Powerful Design Tools—and Common Sense— Can Control Conveyor Cost and Complexity Issues
Computer programs can calculate, simulate and evaluate endless conveyor configurations, but for buyers, a hard look at long-term cost-effectiveness vs. price may be the most important measure
By Russell A. Carter, Managing Editor
Against the backdrop of global economic turmoil and a general trend within the industry toward higher cost-consciousness, the importance of conveyor systems in mining obviously hasn’t diminished over the past few years. If anything, conveyors designers are being pressed to provide systems that can carry more, carry it farther and with lower energy consumption and life-ownership costs than their predecessors. In response, system suppliers are taking a closer look at almost every element of conveyor component design and application, from the rolling-resistance properties of various rubber belt cover compounds to the relative benefits of central vs. distributed drive designs for long overland conveyors. And, as conveyor systems become more complex, Discrete Element Modeling, Finite Element Analysis and other computer-assisted analysis techniques have become increasingly essential, replacing rule-of-thumb assumptions that designers have used for many years to formulate belt, pulley, idler and chute specifications.
Imagine, for example, the number of calculations required to specify, design and fabricate a system such as that recently announced by Sandvik, which signed an agreement with Netherlands energy company RWE Power AG for a turnkey materials-handling system. The $83-million order comprises a complete materials-handling system for the Eemshaven power plant in the Netherlands, and includes a high-performance conveyor system with 38 enclosed conveyors for coal, plus two grab-type ship unloaders, two stackers and three portal reclaimers.
Other recent examples of complex conveyor design include an overland conveyor/belt feeder system installed at the Boddington gold mine, near Perth, Western Australia, owned by Newmont Gold Corp. This system, described by Todd Hollingsworth and Ty Harris of FLSmidth Conveyor Engineering in a paper presented at the 2010 Annual Meeting of the Society for Mining, Metallurgy and Exploration (SME),1 involved design and manufacture of 15 conveyors and 17 belt feeders with belt widths ranging from 450 mm to 2,400 mm and conveyor lengths from 16 m to 2,172 m. Total motor power exceeds 16,700 kW, total length of all belting is almost 11.5 km, and fabricated steel weight totaled about 3,700 mt. It went into service at Boddington in April 2009.
In an entirely different application, a pipe conveyor— billed as the world’s longest, transporting a double load on a single, troughed belt—was installed and commissioned at the Cementos Lima cement operations near Lima, Peru, in early 2008. This system, according to J. Wiedenroth of Germany-based FLSmidth Koch MVT,2 which designed and installed it, had to meet several challenges: It had to follow, by means of an underground tunnel, the path of an existing road through a town for 6.5 km, which required 15 horizontal and 20 vertical curves, some as tight as 60° with a 300- m radius. The conveyor system also had to be very compact so the cross-section of the tunnel could be minimized, and it was necessary to eliminate any transfer points in the tunnel to reduce dust emissions, minimize space requirements and reduce maintenance costs.
Conveyors in certain applications are seen not only as bulk material movers but also as a tool to assist in an operation’s energy balancing and conservation strategies, adding additional complexity. For example, as noted in this issue’s Suppliers Report section, Siemens has again upgraded the downhill conveyor system it installed at Antofagasta plc’s Los Pelambres copper-moly mine in Chile, increasing both the carrying capacity and its generating output. After its installation in 1999, at which time it was configured to carry 7,000 mt/h and powered by eight electric motors rated at 2,500 kW each, it was capable of generating up to 17 MW with sufficient load on its steep downhill route. Following another upgrade in 2006, when two of the conveyor’s sections were given an additional drive—raising total drive output from 20 MW to 25 MW—the system’s capacity was boosted to 8,700 mt/h.
In that configuration, the system produced about 90 million kWh, representing about 15% of the mine’s power needs, reducing energy costs and cutting carbon dioxide output by more than 50,000 mt/y. More recently, Siemens reported the system is capable of generating up to 21 MW in regenerative mode.
A quick glance at any conveyor product directory shows there are a dozen or more well-known software programs and packages available to anyone for analysis of practically any facet of conveyor design. Major conveyor equipment suppliers generally have specific software suites or protocols for designing and simulating their own systems.
