【作者】 孟巧荣；

【导师】 赵阳升；

【作者基本信息】 太原理工大学 ， 工程力学， 2011， 博士

【摘要】 煤的热解称为煤的干馏或热分解,煤热解的结果是生成气体(煤气)、液体(焦油)、固体(半焦或焦炭)等产品,煤气、半焦和焦油是洁净或改质燃料,这些燃料是石油天然气的替代品,又是很好的化工原料。用热解的方法生产洁净或改质的燃料,既可减少燃煤造成的环境污染,又能充分利用煤中所含的较高经济价值的化合物,具有保护环境、节能和合理利用煤资源的广泛意义。煤热解是煤转化的关键步骤,煤气化、液化、焦化和燃烧都要经过或发生热解过程。煤炭地下气化、低阶煤的热力改性、煤的原位热解和煤炭自燃都伴随煤的热解,而这些技术都是实现绿色煤炭的关键技术,热解取得的研究成果对这些关键技术都具有直接的指导作用。煤的热解反应发生在煤固体表面,许多表面是与孔隙裂隙结构相关联的,孔隙裂隙结构影响着煤的热解活性和反应性。综合考虑,热解过程中煤的孔隙裂隙结构变化研究不仅是煤的原位热解中的基础性研究,也是煤炭地下气化、液化和煤的改性提质等煤炭热加工技术的基础性研究,对我国煤炭的可持续发展意义重大。本课题通过对国内多种煤阶的大块度煤样进行热解实验,利用先进的CT225KvFCB微焦点CT扫描,重建其三维细观结构,分析热解温度对煤的细观孔隙裂隙结构的影响。主要研究内容及结果如下：1、利用μCT225KvFCB显微CT系统结合自制高温气氛炉,对(?)1mm的煤样进行扫描实验,研究不同温度下不同煤样的孔隙结构演化特征,得到如下结论：褐煤和气煤的孔隙率,逾渗概率随温度的升高而单调增加,比表面积随温度的升高先增加后减小,褐煤比表面积峰值点为400℃,气煤比表面积的峰值点为200℃。200℃为气煤和褐煤孔隙结构的突变温度。褐煤比表面积在所有煤种中最小,温度高于200℃后,气煤的孔隙率在所有煤种中最高。焦煤、瘦煤和Ⅱ级无烟煤的孔隙率、比表面积和逾渗概率随温度的升高先增加后减小。焦煤和Ⅱ级无烟煤的峰值温度点为500℃,焦煤的比表面积在所有煤种中最大。瘦煤随温度的变化较缓慢,峰值点为400℃。2、在已有研究的基础之上,建立了孔隙孔径分维数,孔隙体积分维数和孔隙表面积分维数,对五种煤样不同温度下的孔隙分形维数进行研究分析,得到如下结论：五种煤中,褐煤的孔径分布分维数最小,气煤的孔径分布分维数较大,Ⅱ级无烟煤孔径分布分维数随温度的升高几乎不变,在常温到300℃的低温段,不同煤种的孔径分布分维数大小为：气煤>Ⅱ级无烟煤>焦煤>瘦煤>褐煤。气煤、焦煤和瘦煤的体积分维数很大,接近于3,随温度的升高几乎不变。Ⅱ级无烟煤的体积分维数变化量最大,褐煤次之,温度高于200℃后,二者的体积分维数也接近于3,随温度升高变化很小。200℃时,五种煤的体积分维数都高于2.96。褐煤和气煤的表面积分维数随温度的升高而增加,焦煤和Ⅱ级无烟煤的表面积分维数先增加后减小,峰值点为500℃,瘦煤的表面积分维数随温度的升高几乎不变。3、利用μCT225KvFCB显微CT系统结合自制高温气氛炉,对(?)7mm煤进行扫描实验,研究不同温度下不同煤样的裂隙产生、发展的演化规律,得到如下结论：裂隙大都产生于煤质较软的软煤质中,或产生于软硬煤质的交界面,遇到硬质颗粒或硬质带后止裂,有的止裂后的裂隙在更高的温度下会穿越硬质颗粒或硬质条带继续扩展,多数裂隙在温度的作用下会顺层理扩展。褐煤、气煤、焦煤、贫煤和Ⅱ级无烟煤的裂隙随温度的升高具有急剧产生的特点。200℃时,褐煤急剧产生大量雁行状和网状裂隙,气煤急剧产生了大量的网状裂隙,Ⅱ级无烟煤急剧产生了大量的缩聚裂隙和垂直层理的裂隙。300℃时,焦煤急剧产生了大量的蜂窝状裂隙,贫煤急剧产生了大量糜粒状裂隙、缩聚裂隙和雁行状裂隙。瘦煤随温度的升高,裂隙的产生扩展很平缓,先后出现了失水裂隙(100℃)、平行层理裂隙(200℃)、蜂窝状裂隙(300℃)和似静压裂隙(500℃),蜂窝状裂隙较多。随温度的升高产生的裂隙很少,裂隙扩展较慢。4、利用裂隙数量——尺度的方法,建立了裂隙分形维数计算公式,对七种煤样不同温度下的裂隙进行了分形研究,得到如下结论：随温度的升高,Ⅱ级无烟煤的裂隙分维数单调减小,Ⅲ级无烟煤的裂隙分维数单调增加,褐煤、气煤、焦煤、瘦煤和贫煤的裂隙分维数先增加后减小。褐煤的裂隙分维数峰值点为300℃,气煤的为200℃,焦煤的为300℃,瘦煤和贫煤的为400℃。从常温到裂隙分维数的峰值点,裂隙主要以产生和扩展为主,从峰值点到600℃,裂隙主要以扩展——搭接——连通为模式。5、通过对七种煤的孔隙裂隙结构随温度的变化研究,综合分析得到几点结论：(1)气煤、褐煤、Ⅱ级无烟煤和焦煤的孔隙裂隙受温度影响较大,在200℃(焦煤300℃),孔隙率达到了30%,逾渗概率达到了25%,裂隙急剧产生,裂隙分维数增量达到最大,对这四种煤而言,热解可以在较低温度提高它们的渗透性。(2)瘦煤和贫煤裂隙受温度影响较大,产生的裂隙种类较多,400℃,裂隙发育最好,分维数达到最大,渗透性在300℃后提高很大。(3)Ⅲ级无烟煤随温度升高产生的裂隙很少,受温度影响不大。(4)常温到300℃,热破裂对孔隙裂隙的产生起主要作用,300℃-600℃,热解对孔隙和裂隙的扩展起主要作用。更多还原

【Abstract】 The pyrolysis is also called carbonization or heat decomposition, it can produce gas coal, tar and semi-coke or coke, which are lustration or modified fuel, and can substitute petroleum and natural gas, and are also good chemical raw material. This method that the pyrolysis produce lustration and modified fuel both reduces environment pollution by burning coal and makes the most of the better economic value compounds in coal, it is important that it can protect environment as well as reasonably use coal resource and save energy sources. The pyrolysis is the key step of coal transformation, it must occur during gasification, liquefaction, coking and burning of coal. The pyrolysis is the first step of Underground coal gasification, modified low rank coal, in-situ pyrolysis of coal and spontaneous combustion of coal which are the key technologies to the environmental coal, so the research