Pyrolysis is a pathway for hydrogen reproduction from sewage sludge. The critical problem in the indirect pyrolysis process is the lower heat transfer performance in the furnace. The circulation of heat media controls the heat transfer in the pyrolizer (e.g., heat carriers (HCs) in the form of alumina balls), which is essential in determining the heat transfer performance and ultimately determining the hydrogen yield. The temperature of the HCs and amount of hydrogen yield are low because the required temperature in the vessel is not satisfied. This study investigated the relationship between the operating conditions and HC temperature profile to determine the optimum conditions for sufficient HC heating. We discuss the HC performance aspects to achieve a more effective operation using low inputs. Using a computational fluid dynamics simulation, we assessed the effect of the inlet gas temperature, inlet gas flow rate, and furnace structure on the heat transfer performance. We validated our model using the test results from a demonstration plant. We observed that by increasing the hot gas inlet temperature by 51 °C, the heat loss was reduced by 2,170 MJ/h, and the thermal efficiency of the entire plant was improved by 5.46%. When the number of hot-gas inlets was split, the efficiency did not change, but the temperature dispersion of the HCs was small. This implied that tar generation, including that of liquid substances, was prevented. At the pyrolysis temperature of 600°C, the cold gas efficiency was 81.2 LHV%.

An energy production system that combines biomass and fuel cells produces much energy with minimal environmental impact. However, the hydrogen sulfide (H₂S) contained in gasified biomass degrades fuel cell performance, thus negating the advantages of this combination. In this study, the removal of H₂S by adsorption after biomass gasification was investigated. Metal oxides with high adsorption performance are common H₂S adsorbents. However, they have a significant environmental impact in terms of metal depletion, which is an environmental impact indicator. Therefore, neutralized sediment materials from mine drainage treatments can be used as H₂S adsorbents. A previous study found that the adsorption performance of H₂S adsorbents is equivalent to that of metal oxides, especially in the high-temperature zone (300 °C), and the environmental impact is considerably lower than that of metal oxides. However, because the neutralized sediment is a powder (Φ 4.5 μm on average), there is a possibility that the gas will not flow due to the pressure drop when it is used in a large adsorption column. Therefore, in this study, we propose the use of granulated neutralized sediments for practical plant operations. No studies have investigated the adsorption performance of granulated neutralized sediment through experiments or quantitatively investigated the effect of using waste material as a H₂S adsorbent to reduce the environmental impact of hydrogen production. Based on these data, the sulfur capture capacity of the granulated neutralized sediment was experimentally investigated. The extent to which the environmental impact of the hydrogen production system could be reduced when granulated neutralized sediment was used as the H₂S adsorbent was assessed. Note that the granulated neutralized sediment is formed with about a Φ 0.56–1.25 mm diameter. The granulated neutralized sediment exhibited approximately 76.8% of the adsorption performance of zinc oxide (ZnO) on a conventional adsorbent. In terms of the LCA, the global warming potential (GWP) and the abiotic depletion potential (ADP) were improved by approximately 0.89% (GWP) and 55.3% (ADP) in the entire hydrogen production process. This study demonstrated that the use of waste materials can significantly reduce the environmental impact on the entire system.

This study focused on the small-scale dual fluidized-bed gasifier for hydrogen (H₂) production from sewage sludge. One of the current problems with the pyrolizer is tar condensation. Tar could reduce the efficiency of the H₂ yield by adhering and condensing on walls and pipes. It was revealed that more tar can be decomposed with higher reaction temperatures. Therefore, this study aimed to increase the tar decomposition efficiency with raising the heat carriers’ (HCs) temperature and analyzing the temperature distribution in the furnaces using a CFD simulation. The tar decomposition rate in the pyrolizer was +34.4%pt. by 100 °C of the HCs’ temperature rising. It is implied that less tar trouble and a longer lifetime of the H₂ production plant could be expected by raising the HCs’ temperature. However, comparing the heat transfer efficiency of the whole system, the lower HC inlet temperature of +7.4%pt., because of the hot gas, which supplies heat to the HCs, required more heat, making the thermal efficiency poorer. In addition, the environmental impact of the AGM was increased by 27.2% with the HCs’ temperature rising to 100 °C. Thus, the heat exchange efficiency of the preheater needs to be improved to raise the HCs’ inlet temperature and reduce the amount of hot gas required.

The fuel-cell (FC) power system, utilizing biohydrogen from biomass resources, is a promising alternative to fossil fuels. However, hydrogen sulfide (H₂S) in bio-syngas can severely degrade FC performance and increase environmental impact, necessitating impurity removal. This study investigates a multi-stage desulfurization process using neutralized sediment (NS) and a metal hydride (LaNi₅) as H₂S adsorbents. NS, a mining waste material, can potentially reduce environmental impact when repurposed as an adsorbent, with its performance influenced by pore configuration and Fe content. However, the purified gas does not fully meet FC fuel specifications. To address this, LaNi₅, which selectively absorbs and releases hydrogen, was incorporated to achieve higher purification levels. In our study, H₂S adsorption tests were conducted using two fixed-bed flow reactors heated to 250 °C, where a gas mixture containing 196 ppm of H₂S flowed through the system. The proposed multi-stage system achieved a breakthrough time of 182.5 h with purified gas remaining under 0.1 ppm and an adsorption capacity of 16.4 g/g-sorbent. These results demonstrate the high desulfurization performance achieved using NS and LaNi₅.

An advanced gasification module (AGM) for green hydrogen production involves a small-scale biomass gasification process owing to the low energy density of biomass. Therefore, significant heat loss and the endothermic nature of gasification system require additional fossil fuel heat, increasing CO₂ emissions. This study focuses on bioenergy conversion with carbon capture and utilization (BECCU), where carbon-neutral CO₂ from biomass gasification is captured and reused as a gasifying agent to reduce the greenhouse gas intensity of green hydrogen. BECCU is expected to achieve negative emissions and enhance gasification efficiency by promoting conversion of char and tar through CO₂ gasification. To evaluate the effectiveness of BECCU in the AGM, we conducted a sensitivity analysis of the reformer temperature and S/C ratio using process simulation combined with life cycle assessment. In both sensitivity analyses, the GWP for CO₂ capture was lower compared with conventional conditions, considering recovered CO₂ from purification and the additional steam generated through heat recovery. This suggests improved hydrogen yields from enhanced char and tar conversion. Consequently, the GWP was reduced by more than 50%, demonstrating BECCU’s effectiveness in the AGM. This represents a step toward operating biomass gasification systems with lower environmental impact and contributing to sustainable energy production.

As the demand for green hydrogen with carbon neutrality increases, this research has focused on hydrogen production via the pyrolysis of biomass resources. Hydrogen sulfide (H2S) is an impurity produced during this process. This pollutant necessitates desulfurization since H2S can react with the platinum catalyst in fuel cells, leading to a significant voltage reduction. Our previous studies explored the possibility of using neutralized sediment (NS)—a mining waste product—as an alternative to metal oxides for desulfurization because of its similar effectiveness and potential for reduced environmental impact. We also considered the use of LaNi5—a hydrogen storage alloy—which can adsorb and release hydrogen and also remove H2S through the reaction of Ni with S. Initially, we discovered that hydrogen gas flow decreases the H2S adsorption capacity of NS due to hydrogen attaching to the NS surface. Subsequently, we examined the performance of a combined NS and LaNi5 adsorbent for the complete removal of H2S, identifying an effective temperature range above 160 °C. Additionally, our results suggested a synergistic effect on the H2S adsorption mechanism when using NS and LaNi5 together.