United Coal Co. (UCC), headquartered in Teays Valley, W.Va., had been looking to add a low-volatile (low-vol) product to its growing portfolio of high-grade metallurgical coals, and the White Mountain Mining Co. acquisition aligned perfectly with the company’s growth strategy. While the Pocahontas coal reserves that were included in the acquisition had highly attractive metallurgical quality characteristics, the East Gulf preparation plant that accompanied the active mine and reserve package was anything but attractive.
The Pocahontas Group is a series of up to eight seams of high rank, bituminous coals that are generally high in thermal content and fixed carbon and low in ash, sulfur, and volatile matter. The high-fixed carbon and low-vol matter make the coals very desirable in producing coke to reduce iron ore to steel. Beckley-based Pocahontas Coal Co., one of UCC’s four subsidiary companies, currently produces a blend of coals in the Beckley, Pocahontas No. 2 and Pocahontas No. 3 seams. All of these coals are recognized by North American, European, and South American coke producers as premium, low-vol coals.
While area coal mining and processing dates back to the early 1900s, the current East Gulf prep plant was originally built in the early 1970s by the Elgin Group. However, after more than 30 years of service, the plant was in extremely poor condition—both operationally and structurally—when UCC assumed operation and started Pocahontas Coal Co. As a result, UCC engineers had to decide whether to try and renovate the existing plant or build a new plant.
“Through the 1980s and 1990s, the industry’s rule-of-thumb was to invest $1 million for every 100 tons per hour (tph) of desired prep plant capacity,” said Ed Toppings, vice president of maintenance services, UCC. “Due to escalating steel prices and the shortage of qualified plant construction companies in recent years, a better estimate for the required investment is now approximately $2 million per 100 tph. Even though you wouldn’t have known it at the time by looking at the outside of the plant, deciding to reconfigure and update East Gulf’s existing circuits was a
more economical course of action.”
“Before the upgrade, the plant’s production capacity was 400 tph, which was not large enough for our planned mine production,” said Toppings.
UCC needed to expand the production capacity to 600 tph. By using the $2 million per 100 tph estimate, UCC would have needed to invest $12 million to construct a new preparation plant. UCC engineers had already estimated that they could upgrade the existing plant to 600 tph for less than half the cost of a new plant. “That made the decision easy for us,” Toppings said. “We had also enjoyed successful prep plant renovations at some of our other subsidiaries.” UCC had renovated a 1,100 tph preparation plant at Sapphire Coal Co. (Letcher County, Ky.), and added a new 500 tph module into the existing Star Bridge prep plant at Carter Roag Coal Co. (Randolph County, W.Va.).
The original East Gulf plant consisted of a rotary breaker, followed by a three stream heavy media (HM)/flotation plant with moisture reduced by a Heyl & Patterson Thermal Dryer, which was considered typical for a 1970s vintage plant. The plant was configured with a Barvoy HM Vessel, Dutch State Mines (DSM) HM cyclone circuit and flotation cells with vacuum filter recovery. The plus 1/4-inch material was handled by the Barvoy, 1/4-inch x 28-mesh was handled in the HM Cyclone circuit, and minus 28 mesh was handled in the flotation cells. For a soft-coking coal processing plant, the operation was second to none. And the technology, with a few exceptions, remains good today.
In an effort to minimize cost, maintenance, and manpower—while increasing production—the circuits in the existing plant were partially or completely modified.
“Although an old structure, the East Gulf plant as it stands and operates today is a modern, efficient operation,” said Lynn Shanks, president, Pocahontas Coal. “With these improvements, East Gulf is now capable of achieving market-acceptable operating costs and customer-desired product quality.”
Toppings is also quick to share the credit with others for the major plant improvements. “Just about everything we did was under the watchful eye of Rob Robertson, the vice president and general manager of Taggart Global,” Toppings said. “I don’t know anyone in our business with more technical knowledge and experience in coal preparation than Rob. He has helped us immensely. Also, East Gulf’s employees have years of experience dealing with the complexities of washing Pocahontas seam coals. They have been instrumental in making sure we made our shipments, as well as helping with the various upgrade projects.”
Coarse Cyclone Circuit
When East Gulf was under previous ownership in the late 1990s, the Barvoy Vessel was replaced with a single, pump fed, 30-inch Krebs HM cyclone. This modification was performed in an effort to replace a worn out, expensive, mechanical piece of equipment with a much lower cost alternative with no moving parts and equal performance. Replacing the Barvoy’s reject drag chain, product lifting paddles and associated bearings, shafts, launders and chute work with a sump, pulping column and cyclone significantly simplified the maintenance requirements at the plant. While the cyclone circuit has its limitations, particularly the cyclone apex capacity and a pump that has to handle slurry of nearly all rock, the modification certainly improved plant availability with virtually no evidence of coal losses in spite of a nominal feed ash approaching 75%.
Fine Heavy Media Cyclones
The only circuit that remains relatively unchanged in form is the DSM HM cyclone circuit. Although the form of this circuit is the same, the capacity is much different. The original 20-inch DSM cyclones have been replaced with large-capacity Krebs 20-inch units. This one change effectively doubled the flow rate of the circuit, while maintaining the pressure head required by the cyclones. The cyclone change, pump motor and sheave change doubled the flow rate, which also doubled the feed rate—all in the same plant area.
At the onset, the magnetite recovery circuit appears to be complex with a roof-mounted magnetite thickener, magnetic separator and dilute media cyclones. The Dutch that designed this circuit in the 1950s did not intend for it to be complicated. But as anyone who has ever operated this type of circuit knows, it needs to be well maintained.
