共查询到20条相似文献,搜索用时 31 毫秒
1.
P.A. Pa War K. Rostami Jafarabad S. B. Sawant J. B. Joshi 《Chemical Engineering Communications》1993,122(1):151-169
Fractional dispersed phase hold-up and overall dispersed phase side mass transfer coefficients were measured in 34, 50, 70 and 95 mm i.d. spray columns using an aqueous two phase system. Sodium sulphate-polyethyleneglycol (PEG) (4000)-water formed the aqueous two phase system and amyloglucosidase was used as a solute for the estimation of mass transfer coefficient.
The dispersed phase hold-up (eD) and volumetric dispersed phase side mass transfer coefficient (KD) both increased with increasing PEG-rich phase velocity. The eDand KDawere found to be independent of the column diameter and column height above a certain critical value. An increase in the phase concentration of sodium sulphate and PEG was found to reduce eDand KDEmpirical and semi-empirical correlations for eD and KDahave been developed. 相似文献
The dispersed phase hold-up (eD) and volumetric dispersed phase side mass transfer coefficient (KD) both increased with increasing PEG-rich phase velocity. The eDand KDawere found to be independent of the column diameter and column height above a certain critical value. An increase in the phase concentration of sodium sulphate and PEG was found to reduce eDand KDEmpirical and semi-empirical correlations for eD and KDahave been developed. 相似文献
2.
F. Yazdian M. Nosrati M. Pesaran Hajiabbas E. Vasheghani-Farahani 《Chemical engineering science》2009,64(10):2455-11543
An external airlift loop bioreactor (EALB) was used for production of biomass from natural gas. The effect of riser to downcomer cross sectional area ratio (Ar/Ad), volume of gas-liquid separator, superficial gas velocity (Usgr), and physical properties of gases and their mixtures [υg (μ/ρ) and Dg] were investigated on mixing time, gas hold-up, and volumetric gas liquid mass transfer coefficients (kLa). It was found that Ar/Ad has remarkable effects on gas hold-up and kLa due to its influence on mixing time. Kinematic viscosity (υg) showed its significant role on mixing time, gas hold-up and kLa when different gases used (mixing time changes directly whereas gas hold-up and kLa change indirectly). Moreover, it was found that diffusion coefficient of gas in water (Dg) has remarkable effect on kLa. The volumetric mass transfer coefficients for methane and its mixtures with oxygen (three different mixtures) were determined at different geometrical and operational factors. In average, the rate of oxygen utilization is approximately 1.8 times higher than that of methane. A gas mixture of 25 vol% methane and 75 vol% oxygen was the best gas mixture for biomass production in the EALB. The correlations developed for predicting the mixing time, gas hold-up, and kLa in terms of Usgr, Ar/Ad, volume of gas-liquid separator, and gas phase properties have been found to be encouraging. 相似文献
3.
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
4.
Yoshinori Kawase Norihisa Hashimoto 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1996,65(4):325-334
The effects of solids loading on gas hold-up and oxygen transfer in external-loop airlift bioreactors with non-Newtonian fermentation media are discussed. Experiments were performed in two model external-loop airlift bioreactors with aqueous solutions of carboxymethyl cellulose (CMC) and xanthan gum representing non-Newtonian flows. Low-density plastic particles of 1030 and 1300 kg m−3 were used and the solids loading was varied in the range 0–20% (v/v). For the inelastic non-Newtonian CMC aqueous solutions, the presence of low-density solid particles slightly increased the riser gas hold-up, ϕgr, but decreased the volumetric mass transfer coefficient, kLa. On the other hand, ϕgr decreased but kLa increased with solids loading in the viscoelastic non-Newtonian xanthan gum aqueous solution. The extent of these effects depended on non-Newtonian flow behavior. Theoretical models of riser gas hold-up and volumetric mass transfer coefficient have been developed. The capability of the proposed models was examined using the present experimental data obtained in the model external-loop airlift bioreactors and the available data in the literature. The data were successfully correlated by the proposed correlations except the results for kLa coefficient in the xanthan gum solution. 相似文献
5.