findings of the pyrolysis have effect on those key technologies directly. The pyrolysis occurs on the surface of coal matter, which is related to pores and cracks in coal, so pore structure and crack distribution can influence the activity and reactivity of pyrolysis. Overall consideration, the research on the evolution of pore and crack in pyrolysis is the basic research on both in-situ pyrolysis of coal and hot processing of coal such as Underground coal gasification, liquefaction, modified low rank coal, it is important to sustainable development of coal industry in our country.In this article, the pyrolysis characteristics of many ranks of coal at home are studied. The three-dimensional mecro-structure is rebuild by scanning coal samples with advancedμCT225KvFCB. The effect of temperature on pore and crack is analyzed. Main contents and conclusions are as follows:1. UsingμCT225KvFCB system and high temperature atmosphere furnace made by oneself, scanning F 1mm coal samples, studying the pore structure characteristic under different temperatures, we can draw conclusions as follows:The porosity and percolation probability of lignite and gas coal increase monotonously with temperature, specific surface area first increases then decreases, the specific surface area of lignite has peak value at 400℃, the specific surface area of gas coal has peak value at 200℃.200℃is the mutation temperature of pore structure of lignite and gas coal. The specific surface area of lignite is minimum in all coal samples, the porosity of gas coal is maximum above 200℃.The porosity, specific surface area and percolation probability of coking coal, lean coal andⅡanthracite first increase and then decrease.500℃is the peak temperature of coking coal andⅡanthracite, the specific surface area of coking coal is the largest in all coal samples. The evolvement of the pore structure of lean coal is gentle,400℃is its peak temperature.2. On the basis of already research, creating aperture fractal dimension, pore volume fractal dimension and surface area fractal dimension, analyzing the pore fractal dimensions of five ranks of coal under different temperatures, we can draw conclusions as follows:In five ranks of coal, the aperture fractal dimension of lignite is minimum, which of gas coal is bigger, which ofⅡanthracite is almost immutable. From room temperature to 300℃, the aperture of kinds of coal is in sequence:gas coal >Ⅱanthracite> coking coal> lean coal> lignite. The pore volum fractal dimensions of gas coal, coking coal and lean coal are almost constant value 3 with temperature, increment of the pore volume fractal dimension ofⅡanthracite is maximum, that of lignite second. The pore volume fractal dimensions ofⅡanthracite and lignite are close to 3 and almost immutable with temperature. At 200℃or above, the pore volume fractal dimensions of five ranks of coas are bigger than 2.96. The surface area fractal dimensions of lignite and gas coal increase with temperature, those of coking coal andⅡanthracite first increase thenⅡdecrease, and have max value at 500℃. The surface