Improvements to traditional equipment and new systems provide a daunting array of options for material handling and processing. And each option has its champions. At most any industry gathering, advice for improving plant efficiency from the face abounds.

“Wherever you can replace trucks with conveyors, you'll save money.”

“Go with a tracked primary, and you can get rid of truck drivers and plant operators.”

“On plants working on multiple benches, you need haul trucks.”

Given the right operation, any of the above statements can be true. Likewise, given the wrong operation, any of the above statements could lead to unnecessary inefficiencies.

Finding better answers for an operation comes from analyzing its singular situation and goals against best available technologies. This can be especially hard when analyzing an already profitable operation.

“It is a big risk to change a successful operation,” says Tommi Lehtonen, sales support manager/specialist in track-mounted crushers, Metso Minerals. “Change is always a risk, but not changing can also be a risk.

“Normally, operations work on 10-year mine plans. A mine plan for truck haulage will look totally different than a mine plan using conveyor haulage. Those differences are evident in how haul roads are used and how, and in what direction, benches are developed. But, when an operation can decide what principle to use, management should consider all options.”

When analyzing an operation, Mark Krause, director of aggregates for Terex, says to view a pile of material as a profit center. “Decide on the profit margin stakeholders want,” he says. “Then determine the most cost-effective way to meet that goal. This is not new. This is business 101.”

With price fixed, consider what factors can be altered to lower cost.

Three main cost areas that can be changed are labor, energy and current capital investment use. Generalities disappear when analyzing the factors and environment affecting these cost areas. Krause says comparing the mine plan to the equipment is one way to weed out options.

First, look at the mine plan, he says. Consider the number and height of the benches. And, consider how much material is dropped per shot.

Next, look at the existing equipment. If an operation plans to buy trucks or loaders soon, it can open up the gambit. “If you have year-old trucks or year-old loaders, then the whole discussion is different,” he says.

Just by considering the mine plan and blasting schedule, an operator should be able to narrow the options to a manageable amount.

Keep on Truckin'

New quarries often start with haul trucks because the plant is relatively close to the face — load and haul is the quickest way to get up and running, says Lee Haak, product manager of excavators/C-products for Komatsu America International.

“There is no need for intermediate conveyors because the hauls are a reasonable distance,” Haak says. “There is a good chance a new operation can get by with a couple of haul trucks and a loader. Five years down the road, the situation might be different.”

Also, in general, a variable deposit does not lend itself to in-pit crushing. “If you are blending on multiple benches, you need trucks and loaders,” Haak says. “You need wheel loaders or hydraulic excavators if you have suitable benches, or hydraulic shovels if you want to load on the same level as the truck. You need the flexibility to move around.”

However, it may make sense to use a combination of haul trucks and in-pit crushing if an operation is committed to haul trucks and the face is far enough away from the main plant.

Vulcan Materials' Chattanooga, Tenn., operation uses this strategy to handle a face that has moved about a mile from the stationary plant. That operation turned to conveyor transport because it needed to move material across a railroad track and a city street. But, the conveyor also provides benefits in terms of efficiency.

A setup like this will allow an operation to blend material off multiple benches. And by moving the primary in-pit, the operation can meet capacity requirements with fewer trucks.

Haak recently conducted a job study to maximize a haul truck fleet's efficiency. The producer asked Haak to break down production into 100-ft increments from the face to the primary based on a fixed production target of 1,000 tph.

“We use an efficiency/hour measurement where we take 83%, 50 of every 60 minutes, as the productive time,” Haak says. “We then chart utilization, whether it is a loading tool or a haul truck.”

Haak started the study with four trucks. As the distance increased, production dropped. When production dropped below 1,000 tph, Haak added another truck, and production shot up.

“As you progress in 100-ft increments, you get a saw-tooth pattern on your chart,” Haak says. The customer learns when to add another truck based on how many feet the operation progresses from the primary each year.

The other part of this equation is when an operation reaches a certain number of trucks, it moves past the capacity of a single loading tool. If the operator needs to buy a second loading tool, costs jump considerably.

At a certain point, an operator needs to abandon the idea of using wheel loaders and haul trucks because that's the way he has always done it. He must make a hard analysis of operation efficiency, even if it means a drastic change in operations at the face. In short, he should consider degrees of in-pit crushing and conveyor haulage.

In Your Face Crushing

An operation using a wheel- or a track-mounted primary to stay close to the face, often uses a dozer to push material down from the pile and a wheel loader to carry material to the hopper.

“In load-and-carry, it is critical not to exceed the wheel loader's tire capabilities,” Haak says. “Typically, a distance of 300 ft would be extreme.”

A homogenous deposit lends itself to in-pit crushing, Haak adds.

And that is just one of several reasons mobile in-pit systems are drawing more attention in North America.

