Bubble Column Research Articles

The Influence of Draft Tubes on the Mass Transfer and Mixing Performance of a Pilot-Scale Internal-Loop Airlift Reactor

The hydrodynamic characteristics, mass transfer, and mixing performance of three different reactors, a bubble column reactor (BCR), a single-stage internal-loop airlift reactor (SSALR), and a four-stage internal-loop airlift reactor (FSALR), were investigated systematically through cold model experiments to explore the influence of draft tube configurations on the pilot-scale internal-loop airlift reactor (ILAR). The findings indicated that the BCR yielded a higher gas holdup and mass transfer coefficient due to its longer bubble residence time. Segmenting the draft tube improved the gas holdup in both the riser and downcomer, and the overall gas holdup in the downcomer increased by 9%. Compared with the SSALR, the mass transfer coefficient of the FSALR in the riser and downcomer increased by 10.2% and 9.3% on average, respectively. In addition, a higher liquid circulating velocity was obtained with the ILARs due to a higher gas holdup difference between the riser and the downcomer. Specifically, the liquid circulating velocity of the FSALR was 134.1% higher than that of the BCR and 15.8% higher than that of the SSALR. The mixing time of the ILARs was reduced due to more intense overall circulation. The mixing effect of the FSALR was the best. The mixing time was reduced by 70.2% and 51.3% compared with the BCR and SSALR for UG ranging from 4.0 cm/s to 9.1 cm/s, respectively. Empirical correlations were proposed for the gas holdup, liquid circulating velocity, mass transfer coefficient, and mixing time on the superficial gas velocity, and agreement with experimental data was satisfactory.

Ectoines production from biogas in pilot bubble column bioreactors and their subsequent extraction via bio-milking

Despite the potential of biogas from waste/wastewater treatment as a renewable energy source, the presence of pollutants and the rapid decrease in the levelized cost of solar and wind power constrain the use of biogas for energy generation. Biogas conversion into ectoine, one of the most valuable bioproducts (1000 €/kg), constitutes a new strategy to promote a competitive biogas market. The potential for a stand-alone 20 L bubble column bioreactor operating at 6% NaCl and two 10 L interconnected bioreactors (at 0 and 6% NaCl, respectively) for ectoine production from biogas was comparatively assessed. The stand-alone reactor supported the best process performance due to its highest robustness and efficiency for ectoine accumulation (20–52 mgectoine/gVSS) and CH4 degradation (up to 84%). The increase in N availability and internal gas recirculation did not enhance ectoine synthesis. However, a 2-fold increase in the internal gas recirculation resulted in an approximately 1.3-fold increase in CH4 removal efficiency. Finally, the recovery of ectoine through bacterial bio-milking resulted in efficiencies of >70% without any negative impact of methanotrophic cell recycling to the bioreactors on CH4 biodegradation or ectoine synthesis.

Numerical and experimental estimation of global gas holdup in a bubble column using computational fluid dynamics (CFD)

Numerical and experimental estimation of global gas holdup in a bubble column using computational fluid dynamics (CFD)

Innovation in natural rubber latex coagulation using CO2 microbubbles

Traditionally, acids have been employed in the production of raw rubber sheets. Using concentrated acids to coagulate natural rubber latex has led to issues such as subpar product quality and the generation of a significant volume of acidic latex serum waste. In contrast, opting for weak acids results in increased production costs. To address these limitations, this research adopts an innovative approach that leverages CO2 microbubbles as a process intensification technique. CO2 was bubbling into a bubble column filled with fresh natural rubber latex and closely monitored the pH and coagulation percentage over time. The physical and mechanical properties of the solid rubber products were characterized, in comparison with the products gained from conventional techniques. The use of CO2 microbubbles yielded shorter processing times and reduced the generation of acidic waste serum. Notably, this approach also led to significant improvements in key properties such as initial Wallace plasticity (P0), plasticity retention index (PRI), nitrogen content, and biodegradability in soil of the rubber samples. Interestingly, the utilization of CO2 as a feedstock highlights its role in promoting a sustainable process. This innovative approach not only minimizes environmental impact but also results in the production of value-added rubber products with enhanced properties.

