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Show Continuous Pilot-Scale Microgrinding The feed for the pilot-scale microgrinding tests was prepared by precleaning Pittsburgh #8 coal using hydrocyclones and conventional flotation. The product was deaerated and classified at 325M in a 6-inch diameter cyclone. The coarse product (48M x 325M) from the cyclone was dewatered to 40 - 50% solids concentration during the classification and used as feed to the pilot stirred ball mill in which the coal was ground to 325M x O. The fine 325M x 0 cyclone overflow from the classification step was stored in drums. It later was recombined with the 325M x 0 stirred ball mill product and used for the feed material in the advanced flotation cell testing. The pilot microgrinding tests were conducted with an 8-liter Netzsch stirred ball mill. The mill (Figure 4) is horizontal with an agitator shaft with a speed range of 700 to 1600 rpm. Figure 4. Nstzsch Pllot·Sca/. Stirred Ball Mill The "target" PSD for the continuous microgrinding tests was detennined from the bench-scale grinding tests previously described. During the testing, the following conditions were varied: feed rate, feed solids, mill rpm, and mill charge. The test conditions for the continuous microgrinding tests are shown in Table 2. Samples of the ground product were taken at each condition and their PSDs were measured with L&N Microtrac~ analyzers. During all tests, power consumption, slurry temperature and pressure, and cooling water temperature and pressure were monitored. Continuous Advanced Froth Flotation Based on a round-robin evaluation conducted by Kaiser Engineering, advanced flotation columns from three de- 6 velopers were recommended for pilot testing. These included the Center for Applied Energy Research (CAER), Virginia Polytechnic Institute and State University (VPI), and Michigan Technological University (MTU)(9). The CAER column flotation cell was selected for the pilot testing at B&W. A 12-inch diameter x 24-foot high CAER column flotation cell rated at 100 - 200 pounds of coal per hour was used for the pilot advanced flotation testing. The test coal was precleaned Pittsburgh #8 coal prepared during the pilot microgrinding tests. Three series of shakedown tests were run on the 12-inch diameter cell with the assistance of CAER representatives. During the shakedown tests, the coal feed rate, collector dosage, and frother dosage were detennined. The collector and Crother were added as one emulsion to the column feed . The feed slurry was not conditioned prior to feeding the column. Based on the results of the shakedown tests, the final conditions for the pilot advanced flotation testing were detennined and are summarized in Table 3. Table 2 CON77NUOUS Af/CROGRINDING TEST Parameter Mill Charge, % Feed Solids, % Mill Speed, rpm Feed Rate , gpm Feed Rate, Ib of coal / hr Condition. 60, 70 42, 43.5, 45 800,1000,1200 0.39, 0.49, 0.61 , 0.95 95, 99, 103, 125, 130, 149, 155, 162 232 Table 3 12·INCH DIAMETER ADVANCED FLOTA TION TEST CONDITIONS Feed Rate - 180 Ib of coal per hr Collector - 2 Ib of kerosene / ton of coal Frother - 1 Ib of MiSe / ton of coal pH-7.7 Parameter Wash Water, gpm Air Rate, cfm Air Pressure, psi Conditions 1, 1.8,2, 3 2,3, 4, 5 30, 45,60 The effects of air flow, air pressure, and wash water rate on column perfonnancc (pyrite rejection and Btu re covery ) for a 1 O~ by weight feed slurry were evaluated. Approximately 750 gallons of slurry were used for the testing. Clean coal froth and tailings samples were taken every 20 minutes. Flows were also measured and used to calculate the flotation column mass balance. |