Vibrating bin dischargers (a.k.a. bin activators) have been used for more than 50 years to promote the flow of bulk solids that would otherwise result in bridging or ratholing if stored in static bins. By replacing the lower portion of the static hopper with a bin discharger (i.e. a single or two-slope shell that includes an inverted, internal “pressure cone”), the result is a shear plane between the vibrating bin discharger and the static bin to prevent ratholes. The internal cone is designed to relieve most of the headload off the outlet to prevent bridging.
The correct bin discharger size for any application is primarily determined by two criteria. The first is the dimension of the bin. Very simply, larger bins will require larger bin dischargers. The second criteria for determining bin discharger size is product flow characteristics. Poor flowing products compared to better flowing products – when stored in identically-sized bins – require larger bin dischargers.
After the bin size is selected, additional product data required for bin discharger size selection includes the bulk density of the product and the product temperature. Bulk density is used to determine the number of hanger arms necessary to support the bin discharger. Product temperature is used to determine the elastomer required for the flexible connector and to determine the paint system, if painted surfaces exist.
The product characteristics that have the most significant effect on product flowability are moisture content and particle distribution. Many products may exist in a continuum that ranges from adequate flow properties when they’re coarse and dry, and therefore not even requiring the use of a bin discharger, to sufficiently poor when wet and fine to make the flow-promoting action of a bin discharger inadequate to reliably prevent either bridging or ratholing. Consider products like coal or lime. When dry and coarse, these products may be stored in bins without bin dischargers, but if enough fines exist to fill the void sections between the larger particles – and hence, increase the strength of the product – then a bin discharger will be needed. Now, add moisture to this product and a larger bin discharger will be needed. Add even more moisture and the flowability may become so poor that a more aggressive type of flow-promoting technology (e.g. silo reclaimer/unloader) may be needed.
Providing accurate data will result in the best bin discharger selection. To mistakenly assume or specify that a dry (~0% H2O) product will include up to 5% H20, for example, results in a markedly different product from a flowability standpoint. Assuming a bulk density of 55 PCF, 5% moisture would translate to nearly three pints of water for every cubic foot of product. Imagine how differently a 12 x 12 x 12 in. box of dry product will flow after three pints of water have been mixed in!
Regarding particle size, often this data is mistakenly only given as a range (e.g. -3/4 in. or ¾ x 0). Having a range of particles is only marginally useful as this only indicates how large and how small the particles might be. What is really needed is a defined distribution of the particle sizes with the amount of the finer particles being of paramount importance. For example, lime with 50% that is sized between ¼ and ¾ in. and with 10% that is -16 mesh will have much better flow properties than one with 10% sized between ¼ and ¾ in. and 50% that is -16 mesh.
Accurate and detailed data will always yield the most accurate bin discharger selection. While correctly indicating to potential suppliers the data of minor upset conditions is prudent, if you arbitrarily or mistakenly identify your product as much finer or much wetter, it will – at best – result in a bin discharger selection that’s larger and more expensive than necessary. Even worse could be an insistence from the bin discharger supplier that other, more aggressive – and more expensive – technologies are required.
Mark Payton, M. Eng., is the application manager of the bin discharger product line at Carman Industries. He can be reached at [email protected] or 812-288-4749. For more information about Carman’s lineup of vibrating bin dischargers, visit the website at carmanindustries.com.
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