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Powder & Bulk Solids, May 2014

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Powder & Bulk Solids 48 TechnicalExclusive M a y 2 0 1 4 ers, and sieve stacks all make up multiple component assemblies that can accumulate high levels of electrostatic charge should any of the components be isolated from a true earth ground. Connections made with items like bonding straps can provide an intentional bond between metal components or assembly mating surfaces may provide an inherent bonded con- nection. Regular disassembly for clean- ing and maintenance can result in bonding connections being missed or not made correctly when the equipment is reassembled. Vibration and corrosion may also degrade assembly connections so it is imperative to ensure that no parts in the assembly become isolated from a true earth ground reference. The most effective way of en- suring that equipment used in powder processing operations cannot accumulate static electric- ity is to provide a dedicated static grounding solution that will moni- tor the ground connection of com- ponents at risk of static charge ac- cumulation and alert personnel to a potential hazard should a com- ponent lose its ground connec- tion. This is especially important if the ground connection point to the equipment is not readily vis- ible or easily accessible. Static Grounding Solutions: Convention Versus Flexibility Most grounding solutions pro- vide grounding protection for discrete pieces of equipment at risk of electrostatic charging like road tanker trucks, railcars, IBCs, and drums. For example, if a road tanker truck requires static grounding protection, a single static grounding system, featuring ground status indicators and inter- locks for the pumping system, will be installed at the loading rack. If the ground connection is lost at any point during the road tanker truck filling operation, the grounding system will detect this and shut down the pump, or close a valve, feeding the road tanker truck. Powder processing equipment presents more of a challenge as there are many metal parts that can make up larger assemblies that are electrically isolated from each other. For example, vibra- tion pads that prevent mechanical destruction may be an inherent design feature, such that electri- cal isolation, by default, is inher- ent to the design of the equip- ment. In other cases, electrical isolation can be an unintended consequence of mechanical de- signs that have not have taken into consideration, or fully ap- preciated, electrostatic ignition hazards. It is therefore important to ensure that multiple compo- nents that come into contact with charged powders do have a means of being monitored for static grounding protection pur- poses. This, however, may be eas- ier said than done, especially if the processing equipment layout, available space and personnel accessibility is restrictive, such that multiple grounding systems may be difficult to install with such limited "real estate" to work with. The only alternative is for plant technicians to take regular measurements with ohm-meters to ensure that none of the plant equipment ever becomes isolated. For many operations this task is time consuming and results in technicians spending less time on critical maintenance and repair work. Summary In the powder processing in- dustries, the generation and ac- cumulation of static electricity presents an insidious ignition risk in potentially combustible atmospheres. The electrostatic charging mechanisms and cor- responding quantities of charge generated are generally higher than those produced by petro- chemical operations handling and processing flammable liq- uids. As such, it is imperative that all conductive components, be they members of machine as- semblies or portable containers, have static grounding protection in place to prevent the accumu- lation and eventual discharge of static electricity as a high energy spark. The installation of conven- tional static grounding systems, designed to monitor discrete equipment, like IBCs and road tanker trucks, are unlikely to be a viable solution for typical powder processing equipment like fluid bed dryers or sieve stacks. The quantity of systems required, the lack of available space and installation difficulty would either be too complicated, too expensive, or a combination of both. For more information, visit www.newson-gale.com. It is important to ensure that multiple components that come into contact with charged powders do have a means of being monitored for static grounding protection purposes. The Sonic V T Ta n k D r y e r delivers 160°F pressurized high volume air without any heaters for complete drying in 30 minutes or less. After C-I-P for Tanks, Totes, Mixers and Piping Portable or Stationary Systems HEPA Filtered Air To 0.3 Microns Sonic Blowers 7.5Hp to 50Hp www.sonicairsystems.com/tank_dryer.php AIR SYSTEMS 800-82-SONIC Fig. 2: A dedicated static grounding sys- tem for road tanker trucks ES425364_PB1405_048.pgs 04.18.2014 03:36 UBM black yellow magenta cyan

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