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24 / March 2020 powderbulk.com • Downward-inclining sections can be used in any mode of conveying if the system layout demands it. PBE References 1. The Geldart Classi cation is a method of identifying materials into one of four possible groups based on their mean particle size and respective par- ticle density. Each group has speci c characteristics as to how the material will respond to uidization, which helps to select the preferred mode of conveying. 2. Line stepping is used when the con- veying line incorporates a section of line that's a larger diameter than the previous section to help control the velocity pro le when a large system pressure differential exists. Jack D. Hilbert, PE (pcchilbert@ hatch.com, 610-657-5286), is a bulk solids pneumatic conveying expert consultant for Hatch. Prior to that, he was the principal consultant for Pneu- matic Conveying Consultants. He holds BS and MS degrees in mechan- ical engineering from Penn State University, State College, PA. He has more than 46 years of experience in the application, design, detailed engi- neering, installation, and operation of pneumatic conveying systems. Étienne Brochu (etienne.brochu@ hatch.com, 438-797-9397) earned a degree in mechanical engineer- ing from École de Technologie Supérieure, in Montréal, Canada. He has been working in the special- ized bulk materials handling group at Hatch for the past 2 years. to the force pushing the slug, and the break's angle causes the second sec- tion of the slug to ride up and over the rst section. This effect has been observed in clear sections of a con- veying line test loop in which slugs were observed to form and break at random intervals. When the convey- ing line returned to horizontal in the test loop, conveying returned to normal dense-phase ow. Line charger position It's good practice to have a pressure system conveying line run as close as possible to the discharge of the product line charger. A long space between the conveying line inlet and the product line charger creates a potential for interrupted ow due to airlock leakage. Conclusion When designing a pneumatic con- veying system, follow these routing guidelines. For acceleration zones: • Ensure the length is adequate. • Ensure the gas velocity is adequate. For bends: • Don't use bends in the acceler- ation zone. • Minimize the number of bends. • Avoid multiple bends without adequate acceleration zones between them. For inclined sections: • Avoid inclined sections when possible. • Use steeply inclined sections (between 45 and 75 degrees) only in a dilute-phase con- veying system. Try to locate the sections toward the end of the system where the convey- ing velocities are typically the highest — unless line step- ping has been incorporated into the system design. 2