Investigation of the industrial NH3 oxidation by CFD simulations including detailed surface kinetics

• Main Author: Wiser, Artur
• Format: Others
• Language: en
• Published: 2020
• Online Access: https://tuprints.ulb.tu-darmstadt.de/17208/25/202000907_Dissertation_Artur_Wiser_doppelseitig_druck.pdf; Wiser, Artur <http://tuprints.ulb.tu-darmstadt.de/view/person/Wiser=3AArtur=3A=3A.html> (2020): Investigation of the industrial NH3 oxidation by CFD simulations including detailed surface kinetics. (Publisher's Version)Darmstadt, Technische Universität, DOI: 10.25534/tuprints-00017208 <https://doi.org/10.25534/tuprints-00017208>, [Ph.D. Thesis]

In the Ostwald process ammonia is catalytically oxidized to NO at short contact times on platinum/rhodium gauzes. Besides NO as main product, N2 and N2O are also produced. Especially the formation of N2O is critical because of its large environmental influence as greenhouse gas. This work describes a modelling approach where a mechanistic model of ammonia oxidation on platinum previously published by Kraehnert and Baerns was implemented in a CFD simulation using the rate mapping approach. Three main application fields for this modelling approach have been handled in this work and the following has been found: • Geometry influence on the process performance of the catalytic gauze The design of catalyst geometries can be improved using the knowledge which has been acquired by CFD simulations with included detailed kinetics. The geometry of the gauzes can be designed avoiding the area with “hot spot” mass transfer coefficients and increased N2O production. Furthermore, using the CFD simulations, the prototype for the geometry can be modeled and tested “in silico” without producing a large number of test samples. This will reduce the costs needed for the design process and the time to market for a new catalysts geometry. • Influence of the catalyst surface restructuring on the process performance It has been shown that the selectivity on the restructured surface are not uniform. The cauliflower excrescences are much stronger involved in the ongoing reaction and produce the largest amount of N2O. • CFD modelling of the laboratory scale reactor including complex chemistry on the wire gauzes. It was found that the existing reactor has very strong wall effects, which influence the production rates of NO and N2O. The heat loss of the catalyst to the wall has a significant impact. Due to a large catalyst area with a low temperature, the production of N2O becomes very high.