Volumetric Mass Transfer Coefficient Research Articles

Intensification of a biocatalytic oxidation under fine bubble aeration in a rotating bed reactor

The utilization of oxidases suffers from insufficient oxygen availability due to its low solubility in gas-liquid multiphase systems. To overcome this limitation, oxygen is continuously supplied to the reaction medium during the course of the reaction, however, it causes significant gas consumption. In this study, a novel experimental set-up was established by installing a sintered frit porous sparger in the SpinChem® rotating bed reactor. Covalently immobilized glucose oxidase on epoxy-functionalized carriers was used in the rotating bed reactor with an activity yield of the immobilization of over 98%. For fine bubble aeration, the volumetric mass transfer coefficient kLa (67.3 h−1) tripled compared to macrobubble aeration (22.5 h−1), while the volume-specific aeration rate remained constant. A maximum reaction yield of 96.5% was reached. The reaction rate was improved by a factor of 12.9 for the fine bubble aeration compared to macrobubble aeration under identical conditions. With fine bubble aeration, the oxygen consumption was reduced by 87.5% over macrobubble aeration, establishing the same enzyme-specific reaction rates at a comparable kLa. Validation was carried out in repetitive batches, achieving the same glucose oxidase specific activity. This study demonstrates the advantages of fine bubble aeration and presents promising results for addressing the sustainable biotransformation processes.

Simultaneous absorption of H2S, MM and COS into a novel SRSG absorbent using a rotating packed bed

In industries, many gases are required to remove hydrogen sulfide (H2S) and organic sulfur. However, it is still a huge challenge to achieve the efficient and simultaneous removal using a single process. Herein, a novel simultaneous removal sulfide gas (SRSG) absorbent is developed to simultaneously absorb H2S, methyl mercaptan (MM) and carbonyl sulfide (COS). The absorption mechanism between the SRSG absorbent and H2S, MM, COS is explored by quantum chemistry calculations (QCC) and controlled experiments in a rotating packed bed (RPB). Results indicate that the interaction between SRSG and H2S, MM belongs to physical absorption while COS absorption in SRSG obeys two molecule reaction mechanism. Furthermore, the effect of different operating conditions, including rotating speed (N), liquid flow rate (L), gas–liquid ratio (G/L) and temperature (T), on the absorption efficiencies (η) and gas volumetric mass transfer coefficient (KGa) of H2S, MM and COS is systematically investigated. It can be found that both η and KGa are dependent on those operating conditions. The optimal η value for H2S, MM and COS is up to 99.99%, 100%, 100%, respectively. Moreover, nondimensional equations for Sherwood number (Sh) are established, and the calculated and experimental values of Sh(H2S), Sh(MM) and Sh(COS) are in agreement with a deviation within ±13%, ±13%, and ±20%, respectively. These results will provide a valuable potential technique for simultaneously removing acidic gas components from industrial gases.

Ultrasound catalytic ozonation to remove 5-hydroxy-1,3-phthalic acid from strongly alkaline and high-salt solutions: Aiding nuclear waste disposal and human health

As a typical precipitation inhibitor and the main component of plasticizers, 5-hydroxy-1,3-phthalic acid (5-HPA) seriously threatens the nuclear waste disposal and human health. OH, 1O2, and O2− induced by the ultrasound catalytic ozonation (US/O3) process achieves a removal rate of 60.67 % of 5-HPA in strongly alkaline and high-salt solutions within 60 min, which is significantly higher than the O3 alone process. This technology is highly resistant to inorganic anions that coexist in industrial production, but the mineralization process is inhibited. Ozone utilization and mass transfer are significantly improved by ultrasound, including reducing the ozone bubble size by 38 %, increasing the ozone utilization rate from 52 % to 75 %, increasing the volumetric mass transfer coefficient by 61 %, and increasing the specific interfacial area by 60 %, reducing the molar ratio of ozone to TOC from 0.45 to 0.23. Through a combination of Density functional theory (DFT) and GC–MS, four pathways for removing 5-HPA are clearly proposed, which are significantly different from the evolution behavior in acidic systems. The US/O3 system has significant application potential in reducing the threat of 5-HPA to nuclear waste disposal and human health.