Thermodynamic and thermoeconomic modeling of humidification-dehumidification desalination systems with bubble column dehumidifier

Humidification-dehumidification (HDH) desalination systems are popular among researchers due to their simple structure, ability to operate with low-grade and renewable energy sources, and the capacity to work with high-concentration water. This paper presents a thermodynamic and thermoeconomic analysis of an HDH system with a multi-stage bubble column dehumidifier. There was a lack of economic studies on bubble column dehumidifier systems in previous literature; also, no research had examined the impact of different geometric and temperature parameters on the entire system's performance. The fixed surface method was used to model the humidifier and dehumidifier, and the effect of mass flow rate ratio, top and bottom temperature, pipe length within each dehumidification stage, and the number of dehumidifier stages on the system's performance was studied. System performance was compared under various conditions, including gain output ratio (GOR), water production, and cost of produced freshwater. The highest GOR is obtained in the highest pipe length and the highest number of dehumidifier stages. Increasing the length of the pipe and the number of dehumidification stages increases the cost, so achieving the lowest cost of produced water is a compromise between higher cost and higher efficiency. The system achieved a GOR of 3.03, the lowest cost price of produced water is 18.29 $m3, and the highest acheived exergy efficiency is 22.4 %.

Modeling of a bubble column for CO2 removal by absorption with NaOH

CO2 capture experiments were carried out in a small-scale bubble column reactor using alkaline solutions of sodium hydroxide. The results of the experiments show that a higher NaOH content in the liquid phase and elevated CO2 concentrations in the gas mixture led to a higher CO2 removal efficiency. A mathematical model was developed to describe the CO2 absorption as a function of CO2 gas inlet and OH- concentrations at low CO2 and OH- concentrations. The CO2 uptake at high OH- concentrations (high pH) was accurately predicted by the model, whereas the CO2 uptake at lower OH- concentrations could not be predicted with the same accuracy.

Global characterization of hydrodynamics and gas-liquid mass transfer in a thin-gap bubble column in presence of Newtonian or non-Newtonian liquid phase

Bubble columns are commonly used as photobioreactors (PBRs) due to their good mixing and mass transfer capabilities. Modification in design and operating parameters are nevertheless needed to intensify volumetric productivity. Thin-gap bubble column can be used in this context to operate with high biomass concentration, up to conditions where the culture becomes non-Newtonian. In the present study, the global hydrodynamics and gas–liquid mass transfer inside a 4 mm thickness thin-gap bubble column are characterized in presence of low viscosity Newtonian fluid (water) and two aqueous solutions of Carboxymethyl Cellulose and Xanthan Gum. These shear-thinning solutions are used to mimic high concentration cultures of Chlorella Vulgaris at 42 g.L−1. A range of superficial gas velocities and different capillary diameters are explored to investigate the effect of sparging on hydrodynamics and gas–liquid mass transfer. Studied parameters are flow regimes, mixing, and gas–liquid mass transfer. Results are compared with literature results in classical bubble columns to put into evidence the original effects of both confinement and liquid rheology. Among others, these results show that compared to Newtonian media, non-Newtonian media result in higher gas holdup and mixing times and a lower gas–liquid mass transfer coefficient. The findings suggest that the presence of smaller bubbles would improve mass transfer due to the increased interfacial area, while the presence of larger bubbles would improve mixing performance due to increased vorticity in their wake and relatively greater species transport.

Euler-Lagrange Simulations of Microstructured Bubble Columns Using a Novel Cutting Model.

