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The bioreactor configuration including a dual-impeller combination, spacing between the impellers, and the diameter of the ring sparger is optimized based on solid suspension (N-jsg) and gas dispersion (N-f and k(L)a) in this work. Then, the solid suspension and gas dispersion performance in this optimized bioreactor are systematically studied. It is found that a smaller sparger (D-s/T = 0.32) achieves better performance in gas dispersion. A pitched-blade disc turbine down-pumping (PDTD) as a bottom impeller achieves the lowest N-jsg value, and has lower N-f value compared with PBTD (pitched blade turbine down-pumping) and TBHA (three-bladed helical agitator). Techmix 335 hydrofoil impeller down-pumping (TXD) as an upper impeller provides higher k(L)a values. TXD+PDTD are more suitable for the requirements of a bioreactor. k(L)a decreases slightly with increasing solid loading, which is beneficial to good gas dispersion in such bioleaching reactors with higher solid loadings (>20 wt%).

Extensive investigations were carried out to determine the mixing time (tm) in bubble columns with diameter of 0.2, 0.3, 0.4 and 0.8 m equipped with different type of spargers for different aspect ratios (H/D) of 0.8–8. The superficial gas velocity (Ug) varied from 0.01 to 0.25 m/s. The effect of temperature variations in the range of 20–90°C and surface tension variations (50–70 N·m) on tm was investigated. Experiments proved that as Ug increased, tm decreased in the homogenous regime and leveled off in the heterogeneous regime in tap water systems at ambient and elevated temperatures. There existed a critical aspect ratio (H/D)cri = 2 where tm varied with H/D reversely. The sparger configuration had a weak effect on tm. By placing the gas distributor pipe at the off centered position, tm could be decreased. In acetic acid solution, there existed a “jump point” in the tm vs. Ug curve at Ucri = 0.1 m/s, and tm was 2–3 times that in the tap water system at this point under otherwise identical conditions. The effect of temperature was determined by distinguishing the test temperature into a far from the boiling point stage and a near the boiling point stage. tm decreased marginally in the former stage and drastically in the latter. The surface tension had no notable effect on the liquid phase mixing behavior. Empirical tm correlations were proposed for various pipe distributors by considering the effect of (H/D)cri.

The power consumption, gas dispersion, and mass transfer volumetric coefficients are investigated in a gas–liquid agitated vessel with a disk turbine for various geometries, positions of the sparger, and directions of gas discharge. A sparger larger than the impeller is effective for obtaining high aeration power consumption and a high mass transfer volumetric coefficient. When the sparger is used, the flooding phenomenon does not occur easily. The gas is sufficiently dispersed when the large sparger is used, even if the gas is not blown directly into the impeller.

The flow characteristics and decomposition performance in the cocurrent upflow bubble column dispersed with micro-bubbles were experimentally examined. A micro-bubble generator was installed at the bottom of the column, and for comparison the sintered glass gas sparger was set at the lower part of the column.When milli-bubbles coexist with dispersed micro-bubbles, micro-bubbles disappear. This is considered because micro-bubbles are absorbed into the wake of milli-bubbles. The volumetric mass transfer coefficient is higher for micro-bubbles than for milli-bubbles, but the mass transfer coefficient is much lower for the former than for the latter. The apparent decomposition rate constant strongly depends on the volumetric coefficient. When the volumetric coefficient is higher, the rate constant of micro-bubbles is higher than that of milli-bubbles.

An experimental study of the effect of gas sparger geometry and agitator location on gas distribution in agitated systems is presented. The results have shown that varying the impeller position modified the size of low void fraction zone. The optimum impeller position for achieving a small low voidage zone without changing the flow pattern has been identified. It was found that impeller positions below or above the optimal location have a negative effect on gas dispersion while the sparger geometry did not affect significantly the overall gas distribution. Low void fraction zone could be detected by a void sensor even if not visually observed.

The aim of this study is to investigate the mass-transfer characteristics of a large paddle impeller by comparing with those of the down-pumping pitched blade turbine and the Rushton turbine, and also to probe the application of surface aeration to batch hydrogenation in polymerization processes and the ethylene oxide additional reaction. Laboratory and industrial data were used for this purpose. As a result, it has been found that, with the large paddle impeller, large kLa values of surface aeration without sparging can be obtained continuously at any liquid level because of the combined effect of surface breakage, bubble entrapment and efficient liquid circulation by axial pumping capacity of the impeller. Using these experimental kLaV data, the improvement in the operation time for a 12 m3 alkoxylation reactor was estimated. The reactor was then retrofitted with a large paddle impeller, and the actual operation time of 17 h was found to be strictly identical to the estimation, that is 75% reduction of the usual 70 h. This result shows the advantage of large paddle impellers in industrial processes and the accuracy of the estimation procedure.

