Phase Mass Transfer Coefficient Research Articles

CO2 quality control through scrubbing in oxy-fuel combustion: Simulations on the absorption rates of SO2 into droplets to identify operational pH regions

Oxy-fuel combustion is a promising CCS technology which is being demonstrated prior to commercialization. While the flue gas in oxy-fuel combustion is concentrated in CO2, it contains impurities such as SO2. The elimination of SO2 can provide a clean CO2 stream ready for storage. SO2 is commonly washed by sodium based spray towers with high efficiency but CO2 impacts are significant.A theoretical model was developed based on the two-film mass transfer model, and considering both the SO2 and CO2 reactions with sodium solutions. This model was firstly used to simulate the dynamic experimental results reported in our previous paper to confirm its applicability. With this model, simulations then were carried out on the absorption rate of SO2 into droplets with three droplet sizes: 100μm, 500μm and 1000μm, one sodium concentration of 0.08M (back calculated from liquid analysis), a range of pH from 4 to 12.5 and a range of SO2 concentrations from 19ppm to 1500ppm.Simulations focus on the impacts of droplet position, gas phase CO2 and droplet size on the absorption rate of SO2. These impacts are closely related with pH values. Taking a typical pH of 7 for example, the absorption rates of SO2 for droplets close to nozzles which move relative to the gas are significantly higher than these below nozzles which are at the terminal velocities, and the differences between two positions are larger for higher concentrations of SO2 with the concentrations range from 200ppm to 1500ppm. CO2 has a negative impact on the absorption rate of SO2 through reducing the gas phase mass transfer coefficient of SO2 in the gas phase controlled region and also through generating more acidic conditions at the liquid phase interface. Reducing the droplet size from 500μm to 100μm has a more significant improvement on the absorption rate of SO2 than from 1000μm to 500μm. Resulthave implications in the controlling region and the operational liquid pH region. The controlling region is related to the droplet position. The droplets close to nozzles are located in the mixed controlled region or the gas film controlled region; and the droplets below nozzles can be located in three regions depending on the concentration of SO2 and pH. A lower concentration of SO2 and a higher pH are favourable for the absorption rates of SO2 to be located in the gas phase controlled region.The operational pH of the exit liquid may be established based on two criteria: a reasonable absorption rate of SO2 and a sodium reagent loss as NaHCO3. The optimal operational region is then in the region 2 where the absorption rate of SO2 is still high and reagent use is minimized. The region 2 can be further divided into four sub regions. In the region 2–1 and the region 2–2, the absorption rate is moderate, but there is too much Na+ wasted for CO2 capture. In the region 2–3, there is a moderate amount of Na+ wasted for CO2 capture. In the region 2–4, Na+ wasted for CO2 capture is minimized, but the effective ratio of Na+ is still not the maximum.The necessary operational pH region graph can be used to guide the operation of a spray tower.

Gas-liquid mass transfer coefficient of methane in bubble column reactor

Biological conversion of methane gas has been attracting considerable recent interest. However, methanotropic bioreactor is limited by low solubility of methane gas in aqueous solution. Although a large mass transfer coefficient of methane in water could possibly overcome this limitation, no dissolved methane probe in aqueous environment is commercially available. We have developed a reactor enabling the measurement of aqueous phase methane concentration and mass transfer coefficient (k L a). The feasibility of the new reactor was demonstrated by measuring k L a values as a function of spinning rate of impeller and flow rate of methane gas. Especially, at spinning rate of 300 rpm and flow rate of 3.0 L/min, a large k L a value of 102.9 h−1 was obtained.

English

Published correlations for estimating the liquid phase mass transfer coefficients of structured packings are compared using experimental evidence on the efficiency of Montz-Pak B1–250MN and B1–500MN structured packings as measured in total reflux distillation tests using the chlorobenzene/ethylbenzene system at two operating pressures. Large differences are found between different correlations with respect to both the absolute values of mass transfer coefficients and the fraction of liquid phase based resistance and their trends with respect to increasing vapor and liquid loads. A new Delft Model liquid side mass transfer coefficient correlation that incorporates a more appropriate definition of the liquid film exposure length is presented which now generates lower values. The revised liquid film model, combined with an enhanced turbulent vapor phase mass transfer coefficient, leads to doubling the fractional liquid phase resistance with respect to that based on penetration theory assuming equal contact times. This effect results in predicting efficiencies which are slightly more conservative and agree reasonably well with experimental HETP data presented in this paper.

