Moving Toward the Circular Economy: The Role of Stocks in the

POLICY ANALYSIS pubs.acs.org/est

Moving Toward the Circular Economy: The Role of Stocks in the Chinese Steel Cycle Stefan Pauliuk,† Tao Wang,†,‡ and Daniel B. M€uller*,† †

Industrial Ecology Programme and Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway ‡ Research Center for Material Cycles and Waste Management, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan

bS Supporting Information ABSTRACT: As the world’s largest CO2 emitter and steel producer, China has set the ambitious goal of establishing a circular economy which aims at reconciling economic development with environmental protection and sustainable resource use. This work applies dynamic material flow analysis to forecast production, recycling, and iron ore consumption in the Chinese steel cycle until 2100 by using steel services in terms of in-use stock per capita as driver of future development. The whole cycle is modeled to determine possible responses of the steel industry in light of the circular economy concept. If per-capita stock saturates at 8
12 tons as evidence from industrialized countries suggests, consumption may peak between 2015 and 2020, whereupon it is likely to drop by up to 40% until 2050. A slower growing in-use stock could mitigate this peak and hence reduce overcapacity in primary production. Old scrap supply will increase substantially and it could replace up to 80% of iron ore as resource for steel making by 2050. This would require advanced recycling technologies as manufacturers of machinery and transportation equipment would have to shift to secondary steel as well as new capacities in secondary production which could, however, make redundant already existing integrated steel plants.

production,5,9 and to improve resource utilization and facilitate sustainable development China issued the Circular Economy Law which addresses “reducing, reusing, and recycling activities conducted in the process of production, circulation, and consumption”.13 Those articles of the law relevant for the steel sector focus on short-term measures such as emission monitoring and the replacement of oil-fueled boilers, but a recent paper pointed out that, eventually, the concept of circular economy requires economic growth to decouple from resource throughput.14 For the steel sector, this would imply a major shift to secondary production which is a long and costly undertaking: Assets in primary steelmaking such as blast furnaces and basic oxygen furnaces represent large capital stocks and are characterized by pay-back times of at least 30 years10 and the lifetime of buildings and infrastructure as the major steel user and potential supplier of scrap is often considerably longer.11,12 Anticipating long-term trends in the steel cycle is hence of great importance both for investment decisions and the transition to sustainable metal use.

1. INTRODUCTION Iron, mostly in the form of steel, is a material whose fair mechanical and chemical properties allow for a variety of applications requiring tensile and compressive strength, ductility, or ferromagnetism. Because of its availability and relatively low price, steel is by far the most utilized metal with a recent yearly production of about 1.3 billion metric tons.1 On the other hand steel production accounts for 25% of all industrial and 9% of global process- and energy-related carbon emissions.2 As long as fundamental technological changes (e.g., improved reduction processes combined with carbon capture and storage (CCS), electrolytic processes, etc.)3 are not in place, recycling and reuse of steel scrap is considered the only feasible route to substantially decrease the carbon footprint of the steel industry.4 Today, China is by far the biggest producer and consumer of steel.5 The Chinese government has been aware of the importance of the domestic steel industry and has made its development a national priority since the 1950s.5 Only in the last three decades however, has a stable production growth, which culminated in a remarkable increase in primary production capacity of several 100 Mt/yr during the recent decade, been achieved. China now disposes of very young assets in primary production that are far from having paid off,6 and even takes measures to limit further capacity extension.7,8 On the other hand scrap availability is far too low to allow for a substantial contribution to steel r 2011 American Chemical Society

Received: June 3, 2011 Accepted: November 17, 2011 Revised: November 16, 2011 Published: November 17, 2011 148

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Figure 1. System definition. Iron cycle in the People’s Republic of China for historic quantification and stock driven mode.

