New coal fines recovery solutions can help miners go green, save greenbacks and grow optionality
by jesse morton, technical writer – www.coalage.com
History is replete with examples of how what is considered a resource at any given 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 technologies originally designed for metals miners. Glencore Technology’s Jameson Cell, proven in Australian coal plants, was originally designed for use on a lead/zinc circuit. Minerals 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 technology 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 30th anniversary of the first deployment 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 assembling 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 targeting increased capacity, reduced complexity, 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 modifications that make the cell cheaper to in- stall and operate, Lawson said.
Another area of potential improvement 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 chemistry 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 debottleneck 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 penetrates 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 results in recirculating fluid patterns, keeping particles in suspension without the need for mechanical agitation,” the company reported.
The bubbles gather on the surface of the column, and the resulting froth is re- moved by froth drainage or froth washing.
The key technology in the system is the downcomer, which feature no moving parts and is based on simple physics to optimize efficiency and cost effectiveness, Lawson said. “You create a hydraulic field and the slurry is drawn up into the down- comer because there is a pressure difference as that plunging jet goes through that orifice,” she said. “It naturally draws air from the atmosphere, so you don’t actually have to use compressors, or any energy associated with compressing air.”
The cell is advertised as excelling at re- covering coal particles smaller than 500 microns, which are typically uneconomical to pursue via conventional flotation technologies and usually end up as waste, Glencore Technologies reported. “The fine bubble size, high intensity and froth washing ability offer major advantages over conventional cells for recovery of the highly hydrophobic, fast floating coal fines,” the company re- ported. “These advantages provide superior, more consistent flotation performance, lower ash concentrates and high recovery.”
The original seed idea for the down-
comer is attributed to Laureate Professor Graeme Jameson of the University of New- castle. In search of a means to optimize flo- tation performance of a lead/zinc concen- trator, he was commissioned by Mount Isa Mines, in Queensland, Australia, to develop the idea, which he patented in 1986 on be- half of Newcastle Innovation Ltd. That year the resulting pilot cell was tested. Three years later, two full-scale cells were installed in the lead-zinc concentrator at the mine. Two more were built that year for a similar concentrator at the nearby Hilton mine.
Soon thereafter, the solution was adopted by a major coal miner in the Bowen Basin in Australia. Within a half-decade, Newlands Coal employed six Jameson Cells, scaled up for the requisite through- put, at recovering coal fines. In Australia, the Jameson Cell is “now the industry standard,” Glencore Technology reported.
The largest installation at Curragh (Australia) treats more than 5 million tons per year of coal, using only 12 cells, Glencore Technology reported. The cells have been deployed to coal operations in Africa, North America, Asia and Europe, the company reported.
In 2013, Jameson was named New South Wales Scientist of the year. That year, Jameson Cells at Australian sites were credited with recovering some $30 billion in export coal. In 2015, the solution won the Prime Minister’s Award for Innovation for its role in the Australian economy.
Such accolades and figures hint at the value the cells could bring to a circuit and plant, Lawson said. To bring peace of mind to a plant manager, she said, the cells offer something invaluable: certainty. “Other devices rely on probability,” Lawson said. “We are now 100% certain that a particle has an opportunity to attach to a bubble.” Currently, roughly 350 units are operating in almost 30 countries around the globe. In each case, the cells were selected as technical solutions to technical problems, Lawson said. “The Jameson Cell can recover all of the coal fines, usually in a single step, to improve the performance of dewatering and now lower the level of chemicals needed,” she said. “By operating the Jameson Cells in series, the second Jameson Cell is able to scalp the tail at lower chemical addition, leading to improved dewatering conditions.”
Adoption is easy, as the Jameson Cell “has direct scale-up from pilot testing,” she said. “So, if you have an existing operation and we pilot on your site, then we will know exactly how our Jameson Cell will operate.” With four generations in operation, three decades of history, and field results from around the world attesting to the vi- ability of the solution, the primary barrier to adoption now is normalcy bias, Lawson said. “We just have to get over some of those barriers that people have to adopting something different,” she said. “The technology does it, and it speaks for itself; they just need to be willing to adopt and reap the benefits of change.”
In Q4 2018, Glencore Technologies announced a 25% capital back performance guarantee on the cells. The guarantee formalizes the confidence the company has in how well the cells will perform, Law- son said. “Show us what you need to get done,” she said. “Work with us and we will demonstrate what can be done and that we stand behind it.”
