Laboratory Scale Bubble Column Research Articles

CO2 Capture Modeling Using Heat-Activated Serpentinite Slurries

We present a model to describe carbon dioxide (CO2) capture using reactive silicate-based mineral slurries exposed to a gas flow containing CO2. The model is validated through experimentation using thermally conditioned or heat-activated serpentinite (hydrous metamorphic ultramafic rock) in a laboratory-scale bubble column reactor. The kinetic model developed advocates a holistic modeling approach, offering an expanded view of the dissolution of heat-activated serpentinite under lean CO2 conditions, in which the gas–liquid–solid system and its influence on CO2 dissolution and the coupled dissolution behavior of the material are considered in their entirety. Modeling incorporates the characteristics of the gas to liquid phase interaction, such as CO2 composition of the gas phase and interfacial area, the composition of the aqueous phase and its temperature, and compositional and morphological features of the solid. We demonstrate that such an approach is essential when considering proton-limiting condition...

Effect of aeration pattern and gas distribution during scale-up of bubble column reactor for aerobic granulation

This study investigates the influence of aeration pattern and gas bubble distribution on aerobic granulation in pilot bubble columns and advances the understanding on crucial factors to be considered during scale-up. Experiments were conducted in a pilot scale bubble column of 22-L capacity. A laboratory-scale bubble column of 5-L capacity, which could achieve granulation in a short time, was used as the control reactor. The pilot reactor was operated with optimal operational conditions evaluated for the control reactor, but the granulation was initially inhibited; improper aeration pattern was found as the most significant factor in precluding granulation. Aerobic granulation in the pilot-scale reactor was achieved upon modifying the gas distributor design. The effect of gas distributor characteristics (i.e., pore size, free area φ, and relative surface area of the gas distributor to the cross-section of the column R) on the aeration pattern has been thoroughly discussed. A scale-up ratio (S) for the gas distributor has been proposed. Reliability of aeration intensity in terms of superficial air velocity usg, which has been commonly used as an indicator of prevailing hydrodynamics and shear stress in lab-scale granular bubble columns, has been discussed; it was demonstrated that usg could not realistically represent the aforementioned conditions in a larger module. Instead, it was suggested that a greater attention should be paid to bubble size and bubble ascending velocity and thus to the subsequent aeration pattern. Gas holdup has been eventually introduced as a crucial and easy-to-measure controlling parameter for the scale-up of granularreactors.

Gas hold-up and mass transfer in a pilot scale bubble column with and without internals

Bubble columns are the reactors of choice for conversion of synthesis gas to liquid fuels (F–T synthesis). The F–T synthesis is an exothermic reaction and cooling internals are installed in the bubble columns to remove the heat generated in the reaction. The presence of the internals affects both the gas and liquid flow patterns in bubble column. This change is expected to reflect on the volumetric mass transfer coefficient. In this work, the impact of vertical cooling internals on overall gas hold-up and volumetric mass transfer coefficients is evaluated on 45cm diameter pilot scale bubble column and 19cm diameter lab scale bubble column. It was found that in presence of internals the gas hold-up in both the columns was increased, however no significant impact of presence of internals on volumetric mass transfer coefficient was observed. The gas hold-up and volumetric mass transfer coefficients evaluated in this work are compared with prediction from existing correlations.

Chlorine Production by HCl Oxidation in a Molten Chloride Salt Catalyst

A molten salt mixture containing 45 mol % KCl and 55 mol % CuCl2 was investigated as a catalyst for the reaction of HCl with O2 to produce Cl2. The HCl conversion for an HCl:O2 molar feed ratio of 1:2 at 450 °C and a total pressure of 1 atm was 80% at a residence time of less than 1 s in a lab scale bubble column reactor. The equilibrium conversion at this temperature and pressure is 84%. The catalyst system was found to remain stable throughout a continuous 24-h experiment. The use of a mixed transition metal/alkali metal molten salt catalyst for HCl oxidation reduces the volatility of supported chlorides and may avoid the mechanical stability limitations of solid catalysts caused by volume changes between the halide and the oxide.

