Peabody Energy constructed and commissioned the new Wild Boar preparation plant during 2010. Despite an accelerated construction timeline, developers were able to incorporate ease of maintenance and accessibility into a simplified flowsheet, which included heavy medium cyclones, compound spirals and de-slimed flotation circuit. Strategically located on a rail line near Lynnville, Ind., the 650-ton-per-hour (tph) Wild Boar today processes coal effectively from three local surface mines, maintaining a high availability at a low operating cost.
Peabody owns the plant and United Minerals operates the plant. During the front end engineering process, prep professionals from both companies collaborated with General Mine Contractors, the company selected to construct the plant, and Ezra Smith, a consultant who used to manage the Black Beauty prep plants. The design team considered several options to minimize plant construction costs while still building a quality facility with good operating and maintenance features. The options included relocating an existing idled facility, building an all-new plant, and building a plant with as much used equipment as possible. They settled on a final design that included several pieces of used equipment, a three-circuit plant for efficient processing of each size fraction, and an overhead bridge crane for improved maintenance access.
“We considered several options for Wild Boar,” said Dan Pilcher, senior preparation manager for Peabody Energy’s Midwest Division. “A few idled plants in the region could have been relocated. A cost analysis was performed on that option. New plant construction is the easiest path, but not necessarily the most cost effective. The third option, which is the one we selected, combined used equipment with a new structure. We wanted a low cost facility, not just with construction costs, but also as far as operating costs.”
One of the more daunting aspects of this project was the accelerated construction schedule. One of the mines that would feed coal to the Wild Boar prep plant came online early. Coal was being trucked to an existing plant one-way 13 miles and those expenses were mounting, Pilcher explained. Construction began during mid-March 2010 and the plant came online and under budget during mid-November 2010—nine months from concept to reality.
Process Flowsheet
The Wild Boar plant can be broken into three main areas: the raw coal handling system, preparation plant and clean coal handling system. The raw coal system includes a truck dump, rotary breaker and a radial stacker with the ability to divert raw, saleable material from the prep plant. Material directed to the plant is cleaned in a simplified three-circuit system (See Figure 1).
“The plant uses a large diameter heavy-media cyclone, compound spirals and a deslime flotation circuit,” Pilcher said. “It’s the only place in the Midwest that [Peabody Energy] is using compound spirals. We have considered them at other locations, but because of the height requirement, it has been too difficult to implement them in existing plants. So we decided early-on it was something we wanted to do with this new plant and they have been performing well.” After cleaning, coal is stored in one of three product piles before being shipped by rail.
“The Wild Boar prep plant has a simplified circuit and the flow sheet emphasizes ease of maintenance and reliability,” Pilcher said. “The primary design considerations focused on safety, followed by process performance and maintenance. We wanted an efficient plant with plenty of room for access.”
Run-of-mine coal is delivered by trucks to a series of ground storage piles. “We are processing coal from three surface mines,” Pilcher said. “Trying to keep those coals separated creates another set of difficulties.”
A front-end loader then blends this material into a 150 ton hopper. After being conveyed to a scalping screen for initial sizing, a rotary breaker reduces the coal top size and removes oversize rock and foreign material. A radial stacker after the sizing station enables diversion of material to a direct ship pile if the product quality is sufficient. If the raw coal requires cleaning, it is instead stored in a raw coal pile which feeds the plant by way of a single vibratory feeder.
The plant feed belt delivers material from the raw coal feeder to a 10- x 20-ft, double-deck Banana screen. The oversized material is nominally 3-inches x 1-mm and reports to a 51-inch heavy medium cyclone (HMC). The HMC underflow reports to a single 8- x16-ft, double-deck horizontal screen for magnetite recovery. A flume screen precedes the vibrating screen to increase drainage area and ensure optimum magnetite recovery.
“One of the key design elements with the screens is the sieve bends in front of the double-deck clean coal screens, which gets the media off of those screens,” Pilcher said.
The HMC overflow reports to two sets of flumes and 8- x 20-ft, double-deck screens set at a slight downward slope. Afterward, the finer HMC product reports to two Tema 1100 screenbowl centrifuges to reduce surface moisture before joining the remaining product on the clean coal collecting conveyor.
