Courtesy of Jocelyn Bouchard
Finding efficiency through better housekeeping Paying attention to process control leads to significant savings for mineral processing plants By Carolyn Gruske
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rocessing plants have the reputation of being energy inefficient, but a recent study has put some hard numbers on their energy usage. After investigating three industrial grinding mill circuits operated by Agnico Eagle Goldex Division, Mine Canadian Malartic and New Gold New Afton Mine, researchers concluded “on average, 79 per cent of the supplied electrical energy was converted to heat absorbed by the slurry, eight per cent was lost through the drive system and approximately two per cent was transmitted to the ambient air. Only nine per cent of the input energy was actually used for grinding.” In this regard, not much has changed in a very long time. As the lead author of the paper “Breaking down energy consumption in industrial grinding mills” (published in CIM Journal Volume 10, Number 4, 2019), Jocelyn Bouchard, a Université Laval associate professor of chemical engineering, believes there are easy efficiencies to be gained and energy to be saved. CIM Magazine spoke to Bouchard and asked him about making processing plants more efficient.
CIM: What can mineral processing operations do to improve their efficiency? Bouchard: A good example is ball mills. In most of the operations, you can process a little bit more material if you find the optimum operating point with roughly the same amount of energy, so the plant [energy] output will not change, but the amount of material you are processing is greater. If you look at the energy per tonnes you are using, it’s going to be a lower number. This, I think, is a good starting point. You try to maximize your asset utilization and use your equipment to a maximum capacity. Just with that, you can probably improve the energy 38 | CIM Magazine | Vol. 15, No. 3
consumption figures by anything from five to 15 per cent. Fifteen per cent could be a bit of a stretch, but from a simulation we are conducting currently, I would say five to 12 per cent is reasonable.
CIM: Could you explain how you achieve this optimization? Bouchard: There are many things you can do. Often people will target a certain product size that is based on offline laboratory work that has been done prior to the project or is being routinely done every few months, just to check if they are targeting the right particle size. But this target should be changing all the time, perhaps every six hours, every 12 hours, or even every hour, depending on the characteristics of the ore you are currently processing. If you measure online – or even offline – more frequently, ask “am I in the right target?” and readjust that target, you may be able to process more ore. You are probably targeting a product size that is much smaller than you actually need to reach your grade recovery target for your final concentrate or even reach the recovery in a gold plant. For instance, typical values are 75 microns. If you just get the 75 microns to 80 or 82 or 83 microns, you might have five, 10 or 12 per cent less power utilization in your plant, so it makes a huge difference.
CIM: Does changing the size affect anything else? Bouchard: If you are already at the right target, then you cannot process more. You can process slightly more, but not by changing the target. One way to do it is to systematically monitor and control the entire distribution online. We have sensors that can do that.