Measurement of Volumetric Mass Transfer Coefficient in Bubble Columns

The paper presents a brief overview of experiments on volumetric mass transfer coefficient in bubble columns. The available experimental data published are often incomparable due to the different type of gas distributor and different operating conditions used by various authors. Moreover, the value of the coefficient obtained experimentally is very sensitive to the particular method and to the physical models used in its evaluation. It follows that the Dynamic Pressure Method (DPM) is able to provide physically correct values not only in lab-scale contactors but also in pilot-scale reactors. However, the method was not correctly proven in bubble columns. In present experiments, DPM was employed in a laboratory-scale bubble column with a coalescent phase and tested in the pure heterogeneous flow regime. The method was successfully validated by the measurements under two different conditions relevant to the mass transfer. First, the ideal pressure step was compared with the non-ideal pressure step. Second, the pure oxygen absorption was compared with the simultaneous oxygen-and-nitrogen absorption. The obtained results proved that DPM is suitable for measuring the mass transport in bubble columns and to provide reliable data of volumetric mass transfer coefficient.

Equilibrium solubility of CO2 in aqueous binary mixture of 2-(diethylamine)ethanol and 1, 6-hexamethyldiamine

CO2 solubility data are important for the efficient design and operation of the acid gas CO2 capture process using aqueous amine mixture. 2-(Diethylamino)ethanol (DEEA) solvent can be manufactured from renewable sources like agricultural products/residue, and 1,6-hexamethyldiamine (HMDA) solvents have higher absorption capacity as well as reaction rate with CO2 than conventional amine-based solvents. The equilibrium solubility of CO2 into aqueous binary mixture of DEEA and HMDA was investigated in the temperature range of 303.13-333.13 K and inlet CO2 partial pressure in the range of 10.133-20.265 kPa. Total concentration of aqueous amine mixtures in the range of 1.0-3.0 kmol/m3 and mole fraction of HMDA in total amine mixture in the range of 0.05-0.20 were taken in this work. CO2 absorption experiment was performed using semi-batch operated laboratory scale bubble column to measure equilibrium solubility of CO2 in amine mixture, and CO2 absorbed amount in saturated carbonated amine mixture was analyzed by precipitation-titration method using BaCl2. Maximum equilibrium CO2 solubility in aqueous amine mixture was observed at 0.2 of HMDA mole fraction in total amine mixture with 1.0 kmol/m3 total amine concentration. New solubility data of CO2 in DEEA+HMDA aqueous mixtures in the current study was compared with solubility data available in previous studies conducted by various researchers. The study shows that the new absorbent as a mixture of DEEA+HMDA is feasible for CO2 removal from coal-fired power plant stack gas streams.

A PBM-CFD Model with Optimized PBM-Customized Drag Equations for Chemisorption of CO2 in a Bubble Column

AbstractIn this work, a computational fluid dynamics (CFD) approach based on two-fluid model (TFM) is introduced to describe the reversible two-step reactions found in the chemisorption process of${\text{C}}{{\text{O}}_2}$by an aqueous${\text{NaOH}}$solution in a lab-scale bubble column reactor. The population balance model (PBM) is applied to track the bubble size distribution with considering the coalescence and breakage terms, which then leads to a CFD-PBM model for describing the chemisorption of CO2in an aqueous${\text{NaOH}}$solution. Drag force is considered for the interfacial momentum transfer and a modified PBM-customized drag model with the correction factor is subsequently adopted, in which the contribution of different bubble size groups in each computational cell is computed. The tested boundary conditions include superficial gas velocities, gas-inlet sparger and the reactor dimension. Detailed and comprehensive investigations are done in the evolution of gas holdup, pH value, concentration distribution and bubble diameter distribution which are essential in optimizing the reactor performance in terms of yield and selectivity. Importantly, the current CFD-PBM model is able to predict the entire reaction process.

Experimental testing of a spatiotemporal metabolic model for carbon monoxide fermentation with Clostridium autoethanogenum

Gas fermentation is an attractive route to produce alternative fuels and chemicals from non-food feedstocks, such as waste gas streams from steel mills and synthesis gas produced from agricultural residues through gasification. An improved strain of Clostridium autoethanogenum, an acetogenic bacteria, was developed by LanzaTech and shows high potential in production of ethanol and 2,3-butanediol from industry waste gas (mainly CO/CO2) via gas fermentation. In this study, a spatiotemporal metabolic model was formulated and evaluated using steady-state CO fermentation data collected from a laboratory-scale bubble column reactor. The spatiotemporal model was comprised of a genome-scale reconstruction of Clostridium autoethanogenum metabolism and multiphase convection-dispersion equations that govern transport of CO, secreted byproducts and biomass. The model provided good agreement with measured ethanol, acetate and biomass concentrations obtained at a single gas flow rate. Then to obtain satisfactory steady-state predictions at three gas flow rates, the upper bound of the proton exchange flux in the genome-scale reconstruction was correlated with the gas flow rate as an indirect means to account for the effects of acetate secretion on extracellular pH. We believe the modeling method established by this work has strong potential to facilitate commercial-scale design of gas fermentation processes for production of biofuel and biochemicals.