than the annual steel consumption, may be a more reasonable way to quantify the service steel provides to society in the long run. Moreover, stocks are hardly affected by short-term oscillations in steel consumption and their inertness and persistence makes them suitable robust long-term indicators of development. If product lifetimes are known or can be estimated, it is possible to determine the required steel production to build up and maintain a stock over time. Such a stock-driven dynamic material flow analysis (MFA) that contains both population and lifestyle parameters has been applied previously to forecast material flows in the housing stock in The Netherlands.21 A similar study investigated the steel stocks and flows in China’s residential building stock.22 Recently, Hatayama et al.23 applied a dynamic stock model similar to ours with population, stock pattern, and product lifetime as central parameters to forecast global and regional steel stocks and flows for buildings, infrastructure, and vehicles. Our approach has a different scope, however, as it covers all categories of steel use, uses China-specific data to estimate the speed of stock development, and refers to a larger set of industrialized countries when identifying possible future stock patterns for China. To assess the environmental impact of building up and maintaining the in-use stock a model comprising all stages of the life cycle of steel-bearing products is required. For the Chinese steel cycle such a model was published by Lu.9,24

Short- and midterm forecasts on steel production are often based on extrapolations of historic production flows and growth rates.15,16 Another common approach is to correlate the flows of steel consumption to external GDP projections, e.g., in the World Energy Model17 or as in a publication by Das and Kandpal.18 The steel module of the POLES model19 assumes that the intensity of steel use per unit GDP follows an inverse U-shape curve mimicking the economic development from agricultural to industrial and eventually a service-oriented economy.20 For sustained exponential growth however, the future GDP level is very sensitive to the assumed growth rates, and forecasting steel consumption based on these extrapolations hence may lead to a very wide range of estimates. Another characteristic of the POLES model is that future decisions on whether to build up primary or secondary production capacities are made on a purely economic basis, irrespective of whether sufficient amounts of steel scrap will be available or not. This approach disregards the dynamics of the in-use stock and is thus not suitable to anticipate potential shortages of scrap that may hinder the transition to a more sustainable steel cycle, especially in developing and transition economies. We suggest an alternative perspective by considering stocks of steel in construction and all other metal-bearing products as a driving force behind the steel cycle. Buildings, machines, and vehicles as major sinks of iron and steel have a service life of many years to decades and therefore considering stocks of steel, rather 149

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6, the apparent final consumption of iron by sector i X2_1,i(t) could be determined. Equation 2 then yields the outflow X1_16,i and eq 1 the accumulation of in-use stock S1(t). For constructions we chose a log-normal lifetime distribution L for all items where the mean lifetime τi equals the standard deviation σi. This distribution has a longer tail compared to the normal distribution in Hu et al.22 and demolishing within a certain cohort happens over a longer period of time. This reflects the inertness of the residential building stock better than a normal distribution. By comparing the model results for supply of old scrap with data on total scrap consumption we estimated the lifetime of historic building cohorts that contribute to present scrap flows to be at least 65 years (cf. S2.5 in the Supporting Information). We use this value as approximate lifetime for all historic cohorts until 2009. Scenario-specific lifetimes for constructions erected later than this year are estimated. Based on a previous study,26 we chose fixed normally distributed product lifetimes for the four other categories with the following means τi: Transportation 25 years, Machinery 30 years, Appliances 15 years, and Others 15 years. σi is set to 30% of the mean τi.26 We refer to S1 for the detailed method and to Wang et al.25 for the data treatment. Future Utilization of Steel in China. To quantify the future level of steel use we base ourselves on the central premise that utilization of steel in China expressed in terms of per capita in-use stock will follow a trajectory similar to that observed in industrialized countries. This approach is in line with the goals for industrialization set by the Chinese government.27 From previous work26 we conclude that once per-capita stock has crossed a threshold at about 2 tons, it enters a period of very strong and sustained growth. This core phase of industrialization is characterized by a dominant role of steel consumption as the stocks in buildings, infrastructure, and machinery are being formed. China has entered this phase in 2006,25 whereas industrialized countries have crossed this line much earlier (U.S. and UK before 1900, France ca. 1920, Japan ca. 1965). We identify two patterns of further development once per-capita stock has reached 8
10 tons: (a) eventual saturation at 10 ( 2 ton/cap as seen in the U.S., the UK, and France, and (b) continued, but slower linear growth over time as seen in Japan, Australia, and Canada with stock levels of 12 ( 2 ton/cap in the year 2005. Construction accounts for the largest stock share in each of the studied countries (g50%) and is also the major contributor to stock growth in countries that follow pattern (b). The other categories show saturation or even decline in almost all cases. To replicate the stock patterns for saturation (a) we apply logistic curves with scenario-dependent saturation levels for each product category to model per capita stock by category of use. Only for construction do the model curves for sustained growth (b) differ from (a). We model the construction pattern in (b) by splitting the final stock in 2100: Half of the final value is contributed by a logistic curve and the other 50% is contributed by a linearly growing fraction starting at zero in 2009. (cf. S2.4) Transition from Historic Development to Future Scenarios (2009
2010). Having determined the eventual stock size we also need to estimate the speed of development. We proposed to characterize industrial development in terms of service provided by the in-use stock rather than the current trend in steel production, and assume consequentially that in-use stock per capita makes a smooth transition from historic development (t e 2009) to the future trajectory (t g 2009) in 2009/10. The three parameters of the logistic curves are chosen in a way that

