In recent years, technological development of fuel cells has progressed, and hydrogen demand for the fuel is expanding. However, since fossil fuel is mainly used as the energy source for hydrogen, from the viewpoint of life cycle assessment (LCA), even if hydrogen is used as energy, it contributes to the emission of greenhouse gases. Therefore, we have been developing biomass-derived hydrogen (Bio-H2) production process. It was deemed that the hydrogen purification process (PSA; pressure swing adsorption) had the most environmental impact. as a solution to that, we developed a 2-step PSA. However, the effective use of energy and the environmental impact in the Bio-H2 production process that introduced 2-step PSA have not been conducted. Therefore, in order to verify the effective use of energy and the environmental impact of the process, we designed Bio-H2 production process using 2-step PSA based on gasification and purification experimental data, and evaluate the effectiveness of energy use of the process using the exergy analysis. In addition, we assessed the environmental impact of the process using LCA analysis. As a result, it was shown that the exergy efficiency of the 2-step PSA case could be improved by 1.7 points over that of the conventional PSA case. Furthermore, compared to the conventional PSA case, LCA analysis resolved that consumption of fossil fuel would be reduced in the case of 2-step PSA case, and the effect of global warming be greatly reduced. By using the evaluation method integrating the exergy analysis and the environmental impact assessment, which was newly proposed in this paper, we believe that it should contribute to promoting technology development of energy conversion process derived from renewable energy.
In order to develop an efficient pre-desulfurization technology for both inorganic and organic sulfurs in coals under the mild condition, oxidative desulfurization using hydrogen peroxide was carried out for five kinds of coals with different rank. The coal samples were agitated in the hydrogen peroxide aqueous solution for 2 h at the room temperature. Pyritic sulfur and sulfate as the inorganic sulfur were removed completely from the solid phase by the treatment. Organic sulfur was simultaneously removed, for example, 84% of organic sulfur was reduced for a low rank coal. The removed sulfur from the solid phase dissolved in the hydrogen peroxide aqueous solution as sulfate. XANES analysis showed that thiophenic sulfurs in the coals changed to sulfoxide and sulfone during the hydrogen peroxide treatment. The removal extent of thiophenic sulfur decreased with the increase of the coal rank and correlated well with the aromaticity of the raw coals.