(239b) Investigations on Agglomeration in Gas Cyclones

A gas cyclone is generally not suitable for the separation of submicron particles. However, in many experimental studies such fine particles have often been found in the coarse dust fraction. Researchers explain this effect by particle agglomeration, where small particles form larger aggregates which can be separated by a centrifugal force. In the present work the results of experimental and numerical investigations concerning agglomeration of fine dust particles in a cyclone are presented. Samples were taken from the apex region of a 400 mm cyclone. The particles in the extracted purge air flow were separated on a membrane filter and subsequently analysed by light and electron microscopy. Photos of three different types of agglomerates revealed by the analyses are presented. The agglomerates are characterised in terms of their shape and size parameters and in terms of the location in which they appeared. CFD simulations of the separation process in the cyclone were performed. For this, the two phases were calculated in an Eulerian-Lagrangian frame of reference with the commercial cfd code Fluent. For the dispersed phase, the code was extended to incorporate stochastic models from the literature in order to account for wall roughness, particle-particle collision and agglomeration effects. The results of parameter studies with the agglomeration model are presented in terms of grade efficiency curves. Finally, the results of experimental and theoretical investigations are compared. From this comparison a strategy is deduced by which the agglomeration model can be adapted in order to predict agglomeration more reliably in future.