A worn sieve bend, a hole in a screen, excessive rinse water, or a plugged cyclone will play havoc with the balance of the circuit. Therefore, the secret is to maintain it “as is” and not change it. East Gulf plant management is currently working on upgrades that include improved pumps with high-chrome components, fish tail sprays, and rain boxes with high-volume nozzles. Overall, the basic circuit design will remain the same. Except for the magnetic separator and equipment mentioned previously, there isn’t much more that can be done to improve results.
The original circuit had a double-drum concurrent arrangement, which gives good magnetite recovery while removing non-magnetic material from circulation. This same effect is achieved with the presently installed high-gauss six pole magnet with a “Climaxx” tank, which wasn’t available decades ago. These modifications were made prior to UCC’s acquisition of the property in late 2005. Since that time, additional enhancements have been made to the plant’s capacity and performance.
In 2006, Pocahontas Coal completed another plant upgrade at East Gulf by adding a spiral circuit. This was performed along with a few other process adjustments to increase the plant feed rate from 400 tph to nominally 600 tph. Essentially, the spiral circuit was an addition of a full, new washing circuit to remove undersize (minus 1 mm) in the fine HM cyclone circuit and oversize (plus 150μ) in the flotation circuit. By increasing the mean grain size of material in the fine HM cyclone circuit, the effective desliming and drain-and-rinse capacity of the screens nearly doubled with the same screen area. As a result, the cyclone circuit capacity increased. Likewise, by removing the 1/2 mm x 150μ fraction from the flotation cells, narrowing the floatable particle size, the cells become more efficient and less likely to lose misplaced, oversized material.
The spiral circuit receives feed from the slimes (minus 1 mm) passing though the deslime screens after it is sized at 150μ in a bank of 15-inch classifying cyclones. The spirals, located high in the plant in two banks, separate the 1 mm x 150μ material into clean, middling and refuse products. The refuse and middling material is dewatered on a urethane deck dewatering screen. The clean product is collected in a sump and pumped to 20-inch cyclones for primary dewatering prior to screen bowl centrifuges.
Screen Bowl Centrifuges
The most recent circuit modification at East Gulf was the addition of screen bowl centrifuges. Two factors played into the decision to install screen bowls: the cost of rebuilding, maintaining and operating the circa 1970 thermal dryer; and the presence and subsequent loss of material in the thermal dryer scrubber effluent. While the thermal dryer was capable of producing a remarkably dry product (less than 5% moisture), the screen bowl addition represented the next obvious upgrade.
In 2008, the screen bowls were added, while some electrical and control system upgrades and replacements were also completed. Although the plant’s clean coal product is a little higher in moisture, the overall result has been a much more consistent product delivered at a lower cost. Also, in comparison to the thermally dried coal, the centrifuges better prepare the product for handling by decreasing dust. Likewise, there has
been a slight but positive impact on thickener tailings ash as a result of capturing fine coal.
Structural Upgrade and Siding Replacement
Having completed the internal renovation with the upgrade of the plant’s major cleaning circuits, the final piece of the puzzle was to improve the structural integrity of the original frame while giving the plant a much-needed face-lift. Company engineers were concerned about the possible deterioration of I-beams hidden from view beneath the plant’s rusted metal siding. They were also tired of hearing Mike Zervos, UCC’s president and CEO, refer to the plant as the “ugliest plant in the world.”
As a result, during the summer and fall months of 2008, the old siding was removed from the plant to allow inspection of supporting steel beams and girders. Along with replacing many of the girders and some of the main support beams, the original supports were sandblasted and painted. Removing the siding also presented the ideal opportunity to remove a lot of the idled equipment that was replaced with upgraded technology. This also led to increased floor space. Finally, after several years of balancing operational needs with efficiently planned upgrades, the plant was completed with the installation of additional lights and heaters to go along with new, sky blue siding.
One of the most desirable qualities of the Pocahontas-area coals is the low inherent pressure. Most conventional North American coke-makers are targeting 1- to 2-psi in their overall coal blend of low-, mid- and high-volatile coals, depending on the age and design of the coke batteries. The Pocahontas Group coals help keep wall pressures low in coke batteries, which is especially important in older units. Typically, these coals exhibit the following mean quality: 17% dry volatile, 7.50% moisture, 7.25% dry ash, .80% dry sulfur, 8 FSI, 98+ oxidation, 84 maximum fluidity (ddpm), 1.61% reflectance, 27% inerts, 3.97 CBI, 7.03% rank index, 51 calculated stability, and +2-4 sole oven (52/2), 5 psi.
Today, most of the isolated pockets of Pocahontas seam low-vol coal are exhausted, but there is a continual demand around the world for these unique coals.
Ned Payne, president, Piney Land Co., presides over one of the area’s largest reserve holders of high-grade, metallurgical coals. Payne, a locally admired attorney, coal mining professional and historian, is uniquely qualified to comment on the rich tradition of Pocahontas coal mining.
“I’ve been working in this industry for decades, and there is one thing I’m sure about,” Payne said. “As long as steel companies continue to use coal in their steel-making process, Pocahontas seam low-vol coals will always be of highest demand. With its recently modernized, efficiently operated East Gulf preparation plant, Pocahontas Coal, which mines reserves in one of the few remaining large blocks of Pocahontas coals, is positioned to serve this market for many years to come.”