Indirectly heated rotary tubular kiln

Claim 1

A rotary tubular kiln for carrying out gas-solids reactions, comprising an indirectly heated outer reaction tube, said outer reaction tube being rotatable, said outer tube having an interior surface, a charging hopper in communication with said outer reaction tube, and disposed at one end of said outer reaction tube, a gas inlet in communication with said outer reaction tube, said gas inlet disposed at an end of said outer reaction tube which is opposite to the end wherein the charging hopper is disposed, a gas outlet in communication with said outer reaction tube, said gas outlet disposed at the same end of the outer reaction as the charging hopper, a product outlet in communication with said outer reaction tube, said product outlet disposed at the same end of the outer reaction tube as the gas inlet, a central tube disposed within said outer reaction tube, said central tube running along almost the total length of the kiln, each end of the central tube covered with a sealing top, said gas inlet and product outlet being disposed in a hollow chamber disposed at a distance from a sealed top end of the central tube that is opposite said hopper, said chamber containing a spiral baffle, a spiral having a plurality of turnings, said spiral being tightly fixed between the central tube and the interior surface of the outer reaction tube, said spiral forming a plurality of channels between said turnings, and a plurality of longitudinal lifing blades extending from the interior surface of the outer reaction tube and being between adjacent turnings, the height of the lifting blades being such that solids which fall from the lifting blades do not come into contact with the central tube, the lifting blades having an angle of respose with respect to the interior surface of the outer reaction tube.