Modelling of flow through porous packing elements of a CO2 absorption tower

[摘要] ENGLISH ABSTRACT: Packed beds are widely used in industry to improve the total contact area between twosubstances in a multiphase process. The process typically involves forced convection ofliquid or gas through either structured or dumped solid packings. Applications of suchmultiphase processes include mass transfer to catalyst particles forming the packed bed andthe adsorption of gases or liquids on the solid packing.An experimental study on the determination of air flow pressure drops over differentpackingmaterialswas carried out at the Telemark University College in Porsgrunn,Norway.The packed bed consisted of a cylindrical column of diameter 0.072m and height 1.5m, filledwith different packingmaterials. Air was pumped vertically upwards through a porous distributorto allow for a uniform inlet pressure. Resulting pressure values were measured atregular height intervals within the bed. Due to the geometric nature of a Raschig ring packingwall effects, namely the combined effects of extra wall shear stress due to the columnsurface and channelling due to packing adjacent to a solid column surface, were assumed tobe negligible.Several mathematical drag models exist for packed beds of granular particles and animportant question arises as to whether they can be generalized in a scientific manner toenhance the accuracy of predicting the drag for different kinds of packing materials. Problemswith the frequently used Ergun equation, which is based on a tubular model for flowbetween granules and then being empirically adjusted, will be discussed. Some theoreticalmodels that improve on the Ergun equation and their correlation with experimental workwill be discussed. It is shown that a particular pore-scale model, that allows for different geometriesand porosities, is superior to the Ergun equation in its predictions. Also importantin the advanced models is the fact that it could take into account anomalies such as deadzones where no fluid transport is present and surfaces that do neither contribute to shearstress nor to interstitial form drag. The overall conclusion is that proper modelling of thedynamical situation present in the packing can provide drag models that can be used withconfidence in a variety of packed bed applications.

[发布机构] Stellenbosch University