Bubble Column System Research Articles

Modeling gas holdup in a multiphase oxygen slurry bubble column reactor for Cu-Cl hydrogen production using CFD

The hydrodynamics of the oxygen bubble column reactor is investigated numerically using CFD analyses to predict the values of the gas holdup using Eulerian model and k−ε turbulence method. It is shown that, at any given static liquid height and solid concentration, increasing the superficial gas velocity leads to a higher gas holdup. Also, the gas holdup reduces when the static liquid height increases and/or the solid concentration increases at any given superficial gas velocity. All gas holdup findings were verified by experimental results from prior literature, showing excellent agreement and validating the models' applicability to this kind of a slurry bubble column system. Profiles of gas holdup obtained from CFD simulations were shown to generally under-predict the experimental data. Also, it is shown that CFD models accurately anticipated the experimental effects of the superficial gas velocity, static liquid height, and solid concentration on gas holdup.

Hydrodynamic characterization of bubble column using Dynamical High Order Decomposition approach

Bubble columns play a crucial role in a wide range of industries, including chemical and biochemical processes, petrochemicals, and environmental engineering. Understanding the dynamics of bubble columns is essential for optimizing their performance in various applications. This study proposes a data-driven approach for analyzing the dynamics of a two-dimensional bubble column system. We conducted simulations with varying superficial velocities and generated a comprehensive training dataset encompassing the entire velocity and pressure fields to achieve this. We then compared the performance of two approaches, the Fast Fourier Transformation (FFT) and the High-Order Dynamic Mode Decomposition (HODMD), in representing the system’s dynamics. Our findings demonstrate that the conventional FFT approach fails to adequately capture the complex dynamics of the dispersed multiphase flow system. This limitation arises due to the distribution of frequencies along the domain. Conversely, our work highlights the success of the HODMD method in accurately representing the system’s dynamics using only a few arbitrary sampling points within the domain. The implications of this study are significant, as it sheds light on the potential benefits of employing HODMD for analyzing bubble column dynamics. By utilizing this approach, industrial processes can be optimized more effectively across various applications.

Improvement of extracellular polysaccharides production from Cordyceps militaris immobilized alginate beads in repeated-batch fermentation

Cordyceps militaris (C. militaris) is a unique medicinal fungus of the genus Cordyceps. It has high economic value due to various biological functions from the extracellular polysaccharides (EPSs) it produces. The aim of this study was to establish a mycelium-immobilization system for EPS production in a bubble column system. First, EPS production was optimized by 90.2% (from 0.72 to 1.37 g/L) using response surface methodology under an alginate-immobilized mycelium system with 6 days of cultivation. The highest EPS production was obtained (5.3 g/L) in a flask system through elongation to 15 days of cultivation. EPS production subsequently further increased to 10.42 g/L utilizing a bubble column reactor. Furthermore, the system can be reused for at least three rounds. In the EPS characteristics analysis, the produced EPSs were mainly composed of glucose and galactose. They presented strong antibacterial activity against Staphylococcus aureus. In terms of antioxidant activity, respective the EPS concentration that caused 50% scavenging of DPPH and ABTS free radicals values (IC50) were 4.65 and 7.92 mg/mL. In summary, these findings should be helpful for establishing a suitable industrial fermentation system for C. militaris and can be studied in the food and medical industries in future work.

Bubble column and airlift bioreactor systems for animal cell culture applications

AbstractMany biopharmaceutical industries have focused on the screening for novel cell lines and producers for manufacturing of advanced therapeutics. Commercial scale productions at reduced cost and improved productivity are only possible with the bioreactor systems. Animal cell culture bioreactors have all started to draw attention in view that 20th century and advanced significantly over the previous few a long time especially with the need for viral vaccine productions, monoclonal antibody productions and in vitro meat productions. To produce these high value‐added products in large scales, bioreactor configurations are advanced to reduce investment and operational costs, control the process parameters, enhance productivity, and make easier scale‐up. Although novel bioreactor systems have interested in recent years, conventional bubble column and airlift systems are still the most familiar and experienced bioreactors. Pneumatically agitated bioreactors have been studied for many years in animal cell culture. This current review intends to provide an overview of pneumatic bioreactor productions for animal cell culture applications in key items of cell culture and bioreactor technology, for example, design parameters, transport phenomena during cultivation, shear sensitivity of cells. Besides, the previous studies, investigated that the design parameters and process conditions for productivity and shear sensitivity, have been reviewed and summarized.

