Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/94387
OPERATIONS ILLUSTRATED M Voices of Experience Gary Yelvington oving material efficiently is the name of the game at Daytona Beach, Fla.-based Conrad Yelvington Distributors, a part of the Oldcastle Southern Group. According to Gary Yelvington, president, the company has moved as much as 10 million tons per year of aggregate during peak production years. "The Federal Railroad Administration has determined and classified our railroad operation as a Class 3 Industrial Switching Company. We are compliant with hours of service regulations, along with many other sections of the transpor- tation code," Yelvington says. "Simply put, we can do a lot of things that not many folks do in our industry." Typical rail movement of aggregate includes unit trains with a minimum of 75 cars and as many as 100 cars. The com- pany owns or leases more than 1,300 rail cars, which includes about 40 gondola cars, but most are bottom-drop cars. A bucket-type machine — typically an excavator — is used to scoop material out of the gondola cars into trucks. "We do some of that, but it's only for the big rip rap material that you can't drop through the bottom of a car," Yelvington says. For peak efficiency, however, Yelvington explains that he Bob Domnick, P.E. improve overall metrics. "In the past, I think there just had never been a study of process flow for rail unloading," says Bob Domnick, vice president of sales, marketing, and engi- neering for Morris, Minn.-based Superior Industries, LLC. Factors such as the size of the hopper and the mix of rail cars sometimes vary widely, which can lead to inefficiencies in the process. "It seems to me that, in the past, operators would build W pits with as big of a hopper as they could," he says, noting that size would be the maximum available, based on the site's water level to ensure that pumping would not be necessary. "By and large, there would have been several hoppers and then a conveyor under those hoppers. "Today, simplicity is chosen, so if a single hopper with one discharge point under that conveyor can be done, that's what is chosen because you don't need as much depth to accommodate the conveyors," Domnick says. "That way, the operator doesn't have another drive to maintain, which can be AGGREGATES MANAGER ith big money on the line, many producers mov- ing material by rail are becoming increasingly savvy about how little changes in the process can a headache." The key, Domnick says, is to watch material flow. How long does it take to move from one car to another? "Ideally, the hopper would just be emptying as you get to the next car and start dumping. This ensures continuous flow, and it's nice for the drives on all the conveyors going away from the rail because they can be sized efficiently," he says. "Otherwise, you will have surges, which means wider belts and higher capital costs." Another step toward more efficient unloading of cars is for each train to be comprised of the same type of rail car. "Some- times, there are aggregate cars that have two hopper bottoms, some have three, some have four. They just vary in size; they aren't all 100-ton cars," Domnick explains. "If the rail cars themselves are identical, you can get a much nicer flow." Often, the cars are owned by the railroad, which can make the composition of the unit train a little more difficult to control, but Domnick says that, in the situations he's seen, approximately two-thirds of the cars have been the same. "More and more, people are trying to get them identical, so the trend is toward better flow," he adds. prefers the bottom-drop cars. "Most of our cars are bottom- drop cars," he notes. "Those are the fastest cars to unload, but you have to have infrastructure to unload those types of cars." When a train is unloaded at one of the company's yards, a cut of approximately 15 cars is pulled across a pit by one of its locomotives. Yelvington says the company has about 35 locomotives, with second units at its busiest sites to allow for maintenance or breakdowns. Workers open the doors on the bottom-drop cars, and the material falls into an underground hopper where it is discharged onto a feed conveyor that carries it up at about a 15-degree angle along a path that leads a couple hundred feet away from the track. Material is then discharged onto a radial stacker, which has a 270-degree arc. The stacker is used to stockpile material into various sizes. "Depending on the product, we unload 12 cars per hour," Yelvington says. "If it's base or screenings or a fine product, it might be 10 cars per hour. If it's a coarser material that flows and spreads freely, we might do as many as 14 per hour." ▼ ▼