Methodologies for the evaluation of grinding media consumption rates at full plant scale

Abstract

Due recognition of the significant impact of the cost of grinding media on the overall economics of comminution facilities worldwide has created the need for reliable, practical methodologies to compare—over extended control periods—different operating conditions, arising from eventual changes in ore type, ball supplier or simply, a trial of new products from the same supplier. The current publication describes the main aspects to be considered in the planning and execution of a full scale evaluation campaign, the actual data to be recorded and the required calculation routines, including the theoretical framework justifying their applicability. The Linear Wear Model, herein described, provides a theoretical framework for the best estimations of comparative grinding media wear performance (in the absence of ball breakage) in any given application, on the basis of the Specific Wear Rate Constant, k d E (μm/(kW h/ton)), derived from the Specific Consumption Rate (gr/kW h), corrected by actual make-up ball size (mm). When significant ball breakage is to be expected—as in semiautogenous grinding (SAG) applications—an expanded, conceptual model, based on pilot Drop Ball Testing (DBT) results is gaining acceptance as a way to incorporate breakage as a possible media consumption mechanism. Ideally, evaluations should be conducted in parallel grinding sections, in order to have the option of establishing multiple sequential, concurrent or cross-reference comparisons. The evaluation period should cover at least 6 months after the complete ‘purge’ of the string of balls being substituted, which may well take from 3 to 6 months. As a result, the evaluation period required for reliable conclusions should typically exceed 9–12 months of fairly undisrupted, normal operation. The methodologies here proposed make intensive use of Moly-Cop Tools, a software package developed by the international Moly-Cop Grinding Systems organization (formerly, ARMCO Worldwide Grinding Systems) with the specific purpose of helping process engineers characterize and evaluate the operating efficiency of any given grinding circuit, following standardized methodologies and widely accepted evaluation criteria.