Variation Trend and Driving Factors of Greenhouse Gas Emissions

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Policy Analysis

Variation Trend and Driving Factors of Greenhouse Gas Emissions from Chinese Magnesium Production Feng Gao, Yu Liu, Zuo-Ren Nie, Xianzheng Gong, and Zhihong Wang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b01860 • Publication Date (Web): 12 Oct 2015 Downloaded from http://pubs.acs.org on October 12, 2015

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Environmental Science & Technology

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Variation Trend and Driving Factors of Greenhouse Gas Emissions from

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Chinese Magnesium Production

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Feng Gao*, Yu Liu*, Zuo-Ren Nie, Xianzheng Gong, and Zhihong Wang Center of National Materials Life Cycle Assessment, College of Materials Science and Engineering, Beijing University of Technology, No.100 Pingleyuan, Beijing, China

ABSTRACT: As the largest magnesium producer in the world, China is facing a great challenge of greenhouse gas (GHG) emissions reduction. In this paper, the variation trend and driving factors of GHG emissions from Chinese magnesium production were evaluated and the measures of technology and policy for effectively mitigating GHG emissions were provided. First, the energy-related and process-oriented GHG inventory is compiled for magnesium production in China. Then, the driving forces for the changes of the energy-related emission were analyzed by the method of Logarithmic Mean Divisia Index (LMDI) decomposition. Results demonstrated that Chinese magnesium output from 2003 to 2013 increased by 125%, while the GHG emissions only increased by 16%. The emissions caused by the fuels consumption decline most significantly (from 28.4 to 6.6 t CO2eq./t Mg) among all the emission sources. The energy intensity and the energy structure were the main offsetting factors for the increase of GHG emissions, while the scale of production and the international market demand were the main contributors for the total increase. Considering the improvement of technology application and more stringent policy measures, the annual GHG emissions from Chinese primary magnesium production will be controlled within 22 million tons by 2020. TOC/Abstract Art

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1 Introduction Magnesium, a lightweight engineering material, has great potential for application in aerospace, transportation, electricity&electronics and other industries. Magnesium is primarily used as an adding element in aluminum alloys, followed by the magnesium alloy die casting accounting for 35% of the total global consumption1. In recent years, the demands for lightweighting, energy conservation and emission reduction in the automobile and aviation industries have resulted in numerous opportunities for the development and application of magnesium alloy materials.2,3 However, life cycle assessment (LCA) must be performed to determine the comprehensive environmental impact of using magnesium as a lightweight material. As an indispensable international standard and mainstream evaluation method for achieving sustainable development, LCAs has been widely applied in product ecological design, cleaner production, environmental labels and declarations, green purchasing and product environmental policies.4,5 The high CO2 emissions in the production stage is one of the most important drawback of magnesium, despite it has many benefits as a lightweight material in the use stage of vehicles. During the past years, a number of LCA researches on the environmental impacts of the primary magnesium production including the Pidgeon process in China, the carbothermal process and the electrolytic process in Australia, the Rima process in Brazil and the Gossan-Zuliani process in Canada have been carried out internationally.6-12 Unfortunately, a wide range of assumptions such as system boundary of technology processes, local energy structure, and emission factors of greenhouse gas (GHG) have been adopted, therefore, it is difficult to compare the results of GHG emissions among the different studies. Since 2002, there have been significant changes in the magnesium production and technical structure across the globe. Researchers have conducted various studies on the environmental impacts of the primary magnesium production process and magnesium products, most of which focused on GHG emissions of the Chinese Pidgeon process. It was shown that GHG emissions in the Chinese Pidgeon process (37-47 kg CO2eq./kg Mg6) was nearly twice that in the electrolytic process (20.4-26.4 kg CO2eq./kg Mg7). This result was widely used as an evaluation basis in a number of studies to assess the feasibility of using lightweight materials (e.g., aluminum or magnesium) to replace iron and steel autoparts.13-17 The negative evaluation results on energy consumption and GHG emissions during the magnesium production have limited the promotion of magnesium products. Climate changes induced by GHG emissions, as represented by environmental indicators, are among the most pressing issues identified by the international organizations, such as World Steel Association (WSA), International Aluminum Institute (IAI) and European Aluminum Institute (EAA)18-20, for sustainable development. In the target application industries such as the global communication and transportation industries, the lack of LCA-based environmental data prevents the dominant use of magnesium among other materials.21 In 2013, the International Magnesium Association (IMA) issued a LCA report for magnesium components in vehicle construction, which played a positive role in supplementing the LCA data for magnesium.22 Magnesium resources are abundant and widely distributed in China. With the wide application of magnesium production by the Pidgeon process, China has dominated more than 80% of the world market share (Figure 123), and has become the main force behind changing the production pattern and technology structures in the global magnesium industry. However,


