A handle on stacks of stockpiles
Stackers remain a critical component of effective stockyard management, writes Leon Louw.
As the world enters the fourth industrial revolution, we need to review the way things are done, and how that will change in the future. Even the simplest of operations are bound to be altered by more efficient methods of production. Automation, mechanisation, artificial intelligence and the Internet of Things (IoT) have become more than just buzzwords.
Drastically cutting carbon emissions and reducing our environmental footprint is now almost as important as being profitable. This ‘great leap forward’, however, does not necessarily mean we have to re-invent the wheel. Adding new technology to old equipment can be as effective as designing a brand-new robotic machine.
Take stackers and reclaimers, for example. These large, creaking stalwarts of bulk material handling have not changed much over the last fifty odd years. They’ve continued stockpiling and reclaiming material of different shapes and sizes in stockyards around the world unabated, while the world around them moved into the next century at breakneck speed. What has changed though, is that they are no longer controlled manually, but from a remote office, often not even close to site. Some older machines may still be manually operated or controlled however, most modern stackers and reclaimers are either fully or semi-automated. A vast amount of integrated input data allows for a completely automated stockyard system.
Relooking old methods
According to Jacques Steyn, general manager materials handling at thyssenkrupp Industrial Solutions (tkIS) Africa, one of the leading manufacturers of stackers and other stockyard machines in the world, the concept of how these machines operate has remained the same throughout the years, as has the mechanics of stacking and reclaiming. “What has changed significantly though, is the control systems and the way of feeding information to and from the equipment. Automating the entire process and knowing exactly where the stackers and or reclaimers are, how they move, what quality and quantity of material they process and the grade of material that is conveyed, has altered the way stockyard managers think about stockpiles, and enabled them to plan better,” says Steyn. Minor technological additions have pumped new blood into old veins and made sure that these stockpiling systems remain cost effective and efficient, forcing modern managers to revisit old methods.
Stockyard systems can be autonomously managed where the current status of each stockpile is automatically known – for example volume, grade, height and width. The stockyard information can be accessed and or controlled from anywhere in the world. The stacking philosophy will typically be based on a thorough analysis of the material entering the stockyard, whereafter the stacker is automatically programmed to deal with that specific material by stacking it on the correct stockpile in the correct pattern. “The stacker operator is therefore no longer the one who decides where or how material should be stockpiled.”
Stackers are not very complex machines but with new technology stockyard management systems and decisions about how and where material needs to be dumped has become a lot easier and is more efficient. Even a simple exercise like lowering the boom of a luffing and slewing stacker to control dust pollution and material degradation can be controlled autonomously. Steyn says that stackers will no doubt play a very important role in the future of modern mechanised and autonomous bulk materials handling.
In line with Industry 4.0 enhancements on mining operation, tkIS provides analytical process control for stockyard blending and homogenisation and scientific control of mineralogy of stockpiles, by employing online analysers. In recent years, Chute and Cross belt analysers, have been installed in many mining and materials handling solutions across the globe, which allowed manufacturers to improve on designs and reliability. On-Line PGNAA (Prompt Gamma Neutron Activation Analysis), determines the presence and amount of many elements simultaneously, without the need to take samples to a laboratory, to determine mineralogy and grade of mineral ores. In some cases, cut-off grades, can be determined within 30 seconds allowing for quick decision making by control systems. This information is used as input by the thyssenkrupp stacker and stockyard management systems to achieve an optimum blend of mineral stockpiles, ensuring a constant mineralogy feed to process plants, vitally important to ensure maximum plant efficiency.
“In most cases a stacker is a crucial component of any continuous processing system. A mine always needs non-stop feed of material into its processing plant and remotely operated machines that can pile material and then reclaim it efficiently and reliably at a constant rate to feed the plant,” says Steyn.
Modernising mining
A number of factors in the global economy have recently conspired to create an environment where operations can only survive if they become more efficient and productive. In the mining and quarrying industries, for example, reducing operating costs has become paramount. Moreover, mines need to eliminate human fatalities and address health and safety concerns, while at the same time start contemplating climate change, and how to manage carbon emissions. This is what the modernisation of the mining industry is all about.
Owning or leasing a large fleet of ‘yellow equipment’ that hauls, stockpiles and re-handles material might seem enticing on a balance sheet in the short term, but over the life of mine using automated Stacking and Reclaiming equipment might just be a better bet. The initial capital outlay of investing in these machines looks daunting though, but, according to Steyn, enough research has been done to prove that the operational costs decrease considerably in comparison to yellow machines. “Yes, you can use front end loaders and trucks and mobile equipment to stockpile product, but operationally it’s much more expensive and even more important, a lot less reliable and efficient,” he says.
