基于计算流体力学气相法聚乙烯流化床反应器的多尺度模型化研究
发布时间：2019-06-12 12:02
【摘要】：聚烯烃生产技术反映着一个国家的工业发展水平,其技术创新源于对该过程所包含的物理传递现象(质量、动量和热量传递)和化学反应特性的深入理解和剖析。气相法聚乙烯生产过程涉及复杂的气固两相流动、混合及聚合反应,同时也包含着时间和空间的多尺度现象。流化床反应器因其相对简单的结构和优良的热质传递性能被广泛应用于气相法聚乙烯生产工艺中,其内部的传递特性、反应状况及聚合物产品质量均受到流化床内气固两相性质和反应器操作状态的影响。因此,针对其中耦合了传递和聚合反应的过程采用多相流反应工程理论,利用计算流体力学耦合群体平衡模型的方法研究气固两相流动、混合和反应状况一直以来都是聚合反应工程的研究热点,极富挑战性。相关的模型化研究不仅具有重要的学术研究意义而且具有重要的工业应用价值。论文首先针对乙烯气相聚合反应过程结合免造粒生产工艺从UNIPOL聚乙烯工艺出发,通过单颗粒建模研究聚合物颗粒的生长及颗粒形态的变化过程,通过计算流体力学模拟中试规模工业流化床聚合反应器内的气固两相流动、混合和反应特性以及结合多尺度耦合模型研究该生产过程中的反应器操作性能,探索适用于免造粒聚乙烯生产工艺的反应器操作条件以及设计方案等；然后,针对Borstar双峰聚乙烯工艺,采用耦合了多活性位的多粒模型结合实验表征方法,研究双釜串联生产双峰聚乙烯工艺中聚合物颗粒形态以及聚合物性质的变化规律,以期为双峰聚乙烯的生产调控和质量优化等提供指导。研究免造粒聚乙烯生产工艺对于开发更加节能环保的聚乙烯生产新技术具有重要指导意义,而深入分析双峰聚乙烯生产工艺对于指导开发新产品和新牌号等具有重要影响。通过深入研究和分析,本文取得了以下创新性研究成果：(1)在乙烯气相聚合反应的单颗粒尺度上,需同时考虑物理传递阻力和化学多活性位的共同影响(混合模型)才能更好地描述聚乙烯生产工艺中的颗粒形态以及聚合物性质。而在单颗粒模型中是否需要考虑孔隙率的变化取决于催化剂颗粒的粒径大小及分布,在免造粒生产工艺中,聚合物颗粒内部存在着明显的浓度和温度梯度,不利于聚合反应过程正常进行。为改善免造粒聚乙烯生产工艺,除对催化剂载体进行设计之外还可以采用串级反应器工艺,通过增加预聚合过程实现该工艺的顺利进行。(2)通过对UNIPOL聚乙烯生产工艺的中试规模工业流化床反应器进行两维CFD建模和模拟研究,发现由于放大效应,流化床反应器内部的环核流动结构呈现出核区扩大和环区减小的显著特征,而且通过对比二维和三维的模拟结果,发现反应器中的放大效应呈现出相似的变化趋势。同时,床层扩大段可显著降低聚合物颗粒速度,改善反应器中固体颗粒的流动行为特性,而当流化床反应器处于免造粒生产工艺时,0.90 m·s-1的操作气速可使反应器达到较好的流化状态,但该操作过程变得较为敏感。(3)通过两维CFD-PBM建模和模拟研究,发现受乙烯聚合反应和气固相间的热质传递特性影响,流化床反应器的床层膨胀高度明显增加,气固两相含率分布变得不稳定并且轴向颗粒分布变宽。同时,颗粒动力学(颗粒增长、聚并和破碎)对初始流化阶段的轴向颗粒分布影响较大,而且聚合物颗粒破碎会明显增加床层膨胀高度,流体动力学也会影响聚合物颗粒粒径大小及分布,特别是在流化床反应器的初始流化阶段。在免造粒聚乙烯生产工艺中,由于聚合反应和热质传递的共同影响,也会引起流化床反应器两相流动结构和聚合物颗粒粒径分布的变化。此外,床层扩大段会显著影响流化床反应器在该工艺下的操作状态。(4)通过三维CFD-PBM耦合模型研究发现,在反应器处于传统生产工艺(GeldartB类颗粒)和免造粒生产工艺(Geldart D类颗粒)时,床层内部表现出完全不同的两相流体动力学特征,并且免造粒工艺中的聚乙烯颗粒聚集于分布板气体入口处附近,造成反应器操作不稳定。同时发现,Geldart D类颗粒会产生明显的漩涡和较大的气泡,不利于正常流态化和反应器操作,可以通过调节操作气速以及改变分布板结构实现射流,以达到改善颗粒运动和分布的目的。通过对反应器操作性能的考察发现,在免造粒工艺下,不同床层高度处的床层温度分布相对较低,通过分析颗粒的循环模式和固含率的分布特性,发现在该工艺下,床体的膨胀高度也较低,而且在反应器中会出现聚合物颗粒的明显聚集。同时,中试规模工业流化床反应器的床层扩大段能够限制气泡大小,降低固体颗粒速度和改善聚合物颗粒的流型,有利于该反应器的正常操作。该研究不仅有助于指导工业流化床反应器的结构设计与优化操作,而且还可以指导开发新的聚乙烯生产工艺,提高产能和降低能耗的同时,改善聚合物产品的性能。(5)在Borstar双峰聚乙烯生产工艺中,进行乙烯均聚反应的环管反应器和乙烯与1-丁烯共聚反应的流化床反应器内生产的聚合物颗粒的粒径大小分布以及形貌特征等均存在较大差异,且通过多粒模型建模和数值模拟得到了聚合物颗粒粒径大小与分子量分布之间的对应关系。同时发现,流化床反应器内生产的聚合物颗粒的孔隙率较大,而环管反应器内聚合物颗粒的表面则更为光滑。该研究可以为深入理解乙烯聚合反应过程和调控聚合物微观结构特征提供重要参考。
[Abstract]:The technology of polyolefin production reflects the industrial development level of a country, and its technological innovation is derived from the in-depth understanding and analysis of the physical transfer phenomena (mass, momentum and heat transfer) and chemical reaction characteristics contained in the process. The gas-phase polyethylene production process involves complex gas-solid two-phase flow, mixing and polymerization, and also contains time and space multi-scale phenomenon. The fluidized bed reactor is widely used in the process of gas-phase polyethylene production because of its relatively simple structure and excellent heat transfer performance, and its internal transfer characteristic, reaction condition and polymer product quality are affected by the gas-solid two-phase property of the fluidized bed and the operation state of the reactor. Therefore, a multi-phase flow reaction engineering theory is used for the process in which the transfer and polymerization reaction is coupled, and the gas-solid two-phase flow, the mixing and the reaction conditions are studied by means of a method for calculating the mass balance model of the fluid dynamics coupling group, It's challenging. The relevant model research not only has important academic research significance but also has important industrial application value. in that first place, the process of the change of the growth of the polymer particle and the particle morphology of the polymer particle is studied by means of single-particle modeling, The operation performance of the reactor in the production process is studied by means of computational fluid dynamics simulation of gas-solid two-phase flow, mixing and reaction characteristics in a pilot scale industrial fluidized bed polymerization reactor, and in combination with a multi-scale coupling model, The operation conditions and the design scheme of the reactor suitable for the production process of the non-granulated polyethylene are explored, and then, the multi-particle model coupled with the multi-active bits is used for combining the experimental characterization method for the Borstar bimodal polyethylene process, The morphology of the polymer particles and the variation of the properties of the polymer in the double-kettle series production of the bimodal polyethylene are studied, with a view to providing guidance for the production and control of the bimodal polyethylene and the quality optimization. The research of the production process of the non-prilling polyethylene is of great significance to the development of new technology for the production of more energy-saving and environment-friendly polyethylene, and in-depth analysis of the double-peak polyethylene production process has an important influence on the development of new products and new grades. Through in-depth study and analysis, this paper has obtained the