Abstract
Large-scale separation of substances present at low concentrations is readily performed by adsorption in packed beds that requires recurring energy-intensive regeneration of the adsorbent. The present work uses numerical simulations previously developed for industrial-scale packed-bed benzene sorption on activated carbon with temperature-swing regeneration by steam to investigate the influence of steam properties and regeneration strategy on total energy performance and breakthrough behaviour.It is shown that using saturated steam lowers both the steam mass and energy consumption during regeneration of a fixed amount of benzene, whereas using superheated steam returns the bed to a more fresh-like state after each regeneration stage. The most promising variation tried implies a 19% reduction in the energy consumption. Furthermore, the importance of accounting for the real industrial cycling conditions in the optimization of packed-bed adsorbers is highlighted. It is shown that the participation of different sections of the bed during adsorption varies with the regeneration strategy, but is never as localized as predicted from a model for a fresh bed without cycling. Finally, the present results also show that the effluent purity attained during regeneration increases when high-temperature saturated steam is used, e.g. a 60-degree increase in steam temperature raises the purity by 11%.
Highlights
The purpose of the current work is to study how to optimize a gas-cleaning process based on packed-bed adsorption using numerical simulations
Common applications are found in air and water purification [5], solid fuel gasification [6] and the chemical industry [7], where beds packed with activated carbon have been shown to perform well in removal of volatile organic compounds (VOCs) [8]
Numerical simulations provide access to information about what happens inside the beds that is otherwise difficult to attain in an industrial setting
Summary
The purpose of the current work is to study how to optimize a gas-cleaning process based on packed-bed adsorption using numerical simulations. Common applications are found in air and water purification [5], solid fuel gasification [6] and the chemical industry [7], where beds packed with activated carbon have been shown to perform well in removal of volatile organic compounds (VOCs) [8]. In the removal of VOCs by activated carbon beds, the contaminated stream is led through the bed and the VOCs adsorb to the carbon. This process eventually saturates the carbon with the VOCs, effectively preventing further separation. There are often incentives to regenerate the carbon rather than replace it [9] (most notably lowered running costs and the possible value of the adsorbate), and a multitude of technologies exist that facilitate saturated carbon regeneration [10]
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