Gas Liquid Solid Three-phase Research Articles

Multi-scale modeling of gas–liquid–solid three-phase fluidized beds using the EMMS method

Abstract A multi-scale model for the gas–liquid–solid three-phase fluidized beds is developed on the basis of the principles of the EMMS model. For this purpose, the flowing structure in the gas–liquid–solid system is divided into five phases and considered under different spatial scales: a solid–liquid phase describing the micro-scale interaction between solid particles and liquid, a gas phase, a bubble wake phase and two inter-phases that, respectively, describe the meso-scale interaction of the dispersed bubbles and bubble wakes with the surrounding liquid–solid pseudo-homogeneous suspension. In order to obtain the steady state of such a system with eight unknowns, in addition to seven mass and momentum conservation conditions and an inequality constraint for the mean bubble diameter, the stability condition N st → min is used. The model is solved and checked with the experimental data available in several references which cover a broad range of operating conditions from the conventional expanded fluidized bed to the circulating fluidized bed, indicating that the model is capable of describing the global hydrodynamics of the complex flow in the three-phase system with acceptable accuracy.

Dewetting kinetics on silica substrates: Three phase contact expansion measurements for aqueous dodecylammonium chloride films

The dewetting kinetics between a small air–liquid interface and a silica (negatively charged in water) planar surface in solutions of dodecylammonium chloride (cationic surfactant) has been investigated using the Scheludko cell and digital high-speed video microscopy. The gas–liquid interface was created at the bottom of a small silica capillary of the cell and then was moved towards the silica planar surface. After the rupture of the liquid films between the interfaces, the expansion of the gas–liquid–solid three-phase contact (TPC) line was observed and recorded using a digital high-speed video microscope system, operating at 1000 frames/s. The surface tension of the surfactant solution was measured using the pendant drop technique. The equilibrium contact angle was measured using the Scheludko–Minings method with a silica micro-sphere. The TPC radius was determined as a function of time and compared against the available hydrodynamic and molecular-kinetic models. The experimental data are described very well by the molecular-kinetic model for the TPC line motion. The hydrodynamic model is in agreement with the experimental data only for a short time after inception of the three-phase contact expansion. A simplified model was developed for predicting the time of the TPC line expansion in flotation.

The pilot study for oil refinery wastewater treatment using a gas–liquid–solid three-phase flow airlift loop bioreactor

Aerobic bio-treatment of the refinery wastewater was carried out in a 170 m 3 pilot-scale gas–liquid–solid three-phase flow airlift loop bioreactor (ALR) with a low ratio of height to diameter ( s), in which biological membrane replaced the activated sludge. The influences of pH value, air flow rate (AFR) and hydraulic residence time (HRT) on COD and ammonia nitrogen (NH 4–N) reductions were investigated and discussed. The optimum operation condition was obtained as pH value 7.0–8.0, AFR 3.2 m 3 air (m 3 liquid h) −1 and HRT 6.5 h. Under the optimum operation condition, the effluent COD and NH 4–N were lower than 100 and 15 mg L −1, respectively for more than 40 days, which have achieved the national primary discharge standard of PR China (GB 8978-1996). Furthermore, this pilot-scale airlift loop bioreactor generated only one-third of the sludge waste compared to the traditional activated sludge process.

Nitrifying treatment of wastewater from fertilizer production in a multiple airlift loop bioreactor

An 80 m 3 gas–liquid–solid three-phase flow multiple airlift loop bioreactor (ALR) with a low ratio of height to diameter s, in which biofilm replaced the activated sludge, was used in the nitrifying treatment of the effluent from Tengfei Chemical Fertilizer Plant, Tianjin, PR China. The influences of the ratio of bed (settled) volume to bioreactor volume V b/ V R, superficial air velocity U g, hydraulic residence time HRT and pH value on ammonia nitrogen reduction were investigated and discussed. The optimum operating conditions were obtained as pH value of 7.0–8.0, V b/ V R of 0.65, U g of 0.01 m s −1 and HRT of 6 h were found. Under the optimum operating conditions, the effluent COD and NH 4 N were less than 50 and 10 mg l −1, which was far below the primary discharge standard for chemical fertilizer industry of PR China: COD < 100 mg l −1 and NH 4–N < 40 mg l −1 (GWPB4-1999).

