Fabricator Case Study: Containing Limestone Dust (continued)

Improving the Dust Collection System

Several years ago, ILCI invested in a network of dust collectors that were connected to movable source-capture hoods placed in areas of high dust generation. But given the heavy concentrations of dust in the large cutter bay, which measures 140 feet long x 68 feet wide x 20 feet high, source capture was not effective, and the system was eventually shut down.

lLCI management wanted to stay on top of increasingly stringent OSHA regulations, which limit the allowable level of nuisance dust to 5 mg. per cubic meter of air. "We use wet collection to handle dust in other areas, so we investigated the possibility of knocking down the dust with water and channeling it into our existing water cleaning system," said James. "But when we did the math, we found that the horsepower required to accomplish this would have been off the charts."

In seeking a more practical solution, ILCI contacted Air/Pro Inc., a Cincinnati-based firm that specializes in problem solving for industrial air moving, air cleaning and pollution control applications. "Looking at the room dimensions, we thought in terms of treating the space as a tunnel placing the collectors at one end and sweeping the air up above workers' heads, across the length of the room, and into the dust collectors," explained Tom Woods, a sales engineer with Air/Pro. "In addition, the customer wanted to recirculate the cleaned air back through the work bay to prevent energy loss during the winter months, when the room is heated to a constant temperature for worker comfort. So we designed a system of ductwork to return the air to the other end of the room in a circular pattern."

According to Woods, the concept is based on modular booth-type collection systems that are popular for self-contained areas where source capture is not practical, and hoods could interfere with worker productivity. "This area was too large for standard air quality booths, so in effect we custom designed our own version," said Woods. To filter out the dust, Air/Pro selected the Farr "Gold Series®" collector, a cartridge collection system with a modular configuration that lent itself well to the design.

"We wanted to solve these problems and create a more comfortable and pleasant environment for the 17 to 25 employees who typically work in this area," said ILCI General Manager George James, adding that these artisans are carrying on a tradition of hand craftsmanship that has been with the company for more than 66 years.

The system utilizes four identical collectors with 16 cartridges each, in a shallow configuration of two cartridges deep by eight cartridges wide. This arrangement takes up most of the 68-foot south wall, while occupying minimum floor space. The filters have a patented design that provides 425 square feet of media in each cartridge, meeting the total 67,200 cfm airflow requirement with a much smaller housing than conventional cartridge collectors, while also delivering high-filtration efficiency, excellent energy performance, and long element life. "We liked all these features, as well as the rugged construction of the collectors," said Woods.

Camfil Farr APC worked closely with Air/Pro to customize the collectors as needed to fit ILCI's unique requirements. The manufacturer built baffles into the heavy-duty 10-GA access doors to allow dusty air to enter the cartridge area of the collectors directly through the doors. They also designed special dust pans to fit into the bottom of each module for easy removal of the captured dust.

Custom Gold Series Modules at Indiana Limestone

To ensure adequate airflow through the room, Air/Pro used customized direct drive fans on the units, sized for the collectors and for system static pressure requirements. They also advised ILCI on the need to place auxiliary fans strategically through the room to accelerate the air and help direct it toward the collectors. ILCI closed the outside truck doors and added curtains and flaps to seal off other internal openings to isolate the area being treated, again ensuring that the desired air circulation within the space would not be compromised.

Air/Pro handled the design, engineering and installation of the dust collection system on a turnkey basis for ILCI - including the collectors, custom fans, special control packages, ductwork and other components. They performed the majority of the installation during a scheduled plant shutdown to avoid disruption of cutting operations.