PROCESSING OIL SHALES WITH HEAVY OIL RECYCLE

Recycle of heavy oil (> 340-degrees-C) to the retort, in order to crack coke the oil to lighter fractions, was investigated as a means of producing shale oil of more desirable product slates. Conversion of heavy oil to light oil (< 340-degrees-C) by thermal cracking and coking in the absence of and during oil shale retorting was studied using the CSIRO BIRCOS retort. As expected, the conversion by thermal cracking increased as temperature increased, with most of the net oil loss in the form of gas. By contrast, the conversion by coking alone decreased as temperature increased, with coke representing all the net oil loss. Thermal cracking was found not to be a first-order reaction, by showing a reduced conversion of heavy oil with reduced concentration of oil vapour. Retorting Stuart oil shale with heavy oil feeding and simultaneous cracking and coking showed a conversion of 19.1 g per 100 g feed heavy oil to 10.9 g light oil, 2.2 g gas and 6.0 g coke, with a net oil loss of 3.8 g per 100 g shale oil produced. These data were used to generate a set of parameters for a mathematical model which simulated a heavy oil recycle loop.