孔隙结构对煅烧石灰石碳酸化反应影响研究

The high temperature carbonation reaction of calcium oxide with CO2 is of importance in a number of proposed applications. Ca-based sorbents have received increasing attention for these applications. The evolution and figure of the pore structure during these reactions are the key questions in the research of capture CO2 with Ca-based sorbent. Calcination and carbonation experiments, the express of pore structure and the model test are used in this project. The effect of calcination on the formation of pore, the regulation of carbonation in different condition and the effect of particle size on reactions are systematically studied. .The pore structure feature is investigated under different sorbent kind, particle size and reaction condition integrating with experimental data and kinetic models. The effect of the resistance, including chemical reaction, intraparticle diffusion of CO2 and interparticle diffusion of CO2, on the overall reaction rate is compared. These issues of controlling reaction are analyzed by the reaction dynamical model of calcination. Diffusion through the solid particle is known to depend strongly on the characteristics of the pore structure. The reaction dynamical model can combine the sintering model to describe the evolution of the pore structure of samples. The surface area value and porosity of limestone samples in simultaneous calcination and sintering process is determined by a combined model..The effect of pore structure on reaction rate and conversion is also showed in the different condition. The experiments of various conditions such as the temperature, the concentration of steam during carbonation were conducted in a thermogravimetric analyzer. The understanding of the regulation participating in the carbonation reaction can be arrived at through the use of model interpretations of the rate controlling process. The experimental data were analyzed by means of the random pore model. .The pore volume structure effect is tested in a TGA apparatus, with sorbents of various particle sizes. Chemical reaction and physical diffusion together determine the utility of sorbent. The ultimate capacity of calcined limestone is determined by the pore volume available for product accumulation. The observed variations in reactivity among various particle size limestones can be explained by differences in the pore structure character of their calcined products.Then, the pore structure models in the calcination and carbonation process are developed by incorporation of the pore diameter distribution and the pore length distribution to express the carbonation rate feature in various conditions.

钙基吸收剂与CO2的碳酸化反应既可用于燃烧前脱碳又可用于燃烧后脱碳。本项目将反应过程中的孔隙结构变化作为研究重点，在煅烧过程孔隙结构形成规律、气体扩散在碳酸化过程中影响规律和样品粒径对反应影响规律三个方面展开研究工作。利用煅烧动力学模型，结合实验测试结果，对比化学反应、CO2内部扩散和外部扩散三种控制速度因素对整体反应速度影响程度，揭示外在反应条件和样品粒径对孔隙结构影响规律。将水蒸气浓度、CO2浓度和粒径作为影响因素，利用随机孔隙模型分析碳酸化反应实验结果，着重分析CO2内扩散对石灰石样品反应速率和转化率的影响规律。针对样品粒径对煅烧石灰石碳酸化反应影响的一般规律，利用改进的煅烧模型模拟比表面积和孔隙率变化特征，与随机孔隙模型相结合，揭示孔隙结构在两个反应之间的耦合作用。本项目的研究工作，为理解孔隙结构的生成和作用规律提供理论依据，也为选择合理反应条件、提高样品利用率提供理论指导。

根据光线透过盐水溶液产生衰减原理，利用流场内密度与光照强度的对比关系，提出通过图像灰度确定流场内密度分布特征的测试方法。采用这种实验方法，结合单一点源羽流条件下卷吸作用，模拟由热压产生的置换流动和混合流动。对于无热源的置换流动实验，当出口面积保持在5.1cm2时，进口面积由28.9cm2增加到52.7cm2并不会显著增加体积流量。这表明对于置换通风，当进出口面积相差较大时，流量由进出口中较小的面积开口确定。对于有热源条件下置换流动，随着有效开口面积增加，热分层高度增加，且上部分层高度内的密度降低。实验数据显示，卷吸系数α取0.13时理论预测与实验结果一致。在有固定热羽流条件下进行了混合流动实验，确定流量修正系数ε等于2.21，该系数与开口大小和盐水密度无关，反映固定浮力通量与变浮力通量条件下通过开口流量的比值。.考虑羽流虚拟源点位置的影响，通过测量受限空间内随时间变化的羽流界面位置高度，确定纯羽流条件下卷吸系数，并利用有内热源条件下置换流动实验进行了验证。对两种计算虚拟源方法进行比较，Baines计算方法得到虚拟源位置受到模型长度和高度影响，Hunt的方法确定虚拟源位置仅是源条件的函数，卷吸系数确定过程中，Hunt的方法相比Baines的方法更为合适。根据源参数Γ与卷吸系数关系，利用插值法确定纯羽流即Γ=1时卷吸系数为0.0987。结合与文献中卷吸系数的比较，表明虚拟源点位置修正耦合受限空间羽流界面位置实验是一种确定卷吸系数的有效方法。.中庭是自然通风建筑的一种重要构成形式，可以利用热压作用增强楼层通风。通过理论分析，确定中庭结构增强楼层通风判据，当E>Eisolate时，中庭促进楼层通风；当E≤Eisolate时，中庭抑制楼层通风。通风加强参数E由中庭高度、太阳辐射、中庭上部开口面积确定，而楼层通风参数Eisolate仅与楼层有效面积有关。利用中庭建筑置换通风理论模型，分析中庭开口面积、太阳辐射强度和中庭高度对楼层和中庭界面高度、体积流量、折减加速度的影响，揭示建筑设计基本参数对中庭建筑通风的作用规律。