Sweeping the cinders

Covanta is known as one of the world’s largest operators of facilities dedicated to recovering energy from waste as well as to providing other waste disposal and recycling services.

The company, a subsidiary of the publicly owned Covanta Holding Corp., owns and/or operates 45 energy-from-waste (EfW) facilities that produce electricity for approximately 1 million homes in communities across North America.

The company’s EfW facilities are designed to integrate with municipal solid waste (MSW) systems to maximize the recovery of energy from waste via a complete combustion process. The company also is recovering metals that are byproducts of its combustion process.

Covanta reports that its North American facilities are converting 20 million tons of trash and residuals annually into 9 million megawatt-hours of clean, renewable energy and more than 9 billion pounds of steam sold to a variety of industries.

Unlike incineration, Covanta’s is a complete combustion process that burns MSW as the primary fuel source for energy in specially designed boilers. The controlled combustion process uses state-of-the-art pollution control equipment to scrub emissions and prevent them from being released into the environment, according to James Regan, corporate communications and media relations manager for Covanta.

The EfW process ultimately produces a combined ash comprising two of the byproducts of the EfW process: the bottom ash that remains after combustion and air pollution control residue. The bottom ash that remains after combustion—which comprises approximately 10 percent of the original waste stream by volume—contains valuable ferrous and nonferrous metals. Covanta recovers these metals by retrieving them from the bottom ash that remains at the end of the process. By recovering these metals, recycling rates are improved in the communities that Covanta serves, the company says.

The amounts of metals present in the ash are significant: Annually, Covanta’s EfW facilities recover about 430,000 tons of ferrous and more than 15,000 tons of nonferrous metals from the ash for recycling. That’s the equivalent amount of steel needed to build five Golden Gate bridges and the amount of aluminum in more than 1 billion beverage cans, Regan points out. The company has reported that all U.S. EfW facilities combined, including its own, are recovering more than 700,000 tons of metals for recycling annually. Covanta estimates that some 250 million tons of trash—containing metals—are still going to landfills every year in the U.S. Approximately 3 percent of the waste stream is metal, Covanta says, so potentially 7.5 million tons of metals are lost.

While Covanta’s proportion of about 450,000 tons of ferrous and nonferrous metals seems substantial, the company’s managers learned in 2013 that they could be doing more.
 

Increased recovery

Steve Bossotti, vice president of organic growth and innovation for Covanta, says increased metal recovery has in fact been one objective named in the company’s strategic organic growth initiatives rolled out in recent years. Covanta has highlighted the need to recover more ferrous as well as nonferrous metals from the bottom ash, Bossotti says.

“Two years ago we launched an organic growth initiative to recover more metals,” Bossotti says. Initially, the project was focused on increased nonferrous recovery across Covanta’s locations. Nonferrous metals were previously being recovered at fewer than half of Covanta’s facilities, so the company set up a program for added equipment companywide to recover the as-yet untapped nonferrous stream.

As part of that process, Bossotti and Project Engineer Rich Molter conducted ash tests at some locations to determine the amount of metals remaining in processed bottom ash.

“We realized some of our facilities still had a percentage of ferrous left in the ash,” Bossotti says. That was surprising, he says, because virtually all Covanta facilities were already set up to recover ferrous metals using a variety of equipment, including various electromagnetic drums, overband magnets or permanent magnets.

One facility, though, stood out among the others as having less ferrous content in the processed bottom ash. That was the company’s Delaware Valley plant in Chester, Pennsylvania, which had upgraded its ferrous recovery in recent years, having previously installed a P-Rex permanent rare earth magnet from equipment company Eriez, based in Erie, Pennsylvania.

“When we looked at the performance of our facilities, Delaware Valley stood out as a better performer,” Bossotti explains. “We tried to understand what made them different, and we found it had a rare earth magnet,” he adds.

A natural progression of that discovery, Bossotti explains, was having reason to believe there were missed ferrous opportunities and room for improvement across other Covanta locations as additional performance comparisons continued to indicate recovery differences.

“The ash testing that we did to determine the nonferrous content revealed there was ferrous opportunity, and with the rare earth magnet quality, we realized we could capture it,” Bossotti says.

Bossotti and Molter concluded that some locations had outdated equipment and upgrades would provide opportunity for Covanta and its clients.

Based on the company’s experience in Delaware Valley, its knowledge of how the rare earth magnet performed and the desire to pull material in a way that would allow for maintaining a proper working gap to avoid operational issues, in early 2013 Covanta decided to purchase another rare earth magnetic scrap drum. This time the company’s Niagara Falls, New York, facility was selected for upgrading.

“Our ash testing indicated it would be a good place to start, and the facility was excited to do so,” Bossotti recalls.

The results in Niagara Falls, Bossotti says, were almost instantaneous. “Literally the day we turned it on, there was a considerable increase in ferrous recovery,” he says, explaining that Covanta’s engineers saw a 50 percent improvement in recovery. Those results convinced Bossotti and Molter to continue looking for other upgrade opportunities across the Covanta locations.

“We were so impressed by it at the two facilities, we wound up buying four more,” says Bossotti. In fact, Bossotti adds, the company has decided to replace some scrap drums in other locations, starting with Covanta’s bigger facilities.
 

Considered factors

A key advantage with the rare earth magnet, Bossotti explains, is that because of the drum’s magnetic strength, it can be installed with a greater gap between the conveyor and the drum, where it’s better able to deal with the widely varying sizes of metal objects remaining in Covanta’s bottom ash.

He explains that closer gaps traditionally cause large objects—something like an iron safe—to potentially become wedged between the belt and the magnet, leading to an equipment jam or damage. “The natural thing to do is to set the gap higher than what will cause problems,” he explains.

“With rare earth magnets, I can keep a gap greater than 9 inches, and it can still pick up the material, so that has a real competitive advantage for me,” Bossotti explains. “I’m not wrecking conveyors, and my operator’s not dealing with jams.”

With conventional scrap drums, he adds, “for me to get the same pickup, I would have to get the magnet a lot closer, but then ugly things can happen.”

Another key benefit of rare earth magnets, Bossotti says, is the fact that its magnetic force remains consistently strong across the width of the drum. “With some magnets, the force in the middle is greater.” That means ferrous materials located at the sides of the conveyor belt might not get picked up, Bossotti says.

“Rare earth magnets allow you to get material across the full width,” he adds.

Bossotti now says, as a result of its testing, a variety of upgraded magnets, including some P-Rexes, have been selected for various Covanta locations depending on the increased recovery they will yield, and more are expected to follow.

Bossotti says new magnets in general are an important part of Covanta’s overall goal for improving its ferrous recovery going forward.

“We looked to upgrade six more facilities, and rare earth magnets will be a part of that equation,” he says.

The author is an editor with the Recycling Today Media Group and can be reached at lmckenna@gie.net.