OCR Text |
Show RESULTS AND DISCUSSION Coal The coal used by B&W for testing in this project was Pittsburgh #8 coal from Belmont County, Ohio. The analyses of the raw coal, precleaned feed for the microgrinding and advanced flotation evaluation, and the fmal clean coal product from the 12-inch diameter column cell are shown in Table 4. The advanced flotation column perfonnance was detennined using the precleaned feed as the basis of comparison. Table 4 COAL OUALfTY Analyses (Dry) Raw Precleaned FInal Ash 25.1 8.14 5.27 Total S 4.64 3.75 3.32 Pyritic S 2.75 1.41 0.88 Btullb 10,582 13,323 13,622 Bencb-Scale Microgrinding and Advanced Flotation The cumulative particle size distributions of the 200M , x 0 and 325M x 0 slurries used for the bench-scale advanced flotation tests are shown in Table 5. The ash, total sulfur, pyritic sulfur, and Btu results for the 2-inch benchscale flotation tests are shown in Table 6. Table 5 BENCH-SCALE MICROGRINDING PARTICLE SIZE DISTRIBUTIONS 2OO .... h 325 .... h McrOM %lHa Difference Mcrona %lHa Difference 3X>.00 3X>.00 212.13 212.13 150.00 150.00 106.07 106.07 75.00 100.00 4." 75.00 53.03 95.58 9.26 53.03 37.50 86.30 13.13 37.50 100.00 2.04 26.52 73.17 18.70 26.52 97.96 11.02 18.75 54.47 12.75 18.75 86.95 13.24 13.26 41 .72 10.96 13.26 73.71 18.42 9.38 30.76 10.96 9.38 55.29 19.35 6.63 HUO 8.96 6.63 35.94 13.47 4.69 12.84 4.75 4.69 22.47 8.34 3.31 8.09 2.87 3.31 14.13 5.37 2.34 5.22 1.82 2.34 8.78 3.23 1.55 3.41 1.11 1.55 5.54 1.73 1.17 2.29 0.90 1.17 3.81 1." 0.83 1.39 0.57 0.83 2.37 1.14 0.59 0.72 0.52 0.59 123 0.94 0.41 0.20 0.20 0.41 0.29 029 0.29 0.00 0.00 0.29 0.00 0.00 0.21 0.21 0.15 0.15 CS (Cal Surf Area) .0.79 m21cm3 CS (Cal Surf Area) • 1.22 m21cm3 MMO (043) • 20.36 microns MUD (043). 10.26 microns SUD (032) • 7.56 rricrons SUD (032) • 4.91 rncrons 7 Table 6 2-1NCH BENCH-SCALE FLOTA TION RESUL TS 200M Top Size 325M Top Size Yield (wt. %) 91 .4 89.01 Ash 5.06 3.94 Pyritic Sulfur 0.91 0.73 Total Sulfur 3.33 3.19 Btullb 13,664 13,681 Btu Recovery 95.87 94.04 Ash Rejection 48.50 59.30 Pyritic Sulfur Rejection 25.70 39.60 Efficiency 21 .60 33.60 For the slurry with 325M top size, the pyritic sulfur rejection, the ash rejection, and the separation efficiency were 39.6%, 59.3%, and 33.6%, respectively (separation efficiency = Btu recovery - [100 - pyritic sulfur rejection]). For the slurry with 200M top size, the pyritic sulfur rejection, the ash rejection, and the flotation efficiency were 25.7%, 48.5%, and 21.6%, respectively. Although the tests were not optimized, the data clearly shows that grinding to 325M top size resulted in improved flotation perfonnance. Therefore, the Pittsburgh #8 coal was ground to a "target" 325M top size in the subsequent pilotscale microgrinding tests. The mass mean diameter of this PSD was 11 - 12 microns. Continuous Pilot-Scale Microgrinding Tests The effects of feed rate, mill rpm, feed solids, and mill charge on product particle size and specific energy are shown in Figures 5 through 7. Within the range of the tests, the data show the following relationships: • Errect of RPM - Increasing rpm at constant feed rate results in fmer average particle size and a reduction in specific grinding energy. For grinding slurry to an average mass mean diameter of 11 - 12 microns, an increase in mill speed from 800 to 1000 rpm reduced the energy consumption about 25%. • Errect of Solids - Increased solids at a constant feed rate resulted in a slightly coarser average particle size and higher specific energies. At the same product mass mean diameter, increasing slurry solids from 42% to 45% resulted in an approximate 50% increase in grinding energy. • Errect of Mill Charge - Increasing mill charge volume at a constant feed rate results in a fmer average particle size and lower specifIC grinding energies. However, it should be noted that continued increase in the volume of the media used for grinding in the mill will inhibit throughput and eventually cause an increase in energy consumption. |