【作者】 申春梅；

【导师】 吴少华； 林伟刚；

【作者基本信息】 哈尔滨工业大学 ， 热能工程， 2010， 博士

【摘要】 我国煤炭资源丰富,油、气资源有限,液体燃料短缺已成为制约我国经济发展的重要因素。煤拔头工艺在中低温快速热解条件下通过温和的转化方式从丰富的年轻煤中提取轻质燃料油和高值化学品,可部分缓解液体燃料的短缺。目前,煤拔头工艺已成功与循环流化床锅炉相结合,考虑到我国火力发电行业主要采用粉煤燃烧的方式,为进一步扩大煤拔头工艺应用范围,将煤拔头工艺与粉煤锅炉燃烧相结合的方案被提出,即煤先经过煤拔头的中低温快速热解工艺,获得一定的油气产品之后,剩余的固体残留物(半焦),再用作粉煤锅炉的燃料。在粉煤燃烧发电机组运行过程中,燃煤设备与燃料特性的相互适应非常重要,鉴于此,本文针对不同条件下所得的煤拔头半焦的燃烧反应特性进行了研究,对煤拔头半焦用作粉煤锅炉燃料的可行性进行试验验证,同时,探讨拔头工艺条件与拔头半焦物性之间以及拔头半焦物性与其燃烧反应特性之间的关系,并由此阐明拔头工艺条件与拔头半焦燃烧反应特性之间的关系及作用机理。利用喷动载流床模拟煤拔头工艺的快速热解条件,在不同热解温度下分别制备了不同粒径大同烟煤的拔头半焦,采用工业分析和元素分析对拔头半焦的化学组成进行测试,采用红外光谱分析和X射线衍射分析分别对拔头半焦的官能团和碳结构进行了测试。提出了原煤热解度(Dv)的定义,用于定量分析热解条件对拔头半焦组成和碳结构的影响。利用低温氮吸附法对拔头半焦的孔隙结构进行了测试,利用扫描电镜法对原煤和拔头半焦的表面形态进行观察。根据吸附数据,采用NLDFT理论对孔径分布、孔比表面积分布以及各种孔尺寸进行了求解,而不是前人最常使用的BJH方法;同时,求解了BET比表面积。根据孔隙结构测试结果,对煤拔头中低温快速热解条件下孔隙结构的发展变化及其原因进行了探讨。利用综合热分析仪,在慢加热速率条件下对原煤、拔头半焦及阳泉无烟煤的燃烧反应特性进行了研究,采用着火温度和整体平均表观活化能对样品的燃烧反应性进行评价,同时分析了样品的着火类型。根据试验结果,对煤拔头半焦的燃烧反应特性与原煤和阳泉无烟煤的燃烧反应特性之间的差异进行了对比,对影响样品燃烧反应性的主要因素,如物质组成、孔结构及碳结构,进行了分析。设计、搭建、调试完成一套沉降炉热态试验系统,利用此试验系统,在煤粉锅炉加热速率条件下,对原煤、DT80系列拔头半焦以及阳泉无烟煤的燃烧反应特性进行研究,利用FLUENT软件计算了颗粒在该系统条件下的沉降停留时间,根据固体样品的灰分和元素分析数据,计算得到了燃烧过程中整体可燃物转化率、整体可燃物比转化速率以及碳元素转化率随反应时间的变化曲线。根据试验结果,对原煤、DT80系列拔头半焦和阳泉无烟煤在高加热速率条件下的燃烧反应性进行了对比,对煤拔头半焦的燃烧过程以及燃烧过程中孔隙结构的发展变化进行了分析,讨论了样品挥发分含量以及孔比表面积对其可燃物比转化速率的影响,并将沉降炉试验结果与热分析试验结果进行了对比。本文结果表明,煤拔头半焦的燃烧反应性都高于阳泉无烟煤的燃烧反应性,这说明煤拔头半焦用作粉煤锅炉的燃料是可行的;在煤拔头中低温快速热解条件下存在热失活现象,即煤拔头半焦的燃烧反应性都低于原煤的,热解过程中物质组成和孔隙结构的变化对本文涉及的所有热解温度下的热失活现象都有贡献,而碳结构的有序化仅在原煤热解度达到一定程度(大于0.55)时才对热失活有贡献;煤拔头半焦的燃烧反应性由物质组成、孔隙结构以及碳结构等因素共同决定;煤拔头半焦的燃烧反应性有随挥发分含量的降低和燃料比的升高而降低的趋势,但不是线性变化;热分析试验所得结果与沉降炉试验所得结果基本一致。更多还原

