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1.
Gas-liquid mass transfer in an airlift reactor with net draft tube is investigated. The effects of both the ratio of draft tube to reactor diameter and the reactor pressure on oxygen transfer are considered. The value of the volumetric mass transfer coefficient, kLa, increases with a decreasing diameter ratio at higher air flow rates. The correlation of volumetric mass transfer coefficient with respect to the true superficial air velocity under different reactor pressures is determined. The kLa value decreases with increasing reactor pressure.  相似文献   

2.
Mass transfer and liquid mixing in an airlift reactor with a net draft tube were experimentally investigated. Four different column diameters were considered. The mass transfer was measured using the volumetric gas-liquid mass transfer coefficient which was determined by the dynamic method. The mass transfer coefficients in the airlift reactors with different column diameters were not always higher than those in the bubble columns. The liquid mixing was measured using mixing time which was determined by a pulse technique. Under the same superficial gas velocity, the mixing times of the airlift reactors with a net draft tube were always less than those of the bubble columns.List of Symbols C mol·dm–3 bulk concentration of dissolved oxygen - C0 mol·dm–3 initial concentration of dissolved oxygen - Ce mol·dm–3 saturated concentration of dissolved oxygen - ¯C dimensionless dissolved oxygen concentration - Dc cm diameter of column - DN cm diameter of the nozzle hole - DT cm diameter of the net draft tube - HL cm static liquid height - HT cm height of the net draft tube - kLa hr–1 volumetric mass transfer coefficient - LT cm length of the net draft tube - tM sec mixing time of the liquid phase - t0 sec mixing time of the liquid phase in a bubble column - VL dm3 volume of the liquid phase - Ug cm/s superficial air velocity  相似文献   

3.
A pilot scale airlift reactor with multiple net draft tubes was developed to improve oxygen transfer in the reactor. The reactor was 0.29 m in diameter and 2 m height. A steadystate sulfite oxidation method was applied to determine an overall volumetric mass transfer coefficient. Oxygen transfer of the proposed airlift reactor can be 60–100% higher than that of bubble columns under the same operating conditions.List of Symbols C * mol·dm–3 saturated concentration of dissolved oxygen - C L mol·dm–3 bulk concentration of dissolved oxygen - G mol/min nitrogen flow rate - k L a hr–1 the volumetric gas-liquid mass transfer coefficient - Mo 2 g/mol molecular weight of oxygen - OTR g/min the oxygen transfer rate - U g cm/s superficial air velocity - V L dm3 volume of the liquid phase - in oxygen mole ratio in the inlet gas - out oxygen mole ratio in the outlet gas  相似文献   

4.
Gas hold-up and the oxygen transfer in the zones of the internal loop airlift reactor with rectangular cross-section was studied. It was found, that the downcomer to the riser gas hold-up ratio depends on the gas flow rate, the physicochemical properties of the system and on the reactor height. The ratio of the downcomer mass transfer coefficient to the global mass transfer coefficient was less than 6%. The ratio of the downcomer to the global mass transfer coefficient slightly increased with increase of the gas flow rate and decreased with increase of the liquid viscosity. The proposed correlation for the global overall mass transfer coefficient predicts the experimental data well within 16.6% deviation. It was confirmed that the reactor height is the important parameter for a design and a scale-up of the airlift reactors.  相似文献   

5.
The interrelationships between the three parts of the air lift reactor, the riser, the downcomer, and gas-liquid separator, were examined with relation to the overall mass transfer in the reactor. This involved studying the mass transfer of oxygen from the gas phase to the liquid phase for 20 different reactor geometries. Both one- and two-sparger systems were studied. It was demonstrated that the gas-liquid separator plays a major role in reactor behavior and must be considered in reactor design. It was found that the overall reactor mass transfer coefficient KLA could be correlated to the pneumatic power of gas input per total dispersion volume (P/VD) and to the true riser superficial gas velocity JGR for all experimental conditions examined. The KLA is directly related to the P/VD with an exponent of approximately 1. "Two-sparger" systems, where an auxiliary gas sparger is placed near the downcomer entrance, have higher ab solute values for KLA than single-sparger systems.  相似文献   

