STRUCTURE OPTIMIZATION OF A CIRCULATING MOVING BED REACTOR

A stress distribution model for a liquid-solid circulating moving bed reactor that consists of a bottom reaction chamber, a top regeneration chamber, a coupling standpipe, a particle transportation system, and a bottom standpipe is established based on the equations of continuity and momentum balance. Simulations show that the stress concentration regions are at the bottom of the regeneration chamber and the coupling standpipe. To reduce the maximal stress and increase the operation flexibility in a reactor for the 2000-ton-per-year production of linear alkylbenzene, the regeneration chamber should have a low height-to-radius ratio (about 9), a suitable half-conical angle between 28° and 35°, and standpipe radius of about 0.05 m.     

STRUCTURE OPTIMIZATION OF A CIRCULATING MOVING BED REACTOR

A stress distribution model for a liquid-solid circulating moving bed reactor that consists of a bottom reaction chamber, a top regeneration chamber, a coupling standpipe, a particle transportation system, and a bottom standpipe is established based on the equations of continuity and momentum balance. Simulations show that the stress concentration regions are at the bottom of the regeneration chamber and the coupling standpipe. To reduce the maximal stress and increase the operation flexibility in a reactor for the 2000-ton-per-year production of linear alkylbenzene, the regeneration chamber should have a low height-to-radius ratio (about 9), a suitable half-conical angle between 28° and 35°, and standpipe radius of about 0.05 m.     

Operation characteristics of a new liquid-solid circulating moving bed reactor

The liquid-solid circulating moving bed reactor is a novel one, which consists of two or more reaction chambers and a particle transport system. Particles move down to the lower reaction chamber from the upper reaction chamber through an upper conduit and to the particle transport system through a lower conduit, and then are conveyed into the upper reaction chamber through a riser. The circulating rate of particles and the flow of liquid in the two conduits are key factors to the continuous steady operation of the reactor; they can be controlled by varying operating conditions: the outlet liquid flow rate in the regeneration chamber, the outlet liquid flow rate in the reaction chamber, the inlet liquid flow rate of the reactants, and the flow rate of driving flow. A flow model has been proposed to quantify the operation characteristics of the reactor. The results predicted by the model show satisfactory agreement with the experimental data.     

OPERATION CHARACTERISTICS OF A NEW LIQUID-SOLID CIRCULATING MOVING BED REACTOR

The liquid-solid circulating moving bed reactor is a novel one, which consists of two or more reaction chambers and a particle transport system. Particles move down to the lower reaction chamber from the upper reaction chamber through an upper conduit and to the particle transport system through a lower conduit, and then are conveyed into the upper reaction chamber through a riser. The circulating rate of particles and the flow of liquid in the two conduits are key factors to the continuous steady operation of the reactor; they can be controlled by varying operating conditions: the outlet liquid flow rate in the regeneration chamber, the outlet liquid flow rate in the reaction chamber, the inlet liquid flow rate of the reactants, and the flow rate of driving flow. A flow model has been proposed to quantify the operation characteristics of the reactor. The results predicted by the model show satisfactory agreement with the experimental data.     

液固循环移动床反应器操作规律和模拟

液固循环移动床反应 -再生系统由上下两个或两个以上的反应室、再生室、连通管和颗粒提升管组成 .颗粒经再生室、反应室向下移动 ,进入输送管后被向上输送返回至再生室 .颗粒循环能力和各流股间的窜液行为是循环移动床连续操作的关键 .通过实验对该液固循环移动床的颗粒循环、斜管窜液和连接段窜液的规律进行了研究 ,同时建立了循环移动床的液固流动模型 ,并进行了模拟计算     

液固循环移动床反应-再生系统的颗粒循环量调节和输送

液固循环移动床反应－再生系统由上下两个或两个以上的反应室、再生室、连通管和颗粒提升管组成。颗粒经再生室、反应室向下移动,进入输送管后被向上输送返回至再生室。颗粒循环能力决定了反应室和再生室内的颗粒更新速率。是循环移动床操作的关键之一,对反应器的颗粒循环进行了实验研究,提出了一种射流输送和调节结构并对射流输送行为进行了模拟计算。     

