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.