Conveyors: Getting It Right
the First Time
One of the best ways to avoid ongoing conveyor-system problems is through correct design – not just for the drives, belt, pulleys and idlers, but for transition points and chutes as well.
By Russell A. Carter, Contributing Editor
At the Core: Coordination
As with any equipment-related project that has the potential to impact throughput, the planning and installation of a conveyor system — even the simplest point-to-point configuration — requires coordination among the mine’s engineering, operations, maintenance and purchasing departments. The more complex the project, the stronger the need for coordination and clear definition of performance goals.
We asked Grant M. Graber, vice president and general manager–
material handling design/supply, Fluor Mining & Metals,
which performance criteria, in his opinion, are foremost in the
minds of mine operators. Graber, who has more than 25 years
of experience in global material handling system delivery encompassing
more than 50 kilometer (km) of overland conveyors
as well as dozens of stockyard, plant, loadout and terminal
projects, identified a trio of concerns customers commonly have
about long and/or high-capacity conveying systems, including:
• Safety – Conveyors have numerous moving parts, conveying thousands of tons of crushed rock per hour. The design and proper implementation of effective safety instrumentation, active and passive safety guards and systems is essential to mitigate the risk of injury, property damage and loss of production.
• System reliability/increased availability – Unscheduled downtime due to component failure or improper design can cripple an operation due to lost production and repair time.
• Operating costs – Belt conveyors must continue to offer lower operating costs than trucking, which is the main driver behind overland conveyors. This requires the equipment to operate efficiently, consume minimum electrical power, require minimal maintenance and comprise components that provide longlife operation.
In order to provide a solution that meets performance goals, vendors need detailed knowledge regarding the purpose and physical characteristics of the application and material to be transported. The information curve ramps up quickly as conveyor- system complexity increases. Project owners may decide to turn to a contractor that offers comprehensive engineering, procurement, fabrication and construction services.
Graber pointed out that experienced engineering specialists
(within engineering companies or system manufacturers) with
extensive resources can bring cutting-edge technology to the design
of complex systems as well as implementation of available
component technology into the system configuration. Often,
they can apply design tools such as:
• Advanced dynamic analysis by independent specialists that are part of the engineering team, enabling sophisticated simulation of complex conveyors, which helps in optimizing the selection of critical equipment such as drive systems, belt design, braking systems, motor controls, and idler design and spacing. Optimized selection of these elements can improve conveyor reliability, safety, CAPEX and OPEX.
• Discrete element modeling (DEM), using specialized software enables simulation of bulk material flow in transfer chutes, bins and hoppers. This tool enables sophisticated design of chutes to optimize material flow to reduce chute wear, impact, noise and to mitigate the risk of material blockages and flow problems. Modeling also enables optimal energy transfer by minimizing power required to reaccelerate material on to a downstream conveyor, and to harness available kinetic energy within the material flow to improve transfer efficiency.
• Intelligent design and modeling systems, which enable virtually every system element (steel, components, instrumentation) to be incorporated into a database with information regarding each element’s source, manufacturer, specification, etc. This can be used for inventory management, preventive maintenance and other operational benefits.
In addition, he noted that the range of services available could include implementation of technologies such as system and component health monitoring, which can be used to prevent component failure and to schedule preventative maintenance tasks. These systems include real-time monitoring of component operating parameters such as bearing temperatures, bearing vibration, oil temperature, rotating component noise, conveyor belt integrity and others. Other recommendations could focus on low rolling-resistance conveyor belt rubber compounds, which can reduce conveyor system power consumption.
For large mining projects, the benefits derived from modularization are substantial and can extend to conveyor system construction and installation. Graber said most high-capacity, longer conveyor systems include large drive stations, head/tail structures, transfer towers and electrical rooms — types of major structures that often can be designed for off-site modularization and preassembly, thereby reducing on-site construction costs and reducing site safety hazards. He pointed out that modularization normally will incur somewhat higher fabrication and logistics costs, but these are usually more than offset by reduced construction time and cost and reduced risk.