Stochastic DSMC method for dense bubbly flows: Methodology

A stochastic Direct Simulation Monte Carlo (DSMC) method has been extended for handling bubble-bubble and bubble-wall collisions. Bubbly flows are generally characterized by highly correlated velocities due to presence of the surrounding liquid. The DSMC method has been improved to account for these kind of correlated collisions along with a treatment allowing the method to be used also at relatively high volume fractions. The method is first verified with the deterministic Discrete Particle/Bubble Model (DPM/DBM) using two problem cases: (a) dry granular flow of particles through two impinging nozzles and (b) 3D periodic bubble rise for mono-disperse and poly-disperse systems. The verification parameters are the total number of prevailing collisions within the system, the collision frequencies and the time-averaged liquid velocity profiles (only for the 3D-periodic bubble rise). Subsequently the method is applied to a lab-scale bubble column and validated with the experimental data of Deen et al. (2001). A computational performance comparison with the DBM is reported for the 3D periodic bubble rise case with varying overall gas fractions. The DSMC is approximately two orders of magnitude faster than the deterministic approach for the studied dense bubbly flow cases without adverse effects on the quality of the computational results.

Zeaxanthin production by Paracoccus zeaxanthinifaciens ATCC 21588 in a lab-scale bubble column reactor: Artificial intelligence modelling for determination of optimal operational parameters and energy requirements

The operational optimization of zeaxanthin production by Paracoccus zeaxanthinifaciens ATCC 21588 in a bubble column reactor was performed by coupling genetic algorithm (GA) to an artificial neural network (ANN) model developed using experimental one-variable-at-a-time (OVAT) results. The effects of varying air flow rate (2-5 vvm) and inoculum size (4 and 8%) for different incubation time (30-80 h) were evaluated. Volumetric power input (P/V L ) and energy input (E) to the bubble column were then correlated with the ANN-GA optimized conditions. A maximum zeaxanthin production of 13.76±0.14 mg/L was observed at 4 vvm using an inoculum size of 4% (v/v) after 60 h of incubation in OVAT experiments with corresponding P/V L value of 231.57 W/m3 reflecting an energy consumption of 50.02 kJ during the fermentation period. The ANN based GA optimization predicted a maximum zeaxanthin production of 14.79 mg/L at 3.507 vvm, 4% inoculum size and 55.83 h against the experimental production of 15.09±0.51 mg/L corresponding to a P/V L value of 202.03 W/m3 reflecting to a significantly reduced energy input (40.01 kJ). The proposed OVAT based ANN-GA optimization approach can be used to simulate similar studies involving microbial fermentation in bioreactors.

Characterizing fluid dynamics in a bubble column aimed for the determination of reactive mass transfer

Bubble column reactors are multiphase reactors that are used in many process engineering applications. In these reactors a gas phase comes into contact with a fluid phase to initiate or support reactions. The transport process from the gas to the liquid phase is often the limiting factor. Characterizing this process is therefore essential for the optimization of multiphase reactors. For a better understanding of the transfer mechanisms and subsequent chemical reactions, a laboratory-scale bubble column reactor was investigated. First, to characterize the flow field in the reactor, two different methods have been applied. The shadowgraphy technique is used for the characterisation of the bubbles (bubble diameter, velocity, shape or position) for various process conditions. This technique is based on particle recognition with backlight illumination, combined with particle tracking velocimetry (PTV). The bubble trajectories in the column can also be obtained in this manner. Secondly, the liquid phase flow has been analysed by particle image velocimetry (PIV). The combination of both methods, delivering relevant information concerning disperse (bubbles) and continuous (liquid) phases, leads to a complete fluid dynamical characterization of the reactor, which is the pre-condition for the analysis of mass transfer between both phases.

CFD-PBM Approach with Different Inlet Locations for the Gas-Liquid Flow in a Laboratory-Scale Bubble Column with Activated Sludge/Water

A novel computational fluid dynamics-population balance model (CFD-PBM) for the simulation of gas mixing in activated sludge (i.e., an opaque non-Newtonian liquid) in a bubble column is developed and described to solve the problem of measuring the hydrodynamic behavior of opaque non-Newtonian liquid-gas two-phase flow. We study the effects of the inlet position and liquid-phase properties (water/activated sludge) on various characteristics, such as liquid flow field, gas hold-up, liquid dynamic viscosity, and volume-averaged bubble diameter. As the inlet position changed, two symmetric vortices gradually became a single main vortex in the flow field in the bubble column. In the simulations, when water was in the liquid phase, the global gas hold-up was higher than when activated sludge was in the liquid phase in the bubble column, and a flow field that was dynamic with time was observed in the bubble column. Additionally, when activated sludge was used as the liquid phase, no periodic velocity changes were found. When the inlet position was varied, the non-Newtonian liquid phase had different peak values and distributions of (dynamic) liquid viscosity in the bubble column, which were related to the gas hold-up. The high gas hold-up zone corresponded to the low dynamic viscosity zone. Finally, when activated sludge was in the liquid phase, the volume-averaged bubble diameter was much larger than when water was in the liquid phase.

