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基于Aspen Plus低阶煤热解工艺模拟
Alternative TitleSimulation of Low rank Coal Pyrolysis Process Based on Aspen Plus
Thesis Advisor何险峰 ; 赵月红
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword煤拔头   热解   燃烧   流程模拟   aspen Plus
Abstract我国是一个“富煤、缺油、少气”的国家,以煤炭资源为主的能源结构在未来相当长的一段时间内仍然难以改变。以比较温和的条件从低阶煤中提取高附加价值的液体燃料和精细化学品,在我国次烟煤和褐煤等低阶煤占煤炭资源的总比较高的情况下,在经济上具有较大吸引力。为了实现这个目的,中国科学院过程工程研究所提出了“煤拔头”的工艺设想。 本文对煤拔头工艺所采用的下行床热解反应器进行建模分析,并针对中科院过程所廊坊中试基地的煤热解中试平台使用Aspen Plus完成热解反应器的模拟,最后模拟了平台中燃烧反应器,并结合热解、烟气净化等单元完成煤热解工艺的全流程模拟。本文工作可以为下行床热解反应器设计、热解反应器操作、流程优化等提供参考。具体研究内容和结果如下: (1)目前对下行床的模拟研究多只反映其流体动力学特征,结合热解反应动力学研究下行床热解反应器的模型很少,本文建立了同时考虑了下行床内流体动力学特征与煤热解反应动力学的下行床热解模型。通过此模型可以有效预测在一定条件下,下行床热解反应器的热解产物产率以及床层流体动力学特征,如床层的气固轴向速度、颗粒空隙率、气固停留时间等。 (2)在Aspen Plus对煤热解过程的模拟工作中,多使用经验关联式进行计算或将实验结果直接代入收率反应器,前者有很大的偏差,后者有很大的局限。通过将热解反应器进行分段模拟,不但考虑了热解过程的热效应,而且可以得到煤热解过程中的温度变化情况和热解产物产率,同时可以提高模拟结果的准确性。在本文的研究中,对府谷煤热解过程中操作参数的优化结果表明,将起始物料温度从650℃提高至672℃时,热解反应可以产生更多的焦油产品。 (3)最后,对煤热解中试平台的模拟中,获得燃烧炉内孔隙率分布,结合燃烧反应动力学完成燃烧过程的模拟,并通过燃烧理论计算结果与模拟计算结果对比验证了模拟的可靠性,接着将燃烧、热解和烟气净化等过程模拟结合在一起,初步完成廊坊煤热解中试平台的全流程模拟。在此基础上,对煤灰的排出量这一关键操作参数进行了分析,煤拔头工艺设计的煤灰比在1:6到1:10之间,当煤灰比为1:6时,排出0.61%的灰可以使煤灰比保持恒定,而为使煤热解温度达到优化的672℃,此时灰温度需要达到852℃;当煤灰比为1:10时,排出0.37%的灰即可保证煤灰比恒定,而灰温度达到783℃即可达到优化后的热解温度672℃。
Other AbstractChina is rich in coal, but poor in oil and gas. The coal-dominated energy structure will not be changed for a long time in future. The extraction of high value-added liquid fuels and fine chemicals from low rank coal under mild condition is economic cause of subbituminous coal and lignite account for a high fraction of the amount of coal in China. Based on this consideration, coal topping process is proposed by Institute of Process Engineering (IPE), Chinese Academy of Sciences. In this work, a model of coal pyrolysis in a cocurrent downer reactor is established. Then, pyrolyzer of the IPE coal pyrolysis pilot plant is also simulated using Aspen Plus. Finally, combustor of the pilot plant is simulated while a simulation integrating the pyrolyzer, combustor and gas purification is developed also. The study provides valuable information for the design and operation of the pilot plant. The details and results are described as follows. (1) By far, most studies of downer are focusing on the hydrodynamic characteristics only. In our work, a model of coal pyrolysis in cocurrent downer is developed, in which both the hydrodynamic and the coal pyrolysis kinetics are considered together. The model could predict the yields of pyrolysis products and the hydrodynamic characteristics inside the reactor under different conditions, such as the axial velocities of gases and solids, solids holdup and residence time of gases and solids, which are valuable information for reactor design. (2) Most simulations of coal pyrolysis process based on Aspen Plus are using empirical formulas and experimental data, however, the former has great deviations while the latter has many limitations. In this work, simulation of pyrolysis process is developed by separating the pyrolyzer into several sections (such as 15 sections), which brings many benefits: endothermic effect is fully considered; the simulation could have a better accuracy; temperature variation curve of the pyrolysis process and yields of pyrolysis products are obtained. As results, according to the simulation, Fugu coal pyrolysis could produce more tar while the initial pyrolysis temperature is increased from 650℃ to 672℃. (3) Combining the porosity distribution of the combustor and coal combustion kinetics, a simulation of combustion process is built based on Aspen Plus. The reasonable agreement between the simulation results and the results calculated by ideal combustion theory verifies the correction of the simulation. Finally, simulation of the whole pyrolysis process is developed by integrating the pyrolysis, combustion and gas purification process. Analyses on key operating parameters are performed. As a case, in order to guarantee the coal to ash ratio (1:6) and the pyrolysis temperature 672℃, 0.61% of the heat-carrier ash should be discharged while the ash temperature is needed to be at least 852℃; for another case, in order to guarantee the coal to ash ratio (1:10) and the pyrolysis temperature 672℃, 0.39% of the ash should be discharged while the ash temperature is needed to be at least 783℃.
Document Type学位论文
Recommended Citation
GB/T 7714
张彦. 基于Aspen Plus低阶煤热解工艺模拟[D]. 中国科学院研究生院,2014.
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