It’s definitely not a do-it-yourself undertaking. According to Graber, “Modularization is a specialized execution model that requires a fundamentally different approach to design through fabrication and shipping. It must be implemented at the project outset. It requires early and continuous engagement of engineers, designers, fabricators, logistics and construction. Companies like Fluor specialize in this approach and have applied it to many projects.”
Graber also pointed out a trend that has developed over the past 10-15 years: An alternative approach to project execution in which a single company (or group) is assigned responsibility for the complete design and delivery and, in some cases, installation of a functional system. Owners procure such systems from single, specialist suppliers or contractors as opposed to having them engineered separately, procured in a piecemeal manner, then subsequently erected by a contractor.
Speeding Up Site Surveys
One of the earliest requirements for planning an overland conveyor system is a site survey, and if, for example, the intended route of the system extends for kilometers or crosses rugged terrain, those surveys can be expensive, time-consuming and possibly hazardous for workers. Using drones to perform quick, safe and increasingly accurate aerial surveys is now a legitimate option in many cases, and bulk material transport specialist companies such as the Beumer Group are turning to UAVs for their potential time and cost savings.
In a recent interview, Beumer’s Eugen Doberstein, project engineer–overland conveyor; and Lukas Paul, manager–plant design/bulk material handling systems (sales), highlighted how drones have become an important tool in preparing project bids. Paul explained: “If customers authorize us to supply and install a belt conveyor, we have to submit a detailed quotation beforehand. Here, it is important to assess the project correctly. We usually do not have a lot of time for this. The use of aerial photographs that are analyzed by specialized software provides an effective way to accomplish this. This has made drones an important tool for us. They are equipped with high-performance cameras that provide image data that we then use to create a reliable planning basis with our software.
Doberstein contrasted this method with earlier conventional approaches such as sending out a survey team. “This was quite common,” he said, “but it was time-consuming and expensive, and this is a phase in which it is often not yet clear whether the customer will realize the project at all.
“In the best-case scenario, the users know the field of application because they have previously transported bulk material by truck, for example. Then they are able to provide the required data and we can start working immediately. Later, Google Earth was an alternative. The software superimposes satellite and aerial images of different resolutions with geodata and shows this on a digital elevation model of the earth. However, this data is not as accurate and up to date as [information from] a drone.”
Paul added: “[Drones] save considerable time and costs. If a customer is not yet sure whether they will proceed with the project, we quickly provide them with precise and low-cost data at the time of the project pre-planning phase by means of drone recordings and our further calculations. On this basis, the customer can make their decision: Is the project worth it or not? But we also benefit from significantly less effort and thus manpower, amongst other things and this is reflected in the costs. Drones are presenting an excellent solution to get a first overview.”
Doberstein said that with the aerial photos from the drone survey in hand, “[the] photos are rectified with regard to their perspective and evaluated photogrammetrically. The software calculates a point cloud in order to generate 3D models from the two-dimensional views, i.e., digital terrain models. This is decisive for the quality of the work. Depending on the scope of the project, this can take between one day and two weeks.”
Simulation Leads to Solid Solutions
With literally thousands of possible decision points that involve volume and mass flow, drive system power and layout, belt tension/ takeup requirements, belt configuration and layout, pulley diameters, any need for curves and transition zones and more required for the design of large conveyor systems, converting the resulting mass of data into a useful roadmap leading to a solid solution is a job tailor-made for computer simulation and analysis.
For example, German software developer ESI recently pointed out that Siemens Minerals has used its SimulationX product to optimize conveyor drive design. Performance, investment and operating costs are pivotal factors for any piece of machinery throughout its lifecycle, and Siemens Minerals’ core business mission is to supply mining customers with drives that fit their requirements in these areas — all of which must be considered for a specific drive configuration. Variables that can impact cost include high energy conversion efficiency, maximum load capacity, and slip reduction.
ESI said SimulationX provides Siemens Minerals with a modular, user-friendly solution to build fast and reliable workflows for design, testing and commissioning of belt conveyor drive systems. Designing, dimensioning and modifying drive systems for belt conveyors requires extensive knowledge of a conveyor’s behavior. Because prototypes typically aren’t available, it’s diffi- cult to test certain scenarios and requires time-consuming and costly on-site commissioning processes.
