by Vaclav Smil
Not surprisingly, the single largest finished products of China’s steel industry have been reinforcing bars (Fig. 4.5). By far the largest accumulations of reinforced concrete are in massive gravity dams on the world’s major rivers: the record goes to China’s Sanxia (22.5 GW on the Yangzi) that is 185 m tall and 2.3 km long and contains nearly 28 million m3 of concrete reinforced with nearly half a million tonnes of steel bars (Smil, 2013). China’s domestic demand has not been able to absorb all of the country’s huge steel production, and this has led to higher exports, falling prices, and rising inventories. Already in 2005 the country’s surplus steel capacity was estimated at 80 Mt (Okuno, 2006), and the Chinese exports (in net terms) rose from 22 Mt/year in 2010 to 43.4 Mt in 2013 and surpassed 60 Mt in 2014.
Figure 4.5 Reinforcing bars on a construction site in Nanjing (Jiangsu province) in China. Corbis.
And it has not been just ordinary rebar or wire; Chinese steel is now embedded in many of the world’s most prominent structures. After the San Francisco–Oakland Bay Bridge (originally opened to traffic in November 1936) was damaged by a 1989 earthquake, the 2002–2013 reconstruction of the eastern section in the form of a self-anchored suspension bridge (the structure’s visual dominant) became a Chinese affair. The bridge’s 28 individual steel deck sections with seismically resistant hinged expansion joints were made by Baosteel in Shanghai, and so was the main cable (the world’s longest looped suspension bridge cable with 17,399 compressed wires) and 158 m tall steel tower (AIG, 2015).
Since 2005 the Chinese government has been promising to reduce the country’s excess capacity, and yet it has persisted. Excess capacity is now a worldwide phenomenon created by the combination of stagnant or declining steel demand in most of the affluent countries and by the precipitous post-2000 expansion of Chinese steelmaking. This has been true not only for the common low-quality categories of steel, but also for stainless steel. Long-standing European overcapacity (EU produces more than twice as much steel as North America) and Chinese over-expansion (in 2007 China produced less than 7 Mt of stainless steel a year; by 2012 the output was above 16 Mt) created the prospect for subdued global growth (Millbank, 2013).
But there has been a major shift in Chinese expectations as the extraordinarily fast expansion of the post-2000 steel production made an inevitable slowdown come much sooner than anticipated by forecasts made just 10–15 years ago. During 2014 Chinese steel demand began to shrink for the first time since the year 2000, and steel prices have fallen to such an extent that by October 2014 one of the most quoted news items presented by Chinese Central Television was the claim that “steel is now almost as cheap as Chinese cabbage,” the cheapest of all of the country’s common green vegetables (CCTV, 2014). But the falling prices failed to stimulate domestic demand, profit margins are meager (on the order of 0.5%), and debt burden has increased (by June 2014 it totaled nearly half a trillion dollars), as have inventories of iron ore and finished steel products.
At the same time, China continued to import high-quality metal for various exacting applications and tried to reduce future steel demand (and also excessive levels of borrowing) by enacting bans on new construction projects. This is an apposite place to note that Sweden is the very opposite of China’s mass production of basic steel products: about 65% of Swedish steel output are special alloys (compared to about 15% in Japan and less than 10% in the United States), and such relatively small companies as Sandvik, Böhler-Uddeholm, Ovako, and Höganäs are the world’s leading producers of, respectively, seamless tubes, tool steel, ball-bearing steel, and iron and steel powder. The country exports about 95% of its high-quality production (Jernkontoret, 2014).
Chapter 5
Modern Ironmaking and Steelmaking
Furnaces, Processes, and Casting
Abstract
In this chapter, I will review first the state-of-the-art performances of modern ironmaking, both in the world’s largest blast furnaces and by the direct reduction of iron (DRI). The DRI processes represent a fundamental ironmaking innovation of the post-WW II era, but, although they have enjoyed some commercial success and are now operating in two dozen countries, these new metallurgical techniques have not fulfilled their early promise: by 2015 only about 5% of the global iron output originated in DRI plants. In contrast, the state-of-the-art processes of modern steelmaking include two processes that were introduced only during the 1950s but whose worldwide adoption has been (a few notable exceptions aside) extraordinarily rapid.
