Gas Liquid Solid Three-phase Research Articles

From molecular dynamics to lattice Boltzmann: a new approach for pore-scale modeling of multi-phase flow

Most current lattice Boltzmann (LBM) models suffer from the deficiency that their parameters have to be obtained by fitting experimental results. In this paper, we propose a new method that integrates the molecular dynamics (MD) simulation and LBM to avoid such defect. The basic idea is to first construct a molecular model based on the actual components of the rock–fluid system, then to compute the interaction force between the rock and the fluid of different densities through the MD simulation. This calculated rock–fluid interaction force, combined with the fluid–fluid force determined from the equation of state, is then used in LBM modeling. Without parameter fitting, this study presents a new systematic approach for pore-scale modeling of multi-phase flow. We have validated this approach by simulating a two-phase separation process and gas–liquid–solid three-phase contact angle. Based on an actual X-ray CT image of a reservoir core, we applied our workflow to calculate the absolute permeability of the core, vapor–liquid H2O relative permeability, and capillary pressure curves.

Effects of rising biogas bubbles on the hydrodynamic shear conditions around anaerobic granule

Anaerobic reactor is one of gas–liquid–solid three-phase bio-reactors and has attracted high attentions worldwide due to biogas, a renewable energy. As is well-known, hydrodynamic conditions play crucial roles in the performance of the three-phase reactors. But the knowledge about the hydrodynamic conditions around sludge (microbial aggregates) is limited. The hydrodynamic shear force exerted on sludge derives from the liquid flow and rising biogas bubbles nearby. The in situ investigation in a two-dimensional micro anaerobic reactor shows that 56.8–96.6% shear rate exerted on one piece of granular sludge (major axis of 2mm and minor axis of 1.5mm) in typical motions stems from the rising bubbles when biogas production rate is greater than 0.1m3kgVSS−1d−1 and the superficial liquid velocity of reactor was fixed at 6.48mh−1 in this study. Furthermore it linearly correlates with specific bubble population with R2 of superior to 0.95. The specific bubble population plays more important roles in the shear rate on granules than the bubble diameter. Liquid flow is also important for the shear rate exerted on moving sludge in term of the relative velocity between sludge and liquid flow rather than the superficial liquid velocity. Thus the shear rate derived from liquid flow would be significantly lower than that part originated from bubbles. A high-speed digital camera and a particle image velocimetry (PIV) system were used to in situ quantify the bubbles and their behavior in reactor. This study could facilitate understanding and improving the hydrodynamic conditions in three-phase bio-reactors.

Numerical simulation of gas–liquid–solid three-phase flow using particle methods

We want to simulate, based on particle methods, the dynamic behavior of multi-phase flows in a gas–solid–liquid mixture system. With the governing equations discretized within the finite volume particle method, the effects of contact and collision between solid particles were modeled by the distinct element method. Applicability of the viscosity model and an empirical drag force model were confirmed for the hydrodynamic interactions between solid particles and fluid. Simulations were performed of a single bubble rising in a tank of stagnant solid particle–liquid. The results for the dynamic behavior indicate that the present computational framework of particle-based simulation method may be useful for numerical simulations of multi-phase flow behavior in a solid particle–fluid mixture system.

Numerical modeling of gas–liquid–solid interactions: Gas–liquid free surfaces interacting with deformable solids

A numerical framework to model and simulate gas–liquid–solid three-phase flows is proposed and implemented in this work. The overall algorithm adopts a non-boundary-fitted approach that avoids frequent mesh-updating procedures by defining independent meshes and explicit interfacial points to represent each phase. Here, we couple our existing solvers, the immersed finite element method (IFEM) and the connectivity-free front tracking (CFFT) method that model fluid–solid and gas–liquid interactions, respectively, for the three-phase models. A modified IFEM algorithm is derived for modeling fluid–solid interactions that accounts for the dynamics of the solid, while the CFFT is used here to simulate gas–liquid multi-fluid flows that uses explicit interfacial points to represent the gas–liquid interface and for its easy handling of interface topology changes. Instead of defining different levels simultaneously as used in level sets, an indicator function naturally couples the two methods together to represent and track each of the three phases. Several 2-D and 3-D testing cases are performed to show the robustness and capability of the coupled numerical framework in dealing with complex three-phase problems, in particular free surfaces interacting with deformable solids.