A non-aseptic bioprocess for production and recovery of 2,3-butanediol via conversion of crude glycerol and corn steep liquor at pilot-scale

The production and recovery of 2,3-butanediol (BDO) through biodiesel derived glycerol valorization by Klebsiella oxytoca ACA-DC 1581 was holistically optimized with regard to the efficiency and cost of the bioprocess. The absence of thermal treatment of the substrate had no negative effect upon the growth of microorganism and the bioconversion of crude glycerol into BDO, enabling the development of a non-aseptic and lower-cost bioprocess. Both digestate and corn steep liquor (CSL), the main by-products of the biogas and corn industries respectively, successfully served as the sole source of nitrogen, contributing to the complete replacement of more expensive sources (e.g., yeast extract). The biochemical pathway of glycerol catabolism was examined under varying concentrations of dissolved oxygen and BDO production was optimized in a fully aerobic environment (volumetric mass transfer coefficient; kLa = 70.5 1/h.) The glycerol consumption rate was 2.80 g/L/h, the BDO productivity reached 1.12 g/L/h and the yield of BDO produced per unit of glycerol consumed was 0.46 g/g, with these values being among the highest ones reported in the literature for wild-type strains cultivated on crude glycerol. In all fed-batch fermentations, final BDO and acetoin concentration reached ∼80 g/L, while a plateau was observed at ∼68 g/L of BDO. Finally, the culture was carried out efficiently in the pilot-scale reactor (250 L). The salting-out extraction (SOE), consisting of ethanol (24 %) and K2HPO4 (25 %), recovered 91.7 % of BDO from the fermentation medium and was studied for the first time in a glycerol-based medium. The study suggests the potential industrialization of the bioprocess through sustainable, pilot-scale and low-cost bioconversion of biodiesel-derived crude glycerol and CSL or digestate into BDO.

Research on the influence of aeration manners on the mass transfer characteristics of bubbles in multi‐column airlift photobioreactor

AbstractMass transfer of bubbles is important in microalgae cultivation. In this study, aiming to improve the microalgae culturing efficiency, computational fluid dynamics (CFD) was adopted to study the influence of the aeration manners on mass transfer of bubbles within ascending columns in multi‐column airlift photobioreactor (PBR) and the hydrodynamic conditions within the PBR under different aeration manners. In addition, the bubble generation time, the detachment diameter, and the average volumetric mass transfer coefficient of bubbles in ascending columns were analyzed. Furthermore, the experimental results were compared with the simulation results obtained from microalgae cultivation. The results showed that the whole aeration manner yields the lowest mixing strength and mass transfer efficiency of bubbles at an aeration rate of 0.2 vvm. Conversely, both the mixing strength of the liquid and mass transfer coefficient of bubbles were enhanced under the half and alternate aeration manners. However, the results demonstrated that the distribution of the flow field was not uniform under the half aeration manner and there were obvious high‐speed and low‐speed zones. In contrast, the flow field distribution in the PBR was more uniform under the alternate aeration manner, which was suitable for microalgae cultivation at high concentration. This study effectively enhanced the mixing strength and CO2 transfer rate in the PBR.

