There is so much going on at a mine site, with the huge shovels and haul trucks and all the equipment and chemical processes to extract the metal from the ore, that a water truck driving around spraying water on the roads may seem like a rather minor player in the operation. The haul truck drivers may sometimes appreciate the water truck keeping the dust down, but they may also sometimes want the water truck to get out of the way. But the water trucks actually play an important role at a mine.
You might think that after all these years of mine operations that the technology of spraying water on roads to keep the dust down would have been perfected. But technology keeps changing, and there is always room for improvement. And a better system for spraying the water has the potential for a lot of benefits, including improvements to safety and the environment as well as cost savings.
There are a variety of water truck spray systems out there. Australian Diversified Engineering, a company based in Brisbane, Australia, has been making water truck spray systems for about 25 years, and developed a new design with a more automated system of regulating the water flow in late 2013. The system is now installed on about 150 mine water trucks in Australia. For about the past three years ADE has had a distributor in South Africa, and the water spray system is now on about 15 trucks in Africa.
In late April 2019 the first ADE water spray system in North America was installed on a truck at the Nevada Gold Mines Phoenix Mine south of Battle Mountain. Every mine has different road conditions and road grades to deal with, so once the new spray system was installed on a truck at Phoenix they started out with some tests.
Testing the system
Phoenix has two Caterpillar 789 water trucks, which hold about 44,000 gallons and are the mine’s primary water trucks, and they also have a Caterpillar 785. One year ago the ADE system was installed on one of the 789s.
“We set up a test circuit that was just over nine miles long,” said Danny Irvine, ADE director and commercial manager, “and we strip sprayed using both trucks. We looked at how many miles we would get out of each tank and what time it took.”
The water truck with the ADE system was able to cover the test circuit with water while traveling at an average speed of about 17.2 miles per hour, while the average speed of the other truck was about 11.7 miles per hour, Irvine said.
Irvine said with the ADE system the water truck “was able to keep the very high 20 miles per hour top speed and still put a good volume of water down on the road.”
That testing indicated the new water spray system would help make it possible to do a good job of suppressing dust in less time.
Using the system
The ADE system adjusts the spray of the water based on the speed of the truck, the grade of the road, and the condition of different sections of road, helping ensure the right amount of water is applied to suppress dust without overwatering, which can make roads too slippery. Also, the automation means the right amount of water is applied even if the water truck driver is inexperienced, and it means the driver can focus on the task of driving.
A little over six months after the ADE water system was installed on one of the Cat 789s at Phoenix, an ADE system was also installed on the mine’s other Cat 789 water truck.
“It’s working out real well,” Phoenix Surface Maintenance Supervisor Nash Johnson said. “Obviously when you first put it into play there was a little bit of unsureness. ‘Is the machine doing it correctly for me,’ versus ‘I know what I’m doing.’ A lot of operators felt like, ‘I can do this better than it can.’ Until you get used to it and you see that it manages itself. It’s pretty neat.”
“The bottom line is, it takes human error out of it,” Johnson said. “So you don’t have the flipping of switches, the adjusting of knobs. It waters the roads so the operator can take full advantage of paying attention to driving the vehicle.”
“The other thing is, being consistent across all of our water trucks,” Johnson added. “Prior to this we had three different systems on three different trucks. So parts were a problem. This is allowing us to have consistency not only with parts, but also consistency for the operators, too. It will be good.”
“It seems to do a really good job for us,” said Cecelia Wells, a water truck operator at Phoenix. “It helps us to not always have to mess with our buttons, so we’re able to see what’s going on in front of us a lot better. … We like it.
“The best part about it for dust is when we’re driving, it lets same amount of water out everywhere we go,” Wells said. “Even if we’re going uphill, the same amount goes out. We’re constantly getting that same flow of water. That helps us out a lot too. We’re not always trying to decide if it’s too much or not enough.”
One way the automated ADE spray system regulates the flow of water is based on the speed of the truck. As the water truck goes faster, more water sprays out to keep a consistent application on the road. The system can also adjust the water flow based on the grade of the road. When the grade is at a certain amount, up or down, the water flow can automatically reduce to a predetermined amount based on an analysis of the mine’s roads.
“All our hauling is downhill laden,” Johnson said. “So we do have to be really careful about not overwatering roads for downhill haul.”
The ADE spray systems are dealing with some new conditions now that they have moved to North America – freezing temperatures.
“We never get below freezing on any mine in Australia,” Irvine said. “We do get pretty close.”
Now the spray systems at Phoenix have gone through their first winter, and the people at the mine reported the spray system continued to perform well and to provide the right amount of road friction through the winter months.