Flow patterns and transitions in a rectangular three-phase bubble column

The flow patterns and transitions in a rectangular gas–liquid–solid three-phase bubble column were studied. The influence of solid volume fraction, particle size and particle density on the flow regime transitions of the three-phase bubble column was investigated experimentally. Experiments were carried out for solid volume fraction Vs=0.03–0.3, average particle size dp=48μm–270μm, particle density ρp=2500kg/m3–4800kg/m3, and superficial gas velocity Ug=0.007m/s–0.7m/s in a rectangular bubble column measured 0.8m tall, 0.1m long and 0.01m wide. Four distinct flow patterns and three transition points were observed in this experimental system, and the four flow regimes were discrete bubble regime, transition regime, bubble coalescence regime and strong turbulent regime, which were determined on the basis of criteria as well as schematic diagrams and typical flow pattern images obtained from a high-resolution digital charge couple device (CCD) camera. Typical flow patterns maps were plotted for illustrating flow regime transitions under different particle conditions. It was found out that particle volume fraction and particle density had an effect on the flow pattern transitions; when increasing the values of particle volume fraction and the particle density respectively, the values of the flow regime transition points all decreased. Particle size had a little effect on flow regime transition points when the particle size shifted in the range of 48μm to 150μm; when particle size was larger than 150μm and increased to 270μm, the operation ranges of the transition regime and the bubble coalescence regime decreased.

New CO2 Capture Process with Gas–Liquid–Solid Three-Phase Circulating Fluidized Bed

The idea of applying the gas–liquid–solid (GLS) three-phase circulating fluidized bed to CO2 capture by aqueous ammonia is proposed in this work. A three-phase circulating fluidized bed test rig wa...

Flow regime identification in a three-phase bubble column based on statistical, Hurst, Hilbert–Huang transform and Shannon entropy analysis

Flow regime transitions in a gas–liquid–solid three-phase bubble column were investigated based on pressure time series. The statistical, Hurst, Hilbert–Huang transform and Shannon entropy analysis methods were applied to differential pressure fluctuation data measured in a two-dimensional (2-D) bubble column measuring 0.1m in length and 0.01m in width equipped with a sintered plate distributor (average diameter of holes was 50μm). Air was used as the gas phase and tap water as the liquid phase. Glass beads measuring 150μm in size with a particle density of 2500kg/m3 constituted the solid phase. Based on sudden changes in both the EMD energy entropy from Hilbert–Huang transform and the Shannon entropy values, two flow regime transition gas velocities were successfully identified: the homogeneous regime shifted to the transition regime at a superficial gas velocity of 0.069m/s; and the transition regime shifted to the heterogeneous regime at a superficial gas velocity of 0.156–0.178m/s. The transition gas velocities showed good agreement with the experimental results. The EMD energy entropy and Shannon entropy analysis methods can reveal the complex hydrodynamics underlying gas–liquid–solid flow and are confirmed to be reliable and efficient as non-invasive methods for detecting flow regime transitions in three-phase bubble column systems.

Prediction of layer inversion velocity in three-phase fluidized beds

A model equation was developed to predict the superficial liquid velocity at the layer inversion point in a gas–liquid–solid three-phase fluidized bed with binary solids. The equation is based on the gas–perturbed liquid model which assumes that the solid particles in three-phase fluidized beds are fully supported by the liquid, the presence of gas bubbles in a bed reducing the available cross-sectional area and thereby increasing the interstitial liquid velocity. The superficial liquid velocity at layer inversion for the binary solids system selected was determined at superficial gas velocities up to 21.5mm/s using a mixing index. The resulting layer inversion velocity decreased with increasing superficial gas velocity. The experimental data are consistent with our model. Predicted layer inversion velocities are compared with experimental data obtained in this study.

An Electrical Conductivity Method for Axial Gas and Solid Holdup Determination in Three Phase Fluidized Beds