An investigation into a laboratory scale bubble column humidification dehumidification desalination system powered by biomass energy

This article describes a biomass powered bubble column humidification-dehumidification desalination system. This system mainly consists of a biomass stove, air heat exchanger, bubble column humidifier and dehumidifier. Saw dust briquettes are used as biomass fuel in the stove. First level of experiments are carried out in bubble column humidifier with ambient air supply to select the best water depth, bubble pipe hole diameter and water temperature. Experiments are conducted by integrating the humidifier with the dehumidifier. Air is sent to the humidifier with and without pre-heating. Preheating of air is carried out in the air heat exchanger by using the flue gas and flame from the combustion chamber. It is observed that the humidifier ability is augmented with the rise in water depth, water temperature, mass flow rate of air and cooling water flow rate, and reduction in bubble pipe hole diameter. It is found from Taguchi analysis that the water temperature dominates in controlling the humidifier performance compared to other parameters. Better specific humidity is recorded with a bubble pipe hole diameter of 1mm, water depth of 170mm and water temperature of 60°C. Highest distillate of 6.1kg/h and 3.5kg/h is collected for the HDH desalination system with preheated air and direct air supply respectively. Recovery of waste heat using an air heat exchanger reduces the fuel consumption from 0.36kg to 0.2kg for producing 1kg of distilled water. Lowest distilled water cost of 0.0133US$/kg through preheated air supply and 0.0231US$/kg through direct air supply is observed. A correlation is developed to estimate the mass transfer coefficient and it agrees with the maximum deviation of 9% from experimental results.

Synthesis, characterization and application of Au-198 nanoparticles as radiotracer for industrial applications

This paper describes synthesis and characterization of radioactive gold nanoparticles (198Au-NPs), and explores their utility as a radiotracer for tracing an aqueous phase in a continuous laboratory-scale bubble column at ambient conditions. The performance of the 198Au-NPs as a radiotracer was compared with the results obtained with a conventional radiotracer i.e. bromine-82 (82Br) as ammonium bromide and found to be identical. A tank-in-series with backmixing model (TISBM) was used to simulate the RTDs of the aqueous phase and characterize flow in the bubble column.

Rigorous modeling of CO2 absorption and chemisorption: The influence of bubble coalescence and breakage

In this study, the impact of bubble breakage and coalescence (B&C) on the mass transfer and on the temporal evolution of species concentration during absorption and chemisorption is investigated. For this purpose, the CO2 absorption in water and the CO2 chemisorption in NaOH solutions of various initial pH serve as model cases. A three-dimensional Euler–Lagrange algorithm is used for the handling of the gaseous and the liquid phase in a model (simulation) of a laboratory-scale bubble column. The algorithm accurately forecasts the mean and fluctuating liquid velocities and predicts the bubble size distribution reasonably well.The results show that B&C critically impact mass transfer, liquid phase mixing, as well as reaction rates in systems with low to moderately large pH. In contrast, for extremely high pH values, shrinkage of bubbles becomes the dominating phenomenon. This is because bubble shrinkage leads to small bubbles, low gas hold-up, as well as little liquid phase agitation in the upper part of the reactor. Consequently, the relevance of B&C events decreases gradually with increasing pH. A plot of the results as function of the overall pH illustrates that a regime change occurs close to pH 12.5. This transition is caused by a dramatic reduction of the gas hold-up, leading to a significant reduction of liquid-phase agitation.

Image Reconstruction of Single Photon Emission Computed Tomography (SPECT) on a Bubble Column Using Expectation Maximization and Exact Inversion Algorithms: Comparison Study by Means of Numerical Phantom

Expectation Maximization Algorithm and the Exact Inversion Formula are two mathematical methods that have been developed for various computational applications, such as in medical imaging, nuclear industries, econometric and sociological studies, as well as chemical engineering industries. These image reconstruction methods are usually used to create the SPECT scan images. However, most of the improvement and development of the images are made by using a medical phantom, such as the human brain phantom. Here, in this paper the reconstruction of images by both algorithms are made by using a numerical phantom of laboratory scale bubble columns due to its wide application in the chemical reaction engineering studies. The results for both algorithms are compared, evaluated and discussed.

