Coal Age

JUN 2013

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o p e r at i n g i d e a s Using Dust Management to Improve Safety and Reduce Maintenance on Conveyors Installed at the bottom of the loading zone skirtboard, Martin Double Apron Seal Skirting employs two wear surfaces on each sealing strip for twice the service life. Orlando Utilities Commission-Stanton Energy Center (SEC) is one of Central Florida's leading environmental stewards, meeting or exceeding all air permit limits with advanced pollution control equipment while generating electricity to serve more than 342,000 residents. The company follows a similar philosophy with respect to its working environment, cleaning the entire coal yard and all handling equipment every day. "Typically each day after we finish filling or bunkering the silos, the whole system is cleaned," said Stuart Cason, material handling supervisor, SEC. "That includes the yard, all the conveyors, chutes, floors, impact zones and rollers. In some places, it's a wet wash-down, while in others we sweep. It's seven days a week, every week of the year." When company officials decided to upgrade the dust containment on one of its primary coal conveyors, they saw several potential benefits. There was the safety aspect: by limiting dust and spillage from one of its principal conveyors, engineers wanted to reduce airborne particles and eliminate a potential source of trips and falls. There was also the understanding that reducing cleanup would save maintenance time, allowing critical manpower to be deployed elsewhere and improving the staff's efficiency. Further, preventing coal dust spillage would help minimize wear on rollers and other moving components, saving on replacement part costs and labor. SEC started by looking at the areas that could benefit most from technology upgrades to the 36-inch conveyor, which travels at about 700 ft per minute. "We were looking for a better method of sealing the transfer zone, for starters," said Brian Moore, plant engineer, SEC. "We had skirt blocks and seals in place, but they were getting old, and some of them were leaking or repeatedly coming loose." "Coal dust is fairly abrasive, and when it got down into the impact rollers, idlers and troughers, it would pretty much eat them up," Cason said. "We tried everything we could think of to improve the service life, but we were constantly replacing them." 52 www.coalage.com To address the situation, Martin Engineering supplied and installed a number of upgraded components, including Double Apron Seal Skirting, which employs two wear surfaces on a single elastomer sealing strip installed along the bottom of the skirtboard in the loading zone. When the bottom side of the sealing strip is worn, it can be inverted to deliver a second service life. The skirtboard sealing system is installed on the sides of the loading zone to contain dust, eliminate spillage and reduce cleanup expenses. Believed to be the first dual-sealing system available, it incorporates a primary seal clamped to the steel skirtboard to keep lumps on the belt and a secondary or "outrigger" strip to capture any fines or dust particles that might pass beneath the primary seal. The secondary seal lies gently on the belt and self-adjusts to maintain consistent strip-to-belt pressure, despite high-speed material movement and fluctuations in the belt's line of travel. An impact cradle was installed to better absorb the force of the falling material and protect the belt and structure. The cradle stabilizes the belt's line of travel to help prevent the escape of fugitive material. Its rugged impact bars are constructed of a top layer of low-friction UHMW resin and a lower layer of energy-absorbing SBR rubber. Each impact bar is reinforced with a bed of steel angles, and the wings can be adjusted to suit virtually any standard trough angle. In addition, a belt support system was added under the skirt board to better support the edges of the belt and eliminate sagging. The cradle helps prevent transfer point spillage by further stabilizing the belt path and facilitates effective sealing of the edges. Belt wear is minimized by eliminating pinch points where trapped material can gouge the belt surface. A belt tracking system was installed to maintain precise centering in the loading zone. Comprised of upper and lower components, the tracker works to reduce belt edge damage, prevent spillage and extend belt life. Designed to withstand the stress associated with wide, thick belts moving at high speeds, the tracker features heavy-duty construction that is well suited to heavy loads. "We could see the improvement right away," Cason said. "It's not just the savings in cleanup time, but also in preventing the idlers from wearing out prematurely. Now I don't have to send my guys out there to replace those failed components, so it saves on labor and replacement parts, as well as the housekeeping time." The System Centerpiece A key element in the material handling system upgrade was addressing the large, under-performing dust collector. "We wanted to upgrade our dust collection equipment because we knew technology had advanced since ours was installed," said Jon Janis, maintenance supervisor, SEC. "Even when it was functioning properly, the old unit was a high-maintenance item." The Martin Engineering team installed a high-efficiency insertable air cleaner with an explosion-proof motor. It's an automatic, self-cleaning design that employs filter elements approximately one-eighth the size of conventional filter envelopes. The smaller filter elements allow a significant reduction in the dust col- June 2013

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