Study On Thermal Decomposition Characteristics And Kinetics Of Cement Raw Meal Under O₂/CO₂ Atmospheres

In China, the CO2 emission of cement industry increases with years, which is second only to the power industry. So it is imperative to reduce the CO2 emission in the cement industry. The concentration of CO2 is highly in the flue-gas during the production of cement, which is much higher than that of coal-fired power plant. It provides an objective condition for CO2 abatement by using O2/CO2 combustion technology in cement industry. However, when large amounts of N2 in air atmosphere being replaced by CO2 during the conventional cement production process, the specific heat capacity, convective heat transfer and radiation characteristic of flue-gas in the precalciner would be changed significantly. Additionly, the reaction balance about cement raw meal decomposition would be changed on account of high concentration of CO2. This might cause obvious effects on the thermal decomposition characteristics and kinetics of cement raw meal. Therefore, it is essential to conduct the experimental study on thermal decomposition characteristics and kinetics of cement raw meal under O2/CO2 atmospheres in the precalciner.In this paper, the thermogravimetric analyzer was used to study the thermal decomposition characteristics and kinetics of cement raw meal under linear temperature program at first.The constituent factor of raw meal which exerts the major influence on the decomposition of raw meal was examined by experiments. The impacts of atmosphere and heating rate on the thermal decomposition characteristics of raw meal were also investigated and the non-isothermal kinetics analysis about raw meal decomposition was carried out. The experimental results demonstrated that the limestone is the main constituent factor affecting raw meal decomposition. O2/CO2 atmosphere exerted an inhibiting influence on the decomposition of raw meal compared with 21%O2/79%N2, which gave rise to higher decomposition temperature shifts in O2/CO2 atmospheres. But the increase of reaction temperature promoted the decomposition of raw meal significantly. The decomposition mechanism of cement raw meal in 21%O2/79%N2 was the phase boundary reaction with contracting model. But the reaction mechanism of raw meal in 21%O2/79%CO2 was found to follow the random nucleation and nucleus growth model.Moreover, the thermal decomposition characteristics and kinetics of raw meal under isothermal condition were studied in the tube furnace experimental platform. The effects of atmosphere and temperature were investigated, and the isothermal decomposition kinetic parameters of raw meal were calculated.This study showed that CO2 partial pressure inhibited the decomposition of raw meal observably, which produced a delay in the time required to decompose.The decomposition rate was increased remarkably by the enhancement of reaction temperature. The decomposition mechanisms of cement raw meal under isothermal condition in two different atmospheres tend to be the random nucleation and nucleus growth model.Finally, the differences on decomposition characteristics and kinetics of raw meal under two kinds of experimental conditions were briefly analyzed. Under different experimental condition, O2/CO2 atmosphere has an inhibiting effect to the decomposition of raw meal, and the increasing reaction temperature promotes the decomposition of raw meal significantly. The different thermal state and decomposition rate caused by different experimental conditions could result in the difference of kinetic parameters.