Synthetic fuel production by indirect coal liquefaction

Abstract

This paper reports detailed process designs and cost assessments for production of clean liquid fuels (methanol and dimethyl ether) by indirect coal liquefaction (ICL). Gasification of coal produces a synthesis gas that can be converted to liquid fuel by synthesis over appropriate catalysts. Recycling of unconverted synthesis gas back to the synthesis reactor enables a larger fraction of the coal energy to be converted to liquid fuel. Passing synthesis gas once over the synthesis catalyst, with unconverted synthesis gas used to generate electricity in a gas turbine combined cycle, leads to less liquid fuel production, but provides for a significant second revenue stream from sale of electricity. Recently-developed liquid-phase synthesis reactors are especially attractive for “once-through” processing. Both “recycle” and “once-through” plant configurations are evaluated in this paper. Because synthesis catalysts are poisoned by sulfur, essentially all sulfur must be removed upstream. Upstream removal of CO 2 from the synthesis gas is also desirable to maximize synthesis productivity, and it provides an opportunity for partial decarbonization of the process, whereby the removed CO 2 can be captured for underground storage. The analysis here suggests that co-capture and co-storage of CO 2 and H 2 S (if this is proven technically feasible) could have important favorable impacts in some cases on liquid fuel production costs. Furthermore, the life-cycle CO 2 emissions from production and use of fuels made by ICL would be lower than with production and use of petroleum-derived transportation fuels. If CO 2 is not captured at ICL facilities, lifecycle CO 2 emissions to the atmosphere would be considerably higher than lifecycle emissions with petroleum-derived fuels.