COMMINUTION & CRUSHING
energy to perform the same task with vertical roller mills over SAG / AG mills .
“ Yet , more than that , the ability to better control the grinding element , and the addition of an integrated classifier that operates via an air swept function , ensures you do not overgrind material .”
Overgrinding has been pinpointed as a major target area for mining companies to address , realising that the production of excess fines and the use of excess energy for a task that does not always generate value represents obvious ‘ low hanging fruit ’.
And , like some other vertical roller mills , Gebr . Pfeiffer ’ s technology can offer higher recoveries at coarser grinds thanks to the ability to generate “ micro cracks ” through a grinding process made up of compression and shearing . Having been proven in test work , this is a particularly useful benefit given the coarse particle recovery trend sweeping through the mineral processing world , Dülfer acknowledged .
The MVR technology , which has a feed size of up to 175 mm , also operates in various operating modes – including a de-sliming mode for separating unwanted fines and impurities – and can make PSD adjustments on the fly to facilitate improved downstream recoveries .
And , speaking of downstream benefits , the ability to offer higher recoveries even at a coarser grind and the reduction in fines production leads to reduced water demand , reduced dewatering requirements in the tailings management process and , ultimately , reduced tailings generation .
In an environment where it is increasingly difficult to obtain new or extended tailings facility permits , this is an important advantage .
Dülfer says there are other ways of improving the downstream process in mineral processing applications , referencing the company ’ s recent investment in NextOre .
Back in November , the two companies announced they were looking to integrate NextOre ’ s magnetic resonance sensors and realtime bulk ore sorting with Pfeiffer ’ s vertical roller mill technology for dry grinding as part of a strategic partnership .
Upstream of Pfeiffer ’ s VRMs , NextOre ’ s magnetic resonance sorters , in a greenfield project scenario , could reduce the concentrator size with the same amount of planned metal output , while eliminating reject material early in the process after primary crushing .
After the VRM has carried out its work in the flowsheet , potentially dry magnetic or density sorting could further reduce the follow-on water requirements in flotation or leaching .
Dülfer says the industry is waking up to these potential benefits , with the biggest impact likely to be seen in bulk commodities , naming copper and iron ore as examples .
He concluded : “ We see an obvious place where our technology – and NextOre ’ s – can help and assist with addressing the industry ’ s megatrends .”
FLS talks up energy efficiencies for all
FLSmidth also boasts an offering including vertical roller mills , with the OEM seeing the potential of this technology in a future dry grinding mining setup .
This potential is currently being firmed up at the company ’ s dry grinding VRM pilot test facility at its Materials Testing and Research Centre in Salt Lake City in the US , among other options .
More broadly , FLS is developing several products and solutions relevant for a future where energy-efficiency and dry processing is a must at mine sites . Fundamentally , it is also evaluating wear part , equipment and process optimisation wherever possible , as well as looking to fit more efficient motors , drives and mill liners . Remote real-time monitoring , datadriven proactive maintenance and performance optimisation – much of which is tied to FLS ’ digital developments – are also available for all customers .
GMDs : built for variability
Could gearless mill drives offer a potential solution to the expected need to ramp up and ramp down grinding equipment in line with fluctuating renewable energy generation at mine sites in the future ? IM found out from Nandhakumar Vijayakumar , Head of R & D at ABB ’ s High Power Rectifiers business unit .
IM : How do you see operators of large grinding mills coping with the fluctuating energy supply that comes with renewable energydominated grids ? NV : Gearless mill drives ( GMDs ) are a variable speed drive system . Hence , the fluctuation in energy supply can be handled by adjusting the mill operational speed . Thereby , its power consumption can be adapted to the renewable energy grid power availability . Typically , a grinding circuit has a SAG and two ball mills . When both SAG and ball mills have variable speed characteristics , the speed adjustment can be performed to match the energy availability .
As a possible mitigation solution to minimise issues in case of sustained lower energy availability from the grid , energy storage solutions like batteries can be installed . However , it needs to be pointed out that the main loss of time and revenue occurs when the grinding system is completely stopped . This has a consequence on the whole process , but most importantly , process restart time is linked to down time . The flexibility of the GMDs minimises this situation and is an asset for absorbing power supply disruptions with as few consequences as possible .
IM : How are you equipping your own drive systems to be able to cope with these fluctuations ? Are they easily able to phase up and down in line with requirements and energy supply ?
When both SAG and ball mills have variable speed characteristics , the speed adjustment can be performed to match the energy availability
NV : GMDs are equipped with a dedicated fast control system . This allows the GMD to alter its speed in a quick manner , thereby its power consumption . This adaptation enables its operation to cope with varying energy supply . Hence , it is straightforward to phase up and down .
One more point to be discussed is that renewable energy dominated grids are characterised by low short circuit power and low inertia . In such grids , voltage and frequency stability issues can occur . In this regard , GMDs can also contribute to grid stability by providing frequency support by its power reduction and voltage support through its ridethrough function . As an example , one of the copper mines in Europe has an ABB GMD operating in a renewable energy dominated grid . This GMD currently provides frequency containment reserve service . Such services also provide additional revenue streams for the mine operators , especially in the reserve market .
44 International Mining | APRIL 2024