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1.
The influence of organic additives (propanol, benzoic acid, isoamyl alcohol and carboxymethylcellulose) on the volumetric mass transfer coefficient, kLa, in an internal loop airlift reactor with low‐density particles (nylon‐6 and polystyrene) was investigated. The kLa values increased with increase in superficial gas velocity, Usg, and decreased with increase in solid loading. A draft tube to reactor diameter ratio, DR/D, of 0.4 gave maximum kLa values. The addition of benzoic acid and propanol increased the kLa values owing to their coalescence inhibiting characteristics. The addition of isoamyl alcohol decreased kLa, owing to the formation of rigid bubbles and recirculation of small bubbles having a low oxygen content. The kLa values decreased with increase in the concentration of the non‐Newtonian fluid carboxymethylcellulose (CMC). The proposed correlations predicted the experimental data well. Copyright © 2006 Society of Chemical Industry  相似文献   

2.
An experimental investigation was made to measure interfacial area, a, and liquid‐side volumetric mass transfer coefficient, kLa, in a downflow bubble column by chemical methods viz., absorbing CO2 in aqueous sodium hydroxide and sodium carbonate/bicarbonate buffer solution respectively. The effect of gas and liquid flowrate and nozzle sizes on a and kLa were investigated. The experimental data obtained in the present system were analyzed and correlations were developed to predict a and kLa in terms of superficial gas velocity. The variation of a and kLa with specific power input were shown in graphical plot and compared with other gas‐liquid systems.  相似文献   

3.
In this work the sulfite oxidation (SOM), dynamic pressure‐step (DPM) and gassing‐out (GOM) methods were compared for volumetric mass transfer coefficient measurement in an airlift reactor with internal loop. As a liquid phase both, non‐coalescent and coalescent media were used. Among the methods discussed here, the mass transfer coefficient (kLa) values obtained by the DPM appear as the most reliable as they were found to be independent of oxygen concentration in the inlet gas, which confirmed the physical correctness of this method. The difference between data measured using air and oxygen was not higher than 10%, which was comparable to the scatter of experimental data. It has been found that the sulfite oxidation method yielded kLa values only a little higher than those obtained by the DPM and the difference did not exceed 10%. Up to an inlet gas velocity (UGC) of ?0.03 m s?1 the GOM using oxygen as a gas medium gave kLa values in fact identical with those obtained by the DPM. At higher flows of the inlet gas, the GOM yielded kLa values as much as 15% lower. The enhancement in oxygen mass transfer rate determined in non‐coalescent media was estimated to be up to +15%, when compared with a coalescent batch. The experimental dependence of kLa vs the overall gas hold‐up was described by an empirical correlation. 1 Copyright © 2004 Society of Chemical Industry  相似文献   

4.
Volumetric mass transfer coefficients (kLa) and power input (P) are often the key parameters in the design of gas‐liquid contactors. However, due to the limitations of most measurement methods, there is a lack of reliable data for predicting kLa for non‐coalescent batches under high energy dissipation rates. Accurate kLa and P correlations are proposed. The reliability of the correlations is ensured by using experimental data from a wide range of process conditions conducted in multiple‐impeller vessels of both laboratory scale and pilot scale, and including both non‐coalescent and coalescent batches. Applying the proposed correlations, the scale‐up and optimization of industrial vessels can be performed more accurately.  相似文献   

5.
The effects of certain pertinent parameters such as gas and liquid flow rates and nozzle position on the behavior of a down‐flow jet loop reactor (DJR) have been studied. The mean residence times of gas and liquid phases and the gas holdup within the reactor have been measured. In addition, the overall volumetric mass transfer coefficient, and the influence of the gas flow rate and the position of the nozzle inside the draft tube on the latter has been determined. Correlations have been presented for the gas holdup and kLa which take into account the length of the draft tube and the nozzle immersion height. The kLa values obtained at different power per unit volume (P/V) values in the DJR used in the present study compare favorably with data presented for stirred tanks and bubble columns in the literature. The liquid residence time distribution (RTD) within the reactor has been studied by tracer analysis for various operating conditions and nozzle immersion height and the results are indicative of the high mixing intensities that can be obtained in such reactions. © 2001 Society of Chemical Industry  相似文献   

