Abstract
The environmental performance of hydrogen production by steam-based gasification processes for fuel cell (FC) applications was evaluated using a Life Cycle Assessment (LCA) approach because the use of metal oxides as adsorbents or catalysts has a significant impact on the LCAs of FC applications. In this paper investigating systems for the removal of impurities from syngas, the process design of a Bio-H2 system was discussed in terms of the eco-burden of the impurity adsorbent. The HAS-Clay (a synthetic substance composed of hydroxyl aluminum silicate and clay) has particular potential as an adsorbent. This composite adsorbent can sequester H2S and/or HCl, though it is generally used in desiccant heat pumps to adsorb CO2 and H2O. By comparing two different removal systems, the role of HAS-Clay as an adsorbent was investigated via the eco-indexes of global warming potential (GWP) and abiotic depletion potential (ADP). Consequently, it was found that HAS-Clay had a direct or indirect capture capacity of H2S and HCl as well as CO2 and H2O. Compared to the conventional case in which a metal oxide is used as an adsorbent, a greater environmental benefit was obtained in the case of H2S removal. In this case, the GWPs of the two-step pressure swing adsorption (2-step PSA) +ZnO or Fe2O3 were 3.18 and 1.43 g-CO2/Nm3-Bio-H2 respectively compared to 19.4 g-CO2/Nm3-Bio-H2 for the conventional system. Furthermore, the ADPs of 2-step PSA+ZnO or Fe2O3 were 7.63×10-6 and 3.42×10-6 g-Sb eq./Nm3-Bio-H2, as opposed to 2.75×10-2 g-Sb eq./Nm3-Bio-H2 for the conventional system. On the other hand, in the case of HCl removal, a blend of HAS-Clay and CaCO3 cannot obtain any environmental benefit without either the regeneration of HAS-Clay or the substitution of clay (a natural resource). Our results may imply that HAS-Clay is an extremely important adsorbent in term of reducing the eco-burden.
