Particle suspension in air-agitated pachuca tanks: Investigation of hysteresis and a novel split air injection technique

Abstract

Particle suspension is an important parameter in the design of an energy-efficient Pachuca tank. The objectives of the present investigation are to (1) establish the phenomenon of hysteresis, (2) examine the effect of a novel split air injection technique on the critical velocity for particle suspension, and (3) determine the optimum state of suspension in full center column (FCC) Pachuca tanks. Extensive investigations have been carried out in three laboratory-scale Pachuca tanks with a maximum slurry density of 25 wt pct solids. Results that have a bearing on the design of energy-efficient Pachuca tanks have emerged. The magnitude of hysteresis in FCC Pachuca tanks is of the order of 20 pct, which is about 10 times less than in bubble columns. Split air injection, with 30 pct air injected into the annulus from the top and 70 pct air injected into the draft tube from the bottom, lowers the critical air velocity for particle suspension by 37 pct, with respect to bottom-blown Pachuca tanks.