B. Gourich Ch. Vial M. Belhaj Soulami A. Zoulalian M. Ziyad 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2008,140(1-3):439-447
Hydrodynamic parameters (gas-induced flow rate and gas hold-up) and mass transfer characteristics (kLa, kL and a) have been investigated in a gas–liquid reactor denoted “Emulsair” in which the distributor is an emulsion-venturi and the gas phase is self-aspired by action of the kinetic energy of the liquid phase at the venturi throat. Two configurations, respectively cocurrent downflow and cocurrent upflow were compared. A chemical method involving the dispersion of a CO2–air mixture in a monoethanolamine (MEA) aqueous solution was used to measure mass transfer parameters. Experimental results showed that only the homogeneous bubbling regime prevailed in the upward configuration, while an annular regime could also be observed for cocurrent downflow at low liquid flow rate. Gas-induced flow rate and gas hold-up were usually smaller for cocurrent upflow, both at constant liquid flow rate and specific power input. The same stood for mass transfer properties. Conversely, specific power requirements were lower at constant liquid flow rate and mass transfer characteristics were enhanced at constant gas-induced flow rate for cocurrent upflow. A comparison with other gas–liquid contacting devices showed that the Emulsair reactor is a versatile tool avoiding the presence of mechanically moving parts when high and quickly adaptable dissolved gas supply is required. The cocurrent upflow configuration can be preferred when high gas flow rates are desired because the evolutions of gas-induced flow rate and mass transfer characteristics exhibit a stronger dependence on specific power input in the homogeneous bubbling regime for this configuration. 相似文献
6.
The gas holdup, ?, and volumetric mass transfer coefficient, kLa, were measured in a 0.051 m diameter glass column with ethanol as the liquid phase and cobalt catalyst as the solid phase in concentrations of 1.0 and 3.8 vol.‐%. The superficial gas velocity U was varied in the range from 0 to 0.11 m/s, spanning both the homogeneous and heterogeneous flow regimes. Experimental results show that increasing catalyst concentration decreases the gas holdup to a significant extent. The volumetric mass transfer coefficient, kLa, closely follows the trend in gas holdup. Above a superficial gas velocity of 0.04 m/s the value of kLa/? was found to be practically independent of slurry concentration and the gas velocity U; the value of this parameter is found to be about 0.45 s–1. Our studies provide a simple method for the estimation of kLa in industrial‐size bubble column slurry reactors. 相似文献
7.
Farid Benyahia Lynn Jones 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1997,69(3):301-308
Gas hold-up and oxygen transfer have been investigated in two geometrically similar external loop airlift reactors of linear scale ratio of 2. In mass transfer experiments, the sampling location was found to be important as significantly different kLa values can be obtained. The variations of kLa with probe location have been explained in terms of non-uniform hydrodynamic properties and the results obtained have been validated by means of high speed video camera recordings. At higher gas flowrates, the gas hold-up was significantly higher in the large-scale reactor. It was found that in order to maintain the gas hold-up or kLa constant in both the small- and large-scale reactor, the small-scale reactor required 25% and 27% more power input per unit volume of liquid respectively. © 1997 SCI. 相似文献
8.
Liquid phase volumetric mass transfer coefficients for oxygen are determined in a three-phase fluidized bed and in a bubble column. The concept of exponential decreasing axial variation of volumetric mass transfer coefficient leads to a better representation of oxygen concentration profiles inside the column. Compared to the bubble column, kla axial variations are more important in the lower part of the fluidized bed column, where solid particles increase the coalescence phenomenum, particularly with viscous liquids. 相似文献
9.
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
10.
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
11.
《Chemical Engineering and Processing: Process Intensification》1990,28(2):101-111
The individual phase holdups and mass transfer characteristics in three-phase fluidized beds with different floating bubble breakers have been determined in a 2.0 m high Plexiglas column of inner diameter 0.142 m. The bubble breaking phenomena by the breakers have been studied via a photographic method in a two-dimensional Plexiglas column. The volumetric mass transfer coefficient kLa in three-phase fluidized beds with hexagonal-shaped breakers is up to 40% greater than that in beds without floating bubble breakers. The bed porosity εL + εg, gas-phase holdup εg, and volumetric mass transfer coefficient kLa increase with an increase in the volume ratio of floating bubble breakers to solid particles, Vf/Vs, up to around 0.15, and thereafter decrease with Vf/Vs in three-phase fluidized beds with floating bubble breakers. Also, kLa increases with increasing breaker density, projected area and contact angle between the floating bubble breakers and the water. The volumetric mass transfer coefficients in terms of the Sherwood number in three-phase fluidized beds with the various floating bubble breakers have been correlated with the volume ratio of floating bubble breakers to solid particles, the particle Reynolds number based on the local isotropic turbulence theory and the modified Weber number. 相似文献
12.
