Mixing of solids

Weidenbaiim, in Drew and Hoopes (eds.). Advances in Chemical Engi-neering, vol. II, Academic, New York, 1958, chap, on mixing of solids. 

Fluid Iron Ore Reduction (FIOR) is a process for reducing ore to iron with a reducing gas in a fluid bed. For thermodynamic efficiency, iron ore reduction requires counter current flow of ore and reducing gas. This is achieved in FIOR in a multiple bed reactor. Precautions are necessary to prevent significant back mixing of solids between beds, since this would destroy counter current staging. 

Weidenbaurn, S. S., Mixing of Solids chapter in Advance in Chemical Ensineerine, Vol. 2, Academic Press, New York, N.Y., 1958. 

Bernard Manowitz, Treatment and Disposal of Wastes in Nuclear Chemical Technology George A. Sofer and Harold C. Weingartner, High Vacuum Technology Theodore Vermeulen, Separation by Adsorption Methods Sherman S. Weidenbaum, Mixing of Solids... 

Manas-Zloczower, I., Dispersive mixing of solid additives, in Mixing and Compounding of Polymers—Theory and Practice. (I. Manas-Zloczower and Z. Tadmor, Ed.) Hanser Publishers, Munich, 1994, pp. 55-83. 

Mixing of Solids Sherman S. Weidenbaum Author Tndex—Subject Index... 

The solids mixing study by injection of tracer particles indicated that the axial mixing of solids in the bubble street is apparently very fast. Radial mixing flux depends primarily on the bubble size, bubble velocity, and bubble frequency, which in turn depend on the size of the jet nozzle employed and the operating jet velocity. 

Figure 2. Diffuse reflectance UV-visible absorption spectra recorded as a function of time after the mixing of solid DPB and H0 57ZSM-5 (a) and after of solid DPB and H6 6ZSM-5 (b)...

A reactor model based on solid particles in BMF may be used for situations in which there is deliberate mixing of the reacting system. An example is that of a fluid-solid system in a well-stirred tank (i.e., a CSTR)-usually referred to as a slurry reactor, since the fluid is normally a liquid (but may also include a gas phase) the system may be semibatch with respect to the solid phase, or may be continuous with respect to all phases (as considered here). Another example involves mixing of solid particles by virtue of the flow of fluid through them an important case is that of a fluidized bed, in which upward flow of fluid through the particles brings about a particular type of behavior. The treatment here is a crude approximation to this case the actual flow pattern and resulting performance in a fluidized bed are more complicated, and are dealt with further in Chapter 23. 

In the mixing of solid particles, the following three mechanisms may be involved ... 

Brothman et al 24 have given an alternative theory for the process of mixing of solid particles, which has been described as a shuffling process. It is proposed that, as mixing takes place, there will be an increasing chance that a sample of a given size intercepts more than one part of the interface, and hence the number of mixed samples will increase... 

There are a number of other reasons for carrying out size reduction. It may, for example, be necessary to break a material into very small particles in order to separate two constituents, especially where one is dispersed in small isolated pockets. In addition, the properties of a material may be considerably influenced by the particle size and, for example, the chemical reactivity of fine particles is greater than that of coarse particles, and the colour and covering power of a pigment is considerably affected by the size of the particles. In addition, far more intimate mixing of solids can be achieved if the particle size is small. 

The bubbles exert a very strong influence on the flow pattern in the bed and provide the mechanisim for the high degree of mixing of solids which occurs. The properties and behaviour of the bubbles are describe later in this Section. 

In addition to the vertical mixing of solids, a degree of horizontal mixing occurs and this is especially important in long, shallow plug flow beds of the type used in fluidized bed drying or freezing (see Chapter 3). 

Effective temperature control of large fixed beds can be difficult because such systems are characterized by a low heat conductivity. Thus in highly exothermic reactions hot spots or moving hot fronts are likely to develop which may ruin the catalyst. In contrast with this, the rapid mixing of solids in fluidized beds allows easily and reliably controlled, practically isothermal, operations. So if operations are to be restricted within a narrow temperature range, either because of the explosive nature of the reaction or because of product distribution considerations, then the fluidized bed is favored. 

The invention of the fluidized bed with its suspended and rapidly mixing solids completely overcame this dangerous situation. This is because the rapid mixing of solids, and the large heat sink (the solids) will only allow the bed temperature to change very slowly, and it can be easily controlled. 

Theodore Vermeulen, Separation by Adsorption Methods Sherman S. Weidenbaum, Mixing of Solids... 

Wiedenbaum SS. Mixing of solids in a twin shell blender. Ceramic Age 1963 (August) 39 3. 

Carley-Macauly KW, Donald MB. The mixing of solids in tumbling mixers-I. Chem Eng Sci 1962 17 493-506. 

Roseman B, Donald MB. Mixing and de-mixing of solid particles part 2 effect of varying the operating conditions of a horizontal drum mixer. Br Chem Eng 1962 7(1) 823. 

Wiedenbaum SS. Mixing of solids, in advances in chemical engineering. In Drew TB, Hoopes JW, eds. New York Academic Press, 1958 209-324. 

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