Removal of ethyl acetate in air streams using a gas–liquid–solid three-phase flow airlift loop bioreactor

The biological removal of ethyl acetate in air streams was carried out in gas–liquid–solid three-phase flow airlift loop bioreactor, in which biological membrane replaced the activated sludge. The influences of temperature, pH and waste gas influx on the removal efficiency (RE) and the outlet concentration of ethyl acetate were investigated and discussed. The optimum operation conditions were obtained as the temperature of 20–30 °C, pH 6.5–7.5 and waste gas influx of 0.05 m 3/h. Under the optimum operation conditions, the average removal efficiency of ethyl acetate is higher than 98%, corresponding to the outlet concentration of ethyl acetate lower than 150 mg/m 3. The maximum elimination capacity (EC) of ethyl acetate in gas–liquid–solid three-phase flow airlift loop bioreactor was higher than that in the biofilters reported in the literature.

Simultaneous removal of ethyl acetate and ethanol in air streams using a gas–liquid–solid three-phase flow airlift loop bioreactor

Abstract A gas–liquid–solid three-phase flow airlift loop bioreactor was applied to treat air streams containing a mixture of ethyl acetate and ethanol. The activated sludge was replaced by biological membrane in the experiment. The influences of pH and jet waste gas influx on the removal efficiency and outlet ethyl acetate and ethanol mixture concentration were investigated. The optimum pH and jet waste gas influx were 6.0 and 4.4 m/s, respectively. Under the optimum operation conditions, the average removal efficiencies of ethyl acetate and ethanol in the mixture were higher than 98%, and accordingly, the outlet concentrations of ethyl acetate and ethanol were lower than 150 mg/m3. The elimination capacities of ethyl acetate (504 g/m3/h) or ethanol (685 g/m3/h) in the mixture as two mixture pollutants, which were higher than those in biofilters (ethyl acetate 400 g/m3/h and ethanol 195 g/m3/h) reported in the literatures [Y.H. Liu, X. Quan, Y.M. Sun, J.W. Chen, D.M. Xue, J.S. Chung, Simultaneous removal of ethyl acetate and toluene in air stream using compost-bases biofilters, J. Hazard. Mater. B 95 (2002) 199–213; D. Arulneyam, T. Swaminathan, Biodegradation of ethanol vapour in a biofilter, Bioprocess Eng. 22 (2000) 63–67], were also higher than those of pure ethyl acetate (480 g/m3/h) or ethanol (671 g/m3/h) as single pollutant in gas–liquid–solid three-phase flow airlift loop bioreactor.

Kinetics for aerobic biological treatment of o-cresol containing wastewaters in a slurry bioreactor: biodegradation by utilizing waste activated sludge

A toxic volatile organic compound (VOC), o-cresol, was biologically degraded by utilizing waste activated sludge in a gas–liquid–solid three-phase slurry bioreactor. The biodegradation kinetics of o-cresol was examined in batch experiments at varying initial o-cresol concentrations (from 30 to 600 mg/L), waste activated sludge concentrations (from 1000 to 11,500 mg/L) and aeration rates (from 0.05 to 1.0 L/min). The kinetic parameters of o-cresol aerobic biodegradation were estimated using Haldane substrate inhibition equation with the correlation factors of approximately 0.95. The oxygen consumption during the biodegradation process was also examined. The oxygen consumption rate was adequately described by the Haldane type model with the correlation factor of 0.965. The biodegradation of o-cresol by waste activated sludge and the change of dissolved oxygen concentration in the slurry bioreactor were successfully simulated.

