Aggregates Manager Digital Magazine
Issue link: https://read.dmtmag.com/i/91809
OPERAT 1 Take environmental issues into consideration Low-Cost and Low- Impact Transportation gates for the Seatt le-based Northwest Division of CalPortland Co. "You have a bett er cost per ton, lower emissions per ton, and you aren't moving trucks up and down the road, so it's easier on the infrastructure," he elaborates. One horsepower/ton estimate rates M Panamax shipping of aggregates at 0.20 horsepower/ton; inland barging of aggregate at 0.35 horsepower/ton, and trucking of aggregate at 12 horsepower/ ton. Based on those estimates, it's easy to understand the lower environmental impact of marine transportation in markets where that option exists. And, although diffi cult to quantify, neighbors and local offi cials tend to respond favor- ably to operations perceived as more environmentally friendly. In terms of economic impact, marine transportation can off er the lowest cost per ton-mile options available, while potentially expanding market opportu- nities. But low cost per ton-mile (aver- aging around 5 cents for Panamax ships and 12 cents for inland barges) is not the same as low cost. Savvy operators understand that marine transportation pays off only if the dock operations are smooth sailing. Th e fi rst step is to get material to the ship, which can be accomplished through a variety of methods including a system of fi xed conveyors, a tripper AGGREGATES MANAGER arine shipment of ag- gregates off ers numerous benefi ts, says Scott Nich- olson, director of aggre- system, loader, or by truck. One recent innovation is a low-profi le truck un- loader that fi ts under portable telescop- ing conveyors. "It's easy to move, and it will handle a 20-ton dump truck in a cycle time of less than one minute," says Bob Domnick, vice president of sales, marketing, and engineering for Morris, Minn.-based Superior Industries, LLC. Th e truck unloader works with the 12-foot feed height on telescopic con- veyors that can be used to load ships. "We need to be able to hit that in one transfer point to minimize degradation," Domnick adds. Once material enters the loading system, operators must balance speed with maneuverability. Depending on the type of loading system being used, speeds can vary greatly. Loading, how- ever, is rarely accomplished in a linear fashion, with ship holds or barge decks being fi lled in a straight-line sequence. Instead, ship captains oſt en have a required sequence to balance the weight of the vessel from front to back. When it comes to unloading ships and barges, fl ow rates are important. With high-speed ship unloaders moving up to 5,000 tons per hour of material, the receiving system must be equipped to handle the combination of volume and speed. "Many ports cannot handle that, so they'll dump it on the dock and pick it up with a loader," Domnick says, noting that double handling of material — while already ineffi cient — also can lead to material degradation. Reducing the number of transfer points reduces downtime when material is not being moved and minimizes material degrada- tion. A truck unloading system that can work with the existing loading system allows material to be quickly moved from a dump truck to a conveyor that loads the ship. When transporting aggregate to the dock area, review regula- tory and permit requirements. Many require enclosed conveyor structures to reduce the impact of wind blowing across the material over waterways. The support structures may also need to be built to mitigate impact on water fl ow and marine life. 4 Minimize the number of transfer points