Liquid-liquid mass transfer studies in various stirred vessel designs

AbstractA general review on correlations to evaluate mass transfer coefficients in liquid-liquid was conducted in this work. The mass transfer models can be classified into continuous and dispersed phase coefficients. The effects of drop size and interfacial area on mass transfer coefficient were investigated briefly. Published experimental results for both continuous and dispersed phase mass transfer coefficients through different hydrodynamic conditions were considered and the results were compared. The suitability and drawbacks of these correlations depend on the operating conditions and hydrodynamics. Although the results of these models are reasonably acceptable, they could not properly predict the experimental results over a wide range of designs and operating conditions. Therefore, proper understanding of various factors affecting mass transfer coefficient needs to be further extended.

Effect of surfactant type on interfacial area and liquid mass transfer for CO2 absorption in a bubble column

The effect of different surfactants (n-octyltrimethylammonium bromide (OTABr), sodium dodecyl benzene sulfonate (SDBS) and Tween 80) with different critical micelle concentrations (CMC) on the CO2 absorption into aqueous solutions in a bubble column is analyzed in the present work. The presence of these surfactants increased the gas–liquid interfacial area, and decreased the liquid phase mass transfer coefficient, but with significant different extent. The results indicated that the CMC can be a key parameter affecting the mass transfer of CO2 absorption into a dilute aqueous solution of a surfactant. Sardeing's model was used to fit the experimental data successfully by re-correlating the parameters.

Mass transfer performance of structured packings in a CO2 absorption tower

This paper studies the mass transfer performance of structured packings in the absorption of CO2 from air with aqueous NaOH solution. The Eight structured packings tested are sheet metal ones with corrugations of different geometry parameters. Effective mass transfer area and overall gas phase mass transfer coefficient have been measured in an absorption column of 200mm diameter under the conditions of gas F-factor in 0.38–1.52Pa0.5 and aqueous NaOH solution concentration of 0.10–0.15kmol·m−3. The effects of gas/liquid phase flow rates and packing geometry parameters are also investigated. The results show that the effective mass transfer area changes not only with packing geometry parameters and liquid load, but also with gas F-factor. A new effective mass transfer area correlation on the gas F-factor and the liquid load was proposed, which is found to fit experiment data very well.

The Effect of Size and Concentration of Nanoparticles on the Mass Transfer Coefficients in Irregular Packed Liquid–Liquid Extraction Columns

This investigation explored the effects of nanofluids on mass transfer enhancement using an irregularly packed liquid–liquid extraction column and the chemical systems of water–acetic acid–toluene. SiO2 nanoparticles with sizes of 10, 30, or 80 nm are dispersed in toluene–acetic acid to produce nanofluids with different volume fractions of 0, 0.01, 0.05, and 0.1 vol.%. The effects of nanoparticle size and concentration on dispersed phase mass transfer coefficient were discussed based on the experimental data. This is for the first time that the effect of nanoparticle size is studied in liquid–liquid extraction systems. It was found that the mass transfer enhancement was more significant in nanofluids with smaller particles. It was also observed that mass transfer coefficient is larger in nanofluids compared to that in dispersed phase without nanoparticles, with a peak enhancement at a nanoparticle volume fraction of 0.05 vol.% for 10-nm particles and 0.01 vol.% for 30- and 80-nm particles. The maximum mass transfer coefficient enhancement was approximately 42% at 0.05% concentration of nanoparticles using smaller particles (10 nm). Finally, a novel correlation for prediction of effective diffusivity in the presence of nanoparticles has been proposed, which is a function of nanoparticle size and its concentration. The main advantage of this approach is that the principal effect of these two parameters is considered in correlation without which the experimental data could not be fitted with an acceptable accuracy.

