Mathematical Modeling of Biomass Pyrolysis in Fixed-Bed Reactors: A Systematic Review of Trends, Challenges, and Perspectives

Accurate simulation of biomass pyrolysis in fixed-bed reactors is crucial for optimizing this promising thermochemical conversion pathway. This review systematically consolidates and critically evaluates contemporary mathematical models that describe the intrinsically coupled phenomena of heat transfer, reaction kinetics, and fluid dynamics within such systems. Employing an enhanced paper-ranking methodology (NIRP 2.0), a curated portfolio of 54 key studies was established and analyzed through integrated bibliometric and systematic content analysis. The synthesis delineates prevailing modeling paradigms, spanning from continuum approaches to advanced discrete particle-resolved methods like computational fluid dynamics-extended discrete element method (CFD-XDEM), and provides a detailed discussion of their governing equations, submodel formulations, and numerical solution strategies. Particular emphasis is placed on scrutinizing common assumptions in critical subprocesses (drying, devolatilization, and char conversion) and on identifying persistent challenges in representing intraparticle gradients, bed shrinkage dynamics, and secondary reaction networks. The analysis reveals significant research gaps and emerging trends, underscoring the pressing need for more integrated, experimentally validated multiscale models. Consequently, this review serves not only as a comprehensive reference for current modeling practices but also as a strategic roadmap for developing next-generation simulation tools to advance the design, scale-up, and operation of industrial-scale pyrolysis reactors.