分级转化系统中热解半焦气化特性的研究

发布时间：2018-04-01 08:33

本文选题：多联产　切入点：分级转化　出处：《南京理工大学》2017年硕士论文

【摘要】：目前,我国对于煤炭的利用大部分仍采用直接燃烧的粗放单一方式。煤炭分级转化多联产利用技术依据煤的组成和反应特性进行分质分级梯级利用,以液体燃料和电力为目标产品,实现煤炭资源的梯级高效利用,有效解决了所面临的资源与环境问题。本文基于煤炭分级转化的思想,提出了煤热解气化燃烧分级转化多联产利用技术,构建了联产热、电、甲醇及燃料油的分级转化多联产利用系统,并对其开展了模拟研究以及系统中关键问题的实验研究。首先,利用Aspen Plus软件对煤热解气化燃烧分级转化多联产利用系统进行了全流程模拟,计算得到了系统热效率、系统总投资、内部收益率和投资回报周期等热力学与经济性指标,并与煤热解气化分级转化多联产利用系统的相关指标进行了对比,全面评估了煤热解气化燃烧分级转化多联产利用系统的可行性。结果表明,煤热解气化燃烧分级转化多联产利用系统虽然设备投资比煤热解气化分级转化多联产利用系统高,但其系统热效率更高,可达47.02%LHV,表明该系统具有一定的可行性。其次,搭建多气氛热解实验台和多元混合气氛热重实验台。开展了热解气氛对半焦结构和气化反应特性的实验研究。在真空水平管式炉中制取了不同热解气氛的热解半焦,采用激光拉曼光谱和氮气吸附等手段表征了半焦的物理结构特性。结果表明,C02热解气氛下制取的半焦无序化程度更高,且比表面积较大,而CO,CH4和H2热解气氛下制取的半焦石墨化程度较高且比表面积较小。热重气化实验结果表明,CO2热解气氛下制取的半焦气化速率最高,而CO,CH4和H2热解气氛下制取的半焦气化速率均低于Ar气氛下的半焦。这可能是由于热解过程中的C02气化反应、CO歧化反应、CH4热裂解反应以及H2的缩合与脱氧反应所导致的。然后,研究了在H20和CO2混合气氛以及H20,CO2,H2和CO多元混合气氛下比表面积对半焦气化机理的影响。采用不同的热解速率制取了具有不同比表面积的半焦样品。实验结果表明,大比表面积半焦的气化速率更符合独立活性位Langmuir-Hinshelwood(L-H)模型假设,而小比表面积半焦的气化速率则更符合共用活性位L-H模型假设。因为大比表面积半焦可提供更多的活性位,H2O与CO2分子之间对于活性位的竞争较小。最后,研究了在H2O和CO2混合气氛以及H2O,CO2,H2和CO多元混合气氛下灰成分对半焦气化机理的影响。采用酸洗法,制取了脱灰半焦,采用盐溶液浸渍法,制取了负载Na盐的半焦。实验结果表明,脱灰半焦的气化速率既不符合共用活性位假设也不符合独立活性位假设。Na盐半焦的气化速率接近于独立活性位假设。因为矿物质脱除会降低半焦催化效果,加剧了 H2O与CO2分子对于活性位的争夺。而碱金属盐对半焦气化反应起催化作用,为气化反应提供了更多的反应活性位,削弱了H2O与CO2分子之间对于活性位的竞争。
[Abstract]:At present, the utilization of coal in our country still adopts the extensive and single way of direct combustion.According to the composition and reaction characteristics of coal, the multi-cogeneration and utilization technology of coal classification and conversion can be used in a graded and cascade way, taking liquid fuel and electric power as the target products to realize the cascade and efficient utilization of coal resources.Effectively solve the problem of resources and environment.Based on the idea of coal classification conversion, this paper puts forward the multi-cogeneration and utilization technology of coal pyrolysis gasification and combustion classification conversion, and constructs the multi-cogeneration and utilization system of cogeneration heat, electricity, methanol and fuel oil.The simulation research and the experimental research on the key problems of the system are also carried out.Firstly, the thermal efficiency, total investment, internal rate of return and the period of return on investment of the system are calculated by using Aspen Plus software to simulate the whole process of the multi-cogeneration and utilization system of coal pyrolysis gasification and combustion classification conversion.The feasibility of multi-cogeneration utilization system of coal pyrolysis gasification and gasification was comprehensively evaluated by comparing with the related indexes of multi-cogeneration utilization system of coal pyrolysis gasification and gasification.The results show that although the equipment investment is higher than the multi-cogeneration utilization system, the thermal efficiency of the system can reach 47.02 LHVs, which indicates that the system is feasible.Secondly, a multi-atmosphere pyrolysis test bench and a multi-element mixed atmosphere thermogravimetric test bench are built.The experimental study on the structure and gasification reaction characteristics of char in pyrolytic atmosphere was carried out.Pyrolytic semi-coke with different pyrolysis atmosphere was prepared in a vacuum horizontal tube furnace. The physical structure of char was characterized by laser Raman spectroscopy and nitrogen adsorption.The results show that the char prepared in the pyrolysis atmosphere has a higher degree of disorder and a larger specific surface area, while the graphitization degree and specific surface area of the char prepared under the pyrolysis atmosphere of COG Ch 4 and H 2 are higher and the specific surface area is smaller.The experimental results of thermogravimetric gasification show that the gasification rate of char is the highest in the pyrolysis atmosphere of CO _ 2, while the gasification rate of the char is lower than that of the char in the atmosphere of COG _ (4) and H _ (2) pyrolysis.This may be due to the CO2 gasification reaction in the pyrolysis process and the pyrolysis of Ch _ 4 and the condensation and deoxidation of H _ 2.Then, the effect of specific surface area on the gasification mechanism of semi-char was studied in the mixed atmosphere of H20 and CO2 and the mixed atmosphere of H20 and CO.The semi-coke samples with different specific surface areas were prepared at different pyrolysis rates.The experimental results show that the gasification rate of large specific surface area semi-coke is more consistent with the Langmuir-Hinshelwood-L-H) model hypothesis of independent active sites, while the gasification rate of small specific surface area semi-coke is more consistent with that of common active site L-H model.Because large specific surface area semi-coke can provide more active sites between H _ 2O and CO2 molecule competition for the active site is smaller.Finally, the influence of ash composition on the gasification mechanism of semi-char was studied in the mixed atmosphere of H _ 2O and CO2 and in the mixed atmosphere of H _ 2O _ 2 CO _ 2H _ 2 and CO.The descaling semi-coke was prepared by acid washing method, and the Na salt loaded semi-coke was prepared by salt solution impregnation method.The experimental results show that the gasification rate of demineralized char does not accord with either the common active site hypothesis or the independent active site assumption. The gasification rate of Na salt semi-coke is close to that of independent active site hypothesis.Because the removal of minerals reduces the catalytic effect of semi-coke, it intensifies the competition for active sites between H2O and CO2 molecules.Alkali metal salts play a catalytic role in the gasification reaction of semi-char which provides more reactive sites for gasification and weakens the competition between H2O and CO2 molecules for active sites.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ530.2;TQ541

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