A loop three-phase fluidized bed reactor

An airlift three-phase reactor in which solid particles are fluidized in the riser by the recirculating liquid was developed. Three particle types of 1.7–8.6 mm in diam., porous and nonporous, spheres and cylinders, were studied in the water–air system. Little effect of the alumina porous particles (apparent density 1.47 × 10³ kg/m³) on the gas holdup and liquid superficial velocity was found. On the other hand, the heavier, nonporous ceramic particles (density 2.4 × 10³ kg/m³) had a significant effect on both design parameters. The axial distribution of particles was also a function of the particle density and liquid superficial velocity.     

ECT imaging of three-phase fluidized bed based on three-phase capacitance model

In this work, the electrical capacitance tomography (ECT) with neural network multi-criteria optimization image reconstruction technique (NN-MOIRT), early developed by the authors, is applied to imaging bubble column and three-phase fluidized bed systems in the real time manner. Air, norpar (paraffin) and glass-beads are used as the gas, liquid, and solid phases, respectively. A three-phase capacitance model coupled with a two-region model is proposed to attain the gas holdup and the solids fraction from the permittivity maps of the three-phase system. The two-region model assumes that the solids fraction in the emulsion phase in the no bubble region is the same as in the bubble region. The three-phase capacitance model combines series and parallel capacitance connections among gas, liquid and solid components to relate the three-phase permittivity to each phase holdup. A direct image calculation to obtain the gas holdup from the permittivity map of the three-phase system is also performed by determining the permittivity threshold for the gas bubbles. Comparisons of the gas holdup obtained by ECT with that obtained from liquid head measurement showed a good agreement, validating the applicability of the model and its associated image calculation.     

Performance of a device for entrainment reduction and smoother operation of a fluidized bed

A device proposed for the suppression of entrainment from fluidized beds has been studied. Particles projected upward at the bed surface entered a particle diverter which returned them to the bed. Measurements were made of the air velocity and mass flux profiles downstream of the device using a rugged hot-film anemometer and an electrostatic mass flux probe. In addition, entrainment rates were measured by weighing the particles collected over a given time in a filter. As initially designed, the diverter demonstrated a significant decrease in the transport disengaging height and a reduction in entrainment of more than 80% at a height of 1.3 m above a 0.33 m dia. bed. Additionally, a significant observation was that the bed ran steadier and smoother than operation without the device.     

Effect of internal on phase holdups of a three-phase fluidized bed

Individual phase holdups are important dynamic parameters in the designing of three-phase fluidized bed systems. The system chosen for the present study is nitrogen as gaseous phase, an electrolyte as liquid phase and glass balls as solid phase. The gas holdup was obtained from pressure drop measurements. The obstruction area of flow path was calculated by considering all the geometric parameters of the composite promoter for evaluating the actual velocity of the fluids through the test section. It is found that the presence of composite promoter has not shown any effect on pressure drop in three-phase fluidized beds. The bed porosity data fitted well with Richardson–Zaki equation with an exponent of 2.53. The infinite dilution velocities were increased significantly because of the presence of promoter. The data on gas holdup, liquid holdup and bed porosity were in good agreement with correlations reported earlier [S.D. Kim, C.G.J. Baker, M.A. Bergougnou, Phase holdup characteristics of three phase fluidized beds, Can. J. Chem. Eng. 53 (1975) 134–139; P. Dakshinamurthy, V. Subrahmanyam, K. Veerabhadra Rao, Indian Chem. Eng. 16 (1974) 3; W.Y. Soung, Bed expansion in three-phase fluidization, Ind. Eng. Chem. Proc. Des. Dev. 17 (1978) 33; S.R. Bloxom, J.M. Costa, J. Herranz, G.L. MacWilliam, S.R. Roth, Determination and correlation of hydrodynamic variables in three-phase fluidized bed, ORNL/MIT-219, Oak Ridge National Lab. (1975)].     

An investigation of mass transfer in a countercurrent three-phase fluidized bed

The rate of absorption with chemical reaction has been measured in a bed of solid spheres fluidized by upward flowing gas and irrigated by downward flowing liquid for different reactant concentrations in the liquid phase and different values of the liquid superficial velocity.Values of the effective inerfacial area per unit volume of a static bed, a, and the gas-film mass-transfer coefficient, k_g, are reported as functions of the liquid superficial velocity.     