However, stocks and in particular the in-use stock as driver and source of postconsumer scrap have not been considered in this work and hence it cannot be used for stock-driven long-term forecasting. The approaches discussed above focus either on the use phase of steel only or pursue a life-cycle approach which neglects stocks. A comprehensive discussion of the relationship between in-use stock and the whole metal cycle however, especially regarding the mix of primary and secondary production, is still lacking. This study provides a physical model of the complete steel cycle in China based on future utilization of steel. We combine a historical analysis of iron stocks in China from 1900 to 2009 (Wang et al.)25 with historic patterns of stock development observed in industrialized countries26 to perform a stock-driven quantification of steel demand and supply of old scrap until 2100. We extend the system by waste management and the routes for primary and secondary steel production to model both challenges and opportunities recycling industries and steel producers might face when responding to future steel demand and scrap supply.

2. METHODOLOGY Throughout the text, the term “steel” includes cast iron and all other iron alloys. The system definition for the anthropogenic iron cycle in China used in this work (Figure 1) contains all major production processes or markets (denoted by process number p), as well as stocks Sp within and flows Xp1‑p2 between different processes. The discrete model time t reaches from 1900 to 2100. We distinguish in particular between primary production of steel via blast furnaces (11 in Figure 1) and basic oxygen furnaces (8), secondary steel from scrap-fed electric arc furnaces (7), and castings from foundries (5). We further divide steel consumption and use into five categories i with specific product lifetimes and recycling efficiencies: “Construction” (buildings and infrastructure, i = 1), “Transportation” (vehicles, ships, etc. i = 2), “Machinery” (industrial equipment, i = 3), “Appliances” (white goods, bicycles, etc. i = 4), and “Other” (e.g., containers, i = 5). The use phase (1) is the central process of this study for two reasons: First, it links utilization in form of the service-providing stock S1(t) to steel consumption X2_1,i(t) and scrap flows X1_16,i(t) via the mass balance (eq 1). Second, it connects future outflows of obsolete products X1_16,i in year t to historic consumption inflows X2_1,i from all years t0 e t via the product lifetime distribution L (eq 2).21 The latter function denotes the probability that a certain inflow at t0 is leaving the use phase at t. It is shaped by category-specific mean lifetimes τi and standard deviations σi. dS1 ðtÞ ¼ dt

5

∑ i¼1

X1_16, i ðtÞ ¼

X 2_1, i ðtÞ
X1_16, i ðtÞ

∑

t0 e t




X2_1, i ðt 0 Þ 3 Lðt
t 0 , τi , σi Þ

ð1Þ ð2Þ

Quantification of the Historic Cycle (1900
2009), “Forward Calculation” (Upper Part of Figure 1). Historic statistical data

on production by process, trade flows by category i, and amount of new scrap from manufacturing have been compiled (green arrows) and by applying the mass balance to processes 2, 3, 4, and 150

