Lignite, liquefaction

Liquid sulfur dioxide was used to separate the liquefaction products from Texas lignite when Tetralin had been used as the hydrogen donor solvent. The large excess of Tetralin present with the lignite liquefaction products did not interfere with the liquid sulfur dioxide separation procedure. The chemical composition of the fractions were similar to that of SRC and SRL. 

Figure 5. Effect of feed gas on lignite liquefaction in tetralin...

Figure 6. Effect of feed gas on lignite liquefaction in tetralin at 800 F. Key to feed gas -----, N2 (Run 61) -...

In absolute terms, the quantities of reactor solids found in various processes do vary considerably. The rate of accumulation is related to several factors, such as coal characteristics, recycle solvent quality and reactor design. However, it can be stated in general terms that liquefaction of low rank coals (sub-bituminous C and lignites) does result in higher rates of accumulation of solids than do similar operations with bituminous coals. For example, during normal operations of the SRC-I pilot plant at Wilsonville, Ala., it has been found that the amount of solids retained varies from about 0.2-0.5 wt.% (moisture-free) for bituminous coals to 1.0-1.9 wt.% (moisture free) for a subbituminous C coal (Wyodak) (72). Exxon also reports much larger accumulations for lignites and subbituminous coals than those found for bituminous coals (73). 

GARCIA SCHOBERT Liquefaction Behavior of High-Sulfur Lignites 215... 

Mechanism of Hydrogenation of Mequinenza Lignite. Our initial work focused on the hy(frx)desulfurization of the Mequinenza lignite the elucidation of the mechanism of this process then led to a further consideration of the role of organic sulfur in the liquefaction process, pesented in the next subsection. 

These results, particularly the indication of a sequential mechanism involving an initial production of liquids which are subsequently hydrotreated on the molybdenum catalyst, were the experimental basis for probing further into the first step - liquids formation - with particular interest in whether the unusually high concentration of organic sulfur in the Mequinenza lignite might have some effect on the liquefaction behavior. 

Pocahontas 3 low volatile bituminous coal, Illinois 6 high volatile bituminous coal, Wyodak subbituminous coal, and Beulah-Zap lignite from the Argonne Premium Coal Sample Bank were used as feed coals m these experiments. Ultimate analyses for these coals are listed in Table I. Coal samples were stored under argon in sealed ampules prior to use in pretreatment and liquefaction experiments. 

The plant processes 26,840 TPSD of low sulfur North Dakota lignite. The sulfur is 1.3 wt%/DAF coal. The coal analysis is shown in Table II. Output from the plant is 268,700 MM Btu/day of SNG, equivalent to 45,000 BOE/day. Total production of by-product elemental sulfur is 161 tons/day. This represents 78 wt% of total sulfur input from the coal feedstock. Since goal gasification and indirect liquefaction facilities are most likely to use Western low sulfur lignite or subbituminous coals, this represents the low sulfur case for coal conversion. 

Properties. Pilot-unit data indicate the EDS process may accommodate a wide variety of coal types. Overall process yields from bituminous, subbituminous, and lignite coals, which include liquids from both liquefaction and Flexicoking, are shown in Figure 14. The liquids produced have higher nitrogen contents than are found in similar petroleum fractions. Sulfur contents reflect the sulfur levels of the starting coals ca 4.0 wt % sulfur in the dry bituminous coal 0.5 wt % in the subbituminous and 1.2 wt % sulfur in the dry lignite. 

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