Turbine Agitator Research Articles

Agitation Effects in Emulsion Copolymerization of n‐Butyl Methacrylate and N‐Methylol Acrylamide

The effects of agitation in emulsion copolymerization have been studied using a semibatch emulsion copolymerization recipe that gave a latex with ca. 44 wt% solids. The two‐stage polymerization process consisted of an in situ seed‐formation step followed by copolymerization of the continuously added n‐butyl methacrylate and N‐methylol acrylamide monomers under monomer‐starved conditions. A 2‐dm3 glass reactor and Rushton turbine agitators of different diameters (4, 6 and 8 cm) were used in the study. Agitation influenced the particle number at the end of the seed stage. This influenced properties like latex viscosity, the amount of water‐soluble polymer, and the particle size in the final latex. Analysis of the water‐soluble polymer using NMR spectroscopy showed that it was mostly a homopolymer of N‐methylol acrylamide. With the 4 cm diameter agitator, the mixing of the pseudoplastic latex was poor during the feed stage. Formation of a zone of poor mixing could be observed on top of the fluid in the reactor, when the monodisperse particles in the latex formed an iridescent structure. Poor emulsification of the added n‐butyl methacrylate monomer resulted in a greater amount of water‐soluble polymer.

Mixing in industrial Rushton turbine-agitated reactors under aerated conditions

A new method of estimating the mixing time in industrial Rushton turbine-agitated reactors under aerated conditions is presented—called the analogy mixing-time model. It is based on the hypothesis of the analogy at the same turbine agitation speed between the mixing time in single liquid phase and that in two gas–liquid phases. This assumption is validated for production tanks equipped with two, three and four Rushton impellers. Furthermore, it is demonstrated that the internal geometry of the reactor, the number of impellers, the distance between impellers, etc., and the degree of homogeneity do not affect the model. Only the location at which the pulse is injected is found to influence the sensitivity coefficient β. This result thus makes the analogy mixing-time model very useful in determining agitation parameters in production stirred reactor. The physical mechanisms behind the model are clarified with general gas–liquid flow patterns described in the literature. The study is completed by the description of the formation of concentration gradients in one of the reactors studied (12 m 3 reactor). The effects of aeration on gradient formation are clarified with both bulk and impeller region injections. The results obtained are used for the design of a scaled-down reactor that mimics the environment created in the tank.

Effect of Stirring Devices on the Intensification of Gas-Fluid Processes

A comparative analysis is made of the operation of apparatus of rotary-pulsation and ejector types with self-suction turbine agitator. The dependence of the efficiency of operation on the output capacity and energy-related characteristics determining power consumption for agitation of gas-fluid mixtures were determined experimentally.

A study on the instability of coherent mixing structures in a continuously stirred tank

Mixing of an inert marker added to the bulk region of a Rushton-turbine-agitated reactor was investigated by planar laser-induced fluorescence. The effect of the turbine agitation speed on the mixing process was initially studied statistically. Average concentration fields, calculated at several sections of the reactor, revealed the general spreading of the contaminant. This approach, however, was found to be unsatisfactory in studying the mechanisms of macro-mixing in the reactor because of the strong intermittence in the flow. Therefore, the concentration data were analysed using conditional techniques, namely the dynamic structural concept, so as to identify the presence of coherent mixing structures and characterise them in space. Instability patterns were observed with increasing turbine agitation speed from 0.3 to 0.7 W/m 3 . Using geometrical concepts, the mechanisms of this spatial instability were further described. General conclusions on the spreading of the contaminant were drawn on the basis of the flow instability with respect to transport by convection and diffusion phenomena.

Improvement of oxygen transfer coefficient duringPenicillium canescens culture

To improve xylanase productivity from Penicillium canescens 10-10c culture, an optimization of oxygen supply is required. Because the strain is sensitive to shear forces, leading to lower xylanase productivity as to morphological alteration, vigorous mixing is not desired. The influence of turbine design, agitation speed, and air flow rate on K1a (global mass transfer coefficient, h(-1)) and enzyme production is discussed. K1a values increased with agitation speed and air flow rate, whatever the impeller, in our assay conditions. Agitation had more influence on K1a values than air flow, when a disk-mounted blade's impeller (DT) is used; an opposite result was obtained with a hub-mounted pitched blade's impeller (PBT). Xylanase production appeared as a function of specific power (W/m3), and an optimum was found in 20 and 100 L STRs fitted with DT impellers. On the other hand, the use of a hub-mounted pitched blade impeller (PBT8), instead of a disk-mounted blade impeller (DT4), reduced the lag time of hemicellulase production and increased xylanase productivity 1.3-fold.