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Figure 2. Steel use by scenario. Total stock, per capita stock, total consumption (inflow), and discharge of iron in all types of products (outflow) from 1940 to 2009 and 2010 to 2100. The values of the central model parameters are highlighted as follows: Red indicates values according to the BASIC scenario and black indicates scenario-specific changes.

the curves are tangent to the historic stock in 2009 for each category of use (2 parameters) and that they eventually reach the saturation levels set above (1 parameter). Stock-Driven Mode (2010
2100), “Backward Calculation” (Lower Part of Figure 1). Future demand for the total in-use stock S1(t) is determined by multiplying population estimates P(t) with a scenario-specific set of per-capita stocks ci(t) for all product categories: S1 ðtÞ ¼ PðtÞ 3 cðtÞ ¼ PðtÞ 3

∑i ci ðtÞ

Two classes of scenarios are developed. First, we examine the consequences of a different utilization of steel by varying both stock level as well as pattern while keeping the lifetime constant: for Stock8 and Stock12 we scale all saturation levels by a factor of 0.8 and 1.2, respectively. This reflects the lower levels in France and the UK as well as the possible case of a correspondingly higher saturation. For LinearStock10 we apply a construction pattern of form (b) as described above to model a sustained growth similar to the trajectory of Australia. Second, we investigate a substantial change in lifetime of the post-2009 cohorts in construction and infrastructure for the BASIC stock pattern (saturation at 10 t/cap): 35 years for Lifetime35 and 75 years in Lifetime75. The first estimate pays attention to reports on the bad quality of some recently erected buildings28 whereas the other reflects a situation more common in Europe or the U.S. where houses are built to last several generations.12,29 For a detailed list of all scenario-specific parameters cf. S2.4 and S2.6. Because recycling and reducing energy demand have become important issues that are also covered by the Circular Economy Law, we assume that for all scenarios the share of external scrap in basic oxygen furnaces will rise gradually to 20% by 2035, as this measure does not require much investment. We assume in line with Allwood et al.2 that from 2010 on, 90% of all end-of-life steel will be available on the scrap market. This ambitious figure shall identify the maximal potential impact of secondary production. Each scenario is run twice: First, the share of secondary production remains at its present value of 9% until 2100. Then, the share is adjusted in a way that all available new and old scrap can be processed within the country. The latter option corresponds to the notion of a circular economy. In 2009, the bulk of crude steel production (ca. 88%) went into build-up and maintenance of the in-use stock. Net export as either finished steel or final products only accounted for 5% and new scrap for 7% of steel production.25 From 2009 on, all scenarios consider therefore only the production needed to fulfill domestic final demand, and hence all trade flows are set to zero except for the ultimate resources iron ore and scrap.

ð3Þ

With the historic time series on apparent consumption X2_1,i(t) given and the future stock S1(t) assumed by eq 3, we can successively compute future scrap flows X1_16,i from the lifetime model (eq 2) and future consumption X2_1,i(t) from mass balance (eq 1) for all years from 2010 to 2100. We make scenario-specific assumptions on lifetime of constructions, endof-life recycling efficiency, the share of scrap use in steel-making, and other parameters to quantify the whole system process by process, starting from the use phase. Finally, the recycling loop of the system is closed at the scrap market where net import/export of scrap is determined from balancing domestic demand and supply. Scenario Definition (Figure 2). Whereas the stock pattern determines future steel services, future steel consumption required to further build up and maintain the stock is governed by both pattern and product lifetime. Since construction is by far the largest category of use26 we only consider changes in the lifetime of buildings and infrastructure. The BASIC scenario serves as reference cycle as it assumes saturation at an average level of about 10 t/cap with the following split into the different sectors: Construction 5 t, Transportation 1.9 t, Machinery 2.3 t, Appliances 0.2 t, other 0.6 t. This sector split and pattern have been observed in the U.S. The mean lifetime of future cohorts in construction is set to 50 years which reflects the more rapid turnover within the construction sector in Asian countries compared to European countries or parts of the U.S.12 151

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Figure 3. Steel demand by sector of final use, 1940
2009 and 2010
2100 (area plot). The black solid line is the consumption of old scrap for fixed split of primary and secondary production. The dashed line shows the maximal supply of old scrap and hence the potential for recycling.

