Dispersion and holdup in a three-phase fluidized-bed bioreactor

Axial dispersion and phase holdup measurements were made using electroconductivity in a fermenting fluidized-bed bioreactor (FBR) and in a model nonfermenting three-phase FBR. Multiple axial conductivity probes were used to nonintrusively monitor the bed conductivity. The gas phase holdup was estimated from a ratio of the average bed conductivity and bulk conductivity. The solid fraction in the three-phase FBR can be estimated from the two-phase liquid-solid FBR. The response to a salt pulse was used to estimate the liquid axial dispersion coefficient. Particle Peclet numbers on the order of 10^-2 were estimated as a function of flowrates and compared to literature correlations.     

Gas holdup in a three-phase fluidized-bed bioreactor

The effects of system parameters on the gas holdup in a three-phase fluidized-bed bioreactor were examined. A valve technique was used to measure the average gas holdup in the reactor. Gas holdup was found to be strongly affected by fluid superficial velocities, bead size and density, electrolyte concentration, type of gas sparger, and temperature. Quantitative and qualitative observations were made regarding the differences between conventional glass-particle systems and low-density gel-particle systems. Most notably, the degree of bubble coalescence and mode of fluidization were highly dependent on each system.     

Measurement of mixing time and holdup of solids in gas–solid fluidized bed using radiotracer technique

Mixing times and holdup of solids were measured in a gas–solid fluidized bed using radiotracer technique. Sand and air were used as solid and gas phase, respectively in the fluidized bed. Gold-198 labeled sand particles were used as radiotracer for mixing time measurement at different operating conditions and ¹³⁷Cs sealed source was used for holdup measurement at different axial and radial positions. The experiments were conducted at different operating conditions. The measured mixing times ranged from 1.4 to 21 s at different conditions. It was observed that at a particular bed height, the mixing time initially decreases with increasing gas velocity and tend to become constant at higher gas velocities. However, mixing time increases with increasing bed height. The holdup fraction of solid was found to be more towards the wall compared to the centre of the column. The study provided inputs to improve the existing design, design of a new system and scale-up of the process.     

Hydrodynamics and mixing in three-phase fluidized bed bioreactors

The effects of solid particles on hydrodynamics and mixing in a three-phase fluidized bed bioreactor were discussed. The gas holdup, bubble size, and liquid-phase axial dispersion coefficient were measured in a 0.25-m id bubble column bioreactors containing low-density particles. The presence of low-density solid particles slightly increased gas holdup. The decrease in average bubble diameter with solid presence was found. For the three-phase system, the liquid-phase axial dispersion coefficients were higher than for the two-phase system. We extended a model for a gas holdup developed for a gas-liquid two-phase bubble column bioreactor to a gas-liquid-solid three-phase fluidized bed bioreactor. Using the present data and available data in the literature, the predictions of the proposed model were examined. The proposed model agreed with a wide range of the experimental data. A theoretical correlation for liquid-phase axial dispersion coefficient was developed using Kolmogoroff's theory of isotropic turbulence. Reasonable agreement was obtained between the predicted and experimental values of axial dispersion coefficient.     

循环流化床生物质气化炉内计算流体动力学模拟——鼓泡流化床内改进的颗粒床模型（英文）

采用改进颗粒床模型的CFD方法模拟了实验室规模冷模装置内鼓泡床的流体流动时空特性。模拟结果表明表观气速是影响气固动态特征和压力波动的主要因素之一：随表观气速的增大，气泡数目增加，气泡体积增大，压力波动增强；气速越高时均压降越大；在内循环鼓泡流化床内固体颗粒呈“单室”流型。上述与实验观察相吻合的模拟结果将有助于放大和设计商业化的内循环流化床生物质气化炉。     

Non-invasive imaging of shallow bubble columns using electrical capacitance tomography

This paper deals with application of non-invasive electrical capacitance tomography to study the hydrodynamics of shallow bed bubble columns. Two bubble columns with different height to diameter ratio were used. Air–kerosene system that represents dielectric two-phase mixture was investigated. The ECT provided good measurement of the gas holdup at different gas velocities compared to the classical pressure measurements. The ECT was able to provide the gas hold up and the bubble velocities distribution across the column diameter at different gas velocities. The study revealed that spatial gas holdup and bubble velocity distributions are sharp with parabolic shape in the small bubble column (H_D/D_C = 5). However, in the large bubble column (H_D/D_C = 4) the gas holdup and bubble velocity profiles were flatter indicating improvement in the mixing homogeneity and leading to well-mixed reactor. 3D graphical visualization of the flow regimes and transition points were also examined using the ECT. In the small bubble column flow regimes were heterogeneous to slugs flow especially at high flow rate, resulted in downward flow near the walls and imperfect mixing.     

