Effects of the gas/solids distributor on the local and overall solids distribution in a downer reactor

Abstract

In the last few years, the downer has been proposed as a new reactor for gadsolids reactions. Compared to state-ofthe-art riser reactoqthe cocurrent downflow of gas and solids should lead to a more uniform flow structure, close to plug flow. Experimental studies showed, that the gadsolids distributor at the top of the reactor is significantly influencing the flow pattern in a downer reactor. Local information about the solids concentration is indispensable for a thorough characterization of the flow structure in gaslsolids flows. To obtain this information, x-ray computed tomography has been used for the experimental investigations.Ces dernieres annees, la colonne descendante a ete proposee comme nouveau reacteur pour les reactions gaz-solides.Comparativement aux reacteurs a colonnes montantes actuels, l'ecoulement a co-courant descendant de gaz et de solides devrait conduite a une structure d'ecoulement plus uniforme proche de l'ecoulement piston. Les etudes experimentales montrent que le distributeur de gaz et de solides au sommet du reacteur influence de maniere significative le profil d'ecoulement dans les reacteurs a colonne descendante. Des donnees locales sur la concentration de solides sont indispensables pour une caracterisation minutieuse de la structure d'ecoulement dans des ecoulements de gadsolides. Afin d'obtenir cette information, dans les etudes experimentales on a employe la tomographie aux rayons X assistee par ordinateur.

Scaling of a catalytic cracking fluidized bed downer reactor based on computational fluid dynamics simulations

“…The simulation was performed using a commercial CFD package of Ansys-uent V15.0 for modeling the CFB downer reactor. Numerous investigators [39][40][41] found that the ow behaviours in the downer reactor were symmetrical in theta coordinate. Thus, 2D simulation was generally applied for studying ow behavior and/or the performance of the reactive ow in downer reactors.…”

X-ray computer tomography — potential and limitation for the measurement of local solids distribution in circulating fluidized beds

“…The downflow of the downer plant is as well made of stainless steel with an inner diameter of 0.15 m and 8.5 m total height. 1st World Congress on Industrial Process Tomography, Buxton, Greater Manchester, April [14][15][16][17]1999 In order to measure the solids distribution inside both plants with the tomographic system four 0.5 m respectively 0.25 m long plexiglas tube elements are inserted between the stainless steel elements. With plexiglas tube elements instead of stainless steel elements the decrease in intensity only because of tube material is reduced.…”

Gas‐solids flow behavior: CFB riser vs. downer

“…group such as Bai et al, 1991a;Wang et al, 1992 and the Ž University Erlangen-Nurnberg research group Wirth et al, . 1998;Lehner et al, 1999 , which both show rather uniform radial profiles. One small difference is that they consistently observed a small peak near the wall, while we only observed the same in the middle developing portion of the downer.…”