PBE Reference & Buyers Guide

PBE 2018 BG website version

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powderbulk.com PBE August 2018 7 Words worth noting from PBE articles in 2018 January — Mixing and Blending "The supplier's rotary batch mixer features a stationary inlet at one end and an opposing stationary discharge spout with a plug-gate valve at the other end. A rotating drum sits in between. Materials is added via the inlet chute while the drum is rotating. Internal mixing flights create a gentle, four-way mixing action that tumbles, folds, cuts, and turns the material." — from "Case history: Mixer thor- oughly blends wood powders" "A mixer's working volume is material specific because some materials fluidize or expand more than others dur- ing mixing. This expansion is calculated based on the ma- terial's characteristics. An equipment supplier may even choose to confirm the calculation with modeled or full- scale testing using the specific material recipe to ensure that the mixer size is correct." — from "Suppliers' tips" February — Screening and Classifying "Particle size classification separates particles into two or more groups with maximum and/or minimum particle sizes (or cut points). Manufacturers use cut points as a basis for differentiating one product from another throughout the bulk solids processing industry, from size reduction to classification." — from "An introduction to dry powder classification," Rob Voorhees "Some older screeners also run into problems with the weight of the overload. Older machines aren't as powerful and capable as newer screeners and tend to lose the energy needed to properly convey the material across the screen when overloaded. The extra weight absorbs the vibrational energy. This in turn slows material discharge and exacerbates the problem by causing the screen to fill up even faster, often resulting in a ripped screen." — from "Suppliers' tips" March — Pneumatic Conveying "When designing a conveying system to handle more than one material and the bulk density of those materials is substantially different, the chosen pickup velocity must be high enough to convey the heavy material. If the system pressure is calculated for this heavy material, however, the pressure will be lower than that required to convey lighter materials." — from "Pneumatic points to ponder…," Jack D. Hilbert "To gently handle fragile or friable materials, including carbon black prills, sugar, and glass bubbles, use a low- velocity dense-phase pneumatic conveying system, which will move the material slowly through the line in slugs. Dense-phase conveying is also a good option for spray-dried products, such as milk powder, instant coffee, and baby foods." — from "Suppliers' tips" April — Drying "The three major variables that affect the removal of moisture from solids in a vacuum dryer are vacuum level, the available surface area of the material, and the amount and efficiency of the heat-transfer surface area. Optimizing each of these variables is the key to efficient drying." — from "Tips for effective agitated vacuum drying," Shawn Hearn "If a dryer has an adjacent cooler, the contrasting climates can cause condensation to form at the interface. A hygienically designed dryer will include an insulated wall at this interface to minimize any condensation and hygiene risks associated with water in the drying process." — from "Suppliers' tips" May — Bagging and Packaging "Recent improvements in film technology as well as health and environmental issues are opening up other industries traditionally associated with paper bags, especially paper valve bags, to the use of form-fill-seal machines. Some of these improvements include reduced dust when filling and better recyclability when compared to combination polyethylene-paper bags." — from "Form-fill-seal machines for bulk solids — vertical or horizontal?" Graham Rawlings "All material contact surfaces should be built from appropriate or upgraded materials, like abrasion-resistant plating where possible, to increase the equipment's service life. Specialized coatings can work but will wear off whereas upgraded materials will last longer." — from "Suppliers' tips" June — Size Reduction "If selected correctly, a specialized pin mill can create up to 150 percent more particle surface area than a conventional pin mill could. Specialized pin mills apply centrifugal force to generate impact energy, allowing for uniform size reduction, greater energy efficiency, less wear and tear on the equipment, and lower horsepower requirements when compared to pulverizers or air classifiers. However, air classifiers may deliver greater particle size reduction and use even less sorbent, but their capital costs and operating costs far exceed that of the specialized pin mill." — from "Milling trona for dry sorbent injection," Steven Bythrow "Selecting milling equipment designed with easy-access doors or covers will allow quick and trouble-free changes of your internal particle-retention components, such as screens, grids, or cutter plates. Selecting a mill with a fixed hammer design will allow a variable-frequency drive to change your operating speed, which will change your mill's particle sizing capabilities and possibly minimize the number of required changeovers." — from "Suppliers' tips" July — Mechanical Conveying "Dust explosions can occur when a sufficient concentration of combustible dust accumulates within the elevator and is exposed to an ignition source, such as a spark that results from a static discharge or the friction between moving parts. Should an explosion occur within the elevator, the equipment design should be capable of suppressing the explosion's effects, relieving the resulting overpressure, and safely venting any flame." — from "Safely conveying hazardous materials in continuous bucket elevators," James Bransfield "When specifying the build details of your conveyor, remember to determine the equipment's materials of construction compatibility with auxiliary conveyor components and how the components will perform in your process with your process materials. Bearings, valves, seals, and internal seal components can be made from metals, plastics, and elastomers. Properly selecting the components should help extend their service life and give better conveyor performance." — from "Suppliers' tips"

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