Fluidization behavior of oil-contaminated sand

Hydrodynamic behavior of oil-polluted particles of sand was investigated in transparent glass column. The onset of fluidization of sand beds increased with the oil content of the bed. An increase of cohesive forces related to the higher content of liquid (oil) caused deterioration of the quality of fluidization. An empirical correlation was developed to predict the dimensionless gas velocity that keeps the bed of sticky particles fluidized. Results of this work can be employed for the design of fluidized-bed remediation units for oil-polluted sands and soils. An erratum to this article is available at .     

Gas Holdups of Small and Large Bubbles in a Large-scale Bubble Column with Elevated Pressure

Gas holdups of large bubbles and small bubbles were measured by means of dynamic gas disengagement approach in the pressured bubble column with a diameter of 0. 3 m and a height of 6.6 m. The effects of su-perficial gas velocity, liquid surface tension, liquid viscosity and system pressure on gas holdups of small bub-bles and large bubbles were investigated. The holdup of large bubbles increases and the holdup of small bub-bles decreases with an increase of liquid viscosity. Meanwhile, the holdup of large bubbles decreases with in-creasing the system pressure. A correlation for the holdup of small bubbles was obtained from the experimen-tal data.     

鼓泡浆液反应器的应用开发研究Ⅰ.气含率和固相浓度分布特性

研究了以粉体氧化铝水合物为固相的鼓泡浆液反应器的平均气含率和固体浓度分布特性。考察了表观气速、体系温度、静液高度、固相浓度及气体分布板的开孔率等对气含率的影响和不同性质氧化铝水合物在塔中的悬浮和轴向浓度分布情况。结果表明气速增大或开孔率较大时气含率增大，但固相浓度大小对气含率没有影响。水合氧化铝固体粉末在鼓泡塔中的浓度分布特性与固体的堆积密度和吸水性能有关，吸水率大堆积密度小的拟薄水铝石在低气速条件下就可完全均匀悬浮。以上结果为用气液固三相鼓泡反应器制备晶粒大小均匀的拟薄水铝石提供了可能性。     

Multiphase Flow Regime Characterization and Liquid Flow Measurement Using Low-Field Magnetic Resonance Imaging

Multiphase flow metering with operationally robust, low-cost real-time systems that provide accuracy across a broad range of produced volumes and fluid properties, is a requirement across a range of process industries, particularly those concerning petroleum. Especially the wide variety of multiphase flow profiles that can be encountered in the field provides challenges in terms of metering accuracy. Recently, low-field magnetic resonance (MR) measurement technology has been introduced as a feasible solution for the petroleum industry. In this work, we study two phase air-water horizontal flows using MR technology. We show that low-field MR technology applied to multiphase flow has the capability to measure the instantaneous liquid holdup and liquid flow velocity using a constant gradient low flip angle CPMG (LFA-CPMG) pulse sequence. LFA-CPMG allows representative sampling of the correlations between liquid holdup and liquid flow velocity, which allows multiphase flow profiles to be characterized. Flow measurements based on this method allow liquid flow rate determination with an accuracy that is independent of the multiphase flow profile observed in horizontal pipe flow for a wide dynamic range in terms of the average gas and liquid flow rates.     

浆态床反应器中相含率及粒径分布的研究

以空气－水－石英砂体系为对象，研究了费托合成浆态床反应器中表观气速、平均淤浆浓度、床层轴向位置等因素对气含率、固体浓度轴向分布和粒径分布的影响，并通过实验得出了气含率与操作变量之间的关联式。     