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with the sharp increase in magnesium production, China is facing enormous pressure for environmental protection of the raw material localities and rational use of resources and energy. The magnesium production enterprises have widely cooperated with universities and research institutes in China, and have made great progress in developing new processes and new equipments. Strategies, such as energy saving reconstruction, carbothermic reduction in vacuum, the use of a vertical retort in the reduction process, and continuous magnesium smelting, have laid a solid foundation for energy conservation and reduction in GHG emissions during magnesium production.24-28 The major suppliers of low-cost magnesium in the global market are those using the Chinese Pidgeon process. In a sense, the widespread implementation of magnesium will depend on its cost of production from competing primary magnesium production technologies. However, current studies still do not consider the influence of the selection and application of sustainable technology in magnesium smelting, the change of energy structure, and the output and the demand of the down-stream sectors on the GHG emissions.

Figure 1. Primary magnesium output in China and other main producers (Chinese data were provided by China Magnesium Association (CMA), and other data were from USGS23) Our goals in this study were (1) to build a time series inventory of GHG emissions of magnesium production using Chinese Pidgeon process and the down-stream products; (2) to identify the main factors that influence energy-related GHG emissions during the primary magnesium production in China; and (3) to analyze the measures for effectively mitigating GHG emissions from the perspective of technology and policy considering the changes in time and demand. This paper will first introduce the methodology, including the system boundary, data collection and calculation of GHG emissions. Then we will provide the results and discuss in detail through the model analysis, thereby put forward appropriate and efficient measures according to the real conditions of China magnesium industry. 2 Materials and Methods 2.1 Chinese Pidgeon process. According to the characteristics of magnesium resources, there are two commercial application of producing magnesium: the chloride molten salt electrolysis process and the thermal reduction process. However, the electrolytic process has been shut down in China due to its higher cost since 2003, and the Pidgeon process has become the unique technique of primary magnesium production till now. The description of the Chinese Pidgeon process was presented in the Supporting Information. 2.2 System boundary. The system boundary of the primary magnesium production is illustrated in Figure 2. The scope of this study is specified as follows:



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(1) The main processes include four major stages of the Pidgeon process and the ferrosilicon production of the major auxiliary material. (2) The main fuels used for the primary magnesium production include coal, semi-coke oven gas (SCOG), coke oven gas (COG), producer gas (PG) and natural gas. The energy-related GHGs emissions are CO2, CH4, and N2O discharged during the burning of these fuels and the electricity consumption during the production process. (3) The GHG emissions from gases obtained as by-products of the (semi)coke production or the coal gasification route were not taken into account, even though there exists a definite environmental burden of these gases which are manufactured through an artificial process. The reason of exclusion of this part of emissions will be discussed in the Section 3.3.1 and Supporting Information. (4) The GHG emissions from process are considered, and these emissions mainly come from the raw materials and reducing agent i.e. dolomite calcination and ferrosilicon production. (5) The GHG emissions caused by the exploitation of dolomite and the transportation of raw materials such as ferrosilicon, fluorite, etc. are not considered, which will be discussed in the section of limitation.

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Figure 2. System description of Chinese magnesium production According to the characteristic of the Pidgeon process, the GHG emissions consist of the direct and indirect emission. The direct emissions occur from the resources that are owned or controlled by the magnesium plants, including the emission from the dolomite calcinations and fuels combustion. The indirect emissions were derived from a consequence of the activities but occur from sources not owned or controlled by the magnesium plants, including the emission from the electricity generation and the ferrosilicon production. 2.3 Calculation of GHG emissions. 2.3.1 Direct emission. Combustion of fuels and dolomite calcination are the two main sources of CO2 emission in the Chinese Pidgeon process. The CO2 emission from combustion of fuels is related to the property and feature of the fuels, as well as the equipment. The calculation of GHG emissions refers to IPCC


