Coal liquefaction process employing fuel from a combined gasifier

Abstract

Conversion of raw coal to distillate liquid and gaseous hydrocarbon products by solvent liquefaction in the presence of molecular hydrogen employing recycle of mineral residue is commonly performed at a higher thermal efficiency than conversion of coal to pipeline gas in a gasification process employing partial oxidation and methanation reactions. The prior art has disclosed a combination coal liquefaction-gasification process employing recycle of mineral residue to the liquefaction zone wherein all the normally solid dissolved coal produced in the liquefaction zone is passed to a gasification zone for conversion to hydrogen, where the amount of normally solid dissolved coal passed to the gasification zone is just sufficient to enable the gasification zone to produce the process hydrogen requirement. An unexpected improvement in the thermal efficiency of the combination process is achieved by increasing the amount of normally solid dissolved coal prepared in the liquefaction zone and passed to the gasification zone to enable the gasification zone to generate not only all of the hydrogen required by the liquefaction zone but also to produce excess synthesis gas for use as process fuel. The gasification zone operates with steam and oxygen injection rates resulting in elevated temperatures in the range 2,200.degree. to 2,600.degree. F. which enhance thermal efficiency by accomplishing nearly complete oxidation of carbonaceous feed. These high temperatures produce a synthesis gas relatively richer in CO than H.sub.2. Because the synthesis gas is utilized as fuel, hydrogen can be recovered from the synthesis gas without degrading the value of the remaining CO-concentrated stream, since the combustion heating value of a concentrated CO stream is about the same as that of an H.sub.2 -rich synthesis gas.