Photooxidative removal of Hg0 from simulated flue gas using UV/H2O2 advanced oxidation process: Influence of operational parameters

Element mercury (Hg0) from flue gas is difficult to remove because of its low solubility in water and high volatility. A new technology for photooxidative removal of Hg0 with an ultraviolet (UV)/H2O2 advanced oxidation process is studied in an efficient laboratory-scale bubble column reactor. Influence of several key operational parameters on Hg0 removal efficiency is investigated. The results show that an increase in the UV light power, H2O2 initial concentration or H2O2 solution volume will enhance Hg0 removal. The Hg0 removal is inhibited by an increase of the Hg0 initial concentration. The solution initial pH and pH conditioning agent have a remarkable synergistic effect. The highest Hg0 removal efficiencies are achieved at the UV light power of 36W, H2O2 initial concentration of 0.125 mol/L, Hg0 initial concentration of 25.3 μg/Nm3, solution initial pH of 5, H2O2 solution volume of 600 ml, respectively. In addition, the O2 percentage has little effect on the Hg0 removal efficiency. This study is beneficial for the potential practical application of Hg0 removal from coal-fired flue gas with UV/H2O2 advanced oxidation process.

Solubility of SO2 in aqueous blend of sodium citrate and sodium hydroxide

The solubility of SO2 in an aqueous blend of sodium citrate (Na3Ci) and sodium hydroxide (NaOH) as innovative absorbent was determined at partial pressures of SO2 in inlet gas stream between 0.355kPa and 0.983kPa, temperature between 293K and 333K, and NaOH to Na3Ci ratio in range of 0.25–1.00. The SO2 solubility was measured using laboratory scale bubble column at atmospheric pressure. From the experimental study low temperature, high partial pressure of SO2 in inlet gas stream and high NaOH to Na3Ci solution ratio were found favourable for SO2 solubility augmentation in aqueous blend of Na3Ci and NaOH. The experimental data were used to develop SO2 solubility model for suitability of the present system.

PH influence on oxygen mass transfer coefficient in a bubble column. Individual characterization of kL and a

Experiments were performed in a laboratory scale bubble column (10L), to investigate the pH influence on oxygen mass transfer coefficient, in order to achieve a better control of biological processes. The liquid-side mass transfer coefficient, kL, and the specific interfacial area, a, were studied individually. The specific interfacial area was obtained using the new automatic image analysis technique developed by Ferreira et al. (2012). The pH was changed by the addition to the system of the most common acids and base used in biological process: hydrochloric acid (HCl), phosphoric acid (H3PO4) and potassium hydroxide (KOH). The results show that aqueous systems containing HCl, H3PO4 or KOH present lower volumetric liquid side mass transfer coefficient, kLa, in relation to pure systems (distilled water), this decrease being not linear. It was found that the specific interfacial area presents higher values in KOH and HCl solutions in comparison with distilled water. However, an opposite behavior was observed in the liquid-side mass transfer coefficient values. The kL behavior on the impure systems was explained based on bubble surface contamination. Higbie's and Fröessling's equations were adapted in the present work in order to be used in bubble dispersion systems.

Effect of surface tension gradient on gas hold-up enhancement in aqueous solutions of electrolytes

The effect of addition of electrolytes on gas hold-up of air/water system was investigated experimentally in a laboratory scale bubble column. The experiments were carried out with four electrolytes, namely, NaCl, MgSO 4·7H 2O, Na 2SO 4 and CaCl 2·2H 2O and the concentrations of the solutions were varied from 0 to 0.3 mol/l. Enhancement of gas hold-up was observed for all four electrolytes at concentrations less than 0.1 mol/l. With the increase in concentration, the gas hold-up showed two different trends; in Na 2SO 4 and CaCl 2·2H 2O solutions, gas hold-up formed a sharp peak after the enhancement and leveled off at a value somewhat higher than that in water, whereas in NaCl and MgSO 4·7H 2O solutions, gas hold-up leveled off immediately after the enhancement without forming any peak. Experiments were also conducted to measure the surface tensions of the solutions with special focus in the low concentration region. A strong relation between the gas hold-up enhancement and the change of surface tension with the addition of electrolyte was found. It was also observed that the concentration at which maximum value of C( dσ/ dC) 2 i.e. ( concentration × surface tension gradient with respect to concentration 2) is obtained corresponds to the concentration at which maximum gas hold-up enhancement occurs.