Monday, 22 April 2013

Is progress in energy-efficient comminution doomed?

There is clearly a lot happening in comminution at the moment (see also my posting Where is comminution going).

Tim Napier-Munn
Progress, or the lack of it, in energy-efficient comminution will be the theme of the keynote lecture at next year’s Comminution ’14 conference in Cape Town. It will be presented by Prof. Tim Napier-Munn, former Director and now Consultant at Australia’s JKMRC. Tim is also a Director on the Board of the Coalition for Eco-Efficient Comminution (CEEC).

Tim’s abstract for the keynote is shown below. It is thought provoking, and we invite your comments, and hopefully your input to next year’s conference.

We are constantly told that comminution is the largest single user of energy on the minesite, and even that it consumes a significant proportion of the world’s electrical power. These two facts are indisputably true; comminution is very inefficient in its use of energy. It would therefore seem that improving comminution energy efficiency should occupy our industry’s capacity for creative thinking more than many of the issues we are asked to confront, especially in a world driven increasingly by the mantra of sustainability. So it is surprising that it barely rates as an issue when companies consider the development of a new mining project or look for operational efficiencies.

The 2012 CEEC Roadmap for Eco-Efficient Comminution taught us that although significant improvements can be made by applying what is already known, the size of the prize is not well understood within the industry. Also current project valuation and discounting practices tend not to identify comminution energy as a significant factor in project optimisation. Other than external regulatory forces, therefore, the motivation for improvement is weak.

There is good theoretical evidence that there is little we can do about it anyway; the physics is against us. In the 1970s Professor Klaus Schonert showed that the most energy-efficient way to break a rock was to place it between two opposed platens and load it until it fractured in tension. This simple mechanism seriously limits the options regarding real innovation in the comminution process. To support this view a glance at a drawing of one of to-day’s cone crushers will show that in all material respects it is identical to a cone crusher manufactured in the 1930s.

Cone Crushers

The same applies to jaw and gyratory crushers. This is good evidence that the best way to crush a rock was worked out a long time ago and the only improvements since then have been in scale, materials and process control, all of them important but peripheral to the main game.

Schonert’s work led to his invention of the HPGR as a way of increasing the rate at which the crushing action could be usefully applied. Despite intensive research, and early claims of high energy efficiencies, HPGRs have still only succeeded in niche applications in mineral processing after 30 years of trying. AG/SAG mills have dominated grinding because of their capital efficiency and operability rather than their energy efficiency. Stirred mills have been a genuine innovation in fine grinding but even they are prodigious consumers of specific energy. Novel flowsheets, especially those with more effective coarse gangue rejection, have been shown to be capable of significant reductions in overall energy consumption but they are by definition limited by the inherent efficiency of the unit operations they link together. So how are we to achieve the nirvana of paradigm change, say a 50-90% reduction in energy? And do we need to anyway?

We still do not know enough about the physics of the fracture of heterogeneous brittle materials such as mineral ores. Comminution science is really a branch of materials science, but materials scientists are only interested in the fracture event itself (read ‘failure event’), not the nature of the products of fracture as we are. The main job of comminution is mineral liberation, and recent research has taught us that liberation is a product of the texture of the ore and to only a limited extent the fracture mechanism. However we now know that the random fracture assumed by the early liberation models for mathematical convenience is not always the prevailing form. Non-random fracture leading to selective liberation of minerals along grain boundaries can also occur, and it is clearly in our interest to promote such liberation. How is this best done?

Other research has taught us much about what goes on in crushers, tumbling mills and stirred mills. But successful research does not necessarily lead to successful innovation. Innovation is a messy and expensive process with no guaranteed outcomes. How can we translate good research into good technology more effectively?

We really have no excuse for not achieving substantial progress in understanding the comminution process more completely, with the impressive array of experimental tools now available to us including computationally intensive modelling, automated quantitative mineralogy, tomography, breakage testing devices and the like. However capturing this knowledge in a useful form and transferring the lessons to industrial practice is as difficult as it ever was.

In deciding whether there is any hope for significant improvement in comminution energy efficiency, the Comminution ’14 presentation will consider the key technical and cultural impediments to progress, and speculate about how the innovation process may yet provide the long-sought paradigm change.


  1. Tim mainly focused on the technical issues of comminution, it is the political issues (at least in Australia) that are really holding back any substantial research.

    I could go on about this; but as my comments are beyond sceptical I will leave it until others show specific interest in this debate..
    Stephen Gay, Australia

  2. I would agree that the rate of improvement has slowed and seems to reaching an asymptote - and it may well be the laws of physics holding us back now. It seems we have to try avoid the the issue rather than just try and hit it harder. In my area (ultrafine <5um) we are held back by energy losses to fluid flow (frictional/heat losses) on the one hand and by futile elastic/inelastic impacts below the yield strength of particles. The more we try to increase energy density to overcome the latter the more the former holds us back. So how do we escape the trap? Love to see us grind in a vacuum, sort of electromagnetic rail-gun jet mills for example... not too easy. Or maybe crank up energy without cranking up velocities - via ultra high pressure grinding? Otherwise we need to seek alternatives to pure mechanical work - weakening ores with microwaves and differential thermal expansion works for some - or for some minerals, deliberate long term weathering. Rarely, biological action too. Cryogenic grinding helps reduce inelastic deformation for a few minerals but again a limited and expensive effect. I agree with Tim, we need to collaborate to break this trend.
    - Jarrod Hart, Cornwall

  3. Agree the changes in crushers have, except for minor changes in cone & mantle profile, been driven by maintenance rather than operations, which has probably reduced downtime by over 50%.

