By Lee Buchsbaum
During December 2010, Mechel OAO, the Russian mining and steel conglomerate that purchased the coking coal assets formerly known as Bluestone Coal Co., announced the start-up of its new K2 coal processing plant near Pineville, W.Va. The $12 million prep plant is capable of processing up to 3 million tons per year (tpy) of raw coal. For 2011, production is expected to exceed 1 million clean tpy. The plant has a raw feed capacity of 500 tons per hour (tph) and is designed to efficiently separate high quality, low-volatile coking coal from the high reject material commonly produced from mining multiple thin seams. To enhance operations, the plant is employing a new flotation system specifically designed to better capture valuable met coal fines. According to Mechel Bluestone, the K2 investment will allow the company to double its overall production of low-volatile coking coal.
The K2 prep plant is located off an isolated mine road high on the hillside of a reclaimed surface mine. Out of view and away from any communities, K2 “doesn’t intrude on anyone’s fishing and there are no noise complaints. We can generate a product and we do it in a way that’s out of sight and out of mind,” said Tom Lusk, president, Mechel Bluestone. More than 4.2 miles of buried waterline was installed to supply K2. Several nearby underground and surface mines feed into the plant. Though all coal is initially loaded into trucks, Mechel continues to load railcars at its Keystone, W.Va., facilities. It also trucks coal from K2 to the company’s Kanawha river terminals.
With 21 dedicated employees, the new K2 prep plant currently runs five day per week, 24 hours per day with occasional Saturday and Sunday shifts depending on coal sales and maintenance schedules. Technically a new plant, the plant was originally constructed near Hazelton, Ind. In service for three years, the prep plant was disassembled and brought to its current site where it was rebuilt and expanded for Mechel by The Daniels Co.
The K2 plant is just one piece of a long-term strategic global expansion. As it washes the low-vol coking coal produced by the company’s operations in McDowell and Wyoming Counties, K2 supplies the low vol piece of a globally desired premium met coal recipe, Lusk explained. Depending on permits, as Mechel adds underground and surface production capacity, the company can expand its processing capacity. K2 itself was built with expandability in mind. “We can add blocks on to it as necessary,” said Lusk.
High Met Prices JustifyLow Recovery Rates
The prevailing price of coal dictates business strategies. Met markets are tight, commanding a premium price, and no coal operator wants a prep plant to become a bottleneck. In the 1980s, when met coal prices averaged $35/ton, most coal seams measuring 36 inches or less were not considered saleable reserves. However, when prices grew to $150/ton or more, suddenly folks were mining 30-inch coal and taking 12- to 20-inches of rock to do it. Most of Mechel Bluestone’s underground mines cut 48 inches or higher. But some of the seams it and other companies are mining are much thinner. At $150-$300/ton, even with the heavier duty continuous miner units needed to cut through the rock, these mines are profitable.
When Mechel acquired the property K2 sits on, there were already multiple active surface and deep mines operating in the area. Currently, K2 washes coal from two surface mines and two deep mines with a third underground mine being developed this summer. In total, K2 receives between 200,000 to 250,000 tons per month of raw coal—or 2.5 to 3 million tpy. Though overall yields can be low as 30%, K2 normally recovers between 35%-40%.
The mines cut coal from the Sewell, Pocahontas and Firecreek seams. Mechel Bluestone’s highly sought after metallurgical coal travels the world. “The Firecreek coal complements the Pocahontas seams. It has some of the valuable properties that the Pocahontas doesn’t have. Most of our customers prefer a blend of the two. The Sewell helps as well. It’s a smaller percentage but the Sewell has a lower ash content. When it is blended, the plant can run at a higher specific gravity for the other coals and still meet ash specifications while increasing yield,” said Dennis Phillips, director of coal preparation, Mechel Bluestone.
