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FLSmidth USA,Inc. <br /> 7158 S FLSmidth Drive • Midvale • UT 84047-5559 • USA LIS M ' D T H <br /> comparison of floc structure and O/F clarity. Settling rates measured through designated <br /> elevation intervals generate settling rate curves for quantitative comparison. <br /> To determine the optimum slurry solids concentration for flocculation, settling flux tests <br /> were conducted. The optimum condition is determined by measuring the initial settling <br /> velocity at various slurry solids concentrations. <br /> A series of slurry solids concentrations were prepared in 250-mL cylinders. A nominal <br /> flocculent dosage was added based upon flocculent screening results. The initial bulk <br /> settling rate was measured and converted into the solids initial settling flux, tpd/mz. The <br /> solids concentration giving the highest initial settling flux was chosen as the criteria for <br /> further testing. <br /> 3.3 2-Liter Thickener Static Simulation Tests <br /> Static 2-L cylinder batch tests verify the initial settling velocity noted in flux testing, as well <br /> as other thickening sizing criteria. A 2-L cylinder diminishes sidewall effects. <br /> To conduct the 2-L static test, the desired flocculent dose is added to the slurry using a <br /> mixing plunger. The mixing plunger adds flocculent to the slurry during mixing in the <br /> cylinder. This methodology simulates the mixing intensity and residence time typical in <br /> FLSmidth E-DUC° feed well systems. Mixing stops after flocculent addition and <br /> measurements of interface height over time are noted. The test runs through the initial <br /> settling time until the drop in interface height ceases. <br /> The Interpretation of the settling data was performed using the FLSmidth sizing program, <br /> which is based on the Wilhelm-Naide flux thickening method. This method sizes the <br /> thickener based on the time it takes for the thickener to reach a mud bed height <br /> corresponding to the underflow concentration required. The unit areas were corrected for <br /> the compression effects of pulp bed on the underflow density. The results obtained are then <br /> used to determine the unit area required for a High Rate thickener, for liquor release and <br /> separation from settling solids in mz/tpd. <br /> 3.4 Continuous Fill Deep Tube Thickener Tests <br /> Several High Rate thickener simulations were performed at preferred conditions. Where <br /> dilute feed streams are tested it is important to carry out settling tests in sufficient volumes <br /> to ensure that a reasonable bed depth is present in the bottom of the cylinder so that the <br /> effect of mud compression can be modeled. <br /> The settling curve generated from these tests over a period of time gives the following <br /> information: <br /> ■ Free settling rates, and <br /> ■ Time taken (residence time) and bed depth needed to reach desired underflow <br /> concentration. <br /> The continuous fill deep tube test serves two purposes: 1) flocculent dose optimization and <br /> confirmation of solids settling flux (unit area selection); and 2) accumulation of a solids bed <br /> as prescribed by the procedure to give a better prediction of the compaction rate and <br /> required bed residence time in a full-scale thickener. <br /> The continuous fill tests are conducted by preparing a batch of feed slurry at the solids <br /> concentration determined from the flux tests. A metering pump supplies the chosen <br /> Page 1 5 <br />