Process for recovering carbonaceous values from in situ oil shale retorting

Abstract From the Canadian patent

A secondary combustion zone is formed in an in situ oil shale retort having walls and containing a fragmented permeable mass of particles containing oil shale. The retort has a primary combustion zone advancing therethrough and a retort feed comprising fuel and oxygen supplying gas is introduced into the retort at a location on the trailing side of the primary combustion zone for forming the secondary combustion zone. The retort feed has a spontaneous ignition temperature lower than the temperature in the primary combustion zone and preferably lower than the temperature at the location where the retort feed is introduced into the retort. Preferably sufficient heat is generated in the …