Development of an Advanced Deshaling Technology to Improve the Energy Efficiency of Coal Handling, Processing, and Utilization Operations
The concept of using a dry, density-based separator to achieve efficient, near-face rock removal, commonly referred to as deshaling, was evaluated in several applications across the U.S.. Varying amounts of high-density rock exist in most run-of-mine feed. In the central Appalachian coalfields, a rock content exceeding 50% in the feed to a preparation plant is commonplace due to high amounts of out-of-seam dilution made necessary by extracting coal from thin seams. In the western U.S, an increase in out-of-seam dilution and environmental regulations associated with combustion emissions have resulted in a need to clean low rank coals and dry cleaning may be the only option. A 5 ton/hr mobile deshaling unit incorporating a density-based, air-table technology commercially known as the FGX Separator has been evaluated at mine sites located within the states of Utah, Wyoming, Texas, West Virginia, Virginia, Pennsylvania and Kentucky. The FGX technology utilizes table riffling principles with air as the medium. Air enters through the table and creates a fluidized bed of particles comprised of mostly fine, high density particles. The high density particle bed lifts the low-density coal particles to the top of the bed. The low-density coal moves toward the front of the table due to mass action and the downward slope of the table. The high-density particles settle through the fluidized particle bed and, upon making contact with the table, moves toward the back of the table with the assistance of table vibration. As a result, the low-density coal particles exit the front of the table closest to the feed whereas the high-density, high-ash content particles leave on the side and front of the table located at the farthest from the feed entry. At each test site, the run-of-mine feed was either directly fed to the FGX unit or pre-screened to remove the majority of the -6mm material. The surface moisture of the feed must be maintained below 9%. Pre-screening is required when the surface moisture of the feed coal exceeds the maximum limit. However, the content of -6mm in the feed to the FGX separator should be maintained between 10% and 20% to ensure an adequate fluidized bed. A parametric evaluation was conducted using a 3-level experimental design at each test site to identify the optimum separation performance and parameter values. The test data was used to develop empirical expressions that describe the response variables (i.e., mass yield and product ash content) as a function of the operating parameter values. From this process, it was established that table frequency and longitudinal slope are the most critical factors in controlling both mass yield and clean coal ash while the cross table slope was the least significant. Fan blower frequency is a critical parameter that controls mass yield. Although the splitter positions between product and middling streams and the middling and tailing streams were held constant during the tests, a separate evaluation indicated that performance is sensitive to splitter position within certain lengths of the table and insensitive in others. For a Utah bituminous coal, the FGX separator provided clean coal ash contents that ranged from a low of 8.57% to a high of 12.48% from a feed coal containing around 17% ash. From the 29 tests involved in the statistically designed test program, the average clean coal ash content was 10.76% while the tailings ash content averaged around 72%. One of the best separation performances achieved an ash reduction from 17.36% to 10.67% while recovering 85.9% of the total feed mass, which equated to an ash rejection value of around 47%. The total sulfur content was typically decreased from 1.61% to 1.49%. These performances were quantified by blending the middlings stream with the clean coal product. At a second Utah site, coal sources from three different bituminous coal seams were treated by the FGX deshaling unit. Three parameter values were varied based on the results obtained from Site No. 1 to obtain the optimum results shown in Table E-1. Approximately 9 tests were performed on each coal source. The average ash content reductions were: Glenwal (= 25.6% to 8.6%), Pinnacle (=17.3% to 9.0%) and Westridge (=20.6% to 7.5%). Under optimum conditions, nearly 70% of the high-density rock was rejected while recovering approximately 100% of the 1.60 float material. In the Powder River Basin, a small portion of the extracted coal is mistakenly diluted with out-of-seam rock. Since coal cleaning is not currently practiced, the diluted coal containing 20%-30% ash is left in the pit as fill material, thereby representing a lost resource. A FGX test program conducted on the high ash sub-bituminous coal revealed the ability to produce clean coal containing 7%-8% ash on a dry basis (5%-6% on an as-received basis) with 62% recovery. The product grade meets typical end user contract specifications for PRB coal.
- Research Organization:
- Univ. of Kentucky, Lexington, KY (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-05NT42501
- OSTI ID:
- 971249
- Country of Publication:
- United States
- Language:
- English
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