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Show Scale-Up Neither of the processes of microgrinding or advanced froth flotation has been commercialized in the coal industry. Therefore, in addition to generating infonnation for scale-up of the microgrinding equipment, experimental data necessary for scale-up of the advanced flotation cell was required. The microgrinding and advanced froth flotation testing at the 100 - 200 lb/hour scale was used to provide the necessary infonnation link between the laboratory testing and the POC operation. During the advanced flotation testing, the effects of coal feed rate, aeration rate, air pressure, and wash water addition rate on the performance of both the 2-inch and 12-inch diameter flotation columns were evaluated in order to verify scale-up. OBJECTIVE The overall goal of the microgrinding and advanced flotation testing was to develop design and perfonnance data at the bench- and pilot-scale to: (1) reduce or eliminate the technical and engineering uncertainties in the design of a 20-tph semi-works advanced flotation plant, and (2) aid in the design, fabrication, and operation of a 2 - 3 tph advanced flotation module. The bench-scale and semi-continuous pilot-scale (100 - 200 lb/hr) testing was perfonned using the pilot coal preparation facility at B&W's Alliance Research Center. Precleaned Pittsburgh #8 coal was used as the feed for these tests. The specific objectives of this evaluation were: Microgrinding • Detennine the appropriate coal particle size distribution (PSD) for effective pyrite removal in the advanced flotation process. • Optimize the grinding conditions (feed solids loading, residence time, grinding media size and volume, etc.) to produce the required PSD. • Develop pilot-scale grinding mill perfonnance data and specific energies. Advanced Flotation • Demonstrate scale-up of bench-scale advanced flotation column performance to pilot-scale. • Develop initial pilot perfonnance data for continuous operation of a 12-inch diameter advanced flotation column. EXPER~ENTALAPPROACH Bench-Scale Microgrinding and Flotation Tests Coal slurry samples with two top sizes, 200 mesh (200M) (74 microns) and 325M (44 microns), were prepared and used for bench-scale advanced flotation testing. 5 U1trafine coal with a top size of 325M was selected for the advanced coal flotation testing because it is a benchmark size of ultrafine coal that has been used previously in other advanced physical fine coal studies. The flotation performance of the ultrafme coal was compared to 200M coal, which is a size frequently used in pulverized coal applications. The two coal slurries of Pittsburgh #8 coal were prepared using laboratory batch mills. Precleaned 48M x 0 conventional flotation product was used as the feed for grinding. No dispersant or other chemicals were used to modify the coal surface during microgrinding. The 325M top size slurry (36.5% solids) was prepared in a laboratory batch stirred ball mill. Small samples of product slurry were tested for particle size distribution using Leeds and Northrup (L&N) Microtrac~ analyzers. The 200M slurry (40% solids) was prepared in a 2-1n. gallon rod mill. Steel rods of three different diameters were used - In. inch, 5/8 inch, and 3/4 inch. A 2-inch diameter x 8-foot high microbubble flotation column purchased from VPI was used for bench-scale advanced flotation testing. Flotation tests were run at approximately 4 minutes retention time. Conditions were varied during the flotation tests to improve the column perfonnance. The changes of frother dosage, wash water rate, aeration rate, and slurry feed rate were based on consultation with VPI. No attempt was made to fully optimize the column perfonnance for each slurry prior to collecting samples. The test conditions for each flotation test are shown in Table I. The column was operated on coal slurry for 20 minutes to establish steady state. The feed, clean coal froth product, and tailings samples were collected after reaching steady state and analyzed for ash, sulfur, and Btu content. Table 1 BENCH-SCALE ADVANCED FLOTA nON TEST CONDmONS Test Number Coal Operating Conditions: Wash Water Flow Rate. gpm Air Flow Rate (20 pslg). c1m Feed Slurry Rate. gpm Feed Slurry Percent Solids Feed Slurry pH (natural) Feed Slurry Particle SIze (top size) Mean Retention TIme (apparent). minutes Reagents Kerosene Kerosene Addition. Ib I ton of Dry Coal Batz M150' Batz Addition. Ib I ton of Dry Coal • Same as Dow Froth M·1 50 PItt . • 8 0.225 0.0616 0.0238 8.6 7.75 200M 3.7 2.78 2 3 4 PItt . • 8 pm .• 8 Pitt. '8 0.211 0.185 0.185 0.0616 0.06 16 0.06 16 0.0238 0.0238 0.0238 8.6 8.9 8.9 7.75 7.63 7.63 200M 325M 325M 3.9 ~ . 4 4.4 2.78 3.05 4.04 |