following innovative research results: (1) on the single particle size of the ethylene gas-phase polymerization, The particle morphology and the polymer properties in the polyethylene production process can be better described by taking into account the common effects of both the physical transfer resistance and the chemical multi-active bit (mixed model). In the single-particle model, it is necessary to consider whether the change of the porosity depends on the size and distribution of the particle size of the catalyst particles, and in the production-free production process, there is a significant concentration and temperature gradient inside the polymer particles, which is not conducive to the normal operation of the polymerization process. In ord to improve that production technology of the non-prilling polyethylene, a cascade reactor process can be adopted in addition to the design of the catalyst support, and the process can be carried out smoothly by increasing the pre-polymerization process. (2) Two-dimensional CFD modeling and simulation are carried out on the pilot scale industrial fluidized bed reactor of the UNIPOL polyethylene production process, and it is found that the ring core flow structure inside the fluidized bed reactor exhibits significant characteristics of the expansion of the nuclear area and the reduction of the ring area due to the amplification effect. In addition, by comparing the two-dimensional and three-dimensional simulation results, it is found that the amplification effect in the reactor exhibits a similar trend. at the same time, the expanded section of the bed can obviously lower the speed of the polymer particles, improve the flow behavior characteristic of the solid particles in the reactor, and when the fluidized bed reactor is in a non-granulating production process, the operating gas speed of 0.90 m 路 s-1 can enable the reactor to reach a better fluidization state, But the operation becomes more sensitive. (3) Through the two-dimensional CFD-PBM modeling and simulation, it is found that the thermal mass transfer characteristic of the ethylene polymerization and gas-solid phase is affected, the bed expansion height of the fluidized bed reactor is obviously increased, the gas-solid two-phase content distribution becomes unstable and the axial particle distribution is widened. At the same time, the particle dynamics (particle growth, polymerization and crushing) have a large influence on the axial particle distribution of the initial fluidization stage, and the fracture of the polymer particles can obviously increase the expansion height of the bed layer, and the fluid dynamics can also influence the particle size and distribution of the polymer particles, In particular in the initial fluidization phase of the fluidized bed reactor. In that production process of the non-prilling polyethylene, the two-phase flow structure of the fluidized bed reactor and the variation of the particle size distribution of the polymer particle can also be caused due to the mutual influence of the polymerization reaction and the thermal mass transfer. In addition, the bed-enlarged section significantly influences the operating state of the fluidized-bed reactor in this process. (4) The study of the three-dimensional CFD-PBM coupling model shows that when the reactor is in the traditional production process (Geldart B-type particles) and the non-prilling production process (Geldart D-class particles), the interior of the bed shows a completely different two-phase fluid dynamics characteristic, And the polyethylene particles in the granulation-free process are gathered near the gas inlet of the distribution plate, and the operation of the reactor is not stable. At the same time, it is found that the Geldart D-like particles can generate distinct vortices and larger bubbles, which are not conducive to normal fluidization and reactor operation, and can realize the aim of improving the particle movement and distribution by adjusting the operating gas speed and changing the distribution plate structure. Through the investigation on the operation performance of the reactor, the bed temperature distribution at different bed heights is relatively low in the non-granulation process, and the expansion height of the bed body is also low by analyzing the distribution characteristics of the circulating mode and the solid content rate of the particles, And there is a significant aggregation of the polymer particles in the reactor. At the same time, the expanded section of the bed of the pilot scale industrial fluidized bed reactor can limit the bubble size, reduce the solid particle speed and improve the flow pattern of the polymer particles, and is beneficial to the normal operation of the reactor. The research not only helps to guide the structural design and optimization of the industrial fluidized bed reactor, but also can guide the development of new polyethylene production technology, improve the production capacity and reduce the energy consumption, and improve the