Optimal design of non-isothermal supercritical water gasification reactor: From biomass to hydrogen

Supercritical water gasification (SCWG) of biomass is a promising technology for large-scale hydrogen production and its success is greatly affected by the performance of SCWG reactor. In this work, a novel mathematical modeling and optimization approach is applied to design optimal tubular reactor for the SCWG of biomass. The tubular reactor is first discretized into cells. Then, detailed mathematical models are developed to represent the reactions occurring in each cell and the mass balances among the cells. By integrating all the models along the reactor, the reactor design problem is formulated as a nonlinear optimization problem. The objective is to maximize the hydrogen yield and multiple constraints have to be fulfilled. After solving the problem, the optimal reactor design (e.g., reactor length, diameter, and axial fluid temperature profile) can be obtained. To demonstrate the applicability of our approach, two design scenarios are studied. The results show that non-isothermal reactors with three-stage zigzag-like temperature profiles are preferred for hydrogen production, instead of traditional isothermal reactors. Compared with isothermal reactors, the optimal non-isothermal ones can increase hydrogen yield up to 25.06% (i.e., 16.67 vs 13.33 mol/kg glycerol). The results provide useful insights on industrial SCWG reactor design for achieving efficient hydrogen production.