3. RESULTS Between 2015 and 2020, while the stock curve attains its maximum growth and inflection point, steel consumption reaches a pronounced peak independent of the scenario (Figure 2). After 2020, consumption exhibits a moderate to sharp decline which is a direct consequence of the stock patterns we apply: after passing the inflection point of the saturation curve at 4
6 ton/cap, growth starts to slow down. In 2010, the in-use stock of steel was about 4 Gt, which is roughly the size of the U.S. in-use stock.30 By around 2045 in-use stock will more than triple and reach a maximum of 14 Gt (BASIC), ranging from 12 Gt (Stock8) to 17 Gt (Stock12). Due to shrinking population it will eventually decline to a level between 14 Gt (Stock12) and 9 Gt (Stock8) by 2100. For LinearStock10 the stock will remain rather constant at 12 Gt after 2040. For the BASIC scenario, consumption peaks at ca. 600 Mt/ year around 2020. Thereafter, domestic demand will drop continuously. Between 2020 and about 2050 demand is dropping due to beginning stock saturation. Thereafter, shrinking population in combination with accomplished saturation causes further decline. At the end of the century, consumption will settle down at ca. 60% of the peak value. The magnitude of the peak is not sensitive to construction lifetime because the expected scrap and reconstruction boom arrives too late to fill in the gap. It is also relatively robust under a change in saturation level, as for a (25% variation (Stock8 and Stock12) the magnitude of the peak only changes by about (100 Mt/year or (15%. For all scenarios the consumption peak will occur before 2020. In LinearStock10 the peak is sharper than in the saturation scenarios but since further capacity extension is avoided the decline in production is less severe in the long run. This scenario shows that postponing steelintensive investments and mitigation of excess production capacity are closely linked. The decline in production immediately after 2010 clearly is an extreme development that could be mitigated by choosing a mix between different stock patterns. Supply of iron in obsolete products follows the consumption boom with a delay of 20
30 years and will rise considerably. It

will exceed 50% of domestic steel production in the period of 2025 to 2035, and around 2050, it will even surpass domestic consumption provided that obsolete products do not accumulate with their former users. Contrary to the peak level, the time when scrap flows will rise sharply is slightly sensitive to construction lifetime (resulting in a shift of ca. ( 5 years) and only little sensitive to the stock pattern. For the benchmark year 2050, our estimates on domestic steel demand lie between 340 and 510 Mt/yr. (Stock8 and Stock12). They are significantly lower than the 610
690 Mt/yr forecast by IEA31 and the ca. 850 Mt/yr recently estimated by the China Energy Group at Berkeley.32 We also forecast a higher potential for secondary production than the latter study. We conclude that scenarios employing saturation of steel utilization based on observations in some industrialized countries are more favorable with respect to recycling and climate change mitigation. Today, secondary steel is predominantly used for construction as quality requirements are lowest and lack of strength can often be compensated by using more steel. However, if all available old scrap should be used within China—as envisioned by the circular economy concept—eventually, secondary steel would have to penetrate sectors other than construction. We propose to rank the five sectors in the following order according to the requirements for steel quality: Construction, Machinery, Transportation, Appliances, and Other. We break down the final demand for steel products in the five use categories and compare it to old scrap supply (Figure 3). We can see that the drop in steel consumption after ca. 2015 mainly is caused by a maturing construction stock. For Lifetime75, the drop in new construction even will be about 80% due to the long lifetime of buildings and infrastructure. This collapse of demand from construction will be partly compensated for by growth in the other four sectors, mainly transportation and machinery. At present, the Chinese steel industry has only ca. 9% of its capacity in secondary production.5 If this low share is maintained, the industry cannot process more than ca. 100 Mt of scrap per 152

