Agitator Blade Research Articles

Development of sorbent manufacturing technology by Agitation Fluidized Bed Granulator (AFBG)

Thousands of ppmv of hydrogen sulfide included in coal gas should be reduced to less than a hundred ppmv in the case of IGCC to prevent a gas turbine from being corroded, and few ppmv to prevent the performance of electrodes from declining in the case of MCFC. In the present paper a laboratory scale AEBG (Agitation Fluidized Bed Granulator) is made and improved. The sorbent for the removal of hydrogen sulfide is produced using an agitation fluidized bed granulator (ZnO 1.5 mole+TiO2 l.0mole+bentonite 5.0 wt%). The techniques for fluidizing fine particles, classified in Geldart C group, in a fluidized bed are developed by installing an agitator blade in a fluidized bed granulator. The fine particles are fluidized and granulated successfully by using the techniques. Statistical, spectral and chaos analyses with granulated sorbent (100-300 Μm) are performed to investigate the hydrodynamics of granulates in a fluidized bed. The average absolute deviation, power spectral density functions, phase space trajectories, and Kolmogorov entropy obtained from pressure fluctuation are plotted as a function of fluidizing velocity. It is shown that the Kolmogorov entropy implying the rate of generation of information can be applied to the control of fluidization regimes.

A method for process monitoring and determination of operational end-point of consumption in agitation granulation

Power consumption was measured and analyzed in order to develop a new method for process monitoring and controlling granule growth by wet granulation in a high speed mixer. It was shown that the power spectral density function obtained by fast Fourier transform analysis of power consumption had two patterns of peaks. The effects of the operational variables on the frequency of these peaks and on behavior of these peaks at every moment of granulation were investigated. It was found that the principal peak was specific to the granulation and had its origin in the collision of the granule particles with the agitator blade. The other peaks, however, were judged to be caused by the electrical characteristics of the motor drive and irrelevant to the granulation. Quantitative relations between the change in the intensity of the specific peak and the granule growth were investigated to demonstrate that the process monitoring and control of the granule growth could be realized by tracing the behavior of the specific peak. Determination of the operational end-point by means of this method was also discussed.

Scale-Up of Agitation Fluidized Bed Granulation. III. Effects of Powder Feed Weight and Blade Angle on Granule Size, Density and Shape.

This paper presents the experimental results of a study on the scale-up characteristics of granule comopaction and sphericity in an agitation fluidized bed granulation. A pharmaceutical standard formulation was granulated using agitation fluidized bed of three sizes (vessel diameter : 125, 230, 500 mm). The effects of powder feed weight and agitator blade angle on the granule properties of size, density and shape were studied. It was found that granules were compressed and made spherical with an increase in agitator blade angle and vessel scale, while they were not influenced by the powder feed ratio.

Application of fuzzy logic to bed height control in agitation-fluidized bed granulation

Development of a new technique for producing spherical and well-compacted granules, and the application of fuzzy control to a fluidized bed granulation process are described. An agitation-fluidized bed, a type of fluidized bed equipped with an agitator blade, was used for granulation; bed height was controlled by fuzzy logic based on a linguistic algorithm employing IF—THEN rules, to maintain a constant bed height and impart effective agitation to the granules. It was shown that bed height control was effective in preventing defluidization and channeling, and was necessary for automatic operation. The effects of bed height and agitator rotational speed on granule properties, such as apparent density, and on granule shape were investigated. A new technique is proposed for utilizing bed height control to produce spherical and well-compacted granules, which cannot be done using conventional fluidized bed techniques.

Determination of end-point with a complex granulation applying infrared moisture sensor.

A granulation experiment was conducted in a complex granulator, which was fluidized bed equipped with an agitator blade. An infrared moisture sensor was used to feed back control the moisture content of the granule particles.Granule properties (mean particle diameter, geometric standard deviation, yield, apparent density and appearance shape) were examined to know the mechanism and the process of moisture feed back control of the complex granulation.To clear up the factors which determine the mean particle diameter of the granules, the influence of the liquid (binder solution) flow rate, inlet temperature and moisture content were examined to get an experimental equation which expressed the mean particle diameter of the granules. The influence of the moisture content and the rotation speed of the agitator blade on the apparent density was also investigated to get an experimental equation. With the basis of both equations, we established a system which can control the granule mean particle diameter and apparent density using a personal computer, and in addition, a self control system from granulation to drying using an infrared moisture sensor.

Modelling mass transfer and agitator performance in multiturbine fermentors

A methodology for mathematically analyzing agitator performance and mass transfer in large multiturbine production fermentors is presented. The application of this approach provides a method for determining axial dissolved oxygen profiles under conditions of known mass transfer rates as a function of agitation-aeration characteristics. A stagewise approach is used which divides the fermentor into a series of mixing cells. This allows for each turbine and mixing cell to be individually optimized. The model also permits the determination of the mass transfer coefficient for each turbine based upon limited dissolved oxygen data. The primary limitation of this approach rests in the limited data and correlations available for multiturbine systems. The structure of the modelling approach can serve as a basis for testing single turbine correlations and adapting them to multiturbine systems. The step-by-step details of the mathematical analysis are presented and interpreted. A series of computer simulations demonstrate the effect of typical fermentor operating variables on the axial dissolved oxygen profile. Further simulations demonstrate the effect of modifying agitator blade numbers on the dissolved oxygen profile and agitator power requirement.

Distribution of Pressure and Velocity on the Surface of Agitator Blade

Distribution of Pressure and Velocity on the Surface of Agitator Blade

TOMOGRAPHIC OBSERVATIONS OF THE FLOW AROUND AGITATOR IMPELLER

To make clear the local flow around each blade of an agitator, tomographic observations and measurements were carried out with a rotating camera and a plane-light source. As the result, the profiles of local flow around an impeller look like a saw-tooth wave from a rotating coordinate projected on a horizontal plane, while the profiles of flow along top and bottom sides of each blade seems to be a pair of helicoids. Two flow models, named vorfex seef model and single vortex model are proposed to explain the action of agitator blade and the flow characteristics near the impeller.