By Lee Buchsbaum, Associate Editor and Photographer
Most mornings after he completes his 5-mile run, Rob Robertson, vice president-coal preparation, United Coal, a subsidiary of the Ukrainian steel producer Metinvest, grabs a cup of coffee and spends time on his iPad checking up on his babies: United’s fleet of prep plants. During breakfast, he’s already dialed in, following the feed rates on his touch-screen and scouting for problems. He toggles from plant to plant, comparing flows, ash specifications, going through the data. Robertson loves data. He tracks the information longitudinally to have something empirical to chart, reference and plan around. Whether it’s about his personal performance, how many miles he’s logged, or recovery rates at United’s plants, he stores the information in notebooks or computers. He even has PDFs of all the operations manuals for each plant on his iPad—just in case. Wherever he goes, as long as he can get a signal, he can plug into whatever’s happening at Froth Central.
Throughout a 30-year career, Robertson has built dozens of prep plants—almost 50 at this point—on nearly every continent. He has a vast wealth of practical knowledge about the design, implementation and maintenance of prep plants, particularly about process control. And he has vaults of data and information, both on paper and stored in his head.
Over the years, Robertson’s designs have involved electronic, pneumatic, hydraulic and mechanical systems as well as computerized automation and control. Through time Robertson’s sense of circuit design has changed with advances in equipment. “Essentially, I want circuits with the largest and least number of pieces of equipment possible. Less equipment equals less downtime. Cyclones, screens, separators, pumps, etc. have all become larger over the years—allowing larger single circuits to be built. This in turn reduces distribution problems, plate work and extra piping,” said Robertson.
Construction materials have also changed tremendously since he started his career in the 1970s. Current components have lowered maintenance requirements and increased reliability. “Ceramic, ultra high molecular weight (UHMW) plastics, hard metal pumps and urethane piping have all been used in our new plants and rebuilds,” said Robertson.
As the former manager of coal processing at Massey Energy, he established and maintained standards for testing and evaluation of the company’s then 18 processing facilities to optimize plant efficiency, availability, product consistency and utilization.
For 10 years, following his exclusive contract with Massey, he owned, managed and directed his own company, Robertson Process & Electrical. RP&E, now wholly-owned by Taggart Global, was an electrical engineering and construction company performing electrical engineering, construction and consulting all over the world with an annual volume approaching $50 million.
Though he flirted with retirement, the opportunity to build up a modern fleet of first-rate prep plants with a near blank slate was just too tempting. Since April 2010, he has held his current position with United Coal. He oversees production, efficiency, cost and safety at five operating prep plants including the new Affinity plant, and the wholly-rebuilt Wellmore No. 8 facility. As these projects wind up, Robertson is planning the surface facilities for United Coal’s new Roaring Creek project near Elkins in northern West Virginia, which will produce coal for steel mills for Metinvest in the Ukraine and a few domestic steel producers.
Permitting Delays
In 2010, United Coal began developing its third operation in West Virginia, the new Affinity Coal Co. Located in Midway, near Beckley, this is just Affinity’s latest evolution. United Coal began by re-opening the older, idled Affinity mine—at least the third to access the storied Pocahontas seam—and redeveloping it to a different level. Simultaneously they initiated construction of a new 500-ton per hour (tph) prep plant. The whole operation represents more than 250-plus jobs to the area, $115 million to the local economy, and potentially more than $4.5 million in taxes to the state of West Virginia. But due to extended review times, the Mine Safety and Health Administration (MSHA) has yet to finally permit Affinity’s full operation and development work has been extended.
The new, ultra-modern Affinity prep plant serves as a metaphor for the best and worst of our current coal market and political climate. Affinity’s technology is cutting edge and inherently safe. The underground mine produces some of the most sought after coal in the world: a low-volatile metallurgical coal from the Pocahontas No. 3 seam. Typical clean coal specs are about 7.5% dry ash; less than 8% moisture; 0.85% sulfur; and 16% volatiles. The mine is scheduled to produce between 1.2 to 1.5 million tons per year (tpy). Since summer of 2011—when the plant came online—less than 100,000 tons has flowed through the plant. Hung up by frustrating MSHA permitting challenges, underground operations are slowly moving forward. To keep operators sharp, while doing development work and running some native coal, United has taken some third party coals from other producers as well. 100 new jobs hang in the balance as Affinity’s 165 crew members continue the slow mine rehabilitation work and await the day they can really let the horses run.
