Powder handling typical processes

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. 

For each of these different process steps, we will review the key equipment parameters that affect the flowability of a bulk solid. These typical handling steps serve as good examples to illustrate the concerns with powder handling but virtually any solids handling application analyzed the same way. 

Powder compact n. A molding material in the form of dry, friable pellets prepared by compacting dry-blended mixtures of resin (typically PVC) with plasticizers and other compounding ingredients. The powder compacts are about as easy to handle and process by extrusion as pellets and offer the advantages of lower heat history and somewhat lower cost than equivalent materials in the form of fused pellets. 

An extension of the reduction-chlorination technique described so far, wherein reduction and chlorination occur simultaneously, is a process in which the oxide is first reduced and then chlorinated. This technique is particularly useful for chlorinating minerals which contain silica. The chlorination of silica (Si02) by chlorine, in the presence of carbon, occurs above about 1200 °C. However, the silica present in the silicate minerals readily undergoes chlorination at 800 °C. This reaction is undesirable because large amounts of chlorine are wasted to remove silica as silicon tetrachloride. Silica is, therefore, removed by other methods, as described below, before chlorination. Zircon, a typical silicate mineral, is heated with carbon in an electric furnace to form crude zirconium carbide or carbonitride. During this treatment, the silicon in the mineral escapes as the volatile oxide, silicon monoxide. This vapor, on contact with air, oxidizes to silica, which collects as a fine powder in the furnace off-gas handling system ... 

Heating, ventilation, and air conditioning (HVAC) is a very expensive utility. However, it is essential and serves a variety of purposes. Not only is it important to maintain constant temperature and humidity, it is also important to balance the pressure in the processing areas to minimize cross-contamination opportunities. Dust collection, as mentioned earlier, is very important when handling powders. The dust generated during some processes may be toxic and may pose an explosion hazard. This system is typically very closely associated with the HVAC system. 

---