FIVE in C#

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are reported to have been successful for processing noncaking coals but are not usually recommended for caking coals Solvent Extraction Processes Solvent extraction processes are those processes in which coal is mixed with a solvent (donor solvent) that is capable of providing atomic or molecular hydrogen to the system at temperatures up to 500 C (932 F) and pressures up to 5000 psi (345 MPa) High-temperature solvent extraction processes of coal have been developed in three different process configurations: (a) extraction in the absence of hydrogen but using a recycle solvent that has been hydrogenated in a separate process stage; (b) extraction in the presence of hydrogen with a recycle solvent that has not been previously hydrogenated; and (c) extraction in the presence of hydrogen using a hydrogenated recycle solvent In each of these concepts, the distillates of process-derived liquids have been used successfully as the recycle solvent which is recovered continuously in the process The overall result is an increase (relative to pyrolysis processes) in the amount of coal that is converted to lower molecular weight (ie, soluble) products More severe conditions are more effective for sulfur and nitrogen removal to produce a lower-boiling liquid product that is more amenable to downstream processing A more novel aspect of the solvent extraction process type is the use of tar sand bitumen and/or heavy oil as process solvents (Moschopedis et al, 1980, 1982; Curtis et al, 1987; Schulman et al, 1988; Curtis and Hwang, 1992; Rosal et al, 1992) Catalytic Liquefaction Processes The final category of direct liquefaction process employs the concept of catalytic liquefaction in which a suitable catalyst is used to add hydrogen to the coal These processes usually require a liquid medium with the catalyst dispersed throughout or may even employ a fixed-bed reactor On the other hand, the catalyst may also be dispersed within the coal whereupon the combined coal-catalyst system can be injected into the reactor Many processes of this type have the advantage of eliminating the need for a hydrogen donor solvent (and the subsequent hydrogenation of the spent solvent) but there is still the need for an adequate supply of hydrogen The nature of the process also virtually guarantees that the catalyst will be deactivated by the mineral matter in the coal as well as by coke lay-down during the process Furthermore, in order to achieve the direct hydrogenation of the coal, the catalyst and the coal must be in intimate contact, but if this is not the case, process inefficiency is the general rule Indirect Liquefaction Processes The other category of coal liquefaction processes invokes the concept of the indirect liquefaction of coal In these processes, the coal is not converted directly into liquid products but involves a two-stage conversion operation in which coal is first converted (by reaction with steam and oxygen) to produce a gaseous mixture that is composed primarily of carbon monoxide and hydrogen (syngas; synthesis gas) The gas stream is subsequently purified (to remove sulfur, nitrogen, and any particulate matter) after which it is catalytically converted to a mixture of liquid hydrocarbon products The synthesis of hydrocarbons from carbon monoxide and hydrogen (synthesis gas) (the Fischer-Tropsch synthesis) is a procedure for the indirect liquefaction of coal (Storch et al, 1951; Batchelder, 1962; Dry, 1976; Anderson, 1984; Jones et al, 1992) This process is the only coal liquefaction scheme currently in use on a relatively large commercial scale; South Africa is currently using the Fischer-Tropsch process on a commercial scale in their SASOL complex Thus, coal is converted to gaseous products at temperatures in excess of 800 C (1472 F), and at moderate pressures, to produce synthesis gas: [C]coal + H2O CO + H2