Studies on transfer processes in mixing vessels: effect of gas on solid-liquid hydrodynamics using modified Rushton turbine agitators

The effect of gas on solid-liquid hydrodynamics in mixing vessels was studied to determine the agitation speed required to just completely suspend all the particles under gassed conditions, Njsg and by measurement of the power consumption associated with this agitation speed.

Studies on transfer processes in mixing vessels: effect of particles on gas-liquid hydrodynamics using modified Rushton turbine agitators

The work presents the effect of solid particles having a mean diameter between 15–1000 μm, on the gas dispersion in a mechanically agitated vessel with standard and modified Rushton turbine agitators positioned singly or doubly on same shaft. For the dispersing and uniform distribution of the three phase (gas-liquid-solid) through the entire vessel section, the modified blade turbines, with the surface fraction of the perforations equal to 0.353, were found to be more efficient, the power consumption being reduced by approximately 50%in comparison with the standard Rushton turbines. The power number in the turbulent mixing of the three phase system is dependent on the aeration rate, the surface fraction of the perforations, the turbine number and the physical and rheological properties of the suspensions.

Studies on transfer processes in mixing vessels: effect of particles on gas-liquid mass transfer using modified Rushton turbine agitators

The effect of suspended inert solid particles on gas-liquid mass transfer has been investigated in the vessels equipped with standard and modified Rushton turbine agitators positioned singly or doubly on same shaft. The relations between the volumetric mass transfer coefficient in various suspensions, specific power consumption and superficial gas velocity were obtained. Mixing with the modified Rushton turbines having the surface fraction of the perforations equal to 0.353, the oxygen transfer efficiency is over 45% higher than that obtained using standard Rushton turbines.

Studies on transfer processes in mixing vessels: power consumption of the modified Rushton turbine agitators in three-phase systems

In this work, the modified blade turbines, with the surface fraction of the perforations equal to 0.353, are used in the study of the relationship between the power consumption in three-phase systems and the superficial gas velocity, mixing intensity, agitator type, solid particles concentration, physical and rheological properties of the suspensions. The power consumption in three-phase mixing with modified turbines, single and double, is approximately 40% smaller than for the standard turbines at the same mixing intensity. The modified blade turbines are simple to manufacture and do not require any modification in electrical motor and drive assemblies.

Suspension of solid particles in turbine agitated contactors

In this present study in liquid-solid contactors using 6-blade (flat) turbine agitators, an attempt has been made to correlate the system parameters useful for scale-up under turbulent agitation conditions, where the power number is constant. A new correlation involving modified Froude number along with the agitation characteristics, is proposed for the estimation of minimum speed required to maintain complete suspension.

Studies on transfer processes in mixing vessels: suspending of solid particles in liquid by modified Rushton turbine agitators

The modified blade turbines are attractive alternatives to the standard Rushton turbine as they do not require any modification in the electrical engine motor and drive assemblies are simple to manufacture and have a reduced power consumption.

Studies on transfer processes in mixing vessels: hydrodynamic of the modified Rushton turbine agitators in gas—liquid dispersions

The modified blade turbines are attractive alternatives to the standard Rushton turbine as they do not require any modification in the electrical engine motor and drive assemblies, are simple to manufacture, have a reduced power consumption and have a greatly increased gas-handling capacity before flooding. The modified blades were obtained through increase in the blade height of the Rushton turbine simultaneously with perforation of the blade surface. The filled surface of the modified blade is equal to the blade surface of the standard Rushton turbine. Power dissipation and hydrodynamic regimes using standard and modified Rushton turbine agitators positioned singly or doubly on the same shaft, in a gas—liquid system, were investigated. The TP3 modified turbine with the surface fraction S G/ S C of the perforation equal to 0.353 is optimum on the basis of the power consumption and of the gas-handling and dispersing capacity.

Studies on transfer processes in mixing vessels: suspending of solid particles in liquid by modified Rushton turbine agitators

Studies on transfer processes in mixing vessels: suspending of solid particles in liquid by modified Rushton turbine agitators

Performance of industrial scale bioreactors with modified RUSHTON turbine agitators

AbstractThe data presented here with respect to the behaviour of industrial scale stirred tank bioreactors equipped with modified RUSHTON turbine agitators in the biosynthesis processes of antibiotics are valid for that case that the power consumption is the same as it is in standard RUSHTON turbine agitators.Each modified RUSHTON turbine agitator was obtained through the variation of the blade surface by adding perforations so that the ratio between the perforation surface area and the full surface area (or the surface fraction of the perforations) is 0.36.In the fermentations of Streptomyces aureofaciens, Streptomyces rimosus and Penicillium chrysogenum producing tetracycline, oxytetracyline and penicillin, respectively, in bioreactors equipped with modified RUSHTON turbine agitators, the relative antibiotic production is increased by more than 30% compared to standard bioreactors.

