Therefore, the improvement of the regeneration process through the minimization of energy consumption can contribute to the design and optimization methods of the TSA process. In addition, Yang and Ž . Lee 1998 studied the adsorption dynamics of a layered bed for the purpose of developing a H PSA process from coke 2 oven gas. The performance of the PSA process could be impr...

The downsizing of a TSA system for an air purification unit using a high flow rate method

“…In a typical air purification TSA unit, the adsorption vessel is packed with layers of two different adsorbents, with activated alumina to remove H 2 O in the upstream side of the adsorption vessel, and NaX type zeolite to remove CO 2 in the downstream side of the adsorption vessel. There are a large number of reports on a layered bed process (Kumar et al 2003;Fujita and Nakamura 1997;Ahn and Lee 2003).…”

Equilibrium theory analysis of thermal regeneration of a humid adsorption column: Selection of optimal hot purge gas temperature

“…In the past researches [17,18,25], a series of breakthrough experiments of adsorption followed by thermal regeneration were carried out. Before performing this experimental campaign, the adsorption column was thermally regenerated in situ at 593K at least for 12 hrs.…”

“…In Ahn and Lee's works [17,18], a 13X column initially saturated with a water vapour at 12740 ppmv (54% relative humidity) was thermally regenerated by flowing a hot nitrogen gas through the column. The thermal regeneration experiments were carried out at a constant purge gas flowrate and three different temperatures, i.e.…”

The role of water on postcombustion CO2 capture by vacuum swing adsorption: Bed layering and purge to feed ratio

“…Conversely, as few adsorbents work equally well for all gas components, adding a prelayer for water removal seems necessary for protecting the CO 2 adsorption layer. Using a layered bed configuration is not a new concept in adsorption‐based technologies . The advantage of using a multilayered column over multicolumns in series is clear in that it reduces the capital cost.…”

“…Layered columns have been used in pressure swing adsorption (PSA) processes for several applications, such as: (1) air prepurification, with an activated alumina layer to remove mainly H 2 O followed by a zeolite layer to remove CO 2 (ppm level) and the other components, in which an extra catalyst layer can be added in between to convert the trace hydrocarbons and carbon monoxide into CO 2 and water and get removed by the subsequent zeolite layers; (2) H 2 purification; (3) upgrading methane from CH 4 /CO 2 /N 2 mixtures . Moreover, layered columns were also used in temperature swing adsorption for air drying . The general principle of using a layered bed involves using a weak adsorbent with a more linear isotherm (e.g., activated carbon) and hence larger working capacity to remove the bulk impurity at the inlet of the bed followed by a strong adsorbent with favorable isotherm to eliminate the residual traces …”