Method and apparatus for igniting an in situ oil shale retort

A method for igniting a fragmented permeable mass of formation particles in an in situ oil shale retort in a subterranean formation containing oil shale and having a void space between the top of the fragmented mass and overlying unfragmented formation, comprising the steps of:

• forming a hole through unfragmented formation to the void space;
• extending a conduit through the hole into the void space with an open end of the conduit adjacent the top surface of the fragmented mass;
• centering in the conduit a burner assembly comprising a primary air pipe having an open end within the conduit and spaced apart from the open end of the conduit, and a fuel atomizing nozzle within the primary air pipe and spaced apart from the open end of the primary air pipe;
• introducing liquid fuel through the fuel atomizing nozzle, primary air through the primary air pipe, and secondary air through the annulus between the primary air pipe and the conduit for vortical flow of the secondary air past the open end of the primary air pipe;
• and
• igniting such fuel for producing a heated ignition gas from the open end of the conduit.