The totally closed system of the Rendall process underlies its superior environmental performance. Importantly, it eliminates all but one of the adverse environmental consequences customarily associated with conventional oil shale retorting processes, most of which are inevitable and unavoidable consequences of the processes themselves. In particular, the Rendall process will avoid fugitive emissions of noxious and biotoxic volatile organic compounds [including aromatics, heterocyclics and dioxins], sulphur dioxide and fine dust particles.
Carbon dioxide is the unavoidable exception emitted by the Rendall process, arising in exhaust gas emissions, but at only one-third or less of the rate from conventional retorting processes. Moreover, most of the carbon dioxide output from the Rendall process could be captured for sequestration, if necessary and if a suitable method is then available at economic cost.
Organic sulphur compounds inherent in the oil shale kerogen are converted to hydrogen sulphide in the process off-gas, and then recovered as merchantable elemental sulphur by a standard oil refinery technique.
The Rendall process also eliminates the need for large volumes of water characteristic of conventional retorting processes, in which water at rates of up to 2 tonnes per barrel of oil is used to quench the hot shale residue on its discharge from the retort to avoid auto-ignition in air.
Finally, the Rendall process also avoids the infamous “popcorn effect” associated with conventional retorting, whereby the volume of spent shale residue is significantly greater than that of the oil shale, as mined. Moreover, unlike the refractory shale residues from retorting, spent shale from the Rendall process is readily amenable to further processing to recover mineral by-products and produce cement. Any spent shale left over from further processing would be aggregated and returned to mined-out areas for backfilling with the overburden. Mine backfill and restoration can be carried out while mining and ore processing proceeds.