影响FCC再生立管输送催化剂影响因素的分析

再生立管是FCC装置再生器和提升管反应器之间再生催化剂循环的输送管,其操作复杂性在于立管内催化剂的流态受多种因素影响。本文中在1.0Mt/a FCC装置上,通过测量立管改造前后不同操作条件时的轴向压力分布,考察再生立管输送催化剂的影响因素。生产运行结果表明,影响立管操作的主要因素包括催化剂密度和平均粒径、立管几何结构、滑阀安装位置、松动风性质和流量等;选用低密度催化剂和高黏度流化介质可以减小气泡尺寸,维持反应温度稳定;松动风流量应根据立管推动力、滑阀压降和反应温度及时调整,避免填充流。另外,立管结构和滑阀的安装位置对立管推动力影响较大,分析结果可供立管设计和装置改造参考。     

Solid concentration and velocity distributions in an annulus turbulent fluidized bed

Solid concentration and particle velocity distributions in the transition section of a?200 mm turbulent fluidized bed (TFB) and a?200 mm annulus turbulent fluidized bed (A-TFB) with a?50 mm central standpipe were mea-sured using a PV6D optical probe. It is concluded that in turbulent regime, the axial distribution of solid concen-tration in A-TFB was similar to that in TFB, but the former had a shorter transition section. The axial solid concentration distribution, probability density, and power spectral distributions revealed that the standpipe hin-dered the turbulence of gas–solid two-phase flow at a low superficial gas velocity. Consequently, the bottom flow of A-TFB approached the bubbling fluidization pattern. By contrast, the standpipe facilitated the turbulence at a high superficial gas velocity, thus making the bottom flow of A-TFB approach the fast fluidization pattern. Both the particle velocity and solid concentration distribution presented a unimodal distribution in A-TFB and TFB. However, the standpipe at a high gas velocity and in the transition or dilute phase section significantly affected the radial distribution of flow parameters, presenting a bimodal distribution with particle concentration higher near the internal and external wal s and in downward flow. Conversely, particle concentration in the middle an-nulus area was lower, and particles flowed upward. This result indicated that the standpipe destroyed the core-annular structure of TFB in the transition and dilute phase sections at a high gas velocity and also improved the particle distribution of TFB. In conclusion, the standpipe improved the fluidization quality and flow homogeneity at high gas velocity and in the transition or dilute phase section, but caused opposite phenomena at low gas ve-locity and in the dense-phase section.     

Design and simulation of a solar chemical reactor for the thermal reduction of metal oxides: Case study of zinc oxide dissociation

A laboratory-scale solar reactor was designed and simulated for the thermal reduction of metal oxides involved in water-splitting thermochemical cycles for hydrogen production. This reactor features a cavity-receiver directly heated by concentrated solar energy, in which solid particles are continuously injected. A computational model was developed by coupling the fluid flow, heat and mass transfer, and the chemical reaction. The reactive particle-laden flow was simulated, accounting for a multiphase model (solid-gas flow). A discrete phase model based on a Lagrangian approach was developed. The kinetics of the chemical reaction was considered in the specific case of zinc oxide dissociation for which reliable data are available. The complete model predicts temperature and gas velocity distributions, species concentration profiles inside the reactor, particle trajectories and fates, and conversion rate assessing the reaction degree of completion. The reaction extent is highly dependent on temperature of the radiation-absorbing particles. Initial diameter of injected particles is also a key parameter because it determines the available surface area for a given particle mass feed rate. The higher the particle surface area, the higher the conversion rate. As a result, reaction completion can be achieved when particle temperature exceeds 2200 K for a initial particle diameter.     

