CHALLENGE OF EFFICIENTLY RETORTING VERY NONUNIFORM BEDS OF OIL-SHALE RUBBLE

Recent experimental pilot-scale retort work has shown significant declines in oil recovery yield as the size of the shale block increases. This paper reviews current analyses of the problem, together with experimental evidence for the key fluid-mechanical, heat-transfer, and mass-transfer processes that cause these lower yields. Loss in retort oil yield is found to be dominated by the flow patterns in the matrix material around the large blocks and by the thermal transient characteristics within the blocks. Use of process-control methods involving air-steam ratio, total flow, and flow variations coupled with monitored exit-gas composition appears feasible to maximize oil production.