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A recycle flow flotation machine model

Authors:	CC Harris A Chakravarti SN Degaleesan

Institution:	Henry Krumb School of Mines, Columbia University, New York, N.Y. U.S.A.

Abstract:	Residence time measurements were made on a Denver laboratory flotation machine with and without the DR ring assembly. Soluble and insoluble tracers were used (a dye and fine quartz, respectively), and the variables studied were tank liquid volume, $V$ , water and air volumetric flow rates, Q and Q_A respectively, and some geometric and design variables.By analogy with nominal residence time, $t_{N} (= V Q)$ , a term “effective residence time” $t_{E}$ is defined by: $f (t)= exp ? t t_{E}$ where f(t) is the fraction of tracer remaining in the tank at time t. Perfect mixing is indicated if and only if: (i) data satisfies the exponential relationship; and (ii) $t_{E} t_{N} = 1$ .Using the soluble tracer the machine behaved substantially as a perfect mixer under all operating conditions, except with the DR ring at values of Q_A nearly double the natural aeration capacity of the machine; condition (i) above was satisfied, but $t_{E} t_{N} ～ 1.1$ .With the insoluble tracer the machine behaved as a perfect mixer only without air. As Q_A increased, $t_{E} t_{N}$ increased from unity to about 1.2, and the effect was emphasized by the DR ring. In all cases condition (i) above was satisfied.A model in which the flow pattern in the tank includes a large component of pulp recirculation through the impeller region is developed. This model can account for the experimental findings but the details remain to be elucidated.

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