6.
The mass transfer process under CO2‐water Taylor flow was experimentally investigated in circular capillaries with different lengths. The measured volumetric mass transfer coefficient kLa was found to reduce with the increase of mass transfer time under the same operational conditions. With computational fluid dynamics simulations, the instantaneous kLa values decreased sharply at the initial stage of the mass transfer process. The effects of numerous experimental parameters on separated contribution of kLa were investigated for different dimensionless mass transfer times. The instantaneous kLa values for arbitary transfer times could be calculated and agreed well with experimental data.  相似文献   

7.
The mixing and mass transfer characteristics of draft‐tube airlift bioreactors (DTAB) for a water‐in‐kerosene microemulsion, as a cold model of petroleum biodesulfurization, were studied. Incomplete gas disengagement at the top‐section of the DTAB and hence high gas recirculation were obtained with the microemulsion system for all the top‐section configurations employed in the present study especially at the high airflow rates. The ratio (S) of the volumes of the riser and the downcomer to the top‐section together with the gas disengagement abilities of the gas separator were both found to affect the mixing performance of the DTAB employed for the microemulsion system. Increase in the draft‐tube height resulted in significant increase in the mixing time (tm) and a slight increase in the overall volumetric oxygen transfer coefficient (kLa). Increase in the diameter of the top‐section and the height of the liquid above the draft‐tube led to a decrease in kLa, the latter effect being less prominent. New correlations were developed that predicted the mixing time and oxygen transfer coefficients obtained in the present work with reasonable accuracy. Copyright © 2004 Society of Chemical Industry  相似文献   

8.
The volumetric gas—liquid mass transfer coefficient (kLa) was measured for low‐ and medium‐consistency pulp suspensions using the cobalt‐catalyzed sulfite oxidation technique. Mass transfer rates were measured in a high‐shear mixer for a range of operating parameters, including the rotor speed (N = 10 to 50 rev/s), gas void fraction (Xg = 0.10 to 0.40) and fibre mass concentration (Cm = 0.0 to 0.10). kLa measurements were compared with the macroscale flow regime in the vessel (characterized using photographic techniques) and correlated with energy dissipation, gas void fraction and suspension mass concentration in the mixer. We found that gas‐liquid mass transfer was significantly reduced in pulp suspensions, even for low suspension concentrations. Part of this reduction was associated with dissolved components leached from the fibres into the liquid phase. This could account for reductions in kLa of up to 30% when compared with distilled water. The fibres further reduced kLa, with the magnitude of the decrease depending on the fibre mass concentration. Correlations were developed for kLa and compared with results available in the literature.  相似文献   

9.
The gas‐liquid mass transfer behavior of syngas components, H2 and CO, has been studied in a three‐phase bubble column reactor at industrial conditions. The influences of the main operating conditions, such as temperature, pressure, superficial gas velocity and solid concentration, have been studied systematically. The volumetric liquid‐side mass transfer coefficient kLa is obtained by measuring the dissolution rate of H2 and CO. The gas holdup and the bubble size distribution in the reactor are measured by an optical fiber technique, the specific gas‐liquid interfacial area aand the liquid‐side mass transfer coefficient kL are calculated based on the experimental measurements. Empirical correlations are proposed to predict kL and a values for H2 and CO in liquid paraffin/solid particles slurry bubble column reactors.  相似文献   

10.
In this work, the gas‐liquid mass transfer in a lab‐scale fibrous bed reactor with liquid recycle was studied. The volumetric gas‐liquid mass transfer coefficient, kLa, is determined over a range of the superficial liquid velocity (0.0042–0.0126 m.s–1), gas velocity (0.006–0.021 m.s–1), surface tension (35–72 mN/m), and viscosity (1–6 mPa.s). Increasing fluid velocities and viscosity, and decreasing interfacial tension, the volumetric oxygen transfer coefficient increased. In contrast to the case of co‐current flow, the effect of gas superficial velocity was found to be more significant than the liquid superficial velocity. This behavior is explained by variation of the coalescing gas fraction and the reduction in bubble size. A correlation for kLa is proposed. The predicted values deviate within ± 15 % from the experimental values, thus, implying that the equation can be used to predict gas‐liquid mass transfer rates in fibrous bed recycle bioreactors.  相似文献   

