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Improved Particle Liberation by High-Velocity Comminution – the new VeRo Liberator®
Abstract
The new VeRo Liberator® has been recently developed by PMS, Hamburg, Germany, and represents a highly efficient impact crushing system for dry comminution of ore, slag, armoured concrete, and aggregate in the 100 t per hour throughput class. The VeRo Liberator® operates with a vertical axle-in-axle system, which is equipped with a total of up to 144 hammer tools, each approximately 90 cm long. The hammer tools rotate on three levels clockwise and anticlockwise against each other at high rotation speeds. The gravitational flow of the material through the machine results in a very low energy consumption. The multiple high-velocity impacts of the tools inflicted on the material achieve unparalleled reduction ratios of up to more than 400 without clogging the system. The VeRo Liberator® achieves also an unusually high degree of particle liberation. Intergranular breakage is the predominant form of particle separation and is caused by the high velocity impacts, inflicted by the hammer tools, casing, and particles on each other. Apparently, the shock waves travelling through the impacted material stimulate the particles to react individually according to their elasticity “E” and compressibility “K” moduli. The specific “reaction” of the various shock-stimulated particles leads apparently to the pronounced intergranular breakage, separation, and thus particle liberation.
... Comminution has existed from ancient times [1] and is known to be the largest consumer of energy in mining operations [2]. It is comprised of the crushing and grinding stages with the former being 10 to 20 times more energy-efficient compared to the latter [3]. In mining-intensive countries like South Africa and Australia, there is always a need to continuously evaluate innovative technical solutions that come in the forms of circuit optimisation or development of new equipment. ...
... The deflection of particles towards internal hard surfaces in a crusher creates further chances for breakage. When the particles are inhomogeneous, as most ores, various components in the composite particle react differently in accordance with their specific compressibility and elasticity moduli resulting in tension and shear stress between different components and thus promoting more breakage along phase boundaries [3]. The consequence is the predominance of intergranular rather than cross-granular fracturing, which results in a high degree of particle liberation. ...
... Whiten [11] initiated the modelling on which most work on cone crushers is based. Napier-Munn et al. [3] and Kojovic et al. [12] extended this approach to vertical impact crushers. Segura-Salazar et al. [13] used the same Whiten model supplemented by the equations describing the variation of parameters K3 and T10 in the classification function and the breakage function respectively, which were described as functions of feed rate and rotor speed. ...
A number of experiments were conducted on a laboratory batch impact crusher to investigate the effects of particle size and impeller speed on grinding rate and product size distribution. The experiments involved feeding a fixed mass of particles through a funnel into the crusher up to four times, and monitoring the grinding achieved with each pass. The duration of each pass was approximately 20 s; thus, this amounted to a total time of 1 min and 20 s of grinding for four passes. The population balance model (PBM) was then used to describe the breakage process, and its effectiveness as a tool for describing the breakage process in the vertical impact crusher is assessed. It was observed that low impeller speeds require longer crushing time to break the particles significantly whilst for higher speeds, longer crushing time is not desirable as grinding rate sharply decreases as the crushing time increases, hence the process becomes inefficient. Results also showed that larger particle sizes require shorter breakage time whilst smaller feed particles require longer breakage time.
... Accompanying scientific research on the characterisation of feeds and products continued but was extended to research, trying to understand the functional principle of the VeRo Liberator® that delivers such innovative and drastically more efficient unintended comminution results. The university research team was enlarged by including the rock mechanics group, to test the initially proposed comminution mechanism (Borg et al. 2015a) and to refine it to our current understanding (Borg et al. 2015bBorg et al. , 2015cBorg et al. , 2016and this paper). Market entry has been achieved in late 2016, when Anglo American, after a series of comminution tests on different ores, ordered a bespoke VeRo Liberator®, specially designed to be used in a large‐scale pilot test at one of their operations. ...
