Coal liquefaction indirect

Background Indirect coal liquefaction differs fundamentally from direct coal hquefaction in that the coal is first converted to a synthesis gas (a mixture of H9 and CO) which is then converted over a catalyst to the final product. Figure 27-9 presents a simplified process flow diagram for a typical indirect coal hquefaction process. The synthesis gas is produced in a gasifier (see a description of coal gasifiers earlier in this section), where the coal is partially combusted at high temperature and moderate pressure with a mixture of oxygen and steam. In addition to H9 and CO, the raw synthesis gas contains other constituents (such as CO9, H9S, NH3, N9, and CHJ, as well as particulates. 

Status of Indirect Liquefaction Technology The only commercial indirect coal liquefaction plants for the production of transportation fuels are operated by SASOL in South Africa. Construction of the original plant was begun in 1950, and operations began in 1955. This plant employs both fixed-bed (Arge) and entrained-bed (Synthol) reactors. Two additional plants were later constructed with start-ups in 1980 and 1983. These latter plants employ dry-ash Lurgi Mark IV coal gasifiers and entrained-bed (Synthol) reactors for synthesis gas conversion. These plants currently produce 45 percent of South Africa s transportation fuel requirements, and, in addition, they produce more than 120 other products from coal. 

TABLE 27-17 Estimated Costs of Indirect Coal Liquefaction Plant (1993 US Dollars)... 

Indirect coal liquefaction is a technology in which coal is first gasified to synthesis gas ("syngas," CO + H2), which is used to synthesize liquid fuel by the Fischer—Tropsch process. 

Indigoid soluble dyes, 7 373t Indigo vat dye, 9 181 Indirect-arc furnaces, 12 297—298 Indirect coal liquefaction, 6 858-867 Indirect cooler evaporators, 21 537 Indirect extrusion, copper, 7 693 Indirect food additives, 12 29, 34 categories of, 12 31 Indirect-gap semiconductors, 14 837 ... 

After World War II, direct liquefaction of coal became uneconomical as the use of lower-cost petroleum products became more widespread. However, the German process of indirect coal liquefaction, the Fischer-Tropsch process, continued to hold some interest. The Fischer-Tropsch process first involved production of a carbon monoxide and hydrogen-rich synthesis gas by the controlled gasification of coal followed by a catalytic reaction process to yield a valuable mixture of hydrocarbon products. Simplified Fischer-Tropsch reactions are shown by the following equations ... 

Fischer-Tropsch. The process most frequently considered for indirect coal liquefaction is the Fischer-Tropsch (F-T) synthesis, developed in 1925 by German chemists Franz Fischer and Hans Tropsch. In the F-T process, synthesis gas is reacted over a catalyst, typically iron or cobalt based, at 1-30 atm and 200-350°C to produce a wide range of mainly aliphatic hydrocarbons, including gas, LPG, gasoline, jet fuel, diesel oil, middle distillates, heavy oil, and waxes. Germany used this technology during World War II to produce nearly 15,000 barrels/day of military fuels. 

Blending the raw distillable products prior to refining takes advantage of their complementary characteristics. High-octane naphtha from direct coal liquefaction is blended with low-octane naphtha from indirect coal liquefaction, and high-cetane diesel from indirect coal liquefaction is blended with low-cetane diesel from direct coal liquefaction. The blended liquids require less refining to meet premium product specifications than if they were refined separately. 

Larson, E.D. and Ren, T.J. Synthetic fuel production by indirect coal liquefaction. Energy for Sustainable Development, 2003, VII (4), 79. 

Over 70% of known catalytic reactions involve some form of metallic component. Industrially, metals are used in catalytic reforming, hydrocracking, ammonia and methanol synthesis, indirect coal liquefaction, oxidation, and a vast number of organic hydrogenation and dehydrogenation processes. Academically, metals are favored for research since they are easily prepared in pure form and conveniently characterized. In fact, most of the fundamental information leading to conceptual theories in catalysis originated with studies on metal systems. 

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