The process of the invention includes the concept of igniting a coal formation in situ with hot granular material and subsequently allowing the material to flow into the burning coal formation to serve as a propping agent in the event of a cave-in. Gasifying agents are injected into the formation in an alternating pattern to alternately oxidize and reduce the coal environment to optimize the BTU content of the recovered gas. Further, a heat receptive liquid is circulated through the casing in the well connecting the coal formation to the surface to strip the sensible heat from the produced gases so that the heat can be used for useful purposes apart from the produced gas.
The apparatus of the invention includes a casing in the well bore which has a plurality of vertically spaced dividers each having a passage therethrough so that a heat receptive fluid can be passed between dividers in a vertical descent through the casing and during such descent strip sensible heat from the produced gas before being brought back to the surface. Hot granular material is placed in the well in contact with the coal formation to ignite the formation and to flow into cavities formed in the formation during the burning thereof to serve as a propping agent.