Two-stage coal liquefaction processes

Nalitham, R. V., Lee, J. M., Lamb, C. W., and Johnson, T. W., Two-Stage Coal Liquefaction Process Performance with Close-Coupled Reactors, Fuel Proc. Technol., 17, 13-27 (1987). 

CSF [Consol Synthetic Fuels] A two-stage coal liquefaction process. In the first stage, the coal is extracted with process-derived oil and the ash removed. In the second, the extract is catalytically hydrogenated. Piloted by the Consolidation Coal Company, Cresap, WV, from 1963 to 1972. See also H-Coal, SRC, Synthoil. 

Neuworth, M. B., and Moroni, E. C., Development of an Integrated Two Stage Coal Liquefaction Process, Fuel Proc. Tech., 8, 231-239 (1984). 

Catalysts and donors do not always perform most efficiently under the same conditions. Hence, optimal application is achieved in consecutive steps, where the best conditions can be selected for each step separately. In such a two-step primary liquefaction process, expensive catalysts, such as Co-Mo and Ni-Mo, are not necessarily employed. These catalysts are more appropriately used when the coal has been depolymerized to soluble products and catalyst poisons are not present in the final upgrading stages. 

Work has also continued on the solvent-refined coal + hydrocracking concept (the NT.SL, or non-integrat-ed, two-stage liquefaction process), and a pilot plant was operated by Amoco, DOE and the Electric Power Research Institute (EPRI) from 1974 to 1992. 

If the mobile phase is present in a significant concentration, as suggested by the results of solvent extraction studies (1,8), the practical meaning of the mobile phase to coal conversion processes may be profound. In coal liquefaction, two stage processes emphasizing the mobile phase and the macromolecular structure separately could well be most economical. In devolatilization kinetics, at least two sets of kinetic parameters are necessary to model the devolatilization phenomena associated with the mobile phase and the macromolecular structure respectively since the mobile phase components devolatilize at much lower temperatures than the macromolecular structure components 0. In addition, the mobile phase appears to have a significant influence on the thermoplastic properties of coal (0 and thereby on coke quality. 

In an effort to obtain higher value products from SRC processes, a hydrocracking step was added to convert resid to distillate liquids. The addition of a hydrocracker to the SRC-I process was called nonintegrated two-stage liquefaction (NTSL). The NTSL process was essentially two separate processes in series coal liquefaction and resid upgrading. NTSL processes were inefficient owing to the inherent limitations of the SRC-I process and the high hydrocracker severities required. 

The H-Coal process produces approximately 3-3.5 barrels of liquid product for each ton of coal.42 Tests showed that the process is best suited for high-volatile bituminous coal the use of low-rank coals significantly reduced throughput and distillate yields. The successful performance of the ebullated bed reactor in the H-Coal process led to its later use in two-stage liquefaction systems. 

Gollakota, S. V, Lee, J. M., and Davies, O. L., Process Optimization of Close-Coupled Integrated Two-stage Liquefaction by the Use of Cleaned Coals, Fuel Proc. Technol., 22, 205-216 (1989). 

A modem direct coal liquefaction plant can produce about 0.5-0.6t of liquid fuel from every ton of dry coal. In the cases where the hydrogen supply is also produced from coal, the overall system can produce about 11 of liquid fuel from every 3—4t of coal. China Shenhua Coal Liquefaction Co. Ltd is currently building a 20,000 bbl/day direct coal liquefaction plant in Inner Mongolia, China. The economic viability of this large-scale direct coal liquefaction remains to be revealed. Economic analysis performed in 19903 showed that the process of the two-stage conversion of CTL has a product cost of 38 per barrel. Several areas, such as improved pretreatment and cleaning methods, novel catalysts, and improved hydrocarbon recovery, were identified as ways to lower the cost further.1... 

A somewhat different alternative for the coprocessing of coal and tyres is the application of two-stage processes. In this case, tyres are first pyrolysed to yield an oil which is then used as solvent in the coal liquefaction. With this approach, the problem associated with the separation of finely divided carbon black dispersed in the viscous oil produced from coal can be avoided. 

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