We designed and tested a 10-kW solar rotary kiln reactor to effect the calcination reaction: CaCO3 - CaO + CO2. The reactor processes 1-5 min limestone particles, producing 95% or higher purity lime with a 40 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. (C) 2003 Elsevier Ltd. All rights reserved.