Experimental study on the effect of process parameters on postcombustion CO2 capture using rotating packed bed technology

AbstractEnvironmental issues are the most discussed in today's industrialized world, and this has always been associated with the emission of greenhouse gases. CO2 emissions, especially from power plants, are considered the major greenhouse gas source. Capturing CO2 from large emission sources is necessary to address the worst impacts of climate change, including more frequent and severe droughts, heat waves, and intermittent rainfall. Conventional post‐combustion CO2 capture has always been questioned because of its high impact on energy costs. Rotating packed bed technology has shown the potential to reduce the cost of CO2 capture. This paper presents an experimental study on an in‐house designed rotating packed bed absorber for the capture of CO2 from a flue gas stream. Effects of process parameters such as rotating speed, liquid‐to‐gas ratio, and monoethanolamine (MEA) concentration on CO2 capture efficiency and overall volumetric mass transfer coefficient were studied. The study showed that as rotor speed increased, the CO2 capture efficiency increased, this can be attributed to higher rotor speed, resulting in more droplet flow, indicating an increase in the area of contact between the flue gas and the MEA solvent. Also, as the concentration of MEA increased CO2 capture efficiency increased, since an increase in concentration results in an increase in the rate of reaction. Finally, the study showed that a rotating packed bed absorber is an efficient unit for CO2 capture since it enhances mass transfer performance.

Nanobubbles produced by nanopores to probe gas-liquid mass transfer characteristics

HypothesisThis study tested the hypothesis of how the nanopore size of membranes and how the surface charge of nanobubbles responds to its pinch-off from the nanopore. This study also tested the hypothesis that nanobubbles that remain in solution after production may increase the dissolved oxygen content in water. ExperimentsThe effect of membrane pore size, hydrodynamic conditions (gas and liquid flow rates), and physicochemical parameters (pH and temperature) on volumetric mass transfer coefficient (kLa) for oxygen nanobubbles formed by the nanopore diffusion technique was investigated. This study experimentally determined the kLa by carefully removing the dissolved oxygen by nitrogen purging from nanobubble suspension to examine the sole contribution of nanobubble dissolution in water to the reaeration. ResultsScaling estimates indicate that the nanobubble pinch-off radius and nanopore radius have a power-law correlation and that nanobubble size declines with the nanopore size. This is in line with our experimental results. The surface charge of nanobubbles delays its pinch-off at the gas-liquid interface. Nanobubbles offered 3-4 times higher kLa than microbubbles. Standard oxygen transfer efficiency in water was found to be 78%, significantly higher than that in microbubbles. However, dissolving stable nanobubbles in water does not considerably increase dissolved oxygen levels.

Liquid-liquid flow pattern and mass transfer in a rotating millimeter channel reactor

Abstract Currently, microchannels are widely used in liquid-liquid heterogeneous mass transfer systems due to its excellent mass transfer performance. However, because of the passive mixing principle of traditional microchannels, the improvement of mass transfer performance has a bottleneck. This work proposes a novel rotating millimeter channel reactor (RMCR), capable of achieving liquid-liquid heterogeneous mass transfer enhance by centrifugal force. Three typical flow patterns of slug flow, parallel-droplet flow, and parallel flow in the RMCR were observed by high-speed photography technology. The volumetric mass transfer coefficient (K O a) of the RMCR increased with the increase of the total volumetric flow rate and rotational speed (N) increased. Compared with N = 0 r/min, the K O a of the RMCR increases by 61.5 % at 200 r/min, ranging from 0.013 to 0.021 s−1. The RMCR proposed in this work is expected to be applied to the liquid-liquid heterogeneous mass transfer system with high processing capacity and easy plugging.

Hybrid AI modeling techniques for pilot scale bubble column aeration: A comparative study

With increased accessibility of process data from the production lines in chemical and biochemical production plants, the use of data-based modeling methods is gaining interest. In this work, three different data-based modeling approaches are applied for modeling aeration in a pilot scale bubble column. In all three modeling approaches the same serial hybrid-model structure is used, combining a species conservation balance based on first-principles with different data-based models for the overall volumetric mass transfer coefficient (KLa). Simple empirical correlations with parameters fit to process data provide transparent models but lack the accuracy of Artificial Neural Networks (ANNs). ANNs provide models with high accuracy within the operation regimes used for training, however, the models are prone to overfitting, and their black-box nature results in models that are difficult to interpret. As an alternative, a symbolic regression-inspired technique is used for discovering symbolic equations, resulting in interpretable models with accuracy that is comparable to that of the ANN.

