Experimental Investigation on Transport Characteristics of Fluidized Geldart A/B Particles in a Geldart D Packed Bed

Redox reactions between fine solid fuels, such as pulverized coal powder, and coarse oxygen carrier particles can be carried out in a fixed/moving bed reactor chemical looping system. 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. A number of challenges exist in transporting/mixing of fuel powder and in removing noncombustible 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 situations. This study describes an experimental approach that examines migration characteristics of fine particles (Geldart A/B), in both spatial and temporal aspects, in a packed bed of coarse particles (Geldart D). The experimental variables include the particle size distribution of the fine powder, the fine to coarse mass ratio, and flow conditions. At a given upward aeration flow within the range that is higher than the terminal velocity of the fine particles but lower than the minimum fluidization velocity of coarse particles (U-t < U-s < U-mf,U-c), the fine particles may travel both upward and downward depending on the gas flow rate and the physical properties of particles and gas. The spatial transport pattern in terms of the upward and static transport partition (wt %) of Geldart A particles can be characterized as an exponential function of a group of dimensionless numbers (e.g., Stk*, Re-p* and U-s/U-t). The time-dependent upward transport rate of fine particles is measured to determine the temporal migration characteristics. Cluster response time (tc) is introduced to describe how fast a cluster of fine particles in a packed bed respond to the ambient flow. This parameter is normalized by the response time of fine particle (tp) and further correlated with the pseudo-particle Reynolds number (Rep*) via an inverse power function with two coefficients.