Attrition cyclone-produced

Attrition in fluidized bed systems leads primarily to a loss of bed material since the cyclones, which are mostly used for the collection of entrained material, are not able to keep the attrition-produced debris inside the fluidized bed system. The material loss through the cyclone is, therefore, usually taken as the attrition rate. This means that among the attrition modes discussed in Sec. 2, namely fragmentation and abrasion, it is abrasion which is the attrition mode of interest for fluidized bed systems. 

Moreover, not all attrition products will be directly elutriated from the cyclone. Instead, a part will be collected by strands of the material and will be transported via the solids return line into the fluidized bed process. In subsequent passes through the cyclone, the accumulated attrition-produced fines will be elutriated due to the sifting effect of the cyclone. 

Despite Tab. 7.2, powders can be the preferred product form for various applications, due, for example, to their high volume-specific surface area and the resulting high reactivity. Even ultra-fine powders can be produced in spray fluidized beds. For this purpose, one follows Fig. 7.1c. However, the coating is created with the sole purpose of its subsequent in situ destruction by particle-particle collisions. The material created by attrition is now the real product of the process, which is carried out of the fluidized bed by the gas and can be collected in a cyclone or in filter bags. The core particles are carriers for the coating and, simultaneously, the promoters of its destruction, so that they have to be heavy and rigid. Metallic carrier particles can be heated by wall contact or by induction, so that the creation of ultra-fine powder can be combined with its thermal treatment. 

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