【Abstract】 China is rich in coal and the resources of natural gas and petroleum are limited. A lack of transportation liquid fuel hampers the fast development of China. A so called“Coal-topping process”applies abundant low rank coal resources to extract liquid products by flash pryolysis under mild conditions for further obtaining light fuel oil and valuable chemicals, through which the problem of liquid fuel shortage may be partly relieved. Up to now, coal-topping process has been applied in circulating fluidized bed system. By considering the fact that pulverized-coal combustion is the main way for power generation in China, the idea of combining coal-topping process with a pulverized coal boiler was proposed to expand its application, i.e. the pulverized coal is pyrolized firstly to obtain liquid and gaseous products, and then the remaining char will be burned in the pulverized coal furnace. The combustion behavior of the char determines the performance of the pulverized burner and furnace, and the pulverized coal combustion is more sensitive to the type of coal. Herein, the combustion characteristics of the char obtained under different coal-topping conditions were studied to test the feasibility of the char as the fuel for pulverized coal boiler. By evaluation of the relation between the pyrolytic conditions and the char’s physical properties, as well as the influence of the char with different physical properties on its combustion characteristics, the effect and the mechanism of the coal-topping conditions on the char’s combustion characteristics were studied.Datong Bituminous coal with different particle size group were pyrolyzed for obtaining chars at different pyrolytic temperatures in a spout entrained reactor. The chemical compositions of the chars were characterized by proximate and ultimate analysis. The change of functional group and carbon structure of the parent coal and the obtained chars were analyzed by a flourier transform infrared spectrometer and an X-ray diffraction. Pyrolysis degree of coal (Dv) was defined to reveal quantatively the effects of the pyrolytic conditions on the char composition and carbon structure.Pore structures of the parent coal and the chars were characterized by nitrogen adsorption analysis. The morphology of the coal and chars was observed under scanning electron microscopy. The NLDFT method was applied to calculate the pore size and the pore surface area distributions, instead of the commonly used BJH method, based on the adsorption data. The BET area was obtained similarly. Pore structure evolution and its reasons during the pyrolysis process were analyzed.The combustion characteristics of Datong bituminous coal, chars and Yangquan anthracite were studied via simultaneous thermal analysis (STA) under experimental conditions of low heating rates. The ignition temperature and the weight average apparent activation energy were obtained and used to evaluate the reactivity of the chars, the parent coal, and the Yangquan anthracite. The ignition type of the chars, the parent coal, and the Yangquan anthracite was also analyzed. Based on the thermogravimetric analysis, the ignition behavior and combustion reactivity under low heating rate of the chars and the parent coal, as well as those of Yangquan anthracite were compared. The major influencing factors to combustion characteristics of the chars, such as material compositions, pore structures, and carbon structure, were analyzed.A drop tube furnace (DTF) was designed, constructed and commissioninged for testing the char combustion characteristics under simulated conditions relavent to pulverized coal boilers. The combustion tests on Datong bituminous coal, chars and Yangquan anthracite were carried out in the drop tube furnace. The particle resident time in the DTF was estimated by the Computational Fluid Dynamics (CFD) software FLUENT. The conversion of combustibles and carbon, as well as the specific reaction rate of combustibles as a function of reaction time were calculated based on the experimental data of different fuels applied. The combustion reactivity under high heating rate of the parent coal, derived char sand Yangquan anthracite is compared. The pore structure evolution during combustion process of chars pyrolyzed were analyzed. The influence of volatile matter content and pore specific surface area on the specific reaction rate of combustibles was discussed. Results obtained from DTF were also compared with those obtained by thermogravimetric analysis.Results from this work show that, reactivities of all derived chars are higher than that of Yangquan anthracite, indicating that it may be feasible to use coal-topping char as fuel of pulverized coal boiler. Thermal deactivation was observed under the pyrolysis conditions in this work. The reactivity of all chars is lower than that of the parent coal. Changes in material composition and pore structure affect the reactivity for chars derived at temperatures applied. Carbon structure ordering contributes to thermal deactivation only when coal pyrolysis degree reaches to a certain level. Combustion reactivity of the chars is determined by their composition, pore structure and carbon structure. The reactivity of chars shows a trend of decreasing as the volatile matter decreases and the fuel ratio increases. Results obtained by thermogravimetric analysis are basically consistent with those obtained from DTF .更多还原