【作者】 许慎启；

【导师】 于广锁；

【作者基本信息】 华东理工大学 ， 化学工艺， 2011， 博士

【摘要】 煤气化动力学作为煤气化技术的基础,其研究的深入与否,直接影响到煤的洁净转化和利用,掌握各种因素对煤气化反应的影响并建立准确的动力学模型,对解决煤气化技术面临的一些问题具有重要意义。因此,研究煤气化动力学具有重要的意义。本论文研究的目的在于掌握中国典型煤种及气化渣中残碳在高温高压条件下热解及气化反应过程中的物理和化学结构变化,探讨煤焦在复杂气氛下的反应规律及机理,建立适应于高温高压不同反应气氛的气化反应动力学模型,为开发适合中国煤种的大规模高效气化技术提供理论依据和基础数据支持。本文以中国典型煤种(神府煤、北宿煤、淮南煤和贵州煤)及其气化残渣为研究对象,研究高温高压条件下煤焦与CO2、水蒸汽的气化反应规律、影响煤焦气化反应活性的因素,探寻煤焦的气化反应活性与煤种之间的定量关系,建立煤焦气化反应的动力学模型；探讨气化渣中残碳的气化反应特性、及渣/灰的熔融对煤焦气化反应的影响。主要研究内容可分为如下几点：(1)考察了热解温度、热解速率及灰的熔融对煤焦孔隙结构的影响。根据四种典型煤种及其煤焦的N2吸附／脱附等温线的类型可知：原煤颗粒以层状孔为主,快速热解煤焦以筒状孔为主,而慢速热解煤焦以瓶状孔为主。灰的熔融特性显著影响慢焦的孔隙结构,堵塞煤焦的部分孔隙,降低煤焦的比表面积,而快焦的孔隙结构受挥发分的影响更为显著。通过CO2吸附分析得到的原煤及煤焦的微孔比表面积远大于由N2吸附分析得到的大中孔比表面积。煤焦孔隙结构特点是：0-1nm的微孔为主,2-200 nm的大中孔为辅。运用分形维数描述了煤焦的孔隙及表面特性。(2)建立了煤焦气化反应的正态分布模型,能较好地描述煤焦的气化反应速率随时间的变化关系。研究了高温高压下神府、贵州和淮南煤焦与CO2、水蒸汽的气化反应；考察了不同分压下CO和H2对煤焦气化反应的抑制作用；通过L-H模型和幂函数模型对煤焦的气化反应动力学数据拟合,得到了煤焦气化反应的L-H模型和幂函数模型参数。(3)定量分析了煤焦的气化反应活性与原煤中固定碳、挥发分、灰分及灰分组成之间的关系,煤焦-CO2和煤焦-水蒸汽气化反应与原煤组成的关系存在一致性。将煤焦的气化反应性与煤种组成相关联,定义了反应特性常数Rc=(Vm)/(FC)·B·100,建立了煤焦的气化反应活性和煤种之间的定量关系,可由式R0.5=A·RcD表示。为判别煤种气化反应活性的优劣,提供了一个简单而实用的准则。(4)考察了粒度对煤焦气化反应的影响,并采用缩芯反应模型对煤焦-CO2和煤焦-水蒸汽的气化反应过程进行了分析。在850-1000℃,四个粒度范围(20-40目、60-80目、100-120目和大于325目)的煤焦与C02、水蒸汽气化反应均为化学反应控制。在低温化学反应控制区,得到了煤焦-C02和煤焦-水蒸汽气化反应的表观活化能,分别为148-171 kJ/mol和149-190 kJ/mol;在高温扩散控制区,分析了粒度对煤焦气化反应的影响。(5)研究了碱金属Na和K对煤焦的气化催化作用；在热解阶段,碱金属的存在导致更加无序的碳微晶结构的形成,生成煤焦的气化反应活性更好。定量地表示了碱金属在热解和气化阶段对煤焦气化催化作用的贡献。将煤焦的催化气化反应定义为催化反应和非催化反应的共同作用,建立了煤焦的催化气化反应模型,模型能较好地描述煤焦的催化气化反应过程；通过气化动力学参数△rcg,0,可判定气化催化作用的大小(6)以多组气流床煤气化的粗渣和细渣为对象,着重研究干粉煤气化生成的粗、细渣残碳的气化反应活性,并与由滴管炉快速热解制得的煤焦的气化反应活性进行了比较；结合SEM和XRD/EDX,深入研究了影响渣中残碳气化反应活性的主要因素,如渣的表面孔隙结构及渣中残碳的石墨化程度、矿物质晶体存在形式等。粗渣含有的具有催化作用的金属元素Al、Ca、Fe和Mg较细渣丰富,以及碳的石墨化程度较细渣低是粗渣残碳的气化反应活性高于细渣的主要原因。(7)将原煤与气化渣和煤灰以不同比例混合,在渣/灰的熔融温度范围(950-1380℃),考察了渣/灰熔融特性对煤焦气化反应的影响。渣／灰熔融会堵塞煤焦的部分微孔,显著降低煤焦的比表面积,阻碍气化剂与煤焦颗粒的接触,抑制煤焦气化反应的进行。更多还原

