导向管喷动床内单相流场及声波对流场影响的数值模拟

为阐明超细粉在声场导向管喷动流化床内的流化机理,并为进一步优化和完善床层结构及操作条件提供基础,采用标准k-ε湍流模型计算了导向管喷动流化床内的单相气体流场,考察了进口流化气速和射流气速对气体流动规律的影响,以及声场对导向管喷动流化床内气体轴向速度分布及其脉动均方根的影响。结果表明:在高速射流条件下,导向管喷动流化床内气体呈内循环流动,气体循环流量随流化气速度的增加而减小,但随射流气速度的增加而增加;外加声场使环隙区和喷泉区的气体流动更加均匀,显著增加环隙区和喷泉区气流的湍动程度,且湍动程度随声压级的增大而显著增大,随声波频率的升高而小幅度降低。     

细颗粒流化床的特性

在二维流化床内,进行了粗颗粒和细颗粒的流化实验,测定了气泡尺寸和气泡数。观察了细颗粒床内的湍动状态。在φ100与φ280流化床内,进行了气体两相分配实验。细颗粒流化床浓相空隙率大干初始流化床的空隙率。并对细颗粒流化床的规模放大问题进行了初步探讨。     

操作温度对鼓泡流化向湍动流化转变的影响

本文采用床层压力脉动计算机分析方法,研究了操作温度(50～500℃)对于鼓泡流化向湍动流化过渡过程。为了揭示颗粒物性的影响,实验中使用了八种不同颗粒,并推荐下列关联式预测不同温度下的流型转变速度u_c。     

气固流化床内费托铁基催化剂的流化特性

为研究费托(Fischer?Tropsch, FT)催化剂在气固流化床内的流动过程,分析了催化剂的主要物性参数,在不同直径流化床内测量了各表观气速下FT催化剂的流动特性,并与广泛应用的流化催化裂化(Fluid Catalytic Cracking, FCC)催化剂的流态化行为进行了对比。结果表明,同为A类颗粒,相较于FCC催化剂,由于FT催化剂的休止角较小(约为FCC催化剂的75%),其临界流化速度较小、床层膨胀高度和气节高度较小;两种催化剂在流化床内流化过程基本相似,随表观气速增大依次出现膨胀、鼓泡、湍动等流型,但各流型转变时的临界速度差异较大。催化剂物性参数对流化特性影响较大,FT催化剂在各阶段流化过程均相对稳定,有利于催化剂在流化床内均匀分布,其气固接触效果优于FCC催化剂;不同催化剂床层高径比下气节高度变化的转折点与流型存在对应关系,可将气节高度随表观气速的变化关系作为判断湍动流化区内流型临界速度的依据。     

芳烃氨氧化双分布器流化床动态特性研究I.流化特性及压力波动信号分析

通过对芳烃氨氧化流化床反应器内局部压力信号的测定,获取了NC-IV芳烃氨氧化催化剂的坍塌特性、临界流化速度和起始湍动速度等基本流化参数;利用截面平均值、标准偏差、功率谱密度和多尺度小波等多种分析方法,考察了表观气速为0.4 m/s条件下床层压力的分布以及波动规律.结果表明:不同径向位置处的时均压力轴向分布曲线基本一致,...     

基于激光后向散射法的湍动流化床颗粒流动参数测量

提出一种基于激光后向散射法的集成测量系统,用于湍动流化床上升管内颗粒速度和浓度的空间分布测量。在湍动流化床上升管上,使用双激光光纤探头获得各测点速度、浓度的光信号,经过信号转换和数据采集后最终在计算机上显示。实验结果表明:该系统能够准确测量湍动流化床颗粒流动参数;上升管内,颗粒分布呈中心稀而壁面浓的现象;随着流化风量的增加,床内颗粒速度增加,但浓度降低;上升管中心区域,颗粒速度随轴向高度的增加呈先增加后减小的趋势。     

鼓泡流态化向湍动流态化过渡的判别

通过对流化床床层压力脉动信号的计算机在线分析,对气-固密相流化床中鼓泡流态化向湍动流态化的转变过程进行了研究.在较大范围内考察了颗粒重度、颗粒尺寸和床层结构条件对这一流型转变的影响.给出了鼓泡流化向湍动流化转变速度U_c的计算式:U_c/(gd_ρ)~(1/2)=[k(D_f/d_ρ)·((ρ_ρ-ρ_f)/ρ_f)]~n并察明Geldart的颗粒分类方法亦可反映床层流型转变的特征,从而赋予了Geldart颗粒分类方法以新的内涵.     