Experimental analyses of mass transfer and heat transfer of post-combustion CO2 absorption using hybrid solvent MEA–MeOH in an absorber

• Mass transfer of MEA–MeOH was comprehensively investigated. • The K G a v of MEA–MeOH is higher than that of MEA–H 2 O. • MeOH is vulnerable to evaporate and should be operated at a low temperature. • Optimizing operating conditions can reduce solvent evaporation. The performance of CO 2 absorption into a hybrid solvent such as monoethanolamine (MEA) in methanol (MeOH) was experimentally investigated in a lab-scale absorber packed with Sulzer DX-type structured packing, and compared with that of aqueous MEA solution. The experiments were performed at various key operating conditions over a MEA concentration range of 2.5–5.0 kmol/m 3 , a CO 2 lean loading range of 0–0.373 mol/mol, a liquid flow rate range of 2.92–16.09 m 3 /m 2 h, an inert gas flow rate range of 24.37–63.54 kmol/m 2 h, a CO 2 partial pressure range of 6.7–13.8 kPa, and an inlet liquid temperature of 10 °C. The absorption performance was presented in terms of the overall gas phase mass transfer coefficient ( K G a v ), CO 2 concentration and system temperature profiles along the height of the absorber, and the system temperatures at the bottom and the top of the absorber, T bot and T top , respectively. It was found that the K G a v for MEA–MeOH was higher than that of MEA–H 2 O. In addition, the experimental results showed that key operating parameters such as MEA concentration, CO 2 loading, liquid flow rate and inert gas flow rate have large effect on the performance of CO 2 absorption into the MEA–MeOH.

Biogas upgrading by CO2 removal with a highly selective natural amino acid salt in gas–liquid membrane contactor

For biogas upgrading, a natural amino acid salt, potassium l-argininate (PA) is studied in a membrane contactor to capture CO2 from biogas. CO2 removal performance in terms of the overall volumetric gas phase mass transfer coefficient, membrane selectivity towards CO2 and the economic cost factor is systematically investigated. It is shown that PA is a highly CO2 selective absorbent and has a better affinity towards CO2 than monoethanolamine (MEA). The highest CH4 content in the upgraded biogas can reach about 99.15vol% by using PA, fully meeting the requirement of biogas upgrading. Furthermore, lower solvent concentration, lower liquid velocity and higher reaction temperature may be adopted when using PA in comparison to MEA. PA also has a better flexibility to the change of CO2 partial pressure and biogas flow rate than MEA. Regarding the economic cost factor of membrane process, CO2 loading of the lean PA solution can be optimized to 0.69–0.78mol/mol as the suitable range. Moreover, CO2 removal performance of l-arginine (ARG) is also explored. Due to the large amounts of bicarbonate other than carbamate formed in CO2-rich ARG solution, ARG has a lower biogas upgrading capability than diethanolamine (DEA) but higher than triethanolamine (TEA).

Mass transfer performance of CO2 absorption by alkanolamine aqueous solution for biogas purification

The CO2 absorption of an aqueous alkanolamine solution is an important research topic in the field of biogas purification. In this paper, an experimental packed tower was set up to investigate the high-concentration CO2 absorption of an ethanolamine (MEA) solution. A mathematical model of the enhancement factor based on a second-order chemical reaction was proposed. This model was used to calculate and analyse the enhancement factor and the mass transfer performance of high-concentration CO2 absorption by an MEA aqueous solution, respectively. The results show that the assumption of a pseudo-first-order reaction is not suitable for the high-concentration CO2 absorption process and the enhancement factor obtained via mathematical prediction by this model is in agreement with the experimental value. Moreover, the high-concentration CO2 absorption of the MEA aqueous solution is a liquid-controlled process. Furthermore, parameters such as gas phase overall mass transfer coefficient KG, liquid phase mass transfer coefficient kL and enhancement factor E increase with increasing MEA concentration but decrease with increasing CO2 concentration. When the gas flow rate is increased, the above parameters initially increase, then decrease, and finally level-off gradually. The results of this study may provide meaningful insights for the research and application of biogas purification technology.

Effect of Liquid Viscosity on the Liquid Phase Mass Transfer Coefficient of Packing

Abstract There are many correlations of liquid phase mass transfer coefficient ( kL ) for packings in the literature; most were developed without data that vary liquid viscosity ( μL ) significantly ( 2 capture by amine scrubbing, μL , of aqueous amine may be significantly greater than water, which makes it important to know how mass transfer is affected by μL . A research plan is proposed to measure the effective mass transfer area ( ae ) and kL in a pilot-scale packed column with μL from 1 to 100 cP. Glycerol was chosen as the viscosity enhancer for its complete solubility in water and the Newtonian behavior of its aqueous solution. Models were built to estimate the physical properties ( μL , ρ , DCO 2 , HCO 2 , γ ) of CO 2 /NaOH/H2O/glycerol based on literature data. Kinetic data ( kg’ ) for the system were obtained with a wetted wall column (WWC). The kinetic data, kg’ , was found to initially increase with glycerol concentration because of the catalytic effect of glycerol, then decrease rapidly because of the increase in μL . The overall reaction rate constant ( kAlk ) was determined from kg’ data, and was found to increase with glycerol concentration until it becomes asymptotic. This model for kg’ will be used for future measurement of ae and kL in a pilot-scale column.

