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Comminution ‘04 Conference Report
Heatwave conditions in Perth Western Australia in March 2004 set the scene for similarly hot discussions on the future of new research methods being applied to mineral processes outlined by several researchers attending MEI’s Comminution 04 conference.
As with previous conferences in the series, there was a broad mix of applied and basic research approaches presented from plant optimisation and design through to rheology – the flow and behaviour of particles in fluids – and discrete element modelling, which simulates the movement of elements within the milling process based on mathematical and physical analysis represented in high definition graphics and animation.
In the minerals sector, comminution takes place mainly within mills as part of run of mine processing. A criticism of the comminution process has been its reliance on high energy consumption to grind coarse material to either separate a precious metal, such as gold, or to produce an industrial mineral, such as concrete.
Since the last Minerals Engineering International comminution conference was held in 2001 in Brisbane, the industries which produce large quantities of mineral through comminution have become much more energy conscious, and research being undertaken globally reflects this move towards a ‘greener’ milling footprint.
Energy reduction and the emergence of the ‘triple bottom line’ imperative in the mining industry – economic efficiency, social responsibility and environmental considerations – was discussed in the context of applying proven technology from other industries to mineral processing. Recycling through comminution techniques in the European context was also discussed.
Comminution 04 essentially achieved its objective to present the ‘state of play’ in comminution research and application on a global scale. There was a potpourri of research topics presented, but a little of something for all 125 delegates from 18 countries represented at the conference.
Sponsored by Xstrata Technology, David Wiseman Pty Ltd and the Gold & Minerals Gazette, the conference was held at the Sheraton Hotel Perth and ran over three days. Fortunately the 40 degree centigrade heat outside was moderated by air-conditioned comfort inside the venue.
By far the largest contingent at the conference were from the University of Queensland’s Julius Kruttschnitt Mineral Research Centre, demonstrating that they are clearly at the forefront of comminution research and still pushing the boundaries of the this field through recent initiatives in rheology, discrete element modelling, mathematical analysis through stereology and power reduction research through the application of high pressure grinding rolls in minerals processing.
Also making an impact at this event were groups from Sweden’s Chalmers University of Technology led by Dr Magnus Evertsson, and researchers from the University of British Columbia, CSIRO, and Metso Process Technology.
To set the scene, conference convenor Dr Barry Wills from Minerals Engineering International gave an overview of the history of comminution, from stamp to autogenous mills. He said comminution was the key to good mineral processing and, in his view the most important part of the processing plant. However, despite its continuing importance across the minerals sector in particular, he lamented the relative low numbers of peer-reviewed papers on the subject compared with other aspects of mineral processing, such as flotation. In 2003, 135 flotation papers appeared in minerals processing literature, compared with 41 in comminution.
Comminution 04 went some way towards addressing this shortfall, reflected in the program which kicked off with Dr Wills’ overview followed by quick-fire poster snapshots covering a broad range of interests in the field.
Topics introduced from the eight poster papers presented started with a presentation from Tomas Sverak from the Brno University of Technology, Czech Republic, on process control related to the use of fine mineral coated fillers in comminution. This was followed by a topic which introduced one of the themes running through the three-day event, being the advances and potential application of discrete element modelling. The topic ‘Simulation of particle flows and breakage in crushers using DEM’ by CSIRO’s Paul Cleary was later expanded on by JKMRC Technical Director Dr Rob Morrison with a more comprehensive look at discrete element modelling. During Paul Cleary’s poster presentation he sought feedback from delegates at the conference, of which he received mostly reserved, yet positive comments about DEM’s future potential. More on that later.
Other poster topics presented in the first session included glass breakage techniques from Japan using a similar approach to JKMRC drop weight testing, a presentation from Camborne’s James Pendrich on the use of baffles in the top of stirred mills, then on to pilot plant studies in Italy of sulphide ore grinding, the development in Chile of a new monitoring system of measuring load filling of SAG mills, Murdoch University’s approach to evaluating breakage parameters and modelling batch grinding through application of JKMRC drop weight methodology, and an enlightening overview on the use of magnetic metal liners in ball mills used in the Chinese iron ore industry.