6.
The oxygen transfer characteristics of a 20-mm O.D. airlift contactor fitted with an oxygen microelectrode were determined by steady-state sulfite oxidation measurements. The volumetric mass transfer coefficient k(L)a was proportional to sparging power input per unit volume raised to a power which varied from 0.41 in water (coalescing bubbles) to 0.76 in NaCl solutions (noncoalescing bubbles). The highest observed k(L)a value was 0.012 s(-1) which is sufficient to aerate Escherichia coli in an NMR spectrometer at moderate to high cell densities, depending on the physiological state of the cells.  相似文献   

7.
8.
Of the various types of industry-generated effluents, those containing organic pollutants such as phenols are generally difficult to remediate. There is a need to develop new technologies that emphasize the destruction of these pollutants rather than their disposal. In this work the white rot fungus, Trametes pubescens, was demonstrated to be an effective bioremediation agent for the treatment of phenolic wastewaters. An airlift loop reactor was optimized, in terms of volumetric oxygen transfer rate (K(L)a = 0.45 s(-1)), to provide an environment suited to rapid growth of T.pubescens (mu = 0.25 day(-1)) and a particularly efficient growth yield on glucose of 0.87 g biomass.g glucose(-1). The phenolic effluent was shown to be a paramorphogen, influencing fungal pellet morphology in the reactor, as well as increasing laccase enzyme activity by a factor of 5 over the control, to a maximum of 11.8 U.mL(-1). This increased activity was aided by the feeding of nonrepressing amounts (0.5 g.L(-1)) of glucose to the reactor culture. To our knowledge the degradation results represent the highest rate of removal (0.033 g phenol.g biomass(-1).day(-1)) of phenolic compounds from water reported for white rot fungi.  相似文献   

9.
The hydrodynamics and mass transfer, specifically the effects of gas velocity and the presence and type of solids on the gas hold-up and volumetric mass transfer coefficient, were studied on a lab-scale airlift reactor with internal draft tube. Basalt particles and biofilm-coated particles were used as solid phase. Three distinct flow regimes were observed with increasing gas flow rate. The influence of the solid phase on the hydrodynamics was a peculiar characteristic of the regimes. The volumetric mass transfer coefficient was found to decrease with increasing solid loading and particle size. This could be predominantly related to the influence that the solid has on gas hold-up. The ratio between gas hold-up and volumetric mass transfer coefficient was found to be independent of solid loading, size, or density, and it was proven that the presence of solids in airlift reactors lowers the number of gas bubbles without changing their size. To evaluate scale effects, experimental results were compared with theoretical and empirical models proposed for similar systems.  相似文献   

10.
Liquid film and diffusional resistances of brewery granules during acetate, propionate, and ethanol utilization were investigated. Substrate utilization rate increased with decreased granule size. Effectiveness factors for acetate, propionate, and ethanol were calculated by comparing the maximum rates of substrate utilization of whole granules (1.8 to 3.0 mm) and fine flocs (20 to 75 mum) derived by disrupting whole granules. For acetate, propionate, and ethanol, maximum specific substrate utilization rates (k(m') g/g VS . d) for the flocs, were 5.11, 6.25, and 5.49, respectively, and half-velocity coefficients (K(g') mM) were 0.45, 0.40, and 3.37, respectively. Calculated effectiveness factors were 0.32, 0.41, and 0.75 for acetate, propionate, and ethanol, respectively. The effect of temperature on substrate utilization was examined at 26 degrees C, 31 degrees C, and 37 degrees C using acetate as sole carbon source. Utilization rates increased with temperature. Flocs were most sensitive to temperature, and whole granules were least affected. The behavior of flocs was well described by the Van't Hoff-Arrhenius equation. Effectiveness factors for acetate utilization by the granules were 0.36, 0.35, and 0.32 at 26 degrees C, 31 degrees C, and 37 degrees C, respectively, indicating little effect of temperature. Based on these results, we conclude that both liquid film and diffusional resistances influenced the rate of substrate utilization in a UASB reactor with granular sludge. Temperature effects were much less important than diffusional limitations within the granules. (c) 1995 John Wiley & Sons, Inc.  相似文献   

11.
The distribution of the solid-phase in an airlift reactor of the concentric draught tube type, with an enlarged degassing zone, has been determined. Samples were taken at eight points of the reactor for various airflow rates, solids loading and density. Hold-up of solids varied considerably within the reactor. The highest value, for all tested experimental conditions, was obtained immediately above the top of the riser and the lowest value near the wall of the degassing zone. © Rapid Science Ltd, 1998  相似文献   

