by Vaclav Smil
Steel cans dominated the beverage market until the 1960s, but in the United States they were entirely displaced by lighter aluminum—for beer by 1994 and for soft drinks by 1996. However, in food industry they remain ubiquitous for preserving meats, fruits, and vegetables: in the United States more than 1500 food items are sold in cans (CMI, 2013). Replacing freezing by canning has a number of environmental gains, above all substantial reduction of acidification, air pollution, and emissions of greenhouse gases. As the cans got more common (in the United States more than 100 million of them are opened every day), they got lighter: in the EU the mass of beverage steel cans was halved in 30 years. The cans come as traditional tinplate steel (with a thin tin coating on both sides), tin-free sheet (Cr2O3-plated), and polymer-coated steel. In the United States, their recycling rate is now about 70% or close to 2 Mt/year; in the EU, their recycling rate rose from just around 25% in 1990 to the US level, in Japan the rate is 85%, and in China it is about 75% (WSA, 2011b).
In the United States, the overall rate of steel recycling rose from the mean of 67% during the first half of the 1990s to as much as 103% in 2008, and it averaged 90% during the years 2009–2014 (SRI, 2014). In the United States, scrap is destined primarily for two categories of steel mills: the first one makes light flat-rolled products that contain about 30% recycled metal; the other one makes a wide range of products, but it is the exclusive producer of structural shapes whose recycled content is about 80% (AISI, 2009). Estimates of global recycling rates by the World Steel Association are, as expected, somewhat lower than the US values: 85% for construction and automotive, 69% for containers, and 50% for appliances, with the overall mean of 83% in 2007 and target of 90% in 2050 (WSA, 2009). These rates make it clear that, overall, steel recycling has been a great success, resulting in substantial reduction of waste disposal and concurrent energy savings.
Rising steel demand and accumulating stores of steel have resulted in generally higher rates of recycling, expanded international trade (with some peculiar, although not really surprising, attributes), and rising (but also rather unstable) scrap prices. In comparison, aluminum is the next most recycled metal, with 67% of all cans (the most common objects made from this light metal) now recycled in the United States, while no more than about 30% of all consumer electronics, 25% of all glass containers, 10% of all plastics, and less than 10% of synthetic carpets are recycled (USEPA, 2014).
Given the highly uneven distribution of steel stocks, the international steel scrap trade was destined to grow: global exports tripled between 1975 and 2000 (from less than 20 Mt in 1975 to about 68 Mt at the century’s end), and they reached the record level of 108.7 Mt in 2011 before falling back to about 95 Mt in 2013 (BIR, 2014; WSA, 1982; WSA, 2015). The United States has been the leading (but fluctuating) exporter, accounting for about 40% of the total in 1975, just below 10% in 2000, 27% in 2010, roughly 30% in 2011, and down to 20% in 2013. In 2014, American steel scrap exports to its main customers declined substantially, by about 20% to Turkey and South Korea, and by two-thirds to China (Recycling International, 2014).
Although some European countries have been steady scrap exporters (Germany, France, the Netherlands) and the EU as a whole is the net scrap exporter, the EU is also the world’s largest importer (it bought nearly a third of the traded total in 2013), while Turkey leads the national import ranking with nearly 20 Mt in 2013 compared to 9.3 Mt to South Korea, 5.6 Mt to India, and 4.5 Mt to China. Besides the United States and EU, the other large scrap exporters are Japan (to South Korea and China), Russia (mainly to Turkey and South Korea), and Canada (mostly to the United States). Chinese scrap imports have been fluctuating: they rose from just 1.2 Mt in 1995 to 10.1 Mt in 2005, 2 years later they fell to 3.4 Mt, they peaked at 13.7 Mt in 2009, and they fell again to 4.5 Mt by 2013. Their only constant has been their dominant country of origin, the United States. This aspect of the Sino-American trade is certainly among the most remarkable indicators of shifting national fortunes, with the world’s largest affluent economy being the leading supplier of waste materials to the world’s fastest modernizing country.
Not surprisingly, scrap collection, sorting, selling, and exporting are highly decentralized, and the world’s largest metal recycler, Britain’s Sims Metal Management, is processing annually only more than 17 Mt of material, mostly steel. Steel scrap prices grew slowly during the first 7 years of the twentieth century and then more than doubled in the early months of 2008 before plunging by about 70% before the year’s end. During 2012, they were as low as $330 and as high as $425; by the spring of 2015 they fell to less than $250 (Steel Benchmarker, 2015).