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year (Figure 3, black solid line) no matter how much scrap might be available (Figure 3, black dashed line). Demand from buildings and infrastructure (dark red area) will be sufficiently high to assimilate all steel recycled from old scrap in this setting which already includes some scrap use in primary production facilities. Around 2025, old scrap supply (black dashed line) will reach 200 million tons/yr and quantity of secondary material will not be an issue anymore. However, if the extent of recycling shall be adopted to the available scrap flow, maintaining the overall quality of steel will become a challenge. Between 2025 and 2035, old scrap supply will exceed total demand from construction sector (black squares in Figure 3) and first, machinery producers will need to settle for recycled steel. Further expansion of recycling requires that at latest between 2030 and 2040, recycled old scrap will have to start to replace primary steel in transportation equipment (black circles in Figure 3) and ultimately in appliances.

scrap export would surpass 100 Mt/yr already around 2025. Large-scale investment in secondary production would open a door to utilize domestic scrap within China (dashed lines in Figure 3). Given the typical lifetime of integrated steel plants of (30 ( 6) years however,10 we then foresee either idle integrated steel works or massive dumping of steel on the world market in the years before replacement of these plants will become costeffective. Each new integrated steel plant is likely to exacerbate potential overcapacities and hence, discontinuing current expansion plans may help to make the transition to a mature steel cycle less abrupt. Quality of Recycled Steel. By the end of the 21st century, China will have a mature steel stock and likely a shrinking population resulting in old scrap supply and steel consumption being at about the same level. Quantitatively speaking a transition to a circular economy with a closed steel cycle would be possible by then. However, quality requirements may impede displacement of secondary for primary steel for applications that require material of high quality and strength. In none of the calculations with closed scrap market can demand from construction alone absorb secondary steel produced from domestic old scrap. If a nearly closed steel cycle is the goal, manufacturers of machinery, transportation equipment, and appliances will have to adapt to secondary steel from ca. 2025 on (cf. Figure 3). Today, secondary steel is often produced from a variety of alloys; and diluting contaminations with tramp elements and other residues is often suitable to meet quality requirements for structural steel. However, demand from construction is likely to drop severely and hence there will be fewer options to dilute tramp elements. In a closed steel cycle waste management will play a central role in managing old scrap flows as secondary resource. In-use stocks will have to be tracked to avoid formation of obsolete stocks and facilitate separation of scrap flows into different alloys to minimize spread of contamination with tramp elements such as copper or tin. Such a system also would make it easier to preserve valuable alloying elements such as nickel and chromium, whose scrap flows are expected to rise much earlier than those of ordinary steel, as pointed out by Reck et al.33 Additionally, advanced refining technologies in secondary steel making may replace dilution of impurities. Reuse and rerolling are concepts that avoid mixing different alloys and that are therefore interesting not only for reducing the steel industry’s energy demand2 but also from a material purity aspect. This analysis revealed three major conditions that need to be fulfilled to establish a circular economy for steel: (1) a sufficiently large and mature in-use stock, (2) a shift of the steel industry toward recycling, and (3) waste management that allows scrap to be recycled into the same product category from which it came. The biggest challenges lie in that the very young assets in primary production may delay the erection of a high-capacity secondary production and in the development of a recycling industry with sufficient performance in sorting and remelting. A different perspective opens if the Chinese steel industry is analyzed as part of a larger system. Other countries, particularly India, which still have per capita stocks at a preindustrial level26 are expected to catch up with material development at a later stage and are potential customers for excess production of both primary and secondary steel or postconsumer scrap from China to fulfill demand from construction. Such a development might relieve some pressure from the steel sectors of both countries but would require a framework across national boundaries and would go beyond of what China intends with the circular economy today.