Rate‐based calculations for trayed and packed columns offer process engineers a more rigorous and reliable basis for assessing column performance than the traditional equilibrium‐stage approach, especially for multicomponent separations. Although the mathematics, thermodynamics, and transport‐related physics upon which nonequilibrium separations theory is founded are generally true, it is also true that rate‐based simulations today suffer from a serious weakness—they are ultimately tied to underlying equipment performance correlations with questionable predictive capability. In the case of packed columns operated countercurrently, correlations are required for the mass‐transfer coefficients, kx and ky, for the specific area participating in mass transfer, am, for the two‐phase pressure drop, (Δp/Z)2?, and for the flood capacity of the column. In particular, it is generally well known that packing mass‐transfer correlations available in the public domain are unreliable when they are applied to chemical systems and column operating conditions outside of those used to develop the correlations in the first place. For that reason, we undertake the development of dependable, dimensionally consistent, correlating expressions for the mass‐transfer‐related quantities kx, ky, and am for metal Pall rings, metal IMTP, sheet metal structured packings of the MELLAPAK type, and metal gauze structured packings in the X configuration, using a new data fitting procedure. We demonstrate the superior performance of these correlations for a wide range of chemical systems and column operating conditions, including distillations as well as acid gas capture with amines. Further, we show that these new correlations lead to predictions for the relative interfacial area participating in mass transfer that can be greatly in excess of the geometrical surface area of the packing itself. © 2011 American Institute of Chemical Engineers AIChE J, 2012 相似文献
13.
The effects of water on the solubilities, C*, and volumetric mass transfer coefficients, kLa, for CO, H2, CH4 and CO2 in a heavy fraction of Fischer-Tropsch liquid were examined at elevated pressures and temperatures at different mixing power inputs. For these gases, higher solubilities were measured in the hydrocarbon mixture saturated with water than those obtained in the hydrocarbon free of water. The kLa values for the four gases were slightly affected by the presence of dissolved water in the hydrocarbon mixture; and they were strongly dependent on the power input per unit liquid volume. Two empirical correlations for kLa as a function of turbine speed and pressure are proposed. 相似文献
14.
In the present work, water and three phase compositions of Solka-Floc, a cellulose fiber for simulating the biomass in bacteria, yeast, and fungal fermentation were studied in a 1.4?m3 stirred airlift reactor. The fractional dispersed phase holdup and the overall volumetric mass transfer coefficients were measured. The dispersed phase riser gas holdup and overall volumetric mass transfer coefficients both increased with increasing riser superficial dispersed phase velocity (0.02–0.1?ms?1) and agitator speed in the range of 0–5?rs?1. An increase in the Solka-Floc concentration (1–3% w/v) was found to reduce ?GR and K L a L . Empirical correlations have been developed for fractional dispersed phase gas holdup and overall volumetric mass transfer coefficients. 相似文献
15.
Qiang Zhang Zhengya Dong Zhikai Liu Guangwen Chen 《American Institute of Chemical Engineers》2022,68(8):e17689
This study aims to investigate the effect of ultrasonic waveforms on the gas–liquid mass transfer process. For a given load power (P), continuous rectangular wave yielded stronger bubble oscillation and higher mass transfer coefficient (kLa) than continuous triangular and sinusoidal wave. For pulsed ultrasound, the kLa decreased monotonically with decreasing duty ratio (D), resulting in weak enhancement at low D (≤33%). For a given average load power (PA), concentrating the P for a shorter period resulted in a higher kLa due to stronger cavitation behavior. For a given PA and D, decreasing the pulse period (T) led to an increase in kLa, which reached a constant high level when the T fell below a critical value. By optimizing the D and T, a kLa equivalent to 92% of that under continuous ultrasound was obtained under pulsed ultrasound at a D of 67%, saving 33% in power consumption. 相似文献
16.
