Dust busters

Chicago, like many areas of the country, is currently going through a building boom. Nearly all categories of construction, from single-family residential to commercial and mixed use, have seen growth in the past couple of years. One result of the uptick is a higher demand for local construction and demolition (C&D) recyclers.

In 2012, two midsized Chicago-based recycling companies merged to become Lakeshore Recycling Systems (LRS), Morton Grove, Illinois. The company has since acquired two more locations, allowing the firm to raise its production to 1.5 million tons of debris processed annually. The company says it is now the largest provider of construction debris disposal containers in the Chicago area.

Along with that increased volume comes a greater amount of dust created at its recycling centers, which has the potential to affect air quality and worker safety. With environmental stewardship a key component of the company’s operating philosophy, company officials wanted to take a proactive approach to dust suppression at its facilities.

“Although we have residential pickup, our main source of material is from C&D projects,” Mark Sredin, production manager for LRS, says. “We receive concrete, wood, drywall, cardboard, glass and paper. All of these materials create their own particulates, along with the years of dust they may have collected prior to demolition.”

Dusty process

photo: Adobestock

Sales of raw separated material contribute to a large portion of the company’s revenue, along with dumping fees and container rentals and transport. In most cases, the company drops off one or more containers at a demolition site, where it’s up to the contractors to control any fugitive material and dust.

When LRS picks up the full container, it is covered with a tarp to contain dust during transport and hauled to one of the company’s three locations. In all, hundreds of vehicles, including the 55 company-owned waste collection trucks, arrive daily to deliver recyclable materials from more than 6,000 commercial and municipal customers. Each incoming vehicle is weighed upon entry and exit to determine its disposal fee.

The recycling process begins when a front loader pushes the bulk material into a 25,000-square-foot, three-walled, open-air structure. The debris is loaded onto a tipping floor leading to a large steel screen with 2-inch openings. Industrial vibrators shake the screen, which is set at a 7-degree slope, to move the material slowly down the incline. Small debris (dirt and aggregate) falls through the holes and onto a lower conveyor belt to be transported to the landfill. The remaining larger debris is conveyed to a sorting area.

Once separated, the screened debris drops onto a 5-foot-wide conveyor belt and is then transferred onto another curved conveyor feeding the large material picking line to be further sorted. Wood, glass, steel, cardboard, brick and concrete are removed. Sorted material is then sold to various vendors for repurposing.

Sredin says larger materials also are manually sorted and placed in pieces in bins. This requires a safe work area, with dry floors and adequate air quality. However, with all the mechanical agitation, the process creates large volumes of fugitive dust and a need for dust suppression.

Dust suppression techniques

photo: Adobestock

LRS started using a large sprinkler system for its dust management needs, which is common in many bulk handling applications, but Sredin and his team quickly realized that it wasn’t adequate.

“It saturated the material and caused pooling water under the sprayer and around heavy machinery,” Sredin says. “It not only made the material hard to handle, it didn’t address the dust issue.”

Company officials performed a detailed search looking online and through trade magazines for a better solution, eventually contacting BossTek, headquartered in Peoria, Illinois, to learn more about the company’s family of atomized mist dust suppression systems.

Convinced they needed to make a change, the firm purchased its first DustBoss DB-30 for one of its locations with the intention of replacing the ineffective sprinkler system. Initial testing was successful, and operators reported a substantial improvement in air quality along the debris sorting line, as well as dramatically reduced pooling and runoff.

Based on that experience, LRS has now installed a unit in each of its facilities, creating safer and more efficient workplaces for the company’s more than 350 employees.

Sredin says that his team chose the DB-30 because of its rugged construction and long warranty.

“We initially tried it in multiple positions and areas in the plant,” he says. “Due to its long range, we found that mounting the DustBoss on the deck over the main conveyor and away from the picking line was the best way to suppress [dust] before it reached employees, letting the mist cover the rest of the conveyor system.”