While awaiting more throughput at Affinity—and thus more data collection opportunities—Robertson has been concentrating on the Wellmore No. 8 rebuild (See p. 26) and drawing up plans for the Roaring Creek mine.
Affinity Equals Apex
The Affinity plant represents the apex of plant design for Pocahontas coal, as well as for operations with respect to safety and maintenance. The layout includes a travelling overhead crane, ergonomic stairways, a large well for equipment access, lots of lighting, and accessible electrical controls. Lots of space allows managers to walk around and observe the overall flow of the facility. It also makes maintenance easier and provides a safer work environment. The preparation process is, however, simplified in several ways because Affinity is currently mining from only one specific coal seam.
The design differs from the typical “one size fits all” approach to coal prep. Plant design must be based on the characteristics of coal being washed and the market that plant serves. The further the raw coal quality is from the clean coal quality, the more complicated the plant becomes.
Though Robertson designed the Affinity plant to run at an average raw feed capacity of 500 tph, he also built in a lot of flexibility. During Coal Age’s tour, the control room readout showed a higher run rate, about 530 tph. “This plant could run as high as 700 tph with the right feed. This plant, like any plant, is limited by its outgoing streams, not the incoming one,” Robertson said. “If you have a higher reject rate, then you might have to turn the feed rate down because it has to handle too much refuse. Similarly, if dilution is minimized and the coal grade on the feed is high, operators might have to turn the feed rate down because the plant will have too much clean coal.”
Evaluating the costs of building and running a plant, in terms of expenses, the most expensive part of the prep plant are the centrifuges. “You try to design the plant so that you never run out of centrifuge capacity, but you don’t want to have too much either because it increases the costs. Again, going back to feed rates, if you have too much raw coal you might have to dial it down because the centrifuges get overrun or the belt presses can’t handle what’s being thrown at them. At the end of the day, despite what so many others claim, the feed rate is irrelevant. It’s the outgoing streams that limit a plant’s true capacities,” said Robertson.
Layers of Prep Plants
The current Affinity mine can somewhat accurately be called the grandchild of the first Affinity mine as a succession of operations have accessed and extracted the Pocahontas seam. The most recent Affinity mine slope came out at the same point as the new one. It had replaced the first Affinity portal that, walled up across from the new prep plant, reads 1937 on its old concrete opening. Like many areas in this part of West Virginia, the current prep plant and surface facilities sit on top of an area that has been mined since the early 20th century. United started demolishing the most recent “old plant” over the summer of 2010. Construction workers finished the new plant in June 2011. Since then the plant has hardly been tested.
Robertson was contracted by United because they wanted his expertise. Management essentially gave him a blank sheet and allowed him tremendous freedom of design. Though he had six fixed points at Affinity (the portal, the railroad load out and a few other non-negotiable items) all they really said was: “we want a 500 ton per hour plant.”
“We have a tremendous amount of preparation capacity,” said Roberston. And when the mine fully comes online—projected for this year—it will just be gearing up for a larger coal prep mission.
The Affinity plant’s four finished products are three sizes of clean coal: plus 1 mm; 1 mm x 150 microns, 150 microns x 0, and the coal refuse. Before any of the coal goes into the Affinity prep plant, it comes out of the mine slope and heads into a stacking tube where United can store 50,000 to 60,000 raw tons. Stockpiled raw coal reports to the raw coal silo. That feeds the plant. Then coming out of the plant, Affinity has a 20,000 ton clean coal stockpile area and a 10,000 ton silo. “We have 30,000 tons of clean coal storage or more and 60,000 tons of raw coal storage,” said Robertson.
From the raw coal stockpile, coal is reclaimed by two feeders and is brought onto a double deck scalping screen, 75 mm on top, 50 mm on bottom. The top material, which is virtually all rock, is thrown into the reject bunker. With the 75- x 50-mm, Affinity can either throw it into the reject bunker and put it on the refuse belt or crush it. All of the coal that passes through that screen is minus 50 mm and reports to a 2,500-ton storage silo. Affinity can batch up into that silo and run out of it into the prep plant for four to five hours.