    But the real trend seems to be in what some call mine-mill systems where blasting, surely the cheapest rock breaker, is used not to create the lowest cost mine product (which means fewer holes and big bangs) but rather more holes and smaller mine-rock so that the mill expenditure on manganese steel is reduced.

    Certainly I am looking for more HPGR usage but capital cost means much more than lower life of mine cost to many miners (always very conservative). However, with current change in financing then there maybe a new look at lowest life of mine costs, and possibly a push on cheaper power. Certainly diesel in remote camps is a project destroyer, LNG and Combined Cycle Gas Powerplants maybe the way of the future, but one needs to think beyond a single unit of reduction equipment.

  4. The objective is to recovery value component of the ore for further processing by mechanical, chemical, biological or pyro-metallurgy; let us develop systems to bypass or atleast reduce the high energy consuming comminution step. What about nuclear technology? Insitu fragmentation using nuclear techniques followed by leaching. These systems would have other advantages.


  5. I am sure many of you know, innovations don't matter until economics is shown in all stages of concept to commercialization. Manufacturers don't want to risk their golden goose without knowing the demand, manufacturing, servicing, and scalability etc. of the new device. Then comes the issue of how fast or how easily customers can buy into the new devices. Comminution plant decision makers want to know the complexity, reliability, and overall processing efficiency of the new device. In the early stages of the new innovation commercialization, there will be many questions with few answers. These machinery/operations are in general cost intensive with long lives. It helps to understand why dynamics of adaptation is quite slow in this field. Due to these reasons, incremental innovation is more the norm in the traditional Comminution field. New approach to this traditional method of innovation, considering the difficulties witnessed with university/research-center/government based manufacturer-operator consortiums, is needed to launch the next phase of innovation in the Comminution field. Until that time, we will all be struggling to find reasons why we can't make significant progress in this field of technology as compared to other fields via innovation.
    Vijia Karra, Consultant, USA

  6. To make significant progress in energy saving, we must redefine the objectives of comminution in mineral processing. We will make very little progress by focussing only at comminution.
    We must exploit progress in other field such as ore sorting, coarser flotation, make significant progress.
    Optimising (comminution + flotation + physical separation) is much better than optimising (comminution) + optimising (flotation) + optimising (physical separation).

    Johnny T Kalala, South Africa

  7. As Prof. Tim Napier-Munn says in his article "Successful research does not necessarily lead to successful innovation. Innovation is a messy and expensive process with no guaranteed outcomes. How can we translate good research into good technology more effectively?" and also mentions "We really have no excuse for not achieving substantial progress in understanding the comminution process more completely". He is absolutely right.

    From an Australian perspective, I looked into research profiles of some of the prestigious universities like University of Queensland, Curtin University, University of New South Wales, University of South Australia (Ian Wark Research Institute), Murdoch University, University of Ballarat, other than UQ (JKMRC) and WA School of Mines (Curtin University) very limited research has been done by other universities related to Comminution.

    My belief is Universities should become factories of innovation. Industries and Universities should collaborate with projects for fostering new methods for solving persistent problems. Universities should have faculties and researchers with out-of-the-box thinking, and be a hub for creative activity and research for students. I am confident universities and research labs will be the incubators for fundamental innovation.

    What we need is a strong government and corporate-funded R&D infrastructure. This leads to commercialization, entrepreneurship, industry creation, job creation and all the other well-known benefits. The technology transfer from university to industry via entrepreneurship needs to become much more widespread. This might be capital intensive and might have long gestation periods. But with the falling commodity prices and increasing costs, the government-industry-academia collaboration is critical. There are research centers like AMIRA, CSIRO, and CRC. I would encourage these institutes to work closely with University research projects. This is not be confused with the scholarships offered by industries to undergraduate students and providing summer vacation work.

    The recent 2.3 billion dollars cuts to university funding as part of the Gonski education reform is extremely disappointing too. Increasing the financial burden on students while also decreasing funding to universities will not help. Unless we change our policies and attitude towards universities progress will be hindered and eventually be doomed.
    Shashi Rao, Australia

    1. Shashi. have a look at the IP policies of those prestigious Universities, and you will see why innovation, cooperation and collaboration are hindered.

      The solution is not to throw more money at them, but to get far better value through changed Govt. policies.

      It is impossible to understand what the Ginski education reform is on about; again this is another case where the politicians are confusing the situation.

      When you say 'we change our policies' has little impact. Do you mean 'your policy, my policy' or 'Govt. policy'? because Govt. policy is in noway a reflection of the will of the people.

      There is virtually no chance the Australian Govt. policy on education/research is likely to change in any useful timeframe (either side of politics).

      This is because the deficiencies have not been exposed to the voters. [The deficiencies in education/research are of course well known by those with wide experience, but the average person is unaware of them.]

      Basically any good qualities of education/research in Australia are a product of dedicated staff, not by Govt. design.

      Progress in energy-efficient comminution can only advance via a collective initiative by the mining industry. However it is very hard for this to be achieved without true Govt. support.

      Much depends on whether the mining industry considers it should have a collective social responsibility. This is contrary to the more accepted American driven view that business is amoral.

      Elisabeth Murdoch coined the phrase 'profit without purpose' to highlight this attitude.
      Stephen Gay, Australia

  8. Richard A Williams25 April 2013 at 00:24

    In my view there could be a completely different approach that may offer a step change in addressing effectiveness in comminution. One such approach is to accept the current limitations in the best available technology and focus efforts instead to properly utilise efficient heat recovery and integrated energy systems across the plant, for example, using new generation cryogenic energy systems. This may give very real savings along with cryogenic power systems delivered at the mine site. See p37 of Time to shift the debate to solutions that can offer a step change?


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