PARTICLE SUSPENSION IN (AIR-AGITATED) PACHUCA TANKS

Particle suspension is an important parameter in the design of an ener gy-efficient Packuca tank. Unfortunately, very little attention has be en focused on the suspension behavior of air-agitated Pachucas. In the present investigation, therefore, extensive experiments have been car ried out in three laboratory-scale Pachuca tanks to examine the effect of design and operating parameters, as well as scale-up, on particle suspension. A mathematical model that combines the Bernoulli's equatio n and the theory of transport of particles in the horizontal flow of a liquid has been developed to predict the critical gas velocity for pa rticle suspension in Pachuca tanks. Some important results, crucial to the design and scale-up of Pachuca tanks, have emerged. Full-center-c olumn (FCC) Pachuca tanks with a draft tube-to-tank diameter ratio (D- d/D-t) on the order of 0.1 are found to be energetically more efficien t in suspending particles than free-air-lift (FAL) and stub-column (SC ) Pachuca tanks. It is also observed that taller tanks require lower a ir flow rates for particle suspension than shallower tanks. Finally, i t is explained why industrial Pachuca tanks operate at lower air veloc ities than laboratory-scale tanks.