Article

Diameter factors affecting ball mill scale-up

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Abstract

In some plants the performance of large diameter ball mills is not as efficient in energy consumption as predicted from the performance of laboratory and pilot-plant ball mills. Ball mill scale-up is primarily by increasing mill diameter. This is subject to diameter relationships varying from the square root of the diameters in an inverse ratio to the diameters raised to the 2.5 exponent in a direct ratio. Another relationship is the ball diameter to mill diameter factor. This determines the number of layers of balls in the mill and the proportion of impact, abrasion and attrition grinding that occurs in a specific ball mill. Additional research work is needed on scaling-up laboratory and pilot-plant ball mill data to predict the performance of large diameter ball mills.

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... A widely known incorrect use of Bond method is its application to assess efficiency of SAG mills, as the internal breakage mechanisms typically result in nonparallel feed and product distributions (Napier-Munn et al., 1996;Amelunxen & Meadows, 2011). This discrepancy is often compensated by applying various correction factors (Barratt & Allan, 1986;Rowland, 1988) and alternate power factors (Hukki, 1961;Morrell, 2004a). An example is presented in Figure 2.38 that illustrates three size distributions obtained from a conventional SABC circuit representing the primary crusher product, the SAG trommel undersize, and the hydrocyclone overflow (Ballantyne, 2020). ...
Thesis
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Comminution, which refers to the process of rock breakage, is an extremely energy-intensive activity in mineral processing. It consumes approximately 37% of the total energy used in mining operations. This process suffers from notable equipment-related inefficiencies. If opportunities for improving this process can be identified, these could lead to significant economic and environmental advantages. However, identifying such opportunities is challenging due to the inherent limitations of the current standard methods used to evaluate comminution circuits. Many of these standards are either based on empirical approaches or lack effectiveness in accurately determining equipment efficiency. Additionally, the existing methods for measurement are excessively laborious and require large sample sizes. These factors can compromise: the accurate characterisation of an orebody when conducting variability test programs; benchmarking studies to evaluate comminution circuit performance; or assessment of the suitability of new technologies. To address these issues, it is proposed that a measure of the practical minimum energy required for comminution, which offers the realistically achievable efficiency of comminution circuits, can provide the benchmark against which to compare current and future technologies and processes. Secondly, the method needs to be simple, relatively fast and have minimal sample requirements. This thesis is focused on developing a novel ore characterisation method for the precise measurement of practical minimum comminution energy. A monolayer of particles is broken using a precision rolls crusher (PRC) – a rigidly mounted (double) roller mill instrumented with precise torque measurement hardware. The torque transducers are mounted on rolls shafts to measure the breakage response of rock particles in the form of precise torque and angular speed readings, which are then converted into energy. Significant efforts have been made to isolate the effect of the grinding environment on breakage and achieve energy measurement at the primary fracture of rock particles. The test iteratively crushes feed particles down to final product size in many controlled breakage stages. The generation of fines in each breakage stage is then plotted as a function of input energy. The inverse of the gradient of this plot provides the size specific energy (SSE) in kWh/t of material generated below a predefined marker size. The PRC has been applied for benchmarking on-site comminution circuits and evaluating the performance of other testing methods that involve different modes of breakage, such as bulk grindability, bed breakage, and single particle breakage. The on-site circuits were found to be inefficient, using 3.2 to 3.8 times more energy than the PRC when using 106 µm marker. Similarly, lab-HPGR exhibited inefficiencies of 2.4 to 2.9 times, while the Instrumented Bond ball mill (IBM) showed even greater inefficiencies, ranging from 3.4 to 3.9 times. These results demonstrate that the PRC has potential to be used as a suitable choice for ore characterisation applied to quantifying the performance of industrial circuits. Additionally, there is potential for the PRC to evolve into a geometallurgical ore characterisation test – it is simple, fast, requires small sample mass (~300 g), and covers a wide feed particle size range (12 mm to 75 µm). Moreover, the analysis of relative size specific energy ratio of full-scale comminution circuits and testing methods in relation to the PRC showed that common concept of comminution efficiency being an absolute number is a myth, with efficiency instead being dependent on the product size against which it is assessed. Finally, fractal dimension analysis was employed to study breakage behaviour of different ore types in the PRC, revealing a transition in breakage mode as the gap decreased during progressive breakage experiment on the PRC. The transition went from less efficient mode of breakage (crushing/ crack branching) at coarser gaps to more efficient mode of breakage (bulk splitting) at finer gaps.
