Cleaning coal density separation

Dense-media separation coal-cleaning method based on density separation, using a heavy-media suspension of fine particles of magnetite, sand, or clay. Dense medium dense slurry formed by the suspension of heavy particles in... 

Physical cleaning of various coals by oil agglomeration reduced levels of As, Cr, Pb, Mn, Mo, Ni, and V by 50-80%, while levels of some other trace elements were reduced by lesser amounts (20). Oil agglomeration appeared to be more effective at removing trace elements than the wet concentrating table or float/sink density separations. This may be related to an increase in the liberation of mineral matter associated with grinding to produce the relatively fine particle sizes required in the oil agglomeration technique. 

The vast majority of the coal cleaned commercially is separated by processes that rely on the density differential of the various components. Technologies that make separations on this basis are particularly effective for treating the coarse to intermediate sizes of coal (i.e., particle sizes ranging from greater... 

Consider, for example, the incombustibles in coal. These can contribute significantly to the particulate content of the flue gases produced on combustion, as well as to the bottom ash volume. Incombustibles are now routinely removed before burning for more than half of the coal produced in North America. This is accomplished by using one or more of the following. The coal is first finely ground. It may then be washed with water on riffle boards, from which the less dense coal particles are carried by the water stream while the more dense rock particles tend to sink and are captured in the cavities of the riffles. In air jigs the powdered mixture is suspended on a bed of air in a fluidized form. The heavier rock particles tend to sink and may be drawn off the bottom, and the cleaned coal is drawn off the top. Or liquid or fluidized dense solid may be used to obtain a more direct sink-float or froth flotation separation of the coal, of density about 1.5 g/cm, from the much denser rock particles and other impurities. 

Curve A is the primary washability curve. Curve B is the clean-coal curve and shows the theoretical percent ash of the clean-coal product at any given yield. Curve C (the cumulative sink ash) shows the theoretical ash content of the refuse at any yield. Curve D, plotted directly fi om the cumulative percent yield of floats versus density, gives the yield of floats at any separation density. Curve E, the curve of near-density material, gives the amount of ma-... 

The yield and quality of the clean-coal product from an industrial coal preparation plant and the theoretical yield and quality determined fi om washability curves are known to be different. In the ideal cleaning process, all coal particles lower in density than the density of separation would be recovered in the clean product, while all material of greater density would be rejected as refuse. Under these conditions the product yield and quality from the actual concentration process and the yield and quality expected from the washability curves would be identical. 

The performance of separators is, however, never ideal. As a result, some coal particles of lower than the separation density report to rejects, and some high-ash particles of higher than the separation density report to clean coal. These are referred to as misplaced material... 

Coal particles of density well below the density of separation and mineral particles of density well above the density of separation report to their proper products clean coal and refuse. But as the density of separation is approached, the proportion of the misplaced material reporting to an improper product increases rapidly. 

Current commercial coal cleaning methods are invariably based on physical separation chemical and biological methods tend to be too expensive. Typically, density separation is used to clean coarse coal while surface property-based methods are preferred for fine coal cleaning. In the density-based processes, coal particles are added to a liquid medium and then subjected to gravity or centrifugal forces to separate the organic-rich (float) phase from the mineral-rich (sink) phase. 

Current commercial coal cleaning methods are invariably based on physical separation chemical and biological methods tend to be too expensive. Typically, density separation is used to clean... 

Generally, precombustion coal cleaning is achieved by the use of physical techniques, some of which have been used for more than a century. Physical cleaning methods typically separate undesirable matter from coal by relying on differences in densities or variations in surface properties. 

Dense-Medium Washing. Dense-medium separations include processes that dean raw coal by immersing it in a fluid medium with a density intermediate between the density of clean coal and that of reject. Most dense-medium washers use a suspension of fine magnetite in water to achieve the desired density. The process is very effective in providing a sharp separation and is relatively low in capital and operating costs. 

Thus, the above results for the Upper Freeport coal indicate that density-based processes (e.g., float-sink separation) should be able to remove significant amounts of mineral matter, while surface-based processes (e.g., froth flotation) will likely be unable to reduce the mineral content significantly. Results of cleaning tests reported elsewhere [5] have generally verified these predictions. 

Use As solvent for oil and grease in metal cleaning. Also used for separation of coal from impurities by density difference. 

The condensate is fed to a central downpipe and evenly distributed by appropriate internals over a hood-type baffle. The tar runs down over this baffle to be collected in the bottom of the vessel. The dust-laden tar is then withdrawn by the central bottom nozzle, while the lighter clean tar rises to the surface and flows off through the clean tar nozzle. The oil, having a lower specific density than water, forms the supernatant phase and is collected in the upper hood. Like the clean tar, it rises to the surface and is withdrawn through the oil outlet.The water leaves the tar separator about half way up between the oil outlet and clean tar outlet. The dust-laden tar settling at the bottom may be recycled to the coal gasification section. 

PVC has a special position in the recycling of plastics [1]. As a result of the relatively weak bonding of chlorine to the polymer chain, the chlorine atom is split off at low temperatures of about 150 °C and hence complicates the material recycling of plastics wastes containing PVC. Corrosion, which could be initiated by the released chlorine or hydrochloric acid produced from it is less of a problem than the coal like polymer residue, which remains suspended in the machine or is distributed in the melt and further in the product. Many times it produces breakdown of the equipment and necessitates cleaning of the screw, barrel and dies. Therefore as a rule, PVC must be carefully removed from mixed plastic waste before most types of recycling - material or chemical. Because the significant difference between the density of PVC and that of other thermoplastics separation with one of the well known methods is possible. It is, however relatively expensive. 

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