Hydrogen production through catalytic supercritical water gasification: Energy and char formation assessment

Abstract

Biomass gasification has a great potential for sustainable energy production, effectively satisfying the growing energy demand. A promising technology for sustainable hydrogen production is the supercritical water gasification (SCWG) of biomass. This study proposes a new model to assess gas yields and char formation in the SCWG process. This research employs a thermodynamic approach to model the reactor, assuming the equilibrium condition. The presence of catalyst on the SCWG is also incorporated in the proposed model, considering a deviation term for the Gibbs free energy of solid char. In addition, a process simulation is conducted to analyze the energy performance of the SCWG unit. Four different feedstocks, including sunflower, corncob, leather waste, and coal, are considered in the SCWG process. The newly developed model considerably improves the prediction of the gas yields and solid char formation, based on the experimental data. Compared to the basic model, the gas yield and formed char from the sunflower, corncob, leather waste, and coal are increased by 85.37, 62.52, 89.30, and 34.05%, respectively. It is found that the basic model fails to obtain the solid char content for coal at 750 °C and 24.55 MPa, while the new model offers an accurate estimation of the coal’s char formation. According to the sensitivity results, the temperature and feed concentration substantially influence the gas yields and char formation, while pressure is less impactful. Moreover, the carbon gasification efficiency (CGE) increases at higher temperatures and smaller biomass concentrations. The outcomes of energy analysis reveal the positive impact of higher temperature, pressure, and biomass concentration. Also, the energy consumption per hydrogen production holds a minimum value at 828.6 °C. The specific energy consumption per hydrogen production unit increases at higher pressures and reduces as the biomass concentration lowers.