Solid/liquid separations, coal

Solid/liquid separation is important at all stages and depends on the extent of coal cleaning during pretreatment, depolymerization of coal macromolecules at the dissolution stage, and catalyst durability through the catalytic process. 

Solid/liquid separation is usually required at the interface of the primary and secondary stages to allow optional upgrading of the crude coal liquids of the primary liquefaction stage, by removing mineral matter, unreacted coal, heavy products, and catalysts (111, 112). Distillation, anti-solvent extraction, and centrifugation have been conventionally employed in liquefaction processes (113, 114). 

Homo- and copolymers of DADMAC are widely used for solid/liquid separations (dewatering) of different slurries in the mining industry. Specific examples of the minerals treated with these polymers include coal, taconite, trona, sand,... 

Coal cleaning, which involves the separation of some of the ash from the coal prior to liquefaction, can yield several benefits. Primarily, it reduces the load on the solid-liquid separator, thereby reducing the amount of organic material rejected with the ash. Other benefits include the reduction of wear on plant components and better utilization of reactor volume. However, removal of mineral matter prior to reaction may eliminate beneficial catalytic effects that coal minerals, particularly iron pyrite, provide. 

Tiller, F.M. Leu, W. Solid-Liquid Separation for Liquefied Coal Industries, Final Report for Project 1411-1, July, 1984. 

In ROM coal, a large portion of both coal and shale is already liberated sufficiently to permit immediate concentration. Because dewatering of coarse coal is much more efficient and cheaper than that of fines, and because many users prefer larger size fractions for their particular processes, the preparation of feed before cleaning has traditionally consisted of as little crushing as possible. Therefore, coal preparation consists mostly of gravity concentration and to some extent flotation, complemented by screening and solid/liquid separation auxiliary processes. 

Moody, G.M. et al. (1997) Novel dewatering system for aiding the solid liquid separation of coal slurries and tailings. XIIICPC Proceedings, Vol. II, pp. 579-588. 

A direct liquefaction technique, the SRC process involves mixing dried and finely pulverized coal with a hydrogen donor solvent, such as tetralin, to form a coal-solvent slurry. The slurry is pumped together with hydrogen into a pressurized, vertical flow reactor. The reactor temperature is about 825°F (440°C) and pressures range from 1,450 to 2,000 psi. A residence time in the reactor of about 30 minutes is required for the carbonaceous material to dissolve into solution. From the reactor, the product passes through a vapor/liquid separation system. The slurry solids remaining in the reactor are then removed and filtered. Various filtration techniques have been developed to remove solids from recoverable oil. 

To separate solids from a liquid, filtering through paper filters (smooth or fluted) is employed. Cotton wool, asbestos fibres, glass wool, crushed coal, porous glass, and a number of other materials can also be used as filters. The liquid separated in filtration is called the filtrate. 

Coal Liquefaction, Steam is used to produce hydrogen for the liquefaction of coal. In the liquefaction process, coal is crushed, dried, pulverized, and then added to a solvent to produce a slurry. The slurry is heated, usually in the presence of hydrogen to dissolve the coal. The extract is cooled to remove hydrogen, hydrocarbon gases, and hydrogen sulfide. The liquid is then flashed at low pressure to separate condensable vapors from the extract. Mineral matter and organic solids are separated and used to produce hydrogen for the process. The extract may be desulfurized. The solvent is separated from the products. There are at least six different liquefaction processes (see Coal conversion process, liquefaction Fuels, synthetic-liquid fuels). 

The products were usually separated into light oils, middle distillates, and residuum. The residuum fraction was filtered (or centrifuged) to ranove any solid material (unreacted coal, mineral matter, and ash) and the remaining material was nsed as a recycle oil for the liquefaction stage. The lighter liquid products were generally hydrotreated to produce stable liquid fuels. 

Coal, clay ore processing Oil, grease and solids separation in chemicals and food industry Non-ferrous metal and process liquids recovery Coal carbonizing, plastics manufacture, metal processing Metal processing Pesticides, dye stuffs Desalination of industrial waters, waste waters with dissolved contaminants... 

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

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