Liquefaction, coal

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

Coal Liquefaction at Wilsonville. Starting ia 1974 the Advanced Coal Liquefaction R D Facihty at WilsonviUe, Alabama operated a 6 t/d pilot plant and studied various coal Hquefaction processiag schemes. The facihty, cosponsored by the DOE, the Electric Power Research Institute (EPRI) and Amoco Oil Co, was shut down ia early 1992. 

W. R. Eppedy and J. W. Taunton, "Exxon Donor Solvent Coal Liquefaction Process Development," paper presented at Coal Dilemma II ACS Meeting, Colorado Spriags, Colo., Feb. 12, 1979. 

Gasoline from Coal, British Coal Liquefaction Project, Point of Ayr, Scodmd, 1992. 

W. H. Wiser, "Some Chemical Aspects of Coal Liquefaction," in Ref. 40. 

H. D. Schindler "Coal Liquefaction A Research Needs Assessment," Vol. 2, Technical Background, Final Report on DOE Contract Mo. DE-AC01-87ER30110, 1989. 

The contributions of Dr Harold F. Chambers, Jr (Coal Liquefaction) and Dr Yuan C. Fu (Coal Liquefaction) who were authors for the Sixth Edition, are acknowledged. 

The technology for coal liquefaction to synthetic fuels is not new. In 1913 Dr. Friedrich Bergius discovered the technique of adding hydrogen to coal at a pressure of 20.3 MPa (2940 psia) and a temperature of about 723 K (842°F). Under these conditions most oxygen was hydro-... 

Direct-Liquefaction Processes Figure 27-8 presents a simph-fied process flow diagram of a typical direct coal liquefaction plant. Specific processes are described in the following paragraphs. 

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 27-16 Estimated Costs of Direct Coal Liquefaction Plant... 

Costs based on plant processing 26,105 Mg/d (28,776 US ton/d) of Ilbnois No. 6 coal. Source Direct Coal Liquefaction Baseline Design and Systems Analysis, prepared by Bechtel and Amoco under DOE contract no. DE-AC22-90PC89857, March 1993. 

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

SOURCE Ftoc. Coal Liquefaction and Gas Conversion Contractors Review Conf, CONF-9508133, Pittsburgh Energy Technology Center, Pittsburgh, Pa., 1995. 

In addition to supplying transportation fuels and chemicals, products from coal liquefaction and extraction have been used m the past as pitches for binders and feedstocks for cokes [12]. Indeed, the majority of organic chemicals and carbonaceous materials prior to World War II were based on coal technologies. Unfortunately, this technology was supplanted when inexpensive petroleum became available dunng the 1940s. Nevertheless, despite a steady decline of coal use for non-combustion purposes over the past several decades, coal tars still remain an important commodity in North America. 

Given, P. H., Cronaucr, D. C., Spackman, W., Lovell, H. L., Davis, A., and Biswas, B., Dependence of coal liquefaction behavior on coal characteristics 1. vitrinite-rich samples. Fuel, 1975, 54, 34 39. 

The rotational operation of a CFB leads to a vortex motion in the freeboard which tends to inhibit particle loss by elutriation. Because of the relatively compact nature of the CFB and the operating flexibility provided by the rotational motion, the CFB has been proposed for a variety of applications including coal combustion, flue gas desulfurization, gas combustion, coal liquefaction and food drying. 

A SIMPUFIED DIAGRAM OF A COAL UQtlEFACTlON PROCESS Figure 8.6 Coal-liquefaction jKocess (Warren et al.. 1995. Courtesy of ASCE),... 

Valves for coal-liquefaction components (TiB2)l l Heating elements (SiC)... 

Curlee, R. M., Materials Coatings for Valves Coal Liquefaction Components and Instrumentation, SAND82-2137, Sandia National Laboratories, Albuquerque, NM 87185 (1982)... 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

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