Multitube Rotary Kiln for the Industrial Solar Production of Lime

We designed and tested a scaleable solar multitube rotary kiln to effect the endothermic calcination reaction CaCO3→CaO+CO2 at above 1300K. The indirect heating 10-kW reactor prototype processes 1-5mm limestone particles, producing high purity lime of any desired reactivity and with a degree of calcination exceeding 98%. The reactor’s efficiency, defined as the enthalpy of the calcination reaction at ambient temperature (3184kJkg−1) divided by the solar energy input, reached 30%–35% for solar flux inputs of about 2000kWm−2 and for quicklime production rates up to 4kgh−1. The use of concentrated solar energy in place of fossil fuels as the source of process heat has the potential of reducing by 20% CO2 emissions in a state-of-the-art lime plant and by 40% in a conventional cement plant.