Calculation of isentropic compressibility and sound velocity in two-phase fluids

Derivative properties from equations of state (EoS) are well defined for homogeneous fluid systems. However, some of these properties, such as isothermal and isentropic (or adiabatic) compressibilities and sound velocity need to be calculated at conditions for which a homogeneous fluid splits into two (or more) phases, liquid or vapor. The isentropic compressibility and sound velocity of thermodynamically equilibrated fluids exhibit important discontinuities at phase boundaries, as noticed long ago by Landau and Lifschitz in the case of pure fluids. In this work, the two-phase isentropic compressibility (or inverse bulk modulus) is expressed in terms of the two-phase isothermal compressibility, two-phase thermal expansivity and an apparent heat capacity, defined as the partial derivative of total enthalpy with respect to temperature at constant pressure and composition. The proposed method is simple (simpler than previous approaches), easy to implement and versatile; it is not EoS-dependent and it requires only a flash routine and the expression of total enthalpy at given pressure, temperature and composition. Our approach is applied to a variety of fluid systems representative of reservoir applications and geophysical situations, including petroleum fluids (oil and gas condensate) and mixtures of water and gas (methane or CO₂). For low gas content in the two-phase fluid, i.e., near bubble point conditions, we obtain significantly lower bulk moduli and sound velocities than predicted within Wood's conventional approach, in which the liquid and gas phases are considered to be “frozen” at the passage of the acoustic wave.     

Particle circulation and oxygen mass transfer in an immobilized cell bioreactor

Two important considerations in the design of an aerobic particulate immobilized cell bioreactor are the provision of sufficient oxygen to maintain the desired metabolism of the immobilized organism, and the biomass holdup (which is proportional to the number of immobilized cell particles in the reactor). The Circulating Bed Reactor, a reactor developed for use with those forms of immobilization that result in particles of essentially neutral buoyancy, operates with an expanded bed of circulating particles. The particle number density attainable in such a reactor has been found to be dependent upon the circulation cell aspect ratio, the individual particle properties, the static bed voidage of the particles, and the superficial gas velocity. The oxygen mass transfer characteristics have been found to be dependent upon the circulatory nature of the system, the particle (solids) holdup, the particle porosity, and the superficial gas velocity.     

Production of cyclodextrins in a fluidized-bed reactor using cyclodextrin-glycosyl-transferase

Cyclodextrin-glycosyl-transferase (EC2.4.1.19), produced by Wacker (Munich, Germany), was purified by biospecific affinity chromatography with β-cyclodextrin (β-CD) as ligand, and immobilized into controlled pore silica particles (0.42 mm). This immobilized enzyme (IE) had 4.7 mg of protein/g of support and a specific activity of 8.6 μmol of β-CD/(min·g_IF) at 50°C, pH 8.0. It was used in a fluidized-bed reactor (FBR) at the same conditions for producing cyclodextrins (CDs) with 10% (w/v) maltodextrin solution as substrate. Bed expansion was modeled by the Richardson and Zaki equation, giving a good fit in two distin ctranges of bed porosities. The minimum fluidization velocity was 0.045 cm/s, the bed expansion coefficient was 3.98, and the particle terminal velocity was 2.4 cm/s. The FBR achieved high productivity, reaching in only 4 min of residence time the same amount of CDs normally achieved in a batch reactor with free enzyme after 24h of reaction, namely, 10.4 mM β-CD and 2.3 mM γ-CD.     

CFD Model of Dense Gas-solid Systems in Jetting Fluidized Beds

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Characterization and evaluation of a macroporous adsorbent for possible use in the expanded bed adsorption of flavonoids from Ginkgo biloba L.

The suitability of the use of macroporous adsorbent Amberlite XAD7HP in expanded bed adsorption processes for the isolation of flavonoids from crude extracts of Ginkgo biloba L. has been assessed. The expansion and hydrodynamic properties of expanded beds were investigated and analyzed. The bed expansion as a function of operational fluid velocity was measured and correlated with the Richardson–Zaki equation. Theoretical predictions of the correlation parameters (the terminal settling velocity u_t and exponent n) were improved by modifying equations in the literature. Residence time distributions (RTDs) were studied using acetone as a tracer. Three measures of liquid phase dispersion (the height equivalent of theoretical plate, Bodenstein number and axial distribution coefficient) were investigated and compared to values previously obtained with commercial EBA adsorbents developed for protein purification. A suitable bed expansion ratio was found to be 1.25 times the settled bed height, which occurred at a corresponding flow velocity of 183 cm/h. For an initial settled bed height of 42 cm, the mean residence time of liquid in the expanded bed was around 28 min. Under these flow conditions, the axial mixing coefficient D_ax was 7.54 × 10⁻⁶ m²/s and the Bodenstein number was 28; the number of theoretical plates (N) was 19 and the height equivalent of a theoretical plate (HETP) was 2.77 cm. Rutin trihydrate was used as a model flavonoid for the characterization of the adsorption properties of Amberlite XAD7HP. Adsorption was observed to reach equilibrium within 3 h with 70% of the adsorption capacity being achieved within 30 min. The estimated maximum equilibrium adsorption capacity for rutin was estimated to be 43.0 mg/(g resin) when the results were fitted to Langmuir isotherms. The adsorption performance was not seriously impaired by the physical presence of G. biloba leaf powders. Assessment of the kinetics of the adsorption of rutin revealed that the rate constant for adsorption was only reduced by 15% in the presence of leaf powders at a concentration of 50 mg/mL. The results demonstrated that Amberlite XAD7HP should be suitable for expanded bed adsorption of flavonoids from crude extracts of G. biloba L.     