CO2 capture using gas-lift pumps operating under two-phase flow conditions

CO2 capture through dissolution in water offers environmental benefits and industry applications. However, current studies mostly focus on CO2 extraction into solvents, overlooking its direct solubility in water. Alternatively, gas-lift pumps may hold significant potential for capturing and storing CO2 in water; but this ability remains unexplored. Therefore, this study experimentally delves into the CO2 capture capacity and hydraulic performance of a dual injection gas-lift pump with a 25.4 mm riser diameter. Operating at a constant submergence ratio of 70 %, the pump is fed with simulated flue gas with flow rates within 5–30 LPM at volumetric CO2 concentrations of 10 %, 15 %, and 25 %, and temperatures of 22 °C (isothermal operation) and 110 °C (non-isothermal operation). Two-phase flow hydrodynamics is also evaluated using high-speed imaging in conjunction with time-series void fraction measurements. Within the riser pipe, three distinct two-phase flow patterns — slug, intermittent, and churn flows — are identified. The results reveal that under both isothermal and non-isothermal operations and across all volumetric CO2 concentration levels, churn flow demonstrates superior mass transfer coefficient and lifted liquid flow rate, while slug flow achieves minimum energy consumption per ton of captured CO2, highest CO2 capture degree, and maximum lifting efficiency. Also, the highest degrees of sensitivity to inlet gas flow rate for volumetric mass transfer coefficient, delivered liquid flow rate, and void fraction were observed in slug flow regime. Both gas temperature and volumetric CO2 concentration positively impacted the mass transfer performance. However, the pump showed remarkably higher lifting efficiencies under isothermal operation conditions. Moreover, compared to four established CO2 capture methods (absorption, adsorption, cryogenic distillation, and membrane diffusion), the gas-lift pump exhibits moderately lower energy consumption, at 38-266 kWh/tonCO2, but with lower CO2 capture degree of 2.3 % to 6.7 %.

Establishing forward mixing model to mass transfer overview in multi-impeller agitated column for rare Earth extraction process

The current study develops comprehensive mass transfer models to optimize the rare earth extraction. A plug flow, axial dispersion, backflow, forward mixing-based mass transfer model was created and solved numerically using the fitting technique. The investigated process is a multi-impeller agitated column designed to provide proper contact between organic and aqueous phases to extract rare-earth ions. Taking Sm(III)–Gd(III) separation as an application case, extraction efficiency in the agitation speed of 200 rpm was obtained equal to 95.14%, 76.67% by this column for Gd(III), and Sm(III) ions, respectively. The model's findings were compared with experimental data, and a significant agreement was achieved with the forward mixing model. The results indicated that the high agitation speed is beneficial to increasing the interfacial area while reducing the mass-transfer coefficient. On the contrary, the circulation within the larger droplet improves the transfer of mass, albeit at the expense of reducing the interfacial area. The results showed that the drop size distribution is a crucial factor as the droplet sizes significantly affect the droplet mass transfer. The mathematical models’ values of Ec for mass transfer parameters showed that the operational variables significantly affect the mass transfer rate and can cause deviations from the ideal flow path. A reasonable and appropriate estimation of the organic-side volumetric overall mass transfer coefficient was provided, which can be applied to this contactor’s design and scale-up.

