【作者】 傅杰；

【导师】 袁渭康；

【作者基本信息】 华东理工大学 ， 化学工程， 2013， 博士

【摘要】 列管式固定床反应器是用于进行强放热气固相催化反应的主要反应器,在化学工业中有着广泛的应用。目前,列管式固定床反应器规模在不断扩大,其操作要求也在不断提高。如何实现反应器的优化设计和操作、提高反应过程的稳定性和经济性是化学反应工程研究的重要议题。本文从反应器设计和操作角度研究列管固定床反应器的流体流动、传热及其数值特征,为大型工业反应器设计及操作提供参考和依据。论文分别建立起并流列管反应器冷却介质流动与均布的计算模型以及盘环型错流列管反应器管间流动与传热的计算模型,研究了并流反应器中影响分布板布孔的主要因素以及盘环型列管式固定床中影响反应器操作性能的主要结构参数。并在盘环型列管式固定床反应器研究的基础上对其数值特征进行了探索,用于反应器的监测和控制。论文的主要研究结论如下：对于并流反应器,在对反应器分布板布孔过程中,相对于环隙孔调节,通过在分布板上固定环隙孔孔径,沿不同径向位置分布不同大小的附加小孔(附加小孔调节)可以得到更大的小孔孔径分布范围,更有利于工程上调节、加工。在分布板环隙孔大小不变的情况下,反应器并流区设计流速越大,分布板上得到的小孔孔径分布范围相应越小。为了增大分布板上小孔分布范围,可以在设计过程中使分布板基准位置(分布板边缘位置)流体的穿孔压降略大于并流区流体均布条件下分流室中流体压降。并流反应器放大过程中,分流室中流体压降会迅速增大,反应器直径每增大10%,分流室中流体压降将增大31～33%。在分布板上进行分布小孔的同时,还需要减小分布板上环隙孔孔径。环隙孔过小会给分布板加工以及反应器装配带来不便,成为反应器放大的瓶颈。对反应器设置较大的中心不布管区域以及增大反应器分流室高度可以降低反应器分流室中流体压降,增大分布板上所要求的环隙孔孔径,达到放大并流反应器的目的。反应器直径每增大10%,分流室高度要增大20%以平衡反应器放大引起的分流室流体压降的增大。在反应器中心设置较大的不布管区域,分流室压降降低效果较为明显。反应器直径增大10%,需要在反应器中心设置30%的不布管区域来平衡反应器放大引起的分流室中流体压降的增大。对于盘环型错流反应器,反应器窗口区(泄流区)会使冷却介质错流流量迅速衰减,使反应器中心区域以及近壁区域冷却介质流量过小,不利于传热。对反应器中心区域进行不布管后,可以保证反应器最内侧反应管周围的流体环境,控制反应器中心区域反应管催化剂床层热点温度,达到减小反应器热点温差的目的。对直径4.6m的反应器,不布管区域大小取反应器内径的10%最为有利。通过调节环板缺口大小可以调整反应器盘环板之间主体区域以及中心窗口区中冷却介质流量大小。环板缺口越大,盘环板之间主体区域中冷却介质的流量越大,但中心窗口区过大,导致反应器中心区域冷却介质流量过小。减小环板缺口可以使反应器中心区域流量增大,但是反应器盘环板之间的主体区域中冷却介质流量相应降低,反应器压降也会因为环板缺口减小而显著增大。在反应器中心不布管区域较大的情况下,适合将反应器环板缺口开大,以增大盘环板间主体区域中冷却介质的流量。当反应器中心10%区域不布管时,反应器环板缺口取反应器内径的25%较为合适。相应地,可以通过调节盘板直径大小来调整壁面窗口区大小。反应器折流板-反应管环隙间距对反应器中冷却介质流动分布以及温度分布影响较大。折流板-反应管环隙间距较小时,冷却介质在反应器中的流动以错流流动为主,冷却介质温度沿流动方向逐渐升高,反应器催化剂床层温度分布较为均匀。折流板-反应管环隙间距较大时,冷却介质在折流板上的流动会出现明显的漏流,冷却介质流量分布以及温度分布都呈现显著的径向分布,催化剂床层的径向温差也较大。减小折流板层间距有助于强化盘环板之间主体区域中冷却介质的移热能力,但是壁面附近反应管中反应的热点位置也会因为折流板层间距的变化移到第二层壁面窗口区的深处,使得壁面附近反应管的热点温度上升,反应器热点温差增大。在对反应器数值特征的研究中,通过对不同操作条件下盘环型列管反应器床层温度数据进行两步Karhunen-Loeve (K-L)展开,第一步展开三项,展开的各项进一步展开一项得到的截断展开可以很好地重建反应器催化剂床层温度分布。催化剂床层温度分布可以由K-L展开式中三个与操作参数关联的系数进行表示,进而反应器催化剂床层温度分布可以简化成系数空间的一个状态点。不同操作变量的变化会使状态点在系数空间沿不同轨迹移动。论文建立了两个模型参数：偏离角度θ以及偏离程度r,分别用于识别反应器操作过程中偏离设计条件的操作变量以及相应变量的参数。更多还原