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national GHG inventory guidelines29 and GHG Protocol Tool for Energy Consumption in China (Version 2.1)30. The calculation of energy-related CO2 emission was presented in the Supporting Information. And the emission coefficients of CO2, CH4 and N2O were listed in Table S1. The data of resources and energy consumption derived from CMA were calculated and compiled by the authors and listed in Table S2. Before 2005, coal was the main energy consumed in the Chinese Pidgeon process. Post 2005, there has been a continuous increase in the number of enterprises using gas fuels as the main energy. At present, most magnesium enterprises in China use gas fuels except the dolomite calcination process which uses coal powder. The production volume of the magnesium plants which use coal powder in their calcination furnace is less 5% of total. The use of COG and SCOG can realize the cascade utilization of energy. It can also reduce the cost of production, when production networks combining the (semi) coke production and magnesium plants are built in an associated enterprise. A considerable amount of COG and SCOG, which was previously in fugitive emission, is used as the major fuel for low cost magnesium production. In addition to being an energy source, dolomite serves as the secondary source of CO2 emission in the Pidgeon process. Dolomite directly discharges a large amount of CO2 during the calcination process. The CO2 emission from dolomite calcination is calculated according to the chemical equation for the decomposition of CaCO3·MgCO3, whose concentration in dolomite is estimated to be 98%. Approximately 0.47 t CO2 will be generated by the decomposition of one ton CaCO3·MgCO3. 2.3.2 Indirect emission. (1) Indirect emission from the electricity consumption. GHG emissions of China power generation is determined by the energy structure. The emission factors of electricity generation vary greatly due to the different technology and energy structure in different times and areas. The primary magnesium outputs on Shaanxi province, Shanxi province and Ningxia province account for over 90% of the total output in China. Therefore, the indirect GHG emissions from electricity consumption is calculated according to the emission factors of northwestern power grid in which the above three areas located in different years. The state grid power emission factors used in this calculation is cited from the reference30. (2) Indirect emission from the ferrosilicon production. Another major raw material is ferrosilicon, of which consumption in Pidgeon process is 1.05-1.10 kg/kg Mg. In particular, its power consumption is 8.0-8.8 kWh/kg ferrosilicon, which influences greatly on the GHG emissions in the primary magnesium production. Ferrosilicon is produced through slaglesss melting process in the electric furnace. And in recent years, the technology and efficiency of ferrosilicon production have not been changed significantly. We used Chinese industrial statistic data, i.e. the consumption of 210-230 kg scrap iron, 1800-1900 kg silica, 885-895 kg coke and 40-50 kg electrode paste for 1 ton ferrosilicon production. 2.4 GHG emissions from the down-stream sectors. For further study on the driving factors of GHG emission in Chinese magnesium industry, it is required to further analyze the consumption rate of magnesium products. The domestic consumption and export of Chinese magnesium from 2003-2013 was illustrated in Figure S1 and S2. The embodied GHG emissions of down-stream sectors were distributed based on the consumption of magnesium products. The details have been presented in the Supporting Information.



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2.5 Index decomposition analysis. The index decomposition analysis is widely used to distinguish the incidence of each factor on the target variable, and then specifically to find out the major factors that influence the target variable. The results derived from the logarithmic mean Divisia index (LMDI) method can better interpret how the changes in activity, structure, efficiency and fuel mix influenced energy use and CO2 emissions in different periods.31,32 So this method which provides a strong quantitative analysis, has been used to find out the influence factors of the GHG emissions and energy consumption both at the industrial and national level, and specifically to put forward recommendations for technology and policy measures.33-36 In this paper, this method was used to identify the factors that impacted energy consumption and related GHG emissions in Chinese magnesium industry, and further quantify the influences of these factors, through decomposing the changes of a target variable into a combination of several influence factors. As for Chinese magnesium production, the factors that influence GHG emissions with the time series analysis include the changes of emission factors (emission factors of fuel and electricity that change with the time), energy structure (different fuels have different emission factors), energy intensity (which reflects the energy consumption per unit product, i.e. the influence that are the enhancement through energy technology used), and production scale. The index decomposition analysis of energy related GHG emissions for Chinese magnesium industry is as follows:

C = ∑ Ci = ∑

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i

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i

C i Ei E P = ∑ Fi × S i × B × P Ei E P i

(1)

Where C represents total energy-related GHG emissions; Ci represents GHG emissions from fuel i, i=1, 2,…, 6, denoting coal, COG, SCOG, PG, natural gas and electricity; Ei represents the consumption of energy source i; E represents the total energy consumption; P represents the production volume of magnesium. Fi, Si and B represent GHG emission intensity of energy source i, energy consumption share of source i, and energy consumption per unit magnesium, respectively. The annual effects of driving factors can be investigated by Eq. (2).