Fluidization is an operation in which solid particles are kept under suspension supported by the upward flow of liquid/gas phase. In classic fluidization the solids density are higher than the liquid, where as in Inverse fluidization the solids density are lower than that of continuous liquid phase. The phase holdup measurements in three phase classic/inverse fluidized beds are very important and difficult to measure. The phase holdups can be estimated with the help of pressure drop data and height of the bed/solids mass balance with an assumption of axial uniform solid holdup. In most of the fluidized bed operations, such as Catalytic fluidized bed and slurry bubble columns the solids holdup varies axially. Such type of systems, holdups estimation is very difficult. The present study is focused on electrical conductivity method to get directly the cross sectional liquid holdup and pressure drop to solve the above problem of axial solid holdup variation and can readily be obtained the cross sectional three phase holdups The averaged normalized conductance and the liquid holdup are related with liquid conductivity with a power law mode of equation. The dependency of conductivity on liquid also varies with electrode size and non-conducting medium (gas/solid). The experimental results showed that the conductivity method developed in this work was convenient for use and had a good accuracy in a wide range of liquid holdup (0.4 to 1) in the Gas-Liquid–Solid three-phase fluidized bed systems. The effect of temperature on conductivity of liquid phase was also verified and successfully correlated

Sequential modular simulation of ethanol production in a three-phase fluidized bed bioreactor

A state-of-the-art sequential modular approach towards the modeling of a complex three-phase fluidized bed bioreactor has been introduced. The aim was to simulate the fermentation process of glucose for ethanol production using immobilized yeast in a gas–liquid–solid three-phase bioreactor. According to the newly-introduced dimensionless number (ASh number), a fluidized bed bioreactor was divided into several sections in which the three phases of emulsion, wake, and bubble were modeled parallel to each other. In the proposed model, two sub-models, namely, hydrodynamic and chemical reaction sub-models, were integrated to take the governing physical and chemical phenomena into account. Emulsion, wake, and bubble phases were considered as CSTR (continuous stirred-tank reactor), PFR (plug flow reactor), and bypass flow, respectively. Afterwards, mass transfer was taken into account right at the outlet of each section. The simulation results were compared with the experimental data derived from the literature in a wide range of gas velocity, liquid flow rate, biocatalyst particle size, and the concentration of glucose in the feed stream, which showed a great consistency. The simulation approach proposed in this study proved to be applicable in predicting the behavior of industrial three-phase fluidized bed reactors successfully.

Transient CFD modeling of toluene waste gas biodegradation in a gas–liquid–solid three-phase airlift loop reactor by immobilized Pseudomonas putida

The biotreatment of toluene was studied in a gas–liquid–solid three-phase airlift loop reactor (ALR) using the CFD method. A transient 3D CFD model was developed for the simulation including the k–ɛ turbulence model, interphase forces, momentum and mass transfer, bubble coalescence and breakup, and the bioreaction. The validation was done by the liquid phase axial velocity from hydrodynamic experiment and the dissolved toluene and removal efficiency concentrations from the toluene treatment experiment. The CFD simulations agreed well with the experiment data. Hydrodynamics and local dispersions of components in ALR were predicted by the verified model. The rate-limiting step was also discussed by quantitative comparison between mass transfer rate and bioreaction rate. Optimized simulation had been done based on the rate-limiting step and had found that the decreased solid bead diameter could effectively improve the removal efficiency.

CFD modelling of phenol biodegradation by immobilized Candida tropicalis in a gas–liquid–solid three-phase bubble column

A three-dimensional transient model, combining three-phase fluid flow, interphase mass transfer and intrinsic bioreaction kinetics, was developed to simulate the dynamic behaviors of batch phenol biodegradation by immobilized Candida tropicalis in a gas–liquid–solid three-phase bubble column (BC). A computational fluid dynamics (CFD) method was used, with a multiple size group model adopted to determine the bubble size distribution, based on a previous three-phase BC hydrodynamic CFD model [1]. Current simulation results of phenol and oxygen concentration changes in the liquid phase were validated by corresponding experimental measurements under various operating conditions. Furthermore, local transient batch phenol biodegradation characteristics such as the oxygen concentration profiles in the gas, liquid and solid phases, the phenol concentration profiles in the liquid and solid phases, and the cell concentration profile in the solid phase were predicted. Comparisons between species interphase mass transfer and bioreaction rates were carried out to identify the rate-limiting step in the immobilized batch phenol biodegradation processes.