Research on mass transfer of CO2 absorption using ammonia solution in spray tower

Research on mass transfer of carbon capture process plays an important role in the design of absorbing device. The effects of ammonia concentration, L/G, gas flow rate, gas temperature, CO2 partial pressure and other factors on the volumetric overall mass transfer coefficient (KGaV), the gas phase mass transfer coefficient (kG) and the effective mass transfer cross-sectional area (aV) were investigated with ammonia solution as the absorbent in homemade spray tower. Experimental results show that KGaV has upward trend with the increasing ammonia concentration, L/G and gas flow rate, and first increases and then decreases with the rises of CO2 partial pressure and gas temperature; kG increases with the increasing L/G, gas flow rate and CO2 partial pressure; aV increases with the increasing ammonia solution and gas flow rates; CO2 partial pressure has less impact on KGaV, kG and aV. Under the experimental conditions, maximums of KGaV, kG and aV are 0.17kmolm−3h−1kPa−1; 0.0022kmolkPam−2h−1 and 99.25m2m−3 respectively.

Spray and packed liquid–liquid extraction columns: drop size and dispersed phase mass transfer

ABSTRACTThe effects of holdup on Sauter mean drop diameter, D32, and dispersed phase mass transfer coefficient have been studied in the spray and packed extraction columns. For both columns, two well‐defined regions for the dependence of D32 on holdup were observed. D32 increased and decreased with an increase in holdup at low and high levels of holdup, respectively. Changes in dispersed phase mass transfer coefficient against holdup were shown to be similar to D32 for both columns. Moreover, empirical correlations have been derived to predict D32 and dispersed phase mass transfer coefficient for both columns. It has been shown that the derived correlations are in a good agreement with the experimental data. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Mass Transfer Characteristics of Nonaqueous Phase Liquid Based on Air–Liquid Interfacial Area in Variably Saturated Porous Media

Vapor phase mass transfer is an important interphase transport process that dominates the overall transport phenomena in liquid–gas system in porous media. Volatilization of nonaqueous phase liquids (NAPLs) in porous media is such system that takes place during the remediation of volatile organic compound-contaminated soil using soil vapor extraction. Usually, interphase mass transfer coefficient is lumped together with the air–liquid interfacial area because of the inaccessibility to quantify this parameter due to the heterogeneous nature of the pore structure of the media and the morphology of the fluid distribution. In this paper, the air–liquid interfacial area is quantified using a simple method derived from pressure–saturation relationship in three glass bead media. A series of one-dimensional NAPL volatilization experiments were carried out in a horizontal column for the same porous media by using toluene as the single contaminant. Experiments were conducted for NAPL saturation range of 13.8 ~ 71 % and pore gas velocities of 0.1 ~ 2 cm/s, and lumped mass transfer coefficients were evaluated. Actual vapor phase mass transfer coefficients were calculated using corresponding air–liquid interfacial area for a specific NAPL saturation and characterized in dimensionless form for all porous media. Results revealed that the vapor phase mass transfer increases with pore gas velocities and grain sizes but decreases with NAPL saturation.

Performance improving with temperature in liquid–liquid extraction using cumene–isobutyric acid–water chemical system

The performance of single drops was investigated in liquid–liquid extraction while temperature was changed within the range of 15–40°C. The recommended system of cumene–isobutyric acid–water with mass transfer resistance mainly in aqueous phase was used. An average enhancement of 75.6% in the rate of transfer was revealed. The extraction efficiency is the most influencing term due to molecular diffusivity enhancement. For modeling, a simple correlation was proposed for the effective diffusivity in Newman's equation, while continuous phase mass transfer coefficient was directly included. Using this model, relative deviation of the overall mass transfer coefficient was within only ±5.6%.

