Kinetics and Deactivation of the NO Reduction by CO on Pt-Supported Catalysts

A modified steam-jet agglomerator employing an adjustable system of two oblong, slit-shaped steam nozzles is presented. Nozzle position and steam flow towards the powder curtain were optimized by judging the size of the agglomerates produced. Wetting the feed material, which mainly consisted of dry agglomerates, had to occur with as little turbulence as possible to give best results. The dry agglomerates, which develop under the influence of ubiquitous attractive forces during feeding, often already possess properties required in instant products while being very fragile. Only thorough wetting and subsequent drying in the steam-jet agglomerator provide the required stability. Here, further size enlargement by agglomeration occurs. The results presented here were mainly derived from experiments with powdered saccharides as main powder component. These materials are fully water-soluble and quickly develop viscous liquid layers when wetted on the surface. Theparticle sizedistributionof the dry agglomerates could be measuredforrealisticfeedratesusinganimageanalysismethod. It could be shown that the dry agglomeration was the major size enlargement step. Among other methods, low-pressure roller compactionandvibrationfeedingwereusedforfeedingandpreagglomerating the powders. The porosity of the final agglomerates was in a range suitable for instant products at e» 0.45 to 0.6. Under certain premises, kinematic agglomeration of the particles can be described by a model. Prior to model calculations, the condition for adherence of colliding particles hadtobedeterminedbyabasicexperiment.Discretepopulation balance simulations were then performed for various operating conditions and step responses to changes in the properties of the feed material were calculated, which confirmed the assumption of a typical start-up time in the order of 2 s. The calculations showed that a wide particle size distribution of the feed material furtherssizeenlargementbyagglomeration.Measurementsand calculationsoftheagglomerationeffectwereingoodagreement.