Investigation of hydrodynamics and mass transfer in a three-phase fluidized bed

On the basis of semiempirical turbulence theory and wave theory of the motion of liquid films, we have composed an engineering method for calculating the energetic, amplitude-frequency, and kinetic characteristics of phase interface, which are used in calculating the processes of absorption and chemosorption.     

Development of a three-phase fluidized bed reactor with enhanced oxygen transfer

A three-phase fluidized bed reactor (TFBR) was developed in this study with the objective to achieve high rates of oxygen transfer from the gas to the liquid phase in the presence of fluidized solid particles. With 2.9 m height, 0.605 m diameter, and a short residence time of 8 h, the TFBR is particularly suitable for industrial applications such as aerobic biodegradation of high-strength wastewaters including refractory compounds. Experiments with tap water and air show that the TFBR enables complete fluidization. With the water and air superficial velocities in the respective ranges of 0.005–0.203 and 0.8–2.0 cm/s, the volumetric oxygen transfer coefficient is 2.3 × 10⁻² s⁻¹, which is higher than that obtained in similar experimental studies on oxygen transfer carried out in the past. These results suggest that the developed TFBR could be very effective in industrial applications where short hydraulic time and high gas-to-liquid mass transfer rates are desirable.     

Heat transfer and bubble dynamics in a three-phase inverse fluidized bed

In this study, surface-to-bed heat transfer experiments were performed to gain insight on heat transfer and hydrodynamics in a three-phase inverse fluidized bed. Air, tap water or 0.5 wt.% aqueous ethanol, and polypropylene were, respectively, the gas, liquid and solid phases. The solid loading was varied from 0 to 30 vol.%, and the gas and liquid superficial velocities from 2 to 50 mm/s and 0 to 21 mm/s, respectively. Visual observations were associated with measured phase holdups and instantaneous heat transfer coefficients. Larger gas velocities lead to an increase in bubble size due to the transition to the coalesced bubble flow regime. The greater turbulence induced by the larger bubbles increases the average heat transfer coefficient. On the other hand, adding ethanol reduces the heat transfer coefficient. Solid concentrations up to ∼13 vol.% increase the average heat transfer coefficient whereas higher solid concentrations tend to lower it. The distribution of instantaneous heat transfer coefficient peak height is wider at higher gas and liquid velocities while the addition of a surfactant narrows it. Gas holdups and average heat transfer coefficients are both compared with existing correlations, which are then adjusted for a better fit.     

Hydrodynamics of three-phase fluidized bed containing cylindrical hydrotreating catalysts

Experiments were performed to study the hydrodynamic characteristics of a cocurrent, gas-liquid-solid fluidized bed containing cylindrical hydrotreating catalysts under conditions of high gas holdup. These conditions were established using an aqueous t-pentanol (0.5 wt. %) solution as the liquid phase in an attempt to simulate reaction conditions for hydrotreating of residual oils and coal liquefaction. Separate three-phase experiments were performed with air and water to investigate the effect of surface tension on hydrodynamic behavior. A mathematical model was developed to describe the minimum fluidization velocity behavior. Bed voidage, gas holdup and terminal velocity of the particles were analyzed and correlated empirically to investigate the effect of particle shape and liquid surface tension. A bubble-wakes interaction coefficient defined by Jean and Fan (1987) was determined for cylindrical particles.     

三相内循环流化床的流体力学研究

以活性碳、陶瓷颗粒、小米为固体粒子,采用体积膨胀法测定气含率,分别考察了气体速度、固含率、粒子种类三个因素对气含率的影响.结果表明:气含率随着气体速度和固含率的增大而增大,但却不能无限的增大.选用小米做固体粒子时在相同气速下的气含率最大.     

