Liquid Radial Dispersion in Liquid-solid Circulating Fluidized Beds with Viscous Liquid Medium

Liquid dispersion in the radial direction was investigated in the riser of a viscous liquid-solid fluidized bed 0.102 m in diameter and 3.5 m in height. Pressure fluctuations in the riser were also measured and analyzed to examine the behavior of fluidized particles. Effects of liquid velocity (0.15–0.45 m/s), solid circulation rate (2–8 kg/m²s), particle size (1–3 mm), and liquid viscosity (0.96–38 mPas) on pressure fluctuations and the liquid radial dispersion coefficient were determined. The infinite space model was employed to obtain the radial dispersion coefficient from the radial concentration profiles of the tracer. The pressure fluctuations were analyzed by means of autocorrelation coefficient as well as power spectral density function. The dominant frequency obtained from the autocorrelation coefficient or power spectral density function of pressure fluctuations decreases with increasing liquid viscosity or liquid velocity, but it increases with increasing particle size. The liquid radial dispersion coefficient decreases with increasing liquid velocity or viscosity, but it increases as the solid circulation rate or particle size increases. The liquid radial dispersion coefficient is related closely to the resultant behavior of fluidized particles. The radial dispersion coefficient has been well correlated with operating variables in terms of dimensionless groups.     

Liquid Radial Dispersion in Liquid-solid Circulating Fluidized Beds with Viscous Liquid Medium

Liquid dispersion in the radial direction was investigated in the riser of a viscous liquid-solid fluidized bed 0.102 m in diameter and 3.5 m in height. Pressure fluctuations in the riser were also measured and analyzed to examine the behavior of fluidized particles. Effects of liquid velocity (0.15-0.45 m/s), solid circulation rate (2-8 kg/m²s), particle size (1-3 mm), and liquid viscosity (0.96-38 mPas) on pressure fluctuations and the liquid radial dispersion coefficient were determined. The infinite space model was employed to obtain the radial dispersion coefficient from the radial concentration profiles of the tracer. The pressure fluctuations were analyzed by means of autocorrelation coefficient as well as power spectral density function. The dominant frequency obtained from the autocorrelation coefficient or power spectral density function of pressure fluctuations decreases with increasing liquid viscosity or liquid velocity, but it increases with increasing particle size. The liquid radial dispersion coefficient decreases with increasing liquid velocity or viscosity, but it increases as the solid circulation rate or particle size increases. The liquid radial dispersion coefficient is related closely to the resultant behavior of fluidized particles. The radial dispersion coefficient has been well correlated with operating variables in terms of dimensionless groups.     

三相循环流化床中气泡上升速度的实验研究

开发了一种新型的光纤探头多相流气泡测试系统,可用于气－液两相和气－液－固三相体系中气泡参数的测定。应用此系统研究了三相循环流环化床中不同径同位置气泡的上升速度分布,气泡上升速度均值的径向布以及操作条件对这现任中分布的影响。     

Studies on Liquid—Gas and Three‐Phase Fluidized Beds with Pulsating Air Flows

The effects of air‐flow pulsation and water and air flowrates on the hydrodynamics of liquid—gas and three‐phase fluidized beds containing 3‐mm glass beads have been studied in a 90‐mm i.d. column. Under steady‐flow conditions, both types of bed contained a relatively large number of small bubbles. With a pulsing air flow, however, a smaller number of much larger bubbles or slugs were formed. This was attributed to different mechanisms of bubble formation at the distributor. Variations in phase holdup were explained in terms of the effects of the operating parameters on the bubble characteristics.     

Discrete Bubble Model for Prediction of Bubble Behavior in 3D Fluidized Beds

A discrete bubble model has been developed taking into account multiple bubble‐bubble interactions and a delayed coalescence method. The obtained simulation results were compared with experimental data reported in literature. The simulation results predicted by the developed model indicate clearly that the multiple interactions of bubbles lead to more reasonable results than those predicted by a binary interaction model. In addition, two types of interaction models were applied and predicted results were compared. The frequency of gas bubbles passing through the bed cross section versus bed height follows the same trend as the experimental data.     