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
17.
Jiin-Shiung Horng Jer-Ru Maa 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1986,36(1):15-26
A single stage mixer—settler was used to investigate the effect of surfactant on the mass transfer rate in the system water—HNO3—30 vol.% TBP/dodecane. The interfacial tension of this system first falls then rises with increasing sodium lauryl sulphate (SLS) concentration. The addition of SLS makes the stage efficiency, which is closely related to kha, the product of the individual mass transfer coefficient of HNO3 in the aqueous phase, and average interfacial area per unit volume of mixing chamber, to increase significantly due to an increase in the value of a. A maximum kha value of 0.53 litres?1, a minimum value of interfacial tension, and phase inversion which converted the aqueous phase from continuous to dispersed were observed at around the critical micellar concentration (100 parts 10?6) of SLS in the system of an aqueous to organic phase ratio of 0.2. 相似文献
18.
Pasi Moilanen Marko Laakkonen Olli Visuri Ville Alopaeus Juhani Aittamaa 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2008,142(1):95-108
We assembled a set of models that allows investigation of local variables that are difficult to measure, validation of mechanistic physical models, and comparison of different numerical solutions. Population balances (PB) for bubbles were combined with local flow modelling in order to investigate G–L mass transfer in an air–water system. Performance of three different impeller geometries was investigated: Rushton (RT), Phasejet (PJ) and Combijet (CJ). Simulations were compared against experimental mixing intensity, gas hold-up, vessel-averaged volumetric mass transfer rates (kLa), and local bubble size distributions (BSDs).The simulations qualitatively predict kLa's with different impellers at the fully dispersed flow region and gave new insight on how kLa is formed and distributed in the stirred vessels. The used bubble breakage and coalescence models are able to describe both air–water and viscous non-Newtonian G–L mass transfer. Difference between experimental mass transfer rates of the three impellers was within experimental error, even trough the flow patterns, gas distribution, and local BSDs differ considerably. The population balance for bubbles was modelled in two different ways, with multiple size groups (MUSIGs) and with the bubble number density (BND) approach. MUSIG calculations took over twice as much computational time than BND, but there was little difference in the results. The Rushton turbine kLa was described with best accuracy, which is not surprising since most phenomenological models are fitted based on RT experiments. We suggest that these models should be validated over a wider range of vessel geometries and operating conditions. 相似文献
19.
This study aims at applying artificial neural network (ANN) modeling approach in designing ozone bubble columns. Three multi-layer perceptron (MLP) ANN models were developed to predict the overall mass transfer coefficient (kLa, s?1), the gas hold-up (? G , dimensionless), and the Sauter mean bubble diameter (dS , m) in different ozone bubble columns using simple inputs such as bubble column's geometry and operating conditions. The obtained results showed excellent prediction of kLa, ? G , and dS values as the coefficient of multiple determination (R2 ) values for all ANN models exceeded 0.98. The ANN models were then used to determine the local mass transfer coefficient (kL , m.s?1). A very good agreement between the modeled and the measured kL values was observed (R2 ?=?0.85). 相似文献
20.
Gas–liquid mass transfer in pulp fibre suspensions in a batch‐operated bubble column is explained by observations of bubble size and shape made in a 2D column. Two pulp fibre suspensions (hardwood and softwood kraft) were studied over a range of suspension mass concentrations and gas flow rates. For a given gas flow rate, bubble size was found to increase as suspension concentration increased, moving from smaller spherical/elliptical bubbles to larger spherical‐capped/dimpled‐elliptical bubbles. At relatively low mass concentrations (Cm = 2–3% for the softwood and Cm ? 7% for the hardwood pulp) distinct bubbles were no longer observed in the suspension. Instead, a network of channels formed through which gas flowed. In the bubble column, the volumetric gas–liquid mass transfer rate, kLa, decreased with increasing suspension concentration. From the 2D studies, this occurred as bubble size and rise velocity increased, which would decrease overall bubble surface area and gas holdup in the column. A minimum in kLa occurred between Cm = 2% and 4% which depended on pulp type and was reached near the mass concentration where the flow channels first formed. 相似文献