Simultaneous measurement of gas and solid holdups in multiphase systems using ultrasonic technique

Ultrasonic technique has been recently developed to measure dispersed phase holdups in multiphase flows. The experimental results obtained in this work have shown that the fluctuations of the sound speed and attenuation of ultrasound are well-defined functions with solid and gas holdups in liquid–solid and gas–liquid two-phase flows. When both solid particles and gas bubbles are present in a liquid flow, gas bubbles appear to be a dominant factor for the instability of ultrasound signals. These findings lead to a new approach for simultaneous detection of gas and solid holdups in a gas–liquid–solid three-phase flow. In this work, canonical analysis and optimization methods are successfully applied to differentiate the contributions of gas bubbles and solid particles to the ultrasonic signals recorded from three-phase systems. The gas and solid holdups determined by the proposed approach are in a good agreement with the experimental results obtained using differential pressure transducers and conductivity probes.

Experimental study on bubble behavior in gas–liquid–solid three-phase circulating fluidized beds

The gas–liquid–solid three-phase circulating fluidized bed (TPCFB) is a novel multiphase reactor with outstanding performance in hydrodynamics, heat transfer, mass transfer and catalyst treatment. The object of this work is to study the bubble behavior in TPCFBs for better understanding of the hydrodynamics of the reactor. The local gas holdup, bubble size distribution, and bubble rise velocity in different radial positions are measured using a fiber optic probe, and the effects of operating conditions on bubble rise velocity are also investigated. Moreover, the bubble rise velocity and its distribution are compared with the data from gas–liquid two-phase external loop airlift reactors and gas–liquid–solid three phase fluidized beds without external circulation of liquid and particles.

Power consumption and solid suspension performance of large-scale impellers in gas–liquid–solid three-phase stirred tank reactors

An experimental investigation into power consumption and solid suspension performance of large-scale impellers was carried out under turbulent conditions. Two types of large-scale impellers, i.e. Maxblend and Fullzone impellers, were employed. For reference, a triple-impeller system, i.e. two four-pitched blade downflow disk turbines (DTs) at middle and upper positions and one Pfaudler type impeller at lower position, was also used. The power consumption and the minimum impeller speeds for off-bottom solid suspension and minimum impeller speeds for ultimately homogeneous solid suspension were measured in unaerated and aerated systems. At a given rotational speed, the power consumption of the Maxblend impeller was roughly half of that of the Fullzone impeller. The decrease in power consumption due to aeration for large-scale impellers was smaller as compared with that for the triple-impeller system. The proposed correlation for power consumption of large-scale impellers in three-phase systems fit the experimental data reasonably well. Interesting and unexpected solid movements caused by the large-scale impellers in the vessels having oval bottom were observed. Since the large-scale impellers create strong axial liquid recirculation flowing downward near the impeller shaft and upward near the wall, usually particles are expected to move outward on the tank bottom. On the contrary, however, solid particles near the bottom moved to the center of the base from the side along the oval tank bottom. The large-scale impellers were found to be more efficient for solid suspension than the triple-impeller system. The Maxblend impeller provided the best solid suspension ability among the three impellers used in this work. We proposed a correlation for power consumption of large-scale impellers in gas–liquid–solid three-phase systems. Empirical correlations were also proposed for the minimum impeller speeds for off-bottom solid suspension, minimum impeller speeds for ultimately homogeneous solid suspension and power consumption at the minimum impeller speeds for ultimately homogeneous solid suspension.

The denitrification treatment of low C/N ratio nitrate-nitrogen wastewater in a gas–liquid–solid fluidized bed bioreactor

A 12 l gas–liquid–solid three-phase fluidized bed bioreactor in which biomass supported on activated charcoal was used to remove nitrate-nitrogen from wastewater and its performance was considered. The effects of temperature, pH, C/N ratio, gas flow rate and hydraulic residence time (HRT) on nitrate-nitrogen reduction were investigated and discussed. The optimum operated conditions such as temperature of 20–35 °C, pH value of 6.5–7.5, HRT of 3 h, C/N of 0.95–1 and gas influx of 0.3 m 3/h were found. Under optimum operated conditions, the average removal ratios of COD and NO x -N are higher than 92% and 96%, respectively. In addition, the radial and axial positions have little influence on the local profiles of COD and NO x -N.

