Bulk in motion
John Bensalhia investigates new ways to innovate the humble conveyor belt
In the late 19th century, American inventor Thomas Edison sought an effective, hassle-free way of ferrying coal and ore for his Edison Ore-Milling Company. The solution came courtesy of another American inventor and another Thomas: Thomas Robins, Jr.
The end product created by Robins, Jr was the conveyor belt, an award-winning invention that would go on to be used in places such as factories, prime-time game shows, and of course, ports.
Conveyor belts equate to speedy, efficient, and money-saving methods of loading and unloading cargo. Mapelli Giuseppe, Bedeschi's sales director explains the benefits: “Conveyor belts allow the use of an automatic system for loading/unloading operations and the highest efficiency, reducing trucks traffic on the quay and relevant risks.
“Usually, with bulk material higher than 2m tons/year, the investment in a conveyor belts system is amortised in short terms, guaranteeing all the environmental advantages and benefits mentioned.”
“A principal benefit of conveyors is their reliability, due to their simplicity and robust construction,” adds Todd Swinderman, retired chief executive of Martin Engineering. “Since port operations are usually intermittent, conveyor maintenance can be easier than in a plant operation that runs constantly, resulting in very high reliability with almost no unplanned downtime.”
Conveyors are generally the only practical choice for high capacity transport of bulk solids on docks, because they are compact compared with other options of truck or rail delivery of the bulk material. “On dry land, the rule of thumb is that conveyors are the lowest cost means of transporting bulk solids for distances over 1 kilometre,” says Mr Swinderman. “Many docks are that long alone without considering the transport distance to the stockpiles.”
In terms of costs, the cost per ton conveyed is dependent on several factors but is generally around 25 cents per ton for medium capacity systems at an installed cost of around $1,500 per foot.
Conveyors are also energy efficient when compared with other forms of bulk transport, with average energy costs of around 8 cents per ton (energy is included in the 25 cent figure, so maintenance and cleaning is around 17 cents per ton), calculates Mr Swinderman.
Conveyor belt technology has been developed to take into account particular problems with loading. One of the biggest challenges is dust.
Mr Giuseppe says that more attention is being paid to loading and unloading automatic systems with particular care of dust control. “For this reason, we conceived quay conveyor belts for ship loading/unloading completely covered in order to reduce at the most the dust emission.”
Joel G. Shirriff, vice president and global practice lead, Terminals & Transportation at Ausenco, agrees that dust mitigation is the most significant challenge for bulk terminals today. He points to recent advances in conveyor technologies making use of Discreet Element Modelling (DEM) to design transfer chutes that move cargo more efficiently and prevent the generation of dust along the system without requiring external dust collection equipment. This in turn has allowed conveyors to run faster to deliver more terminal capacity with the same infrastructure investment.
“Ausenco has successfully applied this technology to an existing terminal operation where we upgraded their original conveyor belts to run faster with new transfer chutes, and nearly doubled their annual capacity without any modification to the terminal footprint.”
Mr Swinderman also agrees that dust is a big issue when loading bulk cargo ships. His solution to this is the development of specialised loading spoons which are applied to unloaders to reduce dust. “These spoons also help with reducing segregation because they can be made to slew: distributing material more evenly in the holds,” says Mr Swinderman.
“Most of the final loading from the conveyor system is done through telescoping discharge chutes that retract as the hold fills and are constructed with double walls to allow for dust extraction. Other methods of dust control are fog cannons on the deck that blanket the hold or dust rings around the exit of the discharge chute.”
Another challenge is the potential for spillage. Because most ports now require zero spillage, belt cleaning is critical. Mr Swinderman says that the regulatory fines for discharges into navigable waters can be very significant, and citations often result in temporary shut-downs of ports, with port and demurrage costs as high as hundreds of thousands of dollars per day.
Martin Engineering Brazil has developed a system to maintain cleaning pressure and back off the cleaner, so when material isn't being conveyed, the scrapers are not engaged, which increases belt and blade life. “This system is currently in use at high-volume iron ore port facilities,” he says.
“It is equipped with sensors that detect material flow, so the blade is not engaged when the belt is running unloaded. What’s unique about this system is the use of pneumatic tensioners with a small air storage tank. The tank is below the volume and pressure limits that would require a certified pressure vessel. This is significant, because in many countries pressure vessels must be inspected annually. When servicing the cleaner, technicians carry a small air compressor and recharge the tank, eliminating the need for a compressed air source.”
Ausenco’s Mr Shirriff adds that historically, the potential for spillage has required fully enclosed conveyor gallery structures and collection trays which are not only capital intensive but require operating labour to keep clean.
A piece of conveyor technology that deals with spillage is the pipe conveyor. “This is essentially a traditional trough shaped conveyor belt which uses special guide rollers to form the belt into a closed pipe shape around the cargo on the belt, which is then contained in a hexagonal array of rollers to maintain this circular shape,” explains Mr Shirriff. “Not only does this provide a 100% containment of the cargo from spillage, it also avoids dust generation and exposure of the product to rain and wind.”
Another benefit of this technology is that the conveyor can accommodate both horizontal and vertical curves, allowing the machine to be routed through complex brownfield operations. “Ausenco utilised this to facilitate the movement of various bulk cargoes from a new inbound dock facility in the Port of Toamasina in Madagascar, to a new train loading facility in another area of the Port,” says Mr Shirriff. “This not only allowed us to route the conveyor around existing obstructions, but it eliminated the possibility of dust from contaminating adjacent agricultural export stores.”
The pipe conveyor can be expensive to install and operate, but it can eliminate much of the concern of windblown dust and cargo spillage. Mr Swinderman says that pipe conveyors can be designed to snake through complex on-shore facilities and handle steeper inclines that would be difficult using conventional conveyors, which generally require straight line paths or large curvature radius and are often limited to 15 degrees of incline (depending upon the cargo handled).
“With increasing regulation on dust and spillage, in the future there will likely be more pipe conveyor installations for port facilities,” he predicts.
MADE TO MEASURE LASER BREAKTHROUGHS
New technological innovations for conveyor belts are resulting in greater efficiency and precise operations. A good example of this is the volume measurement on conveyor belts from LaseBVC.
A total of 15 LaseBVC-systems were provided by LASE for Vale's S11D mining project in North Brazil, where the material volume placed on the conveyor belt had to be determined by precise measurement applications. The LASE system can measure volume and height of the iron ore, accomplished by mounting a laser scanner above each conveyor belt.
The laser systems' scan direction runs across the transfer direction of the material on the conveyor belt to generate 2D profiles: these are compared with zero-profiles, which are stored during initial commission of a conveyor belt. With individual difference and belt speed noted, the precise volume can be determined, and if bulk density is also known, then the mass flow can be worked out.
LaseBVC system's high-resolution laser scanners have a scan rate of up to 100 scans per second, meaning that the details of the material can be noted at faster transportation speeds. Accuracy is ensured by special algorithms inside the LaseBVC software application for adjustment and calibration.
The system's sturdy design also guarantees reliable operations in raw environmental conditions.
Jörg Florin of LASE says that the advantage of this technology is the knowledge about the exact volume, profile and mass flow being transported by the conveyor belt. The main benefits are maximisation of conveyor throughput; loading time reduction; lower maintenance costs; and an increase of the conveyor belt's service life.
“For many customers, it is the first step to make their process automatically and to compare delivered and purchased material volumes,” he says. “This is also a very important business case for material delivery by trucks.”
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