Chemical Engineering Journal 84 (2001) 343–354 Comparison of aerodynamics and mixing mechanisms of three mixers: Oxynator TM gas–gas mixer, KMA and SMI static mixers H. Barru´ e a , A. Karoui a , N. Le Sauze a,∗ , J. Costes a , F. Illy b a Laboratoire de G´ enie Chimique, UMR CNRS 5503, 18 Chemin de La Loge, 31078 Toulouse Cedex 4, France b Air Liquide, Direction Recherche et D´ eveloppement, Centre de Recherche Claude Delorme, 1 Chemin de la Porte des Loges, BP 126, Les Loges en Josas, 78354 Jouy en Josas Cedex, France Received 20 May 2000; accepted 29 November 2000 Abstract In this paper, a new gas–gas mixer, Oxynator, is characterized. The performance of this mixer is compared with two static mixers: Sulzer SMI and Chemineer KMA. In order to study these three gas–gas mixers, first the pressure drop is measured. Secondly, the mixing efficiency is characterized by laser sheet visualizations at the outlet of the mixer. The hydrodynamics and turbulence induced by the mixers are then measured by laser Doppler anemometry (LDA). The purpose of this work is to understand the aerodynamics and the mixing mechanisms of the Oxynator mixer and to compare it with two static mixers. The mixing mechanisms of the Oxynator are very particular. The Oxynator creates eight swirls and a center zone, each zone increasing in space when they go away the injector. The homogeneity is reached when the zones meet and form a single zone. The intensity of turbulence created by this mixer is greater than the turbulence created by the other mixers and the pressure drop is minimum (lower than KMA and equal to SMI). The particularity of this mixer is that there is no impact between the secondary flow and the tube. The influence of flow rate on flow pattern is determined. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Aerodynamics; Oxynator; KMA and SMI static mixers 1. Introduction Chemical plants operation has been improving for 20 years, enhancing energy efficiency, catalyst life, selectivity and yield in order to achieve higher production at lower cost. High selectivity catalysts fully achieve their goal when reactant distribution can be known at their surface. Homo- geneous distribution is preferred as far as operability of equipment is concerned. For a long time gas–gas mixing was considered as a straightforward operation, easy to de- sign and operate. It is now recognized that this operation is not as simple as it might first appear. The general design principles established in the past could be significantly im- proved by taking into account the complex flow structures and the geometry of the various mixing systems. Low viscosity fluid flow is usually turbulent, but not enough to fully eliminate inhomogeneities of concentration or temperature within short lengths of empty pipe when in- jection is standing alone. As an example, from a coaxial ∗ Corresponding author. Tel.: +33-5-61-14-89-62; fax: +33-5-61-14-89-36. E-mail address: lesauze@gch.iut-tlse3.fr (N. Le Sauze). injection device, to obtain a homogeneous mixture, charac- terized by only 1% standard deviation from the mean con- centration, a length of about 100 diameters is needed [1]. Moreover, relatively stable stream layers may be formed if the fluids, especially in the case of gases, exhibit differ- ences in density. Consequently, a long pipe is required to ho- mogenize the fluid (in concentrations and/or temperature). However, short mixing lengths are required when limited space is available. Suitable high efficiency mixing equipment must be developed with particular attention to low pressure drop. Debottlenecking operations with oxygen injection may be one way of improving both process yield and costs, but cata- lyst, other pieces of equipment, and operability range should be addressed: whereas operation may be running smoothly at the new mean oxygen concentration (typically between 22 and 28%), operators may want to assess that there is no local oxygen content peak where specifications are not met any longer. Static mixers, which are commonly used in con- tinuous fluid mixing, often answer to these specifications. Another kind of mixer has been developed by Air Liquide in order to be implemented on an existing compact unit with oxygen injection: the Oxynator TM . It has been designed 1385-8947/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S1385-8947(01)00128-0