EVALUATION OF OIL YIELD LOSSES DURING THE RETORTING OF OIL SHALE AT LOW VOID FRACTIONS. PART 1. THE EFFECTS OF PARTICLE SIZE AND RESOURCE GRADE

ABSTRACT

The economics of vertical modified in situ (VMIS) retorting of oil shale can be improved by decreasing the quantity of oil shale which is mined and transported to the surface. However, decreasing the quantity of oil shale removed from the retort also decreases the void fraction in the shale bed and this can affect the retorting process. The Western Research Institute has completed a series of experiments designed to investigate the effects of different experimental parameters on retorting oil shale at low void fractions. The effects of changes in the experimental parameters, oil shale particle size and resource grade, on oil yield losses have been evaluated using previously described oil yield loss diagnostic methods. These methods show that cracking–plus–combustion losses are the major and more variable source of chemically related oil yield losses. In experiments investigating changes in oil shale particle size, these losses correlate with the temperature differential between thermocouples in the rubble and in the interior of the oil shale particles. The data from the experiments investigating the effects of changes in resource grade on oil yield losses do not follow this correlation because of additional combustion of the produced oil during the lean resource grade experiment. Coking losses from experiments investigating both parameters were found to decrease with increased heating rate of the oil shale when significant differences in the heating rate were observed.