新型循环流化床反应器研究进展

开发新型循环流化床反应器始终是流态化领域研究的热点。本文首先简介了循环流态化的基本原理以及床层内部流体动力学特性,然后从装置构型、操作工况、流动特性以及应用前景等方面综述了近年来新型循环流化床反应器技术的研究进展,并对其进行了系统分类:高密度循环流化床和循环湍动流化床在实现提升管增浓的基础上,极大地改善了流化床体系中明显的不均匀时空流动结构,但是各有弊端,例如高密度循环流化床(HDCFB)中颗粒沿径向混合有很大的梯度,循环湍动流化床(CTFB)中存在强烈的轴向返混以及颗粒停留时间较长,且两者整体偏低的颗粒浓度进一步限制了其在两段提升管催化裂解多产丙烯(TMP)等生产低碳烯烃工艺的应用;变径提升管反应器、内循环型提升管反应器以及多流型提升管反应器等新型反应器将提升管高效的气力输送特性与密相床内较高的颗粒浓度、高效的热质传递等优点相互耦合,在提升管内既能实现高密度输送又能形成均匀的流动结构,消除反应环境对产品分布的影响。最后指出,新型循环流化床的研究应从改善流动结构、发展优化组合技术以及建立统一流动模型3个方面着手。     

液固提升管-流化床组合反应器中流化床径向固含率分布的实验研究

在一套新型液固提升管-流化床组合反应器中,以水-玻璃珠为液-固体系,对f500 mm′4000 mm的液固流化床反应器内不同高度颗粒固含率的径向分布进行了实验,考察了表观液速和颗粒循环速率操作条件对颗粒固含率径向分布的影响. 实验表明,液固流化床内流动区域在轴向上可以划分为分布器影响区、过渡区和均匀流化区,径向上可以划分为中心区和环隙区. 这种分布特征主要取决于分布器的结构、尺寸及其流化介质. 本工作还对液固流化床与气固喷动床的三区流动结构进行了比较.     

有机硅流化床反应器导热油管的传热性能比较

针对有机硅流化床反应器中两种主要的导热油管路——指形管和U形管,从传热管结构、传热性能和传热特性3个方面进行了对比。相比于指形管,U形管导热油管路可获得更好的总传热效果和反应温度条件。采用合理设计的同尺寸的U形管流化床反应器,产能可提升20%以上,并可提高二甲基二氯硅烷反应选择性。     

气固两相流内中空多孔催化剂性能的数值模拟

气固流态化过程中流体和颗粒分别聚集,形成稀密两相,严重限制其传质效率和反应速率的提高。针对此问题,本工作设计了一种中空多孔结构的催化剂颗粒,通过模拟方法研究该颗粒对稀密两相气相传质与反应的影响,及其在稀密相间转换的时间尺度。结果表明,一定的流动强度时,在颗粒稀密相转换的时间尺度内,中空多孔结构的颗粒能够有效地在稀相存储反应气体,并在密相释放,为密相提供额外的反应气体,增强体系的整体反应效率。当催化反应速率高于传质速率时,在所研究的流动条件下中空多孔颗粒体系的反应效率比实心球形颗粒体系高出26.92%~29.55%。可以预见在稀密相分布更广的大型气固流化床反应器中,中空多孔结构的催化剂颗粒能够更为有效地提高反应器的整体效率。     

干法造粒炉黑臭氧氧化流化床技术的开发(Ⅲ)连续反应及炉黑物料在流化床内的停留时间分布

对臭氧氧化干法炉黑物料的连续反应及干法炉黑物料在流化床内的停留时间分布进行了研究．连续反应实验结果表明：在反应条件相同的情况下,一级流化床与—级流化床都能把干法炉黑物料的ｐＨ值降到３．５,但很难反映出干法炉黑物料中真实的ｐＨ值分布．停留时间分布实验结果表明：干法炉黑物料在流化床内的流动为全混流,并得出了ｐＨ为３．５时,多级流化床出口处千法炉黑物料中真实的ｐＨ值分布,通过比较选用三级流化床较为合适．     