In order to examine the characteristics of a concentrator using ultrasonic atomization, an ethanol aqueous solution was used and ultrasonic atomization concentration was performed under various conditions such as different ultrasonic conditions, liquid mixing methods and vessel diameters.The flow rate of accompanied liquid had a maximum against the initial liquid height, and the optimum initial liquid height decreased with increasing ultrasonic frequency. The flow rate of accompanied alcohol increased with increasing net electric power to a transducer, but was hardly affected by the ultrasonic frequency.In the case of mechanical agitation, as the revolution speed of a stirrer was faster, the flow rate of accompanied liquid increased but the alcohol content in accompanied liquid decreased. As a result, the revolution speed had no significant influence on the flow rate of accompanied alcohol. When the gas was sparged into liquid for liquid mixing, with increasing gas velocity, both the flow rate and the alcohol content of accompanied liquid became higher with increasing gas velocity, and the flow rate of accompanied alcohol increased. From these results, the liquid mixing by the sparging gas was found to be effective for the enhancement in performance of ultrasonic concentration.At the relatively high net electric power to an ultrasonic transducer, the flow rate of accompanied liquid increased with increasing vessel diameter, but the alcohol content in accompanied liquid was hardly affected by the vessel diameter.

Microbubble can extreamly enhance the gas–liquid mass transfer because of the increase in interfacial surface. For these characteristics, microbubble technologies have been widely applied to many technologies in recent years. In this work, we tried to apply a microbubble aeration technology to cultivation for aerobic yeast. Rhodoturula mucilaginosa YR-2 was used as yeast and cultivated. As a result, it revealed that it was possible to cultivate at a very low flow rate of microbubble aeration, which was between 1/100 and 1/10 of the gas flow rate required at conventional aeration by a sparger.

In wet limestone gypsum Flue Gas Desulfurizers, flue gas is washed with CaCO 3 -water slurry on the wet walls of a vertical absorption tower, where SO 2 and O 2 are absorbed to form CaSO 3 and CaSO 4 . Though it is required to capture sulfur into calcium sulfate, which is neutral to the environment as deposited, CaSO 3 is not always oxidized completely there to CaSO 4 due to insufficient residence time of slurry on the wet walls and the low absorption rate of oxygen. The rest CaSO 3 should be oxidized in a bubbling tank just under the tower. Therefore appropriate air bubble injectors are required to supply oxygen, just as much as necessary and enough, into the slurry in the tank. Here is proposed an Air Rotary Sparger (ARS) for the vertically and horizontally uniform distribution of small air bubbles in the tank and its performance is investigated with a small-sized conventional paddle type model with a central air injection hole on the bottom and two ARS models.

The enzymatic hydrolysis of shredded office paper as a model of waste paper was carried out in an external loop airlift bubble column with continuous ultrasonic irradiation. The paper used was 6 × 12 mm in size and suspended much less easily compared to a microcrystalline cellulose powder of 35 to 65 μm in diameter. Oxygen in the sparging air exerted no inhibitory effect on the enzymatic hydrolysis and the location of a horn for ultrasonic irradiation in the downcomer was slightly more efficient than that in the riser to enhance the hydrolysis. Even in the case of no ultrasonic irradiation, the enzymatic hydrolysis in the airlift reactor proceeded as a two-stage process as opposed to that in the previous stirred tank reactor. This was ascribed to a shear stress acting on the surface of office paper in the gas-sparging section in the riser in the same way as in the ultrasonic irradiation section in the stirred tank. The enzymatic hydrolysis in the ultrasonic airlift reactor was enhanced by the gas-sparging as well as ultrasonic irradiation. As a result, the external loop airlift bubble column was found to be more advantageous for higher sugar concentrations compared to the stirred tank reactor. The time courses were kinetically analyzed and simulated based on the kinetic model proposed previously. It was shown that the ultimate sugar concentration increased with an increasing initial substrate concentration and ultrasonic intensity, and that the apparent kinetic constant increased with the intensity.

The rectangular airlift sonoreactor combined with sparging ozone was developed. Tetraphenyl porphine tetrasulfonic acid was used as a sample to be decomposed and the decomposition performance was experimentally studied. First, by using only ultrasound, the superficial gas velocity and the riser width were changed, and the decomposition conversion and the flow characteristics were examined. It was found that the decomposition conversion became higher with increasing liquid velocity above the ultrasonic oscillator because the sample was more effectively supplied to the ultrasonic reaction field. Next, the decomposition experiment was conducted by using both the ultrasound and ozone. It was confirmed that the decomposition performance was enhanced by the combination with sparging ozone.

