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36 / March 2021 powderbulk.com The step-by-step calculation method for estimating pressure loss through a dilute-phase conveying line will assist personnel with proper air mover selection, which is the heart of the pneumatic conveying sys- tem. Adopting a total system view, understanding not only the pneumatic conveying system's operation but also its interaction with the solids handling equipment upstream and downstream, should also be carefully considered. PBE References 1. E. Maynard, "Troubleshooting and solving problems with your pneumatic conveying system," Chemical Engineering Progress, June 2010. 2. F. Cabrejos, G. Klinzing, "Minimum conveying velocity in horizontal pneumatic transport and the pickup and saltation mechanisms of solid particles," Bulk Solids Handling, Vol. 14, No. 3, July/September 1994, pp. 541-550. 3. E. Maynard, J. Khambekar, "Proper feeding of pneumatic conveying lines," Powder and Bulk Engineering, July, 2011. 4. L. Moody, "Friction factors for pipe flow," Transactions of the ASME, 66, 8, Nov. 1944, pp. 671-684. 5. D. Shrikant, P. Solt, G. Klinzing, "Understanding bends in pneumatic conveying systems," Chemical Engineering, April 2009. For further reading Find more information on this topic in articles listed under "Pneumatic conveying" and "Solids flow" in the article archive on PBE's website, www.powderbulk.com. Eric Maynard (epmaynard@jenike.com, 978-649- 3300) is a vice president at Jenike & Johanson Inc. He's been with the company for 25 years and has worked on more than 750 projects, designing handling systems for materials including chemicals, plastics, foods, pharma- ceuticals, coal, cement, and more. He's also a principal instructor for the AIChE bulk solids handling and pneu- matic conveying courses and a special expert on NFPA Combustible Dust Committees 652 and 654. Jenike & Johanson Tyngsboro, MA 978-649-3300 www.jenike.com 1,429 lb m h Q = แน air = h 60 min โ 320 cfm @ โ 4.5 psig ฯ air 0.075 lb m ft 3 14 Now that we have a rough estimate of the dilute- phase pneumatic conveying system's pressure, we can determine what air mover would be the best for this system. Earlier in this article, we mentioned three air movers: a compressor, centrifugal fan, or positive- displacement (PD) blower. Typically, for pressures less than 3 psig, a radial blade centrifugal fan can be used. The most common fans used in dust collection applications are machines that typically have maxi- mum pressure ratings on the order of 0.7 to 1.5 psig. Because we have a pressure of 4.5 psig, a centrifugal fan wouldn't meet the pressure resistance requirement for the system. When line pressures exceed 15 psig, a compressor (such as a sliding vane, liquid-ring, rotary screw, or reciprocating) is normally used. A compressor is usually run at 30 to 100 psig, so having this air mover produce compressed air at only 5 psig or so is a waste of energy. For pressures between 3 and 15 psig, a Roots-type PD blower is often used. One of the key features of this PD blower type is that it provides a nearly constant air volume delivery over its operating pressure range. This is important since airflow control in pneumatic convey- ing systems is critical for stable operation. Thus, a PD rotary lobe blower is suitable for this application. A centrifugal fan isn't likely to be a good candidate for this application due to the total pres- sure drop calculation (or estimation). Furthermore, a compressor is overkill. Air mover equipment vendors have performance curves available, which demonstrate operating ranges for the machine under specified conditions, such as pressure, temperature, operation speed, and others.