Keywords
Ironmaking; steelmaking; blast furnace; basic oxygen furnaces; electric arc furnaces; continuous casting
In this chapter, I will first review the state-of-the-art performance of modern ironmaking, both by the world’s largest blast furnaces and by the direct reduction of iron (DRI). The DRI processes represent a fundamental ironmaking innovation of the post-WW II era, but, although they have enjoyed some commercial success and are now operating in two dozen countries, these new metallurgical techniques have not fulfilled their early promise: by 2015 only about 5% of the global iron output originated in DRI plants. In contrast, the state-of-the-art processes of modern steelmaking include two processes that were introduced only during the 1950s but whose worldwide adoption has been (a few notable exceptions aside) extraordinarily rapid.
Without exaggeration, swift diffusion of basic oxygen furnaces (BOFs) and of continuous casting have revolutionized the industry through higher efficiencies, reduced waste, and rising productivity. The third major pillar of modern steelmaking, smelting of recycled scrap metal in electric arc furnaces (EAFs), is a process that has been practiced for more than a century, but only in recent decades has it become more than an also-run compared to open hearth furnaces (OHFs) or BOFs: it is now the dominant (more than 90%) steelmaking process in the Middle East (using scrap and DRI), Africa (nearly 70%), and in the United States (about 60%), and it produces nearly 30% of the world’s crude steel (WSA, 2015). In this chapter, I will review technical advances and the best recent performances of BOF and EAF smelting and continuous casting, and in the next chapter, I will focus on material flows of iron- and steelmaking processes and on their energy requirements.
New Blast Furnaces
Development of modern blast furnaces during the past 100 years can be followed in books by Boylan (1975), Boylston (1936), Geerdes, Toxopeus, and van der Vliet (2009), Hogan (1971), King (1948), Lovis (2005), and Peacey and Davenport (1979). An illustrated look at their construction, charging, and ancillary operations (hot blast stoves, casting, slag processing) is offered by one of their leading builders (Siemens VAI, 2008). A unique tribute to their former glory was assembled by Becher and Becher (1990): the couple had traveled widely in the regions of American and European ironmaking—Pennsylvania, Ohio, Indiana, Alabama, Ruhrgebiet, Saarland, Lorraine—to photograph more than 200 blast furnaces, both working and abandoned, in order to document the now classic phase of Western industrialization.
After more than a century of growth, modern blast furnaces reached their capacity plateau between 1973 and 1980. As already noted, the world’s largest blast furnace (No. 2 furnace at Nippon Steel Oita Works) was blown-in in 1976. Its start-up was preceded (on February 13, 1973) by the completion of Europe’s largest blast furnace, and it was followed (in October 1980) by the blowing-in of America’s largest furnace. Europe’s record holder was Schwelgern 1 at August-Thyssen Hütte in Duisburg-Marxloh, 33 m tall, with a hearth diameter of 14 m, volume of 4200 m3, and daily output of 10,000 t (ThyssenKrupp, 2003). America’s largest furnace, Inland’s No. 7 (East Chicago, Indiana), built by Koppers, had a hearth diameter of 13.5 m, inner volume of 4758 m3, working volume of 3470 m3, and daily output of about 9000 t of pig iron (McManus, 1981). This compared to an average working volume of 1600 m3 at US Steel and about 1800 m3 at Bethlehem Steel (McManus, 1988a). By that time only the Japanese ironmakers had the experience with operating such large furnaces, and the planning and early operation of No. 7 benefited from the advice o
f Nippon Steel.
When these furnaces were planned and built, nobody suspected what reverses lay ahead for Western and Japanese ironmaking, and that these structures would remain record holders for decades to come. OPEC’s first oil price rise in 1973–1974 was followed by the second round in 1979–1981, resulting in record high prices of oil and increased prices of coal, natural gas, and electricity and causing a worldwide economic slowdown. As a result, falling pig iron production—in Japan from 90 to 73 Mt between 1973 and 1983 and in the United States from nearly 92 to just 44.2 Mt during the same 10 years—had not only put an end to the building of ever larger furnaces but had also led to the closure of many older units (Becher & Becher, 1990). Eventually some aging furnaces—including the three record holders—were rebuilt or relined and relaunched as more efficient smelters with more durable linings (graphitic materials) and more efficient and hotter blast stoves.
