Intrinsic Char Reactivity and Kinetic Analysis of Biogenic Residues in Pressurised Entrained-Flow Gasification under Industrial-Relevant Conditions

Char gasification kinetics of biogenic feedstocks like digestate, sewage sludge, pine wood and rhenish lignite as a fossil benchmark are investigated to identify the most suitable feedstock for entrained-flow gasification. By replicating valid char properties to those of commercial gasifiers and to ensure a robust reactivity assessment, the pyrolysis chars are prepared under the same conditions of 1400 °C, 10 bar, 2.4s in a pilot-scale, high-pressure, high-temperature entrained-flow reactor. The obtained chars are characterised in their surface-specific intrinsic reactivity with O₂, CO₂ and H₂O. The Power Law and the Langmuir-Hinshelwood approach are applied for kinetic modelling and evaluated towards their goodness of fit. The broad range of char properties among the feedstocks allowed to directly link the kinetic parameters to the fixed carbon-to-ash ratio and the specific Alkali-Index. The results indicate a strong dependency and demonstrate that inorganic components have a decisive influence on intrinsic reactivities. High-temperature char reaction rates are estimated via measured effectiveness factor, and show that digestate and sewage sludge achieve similar reactivities compared to coal, compensating for the lack of surface area through catalytic effects. The derived reaction rates are crucial for the modelling and design of industrial gasifiers, supporting the optimisation of operating conditions, cold gas efficiency and syngas quality.