Direct liquefaction process

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. 

TABLE 27-14 Direct Liquefaction Process Conditions and Product Yields... 

We will examine three synthetic fuel scenarios and compare their implications regarding sulfur availability with the current and projected market for sulfur to the year 2000. The analysis will consider three production levels of synthetic fuels from coal and oil shale. A low sulfur Western coal will be utilized as a feedstock for indirect liquefaction producing both synthetic natural gas and refined liquid fuels. A high sulfur Eastern coal will be converted to naphtha and syncrude via the H-Coal direct liquefaction process. Standard retorting of a Colorado shale, followed by refining of the crude shale oil, will round out the analysis. Insights will be developed from the displacement of imported oil by synthetic liquid fuels from coal and shale. 

Direct liquefaction processes under development are typically carried out at temperatures from about 450 to 475°C and at high pressures from 10 to 20 MPa and up to 30 MPa. Despite the slow rate at which liquefaction proceeds, the process itself is thermally rather efficient, since it is only slightly exothermic. However, hydrogen must be supplied and its manufacture accounts for an important fraction of the process energy consumption and cost of producing the liquid fuel. The hydrogen itself may be produced, for example, by the gasification of coal, char, and residual oil. 

The three principal routes by which liquid fuels can be produced from coal have been noted to be pyrolysis, direct liquefaction, and indirect liquefaction. A clean fuel that is a solid at room temperature can also be produced by direct liquefaction processes. 

FIGURE 7 Generalized direct liquefaction process train. [Reprinted with permission from Probstein, R. F., and Hicks, R. E. (1990). Synthetic Fuels, pH Press, Cambridge, MA.]... 

The direct liquefaction technologies, which include Solvent Refined Coal, Exxon Donor Solvent and H-Coal processes have never been operated at a commercial scale. As discussed yesterday, these processes are not at advanced stages of development. The products from direct liquefaction processes are basically boiler fuels or synthetic crudes that could potentially be upgraded to... 

Brainard, A. J., "The Application of an Availability Analysis to a Direct Liquefaction Process," paper presented to the 72nd Annual Meeting of the AIChE,... 

TABLE 19.15 Heteroatom Content of Products from Direct Liquefaction Processes... 

Tomlinson, G. C., Gray, D., Neuworth, M. B., andTalib, A., The Impact of Rank-Related Coal Properties on the Response of Coals to Continuous Direct Liquefaction Processes, Sandia Contractors Report, SAND85-7238 (Oct. 1985). 

Direct-Liquefaction Kinetics All direct-liquefaction processes consist of three basic steps (1) coal slurrying in a vehicle solvent, (2) coal dissolution under high pressure and temperature, and (3) transfer of hydrogen to the dissolved coal. However, the specific reaction pathways and associated kinetics are not known in detail. Overall reaction schemes and semiempirical relationships have been generated by the individual process developers, but applications are process specific and limited to the range of the specific data bases. More extensive research into liquefaction kinetics has been conducted on the laboratory scale, and these results are discussed below. 

The liquid products from direct liquefaction processes do require further upgrading before they can be used directly as transportation fuels. This upgrading utilizes standard petroleum refining industry technologies, allowing the products from a... 

Indirect liquefaction processes were developed in Germany around the same time as direct liquefaction processes. In the early 1920s, Franz Fischer and Hans Tropsch patented a process to produce a mixture of alcohols, aldehydes, fatty acids, and... 

The Exxon donor solvent, direct liquefaction process also used hot oil drying. In this process, LRC is dried by a high-pressure hydrogenation reactor contact with hot recycle hydrogen donor solvent prior to entering. Unfortunately, no data were developed for solvent recovery after drying becanse the dried coal and vehicle solvent were reacted immediately with hydrogen in the Uqnefaction reactor. 

The final category of direct liquefaction process employs the concept of catalytic liquefaction in which a suitable catalyst is used to add hydrogen to the coal. These processes usually require a liquid medium with the catalyst dispersed throughout or may even employ a fixed-bed reactor (see p. 394). On the other hand, the catalyst may also be dispersed within the coal whereupon the combined coal-catalyst system can be injected into the reactor. 

Direct Liquefaction Process in which coal is subjected to hydrogenation under high pressure and at a high temperature, thereby converting it directly into a synthetic liquid fuel also known as the Bergius process. 

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