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Show mechanical dewatering at the COTF for the diesel process and thermal drying at dryer vendor facilities for the heptane process. COTF, bench-scale, and vendor data will be used to modify conceptual commercial (200-tjh) plant designs for the diesel and heptane process options, which will then be scaled down to generate design information for the 3-t/h POC module. The design of the 3-tjh COTF incorporated maximum flexibility for possible future modifications. Equipment is generic and based on proven technologies so that specifiC pieces of equipment can be used interchangeably regardless of the design of the agglomeration circuit. Most of the equipment can and will be used in the POC module. The coal crushing and grinding system consists of a hammermill coal crusher, weigh belt feeder, primary and secondary ball mills, and the necessary hoppers and conveyors. The mills are capable of providing feed coal to the process over a range of grinds from a dso of 125 to 25 microns at rates of up to 3 t/ h. Agglomeration circuit startup and commissioning is complete, and a number of test runs have been conducted using Upper Freeport coal. Diesel at dosages of 1-2 wt% on a dry coal feed basis is added to the high-shear mixer to form microagglomerates. Conventional flotation cells are used to separate microagglomerates from the mineral matter. The flotation cell product is pumped to low-shear mixers, where binder is added for agglomerate growth. The binder consists of various concentrations and compositions of asphalt and diesel, depending on the coal grind and target product size, and is introduced to the flotation product by a colloid mill either feeding directly into the low-shear mixers or via a binder contact vessel. The low-shear product is then sent to the dewatering equipment. A series of batch low-shear agglomeration tests using Upper Freeport coal was conducted at the Wilsonville laboratory as a preliminary screening of binder types and to establish an approximate range of binder concentrations for pilot tests. CommerCially prepared asphalt emulsions (cationically stabilized) and asphaltdiesel blends were found to be effective binding agents. Product samples are being tested for material handling properties, such as bin flow characteristics, angle of repose, drop and tumble strength tests, and size consist, as appropriate to each agglomerate type. Preliminary bench-scale tests of several promising dryers, using "green" heptane agglomerates with low binder content (2% AC-5 asphalt) produced at the Wilsonville laboratory, have been conducted at dryer vendor facilities. The dried product agglomerate volatiles ranged from 0.2 to 0.6%, with solids recoveries at 90-95%. An additional set of tests using agglomerates with 3% binder has been scheduled in an effort to reduce agglomerate degradation in the dryer. Operations The COTF test runs that have been conducted thus far have involved 28- and 100-mesh coal slurries at various binder concentrations and compositions in order to produce a range of products for characterization and dewatering tests. For the formation of large agglomerates, binder addition of about 9 wt% to the lowshear mixers is required with 28-mesh grind slurries. For 1 DO-mesh coal slurries, about 12 wt% binder is required to produce large agglomerates. In this context, large agglomerates are defined as those which can be recovered from the low-shear product by continuous screen operations, while small agglomerates must be handled by mechanical dewatering equipment for adequate moisture removal. Tests on 28-mesh grind coal slurry were run using 1% diesel in high shear and asphalt-diesel blends in lowshear. A colloid mill was used to produce the emulsion of asphalt and diesel added to low shear, and binder concentrations in the 8-12 wt% range were tested. The low-shear mixers were operated both in series and individually in order to cover a range of low-shear residence times between 25 and 40 minutes. The products were dewatered via a static sieve bend and vibrating screen. Based on these tests, it was determined that varying the binder composition In this range does not significantly change the product size or strength. Subsequent unit operations tests will focus on the generation of large and small agglomerates to enable the testing of various dewatering equipment. In addition to the static sieve bend and vibrating screen, a screen 7 |