CO2 capture in a novel rotating spiral contactor with hydraulic seal: Hydromechanics, mass transfer and modeling

The efficient capture of CO2 has always been a goal pursued by people. However, low gas handling capacity and low gas–liquid ratio restricts existing gas–liquid contactors, especially for non-rotating ones. In this study, a gas–liquid contactor with high gas handling capacity and high gas–liquid ratio, the rotating spiral contactor, was developed. Hydrodynamic properties of the contactor were experimentally or theoretically investigated. A novel interface model was developed to describe gas–liquid interface shape. CO2 capture using MEA/DMEA aqueous solution were evaluated in terms of space–time yield (τ), overall volumetric mass transfer coefficient (KGae) and CO2 capture efficiency (η). A rate-based model was developed and applied for the first time to predict CO2 capture in the rotating spiral contactor. The hydrodynamic results showed that liquid layer thickness was below 400 μm for the liquid with viscosity of 14.5 mPa.s. Under the rotational speed of 1200 rpm, the gas–liquid ratio ranged from 525 to 2700, while the gas–liquid surface area remained around 667 m2/m3. The interface model predicted interface thickness within a relative deviation of ± 20 %. The results also showed that τ, KGae and η respectively were 3428–17021 h−1, 1.0–6.4 kmol.m−3.h−1.kPa−1 and 38–98 % at the gas–liquid ratio range of 200–1000. The predicted KGae and η by rate-based model agreed well with the experimental data within a relative deviation of ± 15 %. This rotating spiral contactor is ideally suitable for the scenarios with large gas handling requirement and high gas–liquid ratio.

Investigation of hydrodynamic performance in a staggered multistage internal airlift loop reactor

The multistage internal airlift loop reactor (MIALR) has shown promising application prospects in gas–liquid–solid reaction systems. However, traditional MIALRs have a global circulation with strong interstage liquid-phase exchange. This paper proposes a staggered multistage internal airlift loop reactor (SMIALR) that incorporates special guide elements to create a staggered flow. Both experiments and computational fluid dynamics-population balance model simulations were conducted to investigate the hydrodynamic performances of MIALR and SMIALR. The results demonstrate that SMIALR exhibits a local circulation at each stage. Bubbles have a longer residence time in SMIALR, resulting in a 28.35%–55.54% increase in gas holdup and a 7.27%–13.69% increase in volumetric mass transfer coefficient. The gas–liquid mass transfer coefficient of SMIALR was improved by increasing the gas–liquid interfacial area. Additionally, the radial distribution of solids was found to be more uniform. This study offers insights for optimizing MIALR and provides a theoretical foundation for the design and scale-up of SMIALR.

Effects of viscosity on hydrodynamics and mass transfer under a wire mesh-coupled solid particles method

Many practical industrial processes require gas–liquid mass transfer in highly viscous liquids, and liquid viscosity affects bubble characteristics and gas–liquid mass transfer. The current study investigated the effects of liquid viscosity on bubble dynamics and gas–liquid mass transfer via shadow imaging and dynamic oxygen dissolution methods, and the influence of fluid viscosity on the hydrodynamic effect when using a wire mesh-coupled solid particles method. The coupling strategy was associated with a bubble size regulation effect, with greater viscosity increasing the gas–liquid interface area by 27%–55% compared with unreinforced gas–liquid flow, which was superior to embedded wire mesh and added solid particles methods. Increased viscosity weakened the mass transfer enhancement effect of the coupling method, but the coupling method still effectively enhanced the gas–liquid mass transfer process, increasing the volumetric mass transfer coefficient (KLa) by 80%–130% compared to non-enhanced gas–liquid flow. Novel empirical KLa correlation equations were developed to predict the effects of the coupling method on gas–liquid mass transfer processes, and those equations exhibited good reliability and predictive capacity.

CFD evaluation of hydrophobic feedstock bench-scale fermenters for efficient high agitation volumetric mass transfer.

