I have been discussing the climate change posting of 22nd August with Tim Napier-Munn, former Director of Australia’s JKMRC.
He reminded me that that well over half of the energy used in mining is consumed by comminution, which is an incredibly inefficient process, only 1-2% of that energy being used to create new surface.
Increasing comminution energy efficiency could decrease world carbon emissions by detectable amounts, so intensive research in this area is vital.
One of the major themes of next year’s Comminution ’10 in Cape Town is the improvement in environmental sustainability while driving down costs, by designing and operating energy efficient circuits and designing for the next generation of mines.
I hope that comminution research will also be highlighted at Climate Change and the Minerals Industry in Falmouth, in May 2011.
Saturday, 5 September 2009
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Yes I agree with your statement. I have done some calculations which shows if we incorporate energy efficient comminution techniques like High Pressure Grinding Rolls in place of SAG mill in Copper, Iron and gold industry, it can reduce GHG emissions by 1500kt and electricity savings of $62 million. (Figures in per annum)
ReplyDeleteWe should be targeting methods which enhance mineral liberation, by promoting intergranular, rather than transgranular, fracture. Liberation at coarser sizes means lower energy consumption in grinding, improved separation efficiency, and more efficient dewatering of concentrates.
ReplyDeleteIt is worth checking out the work being done at Nottingham University by Prof Sam Kingman and Dr. Chris Dodds.
ReplyDeleteThey have reduced energy consumption by using microwaves. The microwaves heat up locked in moisture, creating steam. The steam pressure is released by breaking up the rocks. http://www.nottingham.ac.uk/chemenv/research/industrial-microwave.php.
It's a shame they did not present at last year's Microwaves '08 conference. Maybe we will see them at Comminution '10 in Cape Town
ReplyDeleteFrom: Murray Pearson Principal Mechanical Engineer, Autoclave Technology, Hatch Ltd, on LinkedIn group CIM
ReplyDeleteA paper on Mineral Liberation and Particle Breakage in Stirred Mills (Paper ID No. 1932) by Reem Roufail and Bern Klein of UBC was presented recently at the COM 2009 conference in Sudbury, Ontario. The paper presents the research findings of the authors related to macro and micro particle breakage and related energy: "The transgranular fracture toughness of a pure single phase mineral was found to be 10 - 14% higher than the intergranular fracture toughness." The paper includes an assessment of how operating conditions can affect trans vs. inter-granular breakage.
I'm not a mineral processing specialist, but I found their presentation very interesting. A copy of the paper can be found in "Mineral Processing of Nickel and Cobalt - Proceedings of the International Symposium", 39th Annual Hydrometallurgy Meeting, published by the Metallurgical Society of CIM.
Way back in 1993 Keith Atkinson and I had a paper published in Minerals Engineering (Volume 6 Issue 7) "Some observations on the fracture and liberation of mineral assemblies". It was basically aimed at sowing the seeds for potential research projects to reduce energy consumption, and improve the efficiency of grinding. It may be worth looking at again. It can be found on ScienceDirect.
ReplyDeleteI'm sure Barry remembers the PhD work that we did looking at fracture toughness and rock mechanics applied to comminution. I still believe that we need more knowledge of the fundamentals that control fracture and breakage, before we can dramatically reduce energy in comminution. HPGR and Schonert's work were great advances, but we still reach physical limits. Microwaves have potential, but are there any other alternatives ? Ted Bearman
ReplyDeleteBrendan Costello Principal Process Engineer at Fluor Canada Ltd
ReplyDeleteFrom LinkedIn (Minerals Engineers)
I think the areas you hinted at are where I'd look. Perhaps concentrate minerals/ore types within mill feeds, selecting them on their resistance to various forms of breakage (i.e. separate hard from soft), so that the appropriate equipment WITH the appropriate settings can accomodate them (e.g. staged HPGR.....hard ore to one roll, soft to another). This would allow for optimisation of energy use and preferential breakage to be maximised - as you stated: along rather than across grains.
High pressure roll crushers didn't work so hot when they tried them at Tilden (taconite). Not sure I believe any of the hype now. Pretty much my understanding is that the tradeoff between pressure and wear didn't work out in the end and it never lived up to it's claims.
ReplyDeleteI did my masters work on wet fine grinding so I feel I can contribute a bit here. Turns out that you can get about a 10-25% boost in grinding efficiency (and lower grinding media usage by about the same amount) by optimizing the grate design in a grate discharge mill. Trouble is that optimizing grate design as far as I know is pretty much a long term trial-and-error problem.
As to the microwave idea...I forgot the name but there was another researcher that put out a paper about 10 years ago that involved using high voltage to fracture rock. It was extremely effective (close to the theoretical energy needed) but he couldn't come up with a practical version. The trouble with microwave and ultrasonic techniques is scalability.
I did some research at company acquired by BASF about 10 years ago and found that agglomerate disintegration for slurrying kaolin clays is directly related to shear...if you achieve the required shear forces, slurrying nearly instantaneous. Trouble was that I wanted to buy perhaps 100-150 of the large ultrasonic transducers that they sell to the medical industry (1 kilowatt) to get to about the right size for a full scale machine plus a few per month to replace them as the old units wear themselves out. I was getting nowhere with the manufacturers of this equipment. They are in a chicken-and-egg scenario...there is tremendous potential by scaling up high power ultrasonic transducers to an industrial scale, but they are still having difficulty selling more than one or two at a time. Since BASF isn't a machine builder, this project died.
Finally, another angle that hasn't been studied closely in my opinion is ring-race mills (aka coal pulverizers of the type commonly seen in pulverized burner systems). These are much more efficient than the traditional approach (ball mills) but have not really received much in the way of theoretical interest. The effect is similar to high pressure roll crushers except that these are practical mills that have been in operation for decades. One fairly famous name is Raymond. I believe Tim Eisele did some peer reviewed publications on this but that's all I've seen done. I've had the occasion to deal with these machines several times and they are popular as relatively low tonnage fine grinding machines for coal (for kilns). Beyond a certain size, ball mills become a necessity for capacity reasons.
Perhaps it is worth checking out the AMIRA project P879A “Microwave Assisted Comminution and Liberation of Minerals”.
ReplyDeleteWe are quite happy with High Pressure Grinding Rolls, seaving some 20-25% energy compared to ball mill. Furthere developments: ultrasonic assistance in compression zone and-or negative pressure operation. Any evidence of someone esle going in same direction?
ReplyDelete