By Steve Fiscor, Editor-in-chief
Screening machines serve several functions in the modern prep plant. First and foremost is size separation, but they also dewater and remove impurities. The U.S. coal industry varies greatly by region and so do screening needs. Not only is the hardness of the coal a concern, but other issues such as rock, clay and acidic water affect a screen’s operation.
The size of the machines continues to grow as well. While some prep plant operators have adopted wider screens, others are reluctant to make the leap. Many of the new U.S. plants are being built as a single-line process and wider screens are probably the best way to increase throughput in that type of system. Aside from capacity, the larger machines also reduce the screening footprint inside the plant—one large screen instead of multiple smaller screens.
Mines in China and Australia are routinely now using 14-ft wide screens. Assuming the U.S. follows suit, many vendors believe 14-ft screens could becomes a reality in the U.S. soon. Right now, the largest screen in a U.S. prep plant is 12-ft wide.
Except for the deck, most screening machines today are pretty much maintenance free. As far as woven wire vs. urethane panels, all of the vendors agree that there are practical applications for both types of decking. Woven wire offers better open area. From a maintenance standpoint and cost of operation, however, it’s difficult for woven wire to compete with the modular urethane panels. Many of the companies that make screen machines also have a division or sister company that makes and sells screening media.
Tabor Offers New Screening Machine, Media
Tabor Machine Co. recently announced the availability of its widest screening machine yet. “During the last several years, we have seen more use of wider screens,” said John Casey, sales and applications engineer, Tabor Machine. “During the 1980s, the mainstay for screening machines was the 6- x 16-ft single deck horizontal screen. The push now is to 14-ft wide, or even 16-ft wide screens.”
The trend toward the bigger machine is continuing albeit a slower pace than what’s happening abroad. “Only one of our customers is using 12-ft screens,” Casey said. “We have customers that refuse to buy a 10-ft screen. They would rather run two circuits with multiple screens. If one circuit goes down, they can still run the plant at half capacity.”
The company introduced a new line of 12-ft multi-slope and horizontal screens during September 2010. “We recently received our first order for the new 12-ft screen,” Casey said. “Those machines are scheduled to go into production within the next month or so.” Tabor screening machines are field proven, well built and that engineering design carries through to the 12-ft screen and eventually the 14-ft screen, Casey explained.
From a maintenance standpoint, Tabor stuck with standardized parts for the new line. “Whether it’s a 12-ft Banana or a 6-ft single-deck screen, we are still using the same parts,” Casey said. “The mines won’t have to carry a lot of extra, new parts to service the machines. The maintenance costs per ton processed decreases on the larger units, but components for a 12-ft machine will be more expensive than a 6-ft machine. Labor costs would be less.”
When it comes to screen media, Casey believes there are applications for both woven wire and urethane. “Urethane’s strongest points are wear life and safety with the ease of replacement,” Casey said. “To say one is better than the other would be foolish.”
One of Tabor’s sister companies, Norris Screen, recently developed a new modular screen media: the Phase 3 Pinless (P3P) system.
“With the P3P, Norris has the ability to offer a snap-in woven wire panel or a snap-in perforated plate,” Casey said. “Instead of replacing a 4- x 8-ft piece of woven wire, the maintenance crews handle a 1- x 4-ft piece of woven wire. That has a huge safety advantage especially with the sloping decks.” With the pinless system, Casey explained, the plant technicians no longer have to worry about dropping pins into the underflow or the chute work. They simply snap in the panel and they are off to the races—a quick, seamless transition.
Derrick Pushes the Envelope for Clay Removal
Derrick designs and manufactures high frequency vibrating machines and screen surfaces used to screen a wide variety of materials and its Stack Sizer has redefined the concept of efficient, fine particle wet screening. It offers high capacity with a minimal amount of floor space.