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Underground Drilling Advances Improve Productivity, Safety While Cutting Costs

LKAB Wassara's Water powered drilling system is mentionend in an article published in the magazine 'Engineering and Mining Journal - 2018.

Below you can read a part of the published article; written by Jesse Morton, Technical Writer

Download the full article as PDF-file here.


Water-powered Drill Saves Wattage

By using strictly Wassara's water-powered drills instead of air-powered down-the-hole (DTH) drills in its underground iron ore mines, LKAB saves roughly $800,000 per year. The miner expects to save 821,577 megawatt-hours (MWh), amounting to almost $25 million, over the next 30 years, Wassara, an LKAB subsidiary, reported.

And those numbers don't speak to the numerous other benefits of using water- powered drills, such as improved blasting and increased productivity, said David Petersson, marketing director. Both result from the accuracy of the drilling. The company reported its drills offer "an average borehole deviation of less than 1%," which bests "other technologies used for production drilling that average a 5%- 20% deviation." A Wassara water-powered drill, such as the Wassara W100, with a 115-millimeter (mm) bit on an Atlas Copco Simba rig, drilling at a length of up to 56 meters (m), creates "straighter blast holes than any other production drilling method," Wassara reported. "Accuracy is the most crucial factor for profitability since it indicates the bore hole length and the scale of operation," Petersson said. "A high accuracy will lower the amount of dilution as well as improve ore recovery, fragmentation and overall productivity."

The drill was originally engineered more than two decades ago for use by the LKAB in Kiruna and Malmberget, currently the two largest underground iron ore mines. At the time LKAB was seeking a solution that allowed them to mine "deeper, bigger and narrower, and at the same time, protect the environment and reduce overall costs." The main goal was to extend borehole lengths from 28 m to 56 m.

Sprutande hammare nere i gruva
Water-powered drilling eliminates the risk that compressed air will

enter and expand existing cracks between the holes.
(Photo: Wassara)

"LKAB at that time was in strong need of upscaling their underground mine operations to be able to compete with the lowcost open-pit iron ore mines," Petersson said. "An upscaled production means lower cost per ton of iron ore." The tech was designed with "close cooperation" of the miner, he said. "The idea of using compressed water as media for a DTH hammer was 'invented' by a couple of engineers in Sweden," Petersson said, "but it was when they came in contact with LKAB that the real product design work started."

The resulting Wassara drill and hammer technology delivers high-pressure water at a high frequency and energy- per-blow rate. When the water leaves the hammer, it evacuates the cutting and debris, thus cleaning the hole.

The primary challenge was extending the service life of the components, meaning being "able to have the hammers in operation for an acceptable period of time in combination with a good rate of penetration," Petersson said. It was found that because the water clears the hole, there is lower wear on the hammer, the company reported. "Due to this guide ribs can be used on the outside of the hammer case," Wassara reported. "These guide ribs will enable a very tight clearance between the hammer and the wall, as close as 1-2 mm."

Additionally, through use of water pressure, as opposed to air pressure, there is less unwanted damage to the host rock, Wassara reported. "When the water leaves the hammer, the host rock will not get pressurized since there is no change in volume of the water," the company reported. "If the host rock gets pressurized by, for example, compressed air, then there is a great risk that existing faults get extended." That could result in an interrupted blast sequence, which would impact the fragmentation.



Rig down the LKAB mineDrill rigs in LKAB's underground iron ore mines are heavily
automated. For example, the rig can be programmed to alert
the operator when it is time to change out the hammer. Such
automation enables one operator to manage two rigs.
(Photo: Wassara)

Water-powered drilling is also more environmentally friendly than air-powered DTH hammers, Wassara reported. It is hydrocarbon- lubricant-free, with the water acting as a lubricant, so there is no oil mist. Further, the water suppresses dust. "Thus, there is less need for ventilation," the company reported. And it "is even quieter than (air compressed) DTH drilling since the water column dampens the noise from the hammer."

In the end, LKAB "achieved the upscaling factor they were looking for, meaning with a similar amount of rigs and operators they can get much more out per blast," Petersson said. Wassara drills were deployed throughout the two mines in 1995. Once drill hole lengths were extended to 56 m, the volume of ore drilled per meter increased by 500% and the required number of sub-levels decreased by 70%, the company reported. "The reason why they stopped at 56 m is that the distance between the top of the holes is getting to be too much, meaning when you blast you get too many large boulders," he said. "Also, it becomes an issue to charge the hole with explosives when the depth is getting too long."

Wassara describes its technology as "much more efficient with a higher frequency compared to an air DTH hammer." The latter delivers a maximum of 2,700 blows per minute (bpm). A Wassara hammer delivers 3,600 bpm. And because the hammer is constantly at the bottom of the hole, the rate of penetration can be as high as a meter per minute with 115-mm drill bits, the company reported. "The 115-mm bit is an optimal size bit for our W100 hammer," Petersson said. "If you use a large bit on the same size hammer, you will have a slight lower rate of penetration, but with other sizes of hammer and the right size of bit for that hammer model, you will get a similar rate of penetration."

That efficiency translates to saved wattage. In LKAB's underground iron ore mines, the drill rigs operate at full pressure daily for 12 hours, with scheduled maintenance stops of eight hours every second week. LKAB reported it drills roughly 1.5 million m per year. "By using the Wassara hammer, LKAB is lowering the energy consumption from the drilling process alone by 27,386 MWh per year."

Unlike air, water is a non-compressible media. It yields easier to the
drill cuttings and evacuates the hole easier than does compressed air.
This results in lower wear on the hammer. (Photo: Wassara)

This gave LKAB a needed advantage, Petersson said. "The iron ore market is very competitive, and you have to lower your production cost to be able to compete with low-cost producing open-pit mines." The technology is suitable for all types of mines and most drilling applications in mining operations, the company reported. Over the years, other miners have deployed Wassara drills in their mines. Examples include the Codelco's Andina Copper mine in Chile; the Rana Gruber mine, a sub-level cave iron oxide mine near Rana, Norway; the San Geronimo mine, an underground copper mine in Chile; and the McArthur River Mine in Canada.

As featured in Womp 2018 Vol 01 - www.womp-int.com