In the concept of a microstructured bubble column reactor, meshes coated with catalyst can cut the bubbles, which in turn results in high interfacial area and enhanced interface hydrodynamics. In previous work, we developed a closure model for the fate of bubbles interacting with a wire mesh based on the outcomes of energy balance analysis. In this paper, the model is validated using Euler-Lagrange simulations against two experimental cases of microstructured bubble columns. Before validation of the model, the definition of the deceleration thickness, as used in the calculation of the virtual mass term, is refined to introduce the effects of liquid viscosity and wire thickness. Proceeding with the validation, the inclusion of our cutting closure model results in an excellent match of the bubble size reduction by the wire mesh with the experimental data. Consequently, the simulations produce a more accurate prediction of the reactor performance for the gaseous reaction in view of the pH and gas holdup profiles. The effect of liquid viscosity on the bubble size reduction by the wire mesh is replicated accurately as well. Noticeably, the significance of bubble coalescence and breakup in bubble dynamics overperforms the role of bubble cutting at high superficial gas velocities; thus, further improvement is needed there. Finally, based on the validated cutting model, we share some perspectives on the design of wire meshes to increase the bubble interfacial area.

Removal and recovery of nutrients from septic tank wastewater using microalgae: Key factors and practical implications

Treatment of septic tank wastewater (STWW) with high concentrations of ammonium (NH4+) and total phosphorus (TP), is challenging in decentralized areas. Utilizing microalgae for STWW treatment can simultaneously recover nutrients in the form of high-value microalgal biomass. However, despite the potential benefits, microalgal treatment of STWW is rarely reported. Therefore, this work utilized bench-scale photobioreactors (PBR) to investigate different factors that could affect microalgal cultivation in STWW and treatment efficiency. Accordingly, it was observed that suspended solids present in STWW did not significantly affect the microalgae growth and nutrient removal efficiencies in bubble column PBR. On the other hand, the effect of endemic microorganism could not be verified in this study due to observed fungal contamination and change in nutrient profile of STWW after autoclave. Nevertheless, the highest microalgal growth and nutrient removal efficiencies of NH4+-N = 79.14% and TP = 41.11% were observed within 14 days of photoautotrophic cultivation in raw STWW. Further, 25 days of upscaled photoautotrophic cultivation in 4-L bubble column PBR was performed to study biomass yield, nutrient removal kinetics, and nutrient removal efficiency. Consequently, 0.75 g‧L−1 dry biomass was produced with improved removal efficiency of NH4+-N (96.16%), and TP (69.57%). Elemental analysis of biomass revealed that 62.99 ± 1.46 mg‧L−1 TN and 11.41 ± 1.42 mg‧L−1 TP were recovered. Further, 1.02 geq carbon dioxide (CO2) was bio-fixed with every liter of STWW treated. The findings of this study revealed that microalgae can be successfully utilized for the removal and recovery of nutrients from STWW.

Isolated bubble ascent in a non-Newtonian media inside an infinite bubble column: a CFD study

Isolated bubble ascent in a non-Newtonian media inside an infinite bubble column: a CFD study

Usability of Ranked-Choice Voting Paper Ballots

Ranked choice voting (RCV) is a method of voting where individuals rank their choices for each race in an election, rather than selecting a single candidate. For paper ballot implementations, there are three basic formats: bubble grid, column, and handwritten. This study aimed to understand which format produces the best outcomes with the fewest errors. Using a between-subjects design, we measured voting time, errors, success rates, and overall subjective usability using the System Usability Scale (SUS). Results showed that the handwritten format took significantly longer to complete. However, the handwritten ballot errors were recoverable and generally did not invalidate the ballots. The column and bubble grid ballots had significant errors, with fewer errors on the bubble grid format. There was no significant difference in SUS scores, nor any contribution of demographics across ballot types. Ballot format directly dictates the time taken to vote, usability, and overall voter success.

Process configurations to lower the temperature of methane pyrolysis in a molten metal bath for hydrogen production

Novel configurations of a process for methane pyrolysis using a molten catalyst bubble column reactor are proposed in this study. These configurations aim to achieve reasonable conversion at temperatures below 1000 °C by recycling a fraction of the hot reactor product gas. Three recycling configurations are assessed: the first utilizes an ejector, the second employs a compressor, and the third combines a compressor with a turbo-expander. The performance of these configurations was evaluated using ASPEN HYSYS to compare them against a reference cycle without recycling. The evaluation criteria included methane conversion and the thermal heat requirement of the reactor. The results indicate that recycling can significantly increase methane conversion, with a maximum improvement of 165%. Specifically, when recycling 80% of the hot products in the first pass conversion using the third configuration, methane conversion increased from 17.8% to 47.2%. The other two configurations achieved conversions of 28%, representing a 57% increase from the baseline of 17.8% under the same conditions. Furthermore, it is possible to achieve a configuration with zero net CO2 emissions by employing renewable power and utilising some of the hydrogen product for combustion to meet the process heat demand.