After a quick tea break for obligatory networking at the nearby trade exhibits, the first technical session under a plant operations theme, chaired by Professor Bob Barley from Camborne School of Mines, led with a case study of the Queensland, Australia-based Mt Rawdon gold mine’s design and implementation of a partial secondary crushing circuit to increase milling capacity, presented by Brian Putland of Orway Mineral Consultants. Brian explained how attempts had been made to apply DEM methodology, advanced by Rob Morrison of the JKMRC and Paul Cleary of CSIRO, to the Mt Rawdon circuit.
The JKMRC’s influence on research presented in the second paper in this session by Metso Process Technology’s Alex Jankovic was also evident in relation to the modelling of stirred mills and its potential for cement grinding. Dr Jankovic said there were indications that stirred mills could be successfully introduced to the cement industry, particularly in terms of realising a potential 50 per cent power reduction. Dr Jankovic used a Barmac vertical shaft impactor to conduct this research.
The final paper before lunch on the first day focussed on a Highland Valley Copper case study from the University of British Columbia’s Percio Rosario on the optimisation of a gyratory crusher system, emphasising improvement to the understanding of liner wear.
To this point of the proceedings a few themes had begun to emerge, particularly in relation to reduction in power draw and the desire to get longer service life from comminution equipment, such as reducing liner wear.
University of Cape Town comminution researcher Dr Malcolm Powell presided after lunch, introducing seven papers on autogenous, semi-autogenous and high pressure grinding rolls research.
Out or the seven papers presented, four were either authored or co-authored by members of the comminution research team at the JKMRC, with the exception of the first post-lunch paper, which was presented by Professor Brian Loveday from the University of Kwazulu-Natal.
Professor Loveday took delegates ‘back to basics’ with a re-appraisal of preliminary batch testing methods for the elimination of rocks. He advocated the use of a 1.2 metre diameter mill for batch tests on FAG and SAG mills combined with the use of a water flush procedure to estimate mill performance.
The second paper in this session presented by JKMRC Technical Director Dr Rob Morrison on discrete element modelling could arguably be ranked first in terms of the amount of comment and discussion it generated throughout the following two days of the conference
DEM simulation involves following the motion of every particle – coarser than some cut off size – in the flow and modelling each collision between the particles and between the particles and their environment, such as the mill liner, grate or pulp lifters. In the CSIRO MIS DEM program the boundary geometry, such as for a ball or SAG mill, is built using a CAD package and imported as a triangular finite-element surface mesh into the DEM simulation package. This provides essentially unlimited flexibility in specifying the three-dimensional geometries with which the particles interact. The particles are modelled as spheres with sizes and density distributions chosen to match the mill charge as closely as possible.
Dr Morrison’s presentation made good use of three dimensional DEM using spheres to give a realistic internal view of a pilot scale mill. The model uses the T10 equation derived by JKMRC Chief Scientist Dr Bill Whiten to estimate breakage from energy collision.
Xstrata Technology process engineer Sarah DeBono later commented that DEM was being used in a practical way to model the IsaMills in operation at Mt Isa. Sarah said DEM was also being used to help scale up an M3000 to an M10000 2.6 megawatt mill.
The JKMRC comminution team was again represented on the dais for the next presentation by physicist Dr Randolph Pax who gave a detailed account of the longitudinal behaviour of SAG and AG mills as determined by non-contact acoustic measurements. Dr Pax continued a population balance theme introduced by earlier papers in this session, but with a difference through the application of non-contact acoustics.
Just prior to tea on the first day, Professor Jorge Pontt from Chile returned to the stage with an expanded account of the resonance effects, power quality and reliability issues of high-powered converters-fed drives employed in modern SAG circuits. Professor Pontt’s paper departed from the DEM theme to look more specifically at power consumption of mill drives and issues of mechanical disturbances affecting mills.
In his summation of the session, Dr Malcolm Powell said that studying drives, particularly high-powered, high torque drives, is very much taken as granted in comminution, and it was pleasing to see important and sophisticated research being conducted in this area.