∆C = C t +1 − C t = ∆CF + ∆CS + ∆CB + ∆CP

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(2)

The aggregated effects of driving factors from baseline year can be investigated by Eq. (3).

∆C T = C T − C 0 = ∆CFT + ∆CST + ∆CBT + ∆C PT

(3)

The subscripts of F, S, B and P in the equation represent emission intensity change effect, energy structure effect, energy intensity effect and production scale effect，respectively. The superscripts of t and t+1 represent the current year and the next year, and T and 0 represent the final year (2013) and the base line year (2003). The detail of the calculation process refers to the literature37. 3 Results and discussion 3.1 GHG emission of Chinese magnesium industry. The time series GHG emissions are calculated based on the data in Table S2 and the methods presented in Section 2.


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3.1.1 Energy-related GHG emissions. From 2003 to 2013, the energy consumption intensity of magnesium production in China had declined by 55% from 340 GJ/t to 153 GJ/t, with an annual average decline rate of 5%. Meanwhile, the GHG emissions intensity also had declined from 47.1 t CO2eq./t to 24.3 t CO2eq./t, decreasing by 4.4% per year, of which, the energy-related emissions had the largest decline, from 28.4 t CO2eq./t to 6.6 t CO2eq./t. The energy-related GHG emissions began to decline rapidly to 4.74 million tons in 2009 after reaching the peak (11.7 million tons) in 2004, and then rose to 6.06 million tons in 2013. Figure 3 showed the energy-related GHG emissions of magnesium production in China from 2003 to 2013. Since 2005, coal consumption has dropped, while gas consumption, especially the SCOG, has increased. The calorific value of SCOG is lower by 40% than that of COG. The ratio of GHG emissions produced by coal combustion in the total energy-related emissions declined from 87.6% to 10% from 2003 to 2013. Among all types of energy, the amount of GHG emissions caused by SCOG was the largest, accounting for 36.5%. The proportion of COG reached its peak (32.7%) in 2008, and then declined to 10.8% in 2013. Further, PG served as an important supplement when COG and SCOG supplies were unstable, accounting for 22%-27%. Natural gas was used by several enterprises due to its high cost, accounting for only 1%.

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Figure 3. Energy related GHG emissions of China magnesium production 3.1.2 Process oriented GHG emissions. The total GHG emissions of magnesium production in China from 2003 to 2013 were presented in Figure 4. From 2003 to 2013, indirect discharge of GHG emissions caused by power generation increased from 478 kilo tons to 975 kilo tons, and by the ferrosilicon production from 4.14 million tons to 8.87 million tons. In the same period, the direct discharge of GHG emissions caused by the dolomite calcinations increased from 1.77 million tons to 3.8 million tons, while GHG emissions caused by fuel combustion presented a dramatic decline from 11.1 million tons (the peak value) in 2004 to 5.09 million tons in 2013. The magnesium output in China increased 125% from 2003 to 2013; however, the GHG emissions only increased 16% during the same period. The total emission amount declined sharply from 2007 to 2009, but had an explosive growth from 2009 to 2010. This was closely related to the drastic fluctuation of magnesium output in China caused by the global financial crisis in 2008. Since 2009, the proportion of direct emission has decreased to 47% of the total emission, less than that of indirect emission, which shows that the Chinese magnesium industry has made highly effective efforts in energy conservation and emission reduction.



