We designed and tested a 10-kW solar rotary kiln reactor to effect the calcination reaction: CaCO3 → CaO+CO2. The reactor processes 1-5 mm limestone particles, producing 95% or higher purity lime with a t 60 reactivity ranging from 14 s to 38 min. The degree of calcination and the reactivity both depend on the reactant's decomposition temperature (1323-1423 K), residence time (3-7 min), and feed rate (10-50 g/min). The reactor's efficiency, defined as the enthalpy of the calcination reaction at a specified temperature divided by the solar energy input, reached 20% for solar flux inputs of about 1200 kW m-2 and for quicklime production rates of about 1.3 kg/h. The solar lime reactor operated reliably for more than 100 h for a total of 24 sunny days, withstanding the thermal shocks that occur in solar applications.
Bibliographical noteFunding Information:
This work is being funded in part by the Swiss Federal Office of Energy (BFE). We thank A. Steinfeld and C. Wieckert for fruitful discussions. We thank M. Brack for help with calibrating the flux measurement system and A. Frei for the chemical analyses.