By Carol Wasson
More and more coal prep operations are realizing the advantages of polyurethane and rubber screen media versus woven wire and steel punch plate—namely, significantly extended wear life, ease of maintenance, greatly improved safety, reduced noise, as well as increased magnetite recovery, plant yield, and product quality. The Martin County, Kentucky-based Pinnacle Processing plant, which is owned by Booth Energy, is experiencing each of these benefits after installing Polydeck modular synthetic screen media in several key processing circuits.
“We’re a very proactive company that thinks outside the box,” said Joe Brumfield, maintenance supervisor, Pinnacle Processing. “Just because we had always gone with wire previously doesn’t mean it’s the only way to go. We found converting to synthetic screen media has extended wear life by more than 60%, while also lowering our screen maintenance and labor costs by more than 40%.” Brumfield also stressed that the use of synthetic media is one more initiative that has allowed the operation to maintain an excellent safety record and remain completely compliant with MSHA regarding noise reduction.
It is Pinnacle’s “outside the box” philosophy that allowed Polydeck Screen Corp. to install its modular synthetic screen media in various applications within the plant. Polydeck guaranteed improved performance and, although skeptical at first, Brumfield and Virgil Mills, plant superintendent finally agreed to run a test on one deslime deck. They quickly became believers. “I’ve worked in the coal industry for more than 30 years and have never experienced better service and expertise. They are hands-on and here whenever we have a problem,” said Brumfield.
Brumfield works closely with Steve Parsons, a Polydeck regional manager. Parsons said the company’s goal is to increase its customers’ performance efficiency while lowering operating costs. “If you can do that, you’re adding to their profit line,” Parsons said.
Drain-and-Rinse Applications
The first conversion took place at the vessel’s clean coal, drain-and-rinse circuit where woven wire and stainless steel decks on two 8- x 16-ft screens were replaced by polyurethane screen panels. The top deck was fitted with a VR panel design with 38-mm (1.5-inch) openings. “The VR panel, with its zig-zag openings, is a very flexible, active panel. Because the openings are continually moving and vibrating, it is resistant to pegging or blinding, which would reduce magnetite recovery,” said Parsons. “We are also using screen panels with molded dams on this deck and as particles tumble up and over the dam, that is the ideal place to hit it with spray water—and we can place dams anywhere on the deck to achieve maximum efficiency. That is something that cannot be done on a woven wire deck.”
On the bottom deck, 0.5-mm polyurethane continuous slot screen panels replaced a 0.5-mm stainless steel profile wire deck. Parsons said that for drain-and-rinse applications, continuous slot panels provide the maximum amount of open area to allow optimal efficiencies and recovery rates. The openings must be precise and consistent to prevent misplaced material while washing and cleaning magnetite off the coal.
“The magnetite recovery rate was not as good with the prior stainless steel media, which is roughly the same cost per square foot as the polyurethane, but would last only about 25% as long,” said Brumfield.
“Some would think that the efficiencies would be the same between either type of media if each has 0.5-mm openings, but that is not the case,” said Parsons. He explained the stainless steel media limits the retention time and the particles slide off quickly and smoothly. “In truth, you want the particles to tumble a little bit—similar to the agitation in a washing machine—and that is exactly what happens on the polyurethane continuous slot panel. It will outperform stainless steel by providing a more efficient rinse, while increasing wear life by up to four times,” Parsons said.
Raw Coal Separation
Next, Polydeck worked with Pinnacle Processing to increase the efficiency of the raw separation circuit where woven wire was removed and modular polyurethane screen panels were installed on each of four 6- x 16-ft double-deck inclined screens. The top deck was fitted with 19-mm (0.75-inch) slotted openings and the bottom deck featured 11-mm (3/8-inch) zig-zag openings, which effectively eliminated any blinding or plugging issues. The oversize material travels to the vessel circuit while the undersize reports to the cyclone circuit. Brumfield said he is seeing approximately 5% increased separation efficiency since the installation, in addition to the extended wear life and reduced labor costs. Also, with the wire screen sections, worn edges would become razor sharp and pose safety hazards—an issue that’s eliminated by the use of modular polyurethane panels. “It’s far safer to have one worker pulling out a modular polyurethane panel versus four workers crawling under the top deck to change out an entire wire screen on a bottom deck,” said Brumfield.
Scalping
Although scalping is obviously the first screening process in the plant, it was the last circuit to be converted to synthetic media. “This screen is the jugular vein and if the synthetic media did not perform there, it would affect the efficiency of the entire plant. Many operations are reluctant to remove woven wire from a scalping circuit because they feel they will sacrifice open area,” said Parsons.
“We are scalping the 4-inch-plus material and re-crushing it to achieve better efficiency,” Brumfield said. “With the prior use of woven wire, we were changing out the screen almost every week. It was a maintenance nightmare, made worse by up to 100% blinding from clay material on the screen, and the breakage of the woven wire due to the impact of the material on the deck. The breakage was expensive and particularly problematic as we certainly didn’t want a load of contaminants in the coal.”
The woven wire was replaced by Polydeck 1- x 2-ft Flexi rubber panels on the 7- x 20-ft scalping screen. “These are the best dollars we’ve spent on the plant,” Brumfield said. “The Flexi product works extremely well. After more than three months, we haven’t touched it, and we haven’t had a single blinding issue.”
“We selected our Flexi rubber compound for this application because it is a very responsive, live rubber which presents natural characteristics for resiliency, abrasion resistance and tensile strength,” said Parsons. He said the open area was not an issue due to the use of a slotted opening. “The slotted opening will outperform a square opening on an inclined screen, since the slotted design features a longer opening, providing the particles with a greater opportunity to get into it and pass through. Also, the 1- x 2-ft panels feature a ‘maxi-panel’ design which allows more openings per panel and up to 30% more open area over competitive screen panels,” Parsons said.
“Because of Polydeck, it is a lot easier to manage our processes,” said Brumfield He especially appreciates the improvements in safety, noise reduction, separation efficiency and magnetite recovery. The operation is enjoying its biggest bonus—an enhancement in the quality of the final coal product.
This article was commissioned by Polydeck Screen Corp. Wasson is a freelance writer and public relations specialist for the mining industry. She can be reached at 260-724-4508 or E-mail: wasson@decaturnet.com.
