| http://www.w3.org/ns/prov#value | - In the novel process, a portion of a rubblized mass of oil shale in an underground retort is preheated with an inert gas, such as steam, nitrogen, off gases emitted from the retort or other gases containing an insufficient amount of molecular oxygen to support combustion, to above the oil shale ignition temperature of 650??? F. and preferably above the minimum oil shale retorting temperature of 75
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