K2’s Three Coal Circuits
The process of washing met coal differs substantially from that of steam coal. “With steam coal it’s all about calorific value or Btus. Coking coal is a little more complicated. The parameters that one looks for are different. The coke maker is looking for a very consistent ash, consistent moisture, and for the right chemistry. Now, God takes care of the chemistry and we have to take care of cleaning the ash and washing the coal,” said Lusk.
K2’s prep plant has three circuits: a coarse, fine and an ultra-fine. “K2 is specifically designed to recover and clean met coal fines It classifies by size, which in this case is 6.5 mm x 1 mm, 1 mm x 0.15 mm (100 mesh), and 100 mesh x 0. Using heavy media cyclones, spirals and flotation cells, K2 is able to recover much of the coal fines that other prep plants might let go,” Phillips said.
Unlike many prep plants, K2 uses screen bowl centrifuges to dewater the spiral product. “We use different types of coarse coal dryers and a new flotation system,” said Phillips. K2 features three 12- x 6-ft high StackCell flotation cells in a series. A relatively new product offered by Eriez, K2 employs the first three-in-a-row StackCell flotation cell system to be used in the U.S. “We are really focused on removing high-ash clays from the product,” said Phillips.
K2’s main coal washing circuit begins with a scalping screen outside the plant where Mechel removes the plus 2.5-inch rock. Raw coal reports to a 10- x 20-ft single deck raw coal de-slime screen with a new flume screen where K2 makes a 1-mm cut for its fine coal circuit. Plus 1-mm is pumped through a Krebs 40-inch heavy media cyclone and the products report to the clean coal and refuse drain and rinse screens. Since the plant was originally built as a 350-tph circuit, K2 replaced both of these screens with new Connweld banana screens. The dryer was changed to a CMI EBR-42 clean coal centrifugal dryer. “Only the bottom deck coal is dried because there’s not much coarse coal on the top deck to be dried,” Phillips said.
The magnetite is rinsed from the coal and refuse on the drain and rinse screens and this diluted media water is then pumped to magnetic separators to retrieve the magnetite and return it to the media sump. The tails from the magnetic separators go to the deslime screen where the 1-mm x 0 coal flows to the classifying cyclone sump and is then pumped to a bank of five Krebs 15-inch raw coal classifying cyclones. The cyclone overflow goes to flotation and the underflow heads to two banks of eight triple-start spiral concentrators. “These new two-stage spirals are a taller version of what was originally conceived. This circuit was beefed up as we went from three cyclones to five,” Phillips said.
The two-stage spirals are a first for Mechel and relatively new to the industry overall. “They’ve been around for about five years now. Several companies are making them, but we’re employing a two-stage model. They basically make about three turns, taking the clean coal and the midds into a little box with a couple baffles, re-mixing it and going again. This improves the separation and lowers the gravity cut-point. Then the product goes through two pairs of two-stage fine coal dewatering sieves, which helps take any clays and high-ash fines out of it. From there the product heads to two 44- x 132-inch screen bowl centrifuge dryers,” Phillips said.
The classifying cyclone overflow reports to three new 12-ft diameter x 6-ft high StackCell flotation cells. “It’s three in a series, not unlike the old ‘hog-trough system’ which are conventional cells set along a trough. You go cell to cell but the units at K2 are literally stacked on top of each other similar to a set of stairs. Basically, the feed slurry flows by gravity from one cell to another and the products flow into the de-aeration tank which then feed the screenbowl centrifuges. The washwater system helps remove the high-ash clays from the product. The flotation tails report to the thickener and two 3 m Phoenix belt presses dewater the thickener underflow,” Phillips said.
Mechel has designed K2 to maintain a low ash coal and operate around a specific gravity cut point of 1.55 and above all the time. “Right now the market is good, and we can push the envelope. Product specifications range from 6.5% to 8% ash. In the current market it’s easier to move coal at the high ash end of the range than before,” said Phillips.
