Georgia-Based Dos Santos International specializes in high angle conveyors, and has supplied two DSI Gently Pressed Sandwich (GPS) high angle conveyors to a tunnelling project in Paris.
The extension of the Grand Paris Express has been called the most ambitious new metro project in the western world. The extension is an EUR 20.36bn (USD 25bn) expansion of the century-old Paris Metro.
Each of the two DSI GPS will elevate 800t/h of tunnel muck at a 90-degree angle. These conveyors will be reused throughout the life of the project.
The current contract with H+E at the Paris Metro is for two vertical GPS units. The first unit is at Shaft OA 802 at Noisy-Le- Grand and the second at Shaft OA 813 at the adjacent Champigny-Sur-Marne areas of Paris.
“We have a number of other outstanding offers to H+E at various projects around the world,” says Joseph Dos Santos, president of DSI. “We appreciate the confidence H+E has shown in our expertise and capabilities to meet the challenges of such an important and highly touted project.”
The sandwich belt high angle conveyors use all conventional conveyor equipment and components, including smooth surfaced rubber belts that discharge the material completely and can be continuously scraped clean. Dos Santos explains that they run at conventional belt speeds up to and beyond 5m per second. Conventional conveyor components and belts are available for belt widths up to 3m wide.
“This makes the possible throughput rates much higher than any other vertical means of conveying up to thousands of tons per hour,” he says. “By comparison, pocket belts are limited in belt speed partially because of their inability to discharge the material completely. In an actual case, a single vertical sandwich belt high angle conveyor of 60-inch belt width replaced twin pocket belts, each of that same 60-inch belt width, while increasing the throughput rate by 25 per cent. Indeed, that replacement occurred because the pocket belts could not be run faster to achieve the mere 25 per cent increase.”
For the Paris project the client H+E required a system that will be reusable in future projects. “Accordingly, we are designing the system with a high degree of versatility and extendibility,” he says. “With all of the drive and take up equipment concentrated at the head end, we have designed the vertical portion as a hanging structure with the possibility of extending and even contracting the height in increments of a GPS pressing module for future applications.
“This has required designing for the possibility of higher lifts at future applications. In tunnelling projects, a recurring challenge is to accomplish the sandwiched, curved transition from the low conventional loading angle, up to the typically vertical high angle while conforming to the vertical radius of curvature constraints of troughed belts.”
Dos Santos says, “this is something that we understand very well and our competitors don’t. Often they offer transition curves that are too tight and simply don’t work. This results in premature failure of the belt due to edge overstress and material spillage due to the belt’s relaxation at the middle. We have proven that we can always solve these problems without compromising the technology, performance and belt life.”
The DSI conveyor uses two conveyor belts, face-to-face, to gently, but firmly contain the product being carried, hence making steep inclines and even verticallift runs easily achievable. The sandwich belt high angle conveyor hugs the bulk materials by the use of radial pressure, which is due to the belt tension and alternating curving profile geometry.
Materials are conveyed along the convex curves in a “snaking” profile as they are elevated to the highest of angles.
Peter Nevels, chief engineer and project manager for DSI, explains how the system works in Paris: “The two conveyor designs are identical, however, one is shorter than the other and this difference is in the intermediate vertical sections.
“Furthermore, we designed it for the possibility of increasing the lift to 40-45m. The systems in Paris have 24.6m and 26.3m lifts and they are both designed to be increased to 45m. This means each is useful for any intermediate structure up to the design maximum height, making them very versatile.”
In terms of timing to install and set them up, Dos Santos explains, “Engineering and supply for projects like the Paris Metro project take around 25 weeks. “The installation will depend on the customer and how dedicated they are to getting it installed. This can take anywhere from four to eight weeks. Typically it takes a couple of months.”
Dos Santos adds that the conveyor is very low maintenance, requiring the same effort as conventional conveyors operating in the same capacity. “There are no limitations on capacity because we can choose a wider belt and change the speed for every rate,” he says.
“There is also no requirement for a dedicated operator and minimal monitoring is required. The DSI sandwich belt high angle conveyor is made up of all conventional conveyor parts, so it ensures economy and fast delivery of replacement parts.
“There is no angle limit as 90 degrees is the highest possible angle. Additionally, Sandwich belt high angle conveyors are available in widely ranging profiles of “C” and ‘S’ shape. “To date, the highest lift is 175m, but this is not the limit. Recently we provided a proposal for a customer with a height of 375m. When installed, this unit will handle very large rock.”
Nevels explains that one of the main challenges of the Paris project was the limited space available. “In order to develop the necessary radial hugging pressure due to belt tension to elevate the material without over-stressing the belt edge, a minimum radius of curvature is required,” he says. “Because space was limited in the shaft, a very small radius of curvature was needed for the conveyor to fit. In order to reduce the minimum radius of curvature allowed, we used long-center-roll troughing idlers. The use of long-center-roll idlers lowers the neutral axis of the troughed belt, allowing a smaller radius of curvature to be used without over-stressing the belt edge.”
