Getting the lead out

Although newer technologies have claimed most of the market share formerly belonging to makers of cath- ode ray tube (CRT) televisions and computer monitors, old CRT devices continue to be collected for disposal or recycling.

Regardless of whether a CRT was dropped off at a landfill or picked up by a recycling company, if it has reached the end of its useful life in the northern Midwest, it may well end up in the hands of Kuusakoski Recycling. Finland-based Kuusakoski operates a facility in Plainfield, Illinois, that it says is one of the few plants in the United States equipped to address the complexities of recycling CRTs.

Modern flat screens made of panel glass have been on the market for nearly two decades and use different technology from older CRT units made of leaded “funnel glass.” However, Kuusakoski’s Production Supervisor Marc Artozqui says, “Old TVs are still around. In fact, there is currently a five-year backlog of recyclable CRT stock just in our area alone.”

A CRT is a vacuum-sealed tube made entirely of funnel glass, ending in a fluorescent screen with one or more electron guns on the narrow end. Containing a high level of lead, funnel glass is less fragile and is intended to protect consumers from X-rays emitted by the electron guns while the television or monitor is on.

“During the recycling process, the tubes produce a considerable amount of dust, requiring all of our employees to wear protective coveralls and face masks when in the facility,” Artozqui says.

“We invited Dust Control Technology to the plant to make an assessment, and after a thorough inspection, their team came up with a solution that has eliminated the hazy, dusty atmosphere,” he adds.
 

Process of elimination

For more than 100 years, Kuusakoski has recycled materials according to the philosophy of its founder, Donuard Kuusakoski: “Everything is reused.” The slogan applies to Kuusakoski’s current treatment of CRTs.

Television sets and monitors are delivered whole or in pieces to the Illinois facility, where the units are immediately loaded into a hammer mill to crush them. The resulting scrap is then conveyed through a separation process, in which metal is discharged by magnet and plastic also is removed. What’s left is crushed leaded funnel glass and inert panel glass.

Unlike funnel glass, panel glass breaks into beads, which makes it easy to screen out before the two types of glass are transferred to an observation conveyor. There, workers closely inspect the size and quality of the end product.

Once deemed adequate for transport, the funnel glass is transferred to a loading conveyor and dropped through one of two tall spouts into a specially designed 40-cubic-yard steel transport container with a liner that is tightly sealed before it leaves the plant. After one container is full, the conveyor is switched to the second spout so there is no break in loading. The product is then transported by truck to a partner facility where deleading renders it inert, allowing it to be made into Klean Kover, an alternative daily cover for landfills.

“We produce approximately 35,000 pounds of processed recyclable glass every hour,” Artozqui estimates.

“The air quality control measures include a plantwide HVAC (heating, ventilation and air conditioning) system, but fugitive dust can still be a problem inside the facility if it’s left unchecked,” he adds.
 

A combination of methods

The Kuusakoski plant is enclosed, with as many as 22 people working on a shift. In addition to requiring protective gear to avoid lead exposure, the company’s objective is to further reduce potential worker exposure by addressing all sources of airborne dust.

“Our hammer mill has a baghouse attached to it, and the entire unit is located in a sealed room with its own HEPA (high-efficiency particulate arrestor) filtration system,” Artozqui says. “This solution took care of a major issue but didn’t mitigate dust produced at different transfer points and our next biggest culprit: the two transport container discharge spouts.”

Dropping 8 feet into the container, fine pulverized funnel glass emitted fugitive dust particles into the air that lingered throughout the facility before being caught and cycled through the HVAC system.

Derek Schussele, a dust control specialist with Peoria, Illinois-based Dust Control Technology (DCT), headed the team that initially visited Kuusakoski.

“I’ve seen this cargo loading process before with other applications, similar to the way coal is put onto a train or barge,” Schussele says. “However, it’s rare that we apply our dust suppression technology in a totally enclosed space like that. One of our goals in this application was to avoid water pooling and excessive runoff.”

The team first tested the volume of atomized mist needed to be effective, using a 26-inch-diameter DustBoss Ring (DB-R). The stainless steel ring manifold was fitted with low-volume misting nozzles, producing millions of water droplets just slightly larger than the diameter of a single human hair. The mist flows out of the ring much like a curtain drawn around the discharge, trapping fugitive particles and directing them back into the container using the company’s variable particle sizing (VPS) approach, matching droplet size to dust particle size for maximum suppression.

After testing, the DCT team determined a smaller unit could produce even more effective results.

Placed at the end of each spout and surrounded on the outside by 20 overhanging rubber flaps to further aid material flow, the two 23.5-inch stainless steel DB-Rs took less than an hour to install. A standard garden-type hose connects to the 60-PSI municipal system and feeds water through an inline 75-mesh, 200-micron filter and into the manifold. The water is then forced through 18 specialized nozzles that fracture it into a fine mist.

“We adjusted the water volume to the lowest possible gallons per minute to control flow rate and still maintain the required dust suppression level,” Schussele says. “Using VPS without outside wind disturbance achieved the optimum particle capture rate with much less water than typical outdoor applications.”
 

Scientific particle sizing

Rather than saturating surface material like a high-flow sprinkler system, VPS matches the size of the droplets to that of the fugitive particles. Every substance—from funnel glass to coal—produces different sized particles based on its characteristics and the method of processing, says Schussele.

To achieve optimum effectiveness, droplets and dust must be roughly the same size, inducing the maximum number of collisions with the particles and pulling them to the ground. Droplets that are too large create a “slipstream effect,” in which air travels rapidly around the droplet as it falls, causing smaller particles to get caught within the air stream and deflected around the droplet rather than being absorbed.

For example, according to the National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, particles are visible at around 50 microns, inhalable up to 100 microns and tend to linger in the air at sizes of up to 200 microns.

Standard flat-head industrial sprinkler systems produce rainlike droplets between 200 and 1,000 microns in size, which are too large to capture smaller particles. The water saturates surface material but does not address particles that are already airborne. A low-volume atomized mist unit produces droplets between 50 and 200 microns in size, creating a larger percentage in the low size range while using less water. After following the material flow into the container, the mist settles, suppressing surface dust as well.

“The inhalable glass dust particles that try to escape the material stream can’t avoid the curtain of atomized mist surrounding it,” Schussele says. “By determining the correct droplet size range and water flow rate, we provided adequate dust suppression both in the air and on the surface while still being able to avoid filling the container with liquid.”

Flow rate is important in this application as the volume of water may increase the container weight and change the consistency of the delivered material, potentially affecting transport costs and subsequent processing. The 23.5-inch DB-R’s maximum water usage is 9.52 gallons per minute, causing little or no pooling or runoff within or outside of the transport container.

Artozqui says Kuusakoski’s staff was surprised by how quickly the system cleared the haziness within the plant.

“DCT visited us on several occasions. They really took the time to assess the issue and come up with the best and most cost-effective solution,” he says.

This article was supplied by Dust Control Technology, Peoria, Illinois, www.dustboss.com.