When faced with a difficult grain conveying situation, such as long distances and many obstacles, a conventional solution can be difficult to implement.
Additionally, when handling difficult materials, such as those that are corrosive, hygroscopic or even toxic and require environmental precautions and a dustless solution, some innovation is required. An initial solution may be going back to a system of running individual loads in trucks. While this requires a lower capital investment, the operational costs are high.
In general, the longer the distance and the higher the capacity, the more likely that a continuous system will be the most effective option. The following are some interesting and innovative bulk-solids handling systems that may not be well known to the grain handling industry.
The RopeCon is a high-tech Austrian system that combines rope technology to transport people and loads on hanging ropes with conveyor belt technology.
The Pipe Conveyor system is a Japanese design in which the open belt passes through a series of transition idlers to form a pipe shape.
The Manutube, from France, is an enclosed belt conveyor with a belt running inside a plastic tube with no idlers, fully enclosed.
The Overland Conveyors/Curvoducts, from France, are effective for very long distances with horizontal curves of low radius.
Troughed conveyor belts are the most widely used continuous transport system for bulk materials. Since their inception in the beginning of the 20th century, they have grown enormously in length, installed power and capacity while reducing their specific energy consumption. Their main disadvantage is their limited ability to achieve vertical and horizontal curves. This ability is reduced as capacity and belt tensions increase.
Main applications are in the mining industry, where belts would allow for very long flights without intermediate drives. The length of individual sections is limited by economic reasons, as the savings on transfer stations are neutralized by the additional cost of the high tension belts.
There are installations in the mining industry with capacities achieving 40,000 tph, but long-distance conveyors are normally limited to 25,000 tph. In the mining industry, the products handled have high densities — between 1.5 to 2.5 tonnes per cubic meter — which is twice or triple the grain density. Developments in belt fasteners technology allow the use of high tension belts, with large installed power. Better understandings in the design of belt conveyors and their dynamic behavior and loading systems have allowed the use of faster belts, with successful references of up to 8.5 meters per second for overland conveyors.
Pipe conveyors overcome several of the problems commonly associated with conventional conveyors, such as spillage of material, belt training and limited angle of incline, horizontal curves and multiple flights.
The conveyor resembles a conventional troughed conveyor at its tail end where the material is loaded. The open belt then passes through a series of transition idlers to form a pipe shape which is maintained for the length of the conveyor. Just before the discharge pulley, the belt opens up again and allows the material to be discharged in the normal fashion.
The material being transported by a pipe conveyor is fully enclosed by the conveyor belt for the major portion of its travel. This has benefits including minimizing environmental pollution, protecting the product from outside contamination and theft, and transporting product in the return pipe.
In curved transport, the pipe shape of the belt permits the conveyor to curve horizontally as well as vertically. A single pipe conveyor can thus replace several conventional belt conveyors. This reduces the need for multiple transfer points and drives, degradation of the product, and costly chute liner replacements.
Invented in the early 1980s and known initially as “Japanese Pipe Conveyors” (JPC), owned by Bridgestone Japan, the technology is mature and applied to a variety of applications. Advantages of pipe conveyors include: enclosed transport, thus protecting from contamination; the ability to have tight vertical and horizontal curves; and the capacity to operate on vertical inclinations up to 30 degrees.
The main disadvantages are the cost in many applications and the higher power consumption when compared to conventional conveyors. The longest pipe conveyor in operation is 8,200 meters long.
Ropeway installations achieve capacities of up to 1,500 tph for bulk materials with single loads of up to 50 tonnes. Rope spans between support towers can achieve up to 3,000 meters.
RopeCon is a new technology developed in recent years by Austria-based Doppelmayr that combines the benefits of the ropeway and the conventional conveyor belt. A flat belt with corrugated side walls and integrated wheel sets runs on fixed anchored track ropes guided over towers. The hauling function is performed by the belt.
Conveying lengths of up to 30 kilometers are possible with a conveying capacity of up to 25,000 tph. Vertical rise in one section can be up to 1,000 meters, along with an inclination of more than 60 degrees, and belt speed up to 8 meters per second. The tower spacing can reach up to 1,500 meters.
The RopeCon operates off the ground, thus minimizing space requirements and easily crossing buildings, roads, rivers or other obstacles. The top of the support towers is attached to the track ropes and hinges are mounted at the bottom. Top and bottom belts each run on two track ropes. Full-locked coil ropes act as track ropes.
The Manutube is a dustless conveyor technology, which consists of a fully enclosed belt conveyor transporting material through a plastic tube. The belt slides inside the tube with no idlers, generating a natural airflow. The dust-tight technology can guarantee less than 1 mg of dust per cubic meter of air for cleaner working area and longer lasting equipment.
It comes in different versions with belt return open with protection grid, or belt return totally closed and return casing with dust cleaning/reclaiming system. It is particularly adapted for process application involving powders or dust generating materials. Capacities vary from 10 cubic meters per hour to 3,000 cubic meters per hour.
The main features include: a belt conveyor with no attrition on the product; transfer of dangerous materials with no contamination of the environment; mastering of explosion risks by dust, hygrometry and oxygen control; optimum for conveying fragile, corrosive and hygroscopic products as fertilizers, salt and others.
A conveying inclination of up to 60 degrees is possible. The equipment is lightweight since it consists of a plastic tube with no idlers. The free span between supports is possible up to 50 meters and no sidewalks are needed.
It is difficult to make a simple comparison between alternative technologies, as the factors that influence their performance are extremely dependent on each application. However, a few key parameters can be analyzed to show indicative comparisons. Conventional belt conveyors and Ropecons have a clear advantage in the large capacity range.
There are over 1,000 overland conveyor systems above 1 kilometers long operating around the world, while there are about 500 pipe conveyors and 4,000 Manutubes. The Ropecon is a new development.
Pipe conveyors are more competitive when there are several curves of short radius, and there is a need to avoid transfer points and spillage. Manutube is the solution when there is a need to convey capacities up to 2,000 tph and materials with explosion risks, contamination risks and strong environmental issues.
Depending on the terrain profile and soil properties, the civil works can be a determinant factor in the cost equation. There are projects located on difficult terrain, with large earth movement requirements and poor soil conditions.
The need of using elevated structures to allow free passage of people and/or vehicles or to deal with flooding and drainage issues can also influence the decision of the type of system to be used. In this type of application, the ability of pipe conveyors and the Ropecon system to adapt to difficult terrain might be the best alternative.
Transfer points are very expensive, generate wear and tear in belts, require support towers, electrical controls, more energy consumption and dust control systems.
Manutubes reduce and simplify transfer points, as they do not need dust control, can go steeper (up to 60 degrees inclination) and are lighter units, with less support towers. They can weigh half of the conventional conveyors, allowing bigger spans between towers.
Pipe conveyors present higher power consumption due to the increased number of idlers and the higher forces involved. Manutubes have fewer moving parts so there are almost no idlers. Ropecon systems and ropeways present the lowest specific power consumption among the alternatives compared, on average about one third of conventional conveyors.
Roberto Hajnal is the international business director of Tecnologia em Movimentação SA (TMSA), Brazil/Bulktech Argentina SA and board officer of Asociación Argentina Poscosecha de Granos (APOSGRAN). He can be reached at firstname.lastname@example.org.