循环流化床锅炉流体动力学研究

在循环流化床锅炉炉膛内，分为湍流床和快床２个区域，论述了由鼓泡流化床与从气力输送状态向循环流化术转化过程中的炉内流体动力学现象，研究了湍流床开始出现到完全转化为湍流化床及快床时，炉内气体速度变化的规律和相庆的计算公式。     

水泥生料球在方形喷动床中流化特性试验研究

喷动流化是流态化体系里的一种操作方式，其优越性将对水泥熟料煅烧工艺产生较大的影响。本文着重研究了方形截面喷动床内不同物料粒径、不同喷动口结构对水泥生料球喷动流化特性的影响。并对水泥生料球的内循环现象作了初步描述与分析，提出移动——内喷动床的概念。     

喷动—流化床流动特性的试验研究

分析了两种窄筛分Ｄ类颗粒在不同喷动－流化操作条件下的床层行为特征及床层总气流阻力，研究了平底型三维喷动－流化床内的气体流动模式，从而导出在固定床阶段床层总气流阻力的表达式，得出喷动－流化操作具有优越性的结论。     

Comparison of fluidized bed flow regimes for steam methane reforming in membrane reactors: A simulation study

An important decision in the design of fluidized bed reactors is which of several flow regimes to choose. Almost all fluidized bed reactor models are restricted to a single flow regime, making comparison difficult, especially near the regime boundaries. This paper examines the performance of fluidized bed methane reformers with three models—a simple equilibrium model and two kinetic distributed models, based on different assumptions of varying sophistication. Membranes are incorporated to improve reactor performance. Eighteen cases are simulated for different flow regimes and membrane configurations. Predictions for the fast fluidization and turbulent flow regimes show that the rate-controlling step is permeation through the membranes. Bubbling regime simulations predict somewhat less hydrogen production than for turbulent and fast fluidization, due to the effects of interphase crossflow and mass transfer. Overall reactor performance is predicted to be best under turbulent fluidization operation. Practical considerations also affect the advantages, shortcomings and ultimate choice of flow regime.     

From bubbling to turbulent fluidization: Advanced onset of regime transition in micro-fluidized beds

Membrane fluidized bed reactors have been proposed and demonstrated as an effective reactor concept for ultrapure hydrogen production with integrated carbon dioxide capture. Recent experimental studies have shown that the hydrogen permeation rate through the membranes and the mass transfer rate from the bubble phase to the emulsion phase are the two main limiting factors in this type of reactors. To this end, we propose the concept of a micro membrane fluidized bed reactor (MMFBR) as a possible method to remove those two limitations. The idea of the MMFBR is that a significantly larger membrane area per unit reactor volume can be accommodated, thereby removing the limitation of the hydrogen permeation rate through the membranes. Furthermore, we numerically show with discrete particle simulations that the onset of turbulent fluidization is advanced significantly in a MMFBR, which allows the bed to be operated at the turbulent fluidization regime at a relatively low gas velocity. This is quite beneficial, since it provides a gentler environment for the membranes, and indicates a significant attenuation or possible removal of mass transfer limitations due to the well-known excellent mass transfer characteristic of turbulent fluidization.     

Computational Fluid Dynamics Study of Heat Transfer in Turbulent Fluidized Beds

The fluidization and heat transfer behaviors of a turbulent fluidized bed were investigated using computational fluid dynamics (CFD). The effects of inlet superficial velocity on heat transfer behaviors in a turbulent fluidized bed were analyzed and compared with those operated in other fluidization regimes. The effects of using particles belonging to different Geldart groups in a turbulent fluidized bed on fluidization and heat transfer behaviors were evaluated. For both fluidization regimes investigated, the solids temperature distribution during the heat transfer process became less uniform when the particle size was reduced.     

Fluidized bed catalytic reactor modeling across the flow regimes

Fluidized bed reactor models are generally specific to a single flow regime resulting in ambiguities and discontinuities at the regime boundaries. In practice, only the bubbling, turbulent and fast fluidization regimes are of industrial significance for catalytic reactions. The turbulent fluidization regime is especially advantageous because of improved interphase mass transfer, resulting in improved selectivities and conversions. It is shown that some of the difficulties in modeling can be resolved by means of the probabilistic-averaging model, recently published by Thompson et al. (1999). This model interpolates between the Grace (1984) two-phase bubbling bed model at low velocities and single phase axially dispersed flow for fully established turbulent fluidization conditions, leading to improved predictions of conversion and selectivity for catalytic fluidized bed reactors operated at flow rates covering the full range between bubbling and fully turbulent fluidization. An analogous approach should be useful for beds operated at higher gas velocities as fast fluidization conditions are approached.     