A non-biological floc system consisting of clay minerals and an organic flocculating agent was used for the determination of mechanical stresses in turbulent multiphase flows. The floc disintegration kinetics i.e. the time and stress dependent size distribution of the flocs were observed with an optical in-line particle-system analyser and the raw data transformed. The concomitant measurement of floc disintegration in a reference system, a couette system, enabled the assignment of the effective mechanical stresses. The volumetric power input resulting of isothermal expansion of gas has been derived to be the governing factor for the effective shear stresses in bubble columns and airlift loop-reactors. Furthermore the effects of gas phase distribution (originated from the sparger design) and solids loading on shear stresses were determined for fluid systems with low viscosities. Especially the interactions between finely dispersed bubbles and particles seemed to cause a drastic change of turbulence.

Measurement of mass transfer rate was carried out in an agitated vessel with gas sparging. The performance of mass transfer of several commonly used impellers (i.e. Lightnin A315 and A310, 45° pitched blade turbine, concave blade turbine, Rushton turbine, and Rushton turbine with holes) were examined systematically under the same fluid and tank conditions. A dynamic gassing-out method was used to measure the mass transfer rate of oxygen from gas to the de-ionised water. The variation of the dissolved oxygen concentration of the water was measured by a polarographic dissolved oxygen probe (ORION PCM800). The present data shows reasonable agreement with that in previous publications such as those of Linek et al. (1987), Hickman (1988), Warmoeskerken and Smith (1989), Martin et al. (1994), and Chen and Chen (1999). All the data collected here shows that van’t Riet’s (1979) expression, i.e.: kLa = α(P/V)0.4Us0.5 represents reasonably, well (to within ± 30%) the correlation of kLa with specific power P/V and superficial gas velocity Us. However, the present data seem to indicate that the radial flow impellers provide slightly higher (17%) mass transfer rate than the axial flow impellers.

For a bubble column with draft tube sparging gas into the annulus, the effects of equipment dimensions and liquid properties on the circulation flow rates of liquid and gas are experimentally studied. The gas circulation flow rate is estimated by comparing gas holdup in the downcomer with that in a gas-liquid cocurrent downflow bubble column. The liquid circulation flow rate becomes higher as the distance between the upper end of draft tube and the liquid surface at aeration lengthens, and it remains unchanged when the distance is beyond double the column diameter. It increases with increasing draft tube diameter and with increasing bubble size. The gas circulation flow rate is strongly governed by the liquid circulation flow rate. The driving force for gas circulation is the difference between the descending velocity of liquid and the rising velocity of bubble swarm in the downcomer. Based on the energy balance, an empirical equation of the loss coefficient in the zone above the upper end of the draft tube is obtained. The circulation flow rates of liquid and gas calculated by using the energy balance and correlations, agree with the measured data within an error of ±30%.

The effect of kind of gas sparger, outer diameter Do and length Ld of draft tube, lower clearance, superficial gas velocity and clear liquid height HL on gas holdup eG in a 0.16 m I.D. bubble column with a draft tube for gas dispersion into the annulus and for an air-water system was experimentally studied.eG depended on the kind of gas sparger in the range of φ ≤ 0.713, but hardly depends on them at φ = 0.875. φ is the ratio of (Do/DT) and DT is the inner diameter of the bubble column.At a given HL and in the range of φ ≤ 0.713, eG hardly depends on φ and Ld. But eG decreases clearly with increasing Ld at φ = 0.875.eG decreases with increasing HL. The effect of HL is well expressed by the modified three-region model.The experimental data for eG is correlated.

The liquid mixing time of a bubble column with a draft tube is experimentally studied. The diameter and height of the column, the diameter and length of the draft tube, and the mode of sparging gas were changed and the liquid mixing time was measured.The lengths of bottom and top clearances have significant effects on the liquid mixing time. The liquid mixing time increases with increasing column aspect ratio of height to diameter. The liquid mixing time of the bubble column with a draft tube is longer than that of a standard bubble column when the column aspect ratio is relatively high. The liquid mixing time has a minimum when the diameter ratio of draft tube to column is 0.5 to 0.6. These effects of equipment dimensions are expressed by an equation. In the experiment using different solutions, the liquid mixing time becomes shorter with increasing liquid surface tension, or with increasing liquid viscosity.

This paper reports a study of bubble produced by spargers with very fine pores. The experiments are carried out such that the effects of coalescence and gas flow induced turbulence on bubble size distribution is minimised. It is therefore expected that the observed size distribution corresponds to that actually generated on the sparger surface.