Overland Conveyor Co. (www.overlandconveyer.com) says its Belt Analyst 9.1, released late last year, offers complete design evaluation of any bulk material handling belt conveyor, allowing users to input any vertical and horizontal profile with up to 360 flights, 48 pulleys and 20 unique drive locations. The program allows use of CEMA 5th Edition calculation methods, newer CEMA 6th Edition power methods or International ISO/DIN methodology. A new Pulley Setup Wizard helps input all the belt line dimensions and automatically calculates all pulley wrap angles. A two-dimensional, to-scale drawing illustrates exact inputs and what is used in the calculations.
Other new features include a 3-D viewer that shows toscale drawings of the entire conveyor or any section, and allows the user to rotate, pan and scale the drawing. A new Lagging Analyst evaluates the interaction of the belt and lagging at each drive pulley.
Overland Conveyor also developed a belt conveyor mathematical modeling tool, called Belt Wizard, used exclusively by Fenner Dunlop Americas ensures the compatibility of the conveyor system specified and the Fenner Dunlop belting recommendation.
FLSmidth Conveyor Dynamics (www.conveyor-dynamics. com) offers BeltStat 7.0, which it says can analyze conveyors of any length and topography having up to 10 drive/brake stations, without restriction as to location. The program can analyze downhill, regenerative conveyors, and belt widths from 24 to 120 in. Drives may be conventional head type, tail and/or intermediate drives of any combination. Both acceleration and braking action can be analyzed using either independently controlled starting/stopping times or controlled acceleration/braking torque. Starting and stopping torques may be proportioned as desired among the multiple drives.
In the latest version of BeltStat, a new Quick Start menu allows users to conveniently analyze a wide variety of conveyor systems. By inputting basic conveyor information users can quickly determine critical conveyor specifications and components. An improved element table gives the designer a visual image of the conveyor system as it is being built. It also allows vertical curves and IP points to be dynamically modified on the fly.
Other conveyor design programs include Beltcomp (www.beltcomp.com), Helix delta-T (www.chempute.com), Pro-Belt (www.pro-belt.com), Sidewinder (www.actek.com) and mConveyor (www.mineconveyor.com), to name a few.
Focusing on Cost-Effectiveness
With all of this design power available, and taking into account the hundreds of millions of dollars spent every year on new systems, upgrades and parts replacement, a reasonable question might be: Are customers getting fair value, or better, for the price of their conveyor systems, or are these systems being under- or over-engineered? Over the years, there seems to have been a tug-of-war between these issues, but technology advances now provide greatly improved capability to make fully informed design decisions—if the customer looks at the design from the proper perspective.
To illustrate: In 2003, Lawrence Nordell, president of FLSMidth Conveyor Dynamics, wrote: “Traditionally, belt conveyors for both in-plant and overland systems have been notoriously over-designed. Fifty-year-old engineering design standards and methods are still being applied today. The use of these standards results in substantially higher capital and operating costs when compared with those incorporating today’s technical advancements.”3
More recently, Todd Swinderman, chief technology officer for Martin Engineering, suggested conveyor designers and suppliers may actually be doing too good of a job, by providing customers with systems that continue to perform adequately under adverse conditions—including outright abuse from overloading and neglect.
He described 10 common mistakes in conveyor design
choices made solely on price considerations, their eventual
consequences and recommendations for avoiding them.
Some of these include:
• Not knowing your bulk material—Using only data from tables listing bulk density and angle of repose for the material to be conveyed can result in a conveyor system that can’t carry the required tonnage, or that has improperly sloped chutes and hoppers, if the actual material differs from the table data. Swinderman said a typical set of tests to define a particular bulk material might cost about $30,000—while the cost of conveyor downtime can be $1,000 or more per minute. “Over the lifetime of the conveyor system if just one plugged chute episode can be avoided, the testing will have paid for itself,” he explained.
• Lack of access—Conveyors are often located in enclosures or tunnels where one side is so close to the wall there’s no room for a worker to even shuffle sideways along the belt. Access doors may be located in odd positions that allow a view of nothing and may be so small that maintenance can’t be conducted through them. In other instances, conveyors might be so low to the ground there’s no room to clean up under the belt, and platforms at the head pulley are often so low it’s impossible to reach components on the drive side for maintenance. These design flaws often extend into the practice of covering key conveyor components with piping and conduit, Swinderman noted. Because the support structure of the conveyor provides a convenient rack for mounting electrical conduit and piping for plant air and water supplies, these items often limit access to or proper location of belt wander switches, belt cleaners, plows and return idlers. “Conduit or piping rarely needs service or relocation, while the components it ‘incarcerates’ typically need frequent inspection and service,” said Swinderman.
