In Situ Conversion of Texas Lignite to Synthetic Fuels

A one-year technical and economic feasibility study to determine if the large deposits of deep basin Texas lignite can be recovered using in situ gasification has been completed. The study has consisted of engineering and geological analysis as well as limited experimentation. Since the project's inception in September 1974, a total of seven faculty and staff, ten graduate students, and seven undergraduates have been involved in the research. The principal funding for this project has been provided by the National Science Foundation, RANN division. Other research funds have been provided by Texas Utilities Company, Continental Oil Company, Mobil Oil Corporation, and the Shell Development Company.

As of November 1975, the project is in phase with the goals as originally proposed for the one-year feasibility study on in situ gasification of Texas lignite. An economic model (computer program) for in situ gasification of Texas lignite has been completed. The results of this analysis indicate that in situ gasification by the percolation technique will be economic for depth to seam thickness ratios approaching 150 (compared to 15 for strip mining). The available operating data, mainly from Russian and British field tests as well as from the recent ERDA test in Wyoming, have been analyzed. A computer model of an in situ reactor has been completed, and it gives good agreement with previous field test results.

Maps of lignite-bearing units in the Wilcox and Yegua formations have been prepared. This should help determine candidate field test sites as well as further clarify the Texas lignite resource picture. A review of the critical environmental factors has been undertaken, and the hydrological conditions for minimizing negative environmental effects have been established. Geological mapping of variables such as percent sand has indicated where environmentally feasible sites are located.

The ALCOA strip mine near Austin is being used at present for a prototype lignite deposit. Chemical and physical property analyses are being run. An effective way to seal lignite cores at high temperatures has been developed. Combustion tube designs have been completed. Equipment to obtain mechanical properties of lignite and overburden has been constructed. Calculations on roof collapse can be facilitated with the above apparatus and a finite element computer program, which is nearly completed.

The results of the one-year feasibility study have shown that in situ gasification of Texas lignite is technically and economically feasible, which warrants a two-year program of research and development to bring it to the field demonstration stage.