Identification of the physical phenomena involved during thermally assisted mechanical dewatering by pore pressure measurement
Identification des mécanismes mis en jeu lors de la déshydratation assistée thermiquement par suivi de la pression de pores
Résumé
In the scope of thermally assisted mechanical dewatering process, this work focuses on the identification of physical mechanisms involved in the thermally assisted mechanical dewatering. Operating conditions ensure that the water is expelled in liquid phase. An experimental study on talc and cellulose saturated suspensions highlights the gains in terms of final dry solid contend involved by the thermal intensification. The filtrationcompression test cell is instrumented with pore liquid sensors along the cake thickness that allows to measures the pressure of the interstitial liquid phase. Obtained data highlight an increase of the liquid pressure in the heated side of the cake during thermally assisted mechanical dewatering. Indeed, as the temperature increases the water density decrease. As the cake consolidation restricts the flow a liquid pressure gradient reappears inside the cake. As the temperatures on the filter side of the cake increase, the thermally induced liquid pressure gradient vanishes with an additional filtrate outflow. In order to measure the porous media properties a compression-permeability cell has been build. This apparatus allows permeability measurement to be conducted for different temperature and loading on the porous media. A physical model including the thermal pressurization has been implemented in COMSOL Multiphysics in order to simulate the process. The model confirms the thermal pressurization occurring during thermally assisted mechanical dewatering, but because of deviation in the calculated mechanical behavior and temperature of the porous media, the model can’t depict the experimental additional filtrate outflow.
Ce travail s’intéresse à l’identification des mécanismes physiques en jeu lors de la déshydratation assistée thermiquement. Une cellule de filtration/compression a été instrumentée avec des capteurs de pression liquide. Ces mesures permettent de suivre la formation du gâteau de filtration, sa consolidation puis les évolutions thermomécaniques induites par l’apport de chaleur. Sous l’effet du chauffage, elles montrent l’apparition d’un gradient de pression liquide, qui induit un écoulement additionnel. Un modèle mathématique est ensuite proposé. Des caractérisations en cellule de compression/perméabilité sont utilisées pour déterminer les lois d’évolution des propriétés du milieu poreux. Le modèle permet de retrouver les évolutions des grandeurs macroscopiques et locales mais pas les cinétiques. Ceci a été attribué au modèle de déformation du milieuporeux choisi.
Origine : Version validée par le jury (STAR)