Pellet formation

Operabihty (ie, pellet formation and avoidance of agglomeration and adhesion) during kiln pyrolysis of urea can be improved by low heat rates and peripheral speeds (105), sufficiently high wall temperatures (105,106), radiant heating (107), multiple urea injection ports (106), use of heat transfer fluids (106), recycling 60—90% of the cmde CA to the urea feed to the kilns (105), and prior formation of urea cyanurate (108). 

Ehnayergi H. (1975) Mechanism of pellet formation of Aspergillus niger with an additive. J Ferni Technol 53 722-729. 

Byrne GS, Ward OP, Effect of nutrition on pellet formation by Rhizopus arrhizus, Biotechnol Bioeng 33 912—914, 1989. 

Vecht-Lifshitz SE, Magdassi S, Braun S, Pellet formation and cellular aggregation... 

Fig. 3.12. Approximate capacity of inclined discs of various diameters for pellet formation.

It is usually relatively simple to find the optimum conditions for a single response that does not depend on more than four factors once the coefficients of the model equations have been estimated, provided, of course, that the model is correct. Real problems are usually more complex. In the case of pellet formation, it is not only the yield of pellets that is important but also their shape (how near to spherical), friability, smoothness, and ease of production. The optimum is a combination of all these. 

Those results indicate two st lges of zeolite crystallization in silica pellets formation of small zeolite ZSM-5 crystals (0.025 pm) in the silica mesopores and large zeolite crystals (1-4 pm) in the silica macropores and on the outer surface of silica pellets followed by faster crystallization in the interior of the carriers pellets. At this second stage the mesopores and small zeolite crystals inside them do not grow but the pellets structure fails forming large slabs of amorphous silica with incapsulated zeolite crystals not accessible for adsorption and catalysis. 

The ultrafme powder obtained from the treated samples resisted pellet formation by extrusion. Thus a pellet-pressing method was used. Sample surface properties and their catalytic activities are listed in Table 1. It is evident from the data that a significant improvement in catalytic performance (for example, the selectivity increases by 23%) as compared with spent catalyst (Dl) can be achieved as a result of mechanochemistry, but it is not possible to regain the initial efficiency of the samples (F). 

Pellet formation essentially involves three steps nucleation (consolidation of several grains into a nucleus), transition (joining of several nuclei to form larger entities), and ball growth (growth... 

Burrow and fecal pellet formation alters reaction and solute diffusion geometries, creating a mosaic of biogeochemical microenvironments rather than a vertically stratified distribution (see Chapter 4). 

Ryoo, D. (1999). Fungal fractal morphology of pellet formation in Aspergillus niger. Biotechnol. TechnoL, 13, 33. 

Last, but not least, pellet processing should be mentioned here (Metz and Kossen, 1977 cf. Sect. 5.8.2). Usually investigators consider pellet formation... 

In order to simplify the procedure above, a one-stage technology has been developed together with the fiber producing company Cordenka based on direct feeding of short cut fiber pellets into the extruder [15]. The actual novelty in this respect is presented by the pellets themselves, since pure short cut rayon fibers cannot be fed into the extruder by usual techniques due to their wadding-like structure and thus low bulk density. Therefore, the fibers were coated with a special sizing to provide fiber adherence and pellet formation. 

Figure 10 Particle size distribution of spherical glass filler used in a wide variety of plastic products as an adjunct to the resins prior to pellet formation.

Ghebre-Sellassie I. Mechanism of pellet formation. Ghebre-Sellassie I, ed. Pharmaceutical Pelletization Technology. Vol. 37. New York Marcel Dekker, Inc., 1989 129. 

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