Production of expanded clay and shale

In a process for producing expanded clay or shale aggregate material in a rotary tubular kiln presenting an essentially linear product conveying and treating region free of lateral offset, the kiln including a raw material charging end and expanded material discharge end at respectively opposite ends of the conveying and treating region and being provided with a burner located in the vicinity of the discharge end for heating the conveying and treating region with the conveying and treating region being composed of a preheating zone and an expansion zone following one another in the direction from the charging end to the discharge end, the preheating zone being more proximate to the charging end and the expansion zone being more proximate to the discharge end, which process is carried out by operating the burner to introduce heat into the conveying and treating region while introducing raw material into the conveying and treating region via the charging end, and conveying the material through the preheating zone in order to dry and heat that material and then conveying the material into the expansion zone to produce the expanded material, with the heat produced by the burner acting to cause essentially all expansion of the material to occur in the expansion zone, and then discharging the expanded material via the discharge end, the improvement comprising providing at least one additional burner having a flame outlet orifice, mounting the additional burner on the kiln to rotate therewith in a position such that the flame outlet orifice is located within the kiln between the expansion zone and the material charging end and is oriented to direct a heating flame toward the material charging end, and supplying additional heat to the raw material in the preheating zone by operating the at least one additional burner to produce the heating flame.