CAS OpenIR
MTO/MTP大型反应器的多尺度CFD模拟
牛燕
Subtype硕士
Thesis Advisor鲁波娜
2018-07
Degree Grantor中国科学院研究生院
Degree Name硕士
Degree Discipline化学工程
KeywordMto,Mtp,反应动力学,Cfd,多尺度
Abstract

甲醇制烯烃(MTO)和甲醇制丙烯(MTP)技术是两个重要的烯烃生产新工艺,打通了煤/天然气经由甲醇生产低碳烯烃的新途径,从而架起了煤化工和石油化工之间的桥梁,对“缺油少气多煤”的中国具有重要的战略意义。在众多MTO工艺中,大连化学物理研究所(DICP)开发的MTO工艺(DMTO)在工业应用中最为成功。DICP在第一代DMTO工艺的基础上,也正逐步开展结合MTO反应、乙烯和甲醇烷基化反应、C4以上重组分催化裂解的DMTP工艺。本论文主要聚焦DMTO/DMTP反应器的CFD模拟,为新一代的DMTO工艺及DMTP工艺的工业化提供可靠的基础参数。论文第一章介绍MTO/MTP工艺的发展历程、现状及工艺特点,以及相关的模拟方法和已展开的模拟研究。本课题组与DICP进行合作,开展了一系列的模拟工作,但仍存在以下问题:1)MTO反应动力学模型采用仅考虑平行反应的七集总模型,该模型未考虑烯烃之间的相互转化,且其失活函数的建立对反应器的依赖性较大;2)由于MTO反应主产物(乙烯、丙烯)的选择性与催化剂上的焦炭含量密切相关,研究者认为可能是催化剂的循环(新鲜催化剂的连续补充和失活催化剂的排料)导致焦炭含量在反应器内存在较宽分布,而当前基于双流体模型(TFM)的反应模拟无法区分具有不同反应属性的颗粒的差异,从而不足以准确预测产物的分布。针对上述问题,论文第二章围绕工业DMTO反应器展开研究,首先比较了七集总平行动力学模型(Kinetic A)和DICP最新提出的考虑产物转化反应的交叉动力学模型(Kinetic B)对模拟结果的影响。研究表明,两种模拟均可准确捕捉反应器内的湍动流化特征;在对产物分布预测方面,基于Kinetic B预测的乙烯与丙烯的比值为1.544,与基于Kinetic A的预测值(1.5675)相比,虽更接近实验值(1.0085),但对反应结果预测的提升较为有限,造成这种现象的原因可能是TFM耦合反应动力学模型进行模拟计算时,未能区分具有不同反应属性的颗粒,如随着反应的进行,现有TFM模拟无法区分随时间和反应的进行而产生的较宽焦炭分布,从而无法准确模拟出焦炭含量变化对反应模拟的影响。因此,本章随后采用跟踪两种焦炭组分(从固相进料口进入的新鲜催化剂上的焦炭和反应器内初始装填的催化剂上的焦炭)的方法,着重考察焦炭分布变化对反应模拟的影响。结果表明,与之前的模拟结果相比,乙烯与丙烯的质量比值随着模拟时间的增加而降低,且随着模拟时间的增加,该比值逐渐接近实验值,这也验证了催化剂的循环是造成宽焦炭分布的主要原因。目前的模拟受限于计算速度(计算100秒实际过程需要的物理时间为66天),很难完整模拟出一个颗粒平均停留时间为4800秒的实际过程。在未来的研究中,可引入PBM(群平衡模型)设置更多焦炭组分,进一步建立合理的焦炭初场分布,有望准确揭示焦炭分布对反应模拟的影响。DICP在成功开发的MTO工艺基础上,也不断推进MTP工艺的研发。在其专利CN101177374中提出了结合甲醇制烯烃反应、乙烯和甲醇烷基化反应和C4以上重组分催化裂解反应来最大限度的生产丙烯。鉴于MTP工艺和MTO工艺的相似性,如MTP工艺的第一阶段是在SAPO-34的催化下,在流化床反应器中生产富含丙烯的混合烃,因此可利用类似于MTO反应器的模拟方法来研究MTP反应器,进而为MTP工艺的工业放大提供可靠参数。论文第三章采用TFM结合EMMS/bubbling的方法,对DICP初步设计的三种不同结构的工业MTP反应器进行了模拟,研究各种构体参数(如固相进料位置、分区挡板等)对流场分布的影响。研究发现,固相入口高度对反应器的流场分布有影响,特别是密相区(H? 4 m)的流场分布(Case2中主体区底部浓度约为0.37,Case1中主体区底部浓度约为0.41);加入分区挡板后,流化床反应器内呈现不同的流场结构,挡板上面的固相浓度约在0.03-0.25之间,挡板下方区域的固相浓度约为0.1-0.35之间,呈现明显的分区现象。因此未来可针对不同的流动结构,结合不同反应,实现丙烯的高产率和高选择性。 论文最后对全文进行了总结,并对未来如何完善工业MTO/MTP反应器的模拟工作进行了展望。 ;The methanol-to-olefins (MTO) and the methanol-to-propylene (MTP) technologies are two newly important technologies to produce ethylene or propylene. MTO/MTP provides an economical route to produce light olefins from abundant non-petroleum natural materials (e.g., coal or natural gas). MTO/MTP is believed to link the coal or natural gas based chemical industry to the modern petrochemical industry, and thus MTO/MTP technology is very important, expecially for China. Among many MTO techniques, DMTO is the most successfully used technology. Based on the first DMTO technology (DMTO-I), DICP is developing a MTP process (called DMTP). The DMTP process combines MTO reaction, alkylation reaction of methanol and ethylene and the catalytic cracking reaction of components above C4. This study will focus on CFD simulation of the DMTO/DMTP, and the purpose of this study is to provide reliable parameters for the next generation DMTO/DMTP process.In Chapter 1, a literature survey for the development of MTO/MTP process, the related simulation approaches and simulation studies of MTO/MTP fluidized beds is presented. DICP cooperated with IPE (Institute of Process Engineering) to study the hydrodynamic behaviors and reaction behaviors in MTO reactors by using computational fluid dynamics (CFD) simulations, but there exist some problems for simulations of large-scale MTO reactors: 1) the seven-lumped kinetic model used in CFD simulation only considers the parallel reactions and neglects the olefins interconversion. The parameters of deactivation function heavily depend on the types of reactors; 2) the coke content is closely related to the selectivity of the light olefins (ethylene and propylene). There is a wide distribution of coke content which could be attributed to the circulation of catalysts (the continous feed-in of fresh catalysts and the discharge of spent catalysts). However, the present TFM combined with the kinetic model could not capture the chemical differences between particles (i.e., the particles with different coke content), and thus it is unable to accurately predict the distribution of products.This study aims to resolve these problems. In Chapter 2, an large-scale MTO reactor is simulated, and comparison of a seven lumped kinetic model (called Kinetic A) and the new kinetic model (called Kinetic B) considering the further conversion between products is made. The results show that hydrodynamic behaviors can be well predicted using both models. For reaction behaviors, the predicted ratio of ethylene to propylene by using Kinetic B (1.544) is closer to the experimental value (1.008) than that by using Kinetic A (1.5675), however this improvement is very limited. The present TFM simulation may be responsible for the aforementioned predictions, because the variation of coke distribution with time and reaction is not accurately captured. So an approach of tracking two kinds of coke (the coke on fresh catalysts and the coke on patched catalysts) is designed to mainly investigate the effect of the evolution of coke content on reaction behaviors. The simulation shows that the ratio of ethylene to propylene is decreased with the increase of simulation time, and it is expected to approach the experimental value if the simulation time is long enough. This result also proves that the circulation of catalyst results in a wide distribution of coke content in the large-scale DMTO reactor. Limited to current computational ability (simulation of a 100-second realistic process needs 66 days), so the required time for simulation of a process with average residence time of 4800 s is virtually formidable at present. In future, PBM (Population Balance Model) will be introduced and further combined with a reasonable initial model to more accurately reveal the influence of coke distribution on reaction behaviors.Based on the sucessfully developed DMTO process, DICP is developing the DMTP process. In DICP's patent CN101177374, the combination of MTO reaction, alkylation reaction of methanol and ethylene, and the catalytic cracking reaction of components above C4 is proposed to maximize the selectivity of propylene. Given the similarity of DMTO and DMTP technologies, a similar simulation method for studying MTO reactor can be also used to investigate the MTP process. In chapter 3, TFM combined with EMMS/bubbling is used to simulate three industrial MTP reactors with different geometries, and the effect of various geometrical parameters (such as the position of solid inlet, and the plate for partitioning the reaction zone, etc.) on the hydrodynamic behaviors are investigated. The results show that the position of solid inlet has effect on the overall distribution of solid volume fraction in the reactor (the solid volume fraction varies from 0.34 to 0.03 for Case2 and varies from 0.41 to 0.03 for case1). The introduction of the partition plate results in an obvious difference between two reaction zones (the upper part has lower solid volume fraction within the range of 0.03-0.25 and the lower part has higher solid volume fraction within the range of 0.1-0.35). These hydrodynamic features may be combined with different reaction routes to improve the yield and selectivity of propylene in future.At last, conclusions and future work are presented. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26845
Collection中国科学院过程工程研究所
研究所(批量导入)
Recommended Citation
GB/T 7714
牛燕. MTO/MTP大型反应器的多尺度CFD模拟[D]. 中国科学院研究生院,2018.
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