Intrinsic mechanism of scale-up effects in supercritical water fluidized bed reactors from particle perspective

Abstract

Supercritical water gasification is a promising method for efficient hydrogen production. Among various reactor designs, fluidized bed reactors demonstrate strong industrial potential due to their plugging resistance and favorable hydrodynamic properties. However, scaling up the reactor to industrial applications disrupts the mass transfer-reaction matching relationship established at the particle level, making it challenging to replicate the performance of smaller reactors. To mitigate the scale-up effect of the reactor, a fundamental understanding of particle-scale mechanisms is essential. In this study, high-resolution numerical simulations are employed to investigate particle dynamics across both reactor and particle scales. To enhance computational efficiency, adaptive mesh refinement and heterogeneous computing are utilized. The scale-up laws governing the internal flow structures and chemical reaction performance within the reactor are analyzed. The temperature, diffusion, and chemical reaction performance at the particle level are tracked, and statistical analyses are performed to elucidate the mechanisms driving the scale-up effects. Results reveal that the two scaling approaches affect reactor performance through different mechanisms. Radial scaling has minimal impact on particle mixing and reaction rates, whereas axial scaling reduces particle reaction rates; however, this reduction is compensated by an increased particle count, ultimately enhancing overall hydrogen yield. Additionally, higher superficial velocity enhances feedstock mixing and thermal uniformity, resulting in more uniform particle reactions, although it may hinder homogeneous reactions. These findings offer new insights into reactor scale-up effects and hold promise for guiding optimal and detailed design of future industrial-scale reactors.