Bubble growth and detachment process in surfactant solutions: a study of 90% pure sodium dodecyl sulfate

We have investigated the effect of the surfactant Sodium Dodecyl Sulfate on the bubble growth and detachment processes in a bubble column system. A modified pendant drop model was employed to determine the dynamic surface tension. The dynamic surface tension approached the static surface tension value within a few seconds. A photographic technique and a laser-based electro-optical method were used to study the bubble size variation and the generation frequency, respectively. Parameters like bubble generation frequency, size, growth rate, and contact angle were found to be a strong function of surfactant concentration. Our results show that the addition of surfactant significantly reduces the bubble lifetime at the orifice. Such a decrease in the bubble lifetime has a direct impact on the bubble growth rate and departure size. Furthermore, bubble parameters vary with surfactant concentration only up to the critical micellar concentration.

Laboratory-scale reproduction of lighting conditions for an outdoor vertical column photobioreactor: Theoretical fundamentals and operation of a programmable LED module

The development of tools aimed to predict the productivity of photobioreactors (PBRs) implies immense efforts in the Algae Biotechnology field. Mainly, bubble column systems are widely used for microalgae cultivation. Here, we sought to present a methodology to reproduce the solar lighting conditions of a vertical bubble column reactor located in Santa Fe, Argentina, utilising a commercial laboratory-scale reactor, with a programmable LED module attached. Based on solid, rigorous modelling of solar radiation properties and radiation transfer between surfaces, and keeping constant the effects of geometry and orientation of PBR, and those related to geography such as photoperiod and solar radiation composition (direct and diffuse), the same amount of photosynthetically active radiation (PAR) per volume unit (volumetric radiant flux) has been provided to the indoor unit.Lastly, since the deliverance of radiant energy between the indoor and outdoor units is not the same, the radiant energy field (REF) is obtained for both reactors and compared using the Monte Carlo methodology. Comparisons were made in terms of the distribution and average volumetric absorption rate of PAR photons (〈rPAR〉) for different scenarios (time, day of the year, biomass concentration and photosynthetic pigments concentration). Taken together, the 〈rPAR〉 turned out to be similar for both PBRs, highlighting the potentiality of this approach for its usage either in real or simulated units under varying outdoor conditions.

Simulation Study on Gas Holdup of Large and Small Bubbles in a High Pressure Gas–Liquid Bubble Column

The computational fluid dynamics-population balance model (CFD-PBM) has been presented and used to evaluate the bubble behavior in a large-scale high pressure bubble column with an inner diameter of 300 mm and a height of 6600 mm. In the heterogeneous flow regime, bubbles can be divided into “large bubbles” and “small bubbles” by a critical bubble diameter dc. In this study, large and small bubbles were classified according to different slopes in the experiment only by the method of dynamic gas disengagement, the critical bubble diameter was determined to be 7 mm by the experimental results and the simulation values. In addition, the effects of superficial gas velocity, operating pressure, surface tension and viscosity on gas holdup of large and small bubbles in gas–liquid two-phase flow were investigated using a CFD-PBM coupling model. The results show that the gas holdup of small and large bubbles increases rapidly with the increase of superficial gas velocity. With the increase of pressure, the gas holdup of small bubbles increases significantly, and the gas holdup of large bubbles increase slightly. Under the same superficial gas velocity, the gas holdup of large bubbles increases with the decrease of viscosity and the decrease of surface tension, but the gas holdup of small bubbles increases significantly. The simulated values of the coupled model have a good agreement with the experimental values, which can be applied to the parameter estimation of the high pressure bubble column system.

Comparing Nutrient Removal from Membrane Filtered and Unfiltered Domestic Wastewater Using Chlorella vulgaris.

The nutrient removal efficiency of Chlorella vulgaris cultivated in domestic wastewater was investigated, along with the potential to use membrane filtration as a pre-treatment tool during the wastewater treatment process. Chlorella vulgaris was batch cultivated for 12 days in a bubble column system with two different wastewater treatments. Maximum uptake of 94.18% ammonium (NH4-N) and 97.69% ortho-phosphate (PO4-P) occurred in 0.2 μm membrane filtered primary wastewater. Membrane filtration enhanced the nutrient uptake performance of C. vulgaris by removing bacteria, protozoa, colloidal particles and suspended solids, thereby improving light availability for photosynthesis. The results of this study suggest that growing C. vulgaris in nutrient rich membrane filtered wastewater provides an option for domestic wastewater treatment to improve the quality of the final effluent.

