(350d) Experimental Investigation on Transport Characteristics of Geldart a&b Particles in a Geldart D Packed Bed

Redox reactions between fine solid fuels, such as coal powder, and coarse oxygen carrier particles take place in a fixed/moving bed reactor of chemical looping systems. The migration pattern of the solid fuel powder and its contact time with coarse particles can significantly affect the reaction rate and the product yield. Challenges exist in transporting/mixing of fuel powder and in removing non-combustible waste (e.g., coal ash) from the reactor vessel in the chemical looping operation. Thus, it is important to understand the hydrodynamic behaviors of fine particles in such situation. This study describes an experimental approach that examines fine particles (Geldart A & B) migration characteristics in a packed bed of coarse particles (Geldart D). Variables for the tests include the particle size distribution of the fine powder, the fine to coarse mass ratio, and flow conditions. Given the gas flow from the bottom of the bed, fine particles can travel both upward and downward depending on the gas flow rate and the particles physical properties. The trend of the upward transport partition (wt%) with respect to superficial velocity is characterized an “S” shape. Time-dependent upward transport amount of fine particles in various conditions is obtained to determine the fines migration rate. The parameter, cluster migration response time (τ_c), is introduced to describe how fast a cluster of fine particles in a packed bed will respond to its ambient flow condition. The results of cluster migration response time in all tested cases are able to be normalized by the particle response time (τ_p) and further correlated in terms of the particle Reynolds number (Re_p) via an empirical equation with two coefficients.