Hydrodynamics of cohesive carbon particles in fluidized beds for methane pyrolysis: Mixing, transport, and selective entrainment

Abstract

Methane pyrolysis is a promising carbon‐free pathway for hydrogen production that generates hydrogen and solid carbon without direct CO ₂ emissions. Fluidized bed reactors are attractive for this process due to their excellent heat transfer and potential for continuous carbon removal; however, the hydrodynamics of cohesive carbon particles remain poorly understood. In this study, cold‐flow fluidized bed experiments were conducted to investigate the hydrodynamic behaviour of activated carbon and catalyst‐modelling particles. Activated carbon exhibited cohesive fluidization behaviour, and hydrodynamic analysis based on the experimentally measured minimum fluidization velocity suggested an effective agglomerate diameter of approximately 337 μm, which is much larger than the primary particle size (22.6 μm). Binary particle experiments showed density‐driven segregation at low gas velocities, while enhanced solids circulation promoted catalyst‐carbon mixing above the catalyst minimum fluidization velocity. Transport velocity measurements revealed a large disparity between carbon (≈0.65 m/s) and catalyst particles (≈2.0–3.1 m/s), enabling selective carbon entrainment and recovery using conventional gas–solid separation systems with recovery efficiencies exceeding 98%–99%. These findings provide new hydrodynamic insights into cohesive carbon fluidization and establish a basis for the design and scale‐up of methane pyrolysis fluidized bed reactors with continuous carbon removal capability.