A review on empirical correlations estimating gas holdup for shear-thinning non-Newtonian fluids in bubble column systems with future perspectives

AbstractGas holdup is one of the most important parameters for characterizing the hydrodynamics of bubble columns. Modeling and design of bubble columns require empirical correlations for precise estimation of gas holdup. Empirical correlations available for prediction of gas holdup (εG) in various non-Newtonian systems for both gas-liquid and gas-liquid-solid bubble columns have been presented in this review. Critical analysis of correlations presented by different researchers has been made considering the findings and pitfalls. As the magnitude of gas holdup depends on many factors, such as physicochemical properties of gas and/or liquid, column geometry, type and design of gas distributors, operating conditions, phase properties, and rheological properties, etc., all of these have been discussed and examined. In order to emphasize the significance, relative importance of parameters such as flow behavior index, consistency index, column diameter, gas flow rate, and density of aqueous carboxymethylcellulose (CMC) solution on gas holdup has been quantified using artificial neural network and Garson’s algorithm for an experimental data set of air-CMC solution from the literature. Besides, potential areas for research encompassing operating conditions, column geometry, physical properties, modeling and simulation, rheological properties, flow regime, etc., have been underlined, and the need for developing newer correlations for gas holdup has been outlined. The review may be useful for the modeling and design of bubble columns.

Comparative analysis of top-lit bubble column and gas-lift bioreactors for microalgae-sourced biodiesel production

The development of top-lit one-meter deep bioreactors operated as either a gas-lift or bubble column system using air and carbon dioxide enriched air was studied. The goal was high productivity cultivation of algae with elevated lipid levels suitable for conversion into biodiesel. A theoretical energy requirement analysis and a hydrodynamic model were developed to predict liquid circulation velocities in the gas-lift bioreactor, which agreed well with experimental measurements. The influence of operational parameters such as design of bioreactor, gas flow rates and carbon dioxide concentration on the growth and lipid volumetric production of Scenedesmus dimorphus was evaluated using factorial design. While biomass productivity was 12% higher in the bubble column bioreactor (68.2gdwm−2day−1), maximum lipid volumetric production (0.19gLipidL−1) was found in a gas-lift bioreactor sparged with 6% carbon dioxide due to hydrodynamic and light stresses.

Effects of temperature, pH, and ionic strength on the Henry's law constant of triethylamine

AbstractThe Henry's law constants (KH) of triethylamine (TEA) in pure water and in 1‐octanol were measured for the temperatures pertinent to the lower troposphere (278–298 K) using a bubble column system coupled to a Fourier transform infrared spectrometer. The KH values of TEA in water and 1‐octanol at 298 K are 5.75 ± 0.86 mol L−1 atm−1 and 115.62 ± 5.78 mol L−1 atm−1. The KH values display strong dependence on temperature, pH, and ionic strength. The characteristic times for TEA to establish an equilibrium between gas and droplet with a size of 5.6 µm are ~33 s (298 K, pH = 5.6); ~8.9 × 102 s (278 K, pH = 5.6); ~1.3 × 103 s (298 K, pH = 4.0); and 3.6 × 104 s (278 K, pH = 4.0). The evaluation of TEA partitioning between gas phase and condensed phase implies that TEA predominantly resides in rainwater, and TEA loss to organic aerosol is negligible.

Design, Construction, and Validation of an Internally Lit Air-Lift Photobioreactor for Growing Algae

A novel 28 L photobioreactor for growing algae was developed from a previous bubble column system. The proposed design uses the air lift principle to enhance the culture circulation and induce light/dark cycles to the microorganisms. Optical fibers were used to distribute photons inside the culture media providing an opportunity to control both light cycle and intensity. The fibers were coupled to an artificial light source, however the development of this approach aims for the future use of natural light collected through parabolic solar collectors. This idea could also allow the use of non-clear materials for photobioreactor construction significantly reducing costs and increasing durability. Internal light levels were determined in dry conditions and were maintained above 80 µmol/(s•m2). The hydrodynamic equations of the air lift phenomena were explored and used to define the geometric characteristics of the unit. The reactor was inoculated with the algae strain Chlorella sp. and sparged with air. The reactor was operated under batch mode and daily monitored for biomass concentration. The specific growth rate constant of the novel device was determined to be 0.011 h-1, similar to other reactor designs reported in the literature, suggesting the proposed design can be effectively and economically used in carbon dioxide mitigation technologies and in the production of algal biomass for biofuel and other bioproducts.

