Computed tomography of coals. Quarterly technical progress report No. 5, September 30, 1983-January 1, 1984

A pyrolysis apparatus has been constructed to fit inside the aperture of an x-ray computed tomography (CT) machine. With this equipment the density variations inside pieces of Illinois No. 6 coal have been followed as a function of time. When the sudden temperature rise experienced by, for example, the coal feed to a fixed or fluidized bed gasifier was simulated, then the pyrolysis front penetrated into the coal as a very narrow band 1 to 2 mm wide. The speed of the pyrolysis front can be observed by the CT equipment and also the extent of material loss upon pyrolysis. Very little of the coal is molten at any one time. Two-dimensional finite element analysis of the motion of the pyrolysis front provides time dependent temperature profiles within the coal which can be compared with the CT results. Effective thermal conductivities 2 to 3 times slower than published values will probably be necessary to bring agreement. Pyrolysis gases appear to be escaping via cracks to the outside rather than by diffusion through the coke. From quite early stages the pyrolysis front obeys the (d/sup 2/) law commonly found in experiments on burning fuel droplets. This observation may enable an analytical more » solution for the propagation of the pyrolysis front to be formulated. Further experiments using high water content coals (e.g., lignite) are being planned, as well as extensions from pyrolysis to gasification with CO/sub 2/ and steam. 4 refs., 62 figs., 2 tabs. « less