Investigation of the Mixing Behaviour in a Spouted Bed Reactor for the Surface Treatment of Metal Powders

Kerstin Held

Research output: ThesisMaster's Thesis


To get the advantages of surface treatment all over a work piece, metal powder with small particle sizes can be treated and isostatically pressed afterwards. This thesis deals with surface treatment via reaction gas in a spouted bed reactor. This procedure already exists and is industrially used. Regarding to the fact that the operation is not working unproblematic, there is a high potential for optimization. Surface treatment of metal powder is connected with many factors, which are in correlation with the reactor and the operation mode, those influence the process productivity and the quality of the treated powder. Zones of packed bed in the system cause an enormous increase in treating time, heating duration and cooling rates. To eliminate these dead zones, investigations concerning the powder characteristics and the mixing behaviour in the reactor were carried out. At first it had to be determined, if the powder characteristics are suitable for a treatment in a spouted bed reactor. For this purpose the particle size distribution, as well as the critical values were investigated. To imitate nearly the same conditions as in the original reactor, a pilot plant with the same geometrical proportions was built. In process the reactor is operated at high temperatures charged with reaction gas. These first investigations were put in execution at room temperature using pressurised air. To observe the mixing behaviour over a certain time, tracer material was applied as indicator. Annealed metal powder was used as tracer material. Because of the colour change, the annealing caused, the tracer material could easily be separated from the original powder. The reactor was filled with tracer above the gas inlet in the spout region. The rest of the reactor was charged with original metal powder. After defined time sequences, samples were taken from the regions where originally no tracer material was filled in. Images of the samples were taken via a stereo microscope and a camera. The analysis of the taken samples was realized by a self programmed MATLAB code, which calculates the fraction of tracer material in the metal powder. The concentration of tracer in the outside regions and the progress of concentration over time gave clear information about the mixing behaviour in the plant. Investigations at room temperature showed ideal mixing after short time. This means that the occurrence of dead zones is primarily caused by the process temperature. This is approved by annealing treatments at operation temperature, where agglomerates were built after a few minutes.
Translated title of the contributionUntersuchung des Mischungsverhaltens in einem Sputed Bed Reaktor zur Oberflächenbehandlung von Metallpulvern
Original languageEnglish
  • Raupenstrauch, Harald, Supervisor (internal)
Award date25 Jun 2010
Publication statusPublished - 2010

Bibliographical note

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  • Spouted Bed Mixing Behaviour Tracer Nitriding

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