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Breaking the mold

Oct 31, 2014 | 08:00 PM | Bill Beck


Breakthrough steel furnace technologies like hydrogen flash smelting, the paired straight hearth furnace, molten oxide electrolysis and Siemens VAI Metal Technologies’ Simetal Quantum electric-arc furnace technology are moving from the laboratory to production.

Because of their efficiency, steel furnace technologies tend to have a long shelf life. Basic oxygen furnaces, an outgrowth of the 19th-Century and early 20th-Century blast furnace, have been making steel for a half century. The electric-arc furnace (EF), a mainstay of today’s mini-mill industry, started making serious inroads into steelmaking in the 1970s.

"The technology we have today for iron and steel making—the blast furnace route or the electric-arc furnace route—are both mature technologies," said Lawrence W. Kavanagh, president of the Steel Market Development Institute (SMDI), a business unit of the Washington-based American Iron and Steel Institute. "They are very efficient, very productive."

But at a time when concerns about carbon footprints and greenhouse gas emissions can grab the headlines, both major steelmaking technologies are facing scrutiny. The basic oxygen furnace reduces iron pellets or fines to molten iron by burning metallurgical coal and limestone. The EF uses prodigious amounts of electric power to melt ferrous scrap; much of that electricity is produced in coal-fired baseload electric generating stations.

During most of the 21st Century, the steel industry, in conjunction with the U.S. Energy Department and the academic community, has conducted research aimed at developing both incremental and breakthrough iron and steel making technologies, achieving advances in automation and energy management that continue to improve the steelmaking process. The steel industry is advancing research on the next generation of iron and steel making technologies into pilot projects that could go into commercial production as soon as the end of this decade. And those cutting-edge projects hold the potential to dramatically reduce or eliminate carbon dioxide emissions from U.S. mills.

Breakthrough technologies like hydrogen flash smelting, the paired straight hearth furnace, molten oxide electrolysis and Linz, Austria-based Siemens VAI Metal Technologies GmbH & Co.’s Simetal Quantum EF technology are moving from the laboratory to pilot plant production.

"These were ‘Buck Rogers’ things 15 years ago," Kavanagh said.

For much of its history, the U.S. steelmaking industry has been coal-based. Bessemer steelmaking technologies, developed in England in the mid-19th Century, and open-hearth technologies, which swept the industry in the late 19th Century, often were fueled by charcoal from North American forests. The discovery of metallurgical coking coal in Pennsylvania in the mid-19th Century, and the rapid depletion of forests in eastern North America at the time, led to a shift in steelmaking fuel that has remained productive to this day. During the 20th Century, world production of molten iron from blast furnaces increased from 40 million tons annually to nearly 600 million tons.

Essentially a large vertical shaft made of steel and lined with refractory brick, the blast furnace is charged from the top with iron ore, coking coal and limestone. Blast furnaces typically last a decade or more before having to be pulled out of service to reline the refractory brick. The basic oxygen furnace (BOF) was developed by the predecessors of Austria’s Voestalpine AG after World War II and introduced commercially in the 1950s. An open-topped, pear-shaped converter is tilted to receive a charge of scrap and hot metal and charged with a top-mounted oxygen lance. The BOF was scaled up during the 1960s and 1970s and helped reduce the production time of molten iron to 45 minutes from upwards of 10 hours.

Incremental technologies, such as Corex, Finex and HIsmelt, which used fluidized beds and gas to reduce iron ore to molten iron, emerged in the late 20th Century. Another breakthrough technology, however, captured a growing share of the industry’s production in the last third of the 20th Century: the electric-arc furnace. The EF dates to the late 19th and early 20th centuries, when it was primarily used to produce small quantities of alloy and stainless steel. But after 1970, when Northwestern Steel & Wire Co. built what was then the world’s largest EF mill in Sterling, Ill., the technology continued to upscale and helped create the modern mini-mill industry. The development of improved EF processes and larger mills in the two decades after 1970 allowed U.S. mini-mills to capture all of the long products market from integrated mills.

"In 1960, there were about 20 mini-mills that produced only a few percent of the total steel production in the U.S.," Clyde Selig, former chief executive officer of CMC Texas Inc., wrote in his recently published book, America’s Mini-Mill Industry: A Short History. "By the end of the last decade of the 20th Century, there were 50 such small mills producing nearly 70 percent of the total U.S. flat and long product production."

But the technologies the industry uses to make steel are based on coal, and the 21st-Century economy is rapidly turning away from that energy source due to environmental concerns.

Two factors are driving the steel industry’s search for new steelmaking technologies: the potential for climate change and the emergence of vast new deposits of shale gas, both in North America and abroad.

Joseph R. Vehec, senior director of collaborative research and development at the AISI’s Pittsburgh office, said that much of the impetus for research into new steelmaking technologies stems from concerns about energy efficiency and climate change.

"We started the idea for a lot of these projects during the early rounds of the Kyoto Protocol," Vehec said, noting that the international treaty on global warming in the early 21st Century created a framework for public-private participation in energy and environmental research and development. Vehec and the AISI have worked closely with the Energy Department over the past 10 years on a host of projects dedicated to increasing the competitiveness of the U.S. steel industry, saving energy and enhancing the environment.

"One of the benefits to energy reduction in steelmaking is reducing greenhouse gas emissions," Vehec said. "Steel made in the United States is the lowest in energy usage of any country in the world. Our greenhouse gas emissions are second only to South Korea. That’s why you see so many manufacturing businesses bringing plants back to the U.S."