【Abstract】 Multitubular fixed-bed reactors which are the main reactors to carry out highly exothermic heterogeneous catalytic reactions have been widely used in chemical industry. With the expansion of the Multitubular reactor scales and the highly-demand of the operational requirement, how to optimize the reactor design and operation, and how to improve the stability and economy of the reaction process are the important issues in the field of chemical reaction engineering. In this work, the coolant flow, heat transfer and numerical characteristics in a multitubular fixed-bed reactor are studied from the reactor design and operation point of view, so as to provide the reference and basis for large-scale industrial reactor design and operation.In the work, a coolant distribution and parallel flow model for a multitubular fixed-bed reactor and a coolant flow and heat transfer model for a cross flow multitubular reactor equipped with disk and doughnut baffles are respectively established. The main factors which have an influence on hole-distribution on the distributing plate in the parallel flow reactor and the main structural parameters which have an influence on operational performance in the cross flow reactor equipped with disk and doughnut baffles are studied. The numerical characteristics are explored on the basis of research on the cross flow reactor, which could be further applied to reactor monitoring and control. The main achievements in the thesis are as follows:As for parallel flow reactors, in the process of distributing tube holes and additional orifices on the distributing plate, additional orifice adjustment which fixes the size of the tube holes, and distributes the additional orifices on the distributing plate along the radial direction can obtain much wider range of the orifice size distribution than tube-to-plate clearance adjustment does. It is more feasible to adjust and manufacture the distributing plate through the additional orifice adjustment in an engineering sense. With the increase of designed velocity in the parallel flow region, the range of the orifice size distribution will decrease when the tube-to-plate clearances on the distributing plate keeps constant. In order to increase the orifice size distribution range, the perforation pressure drop in the margin of the distributing plate could be designed a little higher than the pressure drop in the distributing chamber in the design stage. In the process of scaling up the parallel flow reactor, the pressure drop in the distributing chamber will increase rapidly. The fluid pressure drop in the chamber will increase by31-33%when the diameter of the reactor increases by10%. The required tube-to-plate clearance accordingly needs to be decreased even though the additional orifices are well distributed on the plate. This small clearance is the bottleneck for manufacturing the distributing plate and assembling the reactor. Removing the tubes in the reactor central region and/or increasing the height of distributing chamber can reduce the fluid pressure drop in distributing chamber, and enlarge the required tube-to-plate clearance. The goal to scale up the reactor could be achieved. When the diameter of the reactor increases by10%, the height of the distributing chamber has to be increased by20%to balance the increased pressure drop in the chamber in process of scaling up the reactor. Setting a large area of non-tube region in the reactor center could also evidently reduce the pressure drop in distributing chamber. When the reactor size increases by10%, the diameter of the central non-tube region has to be set at least30%of the reactor inner diameter to balance the increased pressure drop in the chamber in process of scaling up the reactor.As for cross flow reactors equipped with disk and doughnut baffles, reactor window zones make the coolant flow rate decay rapidly. Low value of the coolant flow rate is unfavorable for heat transfer in the reactor central and wall adjacent region. Removing the tubes in the reactor central region ensures the proper fluid environment around reactor innermost tubes, keeps the hot spot temperature in the central region in a proper level, and thus reduces the difference of the hot spot temperature in the reactor. For a reactor with4.6m in diameter, the optimal size of the central non-tube region is10%of the reactor inner diameter. The coolant flow rate in the zone between the disk and doughnut baffles and that in the central window zone can be adjusted through adjusting the size of the doughnut baffle opening. The larger the doughnut baffle opening, the higher the coolant flow rate in the zone between the disk and doughnut baffles, but the large opening causes the central window zone large, which makes the flow rate in the reactor center low. Decreasing the doughnut baffle opening could increase the flow rate in the central region, but the flow rate in the zone between the disk and doughnut baffles decreases at the same time. The pressure drop of the reactor increases significantly with the doughnut baffle opening decrease. When the size of the central non-tube region is large, it is advisable to make doughnut baffle opening large, and thus the flow rate in the zone between the disk and doughnut baffles could be high. When the size of the central non-tube region is10%of the reactor inner diameter, the optimal size of the doughnut baffle opening is25%of the reactor inner diameter. Similarly, the wall adjacent window zone could be adjusted through adjusting the size of the disk baffles. Tube to baffle clearance has a great influence on coolant flow and temperature distribution. When the tube to baffle clearance is small, the cross flow is the predominant flow pattern in the reactor, and the coolant temperature increases along the coolant flow direction. The catalyst temperature distribution is desirable in this situation. When the tube to baffle clearance is relatively large, there is obvious leakage flow on the baffle, which makes coolant flow and temperature show marked radial distribution and makes the difference of the hot spot temperature large in the reactor. Decreasing the baffle clearance helps to strengthen the coolant capability of heat removal in the zone between the disk and doughnut baffles, but the hot spot position inside the tubes moves to the depth of the wall adjacent window zone, where the hot spot temperature in the tubes turns high, and makes the difference of the hot spot temperature large in the reactor.As for the research on the numerical characteristics of the reactor, the Karhunen-Loeve (K-L) expansion is performed in a two-step mode on the dataset of the catalyst bed temperature distribution in a multitubular fixed-bed reactor equipped with disk and doughnut baffles under different operating conditions. The two-step K-L expansion, which uses the first three eigenvectors in the first step, and the first eigenvectors in the second step, can reconstruct the bed temperature well. The catalyst bed temperature distribution in both axial and radial directions can be represented by three coefficients related to a particular operating condition. Thus the bed temperature distribution can be reduced to a state point in a coefficient space. The deviation of a particular operating variable makes the state point move along a specific trajectory. Two model parameters (θ and г) are established to recognize the deviated operating variable and quantify the deviated extent.更多还原