基于烧结机制的钙基吸收剂团聚体结构演变模拟

Simulation of Aggregate Structure Evolution of Calcium-Based Absorbent Based on Sintering Mechanism

钙循环工艺是一种具有很大应用潜力的脱碳技术,但其吸收剂晶粒间的烧结现象会随循环而加剧,导致高活性介孔及相应碳捕集能力衰减。根据煅烧进程中钙基吸收剂表界面结构的形成与演变特性,构建了再生CaO孔隙通道的拓扑结构和分级团聚体烧结模型,引入了二面角的影响,探讨了不同烧结机制下钙基吸收剂的孔隙迁移规律,并进行实验验证。结果表明,再生CaO的烧结由表面-晶界-体积扩散联合控制;所建数学模型可揭示钙基吸收剂孔结构动态演变规律,900℃不同烧结时间下(300~600 s),粒径75~150μm的吸收剂(孔径25~75 nm)的模拟计算结果与实验结果的孔体积变化率最大平均相对误差为16.50%,最可几孔径所对应的相对误差在6%内。相同烧结条件下,各粒级吸收剂(38~75、75~150、150~180μm)的烧结颈生长出现明显的三段式生长,颈部生长率均呈前期快速增长、后期平缓趋势,且颗粒间的烧结会随吸收剂粒极的减小而加剧。

Calcium cycling is a kind of decarbonization technology with great potential application,but the sintering phenomenon between the grains of the absorbers will be intensified with the cycling,resulting in the decay of mesopores and the carbon capture capacity.According to the formation and evolution characteristics of the surface and interface structures of calcium-based absorbent during calcination,the topological structure of regenerated CaO pore channels and the sintering model of hierarchical agglomerates are constructed.The influence of dihedral angle is introduced,and the pore migration rule of calcium-based absorbent under different sintering mechanisms is discussed and verified by experiments.The results show that the sintering of regenerated CaO is controlled by surface-boundary-volume diffusion.The mathematical model reveals the dynamic evolution of pore structures of calcium-based absorbers.The maximum average relative error of absorbers with diameters of 75~150μm(pore diameters of 25~75 nm)between simulation and experimental results at 900℃and different sintering time(300~600 s)is 16.50%.The relative error corresponding to the maximum aperture is within 6%.Under the same sintering conditions,the neck growth of each particle grade(38~75,75~150,150~180μm)shows obvious three-stage growth,and the neck growth rate shows a rapid growth in the early stage and a gradual trend in the late stage,and the sintering between particles would intensify with the decrease of the particle pole of the absorber.