Following tea, and three papers left to wrap up day one, University of Nottingham’s Dr Sam Kingman introduced, JKMRC senior comminution researcher Dr Frank Shi who revived the DEM discussion with a paper on the modelling of lifter design, speed and filling effects in AG mills by 3D DEM. Dr Shi compared the differences in aspect ratios between typically shorter Australian AG and SAG mills with the longer South African run of mine mills, explaining the application of the 3D particle flow code – PFC3D – with particular reference to research conducted by the JKMRC’s Dr Nenad Djordjevic.
The final two papers of the day focussed on high pressure grinding rolls, firstly from KHD Humboldt Wedag’s Stefan Kirsch who provided an overview of the world’s first industrial scale application of HPGR for gold ore processing in Siberia in collaboration with Russia’s Mineral Resources Separation Technologies. A challenge for the Siberian work was the freezing conditions which needed to be taken into account for HPGR scale up in that region. Stefan also gave details of the flowsheet incorporating the HPGR in the gold processing circuit, and consideration was also being given to applying HPGRs for copper processing, also in Russia. In his summation, Stefan Kirsch canvassed the inevitable question on comparative costs of roller liner wear compared to SAG liner wear. Although no study had been undertaken, Stefan believes that HPGR liner costs are comparatively low.
JKMRC researcher Mike Daniel had the unenviable duty to deliver the final paper of the day when the attention span was traditionally at its lowest point. Mike Daniel has done a significant amount of research in HPGR model verification and scale up. He advocated wider scale use of HPGRs in the minerals processing sector in the context of reducing world-wide energy consumption.
The closing papers on HPGRs provided an optimistic conclusion to an absorbing program on the first day. Dr Kingman commended Mike Daniel and others for their excellent presentations.
And so it was off to the Perth Zoo for the gala dinner, hosted by sponsors Xstrata Technology and David Wiseman Pty Ltd, which included several hours of international networking.
The first stanza on the second day focussed on stirred milling and the highly sophisticated, highly technical, discussion on the application of rheology to stirred mill research.
Stirred milling specialist Dr Alex Jankovic from Metso Technology Asia-Pacific chaired the first session, introducing papers from Australia, Germany, Canada and the United Kingdom.
CSIRO’s Dr Mingwei Gao represented Australia’s interests in stirred milling and fittingly began the session with the size and scope of stirred milling ‘down under’ where more than 50 units were currently in use. His paper ‘Medium selection for fine grinding stirred mills’ focussed on the IsaMill, the detritor, and the use of silica sand as the medium selection. He also assessed other potential media for stirred mills, such as steel and ceramic beads.
Professor Thomas Nesse from Friedrich-Alexander University in Germany provided a useful transition from Mingwei Gao’s medium selection assessment with a more detailed look at attrition of sandy material inside stirred mills.
University of British Columbia’s Bern Klein progressed the stirred mill session with a look at the highly complex affects of rheology on ultra-fine grinding in stirred mills. UBC research looks at improving energy efficiency in stirred milling and rheology research conducted at the JKMRC by Dr Frank Shi and Professor Tim Napier-Munn. In his summation, Dr Klein advocated the use of lower solids content in stirred mills, although operating with as higher solids content as possible with regards to yield stress.
Noted mineral processing researcher Dr Bob Barley closed the first session on Day 2. His presentation related to the lapse of a commercial-in-confidence phase related to ‘part two’ of UK-based research on the ‘Measurement of the motion of grinding media in a vertically stirred mill using positron emission particle tracking, or PEPT. This work focuses on controlling baffling and per cent solids inside stirred mills to provide a real time data set.
After a tea break, the Comminution 04 program advanced to, for many, ‘core business’ for comminutors in a session on design and simulation chaired by Dave Wiseman. The session started with Rio Tinto’s Dr Ted Bearman’s paper on the detail versus application in modelling comminution processes. Dr Bearman made the somewhat controversial statement that ‘models are what we have instead of reality’. This comment was measured with a follow-up statement that models provide insights into how things should work. In Dr Bearman’s view, models provide confidence to make important financial decisions at the plant and all forms of modelling are potentially useful in the right circumstances. He referred to the crusher modelling method derived by the JKMRC’s Professor Bill Whiten as a starting point for comminution modelling over the past few decades. Dr Bearman observed that the modelling research so far presented at Comminution 04 had been outstanding, providing delegates with a taste of ‘what was out there’.