内循环三相生物流化床处理油脂废水

针对前人应用的三相内循环流化床作了结构上的优化和创新,并制作了9套新型内循环生物流化床反应器处理油脂废水,分别考察了处理废水过程中载体、水力停留时间、pH值、水力负荷、曝气量等操作因素对处理效果的不同影响。研究表明,该新型流化床处理油脂废水的最佳操作条件为:陶粒为最佳载体,pH值6.8—7.8,水力停留时间2.5—3.7 h,曝气量1.0—1.6 L/min,在油脂质量浓度较大时有必要适当添加表面活性剂增加其生物降解程度。该生物流化床具有很强的抗水力负荷及油脂质量浓度负荷冲击能力。     

三相逆流化床的研究进展与展望

三相逆流化床(TPIFB)作为一种新型的流化床反应器,具有诸多优点及巨大的应用前景。本文首先介绍了TPIFB的结构、原理和特点,综述了TPIFB基础研究和应用研究。基础研究的阐述主要包括:流型、压力降、最小流化速度、相含率、停留时间分布、气泡行为、传质和传热等流体力学特性的重要性;操作条件和流体物性对这些流体力学特性的影响规律;一些重要流体力学特性参数的数学模型及数值模拟研究等。TPIFB应用研究主要介绍了其在装置优化、含油废水处理及其他工业废水处理等方面的研究进展和主要成果。最后指出TPIFB瞬态和微观研究较少、实验研究方法单一、实验结论缺少定量关系、实验模型和方法存在局限性、应用性研究少而分散等是目前阻碍TPIFB工业化应用的主要问题,并展望了其今后的主要研究方向,包括反应器装置设计和开发、数值模拟结合实验考察TPIFB瞬态和微观特征、过程优化机理模型与反应器模型的建立、反应器放大及应用性研究。     

Hydrodynamic studies on three-phase fluidized bed using CFD analysis

Three-phase fluidization refers to fluidization of solid particles by co-current, upward flow of gas and liquid-phases for the purpose of bringing three-phases in contact in a single operation. Due to complications in understanding hydrodynamics of three-phase fluidized bed, CFD analysis is used to predict the hydrodynamics of it. In this study, liquid-phase is water which flows continuously, where as the gas phase is air which is distributed discretely throughout the bed. Ceramic particle of 1 mm diameter, density of 2650 kg/m³ is used as a solid phase. Excellent mixing, heat and mass transfer rates are the unique features of three-phase fluidized bed. The selection of distributor plays an important role in the quality of fluidization [1]. CFD model is created as the realistic representation of actual fluidized bed. The liquid and solid flow is represented by the mixture model. The air is injected from the bottom of the fluidized by means of discrete phase method (DPM). Simulation results are obtained by using porous jump and porous zone model to represent the distributor. It is found that porous zone model is best applicable in the industries, since stability of operating conditions is achieved even with non-uniform air, water flowrates and with different bed heights(100 mm, 200 mm, 300 mm, 400 mm and 500 mm).Simulated Pressure drop values of the fluidized bed have good agreement with the experimental findings. As the gas flowrate increases, the pressure drop in the column is decreases, provided the initial bed height, diameter of the column, and liquid flowrate are constant. This is due to decrease in density of the fluid medium in the bed by means of more gas hold up. The approach of the simulated values to the experimental values can be reduced with better understanding the nature of the fluidized bed.     

Wavelet transform analysis of pressure fluctuation signals in a three-phase fluidized bed

The wavelet transform based on localized wavelet functions is applicable to analysis of pressure fluctuation signals from different flow regimes of a three-phase fluidized bed, which usually is nonlinear or nonstationary. The pressure fluctuation has been analyzed by resorting to the discrete wavelet transform such as wavelet coefficients, wavelet energy, and time-scale plane. The dominant scale of wavelet coefficients and the highest wavelet energy in the bubble-disintegrating regime are finer than ones in the bubble-coalescence regime. The cells corresponding to fine scale of time-scale plane in bubble-disintegrating regime are more shaded and energetic, while the cells corresponding to coarse scale in bubble-coalescence regime are more energetic. Therefore, the wavelet transform enables us to obtain the frequency content of objects in a three-phase fluidized bed locally in time.     