PEMFC GDE Oxygen Mass Transport Coefficient Separation with Different Gas Diluents

A parametric current distribution model is proposed for the overall PEMFC reactant mass transfer coefficient determination. The model was derived for a dilute reactant stream and a low cell voltage (limiting current). Separation of the mass transfer coefficient into gas and ionomer phase components is achieved with similar current distribution measurements completed with different molecular mass diluents. An extrapolation to a diluent with zero molecular mass leads to the ionomer phase mass transfer coefficient. The gas phase mass transfer coefficient is subsequently calculated using an additive relationship between the overall mass transfer coefficient and its components (gas and ionomer phase coefficients). Experimental measurements demonstrate the validity of the current distribution model and emphasize the need to use dilute reactant streams to facilitate data treatment.

Liquid Phase Mass Transfer Coefficient of Carbon Dioxide Absorption by Water Droplet

A new experimental set-up was established to measure liquid phase mass transfer coefficient of CO2 absorption by single water droplet. The experiments were performed at 303.65 K and 323.15 K, with a droplet falling height of 0. 41 m and 0.59 m. The droplet formation time varies from 0.352 s to 2.315 s. The droplet diameter changes little and is around 2.5 mm. The effects of temperature, droplet falling height and droplet formation time on CO2 absorption by individual water droplet are discussed.

Experimental and Theoretical Analysis of the Operating Parameters for Precipitating Acetaminophen and Tretinoin with Solution Enhanced Dispersion by Supercritical Fluids

The aim of this work is to analyze the experimental conditions for particle production with solution enhanced dispersion by supercritical fluids. Thermodynamics, atomization process, and mass transfer are separately studied in terms of phase equilibria, disintegration regimes, and mass transfer coefficients of liquid and vapor phases. These calculations are correlated with the precipitation data of acetaminophen and tretinoin. According to experimental results, the smallest and more spherical particles (with fewer aggregates) for both solids are obtained just above the mixture critical point of the antisolvent–solvent system with a high antisolvent–solvent mass flow rate ratio. Theoretical results indicate that a high mass transfer coefficient of the liquid phase and a high degree of supersaturation are produced at those conditions. That means a great antisolvent effect because of the low liquid side mass transfer resistance and a small particle size because of the high supersaturation. Furthermore, resul...

New Correlations of Volumetric Liquid-Phase Mass Transfer Coefficients in Gas-Inducing Agitated Tank Reactors

Abstract Volumetric liquid-phase mass transfer coefficient (kLa) is one of the most important parameters for the evaluation of the performance of a gas-inducing agitated tank (GIAT). In this paper, two equations in terms of power input per unit liquid volume (P/VL) and relative gas dispersion parameter (NI/Ncd), respectively, are developed according to data in literature. They can correlate existing kLa values within ±20% of measured ones for bladed impellers with different impeller submergence to tank diameter ratios in the range of 0.5 -1.23. In order to validate these equations, the liquid phase mass transfer coefficients in a continuous GIAT equipped with a 4-blade straight impeller were measured by removal of oxygen from water. It was found that the equation in P/VL criterion could correlate kLa values within ±12% of the experimental data, and the equation in NI/Ncd criterion could correlate kLa values within ±15.6% with an exception of 26.8% for NI = 16.7 Hz.

Characteristics of gas–liquid dispersion and mass transfer in a multi-plunging jet absorber using gas–liquid two-phase jets

A new type of multi-plunging jet absorber using gas–liquid two-phase jets was devised. The jets were formed through ejector-type nozzles in a sheet of perforated plate. The effects of structural factors of the perforated plate, the number of nozzles and the nozzle arrangement on the product of liquid-phase mass transfer coefficient and gas–liquid interfacial area, the gas holdup, and the penetration depth of bubbles were investigated experimentally. The mass transfer mechanism of the bubble dispersed phase was considered using a coaxial bi-zonal model. The specific gas–liquid interfacial area and the volumetric liquid phase mass transfer coefficient in this absorber were compared with those of other gas–liquid contacting devices. Empirical equations regarding gas holdup and the bubble penetration depth were obtained. The mass transfer mechanism in the multi-plunging jet absorber could be explained by the coaxial bi-zonal model. The multi-plunging jet absorber was found to enhance performance by increasing the number of nozzles.