The denitrification of nitrate contained wastewater in a gas–liquid–solid three-phase flow airlift loop bioreactor

Denitrification of nitrified effluent with high concentration of nitrate, low COD in fertilizer plant was carried out in a 12-l gas–liquid–solid three-phase flow airlift loop bioreactor, in which biological membrane replace the activated sludge. The influences of pH, temperature, C/N ratio, gas–liquid ratio and HRT on the removal of nitrate-nitrogen were investigated and discussed. The optimum operation conditions were obtained as pH value of 6.5–7.5, temperature of 20–35 °C, C/N ratio of 0.95–1, gas–liquid ratio of 62.5 and HRT of 2.5 h. Under optimum operation conditions, the average removal efficiencies of COD and NO x –N are higher than 93 and 96%, corresponding to the effluent concentrate of nitrate <20 mg/l and COD <40 mg/l. The radial and axial positions have little influence on the local profiles of COD and NO x –N.

Local overall gas–liquid mass transfer coefficient in a gas–liquid–solid reversed flow jet loop reactor

Local overall gas–liquid mass transfer coefficients ( K L a) of gas–liquid–solid three-phase reversed flow jet loop reactors have been experimentally investigated by means of a transient gassing-in method. Effects of liquid jet flow rate, gas jet flow rate, particle density, particle diameter, solid loading, nozzle diameter and axial position on local overall gas–liquid mass transfer coefficient profiles are discussed. It was observed that the local overall gas–liquid mass transfer coefficient profiles of the reversed flow jet loop reactor with a three-phase system increase with increase in gas jet flow rates and liquid jet flow rates and particle density and particle diameter, and with decrease in nozzle diameter and axial position. The presence of solids at low concentrations increases the local overall gas–liquid mass transfer coefficient profiles, and the optimum of adding solid loading for maximum profile of the local overall K L a was found to be 0.16×10 −3 m 3 corresponding to a solid volume fraction, ϵ S=2.5%.

Bubble behavior in gas–liquid–solid three-phase circulating fluidized beds

A novel fiber optic probe system has been developed for studying the bubble behavior in gas–liquid–solid three-phase circulating fluidized beds (TPCFBs). Mathematical method to analyze data by probe technique has also been discussed in this paper. The bubble size and its distribution, bubble Sauter diameter, gas–liquid interfacial area and bubble rise velocity, have been experimentally studied using the fiber optic probe. The experimental results show that the bubble size distribution in TPCFBs follows lognormal function. The bubble Sauter diameter has the radial profile with smaller value in the central region than in the near-wall region, different from the conventional three-phase fluidized beds (CTPFBs) without outer particle circulation. The distribution of bubble rise velocity, gas–liquid interfacial area and effect of the operation conditions have been experimentally studied.

Application of the energy-minimization multi-scale method to gas–liquid–solid fluidized beds

A model for gas–liquid–solid three-phase fluidized beds with concurrent gas–liquid up-flow is proposed, which is formulated on the basis of the energy-minimization multi-scale (EMMS) method for gas–solid two-phase flow. The three-phase fluidization system is resolved into the suspending and transporting subsystem and the energy dissipation subsystem, and the former is further divided into three sub-subsystems: liquid–solid phase, gas phase and inter-phase. Force balance is analyzed at three different scales: micro-scale of particles, meso-scale of bubbles and macro-scale of the whole system. In addition to the analysis of multi-scale interactions, the energy consumption in the system is analyzed to establish the stability condition for the system, which is considered indispensable due to the multiplicity of three-phase fluidized beds. The total energy of the system consumed with respect to unit mass of particles is resolved into two portions: suspending and transporting energy and dissipated energy. The stability condition is reached when the suspending and transporting energy of the system, N st, is at its minimum. The model first formulated as a nonlinear programming problem consisting of six variables and seven constraints, is solved by using the general reduced gradient (GRG) algorithm. The calculated results show that the stability condition, N st=min, can be stated alternately as d b=d b max . Thus, the model is finally simplified to a set of nonlinear algebraic equations. The model has been used to calculate the hydrodynamic parameters in gas–liquid–solid fluidized beds with a wide range of physical properties of the liquid and the solid phases. The model predictions show good agreement with experimental data available in the literature.

