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CHEMICAL ENGINEERING TRANSACTIONS VOL. 32, 2013 Chief Editors: Sauro Pierucci, Jiří J. Klemeš Copyright © 2013, AIDIC Servizi S.r.l., ISBN 978-88-95608-23-5; ISSN 1974-9791 1855 A publication of The Italian Association of Chemical Engineering Online at: www.aidic.it/cet Carbon Dioxide Capture and Hydrogen Purification from Synthesis Gas by Pressure Swing Adsorption Cheng-tung Chou a*, Fei-hong Chen a, Yu-Jie Huang a, Hong-sung Yang b a Department of Chemical and Materials Engineering, National Central University, Jhong-Li, Taiwan b Center for General Education, Hwa-Hsia Institute of Technology, Chung-Ho District, New Taipei City, Taiwan t310030@ncu.edu.tw Global warming has become more and more serious, which is caused by greenhouse gases. Cutting down the emission of CO2 has already become one of the major research target in the world. This study utilized a pressure swing adsorption (PSA) process to separate high-purity hydrogen and to capture CO2 from synthesis gas, which is the effluent stream of water-gas-shift reactor. The purified H2 can be sent to gas turbine for generating electrical power or can be used for other energy source, whilst the CO2 can be recovered and sequestrated to reduce greenhouse-gas effects. The PSA process studied is a two stage dual-bed eight-step process at room temperature using adsorbents: modified activated carbon AC5-KS and zeolite 13X-Ca. It is assumed that the gas mixture from which water has been removed enters the PSA process. The feed gas entering the PSA process consists of 1.3 % CO, 41.4 % CO2 and 57.3 % H2. It uses the method of lines combined with upwind differences, cubic spline approximation and LSODE of ODEPACK software to solve the equations. The optimal operating condition is obtained by varying the operating variables, such as feed pressure, bed length, step time, etc. Furthermore, the first stage H2-PSA could achieve 99.98 % purity and 79 % recovery of H2 as the top product and the second stage CO2-PSA could obtain about 92 % purity and 98 % recovery of CO2 as the bottom product. By PSA process, the goal of energy generation and environmental protection could be achieved at the same time. 1. Introduction In recent years, increasing concentration of CO2 in the atmosphere is requiring mankind to consider ways of controlling emissions of this greenhouse gas to the atmosphere. The United Nations Intergovernmental Panel on Climate Change (IPCC) has studied these problems and a general conclusion has been achieved between researchers, industry leaders, and politicians that dramatic reductions in greenhouse gas emissions must be achieved in order to stop climatic changes (IPCC, 2005; Abu-Zahra et al., 2009). So using coal more efficiently and turning it into a clean energy source is an important issue for the whole world. An integrated gasification combined cycle (IGCC) is a potential electric power technology that turns coal into synthesis gas, which can be burned to generate power. The CO composition in syngas reacts with steam to generate CO2 and H2 via the water-gas-shift reaction, CO + H2O→CO2 + H2. In this study pressure swing adsorption (PSA) is utilized to separate CO2 and H2 from the effluent of water-gas-shift reactor through H2-PSA and CO2-PSA at room temperature by two different adsorbents. PSA is a cyclic process that separates gas mixtures based on the difference of adsorption capacity of each component on an adsorbent. This technology consists of gas adsorption at high pressure and desorption at low pressure to produce high-purity products. As required by the U.S. Department of Energy, it is important to be able to concentrate the captured CO2 into >90 % concentration that is suitable for underground storage. Yang et al.(1995) used a single-column PSA process with zeolite 5A to concentrate two binary systems, H2/CO2 and H2/CO mixture (70/30 volume %), by experiment and simulation. The hydrogen could be concentrated from 70 % to 99.99 % (recovery 67.5 %) in the H2/CO2 system and to 97.09 % (recovery 67.5 %) in the H2/CO system. Lopes et al. (2009) studied a new adsorbent for a PSA process; a commercial activated carbon (AC) was used for the preparation of a new material, AC5-KS, with enhanced capacity toward contaminants (CO2, CH4, CO, and N2). Adsorption equilibrium and kinetics were studied on the modified AC and compared to the original AC results. An improvement of CO2 adsorption capacityPDF Image | Carbon Dioxide Capture and Hydrogen Purification PSA
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