流化床在甲烷临氧CO2重整反应中的作用研究

在流化床反应器中进行甲烷临氧CO₂重整制合成气反应。通过计算分析了催化剂颗粒在床层内的流化特性。对比实验表明,流化床反应器在催化剂活性、稳定性、自热过程以及催化剂积炭等方面均体现出比固定床反应器的优越性。在流化床反应器中进行的甲烷自热重整反应,甲烷的转化率接近热力学平衡值,床层温度梯度小于10 ℃, 反应20 h后,催化剂表面无积炭。     

气固环流反应器的研究进展

气固环流反应器是将气液环流理论与稠密气固流态化理论进行合理移植、耦合而形成的一种新型气固流化床反应器。对近年来国内外学者在该领域的研究进行了回顾,参考了内循环流化床的一些研究结果,对操作条件、几何结构对气固环流反应器内两相流体力学行为的影响规律进行了总结和分析,并对进一步的研究进行了展望。     

过程所与流态化-庆祝过程工程研究所建所60周年

中国科学院过程工程研究所自1958年创建以来已经走过60年一个甲子的历程. 该所坚持面向科学前沿、面向国家重大需求、面向国民经济主战场的中国科学院办院方针,在应用基础研究和工业应用两方面均取得了一系列重要成果,在流态化科学与技术领域尤为突出. 在已故所长郭慕孙院士的领导下,过程所在流态化科学与技术领域长期处于世界领先地位. 本文回顾和概述了该所在流态化理论与工业应用两方面所取得的一系列重要成果. 理论方面包括诸如广义流态化理论、无气泡气固接触理论、气固流态化的散式化理论、流化床结构?传递关系理论、EMMS理论与介科学、微型流化床的提出及定义等;工业应用方面涉及诸如贫铁矿的流态化磁化焙烧、煤的流态化热解、锰矿的流态化还原、高湿高氮燃料的低NOx双流化床解耦燃烧、低焦油流化床两段气化、中石化MIP(Maximizing Iso-Paraffins)循环流化床技术的计算机模拟放大等. 仅以此文作为献给过程所创建60周年的生日礼物,以此激励我们继承与发扬老一辈科学家的求真务实爱国敬业精神,在科研工作中取得更大的成就.     

有机硅单体合成的气固流化床的三维数值模拟

为了探索有机硅单体合成气固流化床内硅粉颗粒的流化特性,作者利用计算流体力学CFD软件,采用双欧拉气固两相流模型及SIMPLE算法,模拟了三维的气固流化床内硅粉颗粒的流化特性;分析了气泡生成、长大和破裂的过程,及不同床层高度的固体颗粒运动速度矢量图,不同床层高度处横截面颗粒体积分数变化。结果表明:三维模拟能直观的表现颗粒在流化床中的流化状态,为工业生产及应用提供了有效的依据。     

Experimental investigation of particle contact time at the wall of gas fluidized beds

The contact time of particles at the walls of gas fluidized beds has been studied using a radioactive particle tracking technique to monitor the position of a radioactive tracer. The solids used were sand or FCC particles fluidized by air at room temperature and atmospheric pressure at various superficial velocities, covering both bubbling and turbulent regimes of fluidization. Based on the analysis of tracer positions, the motion of individual particles near the walls of the fluidized bed was studied. The contact time, contact distance and contact frequency of the particles at the wall were evaluated from these experimental data. It was found that in a bed of sand particles, the mean wall contact time of the fluidized bed of sand particles decreases by increasing the gas velocity in the bubbling and increases in the turbulent fluidization. In other words, the particle-wall contact time is minimum at the onset of turbulent fluidization in the bed of sand particles. However, the mean wall contact time is almost constant in both regimes of fluidization in the bed of FCC particles. All the existing models in the literature predict a decreasing contact time when the gas velocity in the bed is increased. It was also shown that the contact distance increases monotonously by increasing the gas velocity in the bed of sand particles, while it is almost constant for the bed of FCC particles. Contact frequency has a trend similar to that of the contact time for both sand and FCC particles.     

Optimization fluidization characteristics conditions of nickel oxide for hydrogen reduction by fluidized bed reactor

We evaluated the optimal conditions for fluidization of nickel oxide (NiO) and its reduction into high-purity Ni during hydrogen reduction in a laboratory-scale fluidized bed reactor. A comparative study was performed through structural shape analysis using scanning electron microscopy (SEM); variance in pressure drop, minimum fluidization velocity, terminal velocity, reduction rate, and mass loss were assessed at temperatures ranging from 400 to 600 °C and at 20, 40, and 60 min in reaction time. We estimated the sample weight with most active fluidization to be 200 g based on the bed diameter of the fluidized bed reactor and height of the stocked material. The optimal conditions for NiO hydrogen reduction were found to be height of sample H to the internal fluidized bed reactor diameter D was H/D=1, reaction temperature of 550 °C, reaction time of 60 min, superficial gas velocity of 0.011 m/s, and pressure drop of 77 Pa during fluidization. We determined the best operating conditions for the NiO hydrogen reduction process based on these findings.