Mathematical Model of a Catalytic Process on a Porous Grain in a Gas–Liquid–Solid Three-Phase System

Mathematical Model of a Catalytic Process on a Porous Grain in a Gas–Liquid–Solid Three-Phase System

Solid–liquid mass transfer in a gas–liquid–solid three-phase reversed flow jet loop reactor

Solid–liquid mass transfer in gas–liquid–solid three-phase reversed flow jet loop reactors was experimentally investigated by means of an electrochemical method, and the effects of liquid jet flow rate, gas jet flow rate, particle size, particle density and nozzle diameter on the solid–liquid mass transfer coefficient were evaluated. The solid–liquid mass transfer coefficients in gas–liquid–solid three-phase reversed flow jet loop reactors are higher than those in the corresponding liquid–solid two-phase reversed flow jet loop reactors. A generalized correlation is developed which more accurately and conveniently predicts solid–liquid mass transfer in gas–liquid–solid three-phase reversed flow jet loop reactors.

Local overall volumetric gas–liquid mass transfer coefficients in gas–liquid–solid reversed flow jet loop bioreactor with a non-Newtonian fluid

The local overall volumetric gas–liquid mass transfer coefficients at the specified point in a gas–liquid–solid three-phase reversed flow jet loop bioreactor (JLB) with a non-Newtonian fluid was experimentally investigated by a transient gassing-in method. The effects of liquid jet flow rate, gas jet flow rate, particle density, particle diameter, solids loading, nozzle diameter and CMC concentration on the local overall volumetric gas–liquid mass transfer coefficient ( K L a) profiles were discussed. It was observed that local overall K L a profiles in the three-phase reversed flow JLB with non-Newtonian fluid increased with the increase of gas jet flow rate, liquid jet flow rate, particle density and particle diameter, but decreased with the increase of the nozzle diameter and CMC concentration. The presence of solids at a low concentration increased the local overall K L a profiles, and the optimum of solids loading for a maximum profile of the local overall K L a was found to be 0.18×10 −3 m 3 corresponding to a solids volume fraction, ε S=2.8%.

Scale-up effects in nonlinear dynamics of three-phase reactors

The scale-up effect on the dynamic behavior of gas–liquid–solid three-phase reactors was investigated by using columns of three different diameters (200, 400 and 800 mm). The local and time-dependent behavior of bubble and particle motions in three-phase reactors were characterized in terms of the correlation dimension obtained by the deterministic chaos analysis for the series of the time intervals between successive bubbles or particles by means of the embedding method. With regard to the dynamic behavior of gas phase, the large-scale column was found to have a relatively small correlation dimension because of the coherent gross circulation flow structure induced by the bias in the bubble formation on the distributor. No significant column size effect on the chaotic dynamics of solid particles was observed.

Liquid-phase flow structure and backmixing characteristics of gas–liquid–solid three-phase circulating fluidized bed

A gas–liquid–solid three-phase circulating fluidized bed (GLSCFB) possesses a large application prospect with many advantages. The radial distribution of liquid velocity and liquid phase dispersion characteristics in a GLSCFB of 140 mm i.d. was studied by using the electrolyte tracer method. It was found that liquid velocity distribution was non-uniform in the radial direction. A increase of superficial liquid and/or gas velocity and average solid holdup led to an even radial distribution for the local liquid velocity. Radial distribution of liquid velocity in a GLSCFB is more uniform than that in conventional three-phase fluidized beds. The axial liquid dispersion coefficient is almost independent of the liquid velocity, but tends to increase with the increasing gas velocity and solid holdup. The radial liquid dispersion coefficient increases with the increases of gas velocity and solid holdup, but decreases with the increasing liquid velocity.