Bubble Column Contactor Research Articles

Post-combustion CO2 capturing by KOH solution: An experimental and statistical optimization modeling study

A pilot-scale bubble column contactor has been utilized for carbon dioxide chemisorption from simulated flue gas in the temperature range 30°C to 50°C. The influence of the most important operating parameters has been investigated. A total of 25 experiments were designed using the response surface methodology (RSM) and were then carried out in the bubble contact column. The results revealed that the liquid volume in the column, the alkaline concentration, and the temperature had a positive effect, while the gas hold-up had a negative effect on the CO2 removal efficiency. A statistical model has been developed using the RSM D-optimal experimental design method. To achieve the highest CO2 chemisorption, several operating conditions have been optimized. The model predicted that the maximum percentage of carbon dioxide removal would be 86.64%, and under the same operating conditions the experimental removal efficiency was 87.12%.

Effect of drag correlation and bubble‐induced turbulence closure on the gas hold‐up in a bubble column reactor

AbstractBACKGROUNDGas–liquid hydrodynamics play an important role in processes across a wide range of applications in chemical technology and biotechnology. In most of these applications, gas is bubbled in the bottom of the reactor to conduct physical mixing or mixing‐induced chemical reaction. In either case, the gas bubble hydrodynamics play a critical role on the overall performance of these processes. In the present study, the gas–liquid multiphase system is simulated using a Eulerian–Eulerian two‐fluid Computational Fluid Dynamics (CFD) model.RESULTSThe physical model is a cylindrical bubble column contactor wherein gas is sparged into liquid through a perforated sparger with a superficial gas velocity of ≈3–40 cm s−1. The CFD model for the contactor is built using the free and open source tool OpenFOAM v.4.0 to simulate the gas–liquid system. The time‐averaged volume fraction distribution was studied at different heights in the column. The effect of drag force and bubble‐induced turbulence are studied to arrive at appropriate closures for the CFD model. The results obtained from the numerical simulations were validated against available experimental results found in literature.CONCLUSIONThe recommended models, based on the present CFD study of the bubble column reactor, are the Ishii–Zuber drag closure with the modification that the parameter p is set to 2 for superficial gas velocities ≤20 cm s−1 and is set to 4 for 40 cm s−1 superficial gas velocity) and the mixed k–ϵ model to account for drag correlation and bubble‐induced turbulence closure, respectively. © 2019 Society of Chemical Industry

The effect of water type on the absorption and desorption of carbon dioxide in bubble columns

This study investigates the effect of alkalinity and salinity on the transfer rate of carbon dioxide, CO2, from/to several aqueous phases. The CO2 absorption and desorption experiments were performed for several water types including distilled, reverse osmosis, brackish, and brackish reject waters in addition to seawater, inside a bubble column contactor. Findings indicated that the direction of transfer (i.e. absorption or desorption) had a strong influence on the rate of mass transfer with higher values recorded for the absorption experiments. The results also showed that for the absorption and desorption experiments the volumetric mass transfer coefficient, kLa, values always decreased with increased salinity until a “threshold” value was attained, above which kLa increased again. The effect of alkalinity on kLa values was not as conclusive where the experimental results indicated that for adsorption kLa values decreases almost linearly with the increase in water alkalinity while no discernible trends were observed for the effect of alkalinity in the desorption experiments.

Method for High Frequency Underway N2 Fixation Measurements: Flow-Through Incubation Acetylene Reduction Assays by Cavity Ring Down Laser Absorption Spectroscopy (FARACAS).

