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Comparison of greenhouse gas emission accounting methods for steel production in China
Journal of Cleaner Production 83 (2014) 165e172
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Comparison of greenhouse gas emission accounting methods for steel production in China Ran Jing, Jack C.P. Cheng*, Vincent J.L. Gan, Kok Sin Woon, Irene M.C. Lo Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 January 2014 Received in revised form 12 May 2014 Accepted 7 July 2014 Available online 15 July 2014
Steel production is an environmentally sensitive process accounting for 10% of greenhouse gas (GHG) emissions in China, which represents 4e5% of the world's total anthropogenic GHG emissions. This study presents and compares three GHG emissions accounting methods for steel production in China, which are the Intergovernmental Panel on Climate Change (IPCC) method, the Life Cycle Inventory Localization (LCIL) method, and the Comprehensive Energy Consumption (CEC) method. Different criteria such as sources of data, energy input-based and process-based analyses, and benefits and limitations of the three methods are compared and discussed. On the basis of the data collected and system boundary defined in this study, the total GHG emissions of the IPCC, LCIL, and CEC methods are estimated as 1.717, 1.715, and 1.959 kg CO2-e/kg steel, respectively. The results of the IPCC and CEC methods show that the coal and coke combustion contributes 90.2% and 84.5% of total energy related GHG emissions during steel production in China, respectively. For the LCIL method, it quantifies the GHG emissions from each individual sub-processes associated with the sintering process to the electric arc furnace process. The results of the LCIL method indicate that the hotspot area for GHG emissions during steel production is the blast furnace process, which accounts for 78.4% of the total energy related GHG emissions. These three methods can be applied to other countries to investigate their GHG emissions. Moreover, the comparison of these three methods provides insights for adopting appropriate methods to calculate GHG emissions for steel production. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Comprehensive energy consumption Greenhouse gas Intergovernmental panel on climate change Life cycle inventory localization Steel production
1. Introduction In 2012, the world's steel production was 1545.01 million tonnes (WSA, 2013a). China produced 716.54 million tonnes of steel (WSA, 2013b) and it accounted for 3-4 percent of China's GDP in 2012 (Stanway and Lian, 2012). The steel production in China increased by 3.1 percent in 2012 due to the economic growth and demand for road and railway constructions (Asian metallurgy, 2013). According to the Chinese Statistics Bureau, it's the 31st annual increase in steel production and came as the world's second-largest economy expanded 7.8 percent in 2012 (Asian metallurgy, 2013). Steel production is a high energy intensive industry with large emissions of greenhouse gas (GHG) (Burchart-Korol, 2013). According to Tian et al. (2013), steel production accounts for approximately 4e5% of the world's total GHG emissions. In China, steel production is the third largest GHG emissions sector accounting for 10% of total GHG
* Corresponding author. Tel.: þ852 23588186; fax: þ852 23581534. E-mail address: [email protected] (J.C.P. Cheng). http://dx.doi.org/10.1016/j.jclepro.2014.07.016 0959-6526/© 2014 Elsevier Ltd. All rights reserved.
emissions (Zeng et al., 2009). Estimation and assessment methods for GHG emissions from steel production have been developed in China (Price et al., 2002; Wang et al., 2007; Shangguan et al., 2010). Shangguan et al. (2010) calculated the CO2 emissions from steel production in China based on the analysis of carbonaceous flow, in which the CO2 emissions from energy consumption in the steel industry in China accounted for over 90% of the total CO2 emissions. Price et al. (2002) examined the CO2 emissions from the steel industry by modifying the official Chinese energy consumption statistics for steel production in China in order to avoid doublecounting of certain data such as the coal-based energy consumption. Price et al. (2002) found that the energy use and CