An Environmental Process Design for H2S Removal Based on LCA Thinking Using CFD Modeling

Recently, H[[inf]]2[[/inf]] production from biomass resources has attracted increasing attention because of its eco-friendliness. It generates syngas, including impurities. The product of H[[inf]]2[[/inf]] can be obtained through purification and removal processes. However, since the use of H[[inf]]2[[/inf]] containing H[[inf]]2[[/inf]]S damages fuel cell devices, a removal scheme is necessary. A common adsorbent of impurities is metal oxides such as ZnO and Fe[[inf]]2[[/inf]]O[[inf]]3[[/inf]], which are practical to adsorb but have significant environmental impacts. Neutralized sediment (NS), which is always generated while treating mining wastewater, is an alternative to conventional adsorbents because it contains iron. Compared with ZnO, although NS has shown to perform approximately 26% lower at 300 °C, it has a markedly smaller environmental impact. In previous studies, NS captured more H[[inf]]2[[/inf]]S at higher temperatures. However, the inner temperature distribution of a reactor may not be uniform because of operating conditions such as temperature differences from the outside, the size of a reactor, and active time. Thus, there can be a difference between the actual required amount of NS and the steady-state calculation result of it. Therefore, it is important to clarify time and positional changes to suggest a more efficient reactor geometry and an appropriate used amount. Computational fluid dynamics (CFD) helps simulate the time and positional changes. CFD modeling was used to investigate the performance due to the inner temperature distribution of a reactor. Then, we estimated the amount of NS with changing reaction temperature: at low temperature, 40 °C, and at high temperature, 300 °C. Finally, we compared the environmental impact in each case with global warming potential (GWP) and abiotic depletion potential (ADP). Consequently, the breakthrough time of NS at high temperatures became 85% of that of the previous study due to heat release from the reactor. In the life-cycle assessment, the ADP was almost the same in both cases; however, the GWP at high temperatures was 78.5% of the value at low temperatures.