Process of calcining limestone in a rotary kiln

In a process for the calcining of limestone or hydrated lime by thermally treating the same with hot gases in a rotary kiln through which the kiln atmosphere and the limestone or hydrated lime charge are countercurrently passed and into which oxygen containing gases are introduced through shell pipes at a plurality of points, the improvement which comprises producing at least part of said hot gases by feeding solid carbonaceous fuel into the rotary kiln at the charging end thereof, injecting oxygen-containing gases through nozzle blocks into charge material disposed over said nozzle blocks at a horizontal region of the rotary kiln which is defined by a point along the length of the kiln where ignitable particles of said solid fuel first appear and a second point along the length of said rotary kiln which is spaced from the charging end of said rotary kiln by not more than 50% of the length of the kiln, and injecting oxygen-containing gases through shell pipes into the free space of said rotary kiln at least into said horizontal region.