The DB-30 uses a 7.5-horsepower fan delivering 9,200 cubic feet per minute to project a 100-foot cone of dust-trapping mist. With an adjustable throw angle of 0 to 50 degrees in height, the unit has a coverage area of 31,000 square feet when equipped with an optional 359-degree oscillation feature.

The company’s three-sided building configuration poses a unique challenge for LRS. Even though it is an enclosed space, operators still have to contend with the elements such as wind, rain and severely low temperatures. According to Sredin, merely adjusting the unit’s spray angle allows the unit to negate the swirling wind within the complex.

“Our DustBoss is on all day, every day. When it rains or snows, there’s less dust, so we simply turn off the atomizer and allow the strong fan to clear the air. It’s very versatile,” he says.

The slipstream effect

Sprinklers are used by many industries for dust suppression, but they have been proven to be ineffective unless material is totally saturated prior to any disturbance.

The primary reason is that a water droplet from a sprinkler is typically between 2,000 and 6,000 microns in size. In contrast, dust particles are generally 50 to 100 microns in size. Because of the larger mass of the droplet, two issues can arise that prevent effective dust suppression.

First, the impact of the droplet on settled dust can actually cause the dust to become airborne. After being set aloft, fugitive dust particles are carried by air currents, becoming subject to the second issue: the “slipstream effect.” This happens when the size and velocity of the sprinkler droplet affects the airflow around it. The large droplet approaches airborne particles, but the airflow deflects the particles without a collision, preventing effective dust management.

To overcome this tendency, the atomized mist emitted from the DB-30 is made up of millions of droplets between 50 and 200 microns in size. The unit injects 100 pounds per square inch of water through a brass ring equipped with atomizing nozzles, creating minuscule droplets that are propelled by the fan and travel with the dust, colliding with particles to capture them and pull them to the ground.

Pooling and runoff

Pooling and runoff are among the biggest concerns when using dust suppression, especially indoors or near walkways. According to the U.S. Department of Labor, “Slips, trips and falls constitute the majority of general industry accidents. They cause 15 percent of all accidental deaths and are second only to motor vehicles as a cause of fatalities.”

While large sprinklers can apply 500 gallons per minute (gpm) or more, the DB-30 uses 3 gpm. “Even running the atomizer all day long, there is no pooling,” Sredin says. “Also, our water bill has gone down considerably.”

When LRS acquired its Southside Chicago location from a smaller competitor, it found that similar inefficiencies were leading to lackluster dust suppression on-site.

“For dust suppression, they were using a garden hose with a spray nozzle you would buy at the hardware store,” Sredin says. “It wasn’t doing anything to the dust, and the floor was wet all the time. We immediately brought in the DB-30 and mounted it in a fashion similar to our primary facility. The safer workplace and higher air quality was an instant morale booster for everyone on the sorting line.”

In 2014, the company purchased Heartland Recycling in Forest View, Illinois, which had installed three small atomizers that didn’t contain adequate fans.

“The mist just fell to the floor and pooled without capturing much dust,” Sredin says. “I think the previous owners had the right idea, but with low coverage and no oscillation, the units didn’t do much. We installed one DB-30 to replace all three units and solved the pooling and the dust problems at the same time.”

Recycling Chicago

The city of Chicago, in partnership with LRS, has concentrated on recycling programs involving C&D materials by offering incentives to businesses that reduce service charges for keeping materials out of landfills. According to Chicago officials, “C&D debris accounts for 30 percent of all solid waste produced.”

The city’s incentive plan has increased the volume of recycled C&D debris above that of residential materials. C&D debris now accounts for 85 percent of all recycled material, with approximately 500,000 tons recycled each year.

A company spokesman says LRS will meet increased production expectations for C&D material as the construction market continues to be strong. Sredin says with each new facility, there is anticipation that dust suppression equipment will continue to play a pivotal role in helping LRS keep workers comfortable and safe, while allowing the company to take on larger volumes.

Mike Lewis is a sales manager for BossTek. He can be reached at mikel@bosstek.com.