固体热载体低阶煤热解催化作用机制研究

发布时间：2018-08-31 13:52

【摘要】：中低阶煤在我国煤炭储量中占一半以上,具有挥发分含量高、水含量高和发热量低等特点。通过热解转化可得到提质半焦,热解气和煤焦油(高附加值化学品),实现低阶煤分级炼制与清洁转化。为提高热解焦油收率、改善焦油品质,方法有:一是要强化煤热解初期的分解程度,尽可能多的产生小分子,充分利用煤颗粒自身和环境中的氢及小分子自由基片段;二是要对热解初次产物(焦油前驱体)的二次反应进行调控,实现温和条件下焦油中某一类组分的富集转化。当前,采用半焦热载体的煤热解提质技术,可回收产物半焦部分显热,提高系统热效率;热解过程释放的挥发分可经半焦裂解,焦油轻质组分含量增加。本文在课题组前期研究基础上,主要采用固定床反应器考察陶瓷球、橄榄石、石英砂、半焦热载体对呼伦贝尔褐煤和神东长焰煤热解的影响。结合焦油轻质组分测定结果,分析挥发分在不同热载体作用下的裂解转化;在神东煤热解中引入神东煤直接液化残渣,研究两者共热解相互作用;考察共热解焦为固体热载体类工业条件的循环稳定性,分析产物组成及半焦粒度变化;对于半焦热载体神东煤热解的作用机制,结合焦油组成及反应前后热载体半焦物化性质改变,分析温度对半焦热载体裂解挥发分的影响。主要结果如下:1.不同热载体褐煤热解实验表明,陶瓷球作用下褐煤挥发分深度裂解,伴随热解水生成。以褐煤半焦为固体热载体时,挥发分与半焦作用,焦油轻质组分增加,热解气中H2和CO2不同程度的提高。热重分析表明,褐煤半焦热载体表面沉积的碳物种可促进其在更高温度下的热解。2.验证了焦油回收过程-先用四氢呋喃洗涤,旋蒸除去溶剂和热解水,再用正己烷萃取得到轻质组分方法的可靠性。对不同热载体作用下神东煤焦油轻质组分进行GC-MS测定,依据物质定性结果划分为四类组分;结合相对含量变化结果,认为焦油中的酚类会向芳烃结构转化。3.考察了共热解焦固体热载体的神东煤与液化残渣共热解相互作用,与石英砂热载体相比,共热解焦对挥发分有裂解作用;与共热解理论计算值相比,共热解过程中产生正协同作用(ΔY0)。共热解焦固体热载体的10次循环共热解实验表明,经过一定次数循环后,半焦黏结团聚与新生成半焦补充存在的抵消作用,共热解焦热固体载体粒径分布趋于稳定。4.改变半焦热载体初始温度得到神东煤热解焦油收率变化,是由热载体与反应物料的温差引起的瞬时加热速率差异,煤的热解深度、焦油前驱体物种的裂解、挥发分与热载体半焦作用等因素综合影响的结果。5.煤热解挥发分受到热载体半焦催化裂解和高温热裂解共同作用,前者在较低温度范围内明显,后者在高温范围内明显。高温不利于焦油中酚类的稳定存在,导致酚羟基分解或缩聚,焦油中多环芳烃结构含量增加。挥发分与半焦热载体作用对半焦碳结构影响不大;挥发分的部分缩聚产物在半焦表面沉积引起其表面一些官能团结构变化,影响半焦的后续利用。6.随着半焦热载体初始温度增加,在热载体表面的形成的碳物种不仅有量的区别,还有结构上的差异。热解过程中在热载体半焦表面发生焦油附着、裂解和缩聚积碳产物的沉积,对半焦CO2气化反应性促进作用大于比表面下降的不利影响。
[Abstract]:Medium and low rank coal accounts for more than half of China's coal reserves, and has the characteristics of high volatile content, high water content and low calorific value. One is to enhance the decomposition degree of coal at the initial stage of pyrolysis, to produce as many small molecules as possible, and to make full use of hydrogen and small free radical fragments in coal particles and the environment; the other is to control the secondary reaction of the primary product (tar precursor) of pyrolysis, so as to realize the enrichment and transformation of a certain kind of components in tar under mild conditions. The coal pyrolysis technology with semi-coke heat carrier can recover the sensible heat of semi-coke and improve the thermal efficiency of the system; the volatile matter released during pyrolysis can be pyrolyzed by semi-coke, and the content of light components in tar increases. The pyrolysis of Hulunbeier lignite and Shendong long flame coal was studied. The pyrolysis conversion of volatile under different heat carriers was analyzed by combining the results of determination of light components of tar. The main results are as follows: 1. The pyrolysis experiments of lignite with different heat carriers show that ceramic balls are used as ceramic balls. When lignite semi-coke is used as solid heat carrier, the light components of tar increase, and H2 and CO2 in pyrolysis gas increase in varying degrees. Thermogravimetric analysis shows that carbon species deposited on the surface of lignite semi-coke heat carrier can promote its pyrolysis at higher temperatures. The recovery process of tar was studied. The light components of Shendong coal tar were determined by GC-MS under the action of different heat carriers. According to the qualitative results, the tar was divided into four types. The co-pyrolysis interaction between Shendong coal and liquefied residue was investigated. Compared with the quartz sand heat carrier, the co-pyrolysis coke had a pyrolysis effect on volatile matter. Compared with the theoretical value of co-pyrolysis, the co-pyrolysis process had a positive synergistic effect (Y0). The results of 10 cycles of co-pyrolysis show that the particle size distribution of thermal solid carrier tends to be stable after a certain number of cycles. 4. The change of tar yield of Shendong coal pyrolysis is induced by the temperature difference between thermal carrier and reaction material. The results show that the instantaneous heating rate is different, the pyrolysis depth of coal, the pyrolysis of tar precursor species, and the effect of volatile and heat carrier char on the pyrolysis of coal. 5. High temperature is not conducive to the stable existence of phenols in tar, resulting in the decomposition or condensation of phenolic hydroxyl groups, and the increase of polycyclic aromatic hydrocarbons in tar. 6. As the initial temperature of the semi-coke heat carrier increases, the carbon species formed on the surface of the semi-coke are not only different in quantity, but also in structure. Ringing.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ530.2

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