Mike Moody explains how an ore mine is using air cannons to unclog chutes
Clearing material from hoppers, chutes, bins and vessels can be done using manpower and tools on hand, but safety experts recommend considering a solution that prevents exposing workers to potential hazards. Operators at modern mining sites, such as Eagle Mine located in Western Marquette County of Michigan’s Upper Peninsula, understand that using specialised equipment reduces worker exposure, offers the safest mode of production and provides the most cost-effective lasting results.
“Safety is a top priority for us,” says Ted Lakomowski, lead reliability technician at Eagle Mine. “When we experienced clogging and downtime at the processing mill, our crew naturally swung into action to resolve it, but we immediately sought a safer long-term solution.”
Owned by Lundin Mining, a globally diversified base metals mining company headquartered in Toronto, Canada, Eagle Mine is the only primary nickel mine in North America, producing 1.5% of the world’s total nickel production. Ore from the mine is stored in a covered coarse stockpile facility prior to transport by road approximately 65 miles (105 km) to the Humboldt mill.
Eagle Mine’s initial solutions to the sludge problem
Clogging issues were found in an undersized chute in the milling process. Although material was damp when mucked, it was further exposed to rain, snow or summer humidity during transport by truck to the mill. Accumulation would stop the entire crushing process three to four times per shift for as long as an hour, blocking input of material all the way back to the ore storage area. The breaks in production and ensuing downtime had an immediate effect on the cost of operation.
Workers attacked the clog with 15ft (4.5m) long air lances from the top of the hopper and bottom of the chute. The method used a tremendous amount of compressed air and diverted manpower from other essential duties. Moreover, air lances caused excessive splash-back of wet material, which was extremely messy and potentially hazardous.
Scepticism about using compressed air as a solution
The technical team at Martin Enginering observed that previous solutions did not adequately aid the flow of material. “We proposed installing air cannons at strategic points throughout the chute to dislodge material and aid flow, but managers had some initial reservations,” says territory manager Jason Haynes.
“Compressed air is almost a currency here, so we were naturally sceptical of using a solution that impacted pressure,” Lakomowski clarifies. “Many in the organisation had experience with older air cannon designs and knew the potential drain they could put on a system.”
Eagle Mines deploys air cannon technology
Air cannon technology uses compressed air to promote proper flow by quickly filling a tank, delivering a powerful shot to the vessel wall in the direction of the moving cargo, dislodging adhered material and introducing it back into the stream. After Haynes detailed the low impact that new air cannon technology has on compressed air systems, Lakomowski advocated for the initial installation of five 35 litre (9.25 gallon) Martin Hurricane air cannons, followed by two more placed in essential spots in the chute. All of the tanks were accompanied by a 4in (101mm) pipe assembly ending in fan jet nozzles.
Designed with safety and low maintenance in mind, the cannons feature a centrally located outward-facing valve assembly that can be replaced within minutes, without the need to remove the tank from the vessel. To prevent the risk of unintentional firing due to drops in pressure, the innovative valve design requires a positive signal from the solenoid in the form of an air pulse to trigger release.
Installation and testing in the ore mine
Beginning with five cannons, one unit was placed at the area where material discharged into the hopper, two others were positioned at the hopper slope where the most accumulation was observed and two more were placed along the drop chute. These used straight pipe nozzles to shoot air across the vessel to dislodge adhered material and promote flow.
“The initial installation reduced the amount of downtime, but testing showed it did not cover enough area to fully evacuate adhered material,” says Haynes. “More accumulation built up in transition sections of the hopper and discharge slope than initially thought. So we installed one more cannon at the top of the hopper and one at the bottom of the chute where it discharged. We also added fan jet nozzles to the pipe assemblies to cover more area, and that did the trick.”
The results of Eagle Mine’s air cannons installation
Operating on a regular firing schedule of every one-10 minutes – readjusted for production volume, time of year and moisture level – the seven-cannon configuration reduced clogging issues and downtime. This significantly lowered the risk to operators and reduced the cost of operation.
“When I did the cost assessment, I was surprised to discover that there was a 1,000% savings in using the air cannons over the air lances,” Lakomowski says. “It’s a significantly lower effect on our system than initially predicted, and managers are very happy about that.”
The project also improved safety, as workers spent less time diverted from other assignments to use air lances or create vibration by beating on the vessel walls.
“Just from a safety aspect, this solution has paid for itself,” Lakomowski concludes.
Mike Moody is with Martin Engineering