Title : Hydrogen production from contaminated residual biomass: An integrated gasification and SEWGS process study
Abstract:
The restoration of heavy metal-contaminated soils through Plant-Assisted BioRemediation (PABR) represents a sustainable environmental strategy, yet it generates a significant secondary waste stream: contaminated biomass that requires specialized disposal. This study investigates an innovative and sustainable pathway for the energy conversion of such biomass into green hydrogen through an integrated thermochemical process, comparing the performance of contaminated poplar prunings with traditional, non-contaminated poplar samples. The research follows a multi-stage experimental approach, beginning with a comprehensive physicochemical characterization. Both biomass types were analyzed to assess their energy content, structural composition, and, specifically for the PABR-derived samples, the concentration of heavy metal pollutants accumulated during the phytoremediation process. The thermochemical conversion was performed in a 1.5 kW prototype fluidized bed gasification plant operating at temperature of 850°C. Atmospheric air was employed as the gasifying agent to evaluate the baseline composition of the resulting syngas, tar production, and residual ash quality. A key focus of the investigation is the fate of heavy metals during high-temperature gasification. Experimental results demonstrate that the thermochemical process effectively acts as a separation stage: a vast majority of the inorganic pollutants are confined and concentrated within the residual ash, significantly reducing the volume of hazardous material to be managed. Interestingly, the study highlights that the syngas obtained from contaminated poplar is qualitatively comparable to that produced from traditional residual biomass, showing no significant deviation in terms of primary gaseous pollutants or lower heating value (LHV). To further upgrade the gas quality, the syngas was processed in a Sorption-Enhanced Water Gas Shift (SEWGS) stage. In this phase, conducted at a controlled temperature of 300°C, carbon monoxide (CO) reacts with steam to produce hydrogen (H2) and carbon dioxide (CO2). The process utilizes a calcium oxide (CaO) adsorbent to perform in-situ CO2 capture, shifting the thermodynamic equilibrium toward the products and allowing for the production of a high-purity, H2-rich syngas stream. The primary objective of this research is to demonstrate a viable, circular economy route for the valorization of "dirty" biomass. By integrating gasification with SEWGS, the process not only ensures the safe management of heavy metals by concentrating them into a stabilized mineral residue but also promotes the generation of high-value energy carriers. This integrated approach transforms a remediation byproduct into a strategic resource for the hydrogen economy, providing a scalable solution for the dual challenge of soil decontamination and decarbonized energy production.
