Production processes pelletizing

Figure 8.2-7. Comparison of costs of high- and low-pressure processes. Capacity 100,000 t/a, on 1997 prices, production of pellets.

Some creative approaches to try to match the regular demand of a tapioca production process with the irregular supply of feedstock have been taken. Meuser et al.27 demonstrated that starch could be recovered from either cassava chips or pellets, although the starch is obtained at some sacrifice of quality. Nauta28 has proposed large silos for the storage of tapioca starch, similar to those used in the potato processing industry. At present, the primary supply of tapioca starch remains fresh roots. 

As formed, carbon black is a fluffy powder possessing low density. The densification process involves the removal of occluded air by agitation and followed by dry or wet process pelletization. In both the dry and wet pelletization process, nearly spherical pellets or beads will form that are typically composed of >99% carbon black and trace impurities such as sulfur. Thus, carbon black is sold as a low density powder or as a pelleted form in pigmenting and other end uses. The choice of a fluffy or pelleted carbon black for dispersion in a given system depends upon the dispersion and handling equipment and end use. For example, pelleted carbon blacks are used most frequently in production of black masterbatch carbon black powders are typically used to tint chromatic compounds. 

Companies will custom formulate colorant and additive products designed to be used by plastic molders, who will, in turn, produce the final consumer products. The raw materials for colorant and additive products may be in powder, liquid, or solid form. The products formulated from them may also be in powder, liquid, or solid form. Dry color formulations (powder form) currently comprise less than 5% of the total colorant and additive products being produced today. Liquid formulations account for another 5% however, this form of product is increasing in popularity and is expected to capture a larger share of the colorant and additives market in the near future. The solid form, known as concentrates or masterbatch products, are concentrated ingredients encapsulated in a carrier resin that is usually in pellet form. This type of product comprises the overwhelming majority of the formulated products used by molders and compounders today. A discussion of the basic production processes associated with the production of the various colorant and additive product types is presented below. 

The materials used in the production of hot-melt extruded dosage forms must meet the same levels of purity and safety as those used in traditional dosage forms. Most of the compounds used in the production of hot-melt extruded pharmaceuticals have been used in the production of other solid dosage forms such as tablets, pellets, and transdermals. The materials used in hot-melt extruded products must possess some degree of thermal stability in addition to acceptable physical and chemical stability. The thermal stability of each individual compound and the composite mixture should be sufficient to withstand the production process. 

It must be emphasized that the equivalence in costs is based on the assumption that the pyrolysis unit as well as the pellet production is equipped with a steam dryer enabling sales of low-pressure steam. In practice, this is today the situation for several pellet manufacturers, whereas none of the pyrolysis processes has been evaluated with this condition. Hence, if the present pellet production were compared to proposed pyrolysis liquid production, the pellets would be advantageous by some 5-10 USD/MWh (pyrolysis liquid some 5 USD more expensive and the present pellets 5 -10 USD cheaper). 

The problem of UO2 pellet densification under irradiation causes contraction and leads to collapse of the cladding in axial gaps in sections of the fuel columns. The solution is to control the manufacturing process to ensure the production of pellets with higher density and stabilized pore structures (pore size and grain size). Prepressurizing the fuel rod with helium also avoids clad flattening,... 

Basic process steps in the production of ROEMMC fuel pellets are DRYING of the wet raw material, SIZE REDUCTION of the dry material, and DENSIFICATION of the dry, fine material. The thermal energy for the drying process is derived from the combustion of fines separated from the dry, fine material. The only external energy input to the production of pellets is electrical. The hardware embodiment of these processes is described in these paragraphs, as employed in the Stillwater, Minnesota, plant. This plant was designed to have an output production rate of 150 tons per day, continuous operation. 

Intraparticle mass transfer. For some practical situations mass transfer limiting step is localized in the interior of a solid phase. This is the case for certain mycelial fermentations where the oxygen transfer via pellet or mycelial clump interior may limit growth or production processes. This situation, employing the effectiveness concept, is reviewed by Moo-Young and Blanch (lA). In the following, some other elementary phenomena and processes connected with mass transfer are reviewed. 

Mineral impurities come from quench and pelletization steps in the carbon black production process. As presented before, the decrease in temperature of carbon black and exhaust gases is mainly obtained by injection of a great mass of water. Additional water is also added to carbon black during pelletization. Even if this water is purified, the remaining mineral salts precipitate onto the carbon black surface and, because of the high temperature, are reduced to basic salts. Mineral impurities of carbon blacks can easily be extracted by solubilization in water, as in the so-called pH of carbon black, in which carbon black is suspended in water and the pH then filtered and the pH of the filtered water measured. Mineral impurities don t seem to alter carbon black reinforcement properties but they have a significant effect on vulcanization speed, which increases with the pH value of carbon black. 

This observation allows us to believe that acidic groups on carbon blacks are mainly produced by surface oxidation in the production process, probably during drying following pelletization. Therefore, acidic groups could be considered an alteration of carbon black surface. 

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