Recovering Ultrafine Coal
Minerals Refining Co. (MRC) reported it is building the first commercial Hydro- phobic-Hydrophilic Separation (HHS) system-based plant at a coal mine in east- ern Kentucky.
The plant will process 40 tons per hour (tph) of solids from a fine-coal slurry that would otherwise be destined for the thickener. “Typically, mines throw away 3% to 5% of the coal mined,” Dr. Stanley Suboleski, president, MRC, said. “We are focused on recovering that material.”
The system should enable the plant to capture 20 tph of high-quality coal fines for market. “About half of the slurry solids is ash,” Suboleski said.
The final product will average under 4% ash, he said. “We can control the moisture,” he added. “We can dial that in.”
The partnership framework with the mine is complicated, Suboleski said, but ensures MRC will have coal to sell.
HHS shares characteristics with traditional flotation systems. Instead of being attracted to bubbles in a water tank, the coal fines are captured using an oil to coat the particles and form agglomerates.
Oil molecules simply perform better at grabbing hydrophobic particles, Suboleski said. “It is a matter of contact angle,” he said. The system can recover particles that are both larger and smaller than those re- covered by traditional flotation methods. “We’ve recovered particles down to single micron size and even smaller,” Suboleski said. “We don’t know how fine we can go with this technology.”
The system employs several steps. In the first step, the oil and slurry are mixed mechanically. “We have to mix this stuff pretty thoroughly, because if we don’t get the oil on the coal, it doesn’t get recovered,” Suboleski said.
The mix is then piped to a second tank to be more gently agitated.
Gentle agitation is a crucial step in separating the coal from the water and ash. “These oil-covered particles are attracted to each other,” Suboleski explained. “They bump into each other and form coal-oil agglomerates that float on the water-ash mixture.” However, at this stage, those agglomerates contain entrapped water droplets. “The impurities are hydrophilic, so they want to go where the water goes,” Suboleski said. “And when the moisture is trapped inside the agglomerate, it also raises the impurity level, which is the reason that agglomeration has not been used widely in the past, even though it was first discovered in the early 1900s.”
The patented method for releasing the trapped water and waste was discovered and invented by Dr. Roe-Hoan Yoon, director, Center for Advanced Separation Technologies, Virginia Polytechnic Institute and State University (Virginia Tech). “It largely involves the application of the correct amount of energy, although other factors are involved as well,” Suboleski said.
The agglomerate-breaking component at the heart of the method and technology is called the Morganizer, after MRC Board Chairman E. Morgan Massey, former CEO of the A.T. Massey Coal Co. “The name came from the developers of the initial test unit several years ago and has stuck, somewhat to Mr. Massey’s embarrassment,” Suboleski said.
The oil-coated coal fines rise to the top and the now-released impurities and water are drained from the bottom of the Morganizer. The oil-coal mix is then piped into a vacuum filter, and then put through an evaporator, which enable the process to capture and recycle the oil.
The final product, which has at times been of a reportedly high-enough quality to be categorized as “nearly pure carbon,” emerges dry from a chute.
It is the result of roughly seven years of research and development.
MRC began brainstorming on, and test-tube-scale tests of, the technology in 2011. After making the process continuous at lab scale, a proof-of-concept unit was constructed that processed 100 pounds per hour. “Based on results of tests from seven different coal plants, we went ahead and commissioned a company that specializes in building pilot plants to build one for us,” Suboleski said. “The design and construction consumed all of 2014 and the first half of 2015.”
The pilot plant was tested for two years. The feed solids averaged 58% ash, and the resulting clean coal averaged between 4% and 4.5%. “We discovered then that we could control the moisture,” Suboleski said, “and typically maintained it between 5 and 9%.”
MRC stopped testing in late 2017 and “started our initial commercial plant de- sign,” Suboleski said. Because it uses only the existing slurry water and otherwise is self-contained, it will operate under a modification to the existing water and air permits for the processing plant.
With the long-lead-time equipment ordered, and construction initiated, com- missioning of the plant is scheduled for late 2019.
Energy tech company Arq will start commissioning this quarter an Arq Fuel pilot plant in Corbin, Kentucky, on a site where U.S. Steel previously operated a processing plant. Roughly 75% complete, the $75 million, 50,000-ft2 plant will produce 12.5 tons per hour of micro-fine hydrocarbon powder from a feed of coal waste.