膜分离式酶解反应器流体流动特性

讨论了膜分离式酶解反应器进行酶解反应操作时流体流动的特性。导出停留时间分布函数方程式，采用降阶法的阶跃方式进行了实验验证。结果表明：实验值与按分布函数方程式的计算值吻合良好，通过与连续釜式反应器（ＣＳＴＲ）停留时间分布的特征值的比较，显示出这种反应器的优越性。     

微通道结构数值模拟及实验性能评价

Fluent软件的数值模拟结果显示伞形微通道结构比U形直线形微通道结构具有更加高效的混合效率,但该结构也存在流动死区,结合优化方向提出一种压降更小、混合效率较优更适用于液-液非均相反应的菱形微通道结构。同时,本文利用前述3种不同微通道结构反应器及常规反应器开展丙烯酸十四酯的合成评价对比实验,红外光谱及核磁谱图对反应产物的分析表征均证明了丙烯酸十四酯的生成。常规反应器和微反应器在相似工艺条件下,丙烯酸十四酯的收率仅为82%,停留时间更是长达300min,而微反应器中收率均达到90%以上,停留时间不超过3.5min,且菱形微通道结构反应器比U形直线形和伞形微通道结构反应器所得丙烯酸十四酯的收率都大,达到97%,说明菱形微通道结构更加有利于物料间的充分混合反应,这与菱形微通道结构数值模拟显示的结果是一致的,从而验证了数值模拟结果的可靠性。     

ＣＦＢ稀相段直长对颗粒内循环流动规律的影响

采用光纤探头测定Ｄ１m射流循环流化床（半圆形）稀相区颗粒速度、颗粒浓度和颗粒流通量的径向分布规律,并考察了操作条件及其轴向的影响,实验结果表明,在循环流化床（ＣＦＢ）中,颗粒流动在床层径向有较大的不均匀性,并呈明显的内循环流动结构,进而考察了影响其流动规律的,以期进一步理解循环流化床颗料流动机理,强化和改善反应器的设计操作。     

动态膜分离式酶反应器连续操作特性研究

在应用动态膜分离技术开发研制的新型多功能酶解反应器上进行了边反应分离的连续操作过程。通过在该反应器上进行菊粉酶等单基质酶不同操作形式的水解实验，考察了不同操作方式下反应器内流体流动的特性，并分别导出了停留时间分布函数式，从而对连续酶解过程的不同运行方式进行了研究。     

反应工程中的停留时间分布理论教学点滴

化学反应工程致力于研究化学反应机理,并根据反应特点设计合适的反应器。停留时间分布理论用于量化真实反应器的非理想流动特性,是反应工程课程的重要内容之一,也是解决反应工程实际问题的重要方法论。多年的教学实践表明,停留时间分布的概念、研究方法和应用部分的学习难度较大。因此,任课教师可以通过讲解虚拟现实模拟、停留时间分布测量技术及生活中的胶囊内镜案例,从宏观和微观尺度全方位揭示反应器内的非理想流动特征,并通过翻转课堂的教学方式让学生真正掌握停留时间分布理论。     

内置螺旋挡板流化床颗粒停留时间分布

采用脉冲示踪法在内置螺旋挡板冷态鼓泡流化床上研究了螺旋挡板、加料速率、流化风速、颗粒粒径和床料高度对颗粒在流化床内停留时间分布的影响. 结果表明,颗粒停留时间的无量纲方差从无螺旋挡板时的0.558减小到有螺旋挡板时的0.085,螺旋挡板可有效抑制颗粒返混,增大颗粒运动的平推流趋势;加料速率增大为约2倍时,停留时间减小为约50%,流动更趋向于平推流;床料高度增加,颗粒返混加剧,颗粒平均停留时间及无量纲方差均增大,颗粒运动向全混流靠近;随流化风速增大,颗粒平均停留时间变长;实验范围内,颗粒粒径对颗粒停留时间分布影响不大.     

