Abstract: The evolution characteristics of pore structure and reaction mechanism of limestone during decomposition were experimentally studied with nitrogen adsorption method, field emission scanning electron microscope and thermal gravimetric analysis. A bimodal distribution of probability density function and mathematical model describing the effect of pore structure on the effective diffusion coefficient was established, and the simulation results validated with the experimental data. The results show that the pore size distributions of calcined limestone in different decomposition stages all have a characteristic of bimodal distribution. The number of mesopore near the main peak of pore sizes about 3 nm increases with the solid conversion ratio and has a step type growth when the solid conversion ratio achieves about 60%. As the solid conversion ratio increases from 50.41% to 68.27%, the effective diffusion coefficient decreases from 0.0162 to 0.0093 cm2/s at 1073 K, which leads to an increase in the pore diffusion resistance affecting the decomposition mechanism of limestone. The critical solid conversion ratio corresponding to the reaction rate controlled by the mass transfer is 60% and 75% at 1073 and 1223 K, respectively.

Key words: limestone, thermal decomposition, pore structure, effective diffusion coefficient, reaction mechanism

摘要： 采用氮吸附、扫描电镜和热重分析法研究了石灰石煅烧分解过程中孔结构演变规律及反应特性，构建了双峰孔径分布概率密度函数与有效扩散系数计算模型，并与实验测量结果进行对比验证. 结果表明，石灰石不同分解阶段煅烧产物的孔结构皆为双峰分布，主峰3 nm附近小尺度中孔数随反应深化逐渐增多，在固体转化率达约60%时呈阶跃式增长；在1073 K煅烧固体转化率由50.41%增大到68.27%时，有效扩散系数由0.0162 cm2/s降至0.0093 cm/s，导致分解反应机理随之变化；在1073和1223 K煅烧温度下，反应机理转为传质控制，相应的临界固体转化率分别为60%和75%.

关键词: 石灰石, 热分解反应, 孔结构, 有效扩散系数, 反应机理