气液固三相循环流化床中气固相含率轴径向的分布

对气液固三相循环流化床中气固相含率沿轴径向的分布进行了实验研究和模拟。实验结果表明：与膨胀床相比，三相循环流化床内的相间接触较为充分；固含率轴向分布的一维沉降－扩散模型模拟值与实验值吻合较好。     

Flow Characterization of a Three‐Phase Circulating Fluidized Bed Using an Ultrasonic Technique

The axial and radial distributions of solid and gas holdups were investigated in an air‐water‐glass bead circulating fluidized bed (GLSCFB) using a new ultrasonic technique, with a new method based on signal fluctuations. The cross‐sectional averaged gas and solid holdups measured at two axial positions appear to be similar at all studied operating conditions. The radial non‐uniformity decreases with increasing liquid velocity but does not change with an increasing solid circulating rate. The radial distribution of gas holdup was more uniform for 1.3 mm beads than for 433 µm glass beads.     

液体粘度对气液固三相循环流化床颗粒循环速度和流型特征速度的影响

实验的三相循环流化床以玻璃珠 (dp = 0.48 mm, ρs = 2460 kg(m(3) 和苯乙烯颗粒 (dp = 1.45mm, ρs = 1264 kg(m(3)为固相,空气为气相,水、0.05%、0.20% (mass) CMCS (羧甲基纤维素钠)水溶液为液相.实验研究了液体粘度、表观液体速度、表观气体速度、辅助液体速度及颗粒密度对颗粒循环速度的影响.随着液体粘度的增加,颗粒循环速度增加;随着表观液体速度和辅助液体速度增加,颗粒循环速度都增加;随着表观气体速度的增加,颗粒循环速度减小.低密度颗粒系统同高密度颗粒系统相比,低密度颗粒系统能提前从三相传统流型进入三相循环流型.实验还研究了液体粘度对低密度颗粒的起始液体速度和过渡液体速度的影响,为得到三相循环流化床的流型图提供了可靠的依据.     

循环流化床的沸腾传热

A model is proposed to predict boiling heat transfer coefficient in a three-phase circulating fluidized bed (CFB), which is a new type of evaporation boiling means for enhancing heat transfer and preventing fouling. To verify the model, experiments are conducted in a stainless steel column with 39 mm ID and 2.0 m height, in which the heat transfer coefficient is measured for different superficial velocities, steam pressures, particle concentrations and materials of particle. As the steam pressure and particle concentrations increase, the heat transfer coefficient in the bed increases. The heat transfer coefficient increases with the liquid velocity but it exhibits a local minimum.The heat transfer coefficient is correlated with cluster renewed model and two-mechanism method. The prediction of the model is in good agreement with experimental data.     

高密度循环流化床研究现状及展望

对高密度循环流化床的研究现状进行了综述，并与低密度循环流化床进行了比较，分析了研究高密度循环流化床，特别是高密度下行床的重要意义，提出了开展高密度循环流化床研究所面临的一些重要问题.     

A Novel Model for Predicting the Dense Phase Behavior of 3D Gas‐Solid Fluidized Beds

A novel phenomenological discrete bubble model was developed and tested for prediction of the hydrodynamic behavior of the dense phase of a 3D gas‐solid cylindrical fluidized bed. The mirror image technique was applied to take into account the effects of the bed wall. The simulation results were validated against experimental data reported in the literature that were obtained by positron emission particle tracking. The time‐averaged velocity profiles of particles predicted by the developed model were found to agree well with experimental data. The initial bubble diameter had no significant influence on the time‐averaged circulating pattern of solids in the bed. The model predictions clearly indicate that the developed model can fairly predict the hydrodynamic behavior of the dense phase of 3D gas‐solid cylindrical fluidized beds.     