A model for the pressure drop in gas—liquid cocurrent downflow through packed beds

A model for pressure drop is proposed for gas—liquid flow through packed beds on the basis of the observed absence of radial pressure gradients and taking into consideration the structure of the bed and the physical properties of the fluids. The model divides the total voitage of the bed into internal and external voidage and appropriately distributes the total liquid holdup into internal and external holdup.Over 2500 experimental data, from the present study as well as those reported in literature, are correlated by the model with an r.m.s. deviation of less than ±9%. The significant parameters affecting the two-phase pressure drop are found to be the bed porosity, the Reynolds number, and the product of the Eötvos and the Morton numbers.     

Expansion and hydrodynamic properties of cellulose-stainless steel powder composite matrix for expanded bed adsorption

For better understanding the influences of solid phase properties on the performance of the expanded bed, the expansion and hydrodynamic properties of cellulose-stainless steel powder composite matrix with a series of densities was investigated and analyzed in an expanded bed. Two kinds of matrix particle diameter fractions, the small one (60-125 microm) and the large (125-300 microm), were used in the present work. In general, the expansion factors decreased obviously with the increase of matrix density. A linear relation between the mean density of matrix and superficial velocity at expansion factor of 2.5 was found for same series of matrices. The Richardson-Zaki equation could correlate the bed expansion and operation fluid velocity for all matrices tested. The theoretical prediction of correlation parameters (the terminal settling velocity U(t) and expansion index n) was improved with the modification of equations in the literature. The residence time distributions were investigated to characterize the hydrodynamic property in expanded bed. Compared with three evaluation factors (the height equivalent of theoretical plate, Bo number and axial distribution coefficient D(ax)), the results indicated that D(ax) is the best parameter to analyze the bed stability of expanded bed under various operation conditions and matrix properties. In addition, it was found that fluid velocity is the most essential factor to influence the hydrodynamic properties in the bed. A linear relation between the D(ax) and superficial fluid velocity for all matrices tested was established.     

Hydrodynamic Behavior in a Tapered Bubble Column

IntroductionBubble column( BC) and slurry bubble column( SBC) reactors have emerged as one of the mostpromising devices in chemical,biochemical and en-vironmental engineering operations because of theirsimple construction,isothermal conditions,highheat and mass transfer rates,and on- line catalystaddition and withdrawal[1_ 4] .The utilization of ta-pered slurry bubble column( TSBC) reactorshas re-cently received much attention ofsome scholars andscientists who are engaged in biochemical rea…     

Numerical simulation of the hydrodynamics of an inverse liquid–solid fluidized bed using combined Lattice Boltzmann and smoothed profile methods

Knowledge of an inverse fluidized-bed fluid hydrodynamics is advantageous in optimal adjustment and designing high-efficiency beds. In the present study, a combination of a single relaxation time collision operator lattice Boltzmann method (LBM) and the smoothed profile method (SPM) is employed to simulate the hydrodynamics of an inverse liquid–solid fluidized bed comprising circular monodisperse and polydisperse particles in a rectangular channel. A numerical instance of inverse fluidization involving 231 particles is illustrated to show the capability of the combined methods. Moreover, comparison of the numerical results is performed with the Ergun equation and the Richardson–Zaki correlation. The comparison demonstrates that the present model can simulate the fluid flow behavior in an inverse fluidized bed. Several different models were also presented to investigate the effect of different fluid properties and size of particles in the bed. Simulations indicate that the more the superficial liquid velocity, the higher the porosity of the bed. The present simulations show that porosity of the bed increases by increasing the particles size, and also the vertical velocity of the bed decreases with an increase in liquid viscosity. Finally, polydisperse particle systems are also simulated. The results show that porosity in an inverse fluidized bed comprising polydisperse particles is more than that of a monodisperse particle bed.