Inland’s No. 7 was shut down for relining in August 1987 and by 1988 the US industry was relining or rebuilding nearly 40% of its remaining active furnaces (McManus, 1988a). And hence when in 1989 a long paper in America’s leading ironmaking periodical asked “Is the blast furnace in its twilight?” (Hess, 1989), the answer could be not yet, as continuing technical improvements and major relining and rebuilding efforts guaranteed to keep the world’s largest ironmakers operating well into the next century. But a decade later the doubts were back: in 1997 no full-size blast furnace was ordered, and in 1998 only China returned to building them—but, once again, the expert consensus was that the demand for pig iron, the global scale of ironmaking, and the progress on alternative iron plants would support blast furnaces for decades to come. By 2015, that verdict was only strengthened, not only because of the intervening expansion of South Korea’s and China’s ironmaking but because cumulative advances and major reconstructions have been giving the world’s largest blast furnace an even longer lease on life.
After its second campaign of 6 years, the Inland Steel’s No. 7 was relined by 1200 workers of Edward Gray Corporation in just 29 days in 1993, and its third relining, completed in March 2004, set it for a 20-year campaign (Gary Works is now a part of ArcelorMittal). The most recent relining of Schwelgern 1 with 5500 t of advanced refractory materials took place in early 2008 after the fourth campaign of about 12 years (ThyssenKrupp, 2008), and during the first 40 years of its operation it smelted 115 Mt of pig iron (WAZ, 2013). In 1993, a larger Schwelgern 2 (14.9 m hearth diameter, 4800 m3) was blown-in. It had produced 78 Mt of pig iron during its first campaign of 21 years, and after relining it began its second campaign in October 2014 (ThyssenKrupp, 2014).
After its first campaign, Oita No. 2 was enlarged from 5070 to 5245 m3 and then averaged nearly 11,200 t of hot metal a day, and on August 8, 1997, it set a new record of 13,368 t. After its second campaign, Nippon Steel rebuilt the furnace in 2004 in just 79 days. The reconstruction used a hydraulic system and piping by Kawasaki Precision Machinery, and it enlarged every part of the structure, setting a new world record: the inner volume from 5245 to 5775 m3, working volume from 4312 to 4753 m3, hearth diameter from 14.9 to 15.6 m, belly diameter from 16.6 to 17.2 m, number of tuyères from 40 to 42, and number of tapholes from 4 to 5 (Haga, 2004). The furnace was blown-in on May 15, 2004. Just a month later the furnace was producing 12,500 t a day, and 5 months later it reached its designed capacity of 13,500 t a day.
In 2009 Oita No. 1, first blown-in in 1972, was enlarged to the same volume as the second furnace (5775 m3), but in that year Japan had narrowly lost its long-held record with the 2009 completion of the Zhangjiagang II No. 4 blast furnace of Shagang Group, China’s largest privately owned company in Jiangsu province: with a volume of 5800 m3 and hearth diameter of 15.7 m, it was the first furnace with nominal capacity of 5 Mt per year and with actual output of 4.8 Mt (WISDRI, 2012). But its record rating lasted only until 2013: in June of that year South Korea’s POSCO renovated (in 108 days) its Gwangyang No. 1 furnace in Gwangyang Steelworks in South Jeolla province. The furnace, built originally in 1987 (3800 m3), was later slightly enlarged to 3950 m3: the second enlargement brought it to 6000 m3, with a hearth diameter of 16.1 m and annual capacity of 5.46 Mt (POSCO, 2013).
By 2013, there were 21 blast furnaces with capacities of 5000 m3 or more, with 12 of them at or above 5500 m3: Gwangyang No. 1, Zhangjiagang II No. 4, Oita No. 1 and No. 2, Pohang No. 4 (POSCO, 5600 m3), Cherepoverts No. 5 (Russia’s Severstal, 5580 m3), Caofeidian No. 1 and No. 2 (China’s Shougang Jingtang Iron & Steel, both at 5576 m3), Kimitsu No. 4 (NSSMC, 5555 m3), Schwelgern No. 2 (ThyssenKrupp, 5513 m3), Gwangyang No. 4 (POSCO, 5500 m3; in 2010 it achieved the world record output of 15,613 t/day), and Fukuyama No. 5 (JFE Steel, 5500 m3). Asian lead was obvious: 10 of the 12 largest furnaces were in Asia (4 in Japan, and 3 each in South Korea and China), just 1 was in Europe, and none were in North America.