‘Yellow equipment’, or stackers?
Whether to use ‘yellow equipment’ or stackers and other automated bulk materials handling machines in your mining operation, ultimately depends on which wound causes the least pain: high initial capital cost, or incremental life of mine costs. Unfortunately, one cannot buy half a stacker, whereas the fleet of ‘yellow equipment’ can be acquired or leased one unit at a time to suit the initial budget. “On a balance sheet, and especially in the first few years, it looks so much better to invest in ‘yellow equipment’. However, once the capital cost of the stacker has been recovered, the life of mine cost diminishes substantially. For one, the maintenance on stackers is minimal, they can continue working 24/7 for the life of mine and longer, and the cost of consumables is negligible compared to ‘yellow equipment’. Then we are not even taking into consideration the operator costs along with labour- related concerns or the safety and environmental benefits of using automated stackers,” says Steyn.
But, costs aside, the importance of blending material into homogenous stockpiles, should probably override cost considerations in any continuous processing plant. To build a homogenous stockpile to feed into a processing plant or heap blended material consistently with front end loaders or trucks, is extremely difficult, if not impossible. Steyn says stacking is critical for reclaiming and achieving a proper blend. “If a mine or quarry has to feed the processing plant with fairly homogenous raw material, or if they export a specific grade of material and the grade from the pit is inconsistent and they have to blend different material to ensure a homogenous stockpile, the first critical stage in the process is stacking,” Steyn explains.
As the material enters a plant, it needs to be stacked in such a way that it can be reclaimed efficiently and in order to achieve a homogenous blend if required. “One of the most important factors of blending material is how it is stacked in the first place,” Steyn emphasises. “If you do not stack material properly, you will always struggle to achieve decent blending and or reclaim rates,” he adds.
In mining and quarrying operations stackers are used to stockpile Run of Mine (ROM) material so that it can be reclaimed again for processing, and for stockpiling different products once the ROM has been processed. It is also used to load trains and trucks. In ports and harbours, product is brought in by trains or trucks and stockpiled before being reclaimed and loaded onto ships. Power plants, for example, needs consistent stockpiles of coal which can be reclaimed to ensure the process never stops, and for that, one needs efficient and effective stackers.
Stackers come in a variety of shapes and sizes – fixed, travelling, luffing, slewing and a combination of the options. A travelling luffing and slewing stacker can serve two parallel stockpiles to the left and right of the stockpile yard conveyor. Controlled remotely, it can build a stockpile in chevron, cone shell, strata or windrow stockpiling modes.
German conglomerate thyssenkrupp’s South African office designs and manufactures their stackers locally and the company custom designs the equipment according to their client’s specs. The company recently delivered a 2 000tph, 100m long, including the tripper, custom-built, stacker to a coal mine in the Waterberg region of South Africa. The machine weighs more than 300 tonnes and was designed and manufactured in South Africa. Their stackers are deployed across Africa at bulk mining operations ranging from iron ore to manganese and coal. Steyn says custom building stackers are important especially for mines with existing infrastructure already in place where factors such as rail gauge specs and existing stockpile width needs to be considered. “When designing a brand-new plant, on the other hand, one can invest in a standard stacker, which has obvious cost savings related to design and overall delivery time” he says.
Maintenance is critical
Stackers are normally designed for the life of mine. However, Steyn says that general maintenance is required to ensure the machine remains in a good working order. “If these machines are properly maintained, they will continue working for 40 years plus, but then you need to look after them. Part of our customer service includes a structural inspection and analysis, which is something clients often neglect. Clients tend to service mechanical, hydraulic and electrical components that can actually be replaced with relative ease. If a major structural component on a stacker however fails, it could be a massive undertaking to replace it or may even result in the scrapping of the machine, not to mention the cost of lost operation.
As the world changes, old equipment only needs to be upgraded to remain as relevant as ever. Even if the mechanics of stackers has not undergone radical change, the machines are destined to be with us for many years to come, even as we enter the fourth industrial revolution.
Leon Louw is a specialist in African affairs and mining. For more about doing business in Africa, mining and mining operations in Africa, and the political risk of operating in Africa, contact Leon or follow him on Twitter, Linkedin and Facebook.handle