Pyrolysis kinetics for oil-shale particles

• Published in: Fuel (Guildford) 1977-01, Vol.56 (3), p.234-240
• Main Authors: Granoff, Barry, Nuttall, H.Eric
• Format: Article
• Language: English
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/0016-2361(77)90001-1

Experimental and mathematical investigations of the pyrolysis kinetics for single particles (12.7 mm diameter cylinders and spheres) of 22 gal/ton (91.8l/t) oil shale are presented. Machined samples of uniform geometry were suspended in a nitrogen stream and pyrolysed over a range of temperatures (384–520 °C), while weight losses were continuously measured with a Cahn recording thermobalance (TGA). In addition to weight-loss measurements, centreline temperature histories were obtained from several samples that were instrumented with microthermocouples. Other samples were partially pyrolysed, quenched, cross-sectioned and visually examined to aid in the understanding of the pyrolysis mechanism. Photographs of partially pyrolysed samples are included and discussed. Two mathematical models were developed in order to represent the pyrolysis process. The weight-loss data were then compared with the results obtained from these models. A non-isothermal shrinking-core model was developed first, as a direct consequence of having observed a shrinking-core mechanism in partially pyrolysed samples. This model resulted in an apparent pyrolysis activation energy of 110 kJ/mol. Subsequently, a simplified, non-isothermal homogeneous model was developed, tested, and resulted in a pyrolysis activation energy of 148 kJ/mol. It was shown that either model could account for the experimental centreline temperature histories and for the pyrolysis rates. The non-isothermal homogeneous representation is considerably less complex than previously published pyrolysis models, and would be preferred for use as a subprogram in a comprehensive retorting model.