All Charged Up

Shredded ferrous scrap has long been endorsed by steel mill melt shop managers as a feedstock that, provided it has the right chemistry, offers many advantages.

At electric arc furnace (EAF) steel mills, which often rely on ferrous scrap to provide the vast majority of the furnace charge, preferences for shredded grades have helped prompt the growth in the auto shredder population in the United States and around the world.

Convinced that using more shred was likely to produce worthwhile results, Ecuador-based steel company Adelca (Acería del Ecuador) recently installed an auto shredding plant adjacent to its mill and measured the results of shifting to predominantly shredded furnace charge.

In Need Of An Upgrade
In a presentation to the Bureau of International Recycling (BIR) Shredder Committee in Shanghai at the World Recycling Convention & Exhibition in May 2013, Marion Andres Albuja Rivadeneira of Adelca described the company as “the most important Ecuadorean steelmaker,” having the ability to produce up to 315,000 metric tons per year of rebar and small shapes.

Adelca was founded in 1963 and is situated near Ecuador’s capital city of Quito. While some of its steel products are consumed domestically, it also exports to Chile, Colombia, Peru and Venezuela.

From 2006 to 2008, Italy’s Sider Engineering S.p.A. helped provide and install the technology for what was commissioned originally as a 160,000-metric-tons-per-year melt shop.

The EAF technology has allowed Adelca to promote “a virtuous cycle” that entails helping Ecuador recycle its own scrap and keep its land clear of illegally disposed of appliances and vehicles.

Another reason to rely on ferrous scrap has been its effectiveness as a charge material in the melt shop. Although Adelca studied EAF production thoroughly before starting its furnace, after Adelca’s melt shop opened in 2008, Albuja said the company still had plenty to learn by monitoring activities.

“Like most new melters, Adelca began its operation focusing on all the costs related with the process, including energy, labor and additives—but particularly on the scrap, which is really 60 percent of total cost,” he told BIR delegates.

Adelca’s original mix of scrap included loose, sheared and baled ferrous scrap, including white goods, small shapes, loose sheet and some auto hulks. The bales proved particularly problematic, said Albuja, as they “had a lot of nonferrous material, such as rocks, nonferrous metals and plastic.”

Adelca’s original scrap mix, as described by Albuja, was:

• 50 percent pressed and sheared;
• 30 percent bundled;
• 10 percent torch cut;
• 5 percent cast iron; and
• 5 percent other scrap types.

The overriding characteristics were “low density and low purity,” Albuja said, which resulted in “long charging and melting times” at the mill.

A New Approach
After scrutinizing its scrap procurement and melt shop performance results for more than one year, Adelca devised a capital investment and productivity improvement plan that entailed a major commitment to shredding.

The first step in Adelca’s plan involved purchasing a new higher voltage furnace transformer from WEG S.A. of Brazil in February 2010.

The transformer tied in to Adelca’s next step, which was the purchase of an auto shredder. “The increased transformer size and power was strategic in that it greatly enhanced the ability to melt a higher percentage of shredded scrap, which must be strategically placed near the furnace walls,” said Albuja.

Two months later, Adelca committed to the purchase of a 4,000-horsepower shredder from the The Shredder Co., based in Canutillo, Texas.

“Adelca was convinced that better scrap would greatly improve production,” said Albuja. “We had tested shredded scrap in the blend going into the furnace,” he told BIR delegates, and the company had found it to provide better density and cleanliness.

Adelca’s commitment involved using shredded ferrous scrap at levels not often matched at other steel mills. “We had reached using up to 40 percent to 50 percent shred in the mix charge successfully; we challenged ourselves to learn how to use 80 percent to 90 percent of shredded scrap,” he remarked.

By April 2011, both the new furnace transformer and the new shredding plant were installed and operating. “Three months later, Adelca’s objectives were reached,” said Albuja, who said the melt shop’s new scrap mix consisted of:

• 85 percent shredded scrap;
• 8 percent torch cut;
• 4 percent bundles;
• 2 percent cast iron; and
• 1 percent other types of scrap.