Aerobic Sludge Granulation: A Computational Fluid Dynamics Study of Fluid Flow Patterns in Bubble Column Reactors

Aerobic Sludge Granulation: A Computational Fluid Dynamics Study of Fluid Flow Patterns in Bubble Column Reactors

Effects of surfactants on bubble-induced turbulence

We use experiments to explore the effect of surfactants on bubble-induced turbulence (BIT) at different scales, considering how the bubbles affect the flow kinetic energy, anisotropy and extreme events. To this end, high-resolution particle shadow velocimetry measurements are carried out in a bubble column in which the flow is generated by bubble swarms rising in water for two different bubble diameters (3 and 4 mm) and moderate gas volume fractions (0.5 %–1.3 %). We use tap water as the base liquid and add 1-Pentanol as an additional surfactant with varying bulk concentration, leading to different bubble shapes and surface boundary conditions. The results reveal that with increasing surfactant concentration, the BIT generated increases in strength, even though bubbles of a given size rise more slowly with surfactants. We also find that the level of anisotropy in the flow is enhanced with increasing surfactant concentration for bubbles of the same size, and that for the same surfactant concentration, smaller bubbles generate stronger anisotropy in the flow. Concerning the intermittency quantified by the normalized probability density functions of the fluid velocity increments, our results indicate that extreme values in the velocity increments become more probable with decreasing surfactant concentration for cases with smaller bubbles and low gas void fraction, while the effect of the surfactant is much weaker for cases with larger bubble and higher void fractions.

3D CFD Simulation of a Bubble Column with Internals: Validation of Interfacial Forces and Internal Effects for Local Gas Holdup Predictions

3D CFD Simulation of a Bubble Column with Internals: Validation of Interfacial Forces and Internal Effects for Local Gas Holdup Predictions

Effects of Operational and Geometric Variables of a Bubble Column Bioreactor on Ethanol Stripping with CO2: Liquid and Gas-Phase Monitoring

Effects of Operational and Geometric Variables of a Bubble Column Bioreactor on Ethanol Stripping with CO₂: Liquid and Gas-Phase Monitoring

Uncertainty analysis of gamma-ray densitometry applied for gas flow modulation technique in bubble columns

The gas flow modulation technique is a recently proposed approach for measuring the axial gas dispersion coefficient in bubble columns. This study presents a quantitative analysis of the experimental uncertainty associated with gamma-ray densitometry and ensemble-averaging of the data. The considered uncertainty sources are the statistics of the photon counting process, a mismatch between the modelled and the real radiation propagation due to the spatial extent of the detector, and a potential mismatch between modulation and sampling frequencies. The analysis is based on a numerical gamma-ray propagation model and a Monte Carlo approach to account for statistical uncertainty. The proposed algorithm supports the selection of an optimal total scanning time based on detector size, modulation parameters, involved fluids and column and source parameters. The analysis reveals that a mismatch between the modulation and sampling frequencies is most critical while the impact of the other considered uncertainty sources is rather marginal.

Thermodynamic analysis of biodiesel production with catalyst and non-catalyst process: incase energy analysis

Biodiesel production from renewable resources needs a certain amount of energy Input. The effectiveness of biodiesel production depends on the energy ratio, i.e. the ratio of energy contained in the biodiesel to the energy input during production, including energy content in the feedstock. The objective of the study is aimed to evaluate the energy ratio in biodiesel production. The input and output energy were analyzed for each process (catalyst and analysist). Materials required in biodiesel production was evaluated in term of their energy content. The equipment used to obtain data on the non-catalytic biodiesel production process was a prototype bubble column reactor designed by the Department of Global Agricultural Sciences at The University of Tokyo, Japan and data on the catalytic biodiesel production process was obtained from the Center for Design and Technology System Engineering, BPPT Serpong,by the design of the equipment owned by the institution. The results showed that the energy ratio and the energy needed to produce per kilogram of biodiesel using the non-catalytic production method with a modified process were 1.00 and 39.63 MJ/kg while using the catalytic method were 0.98 and 41.05 MJ/kg, respectively. The non-catalytic production method with a modified process is better than the catalytic method in energy ratio. The energy needed to produce per kilogram of biodiesel due to the heat exchanger is critical for the performance improvement of the modified non-catalytic process.

