The steam-assisted calcination of limestone and dolomite for energy savings and to foster solar calcination processes

Abstract

CaO and MgO are important industrial raw materials commonly produced by either the decomposition of calcium carbonate at about 900 °C, or the calcination of dolomite, a mixed calcium and magnesium carbonate, calcined either to MgO.CaCO 3 at about 750 °C, or to MgO.CaO at 900 °C. ln this research, the decomposition reaction of 104–147 μm dolomite and limestone particles was investigated, both without and with steam added to the reaction. A series of experiments was performed in terms of relevant parameters such as time, temperature and amount of H 2 O added. Reactants and reaction products were fully characterized and demonstrate the different morphology and specific surface area of the raw carbonate ores and the calcined oxides. Adding H 2 O during calcination has a significant positive effect. The calcination shows that steam can significantly accelerate the reaction rate, and reduce the decomposition temperature by ∼100 °C, thus reducing the cost of the decomposition by increasing the yield for a given reaction time, while also reducing the required sensible heat of the feedstock and combustion air . This ultimately reduces the amount of fossil fuel or alternative energy carriers, thus reducing the CO 2 footprint of the system. The improved operating conditions foster the use of concentrated solar calcination. The CO 2 footprint of the carbonate decomposition can be reduced by ∼4% in traditional kilns , and by as much as 20% if concentrated solar kilns are used. Both applications are currently investigated in pilot-scale operations. • Calcination of dolomite and limestone particles was studied, without and with adding steam. • Steam accelerates the reaction rate and reduces the calcination temperature by ∼100 °C. • Adding steam reduces the energy requirement, thus reducing the CO 2 footprint of the system. • CO 2 emissions are reduced by ∼4% in conventional kilns, and by ∼20% in solar kilns applications.