... These materials include primary ores of metal commodities such as copper, lead, zinc, tungsten, molybdenum, gold, and platinum as well as industrial minerals such as graphite, fluorite, barite, limestone, diatomite, nepheline syenite and others. The following examples of test‐comminuted materials are thus not intended as presentation of full investigation results, some of which have been published elsewhere already (Borg et al. 2015aBorg et al. , 2015bBorg et al. , 2015cBorg et al. and 2016). Additional comprehensive fact sheets, covering the test‐comminution results of most bulk samples tested so far, are also available ‐ unless confidential ‐ upon e‐mail request from PMS. ...
... This observation is relatively well known in other disciplines and has been researched and documented for fracture development (or rather fracture prevention) in technical, laminated composite materials of different viscosity and/or brittleness (Bloyter et al. 1999). The theoretical explanation for such a separation of minerals due to different moduli of deformation (deformation modulus or Young´s modulus) has already been described and illustrated in a previous publication (Borg et al. 2015a) and is apparently one of the causes but probably not the only one. An additional significant aspect is apparently the velocity‐dependence and thus time‐dependence of comminution processes inside the VeRo Liberator®. ...
The efficiency improvement in the comminution of ores has been on the international agenda of the mining industry for some time but substantial advances are still relatively scarce. It is generally agreed upon that major goals include a substantially reduced energy consumption, systems that operate dry, markedly enhanced particle size reduction, and improved particle liberation. The VeRo Liberator® has been invented some five years ago and applies a completely new, mechanical comminution principle, which applies high‐velocity and high‐frequency impact comminution. The industrial scale 100 t/h VeRo Liberator® prototype features a vertical four‐fold axle‐in‐axle system, equipped with a large number of hammer tools, which rotate on three levels clockwise and anticlockwise against each other. The resulting high‐frequency, high‐velocity impacts cause a highly turbulent particle flow and trigger fracture nucleation and fracture propagation preferentially at and along phase boundaries. Breakage occurs from the high‐velocity stimulation of particles, where the elasticity and compressibility modules control differential particle behaviour. This differential behaviour results in the build‐up of stress along particle boundaries and eventual failure and breakage nucleation on mineral phase boundaries. Fracture nucleation and fracture propagation on particle boundaries rather than cross‐ boundary breakage explains the high degree of liberation and low energy consumption, compared to traditional comminution systems that feature breakage development parallel to 1 between point‐loads. Current research and high‐velocity impact experiments support our postulated breakage principle and further our understanding of this new and unconventional comminution process. The improved breakage behaviour results in a drastically reduced energy consumption of between 3 and 13 kWh/t, very high degrees of particle liberation, and particle size reduction ratios of up to 6.250 in single pass comminution. The VeRo Liberator® can either replace several conventional comminution steps or can reduce the application of less (energy) efficient technique to a minimum. The invention and production of the first industrial‐scale prototype (2011‐2012) was followed by extensive test comminution of bulk samples of a wide range of typical ores from various mines around the world (2012‐1014). This test work was accompanied by independent geometallurgical and mineralogical documentation and research (2013‐2015). In‐house presentations to mining houses and at international comminution conferences drew strong industrial interest and resulted in even more extensive test comminution of various types of industry‐supplied ores and smelter‐slags (2015‐2016). Presently, the first industrial‐scale pilot test phase is being launched jointly by PMS and Anglo American to test the VeRo Liberator® at one of their operations beginning in 2017.
... This, however, comes at great energy expense, since particles have to be ground to sizes below 100 µm to achieve meaningful liberation. Unfortunately, the larger amount of energy applied to the comminution process does not contribute to particle breakage, but is rather wasted on processes such as driving the mechanical parts of the equipment, heat, and sound energy [1]. Comminution comprises crushing and grinding, but the former has been proven to be 10 to 20 times more energyefficient than the later [2]. ...