11.
Gas-liquid volumetric mass transfer coefficients, (kLa), have been obtained for “dead-end” autoclave reactors operated in two different modes: (a) gas introduced into the gas phase, and (b) gas introduced through a dip-tube in the liquid. Three different methods of kLa determination have been compared. Effects of agitation speed, impeller diameter, gas to liquid volume ratio (Vg/VL), position of the impeller and reactor size on kLa have been investigated. The kLa data were found to be correlated as: kLa = 1.48 × 10?3 (N)2.18 (Vg/VL)1.88 (dI/dT)2.16 (h1/h2)1.16 The critical speed of surface breakage, at which transition from the surface convection to the surface entrainment regime occurs, was also determined for different impeller positions, impeller diameters and gas to liquid volume ratios.  相似文献   

12.
A statistical experimental design was employed to study the effects of pressure, temperature, catalyst loading, and mixing speed on the solubilities (C*) and volumetric gas/liquid mass transfer coefficients (kLa) for H2, N2, CO, CH4 and C2H4 in a liquid mixture of hexanes containing iron oxide catalyst in a 4-litre agitated autoclave. Statistical correlations for kLa values for the gases used were developed. Mixing speed and solid concentration showed the strongest effects on kLa. At low catalyst concentrations, a maximum in kLa was observed and at concentrations > 37 mass%, kLa decreased by more than one order of magnitude.  相似文献   

13.
The main objective of this work was to propose a new process for household fume incineration treatment: the droplet column. A feature of this upward gas‐liquid reactor which makes it original, is to use high superficial gas velocities (13 m s–1) which allow acid gas scrubbing at low energy costs. Tests were conducted to characterize the hydrodynamics, mass transfer performances, and acid gas scrubbing under various conditions of superficial gas velocity (from 10.0 to 12.0 m s–1) and superficial liquid velocity (from 9.4·10–3 to 18.9·10–3 m s–1). The following parameters characterized the hydrodynamics: pressure drops, liquid hold‐ups, and liquid residence time distribution were identified and investigated with respect to flow conditions. To characterize mass transfer in the droplet column, three parameters were determined: the gas‐liquid interfacial area (a), the liquid‐phase volumetric mass transfer coefficient (kLa) and the gas‐phase volumetric mass transfer coefficient (kGa). Gas absorption with chemical reaction methods were applied to evaluate a and kGa, while a physical absorption method was used to estimate kLa. The influence of the gas and liquid velocities on a, kLa, and kGa were investigated. Furthermore, tests were conducted to examine the utility of the droplet column for the acid gas scrubbing, of gases like hydrogen chloride (HCl) and sulfur dioxide (SO2). This is a process of high efficiency and the amount of pollutants in the cleaned air is always much lower than the regulatory European standards imposed on household waste incinerators.  相似文献   

14.
A statistical approach was developed to investigate the effects of pressure, temperature, mixing speed and solid concentration on kLa for gaseous hydrogen, ethylene, and propylene in liquid n-hexane containing solid polypropylene powder in a 4-litre agitated reactor. The solubilities of the gases appeared to follow Henry's Law. Statistical correlations to predict kLa were proposed and response surfaces were constructed. kLa values appeared to reach a maximum around 15 mass% and sharply decrease above 30 mass%. The effects of pressure and temperature on kLa were found to depend on the gas-liquid system and operating conditions used.  相似文献   

15.
The aim of this work is to investigate a co‐current air‐liquid downward flow bubble column with air entrainment by liquid injection nozzle in order to use it as an aerator in activated sludge treatment plants. The study concerns the determination of mass transfer efficiency by measuring the mass transfer coefficient, kLa, both in clean water and in activated sludge. In clean water, this parameter is determined by three methods, i.e., gassing out method, absorption with chemical reaction and off‐gas method. In activated sludge medium, kLa values are measured by two methods, i.e., sludge reoxygenation and the hydrogen‐peroxide method. The values of kLa obtained in clean water are compared to those obtained in sludge, enabling the assessment of the α factor, i.e., ratio of oxygen transfer coefficient sludge/clean water. The results are in good agreement with those reported previously in the literature.  相似文献   

