MACROSCOPIC FLOW STRUCTURES IN A BUBBLING PAPER PULP-WATER SLURRY

The hydrodynamic characteristics of three-phase slurry columns contain ing water, paper fibers, and air have been experimentally investigated . Such systems are relevant to flotation deinking, a critical but poor ly understood separation process in the production of recycled paper. Two transparent bubble columns were used, one for quiescent liquid and one for cocurrent air and Liquid flow. Water and dilute aqueous pulp slurries were studied using gamma-densitometry to obtain local gas hol dup (void fraction). Results in pulp slurries were significantly diffe rent than in pure water. In the quiescent flow system, network formati on alters bubble size distributions and promotes transition to regimes with lower interfacial area. In contrast, with cocurrent flow, gas ho ldup and interfacial area can be greater in pulp slurries than in pure water. Results are explained in terms of the effects of fibers and fl ocs on flow behavior. Potential applications of this work for improved deinking performance are discussed.