The Discrete element method (DEM) is an invaluable tool for studying comminution as it provides detailed information that can help with process analysis as well as trying out new equipment designs before the equipment is physically built. The DEM was used to analyse previous experimental work to gain some insight into the comminution process in an impact crusher with a single impeller. Further DEM simulations were done on a crusher with a second impeller installed. The energy spectra and threshold energy levels calculated from the drop-weight test were used as the basis of comparison. The simulations indicate that even at much lower speeds, the performance of a double impeller impact crusher is exceedingly superior. However, the energy associated with the double impeller impact crusher is much higher and energy intensification, rather than energy efficiency, is the main gain of the double impeller design. The double impeller also offers more operational flexibility, such as spacing between the impellers, which can be tailored to the particle size range being handled.
... The input energy is lost during the particle breakage to other processes with very little energy contributing to particle breakage. The lost energy is wasted on processes such as driving the mechanical parts of the equipment, heat, and sound energy [3]. This problem has been haunting the mining industry from birth and over time; it became more and more pronounced owing to the increase in mining costs brought about by the depletion of high-grade ores, among other issues. ...
The attainable region (AR) is an optimization method adopted for use in comminution to achieve different objective functions, which all converge to optimising the production of the desired particle size distributions for downstream processes. The technique has so far mostly been used to optimise the breakage of particles in tumbling mills. It achieved the desired purpose by unveiling all possible outcomes derived from a combination of operational parameters that are bound by trajectories showing the limitations of a system. The technique has given the scientific community lenses to see the behaviour of different parameters in ball mills otherwise known as the black boxes due to their concealing nature. Since its inception, the AR technique has been applied to data obtained from the laboratory tests and simulated industrial mills and the results sometimes contradict or confirm the conventional milling practices in the industry. This makes the already conservative mining industry sceptical about its adoption. This review thus assesses the milestone covered as far as the AR development in comminution is concerned. It also helps to clarify the sources of the discrepancies between the AR results and the conventional knowledge concerning the optimisation of ball mill operational parameters.
The comminution of commodity particles such as ore minerals in mining and metals from recycling of slags, armoured concrete, and incinerator slags by crushing, grinding, and milling makes up the biggest single cost factor in mineral processing. In spite of a marked lack in the development of new and significantly more efficient comminution equipment, an engineering start-up, PMS Hamburg, has invented and produced an innovative high-velocity impact crusher, the VeRo Liberator®, featuring highly improved particle size reduction ratios and very high degrees of particle liberation together with low levels of energy consumption and operational noise and operates dry, i.e. without using any water. The VeRo Liberator® is currently designed for a throughput of approximately 100 t per hour and has been tested on a number of different typical bulk ore and slag samples from mines and smelters around the world. Massive sulphide ore from the classic Rio Tinto Mine of the Iberian Pyrite Belt in Spain has been test-comminuted by the VeRo Liberator®. The ore and rare gangue minerals have been reduced in size by an amazing reduction ratio of 480 and have been liberated to a very high degree. According to our current understanding, these results are due to the unique working principle of the VeRo Liberator®, which is based on high-frequency, high-velocity and therefore high-kinetic-energy impacts inflicted on the material by hammer tools. The hammer tools are mounted on three separate levels of a vertical axle-in-axle system and rotate at variably high speeds clockwise and counterclockwise against each other. The material and particle stream within the machine is thus highly turbulent and each particle is certainly hammered with high impact forces several times at a high frequency. These high-frequency and high-velocity impacts occur apparently so fast, that stress builds up along the particle boundaries due to differential mechanical behaviour of the inhomogeneous materials. The high frequency of the impacts prevents the various minerals from relaxing sufficiently so that the stress between the different particles is not released quickly enough. Eventually this results in fracture formation along particle boundaries. This new comminution concept offered by the VeRo Liberator® allows the significantly more efficient comminution of ores and recycling materials at far lower energy costs and with far higher 13-15 August, 2015 San Luis Potosí, México 278 degrees of particle liberation. Due to its enormous reduction ratio the VeRo Liberator® can also replace two to three traditional crushing and milling stages, saving substantially both in CAPEX and OPEX.
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