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Figure 4. Total GHG emissions of China primary magnesium production 3.1.3 GHG emissions of down-stream products. The distribution of the GHG emissions caused by down-stream products from 2003 to 2013 is expressed in Figure 5 based on the GHG emissions of unit magnesium products, and domestic consumption and export illustrated in Figure S1 and S2. The results showed that the emission from the primary magnesium export was the most important contributor, reaching 10 million tons in 2013, although its proportion of the total emission had changed and declined from 85% in 2003 to 54% in 2013. Thus, the GHG emissions of Chinese magnesium production were influenced by the international market demand to a great extent. Secondly, with the expansion of domestic application fields of magnesium alloy, especially the increase in the consumption of die-casting and metal reduction, the proportions of the GHG emissions in die-casting increased from 2.9% in 2003 to 13.7% in 2013, and in metal reduction from 0.86% to 11.1%. The proportion of emissions due to magnesium being used as an adding element in aluminum alloy changed slowly, from 6% in 2003 to 11.6% in 2013.

Figure 5. Distribution of the GHG emissions caused by the down-stream products 3.2 Influence factors for GHG emissions. The annual effect and aggregated effect of driving forces for the energy-related GHG emissions are expressed in Figures 6 and 7. The results of the annual effect of driving forces demonstrated that the scale of production was the leading influence factor followed by the energy intensity, the energy structure and the emission intensity. The influence of the scale of production was the main driving factor of the growth of GHG emissions except from 2007 to 2009. The rapid increase in Chinese magnesium output in five periods, i.e. 2003-2004, 2005-2006, 2006-2007, 2009-2010 and 2010-2013, contributed to the fast growth of GHG emissions. During 2007 to 2009, the negative growth of output is the most important factor among all four driving forces leading to the reduction of GHG emissions. The negative correlation of the influence of the energy


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intensity played a positive role in offsetting the increase of GHG emissions. The minimum offsetting value of the energy intensity was 110 kilo tons in 2012-2013, and the maximum value was 1.55 million tons in 2006-2007. The influence factor of the energy structure presented different effects in different years. Before 2010, the energy structure showed an offsetting effect on the GHG emissions. It reached its peak between 116 and 237 million tons from 2004 to 2006, and then continuously declined so that its influence could be ignored. The influence of the change of emission factors was obvious from 2004 to 2006 due to the application of PG and SCOG and could be neglected in other periods. The results of aggregated effect of driving forces illustrated that the scale of production and the emission intensity kept positive correlation for the GHG emissions, while the energy structure and the energy intensity kept negative correlation. The adjustment of energy structure in China magnesium industry is the key contributor for the reduction of total amount of GHG emissions. Although the magnesium output increased from 342 kilo tons in 2003 to 770 kilo tons in 2013, the GHG emission of magnesium industry kept negative growth from 2005 to 2013 due to the offsetting effect of the energy intensity and the energy structure.

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Figure 6. Annual effects of driving forces for the energy-related GHG emissions

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Figure 7. Aggregated effects of driving forces for the energy-related GHG emissions 3.3 Sensitivity analysis. 3.3.1 Influence of variation of the gas composition. In our study the variation of gas composition for the influence on GHG emission factors mainly reflected in three aspects: the calorific value, carbon content, and the oxidation rate of different fuels. The assumptions and their impacts are tested by conducting a sensitivity analysis provided in the Supporting Information. The results showed that the data sets of the calorific value and the carbon content lead to results with similar trends (Figures S3 and S4). The emission factor of coal is more sensitive to the GHG emissions than that of coal gas. With the reduction of coal consumption in magnesium production, the variation of GHG emissions per ton