Material Balances of EAFs
World Steel Association puts the recent average of specific material requirements for this, the second most important steelmaking route, at about 880 kg of scrap metal, 150 kg of coal, and 43 kg of limestone per tonne of steel (WSA, 2011a). Remus et al. (2013) offers these ranges for EAFs in the EU (all per tonne of steel): 1039–1232 kg of scrap, 0–53 kg of pig iron, 0–215 kg of DRI, 25–149 kg of lime and dolomite, and 3–28 kg of coal. In 2012, when the worldwide output of EAFs reached 446 Mt (nearly 29% of the total), that translated to about 390 Mt of charged scrap metal, 67 Mt of coal, and 10 Mt of limestone—and every tonne of steel made from scrap instead from pig iron saves about 1100 kg of iron ore, 640 kg of coal, and 2.9 MWh of energy. As already noted, the third route, the DRI ores, has not diffused as rapidly as once hoped. MIDREX DRI, commercially the most successful version, requires 1.7 t of pellets, 240 kg on natural gas, and about 135 kWh of electricity (IEA, 2010).
As with the BOF steelmaking, actual material requirements of EAFs vary depending on the kind and quality of the charged metal, and the charges can be fairly flexible, consisting of combinations of scrap with hot metal (pig iron, making up anywhere between 10% and 50% of the total ferrous charge) and scrap with briquettes. For example, material requirements of a typical design of Siemens’ SIMETAL EAF Ultimate—with tap weight of 120 t, tap-to-tap time of 30 min, and daily productivity of 5760 t in 48 taps—are 45 m3 (about 60 kg)/t of oxygen, 10 kg/t of carbon charged and another 7 kg C/t injected, and 1.2 kg/t of electrodes (Siemens VAI, 2011).
In contrast, charges into a large Turkish EAF show the following specific rates (also per tonne of steel): scrap 908 kg; pig iron 136 kg; coke 18 kg; fluxes 45 kg; ferroalloys 6.3 kg; electrodes 2.3 kg; oxygen 63.8 kg; and 10.9 t of cooling water (Yetisken, Camdali, & Ekmekci, 2013). Specific charges into a small (30-t) Turkish EAF were 1053 of scrap, 49 kg of coke, 36 kg of fluxes, and 92 kg of oxygen, while the waste streams included 86 kg of slag, 120 kg of gases, and 19 kg of dust per tonne of steel (Tunc, Camdali, & Arasil, 2012). And for a German furnace using only scrap, Pfeifer and Kirschen (2002) reported average specific inputs of 1036 kg of metal, 21 kg of coal, 4 kg of natural gas, 28 kg of fluxes, 56 kg of oxygen, and 3 kg of electrodes per tonne of steel, and outputs of 16 kg/t of dust and 235 kg/t of furnace gases.
Although EAF is an inferior hot metal processor compared to BOF, charging of pig iron to replace a portion of scrap reduces electricity consumption and raises productivity, and it is now often done in integrated mills where such metal is readily available. The mass of hot (1150–1350 °C) metal poured into the furnace contains energy equal to about 450 kWh/t and, consequently, if it amounts to 40% of the total charge it will reduce the overall electricity consumption by 180 kWh/t (Toulouevski & Zinurov, 2010). But scrap recycling remains the EAF’s primary mission, and changes in material handling have contributed to their higher productivity and reduced electricity demand.
Large furnaces used to be charged through the open top from two or three scrap-carrying baskets, prolonging the charging time and allowing the escape of furnace gases, but recent practice has converged on charging even the furnaces with more than 100 t capacity from a single basket (loaded with scrap whose density is up to 0.8 t/m3), a practice that requires switching off the current for as little as 3 min, and that also halves the dust emissions compared to
the charging with two baskets. But larger furnaces, such as the 320-t Simetal Ultimate installed since 2007 at Gebze mini-mill in Turkey (processing scrap and pig iron), use two or three baskets (Siemens VAI, 2012).
