Experimental And Process Simulation Study On The Decomposition Characteristics Of Cement Raw Meal Under High CO₂ Concentration Atmosphere

The cement industry is the second largest source of carbon emissions after the power industry and is under enormous pressure to reduce carbon emissions under the carbon peaking and carbon neutrality policy.However,with the continuous improvement of the new dry process cement production process and the increasing energy efficiency of cement plants,the potential to further reduce CO₂ emissions by improving the efficiency of cement raw meal decomposition is extremely limited.The use of a high concentration CO₂ atmosphere for the decomposition of cement raw meal can achieve a CO₂ concentration of over 90%at the tail end of the precalciner,creating favourable conditions for subsequent CO₂ capture,purification and compression,thus achieving near zero CO₂emissions from cement production.However,the decomposition characteristics,reaction mechanisms and control mechanisms of cement raw meal in unconventional atmospheres such as high CO₂ concentration are still unclear,and the relevant technologies cannot meet the needs of engineering applications.To this end,four studies have been carried out on the physical and chemical properties of coal and cement raw meal,the decomposition characteristics of cement raw meal under high CO₂ concentration,the modelling and validation of the decomposition process of cement raw meal at an industrial scale of 5500t/d,and the regulation and evaluation of industry-scale cement raw meal precalciner operation under high CO₂ concentration conditions,with a view to providing guidance on the use of high CO₂ concentration atmosphere for cement raw meal decomposition in industrial precalciner.Firstly,industrial and elemental analyses of coal and cement raw meal were carried out to grasp the basic characteristics of the raw materials,and the decomposition characteristics and kinetics of cement raw meal were studied using a thermogravimetric analyser.The effects of different atmospheres and mass ratios of cement raw meal on the decomposition reactions were also analysed,the weight loss pattern of the decomposition process of cement raw meal under different operating conditions was discussed,and the kinetic characteristics and kinetic parameters of the decomposition reactions under different conditions were obtained.The results show that the activation energy of the raw meal decomposition reaction is much higher in a high concentration CO₂ atmosphere than in a conventional nitrogen atmosphere.As the oxygen concentration increases,the temperature corresponding to the start and end moments of the reaction moves towards the low temperature region,the maximum weight loss rate increases and the activation energy of the reaction gradually decreases.An experimental system for the decomposition characteristics of cement raw meal was established.Experiments on the decomposition characteristics of cement raw meal under different concentration CO₂ atmosphere,reaction temperature and mass proportion of cement raw meal were carried out using cement raw meal and coal provided by a cement plant in Guangxi.The effects of the above parameters on the conversion of gas and solid products in the decomposition reaction were investigated using a flue gas analyser,an X-ray diffraction analyser and an X-ray fluorescence spectrometer,and scanning electron microscopy（SEM）.The results show that an increase in the volume fraction of oxygen promotes the formation of CO₂,both in the nitrogen atmosphere and in the high concentration CO₂ atmosphere.The decomposition of the raw meal in the high concentration CO₂ atmosphere is inhibited due to the CO₂ partial pressure.With the increase of the reaction temperature,the phenomenon of secondary peaks in the CO₂ generation curve decreases,the total amount of CO₂ generation increases,the product pores and cracks are gradually developed and the pores fuse with each other.The decrease in the mass ratio of raw meal increases the concentration of CO₂ production,while the lack of oxygen supply due to the increase in pulverised coal leads to a longer decomposition time and the combustion ash prevents the decomposition gas from escaping from the raw meal surface.Based on a 5500t/d NST-Ⅰprecalciner of a cement plant in Guangxi,a model for the decomposition reaction of cement raw materials was constructed;at the same time,the simulation of the decomposition process of cement raw meal was carried out by combining the actual structure parameters and process parameters of the decomposition furnace of this Guangxi cement plant,and the simulation results were compared with the actual measurement data of the cement plant to ensure the accuracy and reliability of the constructed model for the decomposition reaction of cement raw meal.According to the developed reaction model,an industrial-scale simulation of the decomposition characteristics of 5500t/d cement raw meal was carried out to investigate the effects of high CO₂ concentration atmosphere,reaction temperature and mass ratio of cement raw meal on the decomposition characteristics of cement raw meal in an industrial precalciner under variable operating conditions.Based on the simulation results of the operation process of 5500t/d cement industrial precalciner,an operation regulation scheme for industrial precalciner under the condition of high CO₂ concentration was established,and the CO₂ concentration of the flue gas exit from the precalciner and the decomposition rate of Ca CO₃ in cement raw meal required for industrial operation were obtained by optimizing the operating parameters.Finally,a comprehensive evaluation system for the decomposition of cement raw meal under high concentration CO₂atmosphere is constructed.The evaluation of the decomposition characteristics of cement raw meal under different operating conditions is achieved by considering the CO₂ concentration of the outlet flue gas and the decomposition rate of Ca CO₃.The system provides guidance and suggestions for the operation and control of the precalciner under high CO₂ concentration atmosphere.