Solar chemical reactor technology for industrial production of lime

We developed the solar chemical reactor technology to effect the endothermic calcination reaction CaCO3(s) → CaO(s) + CO2(g) at 1200–1400 K. The indirect heating 10 kWth multi-tube rotary kiln prototype processed 1–5 mm limestone particles, producing high purity lime that is not contaminated with combustion by-products. The quality of the solar produced quicklime meets highest industrial standards in terms of reactivity (low, medium, and high) and degree of calcination (exceeding 98%). The reactor’s efficiency, defined as the enthalpy of the calcination reaction at ambient temperature (3184 kJ kg−1) divided by the solar energy input, reached 30–35% for quicklime production rates up to 4 kg h−1. The solar lime reactor prototype operated reliably for more than 100 h at solar flux inputs of about 2000 kW m−2, withstanding the thermal shocks that occur in solar high temperature applications. By substituting concentrated solar energy for fossil fuels as the source of process heat, one can reduce by 20% the CO2 emissions in a state-of-the-art lime plant and by 40% in a conventional cement plant. The cost of solar lime produced in a 20 MWth industrial solar calcination plant is estimated in the range 131–158 $/t, i.e. about 2–3 times the current selling price of conventional lime.