Advances, challenges, and future directions in biomass gasification: A critical review of feedstock, reactor designs, and process optimization

• Comprehensive review of biomass gasification feedstocks and reactor designs. • Identifies key barriers in tar reduction, efficiency, and large-scale operation. • Evaluates pre-treatment, drying, and densification impacts on syngas quality. • Discusses thermodynamic and kinetic gasification models for process prediction. • Highlights biochar’s catalytic role in tar reforming and H 2 yield enhancement. • Outlines future directions for hybrid reactors and advanced syngas cleaning Biomass has recently gained recognition as a promising renewable energy resource with the potential to meet the growing global demand for continuous, clean power generation. Among thermochemical conversion technologies, gasification is considered one of the most viable approaches, offering cold gas efficiencies typically between 65% and 80%, depending on the feedstock and reactor design. Nevertheless, integrating producer gas into residential or commercial energy systems remains difficult due to technological and operational challenges. Critical issues include biomass supply chain management, pre-treatment and drying to achieve moisture content ideally below 15%, and effective gas cleaning and conditioning. Tar formation represents one of the most significant barriers, with levels commonly ranging from 2 to 10 g/Nm³, while for engine-grade applications, concentrations must be reduced to below 100 mg/Nm³. Similarly, particulates need to be controlled to less than 50 mg/Nm³, and alkali metals must be removed to prevent fouling and corrosion. Despite the development of various gasifier configurations, such as downdraft, fluidized bed, and plasma-assisted systems, an efficient and scalable design that achieves cold-gas efficiencies above 80% while maintaining tar concentrations below 0.1 g/Nm³ remains lacking. Recent research emphasizes that next-generation gasification systems integrated with advanced gas conditioning techniques—such as catalytic tar cracking, plasma reforming, and hot-gas separation—offer a pathway to overcome these obstacles. Such advancements would enable the production of high-quality syngas suitable not only for thermal power and combined heat and power (CHP) generation but also for hydrogen production.