As Adelca began measuring its results, it quickly became convinced it had made the right decisions.
 

Adelca, a steel company based in Ecuador, saw multiple benefits when it changed its furnace charge to 85 percent shredded ferrous scrap, including nearly doubling its production while reducing its energy consumption.

Multiple Benefits
In contrast to feedstock that Adelca itself had characterized as low density and low purity, the shredded grade was “very high density and very high purity,” Adelca told BIR attendees.

Scott Newell Jr. of The Shredder Co. also has spread the word about the results of the Adelca project. At a presentation made in March 2013 at the Middle East Metals Recycling Conference in Dubai, United Arab Emirates, Newell noted that Adelca was able to reduce its “tap-to-tap” steelmaking production time from 67 minutes to 40 minutes.

This gain in production speed has helped convert Adelca’s mill from producing 14,000 tons per month to 26,000 tons per month while also decreasing power usage. “The use of shredded scrap has saved $35 to $40 per ton in power, electrodes and [melting] additives,” Newell said.

In his presentation to BIR delegates two months later, Albuja confirmed those results and provided additional detail.

With its prior scrap mix, Adelca had to make five charging bucket trips to load the 32 tons of scrap it needed for a heat. Now, using 85 percent shredded scrap, just two charging bucket trips are needed.

Thanks to the greater purity of the material, the company uses less than half of the lime additive it had formerly used.

Another savings takes the form of increasing the life span of electrodes and furnace refractory lining. Refractory linings are lasting more than twice as long as previously and electrodes more than 30 percent longer, thanks to the relative absence of bulky, sharp-cornered bales, which could either break electrodes or damage refractory linings.

Return on investment also has accrued in the form of energy savings. Even with a higher voltage transformer, Adelca is using 445 kilowatt hours (kWh) to produce one metric ton of steel, compared with 580 kWh with its prior methodology.

As also mentioned by Newell, the mill’s tap-to-top time is down nearly 41 percent, which has been a crucial factor toward lifting total hourly productivity from 19.5 metric tons to 36.8 metric tons and total monthly production from 14,000 metric tons to 26,500 metric tons.

Adelca’s melting yield has risen from 85 percent to 92 percent, creating one more advantage at the very end of the steelmaking process: a decrease in slag production from 20 percent of output to just 9 percent.

A benefit at the front end of the process involves the separation of nonferrous metals at a downstream sorting system installed behind Adelca’s shredding plant in October 2012. “Successful recovery was almost immediate,” Albuja said. “Currently we are selling small quantities of Zorba, Twitch, Zurich and stainless scrap to China and other countries.”

Albuja said, “The shredding process has had a strong impact, reducing the overall cost and increasing the melt shop’s productivity. The cost reduction related with shredded scrap use has been approximately $35 to $40 per billet [metric ton] of steel produced.”

Since adding the nonferrous separation equipment downstream of its auto shredder in October 2012, “the value of the nonferrous metal recovered reduces the [net] cost of our scrap between $20 and $25 per [metric ton],” said Albuja, allowing the company to bid more for auto bodies and white goods.

Upon hearing Albuja’s presentation at the World Recycling Convention & Exhibition, BIR Shredder Committee Chairman Jens Hempel-Hansen, whose company H.J. Hansen Recycling Industry A/S operates a shredding plant in Denmark, commented, “I am glad to hear this; we don’t always think we get the premium we deserve for shredded scrap.”

In Newell’s presentation at the Dubai conference, he commented that while Adelca had to make sizable investments in its shredding plant, the level of expenditure was nowhere near what it would have been had the company simply added melt shop capacity to expand from 14,000 metric tons per month to 26,000 metric tons per month without changing its approach to feedstock preparation.

Newell predicted that results like these will help convince more steelmakers that the EAF process fed with ferrous shred is a viable way to compete in the future. He said the advantages of the feedstock include high yield, good density, no electrode breakage, less air pollution or emissions and reduced “tap-to-tap” time in the steelmaking process.

The author is editor of Recycling Today and can be contacted at btaylor@gie.net.