Studies on Particle Suspension in Air-agitated Pachuca tanks

Abstract

The paper presents the findings of an investigation involving extensive experiments on three laboratory scale Pachuca tanks to examine the effect of design and oper-ating parameters, as well as scale up on particle suspension. Some important results, crucial to the design and scale up have emerged. Full center column (FCC) Pachucas with a draft tube to tank diameter ratio (Dd/Dt) on the order of 0.1 are found to be energetically more efficient in suspending particles than Free-Air.Lift (FAL) and Stub Column (SC) Pachuca tanks. It has been established that the energy required for generating suspension from settled particles is more than that is required for maintaining the particles already in suspension. The magn-itude of hysterisis in FCC Pachuca tanks is of the order of 20%. Effect of novel split air injection technique on critical velocity for particle suspension has been rigorously investigated. Split air injection, with 30% air injected into the annulus from top and 70% air injected from the bottom into the draft tube lowers the critical air velocity for particle suspension by about 37% with respect to bottom blown Pachuca tanks. Mechanisms for particle suspension in bottom blow Pachucas as well as those with split air injection are proposed.