Poor lignite fuel quality had plagued the Red Hills Power Plant since it began operation eight years ago. The solution: real-time measurement of coal properties that has allowed Red Hills Mine to carefully monitor fuel quality and adjust fuel collection processes to ensure that only high-quality fuel is delivered to the plant. Now all delivered fuel is consumed, and plant reliability is much improved. It’s a classic win-win project.
The 440-MW Red Hills Power Plant, located in northern Mississippi, burns lignite supplied by an adjacent open-pit mine and exports merchant power to the Tennessee Valley Authority. The Red Hills Mine is owned and operated by Mississippi Lignite Mining Co. (MLMC), a subsidiary of The North American Coal Corp. Red Hills Power is owned and operated by Choctaw Generation Limited Partnership (CGLP), a subsidiary of GDF Suez Energy NA. Construction of the mine and plant began in 1998, and commercial operation was achieved in 2002. MLMC has a 30-year fuel supply contract with CGLP (Figure 1).
1. Close relationship. The mine-mouth Red Hills Power Plant burns lignite supplied by Red Hills Mine. Both have been in operation since 2002. The mine has a 30-year fuel supply contract with the plant. Courtesy: SABIA
Wide Variation in Coal Properties
The Red Hills Mine, the first and only open-pit lignite mine in Mississippi, has a delivery capacity of 3.6 million tons per year and is located close to the power plant. The downside is that the delivered lignite has high moisture content (approximately 43%) and a low heating value (5,100 Btu/lb). The mine uses three overburden removal operations: truck-shovel removal, dozer push, and dragline. The complexity of the lignite coal formations makes for a unique challenge for mining operations. Adding to miners’ headaches is an average yearly rainfall of 52 inches.
The lignite mine has six distinct seams, each ranging from 2 to 5 feet thick. Each seam is separated by inner burdens ranging from 10 feet to 40 feet in thickness. Unfortunately, the coal quality can vary significantly between seams and within each individual seam. That wide variation in fuel quality has been very disruptive to reliable plant operation. One seam, for example, has a pocket of high-sulfur coal (H), while seams D and E are the best and most consistent seams at the mine (Figure 2). Seams G and F both have an inner seam parting that dramatically reduces overall coal quality, requiring the mine to separate these partings from the lignite to improve the delivered quality. The thickest seam mined is about 6 feet thick and the thinnest 6 inches, although the parting problem will never go away (Figure 3).
2. Layered excavation. Fuel is open-pit mined at the Red Hills Mine. When digging, the Easi-Miner can easily pass through multiple layers of different quality lignite. Source: SABIA
3. Parting problem. Each layer or seam of coal can contain wildly different fuel quality. The “parting seam” is coal that does not meet the plant fuel spec and must be removed to expose the next layer of acceptable coal. Courtesy: SABIA
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