JKMRC Technical Director Dr Rob Morrison followed Dr Bearman’s address with a summary of Dr Andrew Schroder’s work in on-line dynamic simulation of grinding circuits, much of which was based on three decades of JKMRC experience in dynamic modelling. Dr Morrison introduced the JKDynaGrind concept – a flexible, general purpose flow-sheet based, dynamic simulator.
Dr Yi Liu of CSIRO kept this theme going with research that had taken a modular approach to dynamic simulation of grinding circuits and the use of a new simulator – Simulink – which involved the creation of a comminution library.
CVRD Brazil researcher Vladimir Alves gave the Brazilian view on using simulation to optimise mill charge. These simulations, typically, combined practical tests using cylpebs, batch grinding and mass balancing. Comparisons were made between the effectiveness of balls compared with cylpebs in a pilot plant situation.
The final paper before lunch on Day 2 saw Dave Morton from CSIRO close the session with recent work in billiard ball modelling, and other shapes used for industrial scale DEM. His goal is to make DEM more accessible to more people, which is where his use of the world wide web comes into the picture, and CSIRO’s attempt to provide a DEM service through Web GF-Mill – a web-based interface as an online service.
Delegates adjourned for lunch with plenty of food for thought.
In chairing the post-lunch session on the second day, Dr Walter Valery introduced four speakers covering a variety of topics from texture-based liberation modelling of ores from the JKMRC’s Dr Stephen Gay, to a three dimensional analysis of media motion and grinding regions in mills from UCT’s Dr Malcolm Powell, followed by Dr Ted Bearman’s explanation of an evolutionary, multi-objective algorithm approach for crusher optimisation and flowsheet design, through to the Swedish perspective from Dr Per Svendensten on finding the optimal machine parameter, wear tolerance and wear part in crusher plant optimisation.
Each speaker in this session demonstrated that they were well on top of their subjects to the point where Dr Stephen Gay enthused about his enjoyment of working in the mineral liberation research field where he presented a conceptual liberation model for comminution.
The final session of Day 2, chaired by Professor Brian Loveday, had a distinctly European flavour with two papers from Sweden focussing on cone crushers and a high performance crusher system, and the final paper of the day from The Netherlands on recycling. The latter paper departed from the largely mineral processing context of the conference to cover the broader application of comminution in recycling streams based on the European experience.
A measure of the value of the information passed on to Comminution 04 delegates was reflected in the final Day 3 program which kept the audience engaged throughout the final two sessions spanning research and development in classification circuits and mill media. The session before tea was chaired by the JKMRC’s Dr Stephen Gay, with Xstrata Technology’s Dan Curry wrapping up the final session. The international nature of the conference was also on show on the final day with eight different countries represented at the speaker’s podium, with Alain Broussaud of France leading the day’s proceedings for Metso Process Technology with an overview of his company’s development of an integrated vision technology for advanced control of grinding circuits. The German flag was then metaphorically raised by Thomas Neesse who presented collaborative German-based research in hydrocyclone control in grinding circuits. Representing the USA was Western Australia’s Brian Packer who gave an overview of the development of a trunnion magnetic separator developed by Eriez Magnetics. The large Swedish contingent from Chalmers University of Technology was represented at the dais by Magnus Bengtsson to present model development and optimisation of a banana screen for robust performance.
The morning tea break provided one last chance for delegates to network with exhibitors before the curtain was closed at lunchtime to provide a midday end to the conference, but not before five papers provided the finale to the Comminution 04.
The final stanza reflected the diverse nature of comminution practice and application that had been evident throughout Comminution 04. The Scandinavian representation followed the tea break with PhD student Juraj Chmelar of SINTEF Norway presenting his research into improving the air classifier performance, much of which was drawn on computational fluid dynamics.
