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Granulométrie des suspensions de particules fines par mesures turbidimétriques spectrales. Application à l'étude de la fragmentation des cristaux dans une cuve agitée.

Abstract : The physical, chemical, mechanical and rheological properties of pulverised solids depend considerably on their granular state. This explains the large range of particle size analysis methods which exist today. Due to their design and technology used, most of these techniques require sampling and preparation which can alter the granular state of the sample. An in situ particle size sensor is thus of major interest, as much for the characterisation and on-line control of a process as for obtaining data on a kinetic mechanism. To this aim, we have developed a spectral turbidimetric sensor. Turbidity measurements are taken by a sensor of small dimensions (liked to a spectrophotometer by fibre optics) which can be used in situ. The particle size distribution of a powder in suspension can be theoretically retrieved from its turbidity spectrum. Different algorithms and their corresponding programs have been developed. The interests and limits of turbidimetry as a particle sizing method are discussed with respect to measured and simulated spectra (for monodisperse latex suspensions) and their corresponding calculated particle size distributions (PSD). The range of sensitivity thus determined for diameters of between 0.1 and 10 µm in and for volume fractions lower than 10-3. These constraints limit the method to dilute suspensions. The second part of this work is devoted to the study of the fragmentation of potassium sulphate crystals in an agitated crystallizer. This phenomenon is essential to cristallisation since it is responsible for the formation of most of the nuclei. The aim is two-fold: prove the feasibility of the turbidimetric method to follow a real process in an industrial type reactor (2, 81) and to characterize in situ the nuclei production. Such an on-line study has never been carried out before. The system parameters studied include the agitator rotation speed, the liquid used, and the number and diameter of the grains ("parents") introduced. The increase in turbidity noticed in experiments is due to the production of small fragments which remain in the liquid bulk. The programs described above were used to determine the size of these particles. In ethanol, these micronic fragments are liberated whilst those in an aqueous saturated solution agglomerate. The influence of most of the operating parameters is explained. The turbidity sensor designed and validated by this work has equally been applied with success to the study of other processes which play a role in cristallisation i.e. primary nucleation, secondary nucleation and agglomeration.
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Submitted on : Friday, July 12, 2013 - 2:24:46 PM
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  • HAL Id : tel-00843935, version 1

Citation

George Crawley. Granulométrie des suspensions de particules fines par mesures turbidimétriques spectrales. Application à l'étude de la fragmentation des cristaux dans une cuve agitée.. Génie des procédés. Ecole Nationale Supérieure des Mines de Saint-Etienne, 1994. Français. ⟨NNT : 1994INPG4211⟩. ⟨tel-00843935⟩

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