Classifier Efficiency and its Application
Nobuhiro TAKAHASHI · Journal of the Mining and Metallurgical Institute of Japan · 1974
Classifier efficiency is a well-known criterion to represent classifier performances. It seems, however, that its practical merit has not been fully recognized and its application in industrial field has been limited. In this paper, the author discussed the character of classifoer efficiency and demonstrated its applicability in practice, principally in wet cyclone practice. Main features are as follows.1) Separation efficiency diagram presented in Fig. 1 is helpful to study the character of separation efficiency and classifier efficiency.2) Relationship between Tromp's partition curve and classifier effociency is made clear with classifier efficiency diagram that is a type of separation efficiency diagram in which partition curve is plotted (Fig. 2).3) The value of classifier efficiency can be calculated at any particle size. And the size dη, where the maximum value of classifier efficiency is obtained, may be the most reasonable one as the size of classification (Fig. 3). However, the determination of dη is so difficult that its application in practice will be limited.4) The size of equalizing misplaced material (ausgleichskorngröße) dH is one of the reasonable sizes of classification. The size dH and the classifier efficiency ηH which is defined at dH are easily determined as illustrated in Fig. 4, and are advantageous for practical applications.5) It is shown that ηH can be applied to predicting the size distributions of two products. The procedures are described (eq. 10 and Fig. 5).6) Effects of operational conditions to ηH should be known in order to apply ηH to prediction and/or evaluation of classifier performances. But it seems difficult to find out directly the relation between ηH and operational conditions.7) It is shown that the correction of void-filling material can be made on classifier efficiency in the same manner as in case of partition curve (Fig. 6), and ηH can be divided into two elemental efficiencies, one of which is the corrected classifier efficiency ηH' corresponding to the corrected partition curve.ηH=ηV×ηH'...(14)8) ηV is determined solely by pulp densities as shown in eqs.(15) and (16).9) ηH' would depend greatly on the distribution ratio of solid. Sixteen data of wet cyclones in operation under different operational conditions are calculated and plotted in Fig. 7 to show the correlation of ηH' to Zs which is the distribution of solid into underflow. It is suggested that the relation between ηH' and Zs would follow eq.(18), and the value of α would nearly be 0.4 in most cases.ηH'=α/1-(1-α) Zs...(18)10) ηH can be directly estimated by eqs.(19) or (20). The value of α would vary with operational conditions.11) The coefficient α means the limitation value ηH' or when Zs is decreased indefinitely to zero. The α values on examples in Fig. 7 are calculated as 0.35 to 0.56 by eqs.(21) or (22)α=ηH1-Zs/ηV-ZsηH...(22)12) It is suggested that the coefficient α would be applied to evaluating directly classifier performances with different pulp densities and/or different distribution ratio of solid.