Agglomeration dynamics in non-reactive fluidized beds: mechanisms, regime transitions, and engineering controls

Gas-solid fluidized bed technology has been extensively used in industries such as powder processing, pharmaceutical manufacturing, catalytic cracking, food production, mineral processing, coating, combustion, and gasification. While particle agglomeration in gas-solid fluidized beds is often promising in applications like granulation, coating, catalysis manufacturing, and food industry, it remains a major operational challenge when it occurs unintentionally. Undesirable agglomeration, driven by mechanical stress, particle size distribution, or interparticle forces such as capillary, electrostatic, adhesive, and chemical bonding, can alter the characteristics of bed hydrodynamics, leading to channeling, defluidization, or complete system failure, particularly at high-temperature or high-moisture conditions. A narrow threshold distinguishes desirable from unintended agglomeration, identifying the crucial transition point despite its complexity. Although several approaches for in-situ detection exist, unintended agglomeration is occasionally inevitable due to intrinsic material properties, the magnitude of interparticle forces, or process instabilities. Consequently, effective mitigation techniques must be utilized to ensure process stability and product quality. This review examines the dual function of agglomeration in non-reactive fluidized beds, emphasizing on the thin line between its positive and detrimental effects. We critically examine recent advances in detection methods and strategies for agglomeration control through reactor design, surface engineering, and externally assisted forces.