灰分沉积特性的理论和实验研究

发布时间：2017-12-26 23:19

本文关键词：灰分沉积特性的理论和实验研究　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：在大型循环流化床中掺烧煤泥、煤矸石等煤洗选加工废弃物不但能提高能源的综合利用效率,而且还能阻止其对大气、水质、土壤污染,具有显著的经济效益和环保效益。然而,已投产的锅炉运行实践表明,在炉膛内部、换热器表面或旋风分离器内表面、落料腿等部位发生的粘附、烧结、板结等灰分沉积现象,会腐蚀设备装置,显著降低锅炉效率,影响锅炉的稳定运行,严重时,会造成停炉停产,甚至带来安全隐患。探究灰分沉积的机理及其影响因素,从而提供减轻灰分沉积倾向的可行方案,对锅炉的稳定运行及新锅炉的设计都大有裨益,进而对洗选废弃物的处理、洁净煤燃烧技术提供支撑。灰分沉积本质上是一个复杂的含化学反应的高温气固两相流边界层问题。灰分沉积包括灰分的粘附、发展、烧结和熔融等过程。本文围绕灰分沉积过程的描述,沉积过程的实验模拟,运行参数、结构参数、物性参数和成分参数对灰分沉积特性的影响规律等,开展了相关的研究工作。本文第一章介绍了灰分沉积特性研究的应用背景和意义、灰分沉积的危害以及关于灰分沉积国内外研究的现状。本文第二章概述了研究灰分沉积特性的实验方法和实验平台。分别对灰熔点测定方法、微观样貌测定方法、灰分成分测量方法及自创的体积形变实验进行了详细的概述和总结。结合循环流化床锅炉灰分沉积的特点,搭建了灰分沉积实验平台。分别对灰分沉积实验平台的设计目标、主要部件构成、工作模式及适用范围作了详细阐述。极限工况实验表明,实验平台不能模拟出灰分沉积、熔融软化的现象,实验平台有致命的设计缺陷。其主要原因是加热元件的不能满足实验需求,灰分颗粒未能被加热到熔融或半熔融状态。最后,对试验炉平台加热系统改进、供料系统的可控性及沉积探针测量拆卸式探头的温度精度的提高等提出了改善性建议。本文第三章首先梳理了前人对沉积机理的探索,指出完备的沉积机理应该包含颗粒尺度模型、颗粒物性模型、颗粒碰撞模型、颗粒受力模型、颗粒输运过程以及颗粒沉积判据。随后,分别对沉积输运模型、颗粒受力模型、及沉积判据等做出了概述性总结。特别地,在对颗粒沉积判据的总结中,得出沉积评价指标是基于结果导向的,每种指标只适用于特定的范围,需探索过程引导的微观颗粒的沉积判据。在气固两相流的受力分析及各种力的尺度等级分析基础上,结合沉积过程的具体现象,得出了不同粒径颗粒在沉积过程中的受力情况。最后,梳理了烟气飞灰颗粒从初始层的形成,到逐渐发展生长,沉积物形成过后内部形态的变化,及最终形成板结的沉积块的完备的沉积描述。本文第四章探究了硅铝比对灰分烧结特性的影响规律。以Si02-Al203-MgO-Fe203-Ca0为原料,制备了五种不同硅铝比的合成灰分样品。在马沸炉中对不同硅铝比的灰分样品进行处理,让样品在马沸炉中存留12小时,以制成烧结样品。综合运用VSR、DIL、SEM、XPS及XRD的实验结果描述了烧结样品的形貌特征及化学成分特征。实验结果表明,烧结过程主要发生在温度超过1000℃的第三阶段,伴随着VSR曲线显著降低。过量的SiO2(S/A=0.45)会导致多孔结构而过量的Al2O3(S/A=0.5)会产生大颗粒团聚物并阻碍共晶体的生成和发展。其他三组样品(S/A=1.5,2.5,3.5),烧结后具有致密的非晶体结构,主要由低熔融温度的共晶体组成(例如辉石、瓦兹利石)。随着硅铝比的增加,烧结温度首先急剧下降到较低水平,然后逐渐上升到一个相对较高的水平。实验结果表明,在灰分中添加富含A1203的添加剂比添加富含Si02成分的添加剂对于减轻灰分的沉积现象更为有效。本文第五章探究了煤灰成分与软化温度之间的关系。在本章中,实验所用的灰分为合成煤灰。选取48种不同成分的煤灰软化温度,运用二元回归分析方法,建立软化温度与酸碱比和硅铝比之间的经验模型。热变形分析方法所测得的软化温度以及X射线衍射所测量的晶体成分,用于验证模型的有效性。实验结果表明,合成煤灰软化温度与晶体成分的实验结果与经验模型吻合,由此可认为,经验模型是合理的。本文第六章对本论文工作进行了总结,提出了关于灰分沉积特性研究有待进一步探究的课题。
[Abstract]:In large circulating fluidized bed, coal washing and processing waste such as coal and coal gangue can not only improve the comprehensive utilization efficiency of energy, but also prevent it from polluting the atmosphere, water and soil, which has significant economic and environmental benefits. However, the practice shows that the boiler operation has been put into operation, and in the internal surface of the heat exchanger or cyclone inner surface, blanking leg occurred adhesion, sintering, compaction and other ash deposition, corrosion equipment, significantly reduce the efficiency of the boiler, affect the boiler stable operation, serious, will cause the stop furnace production, and even bring security risks. To explore the mechanism and influencing factors of ash deposition, so as to provide a feasible plan to reduce the tendency of ash deposition, which is beneficial to the stable operation of boiler and the design of new boiler, and to provide support for the treatment of cleaning waste and the technology of clean coal combustion. The ash deposition is essentially a complex boundary layer of high temperature gas-solid two-phase flow with chemical reactions. Ash deposition includes the process of adhesion, development, sintering and melting of ash. This paper focuses on the description of ash deposition process, experimental simulation of deposition process, operation parameters, structural parameters, physical parameters and composition parameters on the influence of ash deposition characteristics. In the first chapter, the application background and significance of the study on ash deposition characteristics, the harm of ash deposition and the status of the research on ash deposition at home and abroad are introduced. The second chapter of this paper gives an overview of the experimental and experimental platform for the study of ash deposition characteristics. The ash melting point determination method, microscopic appearance measurement method, ash composition measurement method and self created volume deformation test were summarized and summarized. In combination with the characteristics of ash deposition in a circulating fluidized bed boiler, an experimental platform for ash deposition is set up. The design objectives, main components, working mode and scope of application of the ash deposition experimental platform are described in detail. The experiment shows that the experimental platform can not simulate the phenomenon of ash deposition and melt softening, and the experimental