Finding the most energy-efficient and cost-effective layout while delivering expected performance is a priority. According to ESI, most simulation solutions available today represent only a part of the system. They don’t address dynamic, physically realistic conveyor system behavior, including that of the belt, drives and controls.
Siemens Minerals discovered that by using dynamic system simulation, it enables a significant part of the commissioning process to be completed before the equipment is installed. This reduces operational delays and eliminates the need to keep staff on-site for extended periods. Additionally, it makes it possible to explore various scenarios in a cost-efficient manner and without risk to workers or the environment.
ESI said Siemens Minerals uses SimulationX to:
• Create a model of a planned or existing belt conveyor system, based on data from a supplier or operator, as a basis for drive system design, optimization and virtual commissioning.
• Analyze the belt conveyor’s behavior in conjunction with the planned or existing drive system.
• Assess the effects of modifications on the drive system or the belt conveyor (e.g., increased loads, changes in the topology).
• Test control algorithms for the drive system and evaluate the effects on the belt conveyor’s behavior.
• Analyze the belt conveyor’s overall behavior in extreme situations, such as emergency shutdown, power outage or component failure.
For Siemens Minerals, the use of simulation goes beyond design optimizations and virtual commissioning of the belt conveyor. Real-time testing of controller hardware with a Hardware- in-the-Loop (HiL) platform is one of the next steps. In that context, a SimulationX model on the HiL platform represents the behavior of the complete belt conveyor system. Based on that model, the HiL platform provides the same feedback to the controller as that provided by the actual plant.
Taking Time for Transfer Points
Drives, belts, pulleys and idlers aren’t the only components that can impact conveyor system performance: Transfer points and chutes that don’t perform as intended can present operational challenges that result in unplanned downtime, lost production and personnel safety issues. Fluor’s Graber told E&MJ that, in his experience, one of the most common mistakes made in system planning is not allocating sufficient resources/funding for careful design of chutes and hoppers that allows sufficient space and height for proper material flow and transfer. If material can’t be reliably loaded on to a conveyor and transferred to another via chutes and hoppers, even the most sophisticated system can fail.
Help is available from a number of sources. For example, U.K.-based DEM Solutions recently released a new version of its EDEM Bulksim software aimed at achieving optimum material flow through transition points and chutes. EDEM BulkSim employs Discrete Element Method (DEM) technology to allow engineers to evaluate and verify design performance. By predicting bulk material flow and interaction with equipment components, it enables users to identify and remedy potential problems in a design, such as material buildup and blockage, flow dispersion, spillage, size segregation and excessive belt and chute wear, before commissioning. The developer stated that EDEM BulkSim allows for easy deployment across teams and includes a suite of out-of-the-box visualization and analysis tools for both quantitative and qualitative evaluation of transfer point designs.
The latest version (2.0) offers a range of enhancements as well as increased capabilities and performance, including a new user interface for quick simulation set-up and an intuitive workflow. Users now have access to the Generic EDEM Material Model (GEMM) Database to introduce materials in their simulation. GEMM includes more than 50,000 of pre-calibrated material models representing a wide range of rocks and ores. This, according to the developer, means users can access fit-for-purpose material models that produce realistic material behavior and they can fully set up materials for a simulation without being a DEM expert. In terms of performance, the company said users can expect quicker performance with the possibility to run simulations on their computer’s Graphical Processing Unit (GPU) — delivering simulation results up to 12 times faster than by using traditional desktop CPUs. On the post-processing side, users can benefit from faster data export and advanced tools to create more realistic and dynamic videos.
Mark Cook, EDEM product manager, said, “EDEM BulkSim is a key design tool that enables engineers of all experience levels to get critical insight into transfer points performance. It has been developed to easily integrate in the design process and means engineers can increase the quality of their designs by performing ‘virtual testing’ to assess performance under differing operating conditions. Version 2.0 means users can introduce materials quickly and easily by selecting a fit-for-purpose material model from our extensive materials library. Performance has also greatly improved, which means users can run their simulations much faster and perform analysis quicker, leading to increased productivity.”
