Investigation of the Thermomechanical Properties of Coal Subjected to Heat Treatment

摘要

Tensile strengths and coefficients of thermal expansion have been measured for four subbituminous coals of interest to underground coal gasification. These data are important in the context of understanding the interaction between the skin effect of thermal alteration at the walls and roof of a gasifying cavity with the external stress field in situ, which leads to the small scale spalling or rubblization behavior of coal observed from excavation of UCG cavities but not as yet reproduced in the laboratory. Results from the core measurement tests for Wyodak, Widco, Hanna and Brazilian coals show that shrinking behavior of these coals can generally be related to weight loss due to drying and pyrolysis, while the ultimate tensile strength as a function of temperature can be very different for the different coals and not necessarily related to proximate analysis differences. While it is the rule that subbituminous and lower grade coals generally suffer significant reductions in strength upon moderate heat treatment, further heating does not always result in continued loss of strength, and the strength some of these charred coals is not negligible as assumed by many investigators for modeling purposes. Experiments in which thermal alteration of the coal is combined with the application of external loads are required to study adequately this phenomenon in the laboratory. 14 refs., 3 figs., 9 tabs. (ERA citation 12:040358)