Steelmakers need several key ingredients when charging materials into their 1,530°C (2,800°F) furnaces. Iron ore or ferrous scrap and several critical additives are required to produce desirable steel with commercial value.
Many steelmakers also may benefit if nonmetallic waste and scrap byproducts are introduced to their furnaces that can create positive changes to the chemistry of the final product and also increase the energy level in the melt, thus making the steel melt faster and more efficiently.
A team of 14 researchers from the Centre for Sustainable Materials Research and Technology (SMaRT) at the School of Materials Science and Engineering of the University of New South Wales (UNSW) in Sydney has written a report that is based on the research it conducted at the Arrium (formerly OneSteel) Sydney Steel Mill in Rooty Hill, Australia.
“This opportunity lies in the [furnaces’] high temperature environments, which offer sustainable pathways for utilizing chemical reactions to re-purpose waste materials as resources, such as reducing iron oxide to iron and dissolving the carbon in waste materials into metal,” the authors of the report say.
Problem to Opportunity
Australia recycles a healthy percentage of its industrial, commercial and post-consumer discarded materials but also has portions continuing to be landfilled.
The authors of the report, which is titled “The Power of Steelmaking—Harnessing High Temperature Reactions to Transform Waste into Raw Material Resources,” characterise Australia’s recycling efforts as incomplete in terms of plastic scrap and discarded tyres.
“Of the 1.4 million tonnes of plastic [scrap] generated in 2010-2011, just over 20% was recycled, with the bulk going to landfill,” according to the report.
In addition to the 1.4 tonnes of plastic going unrecycled, a considerable number of scrap tyres may be available to Australian steelmakers as a furnace additive. “Of the approximately 20 million passenger tyres requiring disposal in Australia every year, only 23% are recycled, 64% go to landfill and the remainder are dumped illegally,” the authors write.
The opportunity to use scrap tyres in steelmaking furnaces exists well beyond Australia, the report’s authors contend. Despite the efforts of an established and growing tyre recycling sector in many nations, “Worldwide, about 1.2 billion used tyres are thrown away annually and 4 billion or so waste tyres are currently in landfills and stockpiles, posing a risk to human health and the environment,” the report claims.
When plastic scrap or discarded tyres are sent to a landfill, the opportunity is lost for steelmakers to capture the carbon found within these forms of scrap. “Such waste materials consist mainly of carbon and hydrogen—elements vital in the metallurgical industries due to their role as reductants and carburizers,” according the report’s authors.
“These long chain hydrocarbons consist of highly volatile matter with generally low ash content,” the report continues. “This means steelmakers have an opportunity to use waste streams to source free or low-cost raw materials for production.”
Diverting mixed plastic and rubber scrap to steelmakers and away from landfills can benefit not only the steel industry but also taxpayers and commercial scrap generators. “The incentives for local governments and other industries to make such waste streams available for steel production are considerable given steep landfill charges and tight anti-dumping regulations,” they note.
The Australian state of New South Wales (NSW) is cited as an example. “In NSW … the gate cost for disposing of rubbish in landfill was A$80.30 per tonne in 2012 and is pegged to increase A$10 per year plus CPI (consumer price index) to drive local recycling.”
While such a rate increase may have encouraged recycling in some cases, it has also encouraged people to find other ways to avoid the steep charge. “One perverse consequence has been the long distance trucking of waste to [the adjacent Australian state of] Queensland in the north to take advantage of lower tip gate fees.”
A connection between these potential suppliers and a new end market would seem to make sense, provided the addition of such materials in the steelmaking furnace is indeed desirable in the melt shop.
Adding plastic or rubber materials to a steel or ironmaking furnace is not a brand new idea and has proven feasible, according to the report.
The report’s authors cite several previous examples of steelmakers successfully incorporating such scrap into their melt shop routines:
- A Japanese research team investigated reduction behavior during the heating of plastic scrap materials and iron oxide composites;
- Another Japanese research team reported the reduction behavior of iron oxide when scrap polyethylene plastics and wood were added;
- Shredded polymer scrap has been mixed directly into melts at an NKK steel mill in Japan;
- Stahlwerke Bremen in Germany has substituted coke, coal and heavy oils with plastic scrap since 1996; and
- Scrap tyres were tried on a laboratory scale and implemented in industrial production at the Laminés Marchands Européens steel mill in Trith-Saint-Leger, France, where they replaced a portion of the coal typically used.
In Australia, the UNSW researchers developed a polymer injection technology (PIT) process designed to allow a steelmaker such as Arrium “to substitute a meaningful proportion of coke in its electric arc furnaces (EAFs) with a precisely calibrated mix of granulated end-of-life polymers as a carbon injectant.”
In developing the PIT process the researchers say, “We focused on using the polymer material as a carbon replacement for slag foaming. In 2006, [Arrium] adopted the new technique and began replacing part of the metallurgical coke with HDPE (high-density polyethylene) plastic.”
With end-of-life tyres also readily available in Australia, “In 2007, rubber tyres were also considered for commercial reasons,” write the authors. “A mixed blend is now injected into EAFs as standard practice in Arrium’s Sydney and Melbourne plants and in an EAF plant in Thailand.”
With several different types of scrap and rubber feedstock available, the research team has been studying which materials or blends work best within the EAF process. “Our current research is extending our insight into high temperature (1,200 to 1,530°C, or 2,200 to 2,800°F) environments, with melamine, HDPE, polycarbonate and Bakelite, as well as agricultural wastes and tyres. Ultimately, we aim to understand the science behind such transformations to assist industry in recognizing which waste streams have potential as raw materials and, therefore, represent new opportunities for ‘waste-to-value’ processing.”
A Path Worth Taking
After testing several combinations of materials, the SMaRT research team says it is convinced adding high-carbon plastic and rubber scrap materials as furnace charge is a sensible industry practice.
“Our research to date has generated new knowledge which I believe could prove extremely important in the future of steelmaking,” the authors write in the report. “Most notably, the waste streams studied led to better, more efficient furnace operations, when combined with metallurgical coke, than the current standard practice of using metallurgical coke alone.”
Steelmakers may well have flexibility in which scrap materials they seek and how they source them. “[We] believe the potential for sourcing waste as raw materials is as broad as are the range of materials containing hydrogen and carbon,” write the authors. “That means steelmakers could envisage sourcing waste streams locally, depending on local availability; some steelmakers may have easy access to palm char, others to vast mountains of particular plastics.”
A steel mill that wishes to take advantage of the opportunity these waste materials provide only need be willing to check into its local waste and scrap markets. “Industries well understand the commercial and convenience benefits of locally available raw materials as well as the significant environmental benefits of reducing the use of coke, making good use of waste in landfill, reducing transport emissions by sourcing some production inputs locally and the subsequent improvements in furnace efficiency,” the report’s authors write.
The benefits of conducting such a local investigation can be multiple. “This innovation offers an excellent opportunity to improve efficiency while positively impacting the environment through energy savings and the transformation of waste streams,” the authors conclude. “Given the potential to implement such novel recycling solutions is not generally available to other [basic] materials industries operating at relatively low temperatures,” the report’s authors write. “This is an opportunity that could change the way we think about raw material resources for steelmaking into the future.”
The author is editor of both Recycling Today Global Edition and its sister publication Renewable Energy from Waste, and can be reached at firstname.lastname@example.org.
Seeking Sustainable Solutions
To learn more about the research team behind “The Power of Steelmaking—Harnessing High Temperature Reactions to Transform Waste Into Raw Material Resources,” visit www.RecyclingToday.com/rtge0913-energy-from-waste-update.aspx. There, you can also learn about an honor the reports’ authors received.