K2’s staff works hard to meet the ash specification. One way they do this is through precise measurements and continuous testing and analysis. “If ash can’t be controlled exactly, then the plant has to err on the safe side. That costs money because the company would not be comfortable shipping toward the edge of the specifications. When you take that safer route, the company may not be able to maximize its financial returns. But if it goes over, then it faces messing up an entire train. K2’s instrumentation allows it to operate more precisely than it could have a year ago,” Phillips said.
A Lack of Thermal Driers Makes It Unique
K2’s flotation circuit is a unique aspect of the plant. “The combination of the two-stage spirals and the two-stage sieves, plus plenty of screen bowl capacity for de-watering also sets the plant apart. Where its uses screen bowls, other operators would use an EBW drier, but those units do not reduce moisture as well as the screen bowl centrifuges. We are processing a lot of fines due to the soft nature of the coal. By the time it reaches the plant, there are no lumps—nothing bigger than 1 or 2 inches. Even though it’s mined by different means, the surface coal is also soft and has to be crushed and we recovery those fines too,” said Phillips.
The scalping screen prevents the oversize rock from plugging the heavy-media cyclone pump. Mechel has been very pleased with their pump. “It’s a modified Warman 12-10 with a new style impeller. It provides really good flow,” Phillips said.
Though Phillips might lay the plant out differently with a little more space if he were starting from scratch, he’s very proud of what K2 has already proven it can do. “It will wash any coal out there. It’s designed for high ash and a fair amount of clays in the feed, which fortunately we haven’t had too much of here,” he said.
On the downside, the plant only has a small amount of scalability. “Most things here are fairly loaded. While sometimes you can stretch existing circuits, if we had to go to 750 or 1,000 tph, we would just duplicate another plant,” Phillips said.
With the met market continuing to be so tight, K2’s ability to recoup its ultra-fines—essentially dust—is key. “We’ve dealt with some high fines and haven’t had an ash issue. Our raw coal is 25%-30% minus 1 mm. The ash varies by the product, but it’s more the nature of the different coal seams. We have to vary the specific gravity, but we haven’t seen an unexplained jump in ash that was due to fines. As we pull better on flotation, we will see a little higher moisture, but we’re staying under 8% very well so far,” Phillips said.
Moving to bigger screenbowls—44 inches versus 36 inches—allows K2 the greater capacity it needed to take care of that material and subsequently attain better moisture. “We took out the coarse coal dryer that came with the plant and put a small coal dryer for just the bottom deck. We focused on moisture a lot with the drying systems,” Phillips said.
“In the beginning you try to design the best flowsheet and equipment but from then on it is all about having the right people and our plant superintendent, Gary Estep, has put together an excellent crew that really likes to run coal. The crews are implementing maintenance, sampling, and performance programs that will keep us on track. If the plant goes down for anything they don’t stop hustling until the coal is flowing again,” Phillips said.
One piece of advice Phillips offers after being involved in the design and construction of more than 20 plants, is that “if you know there is something you’ll eventually need, go ahead and do it. Oftentimes, if a company holds off, trying to cut corners, that decision will come back to bite them. So, do it right from the beginning. Retrofits are expensive and timely. They either shut down production or they shut in tonnage and those are the last things any coal operator want to do to its prep plant,” said Phillips.
“I have to admit I was skeptical at first, but the design Dennis put together relying on mechanical drying equipment and screening technology has proven the science and the technology are there to do this. K2 is doing its job,” said Lusk.
K2 can produce a low-vol metallurgical product at reasonable feed rates without using one of those behemoth thermal driers, Lusk explained. “The circuitry, design and the technology that our group put together is able to consistently produce product at less than 8% moisture. In the old days we thought we had to have thermal driers with 70-ton evaporative load capacities. We were convinced that it was just impossible to generate marketable metallurgical product without those. K2 is absolute proof that you can,” Lusk said.
Buchsbaum is a Denver-based freelance writer and photographer specializing in industrial subjects. He can be reached through his Web site at www.lmbphotography.com or by phone at 303-746-8172.