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magnesium tends to be stable (Figures S5). 3.3.2 Influence of the electricity emission factors selection. In order to assess the impacts of the electricity emission factors on the results, five sensitivity analysis cases were conducted to examine the impact of different assumptions compared with the baseline scenario. Details of the sensitivity analysis and results are presented in the Supporting Information (Tables S3 and S4 and Figure S6). We find that the national average power network is more sensitive to the GHG emissions than the power network in the main production areas. The factors of different power network were more sensitive to the power consumption of ferrosilicon production. 3.4 Limitation. The GHG emissions caused by the dolomite mining and the transportation of raw materials such as ferrosilicon and fluorite were not considered in this paper mainly due to the following two reasons. Firstly, most of the large magnesium enterprises cooperated with ferrosilicon plants or coke plants in order to control the cost of raw materials, whose output accounted for about 70% of the total magnesium output. Some other magnesium plants purchased the ferrosilicon in the neighborhood. Secondly, the transportation distance of ferrosilicon and fluorite did not exceed 300 km and 1000 km, respectively. Therefore, the GHG emissions from the processes of the dolomite mining and the transportation of raw materials only accounted for less than 0.5% of the total emissions according to the literature38. 3.5 Technology and policy implications. The measures and policies for GHG reduction in China magnesium industry consider three aspects: energy efficiency, resources configuration and scale of production. First, the energy conservation in the Pidgeon process is still the focus of attention. Some announcements, such as the Norm of Energy Consumption per Unit Product of Magnesium Metallurgical Enterprise and the Access Conditions of Magnesium Industry issued by Chinese government, promote the adjustment of energy structure and the reduction of energy intensity. The application of energy-saving technologies reflects the positive effects on GHG reduction in the magnesium production. However, we recommend more stringent measures and access conditions because the energy efficiency of magnesium production could be further improved, considering the popularization rate of waste heat recovery technologies, such as the regenerative high temperature air combustion (HTAC) technology. Second, in terms of resources configuration, it is required to solve a new challenge on reducing the consumption of dolomite and ferrosilicon for the GHG emissions reduction in magnesium production. The proportion of GHG emissions caused by the dolomite calcination has risen from 11% in 2003 to 20% in 2013, and that by the ferrosilicon production has increased from 26% to 47%. Attention needs to be paid to these two emission sources in addition to the energy consumption. So the application of resources reducing technologies should be one of the important directions of policy support. For example, the heat accumulation-type vertical retort, which allows for the reduction of ferrosilicon by 20%-40% as compared with the existing Pidgeon process, should be further developed for industrial-scale application. The electrolytic process should be encouraged and supported in regions that are rich in renewable energy. Finally yet importantly, the production scale is the key factor for mitigating overall GHG emissions. The increase in Chinese magnesium output is due to exports. In the second half of 2008, the international market demand for magnesium slumped in application fields such as


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the aluminum, steel and motor industries, influenced by the global financial crisis. This resulted in the sharp reduction of purchase quantity from China. In 2009, the output, export and consumption of magnesium in China reached its minimum over the past ten years. In 2013, with the sluggish recovery of the international economy, the exports of magnesium products in China had recovered to that of before the financial crisis. At present, the production capacity of primary magnesium in China has reached 1.3 million tons, but the practical use ratio of the capacity is only about 50%. From the point of view of industry policy, it is recommended that capacity utilization should be promoted and elimination of the backward production should be accelerated to resolve the surplus production capacity. Considering the improvement in energy efficiency and resource configuration, the total GHG emissions in the next seven years can be estimated from the GHG emissions per ton of magnesium produced by the Pidgeon process and the electrolytic process, and the average annual growth rate of magnesium output in China. These assumptions and evaluated results are included in Figure S7, S8 and S9. The prediction shows that by 2020, the annual average amount of GHG emissions of primary magnesium production in China will be controlled within 22 million tons. Our study demonstrates a roadmap for how the scale of production, the energy intensity, the energy structure and the emission intensity influence GHG emissions in Chinese magnesium production with a time series. It also recommends a sufficiently aggressive goal for mitigating overall GHG emissions based on technology and policy improvements. ■ ASSOCIATED CONTENT Supporting Information The description of the Chinese Pidgeon process, the calculation of energy-related CO2 emission, supplementary figures and tables for presenting the data resources, and sensitivity analysis, and additional information on prediction of GHG emissions are provided. ■ AUTHOR INFORMATION Corresponding Author *Address: Beijing University of Technology, No.100 Pingleyuan, Chaoyang District, Beijing, China. Phone: +86-10-67396207. Fax: +86-10-67391536. E-mail: [email protected] *Address: Beijing University of Technology, No.100 Pingleyuan, Chaoyang District, Beijing, China. Phone: +86-10-67391536. Fax: +86-10-67391536. E-mail: [email protected] Notes The authors declare no competing financial interest. ■ ACKNOWLEDGEMENT This study was supported by a grant from National Natural Science Foundation of China (NSFC, Project No. 51304009), and National High Technology Research and Development Program of China (863 Program, Project No. 2013AA031602). The authors gratefully acknowledge Prof. Shukun Meng and Qian Sun from CMA for their valuable assistance for this study. ■ REFERENCES



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(1) U.S.