12.
Measurements of local gas phase characteristics are obtained in an external-loop airlift reactor filled with newtonian or viscous non-newtonian liquids. A double-optical fiber probe technique is used. It allows the determination of the axial and radial profiles of gas hold-up, bubbling frequency, bubble size and velocity. In the case of air-water system, the results show a strong effect of radial liquid velocity variation on the gas flow characteristics at the bottom of the riser. In the case of highly viscous non-newtonian solution, the gas flow is strongly affected by the gas distribution just above the gas sparger. This study also points out the bubble coalescence and the break-up phenomena in different liquids and levels in the reactor. Furthermore, the local measurements of bubble size and velocity allows to gain more detailed information on the dynamics of the bubble-flow and shows a tendency of large bubbles to circulate in the column center.  相似文献   

13.
Hydrodynamic studies in an airlift reactor with an enlarged degassing zone   总被引:3,自引:0,他引:3  
The hydrodynamic behaviour of a 60?l three-phase airlift bioreactor, of the concentric draught tube type, with an enlarged degassing zone has been studied. Ca-alginate beads were used as the solid phase. Airflow rate (from 1.9 to 90.2?l/min), solids loading (0% to 40% (v/v)) and solids density (1016 and 1038?kg/m3) were manipulated and their influence on solids and gas holdup, circulation and mixing times and in the interstitial liquid velocity was determined. Riser and downcomer solids holdup was found to decrease with the increase of airflow rate and to increase with solids loading and density. On the contrary, gas holdup in the riser and in the downcomer increased with airflow rate and decreased with solids loading and density. By increasing airflow rate, a decrease in circulation time was observed while the effects of solids loading and density were negligible. Mixing time decreased with airflow rate, increased with solids density, in the studied range, and presented a maximum for solids loading of approximately 20% (v/v).  相似文献   

14.
Summary The hydrodynamics and mass transfer behaviour of an airlift fermentor with an external loop (height 10m) has been investigated by measuring gas and liquid velocities, gas hold-up, liquid mixing and oxygen transfer coefficients. Liquid phase properties, i.e., ionic strength, viscosity and surface tension have been varied by altering the fermentation media. Results are compared with those from bubble column experiments performed in the same unit. It is shown, that more uniform two-phase flow in the airlift leads to advantages in scale-up and operation.Nomenclature a Specific interfacial area per volume of dispersion (m2/m3) - c Local concentration of tracer (kmol/m3) - c Concentration of tracer at infinite time (kmol/m3) - CL Concentration of oxygen in the liquid bulk (kmol/m3) - CL * Concentration of oxygen in the interface (kmol/m3) - Dax Axial dispersion coefficient (cm2/s) - I Ionic strength (kmol/m3) - i Inhomogeneity [defined in Eq. (2)] - Rate of oxygen transfer (kmol/s) - tc Circulation time (s) - tM Mixing time (s) - VR Volume of gas-liquid dispersion (m3) - VSG Superficial gas velocity in up-flow column (m/s) Greek letter symbols L Oxygen transfer coefficient (m/s) - Dynamic viscosity (m Pa s) - Surface tension (m N/m) Presented at the First European Congress on Biotechnology, Interlaken, September 25–29, 1978  相似文献   

15.
Internal airlift reactors are closed systems considered today for microalgae cultivation. Several works have studied their hydrodynamics but based on important solid concentrations, not with biomass concentrations usually found in microalgae cultures. In this study, an internal airlift reactor has been built and tested in order to clarify the hydrodynamics of this system, based on microalgae typical concentrations. A model is proposed taking into account the variation of air bubble velocity according to volumetric air flow rate injected into the system. A relationship between riser and downcomer gas holdups is established, which varied slightly with solids concentrations. The repartition of solids along the reactor resulted to be homogenous for the range of concentrations and volumetric air flow rate studied here. Liquid velocities increase with volumetric air flow rate, and they vary slightly when solids are added to the system. Finally, liquid circulation time found in each section of the reactor is in concordance with those employed in microalgae culture.  相似文献   

