Cementing Its Position

By Claire Swedberg | Jul 15, 2010




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Rock reduction plants, which process rock into products such as cement or sand, require specialty electrical construction that only a handful of electrical contractors have taken on. One such contractor, Farnham Electric Co. of McMinnville, Ore., does this work around the world. In 2009, the company completed a portable rock crusher and conveyor belt for Hawaiian Cement, Maui Concrete and Aggregate Division. The 3,000 feet of conveyor belt and portable rock crusher is one part of a mile-long system that transports tons of volcanic rock from the quarry to the plant where the rock is processed into cement and other products. Farnham Electric was established in 1920 and has specialized in rock reduction plants since the mid- to late 1960s.

“It’s a niche we got into years ago,” said Dennis McGill, vice president of Farnham Electric. “In the early ’70s, we built our first switch house for CC Meisel Co. in McMinnville.”

CC Meisel continues to be a valued customer today, and with a couple of face lifts, that original switch house is still in operation, McGill said. The work, which requires specialty equipment and specialized staff members, has grown from there.

“No two jobs have been alike,” said Waldo Farnham, company president and owner. “Each plant is custom-designed, and each plant operator has his own ideas about just how the final plant will operate.”
There’s two qualities that make these jobs very different: whether the company’s rock quarry will be a permanent plant or if it will require portability.

“If the plant is to be a permanent installation, the wiring method and construction is much different than if it were to be a portable plant,” Farnham said.

If portable, for example, all controls and motors would need to be installed as a plug-and-receptacle arrangement, while a permanent plant would be hardwired.

First and foremost, controlling the plant electrically is the most critical task to get properly identified before the project starts. With each job, Farnham Electric determines whether the plant will be started and stopped by a simple push-button concept and whether it will be controlled by a programmable logic controller (PLC). The PLC offers many options the owner can set. These include selecting electrical interlocking and the use of amperage meters on motors. The PLC can also come with zero-speed switches on conveyors or belt scales installed on the conveyors to monitor production of tons of rocks per hour. It can include field emergency-stop switches on the conveyors as well.

Finally, the installation can vary depending on where the plant will be operated and controlled.

Once those choices have been made, Farnham said, “We offer three to four choices of manufacturers of main switchgear, motor-control containers, soft start starters, PLC frequency drives, etc.” In addition, he said, “We have a discussion with reference to on-site field wiring. We provide this service if the owner or manufacturer wants a turnkey project.”

The switch house, which is built at Farnham’s facility in McMinnville, ultimately contains every aspect of the electrical system for the crushing plant. Once it is completed, the plant is tested as though every motor is already connected.

“Our company then provides an assembly label that is accepted in most countries, along with documentation and drawings of all aspects of the manufactured package,” Farnham said.

An example of Farnham’s work can be found at Hawaiian Cement, a division of Knife River Corp. of Bismarck, N.D. The plant provides integrated construction materials such as cement, aggregate and ready-mix concrete throughout Hawaii. In addition, the company sells bagged masonry cement, golf course sand, decorative stone and landscaping products and materials.

Hawaiian Cement’s facility in Puunene, Hawaii, it needed construction of a belt system to transport rock from the quarry to its concrete operations a mile away, where the rocks are crushed and processed.
When rock is pulled out of the ground, transporting it to processing plants can be done in one of two ways: by truck or by conveyor belt. In the case of belts, the mechanics of a system that typically transfer thousands of tons of rock in a day can’t fail.

“Until the new system was installed, Hawaiian Cement transported crushed rock in trucks,” said David Gomes, Hawaiian Cement general manager.

The company determined in 2008 that it would be less costly to transport that rock using an underground belt system than to fuel and maintain a fleet of hauling trucks. First, the company needed a portable crusher, into which the large rock would be thrown, to follow the perimeter of the quarry. The crusher would then deposit crushed rock onto an above-ground conveyor that would carry rock from the quarry site to an underground belt system that would then transport the rock back to the plant through a tunnel.

Hawaiian Cement engineers designed and installed the underground belt system themselves but contracted out the electrical work for the above-ground belt and portable crusher through its supplier based in Portland, Ore. That supplier subcontracted the electrical work to Farnham Electric.