Hydrodynamics and energy consumption studies in a three-phase liquid circulating three-phase fluid bed contactor

The hydrodynamics and energy consumption have been studied in a cold flow, bubbling and turbulent, pressurized gas–liquid–solid three-phase fluidized bed (0.15 m ID × 1 m height) with concurrent gas–liquid up flow is proposed with the intention of increasing the gas hold up. The hydrodynamic behaviour is described and characterised by some specific gas and liquid velocities. Particles are easily fluidized and can be uniformly distributed over the whole height of the column. The effect of parameters like liquid flow rate, gas flow rate, particle loading, particle size, and solid density on gas hold up and effect of gas flow rate, solid density and particle size on solid hold up, energy consumption and minimum fluidization velocity has been studied. At the elevated pressures a superior method for better prediction of minimum fluidization velocity and terminal settling velocities has been adopted. The results have been interpreted with Bernoulli’s theorem and Richardson–Zaki equation. Based on the assumption of the gas and liquid as a pretend fluid, a simplification has been made to predict the particle terminal settling velocities. The Richardson–Zaki parameter n′ was compared with Renzo’s results. A correlation has been proposed with the experimental results for the three-phase fluidization.

CFD simulation of hydrodynamics of gas–liquid–solid fluidised bed reactor

A three dimensional transient model is developed to simulate the local hydrodynamics of a gas–liquid–solid three-phase fluidised bed reactor using the computational fluid dynamics (CFD) method. The CFD simulation predictions are compared with the experimental data of Kiared et al. [1999. Mean and turbulent particle velocity in the fully developed region of a three-phase fluidized bed. Chemical Engineering & Technology 22, 683–689] for solid phase hydrodynamics in terms of mean and turbulent velocities and with the results of Yu and Kim [1988. Bubble characteristics in the racial direction of three-phase fludised beds. A.I.Ch.E. Journal 34, 2069–2072; 2001. Bubble-wake model for radial velocity profiles of liquid and solid phases in three-phase fluidised beds. Industrial and Engineering Chemistry Research 40, 4463–4469] for the gas and liquid phase hydrodynamics in terms of phase velocities and holdup. The flow field predicted by CFD simulation shows a good agreement with the experimental data. From the validated CFD model, the computation of the solid mass balance and various energy flows in fluidised bed reactors are carried out. The influence of different interphase drag models for gas–liquid interaction on gas holdup are studied in this work.

Structure Optimization of an Improved Inner-Circulating Biological Fluidized Bed by Numerical Simulation

Recently, the structure of inner-circulating biological fluidized beds has been improved for the sake of making them more efficient. In the present paper, the separation zone composed of staggered triangle cones is added, which could prevent the loss of carriers. The presence of more carriers could provide more surfaces for biofilms and is helpful to the mixing of solid, liquid, and gas. The wastewater treatment efficiency could be improved. The main focus of this paper is to optimize the structure parameters of the separation zone by simulating the improved inner-circulating biological fluidized bed. The mixture model and the standard k-ɛ model are employed to simulate the gas–liquid–solid three-phase turbulent flow. Experiments are performed in a lab-scale CFB. The agreements between simulation and experiments verify the reliability of the methods employed in this paper. By simulation, the distributions of velocity and volume fraction in the CFB are obtained. The influences of the structure parameters o...

Experimental measurement and numerical simulation for liquid flow velocity and local phase hold-ups in the riser of a GLSCFB

A gas–liquid–solid three-phase circulating fluidized bed (GLSCFB) with 0.15 m in diameter and 4.35 m in height was employed to investigate the local phase hold-ups and liquid flow velocity. With styrene resin (dp = 1.45 mm, ρ s = 1264 kg/m 3) as solid phases, air as gas phase, and carboxymethyl cellulose sodium as liquid phase, local phase hold-ups are measured simultaneously by micro-conductivity probe technique under a wide range of operation conditions. Liquid flow velocity measurements have been performed using the electrolyte tracer measurement (ETM) technique. Measurement results in a GLSCFB riser presented here give an insight into the distribution laws of the local phase hold-ups and liquid velocity in radial directions. A closed Eulerian/Eulerian/Lagrangian model (E/E/L model) for simulating gas–liquid–solid three-phase local flow properties was developed by combining Two Fluid Model (TFM) and District Element Method (DEM). This model was based on the fundamental equations of fluid mechanics. The motion of particles was described in the Lagrangian co-ordinates, while the gas phase and the liquid phase were described within the Eulerian co-ordinates. Based on IPSA and PSIC solution techniques, the program of simulating gas–liquid–solid local flow properties was achieved. The numerical simulating results of local phase hold-ups and local radial liquid velocity agreed well with the experimental data in a GLSCFB riser, and the applicability and reliability of this model were validated.

