QQ客服 官方微博 反馈留言

题名	微型流化床复杂气固反应动力学研究
作者	刘文钊
学位类别	硕士
答辩日期	2012-05-25
授予单位	中国科学院研究生院
导师	高士秋 ;    许光文
关键词	反应动力学 微型流化床 氢氧化钙 二氧化碳捕集 多孔碳燃烧
其他题名	Kinetic Study on Complex Gas-Solid Reactions in a Micro Fluidized Bed
学位专业	材料工程
中文摘要	热不稳定物质和多孔物质的气固反应过程复杂，其动力学参数的准确测试难度大。热重分析仪(TGA)虽是目前最常用的动力学分析仪器，但难以直接测试热不稳定物质反应。针对多孔物质的强放热快速反应，TG反应皿温度不易控制，同时受到扩散抑制作用严重，导致测试结果偏离本征特性。本论文利用中国科学院过程工程研究所研制的微型流化床反应分析仪(MFBRA)，研究了热不稳定物质与多孔物质复杂气固反应动力学，对比了TGA测试结果。以Ca(OH)2捕集CO2为热不稳定物质反应的代表，发现MFBRA实现了对等温直接反应特性的测试，揭示了其经历中间产物Ca(HCO3)2的反应过程机理。在500-630 ℃，反应产物层的扩散抑制作用阻碍了Ca(OH)2颗粒的完全反应，且实现的最大反应转化率随反应温度升高而增加。而660-750 ℃，反应受热力学平衡控制，使实现的最大反应转化率随温度增加而降低。针对500-630 ℃间的反应，通过等温等转化率法计算求得的活化能随转化率变化而变化，将转化率从小变大的反应历程分解为快速升温，Ca(OH)2/CaO与CO2同时反应，CaO与CO2反应，内扩散/反应协同控制等几个反应区。根据数据计算得到Ca(OH)2与CO2的直接反应活化能为40 kJ/mol，实现了对热不稳定物质的直接反应的分析测试。 针对高比表面多孔活性炭燃烧的多孔物质快速反应，利用MFBRA和TGA分别考察了气速、颗粒粒径、炭种类和石墨化处理对反应特性的影响，在内外扩散抑制作用最小化的条件下分别测试了等温与程序升温过程粒径小于5 μm活性炭在700-1000 ℃的燃烧反应动力学数据。基于MFBRA测试的数据通过等温等转化率法求得：在低温段700-810 ℃的内扩散控制区反应活化能为90-100 kJ/mol，在高温段800-1000 ℃的外扩散控制区反应活化能为20-30 kJ/mol，揭示了反应表观活化能同时与反应阻力和扩散阻力相关联的特性，反应阻力越大，反应受扩散影响越小，表观活化能越大。结合模型函数拟合，发现随机孔模型较好地拟合了MFBRA测得的低温区700-810 ℃的活性炭燃烧数据，得到孔结构参数约0.17 m-3，反应活化能178 kJ/mol，约为受内扩散影响时求得的活化能的两倍，且与炭燃烧的本征反应活化能接近。
英文摘要	The gas-solid reactions of thermally unstable and porous materials have to involve complicated process of physical and chemical changes, and it is uneasy to estimate accurately their reaction kinetics. Although the thermogravimetric analyzer (TGA) has been widely used in studying the gas-solid reactions and their kinetic, it is hard to analyze the direct reaction occurring to thermally unstable solid materials. For the highly exothermic quick reactions occurring to porous materials, the cell temperature in TGA may be seriously affected by the reaction heat, while the reaction has to be greatly influenced by diffusion to cause the deviation of measurement from the intrinsic reaction. This study investigated such complex gas-solid reactions in the so-called micro fluidized bed reaction analyzer (MFBRA) developed by Institute of Process Engineering, Chinese Academy of Sciences, and the measured isothermal reaction kinetics were compared with the data obtained in commercial TGA. By taking Ca(OH)2 to typify the thermally unstable material, the reaction characteristics of Ca(OH)2 with CO2 were investigated in MFBRA and compared with the measurements in TGA. Using MFBRA it was successfully demonstrated that the reaction occurs via the formation of an intermediate product Ca(HCO3)2. At temperatures of 500-660 ℃, the formed product layer inhibited the reaction so that the Ca(OH)2 particle could not fully react with CO2. The realized highest conversion of Ca(OH)2 increased with raising temperature. At 660-750 ℃, the reaction is subject to the thermodynamic equilibrium control so that the realized highest conversion of Ca(OH)2 decreased with increasing temperature. Using the isothermal isoconversional method, the estimated activation energy from the data measured by MFBRA at 500-660 ℃ varied with the conversion, showing that the reaction process consisted of 4 periods：rapid heating，reactions of Ca(OH)2 and CaO with CO2，reaction of formed CaO with CO2, and diffusion-reaction compromised control. Based on the data for the second period, the activation energy for the direct reaction of Ca(OH)2 and CO2 was found to be 40 kJ/mol. The combustion of a high-surface-area carbon was investigated in both MFBRA and TGA to typify the methods for kinetic study on the highly exothermic reactions of porous materials. The effects of gas velocity, particle size, carbon species and graphitizing treatment were tested. With minimized internal and external diffusions, the combustion activation energy for sawdust activated carbon in 0-5 μm was calculated using the isoconversional method on the basis of the data from MFBRA. The activation energy at low temperature (700-810 ℃) was found to be 90-100 kJ/mol, while the activation energy at high temperature (850-1000 ℃) was 20-30 kJ/mol. The former shows certain effect of internal diffusional inhibition on the reaction, and the latter indicates the full control of the reaction by the external diffusion. Generally, the greater the reaction resistance, the less important the diffusion effect is, thus leading to higher value of the apparent activation energy. For the tested combustion reaction, using the random pore model to fit the isothermal reaction data obtained from MFBRA resulted in activation energy of 178 kJ/mol, and the corresponding structure parameter was about 0.17 m-3. This refers actually to the activation energy almost twice of the activation energy containing internal diffusion, but it is very close to the intrinsic activation energy for carbon combustion.
语种	中文
公开日期	2013-09-25
内容类型	学位论文
源URL	[http://ir.ipe.ac.cn/handle/122111/1823]
专题	过程工程研究所_研究所（批量导入）
推荐引用方式 GB/T 7714	刘文钊. 微型流化床复杂气固反应动力学研究[D]. 中国科学院研究生院. 2012.

个性服务

查看访问统计

相关权益政策

暂无数据

收藏/分享

除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。