Geological

Survey

(USGS).

Magnesium

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Statistics

and

Information;

http://minerals.er.usgs.gov/minerals/pubs/commodity/magnesium/myb1-2013-mgcom.pdf

(Accessed

Oct. 24, 2014). (2) International Magnesium Association. Magnesium applications_automotive applications_Mg showcase; http://www.intlmag.org/magnesiumapps/automotive.cfm (Accessed Nov. 4, 2013). (3) Kim, H. C.; Wallington, T. J. Life-cycle energy and greenhouse gas emission benefits of lightweighting in automobiles: review and harmonization. Environ. Sci. Technol. 2013, 47 (12), 6089–6097. (4) Guinée, J. B.; Heijungs, R.; Huppes, G.; Zamagni, A.; Masoni, P.; Buonamici, R.; Ekvall, T.; Rydberg, T. Life cycle assessment: past, present, and future. Environ. Sci. Technol. 2011, 45 (1), 90–96. (5) ISO 14040 International Standard. Environmental management-Life cycle assessment - Principles and framework; International Organization for Standardization: Geneva, Switzerland, 2006. (6) Ramakrishnan, S.; Koltun, P. A comparison of the greenhouse impacts of magnesium produced by electrolytic and Pidgeon processes. Magnesium Technology 2004, 173-178. (7) Ramakrishnan, S.; Koltun, P. Global warming impact of the magnesium produced in China using the Pidgeon process. Resour. Conserv. Recycl. 2004, 24, 49-64. (8) Cherubinia, F.; Raugei, M.; Ulgiati, S. LCA of magnesium production: technological overview and worldwide estimation of environmental burdens. Resour. Conserv. Recycl. 2008, 52, 1093-1100. (9) Aghion, E.; Bartos, S. C. Comparative review of primary magnesium production technologies as related to global climate change; 65th Annual World Magnesium Conference. Warsaw, Poland, 2008. (10) Prentice, L.; Poi, N. W.; Haque, N. Life cycle assessment of carbothermal production of magnesium in Australia; 67th Annual World Magnesium Conference. Hongkong, China, 2010. (11) Franca, F. C. V.; Brito, R. P. Rima's process: green magnesium from a fully integrated plant; 69th Annual World Magnesium Conference. Prague, Czech Republic, 2011. (12) Gossan Resources Ltd. Lowering of CO2 emission for magnesium production by Gossan-Zuliani process; http:// www.gossan.ca/projects/pdf/MgGHGReport.pdf (Accessed Oct. 15, 2012). (13) Koltun, P.; Tharumarajah, A.; Ramakrishnan, S. Life cycle environmental impact of magnesium automotive components. Magnesium technology 2005, 43-49. (14) Tharumarajah, A.; Koltun, P. Is there an environmental advantage of using magnesium components for light-weighting cars?. J. Clean. Prod. 2007, 15, 1007-1013. (15) Hakamada, M.; Furuta, T.; Chino, Y.; Chen, Y. Q.; Kusuda, H.; Mabuchi, M. Life cycle inventory study on magnesium alloy substitution in vehicles. Energy 2007, 32, 1352-1360. (16) Bartos, S.; Laush, C.; Scharfenberg, J.; Kantamaneni, R. Reducing greenhouse gas emissions from magnesium die casting. J. Clean. Prod. 2007, 15, 979-987. (17) Ehrenberger, S.; Schmid, S.; Song, S. B.; Friedrich, H. E. Status and potentials of magnesium production in china: life cycle analysis focusing on CO2eq emissions; 65th Annual World Magnesium Conference, Warsaw, Poland, 2008. (18) World Steel Association. Methodology report life cycle inventory study for steel products; http://worldsteel.org/publications/bookshop?bookID=f636e8bf-cd36-44cc-a2d2-3167ffdad45e. (Accessed Mar. 21, 2012). (19) International Aluminium Institute. Life cycle assessment of aluminium: inventory data for the primary

aluminium

industry

year

2005

update;

http://www.world-aluminium.org/UserFiles/File/LCA.pdf (Accessed Nov. 6, 2008). (20) European Aluminium Association. Environmental profile report for the European aluminium


Page 13 of 14


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

industry - April 2008 - life cycle inventory data for aluminium production and transformation processes in