循环流化床煤燃烧/热解双反应器系统稳定性分析

为了考察循环流化床煤燃烧/热解双反应器系统的稳定性,在冷态实验装置上以电厂锅炉灰为实验物料,其中提升管的内径为100 mm,高为6.7 m,与热解室相连立管的内径为44 mm,高3 m,热解室的截面积为200 mm×200 mm,高770 mm。分别考察了影响系统稳定运行的主要因素,并对系统中存在的几对平衡关系进行了分析。结果表明,旋风料腿内的固体料位高度、热解室内的料位高度以及热解室内的压力等是影响系统稳定运行的关键因素,尤其是热解室内压力的增加有可能使立管内料封破坏,最终导致系统瘫痪。而提升管与热解室立管之间压力的平衡以及提升管与旋风分离器料腿之间压力的平衡等在操作过程中必须保持稳定,否则也会发生窜气、架料、旋风分离器效率下降等现象,影响系统稳定运行。     

循环射流流化床立管中气固流动实验研究

立管是气固循环系统的重要组成 ,其复杂性在于存在着各种流动体系。实验中循环射流流化床选用的循环立管结构是在其末端安置水平挡板作为限流构件 ,考察了水平挡板高度、加料量、射流气速等对立管料柱平衡高度的影响 ;采用气体示踪法测定了颗粒在立管中的流动速度和气体速度 ,并与立管中空隙率进行了关联 ,进而提出预测循环立管移动床流动状况的方法     

负压差立管内气固两相流的流态特性及分析

对于出口插入密相床的立管，管内气固两相的流动特点是下行的颗粒速度大于气体速度和颗粒的逆压差流动，颗粒下行是一个减速运动过程. 管内的气固两相流的流态有两种形式，当GsGsc时，流态是浓相输送流态，气流下行. 两种流态可以互相转变，主要取决于颗粒质量流率的大小. 负压差立管的流态变化与气固两相之间滑落速度和轴向压力的变化密切相关，滑落速度随颗粒质量流率的增加逐渐减小，而轴向压力则逐渐增大以平衡立管的负压差.     

不同充气条件下密相输运床返料系统气固流动数值模拟

采用计算颗粒流体力学对密相输运床返料系统内的气固流动行为进行了数值模拟,分析了曳力模型和颗粒最大堆积浓度等参数对模拟结果的影响,确定了合适的模型参数。通过对比3组工况的模拟结果,获得了与实验结果基本一致的立管压力分布和固体循环流率随充气条件的变化规律,并分析了立管内压力梯度分布、气体流动方向、颗粒浓度分布等。结果表明立管充气口处压力梯度绝对值为局部最大值;当立管充气口气量为零时,会使充气口上方一段距离的压力梯度绝对值较小;充气量增大到一定值时会在充气口附近形成明显的气泡。当缺少立管高位充气时,会导致立管下部区域形成大的压力梯度,增加颗粒下落阻力。充气松动颗粒的作用仅对充气口附近区域有一定影响,更大的作用是在立管内形成均匀的压力梯度分布,使立管内气固流动状态保持上下一致。在制定充气方案时,应根据固体循环流率确定立管压降,补充合适气体量以维持气体下行速度均衡,使得各段的平均压力梯度相同。     

CFB煤燃烧／热解双反应器立管内气固流动模型分析

在循环流化床（CFB）煤燃烧／热解双反应器冷态实验装置上,以硅胶和电厂锅炉灰为实验物料,考察了立管内的气固流动特性,其中立管的内径44mm、高3m。研究结果表明,立管内的气固流动形态为移动床流动,Leung的立管流动模型适合对该系统中立管内移动床流动的描述,经拟合分别得到了立管内气、同速率以及气同相对速率与固体速率之间的经验方程,对热态实验过程中判断立管内的气固流动型态以及料封的稳定性均具有一定的参考价值。     

全混流反应器内流动规律模拟研究

研究了一种接近全混流的小型气固相反应器,可以用于在实验室研究时需要实现全混流接触状态的气固相反应的研究.采用计算流体力学软件(CFD)进行模拟得到最优结构,其结构包括1个圆锥形反应器主体,4个连接在反应器主体底部的进料口,1个连接在反应器主体上部的出料口.气体从4个进料口进入,催化剂在流动过程中从中部掉落,形成气体水平...     