performance of the polymer product. (5) in the Borstar bimodal polyethylene production process, the particle size distribution and the appearance characteristics of the polymer particles produced in the loop reactor and the ethylene and the 1-butene copolymerization reaction of the ethylene homo-reaction and the fluidized bed reactor of the copolymerization of ethylene and 1-butene have great differences, And the corresponding relation between the particle size and the molecular weight distribution of the polymer particles is obtained through the multi-particle model modeling and the numerical simulation. It was also found that the porosity of the polymer particles produced in the fluidized-bed reactor was large and the surface of the polymer particles in the loop reactor was smoother. The study can provide an important reference for the in-depth understanding of the process of ethylene polymerization and the control of the microstructure of the polymer.
【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ325.12;TQ052
，
本文编号：2498006
[Abstract]:The technology of polyolefin production reflects the industrial development level of a country, and its technological innovation is derived from the in-depth understanding and analysis of the physical transfer phenomena (mass, momentum and heat transfer) and chemical reaction characteristics contained in the process. The gas-phase polyethylene production process involves complex gas-solid two-phase flow, mixing and polymerization, and also contains time and space multi-scale phenomenon. The fluidized bed reactor is widely used in the process of gas-phase polyethylene production because of its relatively simple structure and excellent heat transfer performance, and its internal transfer characteristic, reaction condition and polymer product quality are affected by the gas-solid two-phase property of the fluidized bed and the operation state of the reactor. Therefore, a multi-phase flow reaction engineering theory is used for the process in which the transfer and polymerization reaction is coupled, and the gas-solid two-phase flow, the mixing and the reaction conditions are studied by means of a method for calculating the mass balance model of the fluid dynamics coupling group, It's challenging. The relevant model research not only has important academic research significance but also has important industrial application value. in that first place, the process of the change of the growth of the polymer particle and the particle morphology of the polymer particle is studied by means of single-particle modeling, The operation performance of the reactor in the production process is studied by means of computational fluid dynamics simulation of gas-solid two-phase flow, mixing and reaction characteristics in a pilot scale industrial fluidized bed polymerization reactor, and in combination with a multi-scale coupling model, The operation conditions and the design scheme of the reactor suitable for the production process of the non-granulated polyethylene are explored, and then, the multi-particle model coupled with the multi-active bits is used for combining the experimental characterization method for the Borstar bimodal polyethylene process, The morphology of the polymer particles and the variation of the properties of the polymer in the double-kettle series production of the bimodal polyethylene are studied, with a view to providing guidance for the production and control of the bimodal polyethylene and the quality optimization. The research of the production process of the non-prilling polyethylene is of great significance to the development of new technology for the production of more energy-saving and environment-friendly polyethylene, and in-depth analysis of the double-peak polyethylene production process has an important influence on the development of new products and new grades. Through in-depth study and analysis, this paper has obtained the following innovative research results: (1) on the single particle size of the ethylene gas-phase polymerization, The particle morphology and the polymer properties in the polyethylene production process can be better described by taking into account the common effects of both the physical transfer resistance and the chemical multi-active bit (mixed model). In the single-particle model, it is necessary to consider whether the change of the porosity depends on the size and distribution of the particle size of the catalyst particles, and in the production-free production process, there is a significant concentration and temperature gradient inside the polymer particles, which is not conducive to the normal operation of the polymerization process. In ord to improve that production technology of the non-prilling polyethylene, a cascade reactor process can be adopted in addition to the design of the catalyst support, and the process can be carried out smoothly by increasing the pre-polymerization process. (2) Two-dimensional CFD modeling and simulation are carried out on the pilot scale industrial