The capture of carbon dioxide from flue gases in a hybrid process

K. Warmuziński, M. Tańczyk, M. Jaschik, A. Janusz-Cygan
Polityka Energetyczna, 14, 427-439 (2011)

Directive 2009/31/WE concerning geological storage of carbon dioxide (the so-called CSS Directive) is yet another step taken by the EU in limiting CO2 emissions. Since free emission quotas are going to be phased out, our energy sector will be compelled to implement the various CO2 abatement options or, alternatively, buy emission permits. The present study describes a technique for the removal of CO2 from flue gases via a hybrid process which combines pressure swing adsorption (PSA) and membrane separation. The scheme of the process is shown in Fig.1. The procedure for selecting an appropriate adsorbent for the PSA unit is discussed. In Fig.2 experimental CO2 adsorption isotherms are shown for a temperature of 20oC. In Fig.3 a dependence is presented of the CO2/N2 selectivity coefficient on pressure (Eq.1) for both zeolite molecular sieves (ZMS) 13X and activated carbons. It is found that, from the standpoint of CO2 separation efficiency, ZMS 13X perform better than the activated carbons studied. In Table 1 the proposed PSA cycle is shown. Based on extensive simulations the efficiency of the PSA unit is assessed. As can be seen from Fig 4, at feed flow rates below 7.5 mn3/h it is possible to obtain an enriched product that contains over 70 vol. % of CO2, with an almost complete recovery. In addition, experiments were carried out for the separation of a mixture containing 70 % of CO2 and 30 % of N2, using commercial membrane modules. Figs. 5, 6 and 7 show, respectively, permeate and retentate CO2 concentrations and the cut ratio as functions of the pressure difference between the feed side and the permeate side of the module (Δp). It is concluded that the membrane unit can increase the concentration of carbon dioxide from 70 % to over 95 %, which is quite sufficient in terms of transport and storage. Based on the technique proposed in this study a demonstration installation is currently under construction in the Institute of Chemical Engineering, Polish Academy of Sciences. Also, a versatile numerical simulator for the hybrid CO2 separation is being developed.

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