Mobile in-pit crushers fall into two basic categories: wheeled and tracked. Within the tracked category, an operator needs to distinguish between road-portable and nonroad-portable units. In the case of road-portable units, its a matter of size and what the tracked unit is designed to do.

“Not all mobile crushers are created equal,” says Ron Griess, Kolberg-Pioneer's product application engineer. “Because of road weight limits, a lot of mobile tracked units are specifically made for lighter-duty use for contractor crushing and recycling.”

For instance, Kolberg-Pioneer's road-portable 2649 Rocky Trax jaw crusher unit (rated at 400 tph) can be equipped with a magnet for tramp metal. The unit is designed for contract recycle work and hard rock crushing. It has a large feed opening and a hopper that does not need to be folded for road travel — a timesaving detail appealing to contract crushers.

“An operator in New England and another in Salt Lake City are using Rocky Trax for virgin material processing,” Griess says.

The tracked in-pit crushers are large-capacity, nonroad-portable units, which Metso Minerals' Nordberg and Terex America's Cedarapids have been placing more focus on building.

Cedarapids has two of its biggest nonportable tracked horizontal impactors primary units — part of the Cobra line — in place at CRH Oldcastle operations in Maryland. The units crush between 400 and 500 tph.

Metso Lokotrak line has road-portable machines equipped with either horizontal shaft impactors or jaws down to 30 metric tph for the recycle and contractor crushing segment. Metso also builds Lokotraks it says are the largest nonportable in-pit crushers being used in North America.

North American customers typically take 1,000-tph tracked primary crushers, says Metso's Lehtonen. “In several U.S. locations, we are studying how track-mounted crushers and conveyor haulage fit a quarry layout and its capital requirements,” he says.

Metso is not alone. Most every manufacturer is doing cost justification studies. Manufacturers are studying all fixed and variable costs and an operation's short- and long-term goals. They then present an analysis of up-front costs, operational costs and production levels of the most logical competing options for an operation to compare against its own numbers.

These studies are more than selling tools. Producers are learning what technologies best fit their operations. And manufacturers are learning what type of operations best fit their new technologies.

“All cases are so different,” Lehtonen says, regarding the cost justification studies he's been involved with. “We've had a couple cases where operators chose crushing with two tracked machines and conveyors on different faces.”

Cost justification studies do not always show in-pit crushing and conveying as the best way to go.

Two factors usually stop producers from moving from truck haulage to mobile in-pit crushing with conveyors. One is selective mining, where an operation has a variable deposit and needs to mix product from multiple benches. The other is if an operation has made recent purchases of loading or hauling equipment. Selling older equipment may help fund the purchase of a new system. But if the equipment is relatively new, changing may not be economical.

“It is difficult to justify selling a two-year-old loader with a high book value but the resale value is not enough to cover losses,” Lehtonen says.

“However, because an operation has a year-old loader doesn't mean it still can't move to tracks,” Krause says. “It may be able to move that loader to a different plant. With so many factors, there is no way to generalize.”

“All quarries are different,” Lehtonen says. “But, for a new operation that is buying everything, the conveyor system is the only way to go because of its big operating cost savings.”

Jodi Heirigs, application engineer, for Kolberg-Pioneer, offers six arguments for using belt conveyors instead of haul trucks.

• Conveyors create less emissions, noise and dust than haul trucks.
• Fewer personnel are required for conveyors, meaning fewer chances for accidents. Properly maintained conveyors are self-contained, shielded and guarded.
• Labor hours per ton of material are considerably less. Typically, conveyors have lower operating cost with high return on investment and lower energy requirements compared with haul trucks.
• Maintenance is less on conveyors than on haul trucks. The difference is greater when factoring in the costs of road maintenance and water trucks necessary to suppress dust.
• Hours of operation often can be extended because conveyors are quiet, and if properly automated, do not require personnel to operate.
• According to a survey of contractor operations that compared the use of a 35-ton haul truck with 3,700 ft of conveyor, the cost to run the haul truck is 7.8 cents per ton and the cost to run the conveyor is 1.1 cents. The survey also cites that an average truck lasts seven years, while an average conveyor lasts 25 years. The survey doesn't directly target aggregate producers and haul trucks used in many quarries have gotten bigger and more efficient. However, it would take a lot of confounding factors to narrow the gap between the cost of operating haul trucks over conveyors.

Haak also says location can strengthen or lessen the incentive for an operation to move to conveyor transport. For instance, one report shows a haul truck driver in Texas could earn less than $10 an hour. However, in the northeast, a driver may make between $40 to $45 an hour.

Also, he adds, the aggregate industry is dealing with an aging work force. In other words, companies are losing experienced operators due to retirement — operators that are being replaced by younger, and too often, less-talented, less-motivated workers. Operating with fewer personnel, which plays in favor of in-pit crushing and conveying, lessens the work force problem, Haak concludes.

Bill Welgoss is a freelance writer with 10 years experience covering the aggregate industry.