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Pyrolysis of oil shale in a spouted bed pyrolyser Tam, Tina Sui-Man


Pyrolysis of a New Brunswick oil shale has been studied in a 12.8cm diameter spouted bed reactor. The aim of the project was to study the effect of pyrolysis temperature, shale particle size, feed rate and bed material on oil yield. Gas and spent shale yields were also determined. Shale of different particle size ranging from 0.5mm to 4mm was studied using an electrically heated reactor containing sand or spent shale which was spouted with nitrogen or nitrogen/carbon dioxide mixtures. For a given particle size and feed rate, there is a maximum in oil yield with temperature. For particles of 1-2mm at a feed rate of about 1.4kg/hr, the optimum temperature is at 475°C with an oil yield of 7.1% which represents 89.3% of the modified Fischer Assay yield. For the 2-4mm and the same feed rate, the optimum temperature is 505°C with an oil yield equal to 7.4% which is 94.3% of the modified Fischer Assay value. At a fixed temperature of about 500°C, the oil yield increases with increasing particle size. This trend is in agreement with the Fischer Assay values which showed oil yields increasing from 5.2% to about 8% as the particle size was increased. In the spouted bed, the oil yield decreases as the oil shale feed rate increases at a given temperature. The use of spent shales as the spouting solids in the bed also has a negative effect on oil yield. The gas yields which were low (less than 2.1%) and difficult to measure do not seem to be affected by particle sizes, feed rate and bed material. Hydrogen, methane and other hydrocarbons are produced in very small amounts. C0₂ and CO are not released in measurable yield in the experiments. The trend of the spent shale yield has not been successfully understood due to the unreliability of the particle collection results. Attrition of the spent shale appears to be a serious problem. Results of the experiments are rationalized with the aid of a kinetic model in which the kerogen in the oil shale decomposes to yield a bitumen and other by products and the bitumen undergoes further decomposition into oil. The spouted bed is treated as a backmixed reactor with respect to the solids. A heat transfer model is used to predict the temperature rise of the shale entering the pyrolyzer.

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