烟气氛围下富碳材料中纳米孔隙的形成及演变机制研究

A novel method for powdered semi-coke preparation by fast pyrolysis of pulverized coals under flue gas atmosphere is proposed, which is based on the difference of pore formation characteristics caused by coal char ablation with O2, H2O and CO2. Nano-pore is the main space of SO2 adsorption and occurrence of the oxidation product H2SO4 in active cokes; therefore, it is important to study the mechanisms on formation and evolution of nano-pore structures in carbon-rich materials under flue gas atmosphere. First, the highly oriented pyrolytic graphite (HOPG) is used as the research object, and a visual characterization of the nano-pores’ origin, evolution and distribution on the carbon surface is conducted using atomic force microscope (AFM). Then, the mechanism of formation and evolution of nano-pore structures on the carbon surface under flue gas atmosphere can be concluded. Second, four typical coals are used to prepare the semi-cokes by fast pyrolysis on a drop tube furnace under different atmospheres. The fast pyrolysis behaviors of different coals under flue gas atmosphere are studied and the influence of the behaviors above on the formation and evolution of nano-pore structures is also investigated. Based on the mechanism above, the regulation method of semi coke pore structure can be explored. Finally, a pore structure evolution model based on coal chemical reaction kinetics is established. It could predict the pore structure parameters of product semi-cokes prepared under flue gas atmosphere. This study will provide basic data and theoretical guidance for the in-situ preparation of active cokes in a coal-fired power plant.

利用O2、H2O和CO2对煤焦烧蚀成孔特性的差异，提出调制烟气活化、煤粉快速热解制备烟气脱硫用粉状半焦的新方法。纳米孔隙是活性焦吸附SO2及赋存氧化产物H2SO4的主要空间，研究烟气（低氧多组分活化气体）氛围下不同碳材料纳米孔隙形成及演变机理十分重要。本项目首先以高定向热解石墨为研究对象，采用原子力显微镜对不同活化气体氛围下得到的多孔石墨碳表面纳米孔隙的源发点、分布及演变进行直观表征，阐释烟气氛围下碳表面纳米孔的形成及演变过程及机理。然后，以四种典型煤为研究对象，考察不同煤种在烟气氛围下的快速热解行为及其对煤焦中纳米孔隙形成和演变过程的影响，探寻产品半焦孔隙结构的调控方法。最后，建立基于原煤反应动力学的孔隙结构演化模型并进行验证与优化，为烟气氛围下快速热解半焦的孔隙参数预测提供方法。本项目研究将为燃煤电厂脱硫活性焦的炉前制备工艺提供基础依据和理论指导。

本项目利用氧气、水蒸气和二氧化碳等活化气体对煤焦烧蚀成孔特性的差异，提出了调质烟气活化、煤粉快速热解制备烟气脱硫用粉状活性半焦的新方法，而烟气氛围下不同碳材料纳米孔隙形成及演变机制是制焦新方法的科学基础。. 本项目研究阐释了石墨碳表面烧蚀孔隙形成及演变过程。高定向热解石墨（HOPG）的表面烧蚀孔隙呈现多层嵌套阶梯状结构，孔隙边缘有杂原子，表面孔隙主要从反应活性较高的缺陷处产生，在相联系的层上沿着边缘不断扩展，当下层石墨的缺陷产生或暴露时会进一步向下层扩展，产生了层状孔隙。. 本项目研究明确了不同煤种在典型烟气氛围下的快速热解行为及其与煤焦孔隙结构的关联。蒙东褐煤、兖矿烟煤和贫煤在烟气氛围下快速热解制备半焦的孔隙结构受到温度、当量系数、气氛中的氧气浓度、水蒸气浓度和二氧化碳浓度等参数的影响。各影响因素对不同煤种制备半焦的孔隙结构的作用机制不同，可通过上述参数的调整来调控半焦的孔隙结构，找到了不同煤种制备半焦具有最佳孔隙结构（对应半焦的最佳SO2吸附性能）的操作参数。. 本项目研究建立了基于原煤烧失的孔隙结构演变的经验关联。半焦微孔比表面积和微孔孔容积随着烧失率的增大呈现先增大后减小的规律，存在最佳的烧失率范围，对应半焦具有最发达的微孔结构。半焦SO2吸附容量与微孔比表面积和微孔孔容积均呈正相关性。对半焦孔隙进行了分形维数分析，建立了半焦分行维数与制焦参数、孔隙结构参数及其SO2吸附容量之间的关联。. 本项目研究结果将为煤粉制备烟气脱硫用粉状活性焦技术提供重要的理论依据和基础数据支撑，具有一定的应用价值。