Effect of design and operating parameters on gas hold-up in Pachuca (air-agitated) tanks

Abstract

Gas hold-up is a crucial parameter for liquid circulation as well as particle suspension in Pachuca tanks. These tanks, used as leaching vessels in hydrometallurgical industries, are air-agitated slurry reactors, cylindrical in cross-section with a conical bottom and usually equipped with a full-length central draught tube. In spite of the widely varying designs and operating parameters of Pachuca tanks, little attention has been paid hitherto to the gas hold-up in these tanks.

Extensive experiments on gas hold-up in laboratory-scale Pachuca tanks have now been performed. The effects of such design and operating parameters as tank height to tank diameter ratio (H _t/D _t), draught-tube diameter to tank diameter ratio (D _d/D _t), cone angle, superficial gas velocity, particle size and concentration were examined. It was found that gas hold-up in the draught tube increased with an increase in superficial gas velocity, but decreased with increase in H _t/D _t and D _d/D _t ratios, cone angle of conical bottom and tank diameter. It was also observed that gas hold-up increased in the presence of fine particles and decreased in the presence of coarser particles. A correlation–as a function of design and operating parameters, as well as the scale of the tank–has been developed as a first attempt to quantify the gas hold-up in Pachuca tanks.