“As far as the coarse coal, everything reports to a 51-inch [HMC],” said Terry Hillsmeyer, manager-preparation, United Minerals. “Clean coal reports to the 8- x 20-ft clean coal screens, which feed the Tema 1100 dryers and then the clean coal belt. The refuse reports to refuse screens and is discharged to a bin that is hauled back to the pit.”
The raw coal screen undersize material, minus 1 mm, reports to the raw coal sump before being pumped to a bank of seven 15-inch raw coal classifying cyclones. The cyclone underflow reports to a bank of 14 compound spirals focused on cleaning the 1-mm x 100-mesh material.
Everything feeds into the 10- x 20-ft Banana screen, explained Hillsmeyer. “The minus 1 mm reports to a raw coal sump, which pumps to a bank of 15-inch cyclones,” Hillsmeyer said. “The clean coal product reports to a set of spirals. Some of the spiral overflow reports to a screen-bowl dryer. Some reports to a CMI dryer. It depends on the load on the flotation cells.”
The spiral reject is dewatered on a high frequency screen before reporting to the reject belt. Spiral product reports to a clean coal sieve bend for initial dewatering. The sieve bend product then splits between the fine coal centrifuge and screenbowl for final dewatering.
The sieve bend underflow joins the raw cyclone overflow as the flotation circuit feed. Before reporting to the flotation cell, the material is de-slimed in a bank of 10 10-inch classifying cyclones. The overflow is discarded to the thickener while the de-slimed underflow reports to a DEC flotation cell for cleaning. “We are trying to capture as much fines as we can with the flotation circuit,” Hillsmeyer said. “It’s a little bit of a problem when you are washing three seams, but we have found a happy medium with reagents that seems to work well.”
The tailings are discarded to the thickener, and the product joins a portion of the sieve bend product for dewatering in the screenbowl centrifuge. “The screenbowl effluent, high frequency screen effluent and flotation effluent report to the thickener,” Pilcher said. “Thickener underflow is pumped about 12,500 ft with two stage slurry pumps. The discharge of the second pump is 220 psi. It takes a lot of horsepower to get the slurry to the pit.”
The reject belt containing the dewatered HMC and spiral refuse delivers its cargo to a refuse bin. From there, the coarse refuse is returned to the pits for final disposal. The ultrafine refuse in the thickener underflow also returns to the mine for disposal in abandoned pits. The product conveyor transports coal to a series of ground storage piles until it is needed for rail loading.
The clean coal handling consists of one bifurcated coal pile for selective loading according to customer specifications. Mass flow gates gravity feed a 60-inch reclaim conveyor at 3,300 tph, and a flood loading system fills the rail cars. Coal is shipped by rail to customers or to a dock on the Ohio River.
Some of the best practices Pilcher mentioned, included: centralized make-up manifolds and valves; retractable hose reels; the overhead crane; High Bay lighting, which provides very good light; and the control room, which sits outside the plant. “Some operators prefer to be in the plant so it helps to have cameras installed so they can see what’s happening,” Pilcher said. “One of the designs we have been trying to implement in all of our plants is an overhead bridge crane, which improves safety as well as maintenance.”
Normally make-up manifolds are placed above the sumps, Pilcher explained, which is the worst possible place to put them. “We moved them to another area on the second floor above the sumps,” Pilcher said. “Our chemical systems are also located outside the plant which makes them easier to maintain and inspect.”
Pilcher credits Hillsmeyer and his group for finding good used equipment and restoring it.
“Watching the steel go up and setting the equipment in place is a very rewarding experience,” Pilcher said. “It took eight months to build it. It maintains a raw feed capacity of 650 tph and the availability is extremely high. Part of that is good design and part of it is the skill of the people running the plant. The magnetite loss is less than 0.5 lb/ton of raw coal.” Under a collaborative effort between Peabody Energy and United Minerals, the Wild Boar prep plant was successfully designed, built and commissioned under budget and within the time constraints of a very aggressive schedule.
This article is based on presentation that Dan Pilcher, senior preparation manager for Peabody Energy’s Midwest Division, and Terry Hillsmeyer, manager-preparation, United Minerals, gave at Coal Prep 2012, which took place dring May in Lexington, Ky. For more information, go to: www.coalprepshow.com.
