Coal Age

JAN-FEB 2019

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30 January/February 2019 fines dewatering Yesterday's Waste is Tomorrow's Boon New coal fines recovery solutions can help miners go green, save greenbacks and grow optionality by jesse morton, technical writer History is replete with examples of how what is considered a resource at any giv- en point hinges on the technologies of the day. What today is piped to the thickener or the pond may tomorrow be a cash cow for a company with the right equipment and know-how. Similarly, with the right technological breakthrough, today's waste may be tomorrow's fuel. For example, three new solutions that recover coal fines from what otherwise might be considered waste use technolo- gies originally designed for metals miners. Glencore Technology's Jameson Cell, prov- en in Australian coal plants, was originally designed for use on a lead/zinc circuit. Min- erals Refining Co.'s first commercial coal fines recovery plant uses a technique based on one originally developed for copper ore processing in Britain in the early 1900s. Arq's new Corbin plant that will produce from coal waste a powder so pure it can be mixed with fuel oil uses flotation technolo- gy that is commonly used by metals miners. These three solutions are now on the market. The companies report they are looking to branch out, form strategic partnerships and innovate further. More importantly, they seek to empower coal miners to turn what was once considered discard into cold hard cash. Certainty Over Probability With the 30 th anniversary of the first de- ployment of a Jameson Cell imminent, research and development for the fifth generation of the solution is under way, Virginia Lawson, technology manager, Glencore Technology, said. "Every 10 years or so, we are assem- bling changes to address anything that we've learned," she said. "We are just step- ping into the Mark V and looking at areas that might improve the performance of the cells for end users." The current and previous generations featured incremental improvements tar- geting increased capacity, reduced com- plexity, and extended wear life. Feedback from the field will guide some of the future design changes, Lawson said. Future improvements will likely target increased volumetric flowrate and scale, and include bigger cell designs and mod- ifications that make the cell cheaper to in- stall and operate, Lawson said. Another area of potential improve- ment is the wash water system, she said. "The dewatering circuit being constrained leads to inferior quality wash water and this results in problems washing the froth," Lawson said. A "better understanding of the chem- istry of flotation" has inspired "better designs," Lawson said. And one possible solution tweaks the wash water system so that it can better tolerate dirty water and self-clean, she said. "We have a trial under way," Lawson said. "Ensuring wash water is maintained at all times will improve product quality." It will also help debottle- neck a crucial area of the process, she said. The Jameson Cell is described as a high-intensity froth-flotation cell. It creates a high-pressure jet of mixed air and slurry, which shoots through a pipe, called the downcomer, that pene- trates and empties into the flotation cell. The downcomer is where particle and bubble contact first occurs. "The plunging jet of liquid shears and then entrains air, which has been naturally aspirated," Glen- core Technology personnel reported in a white paper. "Due to high mixing velocity and a large interfacial area, there is rapid contact and collection of particles." In the tank, secondary bubble-particle contact occurs. "The velocity of the mixer and large density differential between it and the remainder of slurry in the tank re- sults in recirculating fluid patterns, keep- ing particles in suspension without the need for mechanical agitation," the com- pany reported. The bubbles gather on the surface of the column, and the resulting froth is re- moved by froth drainage or froth washing. Jameson Cells, similar to the one pictured here, are credited with recovering some $30 billion in export coal in 2013 alone. (Photo: Glencore Technology)

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