Evaluating the roads
When ADE water spray systems are installed at a mine, ADE works with people at the mine to determine how much water the various sections of road need, and to see if some sections of road should be improved.
“Once we did the installation, we partnered with them and we went out and did these tests on basically all of our haul roads,” Johnson said.
To do friction tests on various sections of road, they add gradually increasing amounts of water to the road and then someone drives the road and steps on the brakes to go into a controlled skid. Fortunately, although they are testing the roads to see how haul trucks will handle the water on the road, they don’t actually have to put a haul truck into a skid on the road, although that could be kind of exciting. Irvine said through extensive testing, ADE has developed correlation factors so they can skid a light vehicle on the road and extrapolate that information to determine how a haul truck will handle the road.
A driver in a pickup truck with an anti-lock braking system can slam on the brakes, and the rate of deceleration is measured. ADE has a free iPhone app for measuring and calculating the road friction.
“We train people on site how to use that tool to benchmark their haul roads and regularly check them,” Irvine said. “Check to make sure the friction is in the right range for their coverage rates they want to run.”
“When you’re benchmarking it,” Irvine said, “you measure the section of haul road dry, and then with our water truck, because it puts a consistent coverage down, you put 0.3 down, do a friction test again, do another 0.3, do a friction test, and you create what they call a friction curve for that section of haul road. And what you’ll find is if it’s got high clay content, it generally doesn’t take a lot of water for that friction to drop off.
“The recommendation that comes out of that is if you do find a section of haul road that doesn’t take a lot of water to become unsafe, we recommend resurfacing it and improving the friction so it doesn’t become an issue in the future.
“The whole point of that is to highlight potential issues for the mine. Generally, braking areas, coming into an intersection or going down a ramp are the areas that you really want good friction, so you do not want to overwater in those areas. With our system you can measure what the right amount of water is, and if there is an issue, then you can address it with good material.”
The ADE spray system continuously stores information about the water truck routes and the water sprayed on the roads, and the mine can also use this information to help evaluate the roads and the work done by the water trucks.
Irvine and Johnson said calculations show using the new water spray system at Phoenix is resulting in significant cost savings.
“Our ultimate goal right out the gate was that we would get our money back in a year’s time,” Johnson said. “In reality it was four months. It’s kind of a game changer.”
That four-month payback is based on the savings from reduced water truck usage, because the truck can cover more miles per hour. Irvine and Johnson said keeping the right amount of water on the roads will probably also result in lot of other cost savings that are more difficult to measure, but which will add up over time.
“The overwatering of haul roads degrades the haul roads, increasing the risk of tire damage,” Irvine said. “And then there’s the whole area of the potential cost savings with reduced tire wear, and reduced haul road maintenance, getting the grader out all the time; and overwatering haul roads can increase resistance, and the fuel burned by the haul trucks.”
Now that the ADE water truck spray system is up and running at one mine in North America, Irvine and others at ADE are talking with other North American mines about the system. Irvine, who lives in Australia, usually spends a lot of time in North America, but the coronavirus has temporarily put a stop to that and has slowed down the process of meeting with mines about the spray system.
“We have interest from other mining operations in Nevada,” Eric Tomicek, ADE global sales manager, said in May. “Onsite meetings were booked but have had to be postponed due to COVID19.
“We have also been meeting with a mining truck manufacturer in the USA to assist them with the development of an autonomous water truck,” Tomicek added.
Tomicek said ADE has increased its stock levels of the spray equipment at a facility in Los Angeles, and is talking with a Colorado-based mining solutions provider about distributing and supporting the ADE spray system.
“This was made possible thanks to positive feedback passed on by personnel at Phoenix Mine,” Tomicek said.
Irvine pointed out that although the ADE spray systems at Phoenix were put on Caterpillar trucks, the spray system is retrofittable to any make or model of water tank or truck.
Detlev van der Veen, who was the general manager of Phoenix when the ADE spray systems were installed, said looking at new options for the water truck spray systems at Phoenix was part of the focus on continuous improvements at Nevada Gold Mines.
“It’s really us as Nevada Gold Mines looking at opportunities with the OEMs (original equipment manufacturers) to see what innovations are out there for our industry to help out on the safety and the environmental fronts. And this one applies to both safety and environment.”
“We keep looking with the OEMs and seeing what they provide because we want to drive continuous improvement here within Nevada Gold Mines going forward.”
Van der Veen said some of the new technologies Phoenix has adopted include autonomous drills, drones, a radar system for high wall monitoring, and MineStar sensors on their Caterpillar fleet to measure pressure in the suspension and determine haul road conditions throughout the mine site.
“So we continually look at those opportunities to see what we can do, because technology is evolving pretty fast right now,” van der Veen said. “It’s a pretty fast race.”