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
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ENERGY EFFICIENCY 46 E&MJ • MARCH 2017 www.e-mj.com Energy availability is one of the bedrock requirements for successful mine startup, along with water, ore, labor and transpor- tation access, to name just a few. And, like many of these necessities, electrical energy can be expensive, unreliable and increasingly subject to intense competi- tion from other industries. A mine's ener- gy usage may have a social component as well; drawing large amounts of electricity from a stressed national grid, or building a captive power plant that exclusively serves the mine site without providing power for local consumption, for exam- ple, can lead to increased friction with community leaders and government reg- ulators. On a global basis, the extent of a mining operation's growing — or shrink- ing — energy footprint is often used as a measure of its owner's environmental and social consciousness. These trends and concerns make en- ergy-efficiency improvements in mineral processing an attractive and often nec- essary goal — and one of those rare in- stances in which cutting back results in getting ahead. Accordingly, it's tempting to look for large-scale savings involving major process changes, but these can be daunting in terms of capital expense, production interruption and performance risk. In today's business environment where mining companies are pursuing mostly incremental, affordable produc- tion improvements, the availability of similarly incremental energy-conservation measures fits hand-in-glove with the pre- vailing investment climate. Cutting the Costs of Flotation Relative to other concentrator equip- ment, flotation cell energy consumption represents only a small fraction of total energy demand in mineral processing. Although these energy costs may not be immense relative to other process- ing steps, they are sufficiently high that evaluation is warranted. To fully capitalize on this sector, changes to equipment or processes must be easy to implement, low cost and not compro- mise production. Although the ultimate energy savings might be modest, when coupled with flotation-process perfor- mance improvements, for example, such advances can be very attractive to cost-conscious producers. With the addition of the Dorr-Oliver and Wemco flotation cell products to its portfolio, FLSmidth has become a major supplier of flotation technology, and ongo- ing research into the technology enabled the company to introduce in 2016 its pat- ent-pending nextSTEP advanced flotation mechanism, which features a new rotor/ stator technology that is designed to con- sume much less energy than other types of flotation cells. "The nextSTEP rotor/stator provides a step change in flotation metallurgical performance and energy efficiency," said Steve Ware, director of separation prod- ucts at FLSmidth's Technology Center in Salt Lake City, Utah. "It has the lowest operating power of any flotation mecha- nism on the market." This level of performance, according to the company, has been demonstrated in laboratory-scale tests, trials and com- mercial-scale installations, which have shown that nextSTEP improves metallur- gical performance. In real-world appli- cations, FLSmidth said customers have experienced anywhere from 15% to 40% lower energy usage, while maintaining or improving recovery due to improvements in mineral-bubble attachment rates. Asa Weber, FLSmidth's product manager–flotation, said, "Recovery is a function of collision, adhesion and attachment. In order to improve the probability of collision and adhesion, you control the bubble size and aera- tion rate. In the broadest terms, if you decrease bubble size and increase the aeration rate, you can improve bubble/ particle attachment." It's been proven that smaller bubbles have better attachment properties than large ones, but in the normal course of events, an increase in cell airflow produc- es larger, not smaller bubbles, so it's not a straightforward proposition. "In the de- sign of flotation cells, we want to design a machine that produces better dispersion of air," explained Weber. "We want to in- crease the air volume into the machine and reduce the bubble size at the same time, but those qualities are an inverse relationship. As you increase aeration rates, normally the bubble size increas- es, so there's an optimum value. You also want to create the right amount of turbu - lence in the machine, so it improves your bubble/particle contact." FLSmidth spent four years developing nextSTEP, starting from theoretical first principles, then using computational flu- id dynamic models and 3-D printed proto- types to optimize the rotor/stator design. "Once we understood the fundamentals of the machine and how the bubble/parti- cle contact occurs, we wanted to improve Floating Points E&MJ examines some notable new flotation technologies that offer the prospect of improved recovery with lower energy costs By Russell A. Carter, Contributing Editor During the four-year effort to develop the nextSTEP technology, FLSmidth used computational fluid dynam- ics modeling and and 3-D printed prototypes to create an optimized rotor/stator design.