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Presentation was made at AIChE Particle Technology Forum as an Award Lecture.
After a brief review of achievements of fluidization engineering over decades, a discussion is made on one of the latest issues for applications in material industries as well as for the improvements in reliability of many fluidization processes, i.e., granulation and defluidization issues.
For a long period, phenomena associated with agglomerating fluidization have been treated with complete empiricism and scientific lights were shed seldom on them. It was, however, natural because the basic intention of fluidization has long been the better gas and solid contacting and, accordingly, agglomeration has been only one of unwanted side effects, which, once technically avoided, tend to be forgotten. At the same time, knowledge on elementary processes that should be relevant to agglomerating fluidization, e.g., bubble characteristics, forces acting among fluidized particles, surface characteristics of solids etc., was only gradually established during the last decades.
Defluidization/agglomeration issues are, however, quite significant in a majority of fluidization processes probably except for gas-to-gas catalytic processes. In polyolefin processes agglomeration due to softening of plastic particles in local hot spots should be avoided. In a polyolefin reactor it has been confirmed by a DEM simulation of Kaneko et al. (1998) that a stable solid circulation does not help removing the heat of polymerization. Instead, a solid motion induced by the always-fluctuating bubbling action is necessary as shown in Fig. 3.
Ash melting and agglomeration, which finally causes defluidization, limits the operating temperature and pressure of pressurized fluidized bed combustion (PFBC) or gasification (PFBG). Figure 4 shows the so-called "sinter eggs" formed in a FBC boiler that is close to those found in AEP Tidd PFBC. Sinter egg/grain formation is again experienced recently in a commercial scale PFBC in Japan.