Commissioning the plant will be a stepping stone on the path to going glob- al, Paul Groves, chief operating officer, Arq, said. “We will scale this very quickly around the globe to become a major player in the coal market by creating a product that feeds into the oil market,” he said. “We are entering into three further projects with major coal companies around the globe.” For example, within the year, Arq will launch another project in the United States and one at a “big site in Australia,” Groves said.
Groves described the Corbin plant as innovatively engineered to allow the company to trial and compare technologies throughout the process and to determine what fits best. “That is a good thing,” he said. “We have done everything that we can to ensure that we have a high-quality consistent product that comes out on spec, on time, every time for our customers.”
The product, Arq Fuel, is a less-than- 10-micron 99% pure hydrocarbon particle with less than 2% moisture and 1% ash by mass. “Actually, 80% of the particles will have a diameter of less than five microns,” Tudor said. The particles are so pure they can be blended with oil products or amalgamated into Arq Fuel pellets for mixing with met or thermal coals.
According to company literature, Arq Fuel is produced using equipment commonly used in minerals processing and elsewhere.
Coal discard such as that headed for a thickener or found in a pond serves as the feed. “Particle size reduction is achieved by ball milling, high-shear grinding or a combination thereof,” Arq reported. The biggest ball mill at Corbin is 1.5 mega- watts, Tudor said.
Micro-separation is achieved using enhanced froth flotation. “This technology has traditionally been used to separate microfine particles in the minerals and precious metal mining industries,” Arq report- ed. The company deploys a proprietary technique to “enhance that process,” Tudor said. “We push that to the limit.”
The next step, described as a rapid evaporation system, involves de-watering and thermal drying. It leverages “recent techno- logical advancements in the food processing industry,” the company reported.
The process ensures the powder is al- most entirely void of moisture and ash, Groves said. Thus, “we can put up to 35% by weight of this microfine powder into an oil.” The ratio will depend on the application. The customers are from different sectors and have different requirements. “There are a lot of applications we are looking at,” Groves said. “We have a focus on about two or three at the moment. They are at different ends of the spectrum.”
Arq continuously tests various blends to ensure performance, Tudor said. “We are running experiments from 5% up to 35% in various oils and trying to assess that on a case-by-case basis so we have the ideal blend in each scenario for each customer,” he said.
Tests reveal Arq Fuel can be used to stretch and improve the performance of certain residual fuel oils (RFOs) that are burned by thermal power stations, large industrial plants and engines, specifically marine engines. Company literature reports the blends, at varying ratios, are proven to meet a range of critical requirements, to include those covering dispersion stability, fuel integrity, flashpoint, pour point, sulfur, vanadium, sodium, clay and carbon. “Importantly, Arq’s own market entry does not require changes to the supply chain or to engines, boilers and associated equipment,” the company reported. “It delivers significant efficiency
improvements for oil distributors, refiners, industrial users and utility customers throughout the value chain.”
Perhaps most importantly, it delivers improvements relatively inexpensively, Groves said. “We have a very low-cost source oil component that we can produce for around $10 a barrel,” he said. “The ability to augment oil supply by coal discard as your feedstock has some interesting opportunities attached to it.”
With those opportunities in mind, two major global energy companies, Pea- body and Vitol, invested in partnerships with Arq in July 2018.
Arq and Peabody partnered to identify and prioritize mine sites that are candidates for adoption. “We now have access to all of their sites,” Tudor said.
Arq partnered with Vitol, described as the world’s largest independent oil trader, to distribute Arq Fuel globally. “Vitol will work to position Arq Fuel as a low-cost blending component with specific customers,” Arq reported. “These are initially envisaged to include consumers of fuel oil.”
Groves said the three companies were also partnering on “major innovations.”
Those innovations may debut at Corbin or at the plant planned for Australia, described by Groves as at least five times the size of the one at Corbin. “That one will be a little different because it is going to be on an active mine site.”
The size of the site will mandate a “scaling up of the size of the plant and the output as well,” Tudor said.
The company plans to have made final investment decisions on the plant before the close of 2019, Groves said.
Meanwhile, the company, with an office in Lexington, Kentucky, is open to exploring other possible partnerships in the U.S. and abroad, Tudor said. A partnership could present a miner with “a new revenue stream” and “a new line of business,” but with an “environmental angle as well,” he said.
Which is to say Arq could help a coal miner grow optionality, Groves said. “The coal market has proven to be pretty volatile, especially with the waste angle,” he said. “If you could turn that into a product at low cost, and sold into another market, that just gives you some optionality be- cause the coal price doesn’t necessarily follow the oil price or vice versa.”