Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr
Issue link: https://emj.epubxp.com/i/239773
ROPE SHOVELS Electric rope shovels require a reliable, clean source of power to operate, and until recently, this meant power from the grid; however, Cat has developed an off-grid power solution, and demonstrated the system at the Tinaja Hills event (more on that later). To operate efficiently, shovels also need a high face height. As Klingel explained, a rope shovel's digging action is different from hydraulic shovels; they cut from the bottom to the top of the face in an arc-shaped loading profile. Subultra class shovels need a face height of at least 33 ft for efficient dipper loading, while ultra-class models need much more—in the range of 50 ft or so. Even so, their front-end configuration provides additional operating benefits derived from the large working radius from the face and from nearby haul trucks. These include good visibility for double-sided truck loading and easier truck spotting. In addition, the wide working radius keeps the operator far from the face, improving overall safety. Factors to examine when considering a shovel's potential cost per ton fall into two categories: cost and productivity. Cost factors include: • Capital investment, • Machine life, • Fuel or electricity costs, • Cost of replacement parts (new vs. refurbished), • Cost of consumable parts, • Hours to maintain the machine, and • Local labor rates (operator and maintenance). Productivity considerations are: • Loading methods, • Truck/shovel pass match, and • Gaps between theoretical and actual tons per hour, – Skilled truck and shovel operators. – Shovels properly "trucked." There are four primary loading methods: single side, double side, drive-by and modified drive-by. There can be significant productivity differences depending on which method is used and how well it conforms to site conditions and fleet configuration. Each loading method has specific advantages and disadvantages, but as the chart indicates, the modified drive-by method (illustrated in the diagram above) offers the highest potential production rate of all the methods, if the www.e-mj.com proper site conditions and necessary operator skills are available. For prospective or even current customers that are unsure about which method would yield the best results, given a specific site's fleet configuration, terrain, worker experience and other variables, Cat can help in estimating potential productivity, said Klingel. Its senior application engineers have developed an elaborate spreadsheet that takes into account a wide range of loading-related factors and produces an accurate estimate of shovel/truck loading productivity per year for various loading scenarios. Based on input data such as shovel model, truck type and capacity, loading method and dipper capacity, the "Theoretical Shovel Model Production Estimate" spreadsheet supplies an appraisal of maximum annual production capacity for different combinations of the input items. A simplified summary of its results is shown in the chart below. Selecting the Right Configuration Prospective shovel customers also have a number of important decisions to make concerning the actual configuration and pre/post-commissioning support for the shovel. In general, for Cat's machines these include: • Electrical system (incoming voltage, frequency, lighting), • Crowd system (rope vs. HydraCrowd), • Crawler links (width), 7495 Truck model (313 mt) Loading method Number of passes (mt/m3) 7495 7495 795 795 795 Modified Drive-by Double Side Single Side 3 3 3 1.75 1.75 1.75 146,434 134,994 116,751 BCM/year 20,409,812 18,815,295 16,272,688 Metric tons/year 46,432,322 42,804,797 37,020,365 Loose density Trucks/year Source: Caterpillar JANUARY 2014 • E&MJ; 39