Pyrohydrolyse eisenchloridhaltiger Lösungen in Sprühröstreaktoren (English shop)

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This thesis addresses the spray roasting process as a regeneration process for pickling solutions containing iron chloride. Hydrochloric acid is frequently used for treating scaled metal surfaces, removing iron oxide layers. The solution, which becomes increasingly saturated with iron chloride over the course of this process, is subsequently regenerated so that the hydrochloric acid can be returned to the pickling process. Regeneration is carried out by injecting the saturated solution into a combustion chamber typically heated with natural gas. In the process, iron oxide (Fe2O3) is formed as a by-product. Depending on its properties, this by-product can also be used commercially, thus leading to a further cost optimisation of the production process. To date, only few details of particle formation during the spray roasting of iron chloride-containing solutions are known. These are, however, necessary in order to optimise the design of industrial plants.

The focus of this work lies on the experimental and numerical investigation of the iron oxide particles formed. For this purpose, a laminar drop tube reactor was built on a laboratory scale, in which monodisperse droplets of an iron chloride solution were roasted under typical conditions. The solid samples thus obtained were investigated with respect to particle morphology, surface structure and mineral phase composition, which permitted a characterisation and evaluation of the roasting process. The laboratory experiments yielded results that could be used to optimise a model for the numerical simulation of industrial plants. The model represents the particle formation process in a simplified manner, but includes characteristic features of particle formation as well as of the reaction kinetics.

Industrial spray roasting reactors are large-volume plants in which a turbulent, rotating hot gas flow prevails, into which the iron chloride solution is injected. Owing to the complex flow conditions and the droplet size distribution after injection, which spans more than one order of magnitude, an experimental investigation of particle formation in these plants is only possible to a limited extent. The model developed using data from the laboratory experiments could be employed to determine, by means of CFD simulations, the influence of different operating conditions on the properties of the iron oxide particles. Furthermore, the simulations were able to provide information on the flow conditions in large-scale industrial plants. The results lead to an extended understanding of the processes in spray roasting reactors and form a basis for the further optimisation of the process by means of numerical simulations.