A new biomanufacturing platform combining intracellular metabolic engineering of the oleaginous yeast Yarrowia lipolytica and extracellular bioreaction engineering provides efficient bioconversion of plant oils/animal fats into high-value products. However, predicting the hydrodynamics and mass transfer parameters is difficult due to the high agitation and sparging required to create dispersed oil droplets in an aqueous medium for efficient yeast fermentation. In the current study, commercial computational fluid dynamic (CFD) solver Ansys CFX coupled with the MUSIG model first predicts two-phase system (oil/water and air/water) mixing dynamics and their particle size distributions. Then, a three-phase model (oil, air, and water) utilizing dispersed air bubbles and a polydispersed oil phase was implemented to explore fermenter mixing, gas dispersion efficiency, and volumetric mass transfer coefficient estimations (kL a). The study analyzed the effect of the impeller type, agitation speed, and power input on the tank's flow field and revealed that upward-pumping pitched blade impellers (PBI) in the top two positions (compared to Rushton-type) provided advantageous oil phase homogeneity and similar estimated kL a values with reduced power. These results show good agreement with the experimental mixing and kL a data.

A novel synergistic intensification method for CO2 absorption by metal salt and task-specific ionic liquids hybrid solvent in microchannel reactor

A novel metal salt-promoting mass transfer intensification method for CO2 absorption into task-specific ionic liquids aqueous solution was proposed. The mass transfer intensification and intrinsic mechanisms of different concentrations of metal salts (NaBF4, KBF4, KCl, and CuCl2) with task-specific ionic liquids (1-aminopropyl-3-methylimidazolium tetrafluoroborate [Apmim] [BF4]) aqueous solutions for CO2 capture process were visually investigated using a microchannel reactor. The results showed that adding metal salts could remarkably enhance the interaction between metal cations and ionic liquid anions, thereby decreasing the interaction between anions and cations within the ionic liquid molecules and promoting the chemical reaction between ionic liquid cations and CO2. Under the condition of the same salt concentration, the addition of KBF4 has more obvious enhancement for mass transfer in CO2 absorption process. The mass transfer coefficient increases as the gas-liquid phase flow rate rise under slug flow condition. In addition, based on the effects of metal salt concentration, absorbent density, and gas-liquid phase flow rate on the CO2 volumetric mass transfer coefficient kLa, a new correlation for predicting the volumetric mass transfer coefficient of CO2 absorption into the hybrid solvent in microchannel reactor was proposed and validated.

Design parameters comparison of bubble column, airlift and stirred tank photobioreactors for microalgae production

Microalgae are the most propitious feedstock for biofuel production due to their lipid and fatty acid content. Microalgae cultivation shares many features with bioreactors, such as thermal and pH regulation, feeding procedures, and mixing to enhance heat and mass transfers. Aeration and stirring speeds are important parameters to reduce the costs of producing microalgae. In this study, three different photobioreactor types (stirred tank, airlift, bubble column) were characterized and compared for microalgae production. Hydrodynamics, mass transfer, and power consumption were determined for various aeration rates (0.9, 1.2, 1.5 L/min), and stirring speeds (100, 200 rpm), and Chlorella sorokiniana growth performance was compared under the conditions that provided the highest volumetric mass transfer and the lowest mixing time. Photo-bioreactor homogenization was good as indicated by low mixing times (< 10 s). Bubble column had the highest volumetric mass transfer due to its sparger design. Gas holdup and volumetric mass transfer coefficient were found to increase with the air flow rate and stirring speed. For stirred tank, bubble column, and airlift photobioreactors, maximum specific growth rates of C. sorokiniana were 0.053, 0.061, 0.057 h−1, and biomass productivities were 0.064, 0.097, 0.072 gdw/L.day, respectively. Under the conditions tested, growth was limited by the volumetric mass transfer in the airlift and stirred tank and bubble column was the best option for producing microalgae. These findings pave way for more extensive use of these systems in producing microalgae and provide a basis to compare photobioreactors of different designs.

