Optimize Your Production Veil
To kick off this month’s production-related product gallery, let’s take a look at the dryer drum. While producers will peruse the following pages for aggregate and asphalt production services and products, they can get a drum tip right here from BROCK, headquartered in Chattanooga. That tip focuses on flighting to optimize the veil of material in the drum.
Working with consulting engineer Malcolm Swanson, BROCK offers the FlexFlight™, which Swanson designed and for which he has applied for a patent through his company, e5 Engineers LLC, Chickamauga, Georgia. The FlexFlight is designed to address the fundamental challenge of executing a proper shower of material within the rotating drum.
By controlling the shower—or veil—of material in the drum as you change mix designs and/or production rates, you can also control temperatures leaving the drum. Swanson explained: “When you need a good complete veil most, as with open graded mixes and high RAP mixes, the veil is thin or nonexistent on the uplift side of the drum. So, hot gas bypasses material by taking the path of least resistance through the gap in the veil.” To get a more even veil of material for hot gas to spread evenly across, you want flights to “spill” material properly, evenly, and in a reliable fashion even when there isn’t much material in the flight.
“Conventional flights shower differently depending on fullness,” Swanson said. “When very full, they tend to allow material to cascade out early, making the uplift side of the veil too heavy. When they contain little material, as is the case with high RAP mixes, they tend to shower little or nothing on the uplift side and dump what they do have as they start back down. FlexFlight is designed to restrict flooding when full and yet allow showering even when nearly empty.”
Producers and manufacturers alike have long known the benefits of good showering in the dryer. Some of these benefits are higher production capacity, better fuel efficiency, more uniform and thorough drying of aggregates, better control of baghouse temperature, the ability to make higher RAP mixes that could not be made without excellent showering, and lower emissions. Swanson explained that manufacturers have, for many years, made flights that incorporate gaps to address the fill percentage or to prevent flooding of the flight with material, but the gaps have not always been good at allowing material to build and spill efficiently. Instead, the gaps have often allowed aggregate to dribble out.
The FlexFlight design doesn’t incorporate a gap but has a completely surrounded opening with several inches width at its bottom to prevent dribbling. “The opening is centered lengthwise, so you get a good veil at all parts of the circuit,” Swanson said. You can see the design in the photo on this page.
To configure the flights in the drum, they are placed in the drying zone according to the needs of the producer. See the photo on this page for an example of how Ranger Construction has theirs configured. “Going forward, we probably will use a number of flights per row that is a multiple of the drum diameter in feet,” Swanson said. “For example: if a 9-foot drum needs 54 new flights, it could get two rows of nine and two rows of 18 flights. That makes it a bit more rational for direct replacement in existing drums, since this is a pattern of flighting often used by dryer manufacturers.”
For more information, contact e5 Engineers at firstname.lastname@example.org.