Abstract: Carbon-containing solids such as oil shale or coal are pyrolyzed or retorted in an apparatus constructed in such a manner that the heat required for pyrolysis is supplied by burning residual organic material in the pyrolyzed solids in an external combustion zone and in an internal combustion zone that is situated with respect to the pyrolysis or retorting zone such that the heat of combustion is transferred through the walls of the internal combustion zone into the pyrolysis or retorting zone. The pyrolyzed solids are passed from the retorting zone to either the external combustion zone or the internal combustion zone wherein a portion of the organic material in the solids is burned. The partially burned solids exiting this zone are then passed to either the external combustion zone or the internal combustion zone where all or a portion of the remaining organic material is burned.

Abstract: A method for recovering liquid and gaseous products from an in situ oil shale retort containing a fragmented permeable mass of formation particles containing oil shale is provided. A hot ignition gas comprising oxygen at a first selected concentration is introduced into the fragmented mass for heating the fragmented mass top surface. The percentage of the fragmented mass surface that is at a temperature no less than the ignition temperature of oil shale is determined. Thereafter, the concentration of oxygen in the ignition gas is increased by an amount proportional to the determined percentage. Such heating of the fragmented mass top surface establishes a combustion zone in the retort. After the combustion zone has spread horizontally across the retort, introduction of the hot ignition gas is discontinued. Thereafter, an oxygen-supplying gas is introduced into the retort for advancing the combustion zone downwardly through the fragmented mass.