脱硫CaO团聚体晶粒产物层内Ca^(2+)和SO_4^(2-)的扩散行为

The Diffusion Behavior of Ca^(2+) and SO_4^(2-) in CaO Sorbent Aggregate Crystal Production Layer

应用CaO团聚体晶粒双堆砌结构概念和晶体点缺陷扩散理论,研究了脱硫CaO团聚体晶粒的微观结构、硫化反应产物层内离子扩散的微观机制,并对产物层内2种固态离子扩散动力特性进行了模型计算。观察到团聚体晶粒一级气孔有效孔径<50nm,模拟分析发现,CaSO4产物层内存在固态Ca2+离子向晶粒表面迁移以及固态SO42-离子向晶粒深层渗透2种定向扩散流,产物层从晶粒边界向外生长形成纯CaSO4区域并受边界吸附反应制约而线性增厚,向内渗透则形成CaO和CaSO4的混合区,且CaSO4成分含量自外向内递减。研究结果表明:钙基脱硫剂硫化反应控制过程最终由气体扩散转换为固态离子扩散,2种固态离子扩散属于互扩散模式且扩散特性不同。

Applying the double-heaping structure conception of CaO and the crystal defect diffusion theory, the micro-structure of aggregate crystal and the microscopic ion diffusion mechanism in desulphurization production layer were presented, and the diffusion dynamic characteristics of two solid-state ions in the production layer were simulated. It could be seen from the SEM that the effective porous diameter of primary pore ranges 〈50 nm. The simulation results show that there are two directional flows in CaSO4 production layer, the first is the Ca2_ diffuse toward the crystal surface, the other is SO4^2- penetrate toward interior of crystals. The production layer which generated from the crystal boundary formed the pure CaSO4 region, and become thicker while affected by the boundary absorption reaction. Simultaneously, the production layer penetrates toward inner to form the mix region with CaO, in the mix region the CaSO4 content decrease from the outer to inner of the crystal. It could be drawn conclusions that the final desulphurization control process is the solid-state diffusion, the diffusion of the two ions belongs to interdiffusion pattern and has different diffusion properties.