鼓泡流化床内高灰煤气化过程的颗粒尺度特性研究

基于多相流体质点网格方法(MP-PIC)对高灰煤在三维鼓泡流化床气化过程进行了数值模拟研究。在欧拉-拉格朗日框架下将气相和固相分别视作连续介质和离散相处理。首先,将模拟得到的出口处气体组分结果与实验数据进行对比,实验数据与模拟结果具有良好的一致性。其次,研究了煤颗粒在气化炉内的温度、传热系数、速度和停留时间,从颗粒尺度揭示了鼓泡流化床气化炉内的颗粒分布特性和气固流动特征。结果表明:在气化炉入口附近煤颗粒与床层温差最大,传热系数最大;由于流化床内强非线性的气固流动,床中煤温度和传热系数的空间分布不均匀;煤颗粒和床料的瞬时速度具有稳定的波动幅度,其中垂直方向速度波动最明显,且煤颗粒的瞬时速度比床料的瞬时速度略大;由于颗粒间的剧烈碰撞,延长了煤颗粒停留时间。此外,对鼓泡流化床中煤气化过程颗粒尺度的研究,有助于深入了解固体颗粒的流动行为以及气固相相互作用特性,对鼓泡流化床反应器的设计优化具有重要意义。     

连续进出料鼓泡流化床颗粒停留时间分布

针对双流化床气化或双床热解气化工艺中鼓泡床反应器的设计,采用脉冲法研究了Geldart B类固体颗粒在连续颗粒进料和出料的矩形流化床内的停留时间分布(RTD),考察了气速、床料高度、粒径、物料流率等操作参数对RTD的影响. 结果表明,物料流率、床料高度、粒径是影响颗粒RTD的主要因素,而气速则是次要因素. 随物料流率和粒径增加,鼓泡床内颗粒流动向平推流靠近;随床料高度增加,物料在床内的混合更加充分,颗粒流动向全混流靠近. 根据实验结果,推荐采用比理想平推流时间低9%~18%计算平均颗粒停留时间.     

连续操作密相流化床颗粒停留时间分布特性模拟放大研究

采用基于GPU（graphics processing unit）大规模并行的粗粒化CFD-DEM（computational fluid dynamics-discrete element method）方法,耦合多分散、非球形颗粒曳力模型,对连续操作的三维流化床进行了长时间颗粒停留时间模拟。通过对不同尺寸（长度）流化床的模拟发现不同粒径颗粒平均停留时间（mean residence time,MRT）与流化床长度呈线性关系,该关系可以用来预测更大尺寸流化床内的颗粒停留时间。随着流化床长度的增加,不同粒径颗粒MRT的差异变大,说明流化床长度的增加对不同尺寸颗粒的停留时间具有一定的调控能力。     

On two-compartment population balance modeling of spray fluidized bed agglomeration

The present work focuses on the modeling and analysis of a spray fluidized bed granulation (SFBG) process based upon the concept that particles are communicating between the two compartments at some steady state mass flow rate. A numerical technique for solving the proposed two-compartment model (2CM) is developed and validated against some newly derived analytical solutions. Moreover, the inverse technique for extracting the rate constant of one-compartment model (1CM) is extended to 2CM. A correlation of aggregation rate constant of 2CM with the rate constant of conventional 1CM under some restrictions is investigated and it is found that the 1CM cannot be used, in general, to predict results of 2CM. Furthermore, it is observed that the existence of two zones in SFBG is responsible to certain extent for time dependent behaviour of aggregation rate constant. Finally, influence of compartment sizes and particles residence times on particle size distribution is investigated.     

小型气-液-固流化床液相的停留时间分布

采用脉冲示踪技术,研究了3 mm床径的小型气-液-固流化床内液相停留时间分布。以KCl为示踪剂,液相为去离子水,气相为空气,固相为平均粒径0.123~0.222 mm的玻璃微珠和氧化铝颗粒,测量流化床出口液相的电导率,得到其停留时间分布曲线。结果表明,增大表观液速和表观气速,分布曲线变窄,平均停留时间缩短,Peclet数增大;固相的存在使液相的平均停留时间增长。表观液速1.96~15.70 mm×s^-1,表观气速1.18~1.96 mm×s^-1的条件下,流动接近层流;平均停留时间的范围为（19.6±0.34）s~（48.0±0.92）s,建立的Pe经验关联式对实验结果有较好的预测,偏差在±25%以内。研究结果对于小型三相流化床的设计放大具有指导意义。     