16.
Aerobic degradation or polishing is an essential step in the combined anaerobic/aerobic treatment of wastewater. In this study, a type of porous glass beads was used for immobilization of microbial cells in a three‐phase aerobic fluidized bed reactor (AFBR) with an external liquid circulation. The effects of superficial gas and liquid velocities on bed expansion, solid and gas hold‐ups and specific oxygen mass transfer rate, kLa, were investigated. A tracer study showed that the mixing and flow pattern in the 8 dm3 reactor could be simulated by a non‐ideal model of two continuous stirred tank reactors (CSTRs) in series. By treating an effluent from an upflow anaerobic sludge blanket (UASB) digester, the distribution of suspended and immobilized biomass in the reactor as well as the kinetics of COD removal were determined. The specific oxygen mass transfer rate, kLa, at a superficial gas velocity of 0.7 cm s−1 dropped by about 30% from 32 h−1 in tap water to 22 h−1 after a carrier load of 15% (v/v) was added. The measured kLa further dropped by about 20% to 18 h−1 in the wastewater, a typical value of the bubbling fermenters with no stirring. Compared with the aerobic heterotrophs under optimum growth conditions, the microbes in this reactor which was fed with anaerobic effluent plus biomass behaved like oligotrophs and showed slow specific COD removal rates. This might be attributed to the presence of a significant amount of obligate anaerobes and facultative organisms in the aerobic reactor. This was confirmed by a relatively low intrinsic oxygen uptake rate of the microbial population in the reactor, 94 mg O2 dm−3 h−1 or 19 mg O2g VS−1 h−1. © 1999 Society of Chemical Industry  相似文献   

17.
A computational method was developed that determined the mass-transfer coefficient kL or the volumetric mass-transfer coefficient kLa in packed-bed immobilized enzyme (IME) reactors. To study the performance of this method, two experimental systems were considered where an enzyme was immobilized on a non-porous support surface (surface-IME system) or within a porous support (pore-IME system). The values of kL and kLa determined in these packed-bed IME reactor systems were successfully expressed in terms of the substrate concentration at the reactor inlet and the liquid flow rate. Furthermore, the correlations obtained for kL and kLa were used to calculate the unconverted fractions of substrate at the reactor outlet. Comparison showed that the calculated results were in satisfactory agreement with the experimental values.  相似文献   

18.
The volumetric gas‐liquid mass transfer rate, kLa, was measured under batch conditions in a 0.28 m diameter laboratory‐scale retention column. Tests on water, and on unbleached kraft (UBK) pulp suspensions (mass fractions, Cm from 0.013 to 0.09) were made with air or nitrogen sparged through the column at superficial gas velocities between 0.0015 to 0.05 m/s. kLa varied with suspension mass concentration and superficial gas velocity, initially decreasing with increasing mass concentration, reaching a minimum between Cm = 0.03 and 0.06, and then increasing. The minimum in kLa coincided with a change in hydrodynamics within the column, from bubble column behaviour below Cm = 0.03 to porous solid behaviour above Cm = 0.06.  相似文献   

19.
A computational fluid dynamics (CFD) model is adopted to simulate the turbulent immiscible liquid‐liquid flow in a stirred vessel based on a two‐fluid model with a k‐ϵ‐AP turbulence model. An improved inner‐outer iterative procedure is adopted to deal with the impeller rotation in a fully baffled stirred tank. Different drag formulations are examined, and the effect of the droplet size on both the dispersed phase holdup distribution and the velocity field is analyzed. Two different numerical criteria are tested for determining the critical impeller speed for complete dispersion. The simulated critical impeller speeds are generally in good agreement with the correlations in the literature when the fixed droplet size is properly selected. This demonstrates that the modeling approach and the numerical criteria proposed in this work are promising for predicting the dispersion characteristics in liquid‐liquid stirred tanks.  相似文献   

20.
A semi‐theoretical approach for predicting kLa values (referred to liquid volume) in 18 organic liquids [acetone, aniline, 1‐butanol, benzene, cyclohexane, decalin, 1,2‐dichloroethane, 1,4‐dioxane, ethanol (96%), ethylacetate, ethylbenzene, ligroin, methanol, nitrobenzene, 2‐propanol, tetralin, toluene, and xylene] at various operating conditions (including elevated temperatures and pressures) was developed. It was found that the approach is applicable regardless of the hydrodynamic regime (at uG ≤ 0.1 m/s). Temperatures up to 353 K and pressures up to 0.5 MPa were tested. Two different distributors (multiple‐hole and single‐hole type) were employed. The liquid‐phase mass transfer coefficient kL was calculated theoretically from the penetration theory on the basis of original definition of gas–liquid contact time. The interfacial area a was defined with respect to the liquid volume. It was found that their product kLa must be multiplied by some correction factor in order to take account of the non‐spherical (ellipsoidal) shape of the bubbles. When the correction term is correlated to both the Eötvös number (Eo) and the dimensionless temperature ratio, 198 experimental kLa values can be fitted reasonably well (average relative error 9.3%).  相似文献   

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