Solid-Solid Mixing with Static Mixers

Static mixers are in-line devices, which consist of motionless mixing elements, inserted in the given length of the pipe. Homogenization is attained by using the flow energy of the material to be mixed. The mixing effect depends on the continuous separation, distribution, and reunion of particles in the stream of material. There are various element designs available for mixing liquids and they are widely spread for use in industry. For mixing solids there is hardly any industrial usage of static mixer types, therefore, various experiments with solids have been done. The number of elements and their shape required in any application depend on the complexity of the mixing process, more elements being necessary for more complex tasks. Three different types of static mixers were investigated in this paper. The material used was quartz sand of different granulation which was mixed in different mixture ratios. With quartz sand, only the particle size was different, which allowed us to study the countenance of the mixer type and its length to get the best quality mixture, especially when one of the components was in excess. Static mixers have the advantage over other mixers because they are cheaper for use (loss of energy expenses), and they are very easy to install and to clean. To prove their efficiency and to show which of the types used yielded the highest homogeneity, standard statistical methods (standard deviation, variation and mixing indexes) were used as statistical descriptors of the particular mixture. The dynamics of mixing were tested by continuous sampling, and by the flowability of the material for different mixture types. The results of experiments were mathematically calculated to obtain the necessary data for each specific design. The length of the pipe, the shape and the number of mixing elements, were determined by the mixture quality for each specific mixture type.