Biomass and biochar pellet Gasification: a review of bridging feedstock heterogeneity, process parameters, and syngas quality

Fossil energy depletion and environmental concerns have driven the development of biomass energy, with biomass and biochar pellet gasification emerging as a promising utilization route. However, raw biomass heterogeneity and inefficient gasification processes hinder its large-scale application. This review systematically summarizes the integrated process of biomass pelletization, carbonization, and gasification, focusing on bridging feedstock variability, process parameters, and syngas quality. Key findings include: (1) Pelletization homogenizes feedstock physical properties (size, density, strength), reducing feeding clogging and improving heat/mass transfer, while combining with carbonization (pyrolysis, torrefaction, hydrothermal carbonization) further enhances energy density (>10 GJ/m3 for hydrothermal carbonization pellets), lowers moisture (to 5-7%), and mitigates pollutants (e.g., ∼40% chlorine removal via 400 °C pyrolysis). (2) Gasification performance is synergistically regulated by temperature (optimal ranges 700–1000 °C for most pellets), pellet size (smaller pellets boost H2/CO yields by 10–30%), heating rate, residence time, and catalysts (AAEMs enhance char reactivity; Ni-based catalysts double H2 yield and reduce tar). (3) The pelletization-carbonization-gasification linkage mechanism reveals that tailored pellet properties (porosity, density) and matched reactor/catalyst designs are critical for optimizing efficiency. Emerging trends include integrated process intensification, pellet-specific catalyst development (e.g., AAEM-promoted Ni composites), and real-time parameter adjustment via monitoring technologies. Under-researched areas include cost-effective pellet production for low-moisture feedstocks, ash sintering control in agricultural residue pellets, and long-term catalyst stability in industrial-scale systems. This review provides a theoretical foundation for process optimization and promotes the industrialization of biomass pellet gasification by addressing core technical bottlenecks.