Mass and heat transfer behavior of a bubble column fitted with horizontal spiral tubes in bubbly-flow regime

Slurry bubble columns are commonly used for gas-liquid-solid diffusion-controlled reactions. However, they have some shortcomings, such as the high cost of separating the final product from the catalyst particles. This study proposes the use of spiral tubes as catalyst support to address these shortcomings. The liquid-solid mass transfer behavior of spiral tubes under different conditions of gas superficial velocity, spiral tube diameter, and pitch was studied using the electrochemical technique. The mass transfer coefficient was found to increase with increasing superficial gas velocity but decrease with increasing tube diameter and pitch. The data were correlated by a dimensionless equation suitable for the design and scale-up of the reactor. In addition to serving as catalyst support, the internal surface of the spiral tube can be used as a supplementary built-in cooler in conjunction with a cooling jacket for exothermic reactions. This is beneficial for catalytic reactions and biochemical reactions, which are prone to catalyst deactivation and thermal degradation, respectively. A study of the mass transfer behavior of a bubble column fitted with multi-spiral tubes revealed a deviation from the single spiral tube behavior by an amount ranging from 10% to 20%, depending on the operating conditions. Calculation of the ratio between the volumetric mass transfer coefficient and the specific energy consumption (performance indicator for the reactor under different conditions) revealed that the reactor has a high energy utilization efficiency.

Nanoporous hypercrosslinked polymers as cost-effective catalysts to significantly promote the CO2 absorption performance of water-lean solvents for post-combustion CO2 capture

In most cases, the slow CO2 sorption kinetics of water-lean solvents—which include low-volatile organic diluents—are the limiting factor when it comes to post-combustion CO2 capture. This study offers a solution by suggesting the use of catalysts based on nanoporous hypercrosslinked polymers (HCPs) to improve the removal efficiency of water-lean solvents based on diethanolamine (DEA) and to increase CO2 mass transfer. Simple and inexpensive monomers were used to prepare three HCPs: HCP-C, HCP-S, and HCP-B, which stand for benzene, polystyrene, and carbazole, respectively. Blends of DEA and Glycerol (Gly) were used to disperse these polymers. Addition of 0.5 wt% HCP to a solvent mixture of 20% DEA and 30% Gly considerably boosts removal efficiency and increases the amount of CO₂ that can be absorbed until the breakthrough point by as much as 3000%, according to the results. Additionally, various gas flow rates, DEA concentrations, and glycerol concentrations were also investigated to determine the HCP-C catalytic effect on the CO2 absorption. A volumetric overall mass transfer coefficient enhancement of up to 319 % is possible in the investigated ranges when using HCP-C, according to the findings. Moreover, a possible catalytic mechanism was suggested.

Effect of Fly Ash on the Mass Transfer Performance of CO2 Removal Using MEA and DEA Solutions in a Packed Tower

The accumulation of uncollected fly ash from flue gas in post-combustion CO2 capture processes is a significant concern in current coal-fired power plants due to its potential impact on the performance of CO2 absorbent and absorption towers. In order to determine the effect of fly ash on the mass transfer performance of CO2 absorption into monoethanolamine (MEA) and diethanolamine (DEA) aqueous solutions, experimental studies were carried out using a small-sized packed tower equipped with θ-ring random packing. These studies were conducted under various operating parameters, including solution temperature, liquid/gas ratio (L/G), packing height, and fly ash concentration. The results show that the effect of fly ash on the outlet CO2 concentration was primarily observed during the initial stages of the experimental process. Moreover, the presence of fly ash leads to a reduction in the volumetric overall mass transfer coefficient (KGav) when using MEA and DEA solution, and increasing the fly ash concentration further exacerbates this negative impact. However, the effect of fly ash on the reduction in KGav is not significantly related to its chemical composition but rather depends on the operational parameters. With increasing solution temperature, liquid/gas ratio (L/G), and packing height, the KGav values for different solutions exhibit an upward trend. The negative effect of fly ash on KGav remains relatively stable for MEA as solution temperature and packing height increase. Compared to MEA, fly ash has a greater negative effect on DEA solution under the same experimental conditions. The analysis reveals that the detrimental effect of fly ash on KGav primarily stems from its ability to alter the distribution state of the absorption liquid within the packed tower.