Scale-up of mechanically agitated flotation processes based on the principles of dimensional similitude

[摘要] ENGLISH ABSTRACT: The use of dimensional analysis to scale-up mechanically agitated flotation processesand to identify deficiencies in froth flotation plants was explored. The full range ofoperating variables was considered, such as particle size distribution, reagent suite,conditioning time, retention time, machine geometry, aeration, solids suspension, powerrequirements and turbulence. Dimensional analysis offers a methodology to combinevariables into dimensionless groups to guide the scale-up process based on the notion ofsimilarity. Ten dimensionless groups were developed and combined with metallurgicalvariables, such as liberation, reagents dosage and flow diagrams to produce a scale-upand evaluation tool, applicable to any mechanically agitated flotation process. In manyhydrodynamic studies, the researchers considered hydrodynamic variables based onrotor diameter. In this case the hydrodynamic variables based on rotor diameterrepresent mechanism 'ability, while parameters based on cell diameter are considered'requirement.Dimensionless groups have also been applied to the definition of basic parameters of thekinetic constant, such as floatability, bubble surface area flux and froth recovery factor.It also showed that the bubble surface area flux has a maximum with increased aeration,where similar models do not show this dependence.Analysis by computational fluid dynamics and Perspex modelling revealed valuableinsight into the inner working of the Wemco flotation machine, such as air dispersion,turbulence levels, separation zones and solids concentration. Design changes to therotor, disperser, hood and geometrical lay-out produced a marked improvement inflotation conditions. It also supported certain dimensionless numbers measured in fullscale plants.Case studies confirmed that almost all flotation plants, irrespective of the mineralsfloated, suffer from the same deficiencies. Dimensional similitude offers a unique tool toidentify these deficiencies and to predict the effect of recommended improvements. Inalmost every case where the fundamental requirement of similarity was applied, animprovement in performance was observed. Finally a new algorithm is proposed for thescale-up of flotation plants and the application is demonstrated in the design and testingof a pilot plant.

[发布机构] Stellenbosch University