【Abstract】 The study of coal gasification kinetics is the essential for the development of coal gasification technology. Gasification processes have been widely applied for coal utilization. Understanding the factors affecting the coal gasification and establishing proper kinetics model will be essential for designing an efficient gasifier and resolving the practical problems. The main purposes of this paper are investigating the changes of chemical and physical characteristics of coals during pyrolysis and gasification, studying the mechanism of coal char gasification under different reactive agents, establishing proper kinetics model and supplying valuable data for the development of coal gasification technology.Four types of Chinese coals and gasifier slag were chosen as experimental samples. The behavior of char-CO2 and char-H2O gasification and the factors affecting the char gasification reactivities were studied. The normal distribution model was established basing on the relationship between the gasification rate and residence time. Factors affecting the gasification of unburned carbon in gasifier slag have been investigated. Influences of melting slag/ash on char gasification were also studied. The main contents and results were summarized as follows:(1) Effects of pyrolysis on the pore structure of four Chinese coals were studied. Pyrolysis not only influences the specific surface area of chars, but also changes the shape of pores in coal particles. Adsorption/desorption isotherm indicated the possibility of existing slit pores, as the dominant forms of the pore structure for the original coal. The pore type was mainly composed of open cylindrical pore with one dead end for chars FP and bottle-shaped pores were dominating in chars SP. The melting ash very probably inhibited the development of inner porosities and surface morphology when coal particle was pyrolyzed in the slow heating rate at the range of AFT, while volatile matter plays more important roles on the formation of pore structure and surface morphology when pyrolyzed in rapid heating rate. Fractal theory was suitable to describe the pore structure and surface morphology of chars. Fractal dimension not only relates to pyrolysis temperature and heating rate, but also connects to the parent coal.(2) A normal distribution model was proposed to fit the kinetics data. Compared with the random pore model, results show that the normal distribution model can be used to describe the gasification rate changing with reaction time at different temperatures and pressures. The effects of CO, H2 and N2 on char-CO2 and char-H2O gasification reaction were investigated by TGA. nth model and Langmiur-Hinshelwood (L-H) model have been used to fit the reactivity data and kinetics parameters were obtained.(3) The reactivities of 15 coal chars of varying rank with CO2 and H2O have been determined to examine the effects of fixed carbon, ash and volatile matters on the gasification rate of coal chars. A universal correlation between the gasification reactivity of coal particles and coal types was presented. A general index,Rc=(Vm)/(FC)·B·100, which is used to indicate the gasification reactivity of coals with CO2 and H2O was present. Rc depends only on the proximate analysis and ash composition of coal and reflects the gasification behavior in a combined way, so that Rc is called the gasification index of coal.(4) The shrinking unreacted model is applicable for describing Shenfu char gasification. Influences of particle size on char gasification were investigated. At temperature 850-1000℃, the char-CO2 and char-H2O gasification are both controlled by chemical reaction. The apparent activation energies of char-CO2 and char-H2O gasification are 150-170 kJ/mol and 150-190 kJ/mol, respectively. The effects of pore diffusion on char gasification were analyzed at higher temperature range.(5) The catalysis of AM on coal gasification happened not only in gasification phase but also in pyrolysis phase. AM inhibited the progress of graphitization of the base carbon making the crystalline carbon structure more disorder and thus resulting in more reactive char. The kinetic model of catalytic gasification was established, which is suitable to describe the gasification rate changes in the char conversion for catalytic gasification of char.(6) CO2-gasification reactivity of unburned carbon in both coarse and fine slags was studied in a pressurized thermogravimetric analyzer (TGA) and compared with a char obtained from a drop tube furnace (DTF) at 1400℃from the same original coal. Unburned carbon in coarse slag has the highest gasification rate which is always higher than that of corresponding fine slag. The existence of minerals has catalysis on the CO2-gasification of unburned carbon in coarse slag, but inhibits CO2-gasification in fine slag. DTF char has the lowest reactivity, compared to unburned carbon in both coarse and fine slags. Higher ordering of carbon layers and lower content of catalytic mineral components may be the main reasons for the lower reactivity of the unburned carbon in fine slag than that of in coarse slag.(7) The gasification of the mixture of raw coal with corresponding ash/slag from entrained-flow gasifier was investigated in the range of ash/slag melting temperature (950-1380℃). The influences of coal ash and slag on coal gasification were investigated. It was found that gasification rate have more to do with the ash/slag melting characters of coal when gasified at relative higher temperatures.更多还原