BRICK & CLAY RECORD: The Big Dust-Up
Rod Davis has worked for Broken Arrow, Okla.-based Air Cleaning Technologies (ACT) for a long time-23 years to be exact-during which time he's helped to design and install dust collection systems, industrial ventilation systems and engineered exhaust systems for a number of brick manufacturers. As president of Engineered Systems for ACT, it's Davis' job to know dust: how it is released, what it will do if left to its own devices, and, most importantly, how to get rid of it.
As it happens, the formation and effects of dust are relatively simple concepts to master; anyone can pick up a book (or trade publication) and learn the basics in just one sitting. Collection, on the other hand, requires a certain amount of finesse, the ability to match the right tools with a given application.
Dust Production 101
Ask an expert about dust in the brick industry, and you'll soon find yourself buried beneath a heap of technical jargon that runs the gamut from "fines" to "shaker screens" to "hooding"-hardly the realm of the layperson. In the interest of clarity, then, let's discuss the dust producing process (by way of brick making) in simplified terms from beginning to end.Generally speaking, brick manufacturers mine clay from pits and then grind it up in rock crushers to reduce the size of the raw material. This releases dust. A screening process works to further reduce the raw material to a specific size. If material doesn't make it through the screening process the first time, it cycles through again. Size-reduced raw materials, or "fines," are transported to a storing silo, while rejects are returned to the crusher and re-screened until they achieve "fine" status.
Belt conveyors transport raw material through transfer points along this line, from primary and secondary rock crushers, through scalping and shaker screens and on to silos for storage. Of course, all of this movement produces dust, which must be contained by hooding (generally situated at release points) and pneumatically conveyed through ductwork to dust collectors.
Additives that enhance color or texture are added to the fines prior to the extrusion of the brick column; dry additives may also be added to the brick face following extrusion. Again, more dust. Add to this the fact that waste dust is generally screw-conveyed onto the belt that carries fines to storage silos, thus incorporating it back into the process, and one gets an idea of the size of the job Davis and other specialists face.
Collector of Choice
Two decades of work in the air cleaning business have provided Rod Davis with an intimate knowledge of various manufacturers' dust collection offerings, but for the purposes of the brick industry, Davis has narrowed his focus to a single brand name. "Over the years, we have installed other manufacturers' brands, but we've always come back to the fact that Donaldson Torit products are superior," Davis says.
"Donaldson Torit cartridge collectors are smaller and much easier to install than a baghouse," Davis says. "Since the cartridges are pleated, each filter has far more surface area available for filtering air than the typical baghouse filter. You generally expect one cartridge filter to process as much air as 10 baghouse filters, which means cartridge dust collectors have far fewer filters to change. They're also easier to change and service."
"Pressure-drop and horsepower go hand in hand," Davis explains. "If you have the wrong filter for a given application, small particulates will weave themselves into filters, leading to a clogging of sorts and pressure-drop. As engineers and designers of dust collection systems, we want to see constant airflow so our transport velocities remain fairly constant. If things slow down too much, we'll leave a load of dust in the duct pipe and won't get it conveyed back to the dust collector."
No Looking Back
Davis currently has no plans to implement other manufacturers' products in the dust collection systems he designs and installs for clients in the brick industry. "Donaldson Torit products are superior, offering us a bigger and better selection of proprietary filters," he says. "Because Donaldson developed the horizontal cartridge, they are able to implement design features in the collector that can't be repeated by others."Of course, this hasn't stopped competitors from trying to duplicate Donaldson Torit's quality in the design of their own products. Davis says his experience with imitators-or "me-toos," as he calls them-has left something to be desired. "On three occasions, we used an alternate brand that built a me-too collector with horizontal filters, but because they didn't have a stair-step in the tube sheet that was also repeated on the front of the collector (as you would find with the Donaldson product), we encountered a lack of tube sheet stiffness during pulse cleaning, which resulted in dust leaks."
Davis' vote of confidence has led ACT to become a premier dealer of Donaldson Torit dust collectors. And though ACT has the option of selecting equipment from any manufacturer it wants, Davis says his company will continue to select only the best products for its clients' needs. "I've been very happy with Donaldson Torit dust collectors," Davis says. "Their product offering covers mist collectors, fume collectors, baghouse collectors, cyclone collectors-it's all there, from one manufacturer."
For additional information regarding dust collection in the brick industry, contact Donaldson Torit at P.O. Box 1299, Minneapolis, MN 55440; (800) 365-1331; fax (952) 703-4865; e-mail dustmktg@mail.donaldson.com ; or visit http://www.donaldsontorit.com .
For more information on Air Cleaning Technologies, visit http://www.aircleaningtech.com .
SIDEBAR: The Nanofiber Difference
Several years ago, Davis had the opportunity to compare Donaldson Torit filters to a set made by a competitor, side-by-side, at a well-known brick manufacturing facility in the southern U.S. "The plant was experiencing short filter life with their existing system," Davis says. "The Delta P was always at 4 in. w.g.; I was concerned about transport velocity."Davis suggested that the brick manufacturer replace the inefficient filters with Donaldson Torit's Ultra-Web® Nanofiber technology. Davis believed that this would allow the very fine dust from the brick to be trapped on the surface of the filter media, where it could be pulsed off during the cleaning process. The change was made, and Davis found that the dust collector was able to maintain consistently lower pressure-drop and better ventilation.
"The Nanofiber's surface-loading capability not only allows the cartridge to be cleared of dust through pulse cleaning, it also keeps pressure-drop down, which means manufacturers spend less on horsepower while keeping conveying velocities where they need to be," Davis says today. "Without these premium cartridges, pressure-drop rises as particulates work their way into the depths of the cartridge fibers. When pressure-drop rises, it affects the blower's performance curve, so ventilation volume and hooding containment aren't as effective. Simply put, a rise in pressure-drop decreases the fan's ability to perform."
Davis says Donaldson Torit's Ultra-Web Nanofiber cartridges have kept his clients' pressure differentials low, thus keeping their systems working within specs.