Simulation and experiment of gas–solid flow field in short-contact cyclone reactors

A short-contact cyclone reactor has been designed for the particular case of fluid catalytic cracking. The new type reactor mainly includes two parts: a reaction chamber and a separation chamber. So the cracking reactions and the separations between the products and catalysts could occur respectively and simultaneously. A three dimensional model was used to representing key parts of a laboratory cyclone reactor. The Eulerian–Eulerian computational fluid dynamics model with the kinetic theory of granular flow was adopted to simulate the gas–solid two-phase flow. The particle concentration distribution and pressure drop were measured by a PV-6A particles velocity measure instrument and a U-manometer, respectively. Simulated results show that in the reaction chamber solids can be transformed into a homogeneous dispersed flow, particles’ concentration becomes uniform gradually while catalysts flowing down, the concentration is a little higher near the wall because of boundary effect. After the gas–solid flowing into the separation chamber, the gas phase is separated with solids completely. The new reactor has a good contact and separation effect. Simulated results make a reasonable agreement with the experimental findings.     

Determination of standpipe pressure profiles and slide valve orifice discharge coefficients on synthol circulating fluidized-bed reactors

A Synthol Circulating Fluidized-Bed (CFB) reactor utilizes a finely divided, reduced iron oxide catalyst to convert (CO + H₂) to gaseous and liquid fuels. The reactor consists essentially of a fast-fluidized bed with a hopper and standpipe providing a pressure seal sufficient to maintain a high catalyst inventory in the reaction zone. For optimum reactor operation, the catalyst must flow down the standpipe in the dense-phase fluidized-flow regime so giving maximum pressure recovery.Tests carried out on the Sasol 1 commercial reactors showed that the dense-phase flow regime could be maintained with minimal use of added aeration. Work carried out on a large cold-model hopper and standpipe showed that added aeration was vital in maintaining dense-phase flow and in achieving a high pressure recovery. The relatively high pressure operation of the commercial reactors and consequent low compression effect going down the standpipe is such that the entrapped aeration entering the standpipe is sufficient to prevent a flow regime transition to a packed bed. Orifice discharge coefficients determined on the commercial reactors and the cold model agreed closely with values reported in the literature.     

An evaluation of the pneumatic transport reactor

In a pneumatic transport reactor, a dilute suspension of the reacting solid particles is conveyed by the gas stream through the reactor. The system is characterized by very short particle residence times. The relative flow rates of gas and solids are determined by the thermodynamic and kinetic requirements of the reacting conveyed systems. Design considerations for co-current gas and solids flows are presented and a comparison between co-gravity and counter-gravity flow reactors is discussed for the case of iron ore reduction by hydrogen. Kinetic data from single particle studies have been used to predict the performance of a pilot-scale reactor.     

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.     

EFFECTS OF PARTICLE CHARACTERISTICS ON THE PERFORMANCE OF A FAST FLUIDIZED BED REACTOR

A heterogeneous model for the fast fluidized bed reactor which carries out a gas-solid non catalytic reaction is presented. The hydrodynamics of the fast fluidized bed is characterized by the model of Kwauk et al. (1985) which assumes the existence of two phases; a dense phase and a dilute pneumatic transport phase. For a given solid flowrate, the length of the reactor occupied by each phase depends on gas velocity, particle diameter and density and average voidage within the reactor. The gas-solid reaction is assumed to follow the shrinking core model. The solids are assumed to be completely backmixed in the dense phase and move in plug How in the dilute pneumatic transport phase. The gas phase is assumed to be in plug flow in both phases

For given gas and solid flowrates, the transition from the dense phase flow to the fast fluidized bed (containing two regions) as functions of particle size and density is determined using the model of Kwauk et al. (1985). The numerical solution of the governing mass balance equations show that for given solid and gas flowrates, (and average voidage) the gas phase conversion shows an unusual behavior with respect to particle diameter and density. Such behavior is resulted from the effects of particle diameter and density on the reactor volume occupied by each phase and the effect of particle diameter on the apparent reaction rate. The numerical results show that a fast fluidized bed gives the best conversion at large particle density and for the particle diameter which results the fast fluidized bed to be operated near the pure dense phase flow.