The Rendall Process
From the late 1970s, until his death in 2008, John Rendall worked on alternative approaches for converting the organic matter in oil shale (kerogen) into synthetic crude oil. He identified four key criteria essential for commercial success:
After numerous initial efforts with solvent extraction approaches, he settled on the current “thermal solution” approach. Other researchers, most notably in the Colorado School of Mines, Golden, Colorado, confirmed numerous bench-scale tests by him and his colleagues.
Two key process steps
Kerogen conversion: thermal conversion and hydrogenation of kerogen in a closed system at elevated temperature and pressure, with two recycle streams. A heavy oil recycle stream is used in preparing the shale slurry fed to the conversion reactor. After catalytic hydrogenation, a mid-distillate stream provides hydrogen to the conversion process, maximising light oil products and minimising production of tars. Use of totally enclosed fluid systems enables fast and efficient heat transfer, ease of temperature control, and enhanced thermal efficiency.
Supercritical extraction: a supercritical solvent is used to recover product oil adhering to oil shale residue, providing both for maximum oil recovery of oil, and for output of clean solid residues for further processing or disposal.
The “thermal solution” approach clearly meets the four criteria required for commercial success:
Economic viability: Yields are typically twice or more than those achieved by the traditional retorting technologies. Commercial plant capital and operating costs are projected to be low in comparison with other technologies of the same capacity.
Environmentally acceptable performance: Since the process is totally enclosed from start to finish, only oil, CO2 and clean, spent shale residue are produced. Unless recovery of valuable mineral by-products from the spent shale residues is economically viable, the residue material can be used as a benign backfill. Toxic emissions, typical of conventional retorting processes, are eliminated. Water will be recovered from the ore, and should be in excess of all process requirements.
Scalability to large commercial units: The process equipment needed for each step in the Rendall Process is used in other well-established, large capacity, commercial industrial applications, operating under similar or more severe conditions.
Process and equipment reliability: None of the process steps present inherent difficulties in operability or control.
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