Continuous calciner

Apparatus for uniformly heating a continuous supply of fine particles comprising an elongate cylindrical outer wall, a substantially coaxial elongate cylindrical inner wall within said outer wall, means for directing a flow of material spirally through the elongate space between said inner wall and said outer wall in a direction from a first end of said apparatus to a second end of said apparatus, means for supplying air to within the cylindrical inner wall and conveying said air within said inner wall from said inlet to said first end, means within said inner wall for heating said air within said inner wall, means at said first end for conducting said heated air from within said inner wall to between said inner wall and said outer wall, and means at said first end for continuously feeding said fine particles to be heated into said heated air whereby said heated air conveys said fine particles spirally through the length of said elongate space between said inner wall and said outer wall from said first end to said second end and uniformly heats all of said fine particles, means for removing said heated fine particles from said apparatus, means for separating said fine particles from conveying air and means for returning a substantial portion of said air to be reheated by said heating means.