DEM-LES of coal combustion in a bubbling fluidized bed. Part I: gas-particle turbulent flow structure

The gas and particle motions in a bubbling fluidized bed both with and without chemical reactions are numerically simulated. The solid phase is modelled as Discrete Element Method (DEM) and the gas phase is modelled as 2-D Navier-Stokes equations for 2-phase flow with fluid turbulence calculated by large Eddy simulation (LES), in which the effect of particles on subgrid scale gas flow is taken into account. The gas/particle flow structure, the mean velocities and turbulent intensities can be predicted as a function of several operating parameters (particle size, bed temperature, and inlet gas velocity). The lower the inlet gas velocity, the higher the ratio of particle collision. The distributions of the particle anisotropic velocity show that the particles have no local equilibrium, and the distribution of gas kinetic energy corresponds to the distribution of gas-particle coupling moment in the fluidized bed. An intensive particle turbulent region exists near the wall, and the gas Reynolds stress is always much higher than the particle stress. The presence of the large reactive particles in the fluidized bed may affect significantly the gas and particle velocities and turbulent intensities. The effects of the bed temperature and inlet gas velocity on the gas particle flow structure, velocity, and turbulent intensity are also studied.     

Influence of ring-type internals on the solids residence time distribution in the fuel reactor of a dual circulating fluidized bed system for chemical looping combustion

The intensification of gas-solids contact in the fuel reactor of a chemical looping combustion system is enhanced with the installation of ring-type internals. This can be a key issue for achieving the necessary fuel conversion rates. Wedged rings, previously designed and tested, were found to increase the particle concentration in the counter current section of the fuel reactor and hence, to achieve a more homogeneous particles concentration along this zone. The present work investigates the effect of the mentioned internals on the residence time distribution of particles in the fuel reactor of a dual circulating fluidized bed system for chemical looping. The study was carried out in a cold flow model especially designed for the fluid-dynamic analysis of the system equipped with a recently developed residence time measurement device based on the detection of ferromagnetic tracer particles through inductance measurement. Ring internals proved the positive effect on the particles residence time, the residence time distribution is more symmetric and shows lower dispersion, the flow pattern is more plug-flow-like, these effects are intensified with the reduction of the aperture ratio of the rings. On the other hand, the upward particle transport in the counter-current zone of the fuel reactor also increases with the installation of the rings, increasing the bypass flow of solids through the fuel reactor's return loop (internal circulation). For high internal circulation rates the solids residence time distribution of the fuel reactor is dominated by the bypass effect. The findings may be used for focused design improvement of the investigated fluidized bed system.     

Fluidization behavior in a circulating slugging fluidized bed reactor. Part I: Residence time and residence time distribution of polyethylene solids

Square nosed slugging fluidization behavior in a circulating fluidized bed riser using a polyethylene powder with a very wide particle size distribution was studied. In square nosed slugging fluidization the extent of mixing of particles of different size depends on the riser diameter, gas velocity, hold up and solids flux in the riser. Depending on the operating conditions the particle residence time distribution of a riser in the slugging fluidization regime can vary from that of a plug flow reactor to that of a well-mixed system.Higher gas velocities cause shorter particle residence times because of a significant decrease in the hold-up of particles in the riser at higher gas velocities. A higher solids flux also shortens the average residence time. Both influences have been quantified for a given polyethylene-air system.Residence time and residence time distribution were determined for different particle size and the influence of gas velocity, solids flux, hold up and riser diameter was studied. When comparing data from segregation and residence time experiments it is clear that segregation data can predict the spread in residence time as a function of overall residence time, particle size and gas velocity. The differential velocity between small and large particles found in the segregation experiments can predict the spread in residence time as found in the residence time distribution experiments with a powder with a broad particle size distribution. Raining of particles through the slugs was studied as a function of plug length, gas velocity and pulse length. It was found that raining is not the determining mechanism for segregation of particles.