4. DISCUSSION In the course of industrialization and the envisioned transition to a circular economy, the Chinese steel system is expected to shift from a linear process chain focusing on quantitative expansion to a cycle with a relatively stable in-use stock and high amounts of end-of-life scrap allowing for a circular steel economy. Our scenarios identify three major challenges resulting from this development that are expected to emerge already within the next 20 years. Consumption Peak. The present steel production capacity allows the in-use stock to grow at a very high rate of 250
300 kg/cap*yr, a speed at which the saturation level of the U.S. per capita stock would be reached around 2030. Once stock growth ceases in the saturation scenarios, we found that consumption will drop accordingly. If consumption were to be kept on a high level, final demand would have to shift from building up the stock to replacement of products, buildings, and infrastructure. However, the lifetimes of steel-containing products are so long that the production needed to maintain a constant stock is considerably lower than the consumption level around 2015. Therefore domestic steel demand may start to decline heavily after ca. 2020, leaving behind a pronounced peak. The production peak can be mitigated most effectively by slower, but more sustained growth in the construction sector alone. Still the same level of service (expressed in terms of steel stock) would be reached by the end of the century. A slower growth of steel stocks can be facilitated both on the production side by immediately curbing capacity extension and on the consumption side by slowing down urban expansion and rebuilding. Scrap Boom. In all scenarios China will experience a sharp rise of scrap flows between 2025 and 2050 as consequence of the present period of heavy consumption. This major change of the steel cycle will be accomplished before 2050, and for the second half of the 21st century, we expect a largely stable situation with consumption being at about the same level as today, but significantly lower than the all-time high. First of all, however, in-use stock will be built up mainly from primary steel during the first half of the 21st century, and the bulk of this flow will be supplied by the existing steel production capacity which mostly was erected during the past decade. Even if scrap shares in the existing assets were increased to the technological limit (solid black lines in Figure 3) this would be by far insufficient to process all available domestic scrap and hence old 153

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’ ASSOCIATED CONTENT

(20) Long-Term Perspectives on World Metal Use - A Model-Based Approach; RIVM; Bilthoven, the Netherlands, 1999. (21) M€uller, D. B. Stock dynamics for forecasting material flows Case study for housing in The Netherlands. Ecol. Econ. 2006, 59 (1), 142–156. (22) Hu, M.; Pauliuk, S.; Wang, T.; Huppes, G.; van der Voet, E.; M€uller, D. B. Iron and steel in Chinese residential buildings: A dynamic analysis. Resour. Conserv. Recycl. 2010, 54 (9), 591–600. (23) Hatayama, H.; Daigo, I.; Matsuno, Y.; Adachi, Y. Outlook of the World Steel Cycle Based on the Stock and Flow Dynamics. Environ. Sci. Technol. 2010, 44 (16), 6457–6463. (24) Lu, Z. On Steel Scrap Resources for Steel Industry. Iron Steel 2002, 37 (4), 66–71. (25) Wang, T.; M€uller, D. B.; Graedel, T. E. Iron capital formation in China and India: Historic trends, outlook, and consequences. Unpublished work. (26) M€uller, D. B.; Wang, T.; Duval, B. Patterns of iron use in societal evolution. Environ. Sci. Technol. 2011, 45 (1), 182–188. (27) Hao, Z. China to realize full industrialization by 2021. China Daily 2007-08-10, 2007. (28) Qian, W. Short-lived buildings create huge waste. China Daily, April 6, 2010. (29) Bergsdal, H.; Brattebo, H.; Bohne, R. A.; Mueller, D. B. Dynamic material flow analysis for Norway’s dwelling stock. Build. Res. Informat. 2007, 35 (5), 557–570. (30) M€uller, D. B.; Wang, T.; Duval, B.; Graedel, T. E. Exploring the engine of anthropogenic iron cycles. Proc. Natl. Acad. Sci. U.S.A. 2006, 103 (44), 16111–16116. (31) Energy Technology Transitions for Industry - Strategies for the Next Industrial Revolution; International Energy Agency: Paris, 2009. (32) China’s Energy and Carbon Emissions Outlook to 2050; Lawrence Berkeley National Laboratory: Berkeley, CA, 2011. (33) Reck, B. K.; Chambon, M.; Hashimoto, S.; Graedel, T. E. Global Stainless Steel Cycle Exemplifies China’s Rise to Metal Dominance. Environ. Sci. Technol. 2010, 44 (10), 3940–3946.

