Solvent Refined Lignite Process

Pulverized lignite (undried) is slurried with recycle solvent at temperatures on the order of 480°C (895°F) and pressures up to 3000 psi hydrogen (or synthesis gas). The products from the reactor are separated by a series of pressure differential systems to produce the gases, liquids, and the solid product (which may also contain unconverted Ugnite and mineral ash) which can be de-ashed using an aromatic naphtha this solid product can contain as much as 40% w/w of ash and unreacted lignite (Table 19.7). 

The major difference between the SRC process and the SRL process is the option (in the latter process) of using synthesis gas in place of hydrogen. This is, in fact, an opportune application since the low-rank high moisture lignites provide the necessary moisture for the water-gas shift reaction. 

Inspection of Products from the Solvent-Refined Coal II (SRC II) Process (See Also Table 19.5) 

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The solvent refined lignite (SRL) process (Figure 19.13) is a noncatalytic process that is claimed to recover approximately 70% of the lignite feed as a solid product (m.p. 150°C-200°C [300°F-390°F]) as well as quantities of liquids and gases. 

Some coal liquefaction methods, such as the Synthoil (5) process and the CO-steam (6) process, are similar to solvent refining in their approach, but more severe conditions or a catalyst are used to give a fiuid product. In the Synthoil reaction, bituminous coal is pulverized, dispersed in a vehicle oil, and hydrogenated in a packed tubular reactor with or without added catalyst. The CO-steam process uses lignite coal and less expensive synthesis gas. The intended product is a heavy liquid fuel having ash, sulfur, and nitrogen contents suflBciently low to avoid stack-gas cleaning. Reactor temperature and pressure are normally 400°-450°C and 4000 psi, respectively. 

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