Abstract: Sulfur dioxide is removed from a process gas by passing the process gas through a first fragmented permeable mass of particles containing treated oil shale and including alkaline earth metal oxides at a sufficient temperature to remove sulfur dioxide from the process gas. Gas containing sulfur dioxide from the first fragmented mass is passed through a second fragmented permeable mass of particles containing treated oil shale and including alkaline earth metal oxides. Water in the second fragmented mass combines with alkaline earth metal oxides in the second fragmented mass and sulfur dioxide in the gas from the first fragmented mass with resultant removal of sulfur dioxide from gas from the first fragmented mass.

Abstract: To recover liquid and gaseous products from a fragmented permeable mass of particles containing oil shale, a buffer zone containing retorted oil shale is established in the fragmented mass by passing a hot processing gas substantially free of free oxygen through at least a portion of the fragmented mass. Thereafter, a combustion zone is established in the buffer zone, and a combustion zone feed containing oxygen is introduced into the fragmented mass on the trailing side of the combustion zone. This advances the combustion zone through the fragmented mass and retorts oil shale in a retorting zone on the advancing side of the combustion zone. The thickness of the buffer zone is sufficient for reaction of most of the oxygen in the combustion zone feed with residual carbonaceous material in retorted oil shale in the buffer zone.

Abstract: In a process for recovering liquid and gaseous products from an in situ oil shale retort containing a fragmented permeable mass of particles containing oil shale, a heated zone is established in an upper portion of the fragmented mass. For a period of normal retorting operation, an oxygen containing gas is introduced to the fragmented mass on the trailing side of the heated zone at a sufficient rate for advancing the heated zone downwardly through the fragmented mass and liquid products and a relatively lean off gas containing gaseous products are withdrawn from the bottom of the retort. Thereafter, for a period of post-retorting operation, the introduction of gas to the fragmented mass is reduced to a rate such that a relatively rich off gas is withdrawn from the retort. The rich withdrawn off gas preferably has a heating value of at least about 75 BTU/SCF.