循环流化床气固传质实验研究

This study is devoted to gas-solid mass transfer behavior in heterogeneous two-phase flow. Experiments were carried out in a cold circulating fluidized bed of 3.0m in height and 72mm in diameter with naphthalene particles. Axial and radial distributions of sublimated naphthalene concentration in air were measured with an online concentration monitoring system HP GC-MS. Mass transfer coefficients were obtained under various operating condition, showing that heterogeneous flow structure strongly influences the axial and radial profiles of mass transfer coefficients. In the bottom dense region, mass transfer rate is high due to intensive dynamic behavior and higher relative slip velocity between gas and clusters. In the middle transition region and the upper diluter region, as a result of low mass transfer driving force and the influence of flow structure, mass transfer rate distribution becomes non-uniform. In conclusion, among the operating parameters influencing mass transfer coefficients, the superficial gas velocity is the most important factor and the solid circulation rate should be also taken into account.     

三相流化床和两相鼓泡塔内的压强径向分布

利用应变片压力传感器测定了三相流化床和气-液鼓泡塔内压强的径向分布,比较了不同操作条件下床层内不同轴向位置上压强径向分布的特征,初步探讨了体系的流体湍动特性。     

Phase holdup and liquid dispersion in gas-liquid-solid circulating fluidized beds

Axial and radial profiles of gas and solids holdups have been studied in agas-liquid-solid circulating fluidized bed at 140mm i.d..Experimental results indicate that the axialand radial profiles of gas and solids holdups are more uniform than those in a conventionalfluidized bed.Axial and radial liquid dispersion coefficients in the gas-liquid-solid circulating fluidizedbed are investigated for the first time.It is found that axial and radial liquid dispersioncoefficients increases with increaes in gas velocity and solids holdup.The liquid velocity has littleinfluence on the axial liquid dispersion coefficient,but would adversely affect the redial liquiddispersion coefficient.It can be concluded that the gas-liquid-solid circulating fluidized bed hasadvantages such as better interphase contact and lower liquid dispersion along the axial directionover the expanded bed.     

外循环三相流化床处理染料废水

利用外循环三相生物流化床设计准则，通过小试规模的流化床对经预处理的模拟含染料废水和工业废水进行处理，结果表明：在4 h内增加水力停留时间(HRT)，可提高化学需氧量(CODcr)去除率. 气、液、固三相的循环运动使流化床具有较强抗冲击负荷能力，生物膜厚在100~350 mm范围内，进水CODcr浓度在较宽范围内波动时，对出水CODcr去除率影响不大，都能维持在80%以上.     

(气)-液-固循环流化床的研究进展

液-固(L-s)和气-液-固(G-L-s)循环流化床与传统流化床相比具有许多优点。但对L-S和G-L-S循环流化床的研究报道与气一固循环流化床相比较少。由于新加工过程和生物技术的兴起．拓宽了L-S和G-L-S循环流化床的应用新领域。为了理解和掌握这两种液相循环流化床的流动特性,对其近期的研究进展进行了回顾,并对其在生物化工中的应用前景进行了展望。     

循环流化床置换燃烧机理介绍及流动特性研究

介绍了一种基于循环流化床的动力系统方案———循环流化床置换燃烧。这种燃烧系统能在没有能量损失的前提下,将CO2从燃烧产物中分离出来。本文设计建立了一套燃煤循环流化床置换燃烧冷态实验系统,以此为研究对象,选择具有代表性的实验物料,利用测试系统取得多种信号参数,获得反应装置之间的气固流动特性,总结出一定的规律,为以后的热态实验以及进一步探索奠定基础。     

汽液固三相循环流化床蒸发器强化传热和防垢研究

本文在已开发的汽液固三相循环流化床蒸发器装置上进行了条件试验研究。试验表明,这种新型的蒸发器具有明显的强化传热和防垢效果,其传热系数比汽液两相流沸腾传热膜系数提高１．５倍￣２．０倍,并能有效防止污垢的产生。文中对强化传热和防垢的机理进行了探讨。     

气固固循环流化床密相床层压力脉动研究

在不同实验条件下研究了气固固循环流化床密相床层的压力脉动。压力脉动的情况表明：细颗粒的循环及循环量对粗颗粒的流体力学行为有很大影响。气速越低,影响程度越大。