Resolving gradients in an ammonia oxidation reactor under industrial conditions: A combined experimental and simulation study

The industrial production of nitric acid by the Ostwald process is a major emission source of the potent green-house gas nitrous oxide that is formed during the catalytic oxidation of ammonia. A systematic knowledge-based optimization of industrial ammonia oxidation, e.g. with respect to minimizing nitrous oxide formation, is hindered by the limited fundamental process understanding resulting from a lack of experimental insight into the reaction at industrial conditions. Here we bridge this gap of knowledge by resolving concentration and temperature profiles in a bench-scale reactor setup under industrial conditions using capillary profile measurements in combination with detailed CFD simulations. The profile measurement technique has a spatial resolution sufficient to resolve the steep gradients around single catalyst gauze wires. The influence of the sampling orifice diameter and reaction conditions on the sampling region and the resulting spatial resolution is discussed. The importance of the sampling orifice to gauze positioning in order to measure well averaged concentration profiles is shown. A comparison of simulated and experimental profiles demonstrates that the most widely used surface mechanism in CFD simulations of ammonia oxidation, the Kraehnert and Baerns model, shows the correct trends but cannot capture the product distribution quantitatively. The approach presented in this article provides detailed experimental insight into ammonia oxidation under industrial conditions required to develop and validate future kinetic models for knowledge-based optimization of industrial ammonia oxidation.

Subjects

Ammonia oxidation

CFD simulations

Gauze catalyst

Ostwald process

Platinum

Spatial profile measurements

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Resolving gradients in an ammonia oxidation reactor under industrial conditions: A combined experimental and simulation study