fluidized bed reactor of the UNIPOL polyethylene production process, and it is found that the ring core flow structure inside the fluidized bed reactor exhibits significant characteristics of the expansion of the nuclear area and the reduction of the ring area due to the amplification effect. In addition, by comparing the two-dimensional and three-dimensional simulation results, it is found that the amplification effect in the reactor exhibits a similar trend. at the same time, the expanded section of the bed can obviously lower the speed of the polymer particles, improve the flow behavior characteristic of the solid particles in the reactor, and when the fluidized bed reactor is in a non-granulating production process, the operating gas speed of 0.90 m 路 s-1 can enable the reactor to reach a better fluidization state, But the operation becomes more sensitive. (3) Through the two-dimensional CFD-PBM modeling and simulation, it is found that the thermal mass transfer characteristic of the ethylene polymerization and gas-solid phase is affected, the bed expansion height of the fluidized bed reactor is obviously increased, the gas-solid two-phase content distribution becomes unstable and the axial particle distribution is widened. At the same time, the particle dynamics (particle growth, polymerization and crushing) have a large influence on the axial particle distribution of the initial fluidization stage, and the fracture of the polymer particles can obviously increase the expansion height of the bed layer, and the fluid dynamics can also influence the particle size and distribution of the polymer particles, In particular in the initial fluidization phase of the fluidized bed reactor. In that production process of the non-prilling polyethylene, the two-phase flow structure of the fluidized bed reactor and the variation of the particle size distribution of the polymer particle can also be caused due to the mutual influence of the polymerization reaction and the thermal mass transfer. In addition, the bed-enlarged section significantly influences the operating state of the fluidized-bed reactor in this process. (4) The study of the three-dimensional CFD-PBM coupling model shows that when the reactor is in the traditional production process (Geldart B-type particles) and the non-prilling production process (Geldart D-class particles), the interior of the bed shows a completely different two-phase fluid dynamics characteristic, And the polyethylene particles in the granulation-free process are gathered near the gas inlet of the distribution plate, and the operation of the reactor is not stable. At the same time, it is found that the Geldart D-like particles can generate distinct vortices and larger bubbles, which are not conducive to normal fluidization and reactor operation, and can realize the aim of improving the particle movement and distribution by adjusting the operating gas speed and changing the distribution plate structure. Through the investigation on the operation performance of the reactor, the bed temperature distribution at different bed heights is relatively low in the non-granulation process, and the expansion height of the bed body is also low by analyzing the distribution characteristics of the circulating mode and the solid content rate of the particles, And there is a significant aggregation of the polymer particles in the reactor. At the same time, the expanded section of the bed of the pilot scale industrial fluidized bed reactor can limit the bubble size, reduce the solid particle speed and improve the flow pattern of the polymer particles, and is beneficial to the normal operation of the reactor. The research not only helps to guide the structural design and optimization of the industrial fluidized bed reactor, but also can guide the development of new polyethylene production technology, improve the production capacity and reduce the energy consumption, and improve the performance of the polymer product. (5) in the Borstar bimodal polyethylene production process, the particle size distribution and the appearance characteristics of the polymer particles produced in the loop reactor and the ethylene and the 1-butene copolymerization reaction of the ethylene homo-reaction and the fluidized bed reactor of the copolymerization of ethylene and 1-butene have great differences, And the corresponding relation between the particle size and the molecular weight distribution of the polymer particles is obtained through the multi-particle model modeling and the numerical simulation. It was also found that the porosity of the polymer particles produced in the fluidized-bed reactor was large and the surface of the polymer particles in the loop reactor was smoother. The study can provide an important reference for the in-depth understanding of the process of ethylene polymerization and the control of the microstructure of the polymer.
【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ325.12;TQ052
，
本文编号：2498006
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