Solar rotary kiln for continuous treatment of particle material: Chemical experiments from micro to milli meter particle size

Rotary kilns are very robust and versatile reactors and can be used on solar towers to perform high-temperature endothermic thermal decomposition reactions of solid materials with the aid of concentrated solar irradiation. Their easy functioning system allows flexibility with respect to a wide range of operating conditions, such as particle size, residence time, operating temperature, furnace atmosphere etc. In the present study, two different solid materials with different particle sizes are successfully treated to demonstrate the versatility of this reactor: redox oxide granules of mm size are thermally reduced for high temperature thermochemical storage and micrometric particles of CaCO3 are calcined to produce lime (as the main ingredient of cement). Preliminary tests for using the rotary kiln in thermochemical storage were carried out in a closed-chamber configuration, where the reactor atmosphere is separated from the environment. The increase in the oxygen concentration in the outlet gas could clearly indicate the onset and progress of chemical reaction. The increase in residence time has been identified as the key point for increasing the conversion of the solid material. Calcination of CaCO3 was demonstrated in 13 chemical experiments. The heat losses mechanisms have been studied and pointed out that the suction of gas should be optimized to increase the efficiency of the reactor. It has also been shown that the reactor efficiency can be increased by reducing the material conversion. Optimal operation therefore depends on the final target application.