In recent years, however, coal has been identified as a major source of greenhouse gas emissions. The steel industry generally has done a good job of complying with U.S. Environmental Protection Agency regulations governing nitrous oxide and sulfur dioxide emissions, but the federal government is now targeting carbon dioxide emissions, a much more difficult greenhouse gas to control. In June, the EPA announced stringent new greenhouse gas emission rules that threaten to shut down coal-fired power plants in the United States.

The new rules target massive reductions in carbon dioxide emissions by 2030, and it is virtually certain that industries that burn coal—like steel, which essentially generates nearly two tons of carbon dioxide emissions for every ton of steel produced—will fall under the purview of the new rules. One Midwest electric utility executive said the new rules will be "virtually impossible to implement overnight," whether for coal-fired generating stations or steel mills.

Fortunately for the American steel industry, a second factor is easing the pressure on coal-fired industrial production. The exploitation of vast shale deposits in North America by hydraulic fracturing and horizontal drilling has unleashed a flood of domestic oil and gas. In five years, the Bakken shale has made North Dakota the second-biggest oil and gas producer in the Untied States, and wells are being developed in shale gas formations from Texas to Pennsylvania. The United States is expected to be the world’s largest producer of oil and gas by 2020.

Since natural gas generates far fewer emissions than coal, industrial producers are shifting to that fuel, which is opening up the possibility of breakthrough furnace technologies for the steelmaking industry.

"In the last five to eight years, shale deposits have provided a low-cost, stable supply of natural gas," Kavanagh said. "That’s enabled the development of a lot of research."

One project that shows promise of commercial development within the next 10 years is the paired straight hearth (PSH) furnace. Originally designed as a coal-based direct-reduced iron (DRI) and molten metal process for the long-range replacement of blast furnaces and coke ovens, the PSH furnace process—which stacks pellets up in the furnace, and can use virgin iron ore or steel mill waste—has been tweaked to utilize natural gas as a reduction fuel.

Working in conjunction with the Energy Department’s Industrial Technologies Program, SMDI and industry partners ArcelorMittal USA LLC, Chicago, Bricmont Inc., Canonsburg, Pa., and U.S. Steel Corp., Pittsburgh, along with Wei-Kao Lu of McMaster University in Hamilton, Ontario, have already developed pelletizing and pellet-handling systems and processes, solicited and selected engineering design proposals, created comprehensive PSH furnace design concepts, conducted bench-scale testing and developed engineering estimates for a PSH furnace pilot plant design. The partners hope to start up a 50,000-ton-per-year pilot project at a steel mill in the United States sometime in 2015.

"The PSH furnace is much closer to commercial application than other processes," Kavanagh said. "I think we will see commercial operation of that technology sometime in the next 10 years."

But the PSH furnace isn’t the only breakthrough technology that steelmakers, university researchers and Energy Department staffers are investigating. Another promising technology that has been studied since 2012 is hydrogen flash smelting. Developed under the supervision of principal investigator H.Y. Sohn at the University of Utah in Salt Lake City, flash smelting uses iron ore fines or concentrates and natural gas or hydrogen to produce a hot reducing gas that burns at temperatures above 1,300 degrees Celsius (2,370 degrees Fahrenheit). When natural gas is used as the reducing agent, operators can add carbon to the molten iron product and make a DRI product. They also can make the product as a solid for use in an EF.

The AISI and its market development institute are working with the University of Utah, the Energy Department’s Advanced Manufacturing Office and industry partners ArcelorMittal USA, U.S. Steel, Berry Metal Co., Harmony, Pa., and North Canton, Ohio-based Timken Co. on a flash smelting pilot project.

"It’s a technology that would be fantastic for steelmaking," Kavanagh said. "It is suitable for use in steelmaking vessels, and it does not require coke."

The process could reduce energy consumption by up to 20 percent vs. historic levels because it uses iron concentrates that do not require pelletizing or sintering. Besides the significant increase in energy productivity, the flash smelting process also produces fewer emissions, especially carbon dioxide, compared with the conventional blast furnace path to ironmaking. Researchers hope to use a large-scale bench reactor to test natural gas as the fuel reducing agent. The goal for 2015 is to determine the optimum conditions for the flash ironmaking process and outline cost estimates and a preliminary design for an industrial pilot plant.

Another project supported by the AISI and the Energy Department is molten oxide electrolysis (MOE), developed by Donald Sadoway and Antoine Allanore at the Massachusetts Institute of Technology (MIT). Sadoway, the John F. Elliott Professor of Materials Chemistry at MIT, discovered MOE while working on a National Aeronautics and Space Administration grant to discover ways of producing oxygen on the Moon.

Working with Allanore, the Thomas B. King Assistant Professor of Metallurgy at MIT who formerly worked in the steel industry, Sadoway developed an alloy of chromium and iron for an anode to pass current into a molten mix of iron. The anode had to be thick enough to prevent further attack by oxygen but thin enough for electric current to flow freely through it. Sadoway noted that the alloy uses materials that are "abundant and cheap" and produces exceptional-quality steel, with oxygen as a by-product. The two MIT scientists are currently working to design, build and test an MOE reactor.

Siemens’ Simetal Quantum EF technology is currently being evaluated by a Mexican steelmaker. The furnace, which was installed in 2012, recovers energy from hot exhaust gas, consumes only 280 kilowatt hours per tonne with a 100-percent scrap charge. Energy savings of 20 percent are coupled with a reduction of carbon dioxide emissions approaching 30 percent.

The U.S. steel industry has made major strides in the past quarter century, reducing energy intensity per ton of steel shipped by 33 percent since 1990. The industry has become highly automated, with far better control of temperatures, processes and properties. But the improvements have largely been incremental. Now, however, the industry may well be on the cusp of breakthrough technologies that could well transform steelmaking in the next quarter century.


 

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