三相生物流化床处理PET废水的应用

通过对PET废水三级生化处理的实践,总结出了一些实际经验。再结合新型三相生物流化床,使得污水处理达到国家一级排放标准。     

Phase hold-up and critical fluidization velocity in a three-phase inverse fluidized bed

We studied the hydrodynamic characteristics of a three-phase inverse fluidized bed made of a transparent acrylic column of 0.115 m inner diameter and 2 m heights. Air, water and polyethylene particles were used as the gas, liquid and solid phase, respectively. We used both hydrophobic low density polyethylene (LDPE) and hydrophilic LDPE as solid phase, and distilled water as liquid phase, and filtered air as gas phase. The LDPE was chemically treated by chlorosulfonic acid to change the surface property from hydrophobic to hydrophilic. We tried to solely investigate the effect of the surface hydrophilicity of polymeric particles on the phase holdup and the critical fluidization velocity of three-phase inverse fluidization. Thus, we measured the static pressure and eventually observed critical fluidization velocity. Critical fluidization velocity became smaller in case of using MDPE hydrophobic particles than LDPE hydrophilic particles. This was thought to be due to the retardation of rising bubbles near hydrophobic particles and, subsequently, the increase of gas hold-up.     

利用三相流化床半连续生产生物絮凝剂的研究

用多孔聚酯泡沫吸附固定絮凝剂产生菌XN1,比较了其和游离菌发酵产絮凝剂的情况,并分别在摇瓶和三相流化床中进行了固定化菌半连续生产絮凝剂的研究。结果表明,聚氨酯泡沫是XN1菌良好的固定化载体,具有经济、高效等特点。在优化条件下,利用固定化XN1菌摇瓶产絮凝剂可连续达12批次,12批的絮凝剂絮凝活性均>90%;而在三相流化床中产絮凝剂至少可以重复17批,且能一直保持较高的絮凝水平。研究还发现,和游离菌相比,固定化菌生产絮凝剂的生产效率可提高约4倍。     

三相流化床中磷石膏分解渣碳酸化反应研究

通过对磷石膏分解渣在三相流化床中碳酸化反应的实验研究,探讨了不同因素对磷石膏分解渣中CaS转化的影响。实验结果表明:增大CO2气体流量和增加反应时间有利于CaS的转化,随着液固比的增大,CaS的转化率首先是增大然后趋于平缓,而升高反应温度对CaS的转化有微弱抑制作用。得到磷石膏分解渣碳酸化反应的最佳反应条件:CO2气体流量为300 mL/min、反应时间为40 min、液固比(体积质量比)为6 mL/g、反应温度为(25±2)℃。在最佳反应条件下,三相流化床中CaS的转化率为97.34%,釜式反应器中CaS的转化率为86.32%,相差了11%。与釜式反应器相比,三相流化床反应器更有利于磷石膏分解渣的碳酸化反应。     

Gas-Liquid mass transfer in a three-phase fluidized bed with floating bubble breakers

The effects of liquid and gas velocities, particle size and volume ratio of floating bubble breakers to solid particles (V_f/V_s) on both the volumetric mass transfer coefficient, k_la, and the gas-liquid interfacial area, a, have been determined in three-phase fluidized beds with floating bubble breakers. Beds having a volume ratio (V_f/V_s) of about 0.15 showed a maximum increase in both k_la and a of about 30% in comparison to that in the corresponding bed without floating bubble breakers. The volumetric mass transfer coefficient in three-phase fluidized beds with or without floating bubble breakers can be estimated from the surface renewal frequency of liquid microeddies and the particle size.     

三相循环流化床内流化固体颗粒的防除垢机理

汽液固三相循环流化床蒸发器已应用到盐化、烧碱、中药和造纸等工业中,表现出良好的防除垢性能。文中研究了这种新型流化床蒸发器的防、除垢机理。首先揭示出汽液固三相流剪应力对延长污垢的诱导期起主要作用,并对汽液固三相流剪应力和三相流剪应力增长率进行了定量计算,分析其影响因素。其次从污垢附着和剥蚀的角度,考察了固体颗粒的除垢作用。根据理论分析指出三相流剪应力对污垢附着需要的时间和污垢剥蚀比率的影响,从而计算了剥蚀比例和剥蚀速率及其影响因素。