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.

An improved approach for measuring Henry's law coefficients of atmospheric organics

In this work, we present an improved method for Henry's law constant, KH, measurements by coupling a bubble column system with a gas cell/infrared spectrometer. To demonstrate the feasibility of this approach, we measured KH of atmospheric organics from three different classes, namely, toluene (hydrocarbon), sec-butylamine (amine), and cineole (ether). We also reported temperature and ionic strength effects on the KH values of sec-butylamine for the first time. As shown in this work, the method is highly capable of determining KH of atmospheric organic species regardless the presence of heteroatoms and the occurrence of hydration in water. It is very versatile, easy to use, reliable, and efficient. It is also well-suited for undergraduate students to conduct environmental chemical science research during academic semesters.

Quantifying sub-grid scale (SGS) turbulent dispersion force and its effect using one-equation SGS large eddy simulation (LES) model in a gas–liquid and a liquid–liquid system

The one-equation SGS LES model has shown promise in revealing flow details as compared to the Dynamic model, with the additional benefit of providing information on the modelled SGS-turbulent kinetic energy ( Niceno et al., 2008). This information on SGS-turbulent kinetic energy (SGS-TKE) offers the possibility to more accurately model the physical phenomena at the sub-grid level, especially the modelling of the SGS-turbulent dispersion force (SGS-TDF). The use of SGS-TDF force has the potential to account for the dispersion of particles by sub-grid scale eddies in an LES framework, and through its use, one expects to overcome the conceptual drawback faced by Eulerian–Eulerian LES models. But, no work has ever been carried out to study this aspect. Niceno et al. (2008) could not study the impact of SGS-TDF effect as their grid size was comparable to the dispersed bubble diameter. A proper extension of research ahead would be to quantify the effect of sub-grid scale turbulent dispersion force for different particle systems, where the particle sizes would be smaller than filter-size. This work attempts to apply the concept developed by Lopez de Bertodano (1991) to approximate the turbulent diffusion of the particles by the sub-grid scale liquid eddies. This numerical experimentation has been done for a gas–liquid bubble column system ( Tabib et al., 2008) and a liquid–liquid solvent extraction pump-mixer system ( Tabib et al., 2010; Tabib and Schwarz, 2010). In liquid–liquid extraction system, the organic droplet size is around 0.5 mm, and in bubble columns, the bubble size is around 3–5 mm. The simulations were run with mesh size coarser than droplet size in pump-mixer, and for bubble column, two simulations were run with mesh size finer and coarser than bubble diameter. The magnitude of SGS-TDF values in all the cases were compared with magnitude of other interfacial forces (like drag force, lift force, resolved turbulent dispersion force, force due to momentum advection and pressure). The results show that the relative magnitude of SGS-TDF as compared to other forces were higher for the pump-mixer than for the coarser and finer mesh bubble column simulations. This was because in the pump-mixer, the ratio of “dispersed phase particle diameter to the grid-size” was smaller than that for the bubble column runs. Also, the inclusion of SGS-TDF affected the radial hold-up, even though the magnitudes of these SGS-TDF forces appeared to be small. These results confirms that (a) the inclusion of SGS-TDF will have more pronounced effect for those Eulerian–Eulerian LES simulation where grid-size happens to be more than the particle size, and (b) that the SGS-TDF in combination with one-equation-SGS-TKE LES model serves as a tool to overcome a conceptual drawback of Eulerian–Eulerian LES model.