area fractal dimension of lean coal is almost immutable with temperature.3. WithμCT225KvFCB system and high temperature atmosphere furnace made by oneself, scanning F 7mm coal samples, studying the evolvement of crack emergence and expansion with temperature, we can draw conclusions as follows:the cracks emerge in soft coal matter mostly, or in boundary of soft and hard coal matter, the crack arrest is caught by hard grain and hard strip. The crack arrest can go through hard grain and hard strip to go on expanding at higher temperature.The cracks of lignite, gas coal, coking coal, poor coal andⅡanthracite produce suddenly. At 200℃, lignite produces large numbers of echelon and net cracks suddenly, gas coal produces large numbers of net cracks suddenly,Ⅱanthracite suddenly produces large numbers of polycondensation cracks and cracks perpendicular to seam. At 300℃, coking coal suddenly produces many honeycombed cracks, poor coal suddenly produces numbers of rotten grain cracks and polycondensation cracks and echelon cracks.The emergence and expansion of lean coal gradually take place with temperature, dehydrated cracks arise at 100℃, cracks parallel to seam arise at 200℃, and more honeycombed cracks arise at 300℃, like-pressing cracks arise at 500℃.Few cracks ofⅢanthracite arise and they expand slowly with temperature.4. We establish the crack fractal dimension expressions on the basis of crack quantity-scale, and doing crack fractal research on seven ranks of coal spoken of earlier, and drawing conclusions as follows:The fractal dimension ofⅡanthracite decreases monotonically with temperature, which ofⅢanthracite increases monotonically with temperature, that of others coal first increases then decreases. To lignite and coking coal, 300℃is peak temperature at which their crack fractal dimensions reach maximum,200℃is peak temperature of gas coal,400℃is peak temperature of lean coal and poor coal. From room temperature to peak temperature, crack mainly arise and expand, from peak temperature to 600℃, crack mainly expand, overlap and connect. 5. Through comprehensive analyzing the evolvement of the pore and crack of above seven kinds of coal with temperature, we draw some conclusions:(1) The change of temperature has great effect on the pore and crack structure of lignite, gas coal, coking coal andⅡanthracite, at 200℃(to coking coal at 300℃), porosity reach 30%, percolation probability reach 25%, many cracks suddenly arise, the increment of crack fractal dimension is maximum, thus theirs permeability can be improved at low temperature to these four kinds of coal. (2) The change of temperature has great effect on crack of lean coal and poor coal, in which many kinds of cracks produce. At 400℃, crack fractal dimension reaches maximum, crack full develops. (3) The change of temperature has little effect on the crack ofⅢanthracite, few cracks produce in pyrolysis. (4) From room temperature to 300℃, thermal cracking has primary role on production of pores and cracks. From 300℃to 600℃, pyrolysis has primary role on the expansion of pores and cracks.更多还原