... Elevando-se o percentual de sólidos no moinho, há um aumento na eficiência de moagem e redução considerável no consumo de bolas, até um certo ponto, quando a eficiência começa a decrescer [4]. Rowland [5] De acordo com Ribeiro et al. [8], que estudaram a influência do formato do corpo moedor na eficiência da moagem para produção de "pellet-feed", os testes industriais e de uma planta piloto confirmaram uma melhoria de eficiência de moagem de cerca de 26%, quando se substituiu a carga de cylpebs de 28 mm por uma de bolas formada por 50% de bolas de 30mm e 50% de 40mm de diâmetro. Em seus estudos, Taggart [4] e Apud von Krüger [9], mostraram que a carga de corpos moedores é a responsável por gerar trabalho útil, e a intensidade desse trabalho é função da forma, tamanho e quantidade dos corpos moedores e do material de que eles são feitos. ...
... Higher color gradient in the evolution plot of the frequency spectrum between 160-640 Hz decreases with increasing milling time and decreasing particle size distribution.The number of spectral peaks also increases with increasing milling time.This indicates the effectiveness of collision by alumina balls in the processed ilmenite material using dry milling and has potential implications for the use of a more controlled and efficient ball mill in the future of ceramic industry. [17], jumlah bahan yang dimasukkan [18], kecepatan putaran ball mill [19], waktu milling [20] hingga pemantauan proses milling [21]. ...
... However, the energy imparted to the slurry during its passage through the mill will also increase. Rowland (1988) provided a similar view and suggested that in III-190 larger diameter mills residence time was important as well as ensuring slurry velocity was not so great that it disrupted grinding action. It is therefore instructive to look at a range of operational mills and see whether the data indicate whether the Bougainville mill suffered from these problems and whether they were diameter related. ...
... It is widely known that by calculating the energy efficiency using the Bond equation, AG/SAG circuits appear significantly less efficient. A number of researchers have attempted to account for this with a range of correction factors (Barratt and Allan, 1986;Rowland, 1988) and alternative power factors (Hukki, 1961;Morrell, 2004). The underlying reason for the discrepancy is that the Bond equation requires parallel feed and product size distributions in log/log space. ...
Article
This paper explores the relationship between energy and the generation of minus 75 micron material. Rittinger's law of comminution states that the energy input is proportional to the generation of new surface area. An accurate and consistent measurement of surface area, applicable across multiple size ranges, is required to apply this practically. The amount of new − 75 μm material generated has previously been proposed as a proxy for surface area. This has been demonstrated to some extent on a range of different laboratory equipment, but not in a manner suited to equipment-independent ore characterisation. To this end the JK Rotary Breakage Tester (JKRBT) and Schönert breakage device have been used to measure the progressive production of fines from cumulative single impacts starting with 37.5 mm particles down to 250 μm. As per expectation, the generation of − 75 μm material was found to be proportional to the specific energy, but there was a secondary influence of size. A model was developed to describe the breakage and it was found that the standard t10 relationship could be used to effectively calculate the size specific energy. Measuring the intrinsic competence of an ore in this way can then be used to assess the energy efficiency of full-scale mills in relation to a lab scale test. It is envisaged that this relationship also has the potential to be used in the design of new comminution circuits. The methodology and the results from its application are presented for discussion and review.
... As with circulating load, the aspect ratio must be chosen as to reduce overgrinding (large LID) (Rowland, 1988). Large diameters also result in a coarser charge and promote efficient breakage. ...
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Wills' Mineral Processing Technology provides practising engineers and students of mineral processing, metallurgy and mining with a review of all of the common ore-processing techniques utilized in modern processing installations. Now in its Seventh Edition, this renowned book is a standard reference for the mineral processing industry. Chapters deal with each of the major processing techniques, and coverage includes the latest technical developments in the processing of increasingly complex refractory ores, new equipment and process routes. This new edition has been prepared by the prestigious J K Minerals Research Centre of Australia, which contributes its world-class expertise and ensures that this will continue to be the book of choice for professionals and students in this field. This latest edition highlights the developments and the challenges facing the mineral processor, particularly with regard to the environmental problems posed in improving the efficiency of the existing processes and also in dealing with the waste created. The work is fully indexed and referenced. · The classic mineral processing text, revised and updated by a prestigious new team · Provides a clear exposition of the principles and practice of mineral processing, with examples taken from practice · Covers the latest technological developments and highlights the challenges facing the mineral processor · New sections on environmental problems, improving the efficiency of existing processes and dealing with waste.
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Process of Size Reduction Crushing and grinding calculations
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Wet autogenous grinding in tumbling mills
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Calculation of ball mill powers — especially for small mills
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