With one foot in Sweden and the other in the United Kingdom, Sandvik Rock Processing’s Magnus Evertsson, who incidentally also represents Chalmers UT, and Dr Sam Kingman from the University of Nottingham took to the stage as a ‘double act’ to present collaborative research on the influence of microwave pre-treatment on closed circuit crusher performance. Their joint paper addressed issues of energy reduction and improved recovery.
Perhaps slightly underrepresented at Comminution 04 was the typically novel and enthusiastic presentations from Canada as had been experienced at past conferences in this series. However, Dr Peter Radziszewkski from McGill University more than made up for any perceived lost ground with a presentation of work being conducted under the international P9 project framework. Dr Radziszewkski’s paper ‘Determining the steel media abrasive wear as a function of applied force and friction’ drew on wear rate and abrasion tests that he had conducted at the JKMRC while on sabbatical leave from McGill University in 1998.
The JKMRC connection was thread neatly into the penultimate paper for Comminution ’04, which was presented by a world leader in comminution research, Dr Frank Shi, who compared the performance of the low-allow cast iron cylindrical, slightly tapered-shaped ‘cylpebs’ with the traditional use of steel balls as grinding media. Cylpebs have been proven to produce less fines in certain milling situations.
Jaime Sepulveda from Chilean group Moly-Cop Grinding Systems had the arduous task of presenting the final paper for Comminution 04. His paper ‘Methodologies for the evaluation of grinding media performances at full plant scale’ looked at cost-effectiveness in media selection and use. He presented the wear rate constant kdE by way of explaining the framework for reliable estimates of comparative grinding media wear performance. It may have been a heavy duty paper to end the conference, but relevant in terms of the grinding media theme adopted in the final session.
Overall comment about the value of the conference from the sponsors and exhibitors perspective was positive, but like any specialised industry event, there is always room for improvement.
Xstrata Technology technical superintendent Dan Curry said Comminution 04 was useful from his company’s sponsorship perspective in that it brought new developments of old methods in the areas of wear and specifically the performance of stirred mills. He said he saw some of the most practical research that has been done on stirred milling for a long time.
Other standouts in the program included a presentation of microwave technology from the University of Nottingham, and the Discrete Element Modelling research presented by several organisations. Dan said DEM was very useful as Xstrata fund its own research specifically for DEM modelling of the IsaMill. He said Xstrata found DEM useful in terms of establishing basic relationships in the mill, very similar to work done with tumbling mills. But there are still limitations with DEM results. Dan is interested in work that combines CFD models with DEM to provide the full fluid flow and particle interactions. At that point it should be a very accurate tool.
Dan Curry went on to say that the conference was very useful in terms of generating contact with past and future clients in relation to test work for projects. Xstrata’s involvement with Comminution 04 also meant they had an opportunity to participate in the ongoing development of comminution models and the overall advancement of comminution in the industry. He said having leading comminution groups such as the JKMRC at Comminution 04 provides continuity in the development of these projects.
According to Dr Walter Valery, General Manager of Metso Process Technology Asia-Pacific, the MEI comminution conferences provide visibility for this team that larger events don’t do quite as effectively. However, he would like to see the balance of presentations between researchers and operators evened out, which Dr Valery believes is currently skewed in favour of researchers and academics. Nevertheless, having the comminution research community together at one forum provided groups like Metso with valuable information on where relatively new applied research methods such as DEM had reached in their development.
Joint conference sponsor Dave Wiseman of David Wiseman Pty Ltd said that as with previous comminution conferences in the MEI series, it was an ideal conference to be involved with as it was so highly focussed. He said it was pleasing to see almost everyone still in attendance at the end of the conference. Dave commented that a strength of the conference was its blend of academic, operating and equipment papers. He said it was also encouraging to see so many researchers from northern Europe at the conference, and hoped that this presence would lead to increased use of his LIMN:The Flowsheet Processor software in countries from that part of the world.
Dave also said he expected to get involved in the next MEI comminution conference which will be held from 15 -17 March 2006, also at the Sheraton Hotel in Perth, Western Australia.
A further report on the conference by Kyran Casteel, can be found in the June 2004 issue of World Mining Equipment (pps. 47-52).
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