Size enlargement products

FlaSi Drying Special designs of pneumatic-conveyor dryers, described in Sec. 17 can handle niter and centrifuge cakes and other sticlty or pasty feeds to yield granular size-enlarged products. The dry product is recycled and mixed with fresh, cohesive feed, followed by disintegration and dispersion of the mixed feed in the drying-air stream. 

Table 1 Objectives of Size Enlargement Production of a useful structural form...

Classification of size enlargement methods reveals two distinct categories (8,39). The first is forming-type processes in which the shape, dimensions, composition, and density of the individual larger pieces formed from finely divided materials are of importance. The second is those processes in which creation of a coarse granular material from fines is the objective, and the characteristics of the individual agglomerates are important only in their effect on the properties of the bulk granular product. 

Pai+icle size enlargement equipment can be classified into several groups, with advantages, disadvantages, and applications summarized in Table 20-36. Comparisons of bed-agitation intensity, compaction pressures, and product bulk density for selected agglomeration processes are highlighted above in Fig. 20-71. 

Spray Drying Detailed descriptions of spray dispersion dryers, together with apphcation, design, and cost information, are given in Sec. 17. Product quality is determined by a number of properties such as particle form, size, flavor, color, and heat stability. Particle size and size distribution, of course, are of greatest interest from the point of view of size enlargement. 

When dihalo-bicyclo[n. 1. OJalkanes are solvolyzed, ring-enlargement products are formed. In fact, this reaction is often the method of choice for the preparation of medium-sized rings. As far as the stereochemical outcome of the reaction is concerned, there are conflicting reports in the literature. Thus a mixture of (E)-and (Z)-2-bromocyclononenols has been obtained by solvolysis of 9,9-dibromo-bicyclo[6.1. OJnonane [169] in earlier reports only the (Z)-diastereomer was mentioned [170], and the solvolysis in aqueous acetone in the presence of silver tosylate apparently provides only the ( )-isomer [171]. 

Nodulizing is another process of size enlargement by fusion. This employs a rotary kiln like those used for cement manufacture. The product is uniform, about 0.5 in. dia, and more dense than sinter. 

A simple approach to specifying a suitable size enlargement method for a given application is by analogy to techniques currently used for similar materials. If a similar material can be identified in the applications summary of Table 1.4 (or in the more detailed information given in later chapters), and if process objectives are similar in terms of agglomerate size, strength, etc., then the methods used for the established product may well be applicable to the new material. 

In this type of equipment, an Archimedean screw is used to pressurize material in a plastic state and force it through a suitable die. This principle is most widely used in molding and forming operations, such as with plastics [22] and structural clay products [9]. These applications are highly specialized and will not be discussed here since they are usually considered to be outside normal size enlargement techniques. 

From the point of view of size enlargement, the property of most interest is, of course, particle size and its distribution. Some of the variables which can be used to increase the size of spray dried products can be summarized ... 

A number of techniques exist whereby solid materials are converted into a liquid form, dispersed as droplets in a second liquid by some suitable means and solidified to a final particulate product. When the starting material is a massive solid, the process is then one of size reduction [17]. When a powder feed is used, size enlargement results. 

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