Because of the difficulty in resolving the large variability of N2 fixation with current methods which rely on discrete sampling, the development of new methods for high-resolution measurements is highly desirable. We present a new method for high-frequency measurements of aquatic N2 fixation by continuous flow-through incubations and spectral monitoring of the acetylene (C2H2, a substrate analog for N2) reduction to ethylene (C2H4). In this method, named Flow-through Incubation Acetylene Reduction Assays by Cavity Ring-Down Laser Absorption Spectroscopy (FARACAS), dissolved C2H2 is continuously admixed with seawater upstream of a continuous-flow stirred-tank reactor (CFSR) in which C2H2 reduction takes place. Downstream of the flow-through incubator, the C2H4 gas is stripped using a bubble column contactor and circulated with a diaphragm pump into a wavelength-scanned cavity ring down laser absorption spectrometer (CRDS). Our method provides high-resolution and precise mapping of aquatic N2 fixation, its diel cycle, and its response to environmental gradients, and can be adapted to measure other biological processes. The short-duration of the flow-through incubations without preconcentration of cells minimizes potential artifacts such as bottle containment effects while providing near real-time estimates for adaptive sampling. We expect that our new method will improve the characterization of the biogeography and kinetics of aquatic N2 fixation rates.

Hydrodynamic and absorption studies of carbon dioxide absorption in aqueous amide solutions using a bubble column contactor

The present work analyses the carbon dioxide absorption process in aqueous n-alkylpyrrolidones solutions, from the point of view of hydrodynamic studies as well as mass transfer, using a bubble column contactor. An analysis of the influence of solute concentration and gas flow-rate is complemented by the study of the effect caused by the alkyl group on the hydrodynamics and mass transfer. The presence of this kind of substance produces a decrease in mass transfer rate, but on the basis of interfacial area and mass transfer coefficient values, ethyl-2-pyrrolidine (EP) shows suitable characteristics to replace methyl-2-pyrrolidine (MP) in gas separation processes due to its lower safety problems.

Oxygen absorption in polymer + surfactant aqueous solutions

The present work analyses oxygen absorption in a bubble column contactor using different complex liquid phases that include the presence of different solutes (surfactant and polymer) allowing the modification of liquid phases physical properties of liquid phases (mainly surface tension and viscosity). The influence of these properties over mass transfer rate and liquid side mass transfer coefficient has been analyzed using each solute and ternary systems. The joint effect caused by both solutes can produce synergic influences that must be studied to understand the global behavior. Also the influence of gas flow-rate upon the liquid side mass transfer coefficient has been analyzed.

Influence of Chitosan and Chitosan Derivatives on Hydrodynamics and Mass Transfer in a Bubble Contactor

AbstractThe behavior of chitosan and two kinds of chitosan derivatives in carbon dioxide absorption in a bubble column contactor is analyzed. The effects of absorption type (physical or chemical), polymer type, concentration, and liquid‐phase physical properties on hydrodynamics (bubble size, gas holdup, and specific interfacial area) and mass transfer (absorption rate and mass transfer coefficient) are evaluated.

Bubble column gas–liquid interfacial area in a polymer+surfactant+water system

This work studies the influence of two substances – a polymer and a surfactant – upon the gas–liquid hydrodynamics in a bubble column contactor to analyse the effect of a surfactant in a viscous liquid to simulate biosurfactant production. These kinds of substances can have an important influence upon the gas–liquid hydrodynamics, primarily upon the bubble size which has a direct relation to the gas–liquid interfacial area used to transfer the oxygen from the gas-to-liquid phase. The present study analyses the influence of these substances, individually and combined, upon the hydrodynamic parameters (gas hold-up, bubble diameter and interfacial area) to reach conclusions on the joint effect and the possible synergic behaviours. Specifically the surfactant presence shows positive effect upon interfacial area though a viscous liquid phase is used.

Effect of surfactant nature upon absorption in a bubble column

The present work has analysed the gas–liquid mass transfer process of carbon dioxide to aqueous solutions polluted with the presence of different surface active substances. The influence of the hydrocarbonate chain length of surfactant employed upon the value of mass transfer coefficient has been analysed. The influences of surfactant nature, solutes concentration and the gas flow-rate fed to the bubble column contactor have been studied in the present work. Different models have been employed to fit experimental values of mass transfer coefficient.

Oxygen mass transfer to emulsions in a bubble column contactor

Present work deals with oxygen mass transfer in an oil-in-water biphasic medium, employed in the production of γ-decalactone by the biotransformation of methyl ricinoleate. A bubble column contactor was used to carry out the absorption experiments. The influence of operating conditions (gas flow-rate and organic phase composition) upon the gas–liquid interfacial area and mass transfer coefficient has been analysed and experimental results allow describing the mechanism of oxygen transfer from gas phase into the biphasic medium.