bS

Supporting Information. The complete system, the model approach, parameters for the different scenarios, calibration of the historic cycle, and additional results. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]; telephone: +47-735-94754.

’ ACKNOWLEDGMENT We thank Frank Zhong from the World Steel Association for helpful clarifications on reported statistical data. ’ REFERENCES (1) Worldsteel In Figures 2009; World Steel Association: Brussels, Belgium, 2009. (2) Allwood, J. M.; Cullen, J. M.; Milford, R. L. Options for Achieving a 50% Cut in Industrial Carbon Emissions by 2050. Environ. Sci. Technol. 2010, 44 (6), 1888–1894. (3) Meijer, K.; Denys, M.; Lasar, J.; Birat, J. P.; Still, G.; Overmaat, B. ULCOS: ultra-low CO2 steelmaking. Ironmaking Steelmaking 2009, 36 (4), 249–251. (4) Birat, J. P.; Vizioz, J. P.; de Pressigny, Y. D.; Schneider, M.; Jeanneau, M. CO2 emissions and the steel industry’s available responses to the greenhouse effect. Rev. Metall.-Cahiers D Inform. Tech. 1999, 96 (10), 1203–1215. (5) Feng, L. China’s steel industry: Its rapid expansion and influence on the international steel industry. Resour. Policy 1994, 20 (4), 219–234. (6) Wu, Y. The Chinese steel industry: Recent developments and prospects. Resour. Policy 2000, 26 (3), 171–178. (7) Jie, R. Big plan to wipe out overcapacity. China Daily 2010-03-08, 2010. (8) Moody, A.; Lan, L. Overcapacity exacerbated by recession. China Daily 2010-04-12, 2010. (9) Lu, Z.; Yue, Q. The study of metal cycles in China. Eng. Sci. 2010, 8 (2), 2–8. (10) World Energy Outlook 2008; International Energy Agency (IEA): Paris, France, 2008. (11) 2008 Sustainability Report of the World Steel Industry; World Steel Association: Brussels, Belgium, 2008. (12) Service Lifetimes of Mineral End Uses; USGS Award 06HQGR0174; Yale University: New Haven, CT, 2007. (13) Circular Economy Law of the People’s Republic of China. Adopted at the 4th Meeting of the Standing Committee of the 11th National People’s Congress, 2008. (14) Zhu, D. Background, Pattern and Policy of China for Developing Circular Economy. Chin. J. Population, Resour. Environ. 2008, 6, 4. (15) Wang, K.; Wang, C.; Lu, X.; Chen, J. Scenario analysis on CO2 emissions reduction potential in China’s iron and steel industry. Energy Policy 2007, 35, 2320–2335. (16) Yellishetty, M.; Ranjith, P. G.; Tharumarajah, A. Iron ore and steel production trends and material flows in the world: Is this really sustainable? Resour. Conserv. Recycl. 2010, 54 (12), 1084–1094. (17) World Energy Model - Methodology and Assumptions; International Energy Agency (IEA): Paris, France, 2009. (18) Das, A.; Kandpal, T. C. Energy demand and associated CO2 emissions for the Indian steel industry. Energy 1998, 23 (12), 1043– 1050. (19) Energy Consumption and CO2 Emissions from the World Iron and Steel Industry; European Comission - Joint Reasearch Centre/IPTS; Report EUR 20686 EN; 2003. 154

dx.doi.org/10.1021/es201904c |Environ. Sci. Technol. 2012, 46, 148–154