Typically, the conveyors are used to move the product from one process to the next after rock goes through the first crusher. The motors that power the conveyor are chosen according to the conveyor size and function. The 3,000-foot conveyor that feeds the primary plant is powered by two 100 horsepower (hp), 480-volt, three-phase motors. Not only is the environment hard on the belts, there are challenges for constructing them as well.

This Hawaiian Cement phase of work—primarily the crushing plant and conveyor systems—began in 2008 and finished in 2009. The 3,000-foot conveyor is approximately 36 inches wide and works in conjunction with a 1,000-foot conveyor that will feed another series of shorter conveyors. The conveyor system will deliver 1-inch and smaller material to the cement plant for further processing to meet the required specifications; the processed material will then be transferred by conveyor to stock piles. From the stockpiles, the material is transferred by underground conveyor to the next phase of the process.
Initially, Waldo Farnham met with Hawaiian Cement and the equipment manufacturer to discuss motor loads, plant layout and other necessary information to begin the electrical design of the project. When finished, the system would consist of motors, the portable crusher, a generator, switchgear and operations room. Also, part of the project is the switch house, which is centrally located to the equipment associated with it.

This plant was designed to be portable. Once the plant is ready to move, the owners unplug each motor from the switch house, roll the cables back and secure them to the conveyor. Once all of the power cables are removed from the switch and the control booth, a pop-up area is retracted inside the house, and it’s ready to move.

Farnham Electric connected CLX cable that would run from a trailer to each individual motor and built controls for sensors that would then lead back to an interface through which the operator could control the belts. The company also ran power along the catwalk that follows the length of the conveyors, and a safety cable down the full length of the conveyor. This can be pulled or tripped to shut down the conveyor system in the event of an accident or malfunction.

Farnham Electric provided one switch house with an Elrus control booth that acts as a pop-up and contains the controls for the crusher and belt system. The pop-up is a steel structure with insulated walls and windows that are tinted and designed for a 360-degree view. The switch house is designed for an industrial application, so the control booth is insulated from any damage that could result from the operations outside.

After the switch house was fully set up and the controls tested on-site in Oregon, the pop-up control room was retracted and remained inside the switch house. The switch house was transported that way, in one fully enclosed trailer. Also, all material, job boxes and tools were stored in the switch house and shipped directly to the equipment manufacturing company that provides the conveyor belt. That company then shippped the entire set of material—with the intact switch house—by barge to Maui.

“It’s more like a plug-and-play solution,” Brian Nyseth said, foreman for the project.

Once it had arrived at Hawaiian Cement, two Farnham electricians were on-site for about two weeks to consult and assist with the setup.

On-site, Farnham Electric hydraulically raised the booth into place to extend approximately 7 feet above the top of the switch house. With this extra height, the people inside the control booth can view the plant operations. All stone-producing operations are controlled from the computer center, which is perched atop a 60-foot tower in the middle of the plant, giving operators a clear, full-circle view. From this post, operators monitor and balance production to keep various products adequately stockpiled.

The motor connections also were done on-site, with smaller motors connected under the switch house. Because the motors can be easily disconnected, this allows the crusher to pass along the face of the quarry and get closest to the quarry section where rock is being excavated. To move it, operators can unplug the motor leads and roll the cables on the conveyors and, once set up again at the new location, simply plug the motor leads back into the cord ends under the switch house. Big motors also are located under the switch house but are wired to distribution equipment. They don’t plug in like the smaller motors; they terminate in lugs, but it’s still a quick method for a portable plant, Farnham said.

After such a project is completed, the electrical contractor stocks major electrical components to help eliminate downtime and offers 24-hour service if any follow up maintenance is needed. Farnham Electric strives to offer a high level of customer service.

“We want them to have that warm, fuzzy feeling when it’s done,” Nyseth said.

In this case, Farnham Electric’s men have helped install cord and wire the motors, field controls and lighting on-site in addition to the crusher and conveyor.

“We provide a startup service to work out any malfunctions that may occur with the equipment,” McGill said. “We want the operators to be completely satisfied with their plant operation before we leave the site.”

SWEDBERG is a freelance writer based in western Washington. She can be reached at [email protected].

About The Author

SWEDBERG is a freelance writer based in western Washington. She can be reached at [email protected].





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