More Questions and Answers

Q: How do I make my pneumatic conveying system more energy-efficient?

A: Larry Eagan, Smoot, says: The physics behind the answer are relatively simple. Sometimes it's easy to forget that horsepower or watts are really a measure of force required. The more resistance (friction) that a product has to being moved, the more force (power) it takes to get it there. The total resistance comes from the length of the conveyor's run, the number of turns in the run, the friction of both the air and the product masses to the conveying line, and any line impediments between point A and point B.

Certain factors, such as the material, conveying length, number of turns, and necessary conveying speed, are usually fixed for a given customer's product and application. What can be varied to optimize the product flow, however, is the material-to-air ratio within the conveying line.

Traditional dilute-phase systems put a premium on design of air velocities in the pipe. This is because companies that build systems don't want to be "wrong" in the field and therefore err on the side of caution. Often this results in a more dilute product stream than needed to get the material to its destination. The downside to this method is the resulting oversizing of conveying lines and the increase in energy used to move air instead of the material.

Traditional dense-phase systems put a premium on power. This is because the material is being largely "slid" along the conveying line, consuming an exorbitant amount of potential energy. This, in turn, requires the use of air compressors that generate 100 to 125 psig of air that's then often then regulated down to 50 or 40 or even 30 psig for conveyor use. This sophisticated air generation and subsequent relegation wastes a lot of energy in translation.

But what if you could harness the best of both worlds? Optimize a dilute-phase system to run continuously but as close to "full" and as slowly as possible. This setup is much like a dense-phase system, but it operates just above the point where material loses its entrainment in the air and becomes subject to increased friction and potential plugging.

This scenario is possible but requires both specialized equipment for metering the product and air sources together and a material test lab for verification of conveyability factors. By combining these two things it's possible to design a system that uses air power more efficiently so that even a 50-horsepower blower can do the work that a 100-horsepower blower has traditionally done, with the aid of the proper induction and entrainment equipment.

Smoot, a division of Magnum Systems, is a Kansas-based supplier of pneumatic conveying systems and components.