Method of calcining solid materials and single column kiln therefor

A method of calcining solid materials which comprises the step of feeding said solid materials at the top of a materials preheating zone, to permit said materials to flow down said preheating zone, introducing a mixture of combustion gases and secondary air through the bottom of said preheating zone to force them to flow upwardly and in countercurrent flow with said materials, the latter being preheated by the combustion of said combustion gases supported by said secondary air;

• transferring the preheated materials to a primary air preheating zone arranged directly and colinearly below said materials preheating zone and separated therefrom by a partition having a material transfer mechanism including a materials transfer valve which permits the passage of said material downwardly through said partition, injecting cold primary air at the top of said air preheating zone so that it may flow downwardly therethrough and in co-current flow with said falling preheated materials, allowing the materials to fall to a calcining zone arranged directly and colinearly with said air preheating zone as a downwardly extending continuation thereof, injecting fuel at the level defining the bottom of said air preheating zone and the top of said calcining zone, in order to burn said fuel with said preheated primary air to calcine said materials, the combustion gases thus formed calcining said falling materials in co-current flow therewith;
• allowing the thus calcined materials to fall to a materials cooling zone arranged directly and colinearly below said calcining zone as a downwardly extending continuation thereof, injecting cold secondary air at the bottom of said materials cooling zone to force said secondary air to flow upwardly and countercurrently with said falling materials to cool the same and to be admixed with the downwardly directed stream of combustion gases from the calcining zone;
• and recycling the thus formed mixture of combustion gases and secondary air to the bottom of said materials preheating zone to be thereafter exhausted to the atmosphere from the top of said materials preheating zone.

A single column kiln for calcining solid materials which comprises a vertical cylindrical column having a closed top, a closed bottom and an intermediate horizontal partition dividing said column into an upper or materials preheating chamber and a lower chamber, solid materials feed means at the top of said column, calcined materials discharge means at the bottom of said column, preheated materials transfer means at said partition, downwardly directed primary air injecting means arranged below said partition and at a level closely spaced therefrom, downwardly directed fuel injecting and burning means arranged at a lower level than and spaced a predetermined distance from said primary air injecting means in order to constitute a primary air preheating zone therebetween, common gas collector means arranged at a lower level than and spaced a predetermined distance from said fuel injecting and burning means to constitute a materials calcining zone which is a continuation of said primary air preheating zone, upwardly directed secondary air injecting means arranged at the bottom of said column to constitute a materials cooling zone between the level of said gas collector means and the level of said secondary air injecting means, gas duct means extending from said common gas collector means to a level immediately above said partition, and gas exhaust means at the top of said column, whereby the solid materials charged at the top of the column are preheated by the combustion and the countercurrent flow of the combustion gases generated in said calcining zone supported by the secondary air preheated in said materials cooling zone, the primary air is preheated in co-current flow with said preheated materials, the preheated materials are calcined by the burning of said fuel supported by said primary air flowing in co-current flow with said materials, and the second air is preheated by its countercurrent flow with said calcined materials which in turn are cooled to be discharged at an appropriate temperature.