(91b) Effects of Fine Powder Accumulation and Interstitial Gas Flow Rate On the Formation of Particle Bridging In a Moving Bed

Bridging (or arching) of non-fluidized solids particles is a particularly dangerous hazard in the operation of particle handling moving bed system. The analysis of arching mechanism lies on the particulate media mechanics which is originally developed for the discharge characteristics of powders from hoppers with particle layer stress analysis. However, bridging may occur even when the moving bed system is originally designed correctly to allow desired continuous mass flow of solids particles. Experimental study reveals the appearance of bridging of solids particles normally accompanies with appearance and accumulation of fine powders among the moving coarse particles and the change of interstitial gas flow. The counter-current interstitial gas flow provides an opposite resistant in terms of interphase drag to prevent continuous solids flow driven by gravity. Its change may account for stress redistribution inside the layered particles, which yields an interlock among particles and forms a bridge.  The accumulation of fine powders may alter the hydrodynamic characteristics of solids particles as well as greatly decrease the local voidage inside the moving bed. The decrease of voidage may significantly increase the inter-phase drag while the change of hydrodynamic characteristics may change the tendency of bridging of solids particles. In the proposed study, a theoretical stress analysis on layered particles in a vertical moving bed with counter-current interstitial gas flow, which takes into account of the effects of characteristics of fine powder, such as size distribution and volume fraction, and the gas flow rate, will be developed to predict the appearance of bridging phenomenon. Experiments will be performed to validate the theoretical predictions for different combinations of fine powder distribution, percentage and gas flow rates.