The minus 50 mm reports to a single deslime screen along with more than 4,000 gallons per minute (gpm) of water. Affinity deslimes it to 1 mm, so the material that passes over the 50- x 1-mm screen reports to a 1 meter diameter heavy-media cyclone (HMC). That is the first stage. The overflow is the clean coal and it reports to a clean coal screen where it’s sized to about 15 mm. The plus 15 mm reports immediately to the clean coal belt. The minus 15 x 1 mm reports to a centrifuge and that goes onto the belt. The refuse comes out the bottom of the cyclone (underflow) and reports to a refuse drain-and-rinse screen. The refuse comes off the end of that screen and onto the refuse belt. The media recycles from both the clean coal and refuse screens back to the HM sump. “So with a dozen pieces of equipment we wash all of the plus 1-mm product and that constitutes the first stage,” Robertson said.
The second stage of processing is the 1 mm x 150 microns. Everything passing 1mm reports to the raw coal sump and is pumped to a bank of 15-inch gMax classifying cyclones. The plus 150-micron product (underflow) reports to the spirals. The spirals separate this stream into three separate products: clean coal, refuse and middlings. But middlings in this coal are really not middlings, “they are just misplaced product. This coal is really a black and white separation. It either goes one way or the other. So if there is anything in the middlings, it normally represents about 10% of the feed to those spirals. Since it’s really misplaced, we designed the circuit large enough to handle the recycle and send those middlings right back to that sump and sooner or later they decide which way to go: clean coal or refuse,” said Robertson.
The refuse goes onto a refuse de-watering screen where the water is removed and the solid waste material is belted away. The clean coal goes into another classifying cyclone sump. “The reason it goes into the classifying cyclone sump and is classified again is because typically on a spiral, you will get a lot of misplaced fine material. Anything that is finer than 150 microns typically goes with the coal whether it is clean coal or refuse. If it goes with the coal, you have to get it back out or it will contaminate the final product,” said Robertson.
That spiral product goes to the clean coal classifying cyclone circuit. The underflow of the clean coal classifying cyclone circuit, which is nearly all plus 150 microns, goes over a final sieve bend and reports to a screen bowl centrifuge. The minus 150-micron cyclone overflow, along with a lot of water, returns to the raw coal screen.
The minus 150-micron raw coal cyclone overflow goes to Affinity’s third stage which is fine coal flotation, 150 microns x 0. “Here we have four conventional 1,000-cu-ft FLSmidth cells with froth crowders. They are the largest coal cells FLSmidth builds. Though some might argue that these cells give the plant almost twice as much capacity as it needs, no matter what, Affinity does not lose any coal. The plant gets it all,” said Robertson.
The clean coal product from the flotation cells is combined with the clean coal from the clean coal classifying cyclones (spirals) and reports to the screen bowl centrifuges. It is then de-watered and reports to the clean coal stream. The underflow (refuse) from the flotation cells goes to the thickener. The thickener material, which is 150 microns x 0 refuse, is pumped to two Andritz belt presses. These presses, though of a German design, are made in U.S. The fine refuse material combines with a total of the coarse refuse and all of that reports to the overland refuse conveyor. In total, Affinity has one belt feeding the plant, and two belts going away from it.
The material coming off the refuse belt press “looks like a mud-cake,” said Robertson. Once the water is squeezed out, it recycles to the thickener and the solids go out on the refuse belt.
Rationalization of Plant Design
Because of the different densities in coal, Affinity’s circuits are sensitive to the specific gravity of the heavy media. “To optimize a metallurgical coal plant, ideally each stage would produce the same coal quality (ash). This is much different from a steam plant, where the three stages would be adjusted to have the same amount of inert (non-combustibles). Since Affinity is a met plant, we want a 7% ash product. We want 7% ash out of the coarse stage, a 7% ash out of the intermediate stage and a 7% ash out of the fine stage,” said Robertson.
In a steam plant the inert undesirables (ash and water) needs to be equal to optimize Btus. So the coarse circuit would be high ash, low moisture. Intermediate would be intermediate moisture and intermediate ash. Fines ideally would be low ash high moisture.
United has a flotation circuit almost exactly like Affinity’s at the company’s East Gulf prep plant that was built since Affinity. “We started it up last April and we consistently stay above 75%-80% yield in that circuit. We’re getting all of that coal. What I tried to do here was design the plant so operators don’t have to worry much about recovery. You turn it on and it runs. The simpler you can make your plant, the better it will run. You engineer solutions to keep things simple. This way the plant runs and can be depended on,” said Robertson.