Another important energy-reducing measure has been the preheating of the charge scrap. This was done first simply by heating it inside the charging baskets, or in special baskets designed to withstand high temperatures and also cooled by air or water. Two better options use the conveyor method of heating, either in a vertical arrangement (as sectional shaft preheaters) or as horizontal preheaters, with both using the exiting furnace gas. The horizontal belt conveyor, used since the late 1980s by the Consteel process, achieves virtually continuous charging through a sidewall door. Scrap moves through a tunnel (about 30 m long) and is heated by furnace gases and discharged into the furnace at a level that maintains a constant temperature of at least 1580 °C.
Besides increased energy efficiency, this method also reduces arc-generated noise and prolongs the life of water-cooled panels, and because the furnace operates at a negative pressure, it also eliminates any uncontrolled gas emissions through electrode ports. By 2013, the process was deployed in 35 mills on 3 continents, including the world’s largest EAF, a 420-t capacity Tokyo Steel furnace operating at the Tahara plant since June 2010 (Ogawa, Sellan, & Ruscio, 2011). This Danieli design is a twin DC furnace with a diameter of 9.7 m, capacity of 300 t hot metal and 120 t hot heel, maximum power of 175 MW, and tap-to-tap time of 50 min (hence hourly productivity of 360 t), and it consumes 33 m3/t of oxygen delivered by six jets and a supersonic lance.
Despite these accomplishments, the long-term worldwide trend toward more secondary metal was recently even temporarily reversed because of China’s enormous expansion in the smelting of pig iron. The global steel:pig iron ratio was about 0.9 in 1900, it reached 1.41 in 1950, it rose only marginally to 1.48 by the year 2000, and then it fell back to 1.39 by 2010 and increased a bit, to 1.41, by 2013 (WSA, 2015). But the story has been different in the United States thanks to the country’s long history of ferrous metallurgy and its large stores of scrap iron.
The US steel:pig iron ratio rose from 0.72 in 1900 to 1.23 in 1950, it stood just above 2.0 in the year 2000, and, despite the fact that the country has become a major scrap exporter, it rose to 2.82 in 2010 and 2.86 in 2013, when nearly three times as much steel came from recycled material than from iron ores. For comparison, steel:pig iron ratios are high in Germany (1.57 in 2013, scrap sourced from domestic stocks) and South Korea (1.61, scrap mostly from imports), still low in China (1.16 in 2013), and, surprisingly, also low in the United Kingdom. About half of the world’s 90 steel-producing countries, with most of them being small producers in Europe (Bulgaria, Greece, Portugal), the Middle East, Africa, Latin America, and Asia, now rely only on EAFs and on mostly imported scrap.
Chapter 7
Energy Costs and Environmental Impacts of Iron and Steel Production
Fuels, Electricity, Atmospheric Emissions, and Waste Streams
Abstract
Before 1973, energy supply was just another factor in doing business, because for most industries the total cost of purchased energy was not a particularly onerous burden (at that point, the inflation-adjusted price of oil had been going down for more than two decades), and only the makers of the most energy-intensive products had explicit worries about the cost of fuels and electricity and about the total energy required by their industries. Then the two rounds of oil price rises during the 1970s swiftly elevated energy supply, energy cost, and energy requirements to major economic, social, and political concerns as all industries, and especially all major consumers of fuels and electricity, began to look for ways to reduce their energy consumption and to lower the final energy intensity of their products.
Keywords
Fuels; electricity; atmospheric emissions; waste streams; energy supply; water use; life cycle analysis; greenhouse gas emissions
Before 1973, energy supply was just another factor in doing business, because for most industries the total cost of purchased energy was not a particularly onerous burden (at that point, the inflation-adjusted price of oil had been going down for more than two decades), and only the makers of the most energy-intensive products had explicit worries about the cost of fuels and electricity and about the total energy required by their industries. Then the two rounds of oil price rises during the 1970s swiftly elevated energy supply, energy cost, and energy requirements to major economic, social, and political concerns as all industries, and especially all major consumers of fuels and electricity, began to look for ways to reduce their energy consumption and to lower the final energy intensity of their products.
