The quality of mixing of a pulp suspension and chlorine dioxide by a static mixer in an industrial chlorine dioxide bleaching stage was evaluated using electrical resistance tomography (ERT) as a function of process operating conditions, including chemical flow rate, suspension flow rate, and suspension mass concentration. The uniformity was quantified by a mixing index based on the coefficient of variation of the individual conductivity values in each image pixel. An increase in the mixing index, indicating lower mixing quality, was observed when the chemical flow rate increased. In addition, the mixing quality decreased with a decrease in suspension flow rate. On the other hand, a decrease in the suspension mass concentration at a constant volumetric suspension flow rate gave better mixing quality. The results show that ERT can be used to evaluate industrial-scale mixer performance and to monitor the changes in the mixing quality as a function of process operating conditions. The results are in good agreement with those in the literature based on other measurement techniques for similar mixer installations.La qualité de mélange d'une suspension de pâte et d'une solution de ClO2 par un mélangeur statique dans un stade de blanchiment industriel aétéévaluéeà l'aide de la tomographie par résistanceélectrique (ERT) en fonction du processus d'exploitation de conditions, y compris le débit de solution, débit de suspension et la concentration de fibre. L'uniformité aété quantifiée par un indice de mélange basé sur le coefficient de variation des valeurs individuelles de conductivité dans chaque pixel de l'image. Une augmentation de l'indice de mélange, indiquant une qualité inférieure de mélange, aété observée lorsque le débit de solution a augmenté. En outre, la qualité du mélange diminue avec une diminution de la vitesse d'écoulement de suspension. En revanche, une diminution de la concentration de fibre dans la suspensionà un débit constant de suspension volumétrique a donné un mélange de meilleure qualité. Les résultats montrent que l'ERT peutêtre utilisée pourévaluer sur le plan industriel le rendement du mélangeur et pour surveiller la qualité du mélange sous différentes conditions d'exploitation. Les résultats sont en bon accord avec ceux de la littérature basée sur d'autres techniques de mesure pour des installations de mélangeur similaire
Mixing effectiveness was determined experimentally for side jet injection into pipe flow for water and pulp suspensions for a range of fiber mass concentrations (0-3.0%), mainstream velocities (0.5-5.0 m/s), and side-stream velocities (1.0-12.7 m/s). The mixing quality was measured in cross-sectional planes along the pipe using electrical resistance tomography and quantified by a modified mixing index, derived from the coefficient of variation of conductivity. Mixing depended strongly on the flow regime and jet penetration. For turbulent flow, the criteria for in-line jet mixing in water are applicable to the mixing in suspensions, with small differences likely due to differences in fiber network strength and influences of fiber-turbulence interactions in modifying turbulent structures in the bulk. When a suspension flows as a plug, however, the mixing differs greatly from that in water, depending on the fiber network strength in the core of the pipe.
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