The company’s EfW facilities are designed to integrate with municipal solid waste (MSW) systems to maximize the recovery of energy via a complete combustion process. In the meantime, the company is recovering metals left as byproducts of the company’s combustion process.
Covanta–operated facilities are covering a lot of ground: its EfW plants in North America are converting 19 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. The company reports it produces almost 8 percent of the renewable energy generated in the United States, with the exception of hydropower.
Unlike incineration, Covanta’s is a complete combustion process that burns MSW as the primary fuel source for energy, in specially designed boilers. It is a controlled combustion process that 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 Energy.
The EfW process ultimately produces a combined ash comprising two of the by-products of the EfW process: the bottom ash that remains after combustion and air pollution control residue.
The process also supports recycling, because 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 that would otherwise go unrecovered if the MSW was simply landfilled.
Covanta is able to recover 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 amount of metals present in the ash is significant: Annually Covanta’s EfW facilities recover about 430,000 tons of ferrous and more than 15,000 tons of nonferrous metals 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 every year.
While Covanta’s proportion of about 450,000 tons of both ferrous and nonferrous metals seems substantial, the company’s managers learned in 2013 that they could be doing more.
Steve Bossotti, vice president of organic growth and innovation, says increased metal recovery has in fact been one objective named in the company’s strategic organic growth initiatives rolled out in recent years. The company 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 company-wide to recover the as-yet untapped nonferrous stream.
As part of that process, Bossotti and Chief Engineer Rich Molter conducted ash tests at some locations to determine the amount of metals remaining in processed bottom ash. What they discovered surprised them.
“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 its bottom ash. That was the company’s Delaware Valley plant in Chester, PA, which had upgraded its ferrous recovery in recent years, having previously installed Eriez’ P-Rex permanent rare earth magnet.
“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.”
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 from location to location 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 their 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 they could maintain 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, NY, facility was selected for an upgrade.
“Our ash testing indicated it would be a good place to start and the facility was excited to do so,” Bossotti recalls.
The 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.
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.
“With rare earth magnets like the P-Rex, you can keep a wider gap,” he says, explaining 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 nine 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 the P-Rex, 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 that 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.
“We did a quick look at our biggest plants and we determined, it’s definitely worth doing it,” Bossotti says, who adds that new magnets in general are an important part of Covanta’s overall goal for improving ferrous recovery. He also notes that the company figures or plans on earning a return on such investments within a two-year period.
“We looked to upgrade six more facilities, and rare earth magnets will be a part of that equation,” Bossotti says. He notes that Covanta now has six facilities in some form of installation, and the company continues to evaluate further opportunities.
Four of the additional P-Rex drums were expected to be installed by the end of the year, and Bossotti has high expectations.
“We’re hoping that the performance of our other facilities looks just like Niagara did, and creates more of an opportunity for Covanta to recover more metals,” he says.
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Eriez,world authority in advanced technology for magnetic, vibratory and inspection system applications... designs, develops, manufactures and markets magnetic separation, metal detection and materials feeding, screening, conveying and controlling equipment for process and metalworking industries.