Briquette separation

Figure 297. Schematic representation of five different briquette separator designs...

In those cases where it is sufficient to randomly separate briquettes connected by thin and brittle land areas, briquette separators without moving parts can be applied. The static separator depicted in Figure 297(d) works best with D-shaped briquettes from alternate circumferential rows of pockets. The briquettes are diverted alternately in one or the other direction and bent with their flat sides down. The alternate diversion tears the rows of briquettes apart and it is hoped that the bending will cause individual briquettes to break at the land area. 

The hot reduced fines are pneumatically transported to an atmospheric pressure hoi ding dmm from which they are fed to the briquetting machines. The hot briquettes are separated, cooled on a circular grate, and deUvered to an outdoor storage pile. 

An improved approach from the point of view of thermal efficiency is the electrothermal process in which the mixture of zinc oxide and carbon, in the form of briquettes, are heated in a vertical shaft furnace using the electrical resistance of the briquettes to allow for internal electrical heating. The zinc vapour and CO(g) which are evolved are passed tluough a separate condenser, the carbon monoxide being subsequently oxidized in air. 

Solvent-Refined Coal Process. In the 1920s the anthracene oil fraction recovered from pyrolysis, or coking, of coal was utilized to extract 35—40% of bituminous coals at low pressures for the purpose of manufacturing low cost newspaper inks (113). Tetralin was found to have higher solvent power for coals, and the I. G. Farben Pott-Broche process (114) was developed, wherein a mixture of cresol and tetralin was used to dissolve ca 75% of brown coals at 13.8 MPa (2000 psi) and 427°C. The extract was filtered, and the filtrate vacuum distilled. The overhead was distilled a second time at atmospheric pressure to separate solvent, which was recycled to extraction, and a heavier liquid, which was sent to hydrogenation. The bottoms product from vacuum distillation, or solvent-extracted coal, was carbonized to produce electrode carbon. Filter cake from the filters was coked in rotary kilns for tar and oil recovery. A variety of liquid products were obtained from the solvent extraction-hydrogenation system (113). A similar process was employed in Japan during Wodd War II to produce electrode coke, asphalt (qv), and carbonized fuel briquettes (115). 

The most common form of dry granulation is roller compaction. A roller compaction system consists of a feed system which conveys powder between two counterrotating rolls. The powder is drawn between the rolls where a specified force is applied causing the powder to compact into a briquette or a continuous ribbon. The compacted material can then be milled in-fine or collected and milled off-line in a separate processing step (i.e., screening mill). 

The content of the reduction autoclaves is dischaiged into cone-bottomed flash tanks where separation of the powder from the spent liquor takes place. The nickel metal in slurry form is washed, dried, and packaged as powder or pressed into briquettes, sintered, and packaged ready for shipment. The spent liquor containing about 1 gm/liter Co and 1 gm/liter Ni is precipitated with HjS, filtered, and sent to the mixed sulfides stage for cobalt recovery. 

Reduction in physical size is often required before biomass is used as a fuel or feedstock. Size-reduction techniques are employed to prepare biomass for direct fuel use, fabrication into fuel pellets, cubes, and briquettes, or conversion. Smaller particles and pieces of biomass reduce its storage volume, facilitate handling of the material in the solid state and transport of the material as a slurry or pneumatically, and sometimes permit ready separation of components such as bark and whitewood. The size of the pieces or particles can be critical when drying is used because the exposed surface area, which is a function of physical size, can determine drying time and the methods and conditions needed to remove moisture. There are a few exceptions where size reduction is not needed, such as in whole-tree burning. 

Many different methods of separation are feasible. The simplest employ tumble drums or shaking contraptions. In those cases where a continuous string of briquettes is produced, breakers, e.g. such as shown in Figure 297, can be installed. 

Figure 297(a) depicts the production of a checkerboard sheet. D-shaped briquette pockets are positioned alternately in a checkerboard fashion. The resulting sheet is passed between a smooth pair of rollers, the gap of which is set to a width corresponding to pocket depth plus gap width. While the sheet is squeezed, the shear forces created in the land areas will separate the briquettes from one another. 

Methods (a), (b), and (c) only work if the briquette strip does not break in between and if the two pieces of equipment (roller press and separator) operate fairly synchronously. Nevertheless, the briquetted product from, for example, method (c) does not only contain well-formed single briquettes. In addition to doubles and triples, briquettes may not break directly at the land area, which is understandable since this part of the strip is the highest densified and strongest portion of the briquetted material. 

Figure 297(e) shows application of only the bending action. If the briquettes do not separate, the string will be guided against one of the rollers where briquettes will finally break off. However, it should be realized that horizontal rows from multirow rollers do not easily break and separation by contacting a roller considerably increases wear. 

In general, it is easier to separate briquettes made from brittle materials, such as minerals, particularly if strong briquettes are immediately produced. It is most difficult to separate briquettes made from soft, elastic, or malleable materials and those that gain final strength only after curing. 

Good briquettes discharging from the presses are surrounded by a flash which is produced on the land areas between the pockets on the rollers (see Section 4.2.2.4.7). These flashes break off during handling and are separated on the screens (17 and 20) producing so-called chips—relatively hard, compacted particles that require crushing prior to feeding back into the system. 

Emphasis in the field tests of stone briquettes is on the long-term damage suffered by exposed marble and limestone. Because the pH variations for the existing test sites are principally variations between one rain and the next rather than from site to site, the separation of the pH effect cannot presently be achieved (except possibly in runoff chemistry on individual rains). The annual... 

Production of ZrCl4. Zirconium oxide from the hafnium-separation step was mixed with carbon black, dextrin, and water in proportions 142 Zr02, 142 C, 8 dextrin, and 8 water. The mixture was pressed into small briquettes (3.8 X 2.5 X 1.9 cm) and dried at 120°C in a tray drier. The oxide briquettes were charged to the reaction zone of a vertical-shaft chlorinator lined with silica brick. The charge was first heated by carbon resistance strips until it became conductive. During production, the bed temperature was maintained at 600 to 800 C by an electric current passed directly through the bed. After steady conditions were reached, a reactor 66 cm in diameter produced about 25 kg ZrCLt/h. The ZrCU was condensed from the reaction products in two cyclone-shaped aftercondensers in series, and the chlorine off-gas was removed in a water scrubbing tower. 

---