In 2013, 287 large (>2000 m3) furnaces operated worldwide, compared to 234 furnaces with volumes between 1000 and 2000 m3 and 295 furnaces smaller than 1000 m3 (VDEh, 2013). Notable concentrations of very large blast furnaces include Baoshan (Shanghai), Anshan and Benshi (both in Liaoning), Caofeidian and Qian’an (both in Hebei) in China, Yawata in Japan, Pohang in South Korea (Fig. 5.1), Gary (Indiana) in the United States, Cherepovets in Russia and Duisburg, and Nordrhein-Westfalen in Germany. Europe’s largest iron-smelting center is in Schwelgern, just north of Duisburg on the eastern shore of the Rhein, where ThyssenKrupp Steel Europe and Hüttenwerke Krupp Mannesmann GmbH operate six blast furnaces (with hearth diameters of 10.0–11.9 m) producing annually up to 15.6 million tonnes of hot metal (ThyssenKrupp, 2015; Fig. 5.1).
Figure 5.1 POSCO’s steel mill in Pohang, North Gyeongsang province, South Korea (top), and an aerial view of the ThyssenKrupp iron and steel mill in Schwelgern, on the eastern shore of the Rhine, north of Duisburg, in Nordrhein-Westfalen, Germany (bottom). Corbis.
Post-1990 reconstructions tended to have slightly higher capacities even for medium-sized furnaces: for example, nine furnaces relined at Nippon Steel plants between 1990 and 2004 had an average 14% increase of inner volume to 4490 m3 (Kawaoka et al., 2006). And better linings (graphitic refractories with cooling plates) have resulted in unprecedented extensions of typical smelting campaigns, leading to doubling, or even tripling, of the time spans between reconstructions. During the early 1980s, campaigns lasted usually no longer than 3–5 years, by the century’s end campaigns of 8–10 years were common, and the record holder at that time was OneSteel’s Whyalla furnace in Australia, which was relined in 1980 and had a planned overhaul scheduled for 2004 after a generation-long campaign (Bagsarian, 2001).
The complete record for the Nippon Steel furnaces shows that the campaigns of the units blown out during the 1970s (first campaigns of Nagoya 3, Kimitsu 2, and Oita 1) were just 5–7 years; those blown out during the 1980s and 1990s lasted roughly twice as long, 10–12 years, and the blast furnaces blown out just before and after the year 2000 (including the second campaign of Oita 2) lasted about 15 years without losing their high productivity (Kawaoka et al., 2006). Even China’s best furnaces could now last that long: for example, due to reducing the progress of two main problems, breakouts of hearth walls and the erosion of shaft lining, the fifth furnace of the Wuhan Iron and Steel Company, blown-in in 1991, worked smoothly for 15.6 years and produced 35.51 Mt (i.e., 11,096.6 t/m3) without any repairs (Zhang & Yu, 2009). And, as just noted, the first campaign of Schwelgern 2 lasted 21 years.
Shinotake et al. (2004) analyzed the relationship between campaign length and furnace productivity and found that furnaces whose cumulative productivity was less than 10,000 t/m3 had campaigns of 12–18 years, while those whose production reached 14,000 t/m3 lasted 18–25 years. In the past, major problems tended to arise in the shaft, while the longevity of more recent campaigns is usually controlled by the state of the hearth. Measures to prolong the service include the installation of highly conducive cast iron or copper stave for the hearth sidewall below tapholes, lower temper
ature of cooling water, two-step cooling for hearths, and durable carbon blocks and inner ceramic linings for the bottom refractory. Better linings and better stoves—the latest ones having readily identifiable mushroom domes (Siemens VAI, 2008)—have made it possible to raise hot blast temperatures to 1250 °C (maximum dome temperature of 1400 °C) and to increase average daily output by 15–25%. Newly relined large furnaces usually produce between 10,000 and 12,000 t of hot metal a day, and they do so with reduced energy requirements, with major coal injection rates, and, in some furnaces, due to injection of plastic waste.
But the largest furnaces with the highest absolute production do not have the highest specific metal output: the rates for furnaces with inner volumes of 5000 m3 and above and with daily production of at least 10,000 t (and up to more than 12,000 t) range between 2.1 and 2.7 tonnes per day per m3. In contrast, furnaces with volumes between 1800 and 2700 m3 and daily maxima of 6000–9000 t have higher specific daily rates in excess of 3 t/m3. Dutch Ijmuiden No. 6 (belonging to Tata Steel Europe, volume of 2678 m3 and daily output of 7800 t) rates as high as 3.35 tonnes per day per m3 (VDEh, 2013).
