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Title:
低阶煤热破碎特性及其半焦富氧燃烧反应特性研究
Author: 沈国栋
Degree Level: 硕士
Issued Date: 2016-05
Degree Grantor: 中国科学院大学
Place of Degree Grantor: 北京
Supervisor: 王志奇 ; 王辉
Keyword: 低阶煤 ; 半焦 ; 热破碎 ; 富氧燃烧 ; 动力学
Subject: 工学
Alternative Title:
Major: 化学工程
Abstract: 煤炭在我国国民经济和社会发展中占有极其重要的地位,我国以煤为主的能源结构在未来几十年内不会发生根本性改变。随着我国能源需求日益旺盛以及高品质煤资源的逐渐减少,低阶煤的利用逐渐提上日程,如何经济、高效地利用低阶煤资源显得尤为重要。 中科院战略先导专项“低阶煤清洁高效梯级利用关键技术与示范”中提出了“以高效热解技术为先导,先提取煤中业已存在的油气资源,再将半焦燃烧、或经气化定向转化为液体燃料和化学品”的技术路线,“半焦/煤的清洁高效燃烧”是其中一个重要的研究内容。循环流化床燃烧技术是目前国际公认的商业化程度最好的煤或半焦燃烧技术之一,同时也是低阶煤焦高效燃烧首选的装置之一。低阶煤及其半焦在利用循环流化床技术进行燃烧时,颗粒的破碎特性会对床内物料浓度分布产生很大影响,进而影响床内的物料浓度分布,是流化床设计、运行必须要解决的技术问题。另外,低阶煤半焦富氧燃烧及高氧燃烧反应特性研究可为低阶煤半焦流化床燃烧技术提供基础数据,进而为工程放大奠定基础。本文以上述专项提出的路线为基础,开展了低阶煤热破碎特性及其半焦富氧燃烧反应特性的探索研究。选取神木褐煤和神木烟煤两种我国典型的低阶煤为研究对象,首先研究了两者的热破碎特性,然后在不同热解温度下制得各种低阶煤的半焦,考察了各种半焦在不同氧浓度条件下的燃烧反应特性,并进行了反应动力学分析,同时探索了不同气氛对半焦燃烧特性的影响。 利用管式炉平台研究了两种低阶煤的热破碎特性。实验结果发现,粒径为1.0 mm ~ 5.0 mm的褐煤、烟煤在600°C ~ 800°C温度下均发生了一定程度的破碎。低阶煤的热破碎程度与煤阶、粒径大小及温度等因素有关。在研究范围内,煤阶越低、原煤颗粒越大、温度越高,原煤发生的热破碎越剧烈。 利用热重平台研究了不同制焦温度下制得的低阶煤半焦在不同气氛、不同氧气浓度下富氧燃烧反应特性。结果表明,随着烟煤制焦温度的提高,所制得半焦的燃烧失重曲线往高温区移动,燃点、燃尽点均有不同程度升高,反应难度逐渐增大。不同气氛下,半焦富氧燃烧特性也有所差异,CO2、Ar、N2三种气体密度和热扩散系数的不同可能是原因所在。而当氧气浓度大于40%时,三种气氛下半焦燃烧曲线基本重合,特征温度差距也变得很小。因此,当氧气浓度大于40%时,氧化反应速率迅速增大,而因气体物理特性差异产生的影响减弱,不同气氛对半焦燃烧反应特性基本没有影响,可以将三种不同气氛作为一种燃烧气氛。不同氧浓度下半焦的燃烧特性分析表明,随着氧气浓度的升高,半焦燃烧的燃点、燃尽点均降低,提高氧气浓度可以促进半焦燃烧反应进行。燃烧反应的动力学分析结果表明,半焦富氧燃烧符合D6模型的固相反应机制函数,并计算得到了表观活化能E和指前因子A,同时发现不同氧气浓度下半焦燃烧反应之间存在动力学补偿效应,单凭活化能的变化来评估半焦燃烧反应的动力学特性是不合理的。
English Abstract: Coal plays a very important role in the national economic and social development of China. The present situation that consumption of coal occupies a dominant position in energy consumption can not be fundamentally changed in the next few decades. With the gradual reduction of high-rank coal and the increasing demand for energy, the use of low-rank coal is gradually put on the agenda. How to cost-effectively utilize low-rank coal resources is very important. "Demonstration of key technologies for clean and efficient utilization of low-rank coal”, sponsored by strategic priority research program of the Chinese Academy of Sciences, proposed the route that "Firstly extract oil and gas resources in the existing coal by efficient pyrolysis technology, then the surplus char can be used for combustion or conversion to liquid fuels and chemicals via gasification". Clean and efficient combustion of char/coal” is one of the important researches in this technical route. Circulating fluidized bed combustion technology is one of the most successfully commercialized combustion technologies for coal or char. When the low-rank coal and char are used in the technology of circulating fluidized bed combustion, fragmentation characteristics of particles will influence the material density distribution in the bed, which should be solved for the design and operation of circulating fluidized bed. In addition, the studies of oxy-fuel combustion and oxy-enriched combustion reaction characteristics for low-rank coal char can provide basic data for the fluidized bed combustion technology of low-rank coal char, and thus lay the foundation for engineering amplification. In this paper, the characteristics of low-rank coal’ thermal fragmentation and oxy-fuel combustion reactivity of low-rank coal chars were studied. Shenmu lignite and Shenmu bituminous coal, two kinds of