Microstructure And Kinetic Analysis On Limestone Decomposition Under Different Atmosphere

China as the world’s largest cement producer,our cement output always ranks the first in the world,and cement industry has become the main emission source of carbon emissions.At present,the control of greenhouse gas emissions becomes the focus of world’s attention.with the development of CO₂ emissions reduction technology,currently O₂/CO₂ combustion enrichment technology of cement industry has important practical significance.The main composition of cement raw material is limestone,in oxygen-enriched combustion technology,cement decomposing furnace using CO₂ instead of N2,so the importance of analysis of characteristics of limestone under high CO₂ atmosphere decomposition cannot be ignored.In this paper,four kinds of limestones with different microstructures are used as samples.Two limestone structures are loose and the crystallization is poor.The other two limestones structures are dense and the crystals are better.The following results were obtained,the limestone in the air atmosphere was decomposed gently and the decomposition was violent in the CO₂ atmosphere.The higher the CO₂ concentration and the higher the rate of heating,the more obvious the decomposition of the limestone,the higher the temperature required for the decomposition,the decreasing the decomposition temperature range,the gradual increase of the decomposition rate and the decrease of decomposing time.The effect of CO₂ concentration on limestone decomposition will be close to a certain limit when the CO₂ concentration is high.The change of the atmosphere has little effect on the decomposition characteristic parameters of limestones with high structural crystallinity,but has a great influence on the limestone with loose structure.The activation energy of limestone decomposition in all different atmospheres showed a single downward trend.The decomposition process of limestone in air atmosphere is relatively stable,and the change range of decomposition process activation energy is very small.And in air atmosphere,the higher the crystallinity and more compact limestone structure,the higher the average activation energy of the decomposition.In CO₂ atmosphere,the decomposition process is very intense,and with the increase of CO₂ concentration activation energy change curve is more and more steep,the downward trend is very obvious.And the better the limestone crystal structure,the smaller the change of activation energy.Besides,the change of CO₂ concentration has little effect on the change of decomposition energy of better crystal structure limestone.On the contrary,the worse the crystal structure is,the greater the change of activation energy.Limestone Calcination in the atmosphere of CO₂,the reaction contact area is large,and the decomposition rate is higher than the air atmosphere,the decomposition time is short.All these matters affect the process of recrystallization in the decomposition,and then changes the surface morphology of the decomposition products.The micro-surface of the calcined products of limestone with higher crystallization degree is relatively compact than the loose structure limestone.When the crystal structure of limestone is bad,and the structure of the product is completely loose under the same conditions,and the porosity is very high.During the heating process,the original CaCO₃ diffraction peak in the limestone shifted to the left,the 2θ becomes smaller,and the crystallinity and the grain size increased due to the lattice expansion.The larger the crystallinity,the smaller the increase in the grain size of the limestone,whereas the larger the grain size increases.The grain size and crystallinity of the decomposition products（CaO）during the decomposition process are in the same order of that of the original limestones.The higher the degree of crystallization of limestone,the decomposition process of the CaO crystallinity and grain size changes are relatively small.