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.

Get full access to this article

View all access options for this article.

References

Hallett

C. J

. Oxygen mass transfer in Pachuca tanks. Ph.D. the-sis, University of London, 1981.

Roy

G. G.

and Shekhar

. Oxygen mass transfer in air-agitated Pachuca tanks—Part 1: laboratory-scale experimental measurements. Trans. Instn Min. Metall. (Sect. C: Mineral Process. Extr. Metall.), 105, 1996, C9-15.

Roy

G. G.

and Shekhar

. Oxygen mass transfer in air-agitated Pachuca tanks—Part 2: mathematical modelling of volumetric mass transfer coefficients. Trans. Instn Min. Metall. (Sect. C: Mineral Process. Extr. Metall.), 105, 1996, C16-21.

Roy

G. G.

, Shekhar

and Mehrotra

S. P

. Particle suspension in (air agitated) Pachuca tank. Metall. Materials Trans., 29B, 1998, 339–49.

Shah

Y. T.

Design parameter estimation for bubble column reactors. Am. Inst. chem. Engrs 1., 28, 1982, 353-79.

Akita

and Yoshida

. Gas holdup and volumetric mass trans-fer coefficient in bubble columns. Ind. Eng. Chem. Proc. Des. Dev., 12, 1973, 76.

Hikita

and Kikukawa

. Liquid phase mixing in bubble columns: effect of liquid properties. J. chem. Engng japan, 8, 1974, 191.

Koide

, Hiroyuki

and Shinji

. Gas holdup and volumetric liquid phase mass transfer coefficient in bubble column with draught tube and gas dispersion in the draught tube. J. chem. Engng japan, 16, 1983, 413–9.

Koide

Gas holdup and volumetric liquid phase mass transfer coefficient in solid suspended bubble column. J. chem. Engng Japan, 18 (3), 1985, 248–54.

10.

Bukur

D. B.

, Patel

S. A.

and Daly

J. G

. Gas holdup and solid dispersion in a three phase slurry bubble column. Am. Inst. chem. Engrs 1., 36, 1990, 1731-5.

11.

Hague

M. N.

, Nigam

K. P.

and Joshi

J. B

. Hydrodynamics and mixing in highly viscous pseudo-plastic non-Newtonian solution in bubble column. Chem. Engng Sci., 41, 1986, 2321-31.

12.

Pandit

A. B.

and Joshi

J. B

. Three phase sparged reactors—some design aspects. Rev. them. Engng, 2, 1984, 1-84.

13.

Sada

, Kumazawa

and Lee

C. H

. Influence of suspended fine particles on gas holdup and mass transfer characteristics in a slurry bubble column. Am. Inst. chem. Engrs 1., 32, 1986, 853-6.

14.

Kato

The behavior of suspended solid particles and liquid in bubble column. J. chem. Engng japan, 5, 1972, 112-8.

15.

Ostergard

. On the growth of air bubbles formed at a single orifice in a water fluidized bed. Chem. Engng Sci, 21, 1966, 470-2.

16.

Ying

D. H.

, Givens

E. N.

and Weimer

R. F

. Gas holdup in gas liquid and gas liquid solid flow reactor. Ind. Engng Chem. Proc. Des. & Dev, 19, 1980, 635-8.

17.

Clark

K. N

. The effect of high pressure and temperature on phase distribution in a bubble column. Chem Engng Sci., 45, 1990, 2301–7.

18.

Jamialahmadi

and Muller-Steinhagen

. Effect of solid par-ticles on gas holdup in bubble column. Can. J. chem. Engng, 69, 1991, 390-3.

19.

Banisi

Effect of solid particles on gas holdup in flotation column 1. Measurement. Chem Engng Sci, 50, 1995, 2329-34.

20.

Dharwadkar

S. V

, Sawant

S. B.

and Joshi

J. B

. Gas holdup in highly viscous pseudoplastic non-Newtonian solution (CMC soln) in three phase sparged reactor. Can. J. chem. Engng, 65, 1987, 406.

21.

Finch

J. A.

and Dobby

G. S

. Column flotation (Oxford: Pergamon, 1990).

22.

Banisi

E. Effect of solid particles on gas holdup in flota-tion column II. Investigation of mechanisms of gas holdup reduction in presence of solids. Chem Engng Sci, 50, 1995, 2335-42.

23.

Shekhar

and Evans

J. W

. Fluid flow in Pachuca (air-agi-tated) tanks: Part II. Mathematical modelling of flow in Pachuca tanks. Metall. Trans., 21B, 1990, 191-203.