Containment Systems Can Curtail Conveyor
Most conveyor-related injuries occur though routine maintenance or cleanup of spillage and dust, particularly around transfer points and chutes. Controlling fugitive material in these areas should be one of the primary elements in any program aimed at reducing hazards and preventing injuries. “Conveyor operators need only take a broad look at the expense that fugitive material has on a system to realize the full cost that accompanies inefficient transfer point designs,” according to Jerad Heitzler, product specialist at Martin Engineering. “Problems such as improper belt support, badly sealed chutes, damaged idlers and uneven cargo distribution can all result in spillage and belt mistracking. They also contribute to increased costs for lost material, premature equipment failure, maintenance and cleanup, as well as the potential for injury and compliance issues. These factors raise the cost of operation and reduce profit margins.”
Containment is the key to avoiding spillage and dust, and there are a number of components designed for this purpose. Although shaped transfer chutes and rock boxes direct the material flow to mitigate the concussion of material on the belt, most high-volume operations need one or more impact cradles to absorb the force of the cargo stream. Heavy-duty impact cradles can be equipped with rubber or urethane impact bars with a top layer of slick UHMW plastic to minimize belt friction. Able to withstand impact forces as high as 17,000 lbf (53.4 to 75.6 kN) and drop heights of up to 50 ft (15.2 m), support beams in the center of the cradle are set slightly below the receiving belt’s line of travel. In this way, the belt avoids sustained friction when running empty and yet can absorb hard impacts during loading, while still retaining a tight belt seal.
Within the settling zone, located after the impact cradle in the conveyor chute box, slider cradles provide several functions. One is to create a trough angle that adequately centers the load. The trough angle also plays an important part in retaining a tight seal between the belt and the skirt. Lastly, by utilizing track mount idlers in between each cradle, a smooth belt path is created through the settling area — one that can be easily maintained. A smooth belt path should have no gaps, minimizing disruption and promoting containment, allowing dust and fines to settle into the cargo stream prior to leaving the containment area.
With a constant stream of material hitting the impact point of the receiving belt, the transfer point can be extremely turbulent, and this turbulence must be contained. By slowing the airflow in the skirted area, suspended dust is allowed to settle onto the cargo path. To contain the mixture of air and disrupted material a stable, correctly supported belt is needed for the sealing components to function properly. Without a stable beltline, the belt will sag between idlers, and sealing components will not prevent air and fine material from escaping out of the resulting gaps, causing spillage and dust emissions.
To close gaps and keep a tight seal on the belt, apron seals can also be attached to the chute walls to prevent fugitive dust and fines from escaping. Modern designs featuring external skirting require minimal tools and no confined space entry to inspect, adjust or replace wear liners or skirts, and in most cases can be performed by a single worker. The low profile of the skirting assembly needs only a few inches of clearance, allowing installation and maintenance in space-restricted areas. The design drastically reduces scheduled downtime and the potential workplace hazards associated with replacement and adjustment.
In operations with limited space for a settling zone or especially dusty materials, dust bags and curtains may be essential components. Providing passive relief via positive air pressure created at belt conveyor loading zones, dust bags prevent the escape of airborne particulates by venting the air and collecting dust at the same time. Installed at the exit of the loading zone and mounted in the skirtboard cover, dust curtains can help create a plenum for dust suppression and dust collection. For additional dust control, an integrated air cleaner system can be installed at the point of emission, containing a suction blower, filtering elements and a filter cleaning system. Managers concerned with the overall safety and cost of operation need to review potential hazards, the impact of rising labor costs for cleanup and maintenance, combined with the expense of potential fines or forced downtime, to determine specifically how they can affect the bottom line. Using the technologies described here, even poorly performing conveyors often don’t need to be replaced or rebuilt, but merely modified and reconfigured by knowledgeable and experienced technicians installing modern equipment.