Characterization of hydrodynamic properties of a gas–liquid–solid three-phase fluidized bed with regular shape spherical glass bead particles

The hydrodynamic characteristics, viz., the pressure drop, bed expansion and phase hold-up of a cocurrent gas–liquid–solid three-phase fluidized bed has been studied using liquid as the continuous phase and gas as the discontinuous phase. These have been done in order to develop a good understanding of each flow regime in gas–liquid and liquid–solid fluidization. Air, water and glass beads (2.18, 3.05 and 4.05 mm, respectively) are used as the gas, liquid and solid phases, respectively. The experiments were carried out in a 100 mm ID, 2 m-height vertical Plexiglas column. The column consists of three sections, viz., the gas–liquid disengagement section, test section and gas–liquid distributor section. Bed pressure measurements have been made to predict the minimum liquid fluidization velocity. By keeping gas velocity at a fixed value, the liquid velocity was varied and the effect on phase hold-up, minimum liquid fluidization velocity, pressure drop and the expansion ratio was studied for different particle size and static bed height. Experimental study based on statistical design has been made to investigate the expansion ratio of fluidized bed and a correlation has been developed for gas hold-up. It is evident from the correlation that gas hold-up is strongly function of modified gas Reynolds number and independent of liquid Reynolds number. The experimental values have been compared with those predicted by the

Electrical resistance tomography for flow characterization of a gas–liquid–solid three-phase circulating fluidized bed

Electrical resistance tomography (ERT) as an imaging technique was employed in this study for flow characterization, including simultaneous measurements of phase holdups and velocity distribution of individual phases in a gas–liquid–solid circulating fluidized Bed (GLSCFB). Application of ERT in three-phase flow systems is completely new. ERT is a non-invasive technique based on conductivity of the continuous phase, which provides color-coded cross-sectional view of the phases with a frequency of up to 250 Hz. The local conductivity measured by 16 electrodes located at the periphery of the plane inside the ERT measurement section, was then further converted into local phase concentration distribution based on Maxwell's relation. By cross-correlation analysis between the data obtained from both upstream and downstream planes, each consisting of eight electrodes, the phase propagation velocity was determined. Water was used as the continuous and conductive phase, while glass beads and air were non-conductive solid and gas phases, respectively. Qualitative and quantitative radial profiles of the phase holdup and propagation velocities were obtained. Phase holdup was also measured by pressure fluctuation, using online non-invasive pressure transducers and the results were in close agreement with the ERT results.

Treatment of Catalyst Wastewater in a Three-Phase Flow Airlift Loop Bioreactor

A 12-L gas–liquid–solid three-phase flow airlift loop bioreactor, in which micro-organism immobilization replaced the activated sludge, was used for the nitrifying treatment of the original effluent from Catalyst Complex of Qilu Petrochemical Corp. of SINOPEC, Zibo City, Shandong Province, P.R. China. The original wastewater contained a high strength NH4–N of up to 2,437 mg L−1 and solution electrical conductivity (EC) of nearly 22,000 μScm−1 . The influences of temperature, pH value, superficial gas velocity (ug) and hydraulic residence time (HRT) on the reductions of COD and NH4–N were investigated and discussed, respectively. The optimum operation condition was obtained as temperature 30–35°C, pH value 7.0–7.5, ug 10 mm s−1 , and HRT 15 h at the solid hold-up εs up to 50%. Under this optimum operation condition, the average removal efficiencies of COD and NH4 –N were higher than 85 and 99%, respectively, corresponding to the effluent COD, 25 mg L−1 and NH4 –N, 15 mg L−1 , which was in compliance with the national primary discharge standard of P. R. China as COD ≤ 100 mg L−1 and NH4-N ≤ 15 mg L−1 (GB 8978–1996). Additionally, the radial and axial positions in the reactor showed little influence on the local profiles of COD and NH4 –N.

Bacterial Decontamination of Water by Bipolar Pulsed Discharge in a Gas–Liquid–Solid Three-Phase Discharge Reactor

Inactivation of Escherichia coli by bipolar pulsed discharge in an air–liquid–solid three-phase discharge reactor has been investigated. The effect of several operating parameters on the inactivation efficiency has also been studied. Experimental results showed that bipolar pulsed discharge in the three-phase discharge plasma reactor had good performance in the inactivation of E. coli. Power intensity and gas flow rate had a positive effect on the inactivation, while the initial solution conductivity had little effect. An alkaline solution condition was favorable for the inactivation of E. coli in the reactor. In addition, possible mechanisms of the inactivation were also discussed.