platform has fatal design defects. The main reason is that the heating element can not meet the needs of the experiment, and the ash particles can not be heated to the melting or semi melting state. Finally, suggestions for improvement of the heating system of the test platform, the controllability of the feeding system, and the improvement of the temperature accuracy of the probe with the probe of the dismantling probe are put forward. In the third chapter, we first summarize the previous exploration of sedimentary mechanism, and point out that the complete sedimentary mechanism should include particle size model, particle physical model, particle collision model, particle force model, particle transport process and particle deposition criterion. Then, the sedimentary transport model, the particle loading model and the sedimentary criterion are summarized. Especially, in the summary of the criterion of particle deposition, it is concluded that the evaluation index of sedimentation is based on result oriented, and each index is applicable to a specific range, and we need to explore the sedimentary criterion of microscopic particles guided by the process. Based on the force analysis of the gas-solid two-phase flow and the scale analysis of all kinds of forces, combined with the specific phenomena of the deposition process, the forces acting on different particle sizes during the deposition process are obtained. Finally, the formation of flue gas ash particles from the initial layer to the gradual growth and development, the change of the internal morphology after the formation of the sediments, and the complete deposition description of the final forming of the deposition blocks are combed. In the fourth chapter, the influence of silicon and aluminum ratio on ash sintering characteristics is investigated. Five kinds of synthetic ash samples with different Si / Al ratios were prepared with Si02-Al203-MgO-Fe203-Ca0 as raw material. To deal with the different silicon aluminum ash samples than in muffle furnace, let the sample remain 12 hours in boiling, to produce sintered samples. The experimental results of VSR, DIL, SEM, XPS and XRD were used to describe the characteristics of the morphology and chemical composition of the sintered samples. The experimental results show that the sintering process mainly occurs in the third stage of the temperature over 1000 degrees C, with the VSR curve decreasing significantly. Excessive SiO2 (S/A=0.45) can lead to porous structure and excessive Al2O3 (S/A=0.5) produces large particle agglomeration and hinders the formation and development of eutectic. The other three groups of samples (S/A=1.5,2.5,3.5), sintered with dense amorphous structure, mainly consist of eutectic with low melting temperature (such as pyroxene and Waziri S). With the increase of the ratio of silicon and aluminum, the sintering temperature drops sharply to a lower level, and then gradually rises to a relatively high level. The experimental results show that adding A1203 rich additives in ash is more effective than adding additives rich in Si02 components to reduce the deposition of ash. The fifth chapter of this paper explores the relationship between the composition of the coal ash and the softening temperature. In this chapter, the ash used in the experiment is synthetic coal ash. The softening temperature of 48 different components is selected and the empirical model between the softening temperature, the ratio of acid to base and the ratio of silicon and aluminum to the ratio of softening and alkali to the ratio of silicon and aluminum is established by the two element regression analysis. The softening temperature measured by the thermal deformation analysis method and the crystal composition measured by X ray diffraction are used to verify the validity of the model. The experimental results show that the experimental results of the fly ash softening temperature and crystal composition are in agreement with the empirical model, thus the empirical model is reasonable. The sixth chapter of this paper is a summary of the work of this paper, and the subject of further research on the research of ash deposition characteristics is put forward.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ530

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