typical Chinese low-rank coal, were selected as the experimental samples to study the thermal fragmentation characteristics. Then different kinds of low-rank coal chars were prepared at different pyrolysis temperatures to explore their oxy-fuel combustion characteristics. The effects of different atmospheres (CO2, N2 and Ar) and different oxygen concentrations on the combustion characteristics were studied in detail, and kinetic analysis of the combustion profiles of the coal chars with different oxygen concentration was also performed. The thermal fragmentation of two kinds of low-rank coals were conducted using a tube furnace platform. Experimental results showed that fragmentation occurred among lignite and bituminous coal for their particle size from 1.0 mm to 5.0 mm at a pyrolysis temperature from 600 °C to 800 °C. Thermal fragmentation of low-rank coals was exacerbated by the decreasing of coal rank, increasing of coal particle size and the increasing of temperature within the present investigation conditions. Oxy-fuel combustion characteristics of the low-rank coal chars obtained under different pyrolysis temperatures were studied with different atmospheres and different oxygen concentrations using thermal-gravimetric analyzer. The results showed that the TG curve of chars shifted to high temperature zone with increasing the preparation temperature of char, and both ignition temperature and burnout temperature increased accordingly. This means that higher preparation temperature of char does not favor the combustion reaction. Oxy-fuel combustion characteristics of chars were also different by changing atmospheres. And the differences of density and thermal diffusivity among CO2, Ar and N2 may be the reason. When the oxygen concentration was greater than 40%, gaps among TG curves of char combustion under three different atmospheres became very small, and the values of characteristic temperature were almost at the same level. With a higher oxygen concentration, the oxidation rate increases drastically and plays a dominant role, and the difference of the gas’s physical property has hardly influence on the char combustion characteristics. Thus, when the oxygen concentration is greater than 40%, three different atmospheres studied can be treated as one kind of atmosphere for char combustion. Char combustion characteristic analysis under different oxygen concentrations showed that ignition temperatures and burnout temperatures were reduced with increasing oxygen concentration. The kinetic analysis showed that the oxy-fuel combustion reaction of the chars conformed to D6 model of solid phase reaction mechanism function, and then the apparent activation energy E and the pre-exponential factor A were calculated based on the D6 model. Furthermore, it was found that kinetic compensation effect presented between the char combustion reaction under different oxygen concentrations. So the judge of reaction reactivity for char combustion just by activation energy is unreasonable.
Language: 中文
Department: 热化学转化事业部
Available Date: 2016-07-01
DOC Type: 学位论文
Content Type: 学位论文
URI: http://ir.qibebt.ac.cn/handle/337004/9781
Appears in Collections:热化学转化团队_学位论文

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Recommended Citation:
沈国栋. 低阶煤热破碎特性及其半焦富氧燃烧反应特性研究[D]. 北京. 中国科学院大学. 2016.
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