Chemical Processing - September 2007 - (Page 43)

Choosing the right device is crucial for successfully handling solids By Tom Blackwood, Healthsite Associates f you want to volunteer for a hopeless job become your company’s expert on solids blending. It’s not that you’ll always be wrong but it’s very hard to be right all of the time. There’re a host of theories and even more statistical studies but a unified theory for all situations hasn’t been developed — yet. It’s been said that in theory there’s no difference between theory and practice. In practice, however, there is! The person who coined that phrase was talking about solids blending. What makes it so difficult? Why can’t we get every 1 gram container out of 100 lb. of blend to be the same? The answer is that we’re dealing with discrete pieces that have physical size, electrical properties, frictional differences and surface characteristics that can change with the environment. In addition, particulate solids are neither solid nor fluid but are made up of both. The chemical industry makes a vast array of solids, especially products for the consumer (e.g., detergents, cleaning supplies, cosmetics and pharmaceuticals). After all, it’s often more cost effective and less hazardous to ship particulate solids than slurries or liquids. However, the manufacturing www.chemicalprocessing.com I process can be fickle and variable in product color, size, composition and surface characteristics. That variation requires mixing of the batches or even a continuous blending of the production stream to smooth out these variations to get a uniform blend. It’s easy to equate blending with mixing but these are quite distinct processes for solids. Mixing can mean coating of solids, either with other solids or liquids, or combining solids of different physical features (size, color, hardness or composition). Blending is a sub-set of mixing and is done to further improve on the quality and uniformity of the solids mixture, often just prior to a final manufacturing step to ensure minimal lotto-lot variation or a narrow product specification. Other times it’s needed to meet a tight shipping specification of a large quantity of material or a mixture of different chemicals. However, the more you handle solids the more likely there’ll be undesirable results, such as attrition, segregation, change in color (oxidation or contamination) or change in surface characteristics. Even when a product has been blended by the manufacturer, it may not arrive at the consumer in the desired form. Getting a good blend is difficult — keeping it that way can be even harder due to segregation or settling. September 2007 • 43 http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - September 2007

Contents From the Editor Field Notes In Process Energy Saver Compliance Advisor Succeed at Simulation Rethink Your Approach to Process Safety Avoid Blending Blunders Get the Right Cartridge or Bag Filter Wireless Proponents Take HART Membrane Boasts Material Benefits Process Puzzler Plant InSites Chem Show Product Preview ISA Product Preview Equipment & Services Product Spotlight/Classifieds Ad Index End Point

Chemical Processing - September 2007

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