Mixing of suspensions in tall vessels with a draught tube

Formulae for power consumption and suspension speed calculation were determined experimentally in tall vessels mixed by the turbine agitator with six pitched blades rotating in a draught tube. The advantage of such vessels over standard mixing equipment was established by comparison of the agitator power consumption needed for suspension of solid particles.

The role of air in oil agglomeration of coal at a moderate shear rate

The agglomeration of an aqueous suspension of highly hydrophobic coal particles with heptane or hexadecane was investigated with a laboratory mixing unit equipped with a flat-blade, turbine agitator which produced a moderate shear rate. The ground sample of coal from the No. 2 gas seam in West Virginia was subjected to agglomeration conditions both with and without air present in the closed mixing unit. Although compact, nearly spherical agglomerates were produced both in the presence and absence of air, the rate of agglomeration was much greater, and larger agglomerates were produced with a given amount of oil when air was present. Having air present also improved product quality and recovery. The effect of air was greater with smaller amounts of oil than with larger amounts.

Oxygen transfer efficiency in the biosynthesis of antibiotics in bioreactors with a modified RUSHTON turbine agitator

AbstractIn this work, the oxygen mass transfer efficiency and power consumption in a non‐biological system and an antibiotic biosynthesis process, using a modified RUSHTON turbine agitator, were investigated. It was demonstrated that a simple modification of the blades through the increase of the blade height, simultaneously with the discontinuation of the blade surface, could improve the oxygen transfer efficiency by about 30%.Experiments performed in stirred tank bioreactors with an overall volume of 20 m3, equipped with the modified RUSHTON turbine agitator, showed that the power consumption diminished by a factor of 1.18 to 1.6 during the fermentation processes of Streptomyces erithreus, Streptomyces griseus, Streptomyces noursei, and Nocardia mediaterranei, compared to the witness bioreactor.The use of the modified RUSHTON turbine for the antibiotic biosynthesis process may contribute to the decrease of the overall costs and the obtainment of better productivity, allowing an intensive utilization of power inputs for aeration and agitation.

The role of air in oil agglomeration of coal at a moderate shear rate

Abstract The agglomeration of an aqueous suspension of highly hydrophobic coal particles with heptane or hexadecane was investigated with a laboratory mixing unit equipped with a flat-blade, turbine agitator which produced a moderate shear rate. The ground sample of coal from the No. 2 gas seam in West Virginia was subjected to agglomeration conditions both with and without air present in the closed mixing unit. Although compact, nearly spherical agglomerates were produced both in the presence and absence of air, the rate of agglomeration was much greater, and larger agglomerates were produced with a given amount of oil when air was present. Having air present also improved product quality and recovery. The effect of air was greater with smaller amounts of oil than with larger amounts.

Toward a control of lignin and manganese peroxidases hypersecretion by Phanerochaete chrysosporium in agitated vessels: Evidence of the superiority of pneumatic bioreactors on mechanically agitated bioreactors

Phanerochaete chrysosporium and cultivated both mechanically agitated and pneumatic bioreactors. In the pneumatic devices, the yields of lignin and manganese peroxidases as well as extracellular protein, were considerably increased as compared with mechanically agitated bioreactors. Lignin peroxidase and manganese peroxidase activities as high as 4500 U x L(-1) and 1812 U x L(-1) respectively, were produced in an airlift bioreactor. By using enzyme markers, the secretion pathway and the respiration were shown to be dramatically activated in pneumatic bioreactors. The general metabolism of the fungus, when cultivated in the conventional fermentors, is oriented toward the synthesis of biomass at the expense of the synthesis of peroxidases. The use of pneumatic devices for the production of extracellular peroxidases by P. chrysosporium, avoids shear effects due to turbine agitator in the conventional fermentors, and provides a good example for the production of shear-sensitive metabolites.

Production of an exocellular polymer in a mutant strain ofAchromobacter delicatulus on a new type of stirrer

Rushton’s turbine agitation and aeration systems were compared with the novel fermentation stirrer with respect to optimization of bacterial preparation of the industrial exopolysaccharide biopolymer.