Matt Ervin, BRUKS Rockwood Inc., Alpharetta, GA
In 2007 Vulcan Materials Company contracted BRUKS Rockwood Inc. (Alpharetta, GA) to upgrade the existing limestone reclaimer at their plant in Lakeland, FL. This increase was needed because they were doubling the capacity of the plant through the addition of a second production line.
The existing relcaimer was designed for a 90 foot wide limestone storage pile at 40 degrees angle of repose and 310 feet in length. The material being stored and conveyed is 4 inch minus limestone at 85 pounds per cubic foot. The upgrade consisted of increasing the reclaim rate from 250 tons/hour to 600 tons/hour, more than doubling the original design rate of the machine. At the same time the pile capacity was to be increased from 600,000 ft3 to 1,150,000 ft3. The building was modified to accomplish this capacity increase by extending the building and adding new rail for the reclaimer, resulting in a linear pile 729 feet in length.
The storage building and reclaimer form a critical link in the concrete manufacturing process, serving as a storage stockpile between the crusher and two process feed bins. From the feed bins the limestone is delivered to the raw mills. It was critical that installation downtime be kept to a minimum as the plant maintained production throughout the installation of this project.
The machine operates by dragging material to a collection conveyor using a chain and rake conveying method, and a harrow agitator. The reclaim boom travels on rails, and moves into the pile. The harrow travels back and forth across the pile face, agitating the limestone so that it falls into the chain and rake transport area below. There are dual harrows on this machine allowing for bi-directional reclaim. The harrow uses steel spikes placed in critical locations to induce the limestone to fall, so that the entire pile face is agitated evenly, leaving a cleanly dressed pile after each pass. The rakes then carry the limestone across the base of the pile and up an inclined pan to a discharge chute. Once the material reaches the top of the chute it drops onto the take-way belt conveyor to the raw limestone processing mills. All electrical components are powered by a cable and traveling cable reel through an onboard MCC.
The rake and chain conveying system was modified to achieve an increased reclaim rate. The original components were replaced with larger, more robust BRI-designed chain, rakes, and shaft assemblies. The BRI-supplied rakes are specifically designed to achieve maximum material fill while reducing overall weight. Using proprietary calculations and our past experience, the BRI rake design resulted in less horsepower conveying more material. The reclaim drive was increased to a 125 HP through a Sumitomo parallel shaft gearbox. The harrow drive was increased to a 15 HP using a Sumitomo Sim-Cyclo gearbox. There was no need to increase the Sumitomo Paramax travel drives.
The harrow frame structure was replaced with a stiffened version for the higher agitation rate, and a larger Conductix cable reel was installed for the lengthened harrow travel distance. A longer cable and a new cable guide were installed, with new support steel on the travel frame to support the larger cable reel. The discharge chute was replaced to accommodate the higher tonnage. The new discharge chute incorporates an overlay wear material to resist limestone’s abrasiveness.
The installation was completed over a two week period in 2008 during regularly scheduled downtime. After installation the machine ran at the lower reclaim rate to allow for any necessary troubleshooting prior to the increase in production. The machine was put into operation at the higher tonnage in mid-2009. Confirmed by two days of testing and some slight modifications to the controls, the machine achieved the higher rate successfully.
The reclaimer is now capable of supplying 600 tons of limestone an hour to the two feed bins. Each bin takes roughly 900 tons to fill, and this is accomplished in 3 hours time. The production rate varies but is, on average, 160 tons/hour per production line. Typically this mill uses a “chase method”, such that the reclaimer is always reclaiming to keep the bin level full at all times.
The large bonus in reclaiming rate over the use rate allows the plant to operate comfortably, knowing that in the event of unscheduled downtime, their reclaimer is fully capable of recovering the lost time and preventing a loss in production.