Axial distribution of gas holdup was measured by static pressure difference and a void sensor in a square bubble column. There were three regions - the entrance region, the bulk region and the foam layer - in the bubble column. e e , gas holdup in the entrance region, was almost zero and e b , gas holdup in the bulk region, was axially constant. Gas holdup in the foam layer increased with height above the gas spargers. The clear liquid height and kind of gas sparger had no influence on the form of the axial distribution of static pressure and gas holdup. The thickness of the foam layer and the entrance region was correlated. The effect of the foam layer on the gas holdup was large and was correlated.

Gas holdup in highly viscous fluid in two phase spouted bed operated continuously with respect to the gas flow and batchwise with respect to the liquid was investigated using bed expansion technique. Experiments were carried out in three cylindrical spouted beds having diameters of 74 mm, 114 mm and 144 mm and height of 1000 mm under the conditions of superficial gas velocities between 0.0018 m·s–1 and 0.29 m·s–1, liquid viscosities between 0.063 Pa·s and 0.320 Pa·s, six static bed heights of 0.12 m, 0.18 m, 0.24 m, 0.30 m, 0.36 m and 0.48 m, surface tension between 0.0248 N·m–1 and 0.035 N·m–1 and density between 906 kg·m–3 to 928 kg· m–3 using a single nozzle sparger of 10.0 mm diameter. A correlation for the gas holdup was presented, with maximum deviation of 9%. This correlation was compared with those available in the literature.

Production of hydrogen peroxide by electroreduction of oxygen in alkaline solutions was experimentally carried out using a packed-bed electrode of graphite particles or graphite felts. Oxygen sparging into the bed was found to increase overall yield of hydrogen peroxide for a one-pass operation because of the increase in concentration of dissolved oxygen. The current efficiency decreased with increasing concentration of hydrogen peroxide. Effects of packing materials, sparging rate of oxygen and operational conditions on production rate were analysed by measuring potential distribution within the bed. The production rate for the electrolysis using graphite felts was found to be larger than that using graphite particles. The felt cathode had a large electrode surface area and a large volumetric ratio of gas to electrolyte, which might enhance the mass transfer rate of dissolving oxygen. The consumption of electric power for producing hydrogen peroxide was found to range from 2 to 6 kWh·kg–1-H2O2 in the packed-bed electrode with graphite felts.

We experimentally investigated the effects of multiple draft tubes with perforated plates on gas holdup and volumetric mass transfer coefficient in a bubble column with a single-hole sparger as a gas distributor

Experiments were carried out on bubble stripping of aqueous solutions of five organic solutes and oxygen dissolved at initial concentrations ranging from 0.008 to 0.04kg⋅m-3. Little interaction was found to exist among the solutes, as far as gas holdup and overall volumetric mass transfer coefficients at low concentrations are concerned. The liquid-side and gas-side volumetric mass transfer coefficients were obtained from measured overall coefficients. Correlations for the liquid-side volumetric mass transfer coefficients were obtained in terms of liquid-phase diffusivity and gas flow rate for two types of gas spargers: single-nozzle and porous-tube spargers. Correlations for the gas-side volumetric mass transfer coefficients were also obtained for these spargers.

Flow characteristics of the downflow bubble column with a simultaneous gas-liquid injection nozzle were experimentally investigated. The flow pattern was observed and ranges of stable cocurrent downflow operation were examined. Gas holdup and specific gas-liquid interfacial area were measured. When the simultaneous gas-liquid injection nozzle was used in the downflow bubble column, spouting and calm sections were observed to appear in the column. In the spouting section, gas holdup was higher and interfacial area was larger than those in the calm section. In comparison with the results for the perforated sparger, the bubble diameter was smaller and the range of stable cocurrent downflow operation was wider. In addition, it was found that, under a specified condition, the gas holdup was lower and the interfacial area was larger than those in the case of the perforated sparger, and that such differences became more marked with decreasing nozzle diameter and with increasing liquid velocity.

The flow transition from uniform bubbling regime to liquid circulation regime was studied in a vertical two-dimensional bubble column with no net liquid flow. A regular two-loop liquid circulation was observed to occur as a result of violent interactions of unsteady liquid circulation and large bubbles. A critical superficial gas velocity was defined as the velocity at the point of incipient regular circulation and was obtained from the gas velocity at maximum gas hold-up. Under a uniform stable gas distribution the critical gas velocity depends on the ungassed liquid height and is independent of sparger geometry, i.e., the diameter and pitch of holes. When the pressure drop through the sparger is insufficient or inlet gas is distributed in the narrow central region of the sparger, interactions of large-scale liquid motions and large bubbles in the bulk section is suppressed by depleting the growth of large bubbles at the base. This makes the critical gas velocity larger than that under the uniformly sparged condition. A similar dependence of critical gas velocity on ungassed liquid height was confirmed with literature data for three-dimensional bubble columns.