Inevitably, the iron and steel industry has been in the forefront of these efforts. When put into a longer perspective, this has been nothing new: the history of ironmaking can be seen as a continuing quest for higher energy efficiency, and this effort brought typical fuel requirements from almost 200 GJ/t of pig iron in 1800 to less than 100 GJ/t by 1850, to only about 50 GJ/t by 1900 (Heal, 1975), and to less than 20 GJ/t a century later. In relative terms, steel, now requiring less than 20 GJ/t in state-of-the-art mills, is not the most energy-intensive commonly used material: aluminum needs nearly nine times as much energy (175 GJ/t, mostly as electricity), plastics consume mostly between 80 and 120 GJ/t (much of it as hydrocarbon feedstock), copper consumes about 45 GJ/t, and paper’s energy cost is up to 30 GJ/t, while lumber and cement need less than 5 GJ/t, and glass goes up to 10 GJ/t.
But, as stressed in this book’s first chapter, the world’s current annual steel consumption is nearly 20 times that of all four common nonferrous metals (Al, Cu, Zn, Pb) combined, and this, combined with the relatively high-energy intensity of steelmaking, makes the industry a leading industrial consumer of fuels and electricity, and hence also a leading emitter of polluting gases and an important contributor to anthropogenic generation of CO2. Consequently, the first two sections of this chapter will review the recent energy costs of iron- and steelmaking, focusing not only on aggregate needs but also on the requirements of all major specific processes as well as on differences among nations.
Moreover, I will not cite only the latest assessments but will also look at the remarkable evolution of steelmaking’s energy intensity: few industries can match ferrous metallurgy in its old, and continuing, quest for reduced energy inputs; to state this in reverse, we would have never achieved current levels of aggregate output and its affordable pricing if we had to spend as much energy per tonne of steel as we did just after WW II (at that time it was about 2.5 times as much as now), and steel output on the order of 1.5 Gt a year would have been a mere fantasy at the 1900 level of more than 50 GJ/t. As one of the classic heavy industries—highly dependent on coke produced from metallurgical coal, consuming large masses of iron ores and fluxing materials, and producing copious solid, liquid, and gaseous wastes—iron and steel was one of the iconic polluters of the late nineteenth century and of the first half of the twentieth century. That reality has changed considerably with the introduction of extensive air pollution controls and with the adoption of new, much more efficient production processes.
Nevertheless, as both a material- and energy-intensive industry still highly dependent on coal, ferrous metallurgy is a major emitter of air pollutants, a leading industrial consumer of water, a minor source of contaminated liquids, a massive producer of solid waste, and a significant source of CO2. In this chapter’s second half, I will assess these impacts and also note the past advances in controlling common pollutants and increasingly common ways to capture and reuse materials produced by the major waste streams, and compare the industry’s environmental footprint with that of other leading industrial sectors.
As for the industry’s land claims, areas occupied by blast furnaces (BFs) and by buildings housing basic oxygen furnaces (BOFs) and electric arc furnaces (EAFs) are fairly compact, but onsite storage, handling, and processing of iron ore, coal, and fluxing materials claim
fairly large areas. Smaller old European and North America iron and steel mills were commonly located inland, albeit preferably on river or lake shores: for example, Andrew Carnegie’s Homestead Steel Works on the southern bank of the Monongahela east of Pittsburgh occupied about 112 ha (Carnegie Steel Company, 1912). Modern integrated plants with multiple BFs demand much more space: for example, Shougang Jingtang Iron & Steel occupies a new coastal site of about 2000 ha on the Bohai Bay, and seaside locations on artificial islands reclaimed from bays, the practice pioneered by Japan, have been common for new large enterprises in Asia. The Keihin Works of JFE Steel, just south of Tōkyō, are a typical example of this reclaimed location (Fig. 7.1).
Figure 7.1 JFE’s Keihin Works south of Tōkyō: coal and iron storage in the foreground; two BFs and their hot stoves on the left. Reproduced by permission from JFE Steel.
Energy Accounting
Once the era of declining oil prices ended and energy emerged suddenly as the subject of intense interest, it became obvious that we needed to get reliable and comprehensive accounts of energy costs in order to identify the extent and the intensity of energy inputs and to find the best opportunities for the most rewarding savings. In order to undertake such studies, a new discipline of energy analysis emerged during the 1970s (IFIAS, 1974; Thomas, 1979; Verbraeck, 1976). Not surprisingly, new studies concentrated on assessing energy costs of major economic factors, including individual materials (cement, plastics, steel), foodstuffs (corn, wheat), and final products (cars).
