EXPERIMENTAL STUDY OF A TWO-IMPINGING-JET MIXING DEVICE FOR APPLICATION IN PRECIPITATION PROCESSES

摘要

The ability of a Two-Impinging-Jet (TIJ) mixer, immersed in a stirred tank reactor, torncontrol the nucleation stage in precipitation processes is investigated. The mixingrnprocess induces by the TIJ mixer displays two aspects: the mixing of the feed streamsrntogether and their dilution in the surrounding fluid which is, in comparison to the feedrnstreams, highly diluted. Firstly, it is showed that the mixer provides short mixingrntimes, up to 2 ms. Besides, two cases are pointed out: the closely spaced jets (L/do￡5)rnand the widely spaced jets (L/do310). Application to the precipitation of bariumrnsulphate proves that, at relatively high levels of supersaturation (supersaturation ratiosrnof 3000 and 4000, expressed in concentration), the nucleation process can berncompletely controlled by the TIJ mixer. In this case, not only the nucleation, but thernwhole process of precipitation (nucleation and growth) takes place in the TIJ mixerrnzone. In addition, it is found that external stirring has no influence on the nucleationrnprocess, what indicates that it takes place in the very near field of the TIJ mixer. It isrnalso showed that widely spaced jets produced less nuclei than closely spaced jets,rnwhat is due to the dilution occurring prior to impingement. The jet velocity, in thernrange 5 to 20 m/s, has no significant influence on the nucleation process.