Europe;

http://www.eaa.net/upl/4/default/doc/EAA_Environmental_profile_report_May08.pdf

(Accessed Nov. 7, 2008). (21) Modaresi, R.; Pauliuk, S.; Løvik, A. N.; Müller, D. B. Global carbon benefits of material substitution in passenger cars until 2050 and the impact on the steel and aluminum industries. Environ. Sci. Technol. 2014, 48 (18), 10776–10784. (22) Ehrenberger, S.; Dieringa, H.; Friedrich, H. E. Life cycle assessment of magnesium components in vehicle construction; Institute of Vehicle Concepts, German Aerospace Centre: Stuttgart, Germany, 2013; www.intlmag.org/newsroom/2013IMA_LCA_Report_Public.pdf. (23) U.S.

Geological

Survey

(USGS).

Magnesium

Statistics

and

Information;

http://minerals.er.usgs.gov/minerals/pubs/commodity/magnesium/index.html (Accessed Oct. 23, 2014). (24) Xu, R. Y.; Liu, R. Y.; Liu, H. Z. Energy-saving, consumption reducing and discharge abatement are the vitality of silicothermic reduction in magnesium metallurgy. Light Metals 2009, 1, 45-49 (in Chinese). (25) Liu, H. X.; Dai, Y. N.; Li, Y. F.; Tian, Y.; Wang, L. Preparing magnesium by carbothermic reduction of magnesia in vacuum. Vacuum 2009, 46 (5), 82-86 (in Chinese). (26) Feng, N. X.; Wang, Y. W. A method of producing magnesium by vacuum thermal reduction using magnesite and dolomite as materials. The Chinese Journal of Nonferrous Metals 2011, 21 (10), 2678-2686 (in Chinese). (27) Xia, D. H.; Ren, C. X. Development of regenerative reheating magnesium finery based on furnace group. Light Metals 2009, 5, 44-46 (in Chinese). (28) Liu, Y.; You, G. P.; Huang, Y. Y. Current situation and development of vetical retort magnesium reduction process. Light Metals 2011, 6, 45-49 (in Chinese). (29) Intergovernmental Panel on Climate Change (IPCC). 2006 IPCC guidelines for national greenhouse gas inventories Volume 2 Energy; Institute for Global Environmental Strategies (IGES): Japan, 2006; www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html. (30) Song, R. P.; Yang, S.; Sun, M. GHG protocol tool for energy consumption in china (Version 2.1); World

Resources

Institute

(WRI):

Beijing,

China,

2013;

www.ghgprotocol.org/calculation-tools/all-tools. (31) Ang, B. W.; Zhang, F. Q. A survey of index decomposition analysis in energy and environmental studies. Energy 2000, 25, 1149-1176. (32) Xu, X. Y.; Ang, B. W. Index decomposition analysis applied to CO2 emission studies. Ecological Economics 2013, 93, 313-329. (33) Tian, Y.; Zhu, Q. H.; Geng, Y. An analysis of energy-related greenhouse gas emissions in the Chinese iron and steel industry. Energy Policy 2013, 56, 352-361. (34) Sheinbaum, C.; Ozawa, L.; Castillo, D. Using logarithmic mean Divisia index to analyze changes in energy use and carbon dioxide emissions in Mexico's iron and steel industry. Energy Economics 2010, 32(6), 1337-1344. (35) Liu, Z.; Geng, Y.; Lindner, S.; Zhao, H. Y.; Fujita, T.; Guan, D. B. Embodied energy use in China’s industrial sectors. Energy Policy 2012, 49, 751–758. (36) Tan, Z. F.; Li, L.; Wang, J. J.; Wang, J. H. Examining the driving forces for improving China’s CO2 emission intensity using the decomposing method. Applied Energy 2011, 88(12), 4496–4504. (37) Ang, B. W. The LMDI approach to decomposition analysis: a practical guide. Energy Policy 2005, 33, 867-871.



1 2 3

(38) Gao, F.; Nie, Z. R.; Wang, Z. H; Gong, X. Z.; Zuo, T. Y. Life cycle assessment of primary magnesium production using the Pidgeon process in China. Int. J. LCA 2009, 14 (5), 480-489.


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Variation Trend and Driving Factors of Greenhouse Gas Emissions

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