• Substituting speed for belt width—There is a generally accepted belt speed range that designers usually adhere to in order to minimize degradation of the transported material and to control dust. However, this range is often exceeded to meet price objectives. For example, if an 1,800-mmwide belt traveling 3 m/sec can handle 4,000 mt/h, a 1,200-mm-wide belt could provide the same capacity if its speed was increased to 7 m/sec. This could save money on steel and belting costs, Swinderman explained, but the narrower, faster belt could cause trouble, such as increased wear on the belt and chutes, material degradation, loading problems and chute plugging. And, at high speeds, the transported material may never settle down, resulting in constant spillage.
• Failure to allow for needed upgrades—There’s nothing wrong with using standard conveyor components to meet system price targets, but it’s prudent to allow space in the design for problem-solving upgrades to meet production or cost targets. Experience in installing conveyor systems confirms that at least some modifications are usually needed at startup or shortly thereafter to fulfill customer expectations. If the original design allows some flexibility for these modifications, they usually can be installed cost effectively and with minimal downtime.
Swinderman maintains “belt conveyors are designed and purchased much as they have been for the last 50 years while virtually every major safety, regulatory and performance criteria has changed. The traditional approach is to determine the design capacity, do the minimum necessary to meet code and safety requirements and design for the lowest cost of construction. Using the design approach of 50 years ago and thinking equipment can be purchased on low bid to meet the production and regulatory requirements of today are unreasonable expectations. Throw in lower grade fuels or ores and it’s a recipe for plugged chutes, dust, spillage and less than predicted production. A new approach to specifying, designing and purchasing is needed to meet these challenges.”
This system for “Modern Conveyor Architecture” has six
levels of system requirements:
Design Capacity—The system must reliably deliver the required tons per hour of bulk solid; if it cannot (comfortably) achieve the production goals, the scope of the system must be reconsidered.
Safety—The system must approach is to utilize technology to design safe and material efficient structures but to exceed the minimum mandated safety requirements making conveyors safer to operate and maintain.
Cleanliness (Prevention and Control of Fugitive Materials)— The control of fugitive material through improved design is a priority. The system must be designed to minimize the escape of material as dust, spillage and carryback, and to allow the collection of any material that does escape.
Service Friendliness—Many maintenance procedures critical to system operation or control of material can be accomplished safely while the belt is in operation, if the equipment is properly designed and the maintenance people are properly trained. Other tasks that can only be done while the belt is shut down can be made easier and faster if maintenance is considered a priority of the design.
Cost-Effectiveness—Often small upfront engineering changes—at modest cost—provide improvements that will be seen long after the initial concern over the modest added cost has stopped being a concern.
Upgradeability—By building flexibility into areas known to be problematic, the initial price of a new conveyor can be minimized while the long-term cost can be reduced when the addition of specialized components added only in those areas where they are needed.
Swinderman concludes that ‘by including in the design methodology elements that match customer needs for a clean, safe and productive system, a Modern Conveyor Architecture emerges that can be cost competitive yet flexible enough to be easily upgradeable to solve operation specific problems.”
1. Hollingsworth, T., and Harris, T., “Boddington Gold Mine Expansion Project Overland Conveyor,” SME Annual Meeting, Feb. 28-March 3, 2010, Phoenix, Arizona, USA.
2. Wiedenroth, J., “The Longest Pipe Conveyor of the World with Double Load Transport at Cementos Lima In Peru,” SME Annual Meeting, Feb. 28-March 3, 2010, Phoenix, Arizona, USA.
3. Nordell, L., “Overland Conveyor Designed for Efficient Cost and Performance,” Beltcon 12 Conference, 2003, South Africa.
4. Swinderman, R.T., “Ten Common Mistakes in Conveyor Specification and Design,” SME Annual Meeting, Feb. 28-March 3, 2010, Phoenix, Arizona, USA.