According to the washability and size distribution, recovery rates increase as the coal gets finer. At Affinity, because of the strength of the rock, it mostly reports to the coarse circuit and the yield in coarse circuit is roughly 20%. The yield in the intermediate circuit is roughly 65%-70%, and the yield in the fine circuit is about 75%-80%.
One of the few differences about the new plant from all the other ones Robertson has been involved with are the two Andritz screen bowl centrifuges. Affinity has a standard machine and a proprietary one with a different kind of screen design that the manufacturer claims should yield them 1% lower moisture. “These are the first machines that I’ve ever bought from Andritz in my career. We’ll see how they work. It’s an experiment. But the good thing is, I could run this plant on one centrifuge. So if the proprietary design breaks or doesn’t function up to what is promoted, we can take it out and put a standard machine right back in its place. “I’m not ready to brag about the experiment yet because we haven’t run enough coal through it,” said Robertson.
The Modern Control Room
Many plant control rooms are noisy, dusty, dirty, and loud with dozens of vibrating dials, buttons and controls throughout. Not so at Affinity. Located outside but adjacent to the actual prep plant in a separate climate controlled facility, the control room is quiet, clean and very functional. Several banks of touch screen computers line one wall. Remote cameras and sensors monitor flow and data—the same data that Robertson is able to access from his iPad.
Looking at the myriad of on-screen buttons and plant displays it’s easy to initially become confused. But, like all things Robertson is involved in, eventually the design becomes simple. All items marked green are running. If something has a red indicator, it means it’s stopped. If they are purple, they have a stop button pushed in. If marked blue it means the breaker is off. “The way this control system is designed is if something is marked blue, one of our prep plant workers will go to the starter to fix it. If it’s purple you go into the plant to fix it. If it’s green, it’s running. If it’s red, then you’ve got no trouble, it’s just waiting to be started. All part of keeping it simple,” said Robertson.
Of all the many numbers and figures displayed on the bank of monitors, perhaps the most important is the heavy media density indicator. “We’re normally run at 1.55 specific gravity. The specific gravity can vary anywhere between 1 and 2. The cyclone cut point is a little higher than 1.55 normally, making maybe a 1.57 to 1.58 separation. That’s done so we can produce the same amount of ash on all circuits. Most of the tons are coming out of the coarse circuit. Second would be the intermediate circuit, third would be the fine circuit. We adjust the heavy media, spiral cutters, and flotation controls to keep the ash qualities consistent all around,” said Robertson.
The New Load Out a Hundred Feet Away
From the stockpile and the clean coal silo, Affinity has another conveyor that carries coal to the load out. Though the load out is not operated from the prep plant control room, it can be monitored from there. But due to the compact nature of the surface facilities, the new load out sits only 200 ft from the prep plant itself.
Robertson’s subcontractor helped design and built the new load out and rail siding. The new siding off the Norfolk Southern is a little unusual in that instead of using standard wooden cross ties, Affinity put in steel ones instead. Robertson believes that by installing steel ties, “this should be the last time we ever touch this piece of rail. There are a lot of advantages to having steel ties and these will certainly outlast me and everybody here at this mine. The steel ties are more expensive initially, though less than concrete ties. But because you use half the ballast and incur less maintenance long term, steel is cheaper over time, and by the way, we are a steel company,” said Robertson.
Affinity uses a Kanawha double batch-weigh load out. Affinity chose it “because you save $25,000-$30,000 on the structural steel because it’s 10 feet shorter than other options. The railroad dictated where we could place the load out. If we had more room, we may have been able to employ a standard load out, but that wasn’t the case here,” said Robertson. The new load out can dump more than 100 tons of coal into a car in a matter of seconds, and load a whole train in roughly 3.5 to four hours.
Looking back at his new operation, the only thing Robertson doesn’t like about the Affinity plant is the materials handling layout. “I had six points I had to work with and around to design Affinity. We did the best we could in that space and, though it’s very functional, it’s just not as elegant as it should be. The new plant, Roaring Creek, will be exactly like this one except for materials handling, and that will be fixed. I have a true blank sheet of paper over there,” said Robertson.