A parallel bubble column system for the cultivation of phototrophic microorganisms

An incubator with up to 16 parallel bubble columns was equipped with artificial light sources assuring a light supply with a homogenous light spectrum directly above the bioreactors. Cylindrical light reflecting tubes were positioned around every single bubble column to avoid light scattering effects and to redirect the light from the top onto the cylindrical outer glass surface of each bubble column. The light reflecting tubes were equipped with light intensity filters to control the total light intensity for every single photo-bioreactor. Parallel cultivations of the unicellular obligate phototrophic cyanobacterium, Synechococcus PCC7942, were studied under different constant light intensities ranging from 20 to 102 microE m(-2)s(-1) at a constant humidified air flow rate supplemented with CO(2).

Nonlinear forecast of heat transfer coefficient signal in fluidized bed evaporator

The focus of this work is on the local nonlinear forecast of evolution behavior of heat transfer coefficient in an evaporator with vapor–liquid–solid external natural circulation flow. Time series of heat transfer coefficients are calculated from the measured signals of wall and fluid temperatures in the fluidized bed evaporator. The times series predicted by a model of datum driving developed on the basis of reconstruction of phase space, are compared to the obtained signals experimentally according to the time-averaged statistics characteristics, power spectral density functions, phase maps and invariants of chaotic attractor of evolution system including correlation dimension and Kolmogorov entropy. The predictions of average heat transfer coefficients show reasonable agreements, and those of the heat transfer coefficient fluctuations display tendency agreements. The time series predictions for vapor–liquid–solid flow boiling system is not as good as those for vapor–liquid flow boiling and gas–liquid bubble column systems from the point of view of the time trajectory, which indicates certain essential differences between these systems in fluctuation mechanism and nonlinear complexity.

Turbulence energy distributions in bubbling gas–liquid and gas–liquid–solid flow systems

The turbulence energy distributions in the gas–liquid bubble column system and the effect of solids on the turbulence are investigated using the laser Doppler velocimetry and the particle image velocimetry. The superficial gas velocity employed ranges from 0.025 to 7.5 cm/s , covering such bubble-flow conditions as single-bubble chain, bubbly flow and churn-turbulent flow. Turbulence induced by rising bubbles through bubble wakes is also examined. Experimental results indicate that the bubble-induced turbulence dominates over the liquid shear-induced turbulence in turbulence generation under the operating conditions of this study. The development of the flow field and the turbulence energy of the liquid-phase in the nozzle region are probed. Furthermore, a self-similarity phenomenon is observed in a two-phase flow system. The analysis of the power spectra in gas, liquid and solid phases indicates that the Kolmogorov −5/3 law is obeyed in the inertial range. The presence of solids reduces the transition frequency from the energy-containing range to the inertial range. The effect of the solids on the liquid-phase turbulence is complex. It depends on solids properties and flow field around particles. A criterion based on the variation of a parameter defined by U g ( r)/ u mf is proposed to account for the effect of the solids on the liquid-phase turbulence. The prediction based on this criterion matches well with the experimental results.

On the rise velocity of an interactive bubble in liquids

Bubble rise velocity is one of the important parameters characterizing bubble column systems. Mathematical models for predicting the velocity of an interactive spherical bubble rising in-line in liquids for intermediate Reynolds number range [ Re ∼O(100)] are developed in the present study. The equation for the balance of forces on a bubble rising in-line is formulated. The models are derived based on this equation and different assumptions for the forces on the bubble. The ratios of the rise velocity of the trailing bubble to that of an isolated bubble, varying with the separation distance between the leading and trailing bubbles, are predicted by these models at Re of 35.4, 21.5 and 3.06. Comparisons between the predictions and the measurements show that the model incorporating both the wake effect and the bubble acceleration effect which includes the added mass and Basset forces can well predict the rise velocity of the trailing bubble in the far wake region of the leading bubble. The commonly used model which accounts for only the wake effect is found to lead to an overestimation of the rise velocity of the trailing bubble.

Pressure Effect on the Flow Fields and the Reynolds Stresses in a Bubble Column

The hydrodynamics of bubble columns operated at pressures up to 7.0 MPa are investigated using a laser Doppler velocimetry system. Laser Doppler velocimetry is a noninvasive optical technique, which is used to conduct in situ measurements of velocity, with high spatial resolution, fast dynamic response, and the ability to detect flow. The axial and tangential velocities and the Reynolds shear and normal stresses are analyzed and discussed in relation to large-scale structures present in the flow. This study demonstrates the significance of the pressure effect on the flow field in bubble-column systems.