Mass-Transfer Enhancement or Reduction by Surfactant Presence at a Gas−Liquid Interface

We have analyzed the effects of surface-active substances on gas−liquid mass-transfer processes in a carbon dioxide−water absorption process, using a bubble column contactor to bring the two phases into contact. The liquid phases were polluted with surfactant at different concentrations under the critical micelle concentration. The analysis of the influence of liquid-phase contamination on the absorption process was carried out on the basis of the liquid-film mass-transfer coefficient (kL), removing the effect caused by the presence of surfactant and the gas flow rate on the interfacial area (a) and, thereby, on the volumetric mass-transfer coefficient (kLa).

Novel Membrane Pretreatment to Increase the Efficiency of Ozonation-BioOxidation

The effects of membrane pretreatment on the ozonation and ozone-biotreatment of the wastewater from the alkaline bleach plant of Kraft pulp mills were investigated. Membrane pretreatment involved using a ceramic membrane with nominal cutoff of 1,000 g/mol, that separated organics based on their molar mass and structure. The retentate stream, consisting of concentrated high molar mass organics, was treated in an ozonation bubble column contactor. Different parameters including chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total carbon (TC), pH, color, and ozone concentrations in the gas and liquid phases were monitored. The pretreatment process separated the low molar mass and more biodegradable constituents of the alkaline bleach plant wastewater. Hence, more effective removal of high molar mass and recalcitrant organics was achieved in the subsequent ozonation stage. Also, the biodegradability of the wastewater during the ozone oxidation increased significantly (by up to 200%) with the implementation of membrane pretreatment. The ozone demand and consumption for improving the quality of wastewater (i.e., BOD5 enhancement and TC, COD, and color removal) increased by up to about 10-fold compared to the control process involving standalone ozonation. Furthermore, membrane pretreatment reduced the consumption of ozone per unit COD removal from the alkaline effluent.

Decomposition rate of volatile organochlorines by ozone and utilization efficiency of ozone with ultraviolet radiation in a bubble-column contactor

Decomposition of volatile chlorohydrocarbons in the gas and aqueous phases is tested in a thin, rectangular-channel reactor. In the absence of u.v. irradiation, destruction of pollutants in the gas phase hardly occurs, while there is a little in the aqueous phase. Ultraviolet irradiation accelerates the destruction of pollutants in both the gas and aqueous phases, and the destruction rate is proportional to the concentration of reactants and the u.v. intensity. To evaluate the effect of reactor configuration and operational conditions on the performance of the actual water treatment process, a bubble column equipped with a diffuse lamp along the central axis is adopted as a model reactor. The conversion of volatile chlorohydrocarbons and the ozone utilization efficiency are calculated by considering the mass transfer of ozone and pollutants between the gas and aqueous phases, and the self-decomposition of ozone and destruction rate of pollutants in each phase under u.v. irradiation. A simulation on the basis of the experimental data obtained predicts that excessive u.v. radiation decomposes ozone in the gas phase before it is transferred into the aqueous phase, causing a decrease in the utilization efficiency of ozone.

Kinetics of oxygen absorption in aqueous sodium dithionite solutions

AbstractThe absorption and reaction of oxygen in aqueous alkaline solutions of sodium dithionite has been experimentally investigated in a novel gas‐liquid contactor. The novel gas‐lift bubble column contactor was used to study the kinetics over wide ranges of reactant concentrations, temperature, and pH. The oxygen‐sodium dithionite reaction was found to be first‐order with respect to dithionite in the range of dithionite concentration < 0.1 M, and second‐order in the range of dithionite concentration > 0.1 M. The reaction with respect to oxygen was found to be zero‐order for all dithionite concentrations. These results and experimental investigations of the effect of solution alkalinity and temperature on the reaction rate are consistent with previous findings obtained in different gas‐liquid contactors. The results thus confirm the feasibility of using the gas‐lift bubble column for the kinetics of gas‐liquid reactions.