16.
 For a stable and reliable operation of the biofilm airlift suspension reactor (BAS reactor) means to control biomass concentration, biofilm thickness and biofilm morphology are required. For this reason, the influence of applied detachment forces and surface substrate loading on the formation of heterotrophic biofilms in laboratory-scale BAS reactors was studied. Detachment forces were altered by variation of the initial bare carrier concentration or the superficial air velocity. In addition, the dynamics of biofilm formation during start-up of a full scale BAS reactor (300 m3) was monitored and compared with the laboratory-scale start-up (3 l). This study shows that the biofilm morphology and strength were influenced to a large extent by the surface substrate loading and applied detachment forces. A moderate surface substrate loading and a high detachment force yielded smooth and strong biofilms. The combination of a high surface substrate loading and low detachment forces did lead to rough biofilms, but did not lead to the expected high amount of biomass on the carrier, apparently because of the formation of weaker biofilms. The strength of the bio-films appeared to be related to the detachment forces applied during biofilm formation, in combination with the surface substrate loading. The biofilm morphology and biomass on carrier in the BAS reactor can be controlled using the carrier concentration, substrate loading rate and the superficial air velocity as parameters. The dynamics of biofilm formation during the start-up of a full-scale BAS reactor proved to be similar to heterotrophic biofilm formation in laboratory-scale reactors. This indicates that a model system on the laboratory scale can successfully be applied to predict dynamic phenomena in the full-scale reactor. Received: 31 March 1995/Received revision: 11 August 1995/Accepted: 22 August 1995  相似文献   

17.
The influences of geometric configuration, mycelial broth rheology and superficial gas velocity (Usg) were investigated with respect to the following hydrodynamic parameters: gas holdup (), oxygen transfer coefficient (KLa) and mixing time (tm). Increases in Usg and height of gas separator (Ht) caused an increase in and KLa, and a decrease in tm. Consequently, a diameter ratio (Dd/Dr) of 0.71 and Ht 0.20 m were found to be the best geometry and operation parameters to achieve high aeration and mixing efficiency for the high viscous broth system in the cultivation of filamentous fungi. An external airlift reactor (EALR) was developed and designed for the cultivation of filamentous fungi. The EALR with two spargers excels in reliability and high aeration and mass transfer coefficiency, resulting in a fast mycelial growth and high biomass productivity in the cultivation of the fungus Rhizopus oryzae.  相似文献   

18.
Oxygen transfer to mycelial fermentation broths in an airlift fermentor   总被引:2,自引:0,他引:2  
Oxygen transfer rates and gas holdups were measured in mycelial fermentation broths of Chaetomium cellulolyticum and Neurospora sitophila, each cultured in a 1300-L pilot-plant-scale airlift fermentor. These cultures exhibited highly non-Newtonian flow behavior coupled with a substantial decrease in oxygen transfer rates. The volumetric mass transfer coefficients in these cultures were found to be 65-70% lower than those in water. The data were compared with the available correlations obtained for simulated fermentation broths. In general, the data for C. cellulolyticum are in satisfactory agreement with the correlations for the model media but the data for N. sitophila are higher than that predicted by the correlations. Model media based correlations are found to be applicable to the fermentation processes if the culture medium does not possess a high yield stress.  相似文献   

19.
Sucrose from sugarcane is produced in abundance in Brazil, which provides an opportunity to manufacture other high-value products. Gluconic acid (GA) can be produced by multi-enzyme conversion of sucrose using the enzymes invertase, glucose oxidase, and catalase. In this process, one of the byproducts is fructose, which has many commercial applications. This work concerns the batch mode production of GA in an airlift reactor fed with sucrose as substrate. Evaluation was made of the influence of temperature and pH, as well as the thermal stability of the enzymes. Operational conditions of 40 °C and pH 6.0 were selected, based on the enzymatic activity profiles and the thermal stabilities. Under these conditions, the experimental data could be accurately described by kinetic models. The maximum yield of GA was achieved within 3.8 h, with total conversion of sucrose and glucose and a volumetric productivity of around 7.0 g L?1 h?1.  相似文献   

20.
This article deals with the modeling of the oxygen transfer in an industrial airlift fermentor used for lactic yeast production on whey substrates. The purpose of this study was to improve the understanding of the interactions among the various parameters that govern the oxygen transfer phenomena in this type of fermentor. The reliability of the proposed model is demonstrated. The results of the investigations have been put into practice on the industrial scale and have contributed to monitor better the fermentation process. The model was also used to develop new ways of industrial fermentor design.  相似文献   

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