Integrated fluidized beds, particle

Instantisation, in which the fluidized bed is responsible for a significant change to the structure and size of the granules, should not be confused with the use of an integrated fluidized bed drier immediately following spray drying. There are many descriptions in the literature of such processes a recent example of a novel application of this technique (Jha et al, 2002) is in the production of a shelf-stable powdered kheer mix, an Indian dessert which consists of a sweetened mixture of cooked partially concentrated milk and rice flour. This is spray dried, the particles are then dried in a fluidized bed and finally dry blended with sugar. 

With knowledge of the parameters influencing the particle size distribution of spray dried powders, and process cperience with different products, new spray dryers with, for example, integrated fluidized beds are developed. Production of almost dust-free powders is now possible [5.110]. 

Fig. 6.19 SEM picture of agglomerated full milk particle obtained from integrated fluidized bed (FSD-System, by courtesy of CEA Niro Process Engineering, S0borg, Denmark).

Despite these potential problems, remarkably little work has been published on particle degradation in pneumatic conveying systems. That may be explained by experimental problems that are even much more serious than with fluidized beds. According to the different problems mentioned above, there are more individual measurement techniques and assessment procedures required than with fluidized bed attrition. Usually, the assessment is restricted to the comparison of the particle size distribution before and after conveying. Moreover, there is no steady-state attrition that could be measured. It is only possible to measure an integrated value, which... 

When we are interested in the reproducible preparation of metal-supported catalysts it is also necessary to integrate the mesoscopic scale. Indeed, the deposit needs to be homogeneous, with particles anchored not only on all the support grains but also in their porosity. The use of CVD-fluidized bed reactors, for which we have gained some experience [85, 86], is one of the most elegant ways to master a process that fulfils these requirements under relatively mild conditions. 

Qian, G., and Li, J. Particle-Velocity Measurement in CFB with an Integrated Probe, in "Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 320-325. Somerset, Pennsylvania (1993). 

The integral model is a development of a simple scale-up model which allows for mixing and residence time effects, first suggested for fluidized beds by Vanecek et al. (1964, 1966). The mean outlet moisture content is given by summing the product of the particle moisture content and the probability that it emerges at time t ... 

Jprgensen V (2007) Numerical investigation of integrated reactor/separator designs for precombustion with carbondioxide capture. MSc Thesis, the Norwegian University of Science and Technology, Trondheim Jones DRM, Davidson JF (1965) The Plow of Particles from a Fluidized Bed through an Orifice. Rheol Acta 4(3) 180-192... 

In practice, the output from the capacitance circuit can be sent to an integrating DVM or suitable filter to smooth out fluctuations in the signal from the fluidized bed. Calibration of the probe for gas-solid suspensions can be carried out at the extreme points of either an empty or packed bed where the voidage (Xd is know or can be calculated. Intermediate calibration points can be found by expanding a powder in a gas fluidized bed. Larger bed expansions (e.g. 10 %) are most readily obtained using small particles (< 100 pm). For liquid-solid suspensions, both fluidization and sedimentation can be utilized as techniques for calibration. 

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