Improving comminution efficiency using classification: An attainable region approach

Abstract: The AR for the fundamental processes of breakage and mixing was constructed in an earlier paper (Khumalo, N.; Glasser, D.; Hildebrandt, D.; Hausberger, B.; Kauchali, S. (2006). The application of the attainable region analysis to comminution. Chem. Eng. Sci., 61, 5969–5980). This work presents the AR constructed when the process of classification is combined with the processes of breakage and mixing. The process of classification extends the AR. An additional variable of energy consumption is introduced, increasing the dimensionality of the geometric construction from 2-D to 3-D. The AR shows that there is a linear relationship between consecutive particle size distributions with grinding time. However total energy consumption results in concavities when plotted against mass fraction in the median size class. This work demonstrates the degree to which there is an advantage of including the additional fundamental process of classification to particle breakage. The attainable region (AR) of a three particle size distribution can easily be represented graphically. Process targets can be inferred from these graphs. In our chosen system, the classification process has the effect of reducing total energy consumption by 95% to reach an objective of producing 92% of the material in the fines size class. This has cost implications since energy is often the predominant operating cost in size reduction systems. This work also shows that the benefits of classification are a function of the grinding extent for a system which consists of mono-sized feed particles. This suggests that classification should be introduced after some grinding at some point which is easily identified by analysing the AR construction. [Copyright &y& Elsevier]