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Show bowl centrifuge, horizontal belt vacuum filter, and plate and frame filter press will be used for product dewatering. The plate and frame filter press and a pressure belt filter will also be tested for refuse dewatering. These dewatering tests will use low binder concentrations in low shear (3 and 6 wt%) to produce the small agglomerates. The tests will also determine the level of asphalt~iesel addition to the lowshear mixers at which distinct, well-formed agglomerates cease to be formed. The static sieve bend and vibrating screen have performed to expectations when dewatering product agglomerates larger than 1 /2 mm in size. The screen product moisture Is essentially a function of agglomerate size rather than of the initial coal grind. The moisture measurements taken to date have been in the range of 20-30%. Some additional drainage of moisture would be expected during storage of the larger agglomerates. This drainage has been observed, and tests are underway to quantify Its effects. 8.0 TASK 7: EVALUATION OF BENCH-SCALE AND UNIT OPERATIONS TEST RESULTS The objective of Task 7 is to examine the results of the bench-scale testing at ARC and the component testing at Wilsonville to determine whether the areas of uncertainty identified in Task 3 have been satisfactorily resolved. Task 7 is being carried out interactively with Tasks 5 and 6 in order that minor changes may be made in the test work at ARC and Wilsonville, where necessary, to ensure that the test and project goals are achieved. Process Comparison The major feature differentiating the light and heavy agglomerant processes is that the light oil process recovers and recycles the agglomerating liquid whereas the heavy oil process retains the agglomerant as part of the final product. Heptane was selected as the light agglomerant because it provided a good compromise between energy requirements for evaporative removal and condensation recovery, relatively low toxicity, good selectivity for coal matter, and wide availability. Diesel was selected as the heavy agglomerant based on good pyritic sulfur rejection results. Other contrasts between the two processes include: o Pyritic sulfur rejection in high-shear agglomeration. Sulfur rejection using diesel requires a low concentration whereas the heptane process shows lower sensitivity to oil concentration. o Agglomerate recovery from high shear. Heptane agglomerates are of sufficient size to be recovered from the process slurry by screening whereas diesel microagglomerates are best recovered by flotation. o Application of binder in low shear. Asphaltic binder used in the heptane process is dissolved in heptane and applied as a low-viscosity solution. In the diesel case, binder is applied as a high-viscosity blend. o Low-shear binder concentration. In the diesel process the size of the product agglomerate is a function of the binder concentration applied in low-shear mixing. The heptane process agglomerate size Is essentially independent of the binder concentration: the heptane concentration and mixing conditions are used to control product agglomerate size and the binder concentration Is used to control agglomerate strength. 8 |