Phases distribution in slurry bubble columns: Insights from single-source computed tomography and gas holdup measurements

In this study, a cylindrical stainless-steel column with dimensions of 250 cm in height and 16.2 cm in diameter was employed to investigate how fluid properties influence phase distribution within slurry bubble columns. The research focused on various superficial gas velocities and operating pressures. Data collection was carried out using single-source Computed Tomography and overall gas holdup. The gas holdup was found to be directly proportional to both the superficial gas velocity and the operating pressure. Results revealed that both liquid properties and operating pressure have a considerable impact on flow regime transition. Interestingly, when comparing water to Therminol LT, higher gas holdup measurements were observed when water was used, displaying a relative difference of approximately 29% in the bubbly flow regime under ambient conditions. The effect of liquid properties on holdup profiles became more pronounced at high pressures. For example, under higher pressure conditions, Therminol LT exhibited a higher gas holdup rate due to its lower viscosity and surface tension, leading to an increased rate of bubble breakup. While the influence of physical properties on the solids' holdup profile was relatively less significant, it remained noteworthy when compared to its impact on the gas holdup profile.

Single-Bubble Rising in Shear-Thinning and Elastoviscoplastic Fluids Using a Geometric Volume of Fluid Algorithm.

The motion of air bubbles within a liquid plays a crucial role in various aspects including heat transfer and material quality. In the context of non-Newtonian fluids, such as elastoviscoplastic fluids, the presence of air bubbles significantly influences the viscosity of the liquid. This study presents the development of an interface-capturing method for multiphase viscoelastic fluid flow simulations. The proposed algorithm utilizes a geometric volume of fluid (isoAdvector) approach and incorporates a reconstructed distance function (RDF) to determine interface curvature instead of relying on volume fraction gradients. Additionally, a piecewise linear interface construction (PLIC) scheme is employed in conjunction with the RDF-based interface reconstruction for improved accuracy and robustness. The validation of the multiphase viscoelastic PLIC-RDF isoAdvector (MVP-RIA) algorithm involved simulations of the buoyancy-driven rise of a bubble in fluids with varying degrees of rheological complexity. First, the newly developed algorithm was applied to investigate the buoyancy-driven rise of a bubble in a Newtonian fluid on an unbounded domain. The results show excellent agreement with experimental and theoretical findings, capturing the bubble shape and velocity accurately. Next, the algorithm was extended to simulate the buoyancy-driven rise of a bubble in a viscoelastic shear-thinning fluid described by the Giesekus constitutive model. As the influence of normal stress surpasses surface tension, the bubble shape undergoes a transition to a prolate or teardrop shape, often exhibiting a cusp at the bubble tail. This is in contrast to the spherical, ellipsoidal, or spherical-cap shapes observed in the first case study with a bubble in a Newtonian fluid. Lastly, the algorithm was employed to study the buoyancy-driven rise of a bubble in an unbounded elastoviscoplastic medium, modeled using the Saramito-Herschel-Bulkley constitutive equation. It was observed that in very small air bubbles within the elastoviscoplastic fluid, the dominance of elasticity and capillary forces restricts the degree of bubble deformation. As the bubble volume increases, lateral stretching becomes prominent, resulting in the emergence of two tails. Ultimately, a highly elongated bubble shape with sharper tails is observed. The results show that by applying the newly developed MVP-RIA algorithm, with a tangible coarser grid compared to the algebraic VOF method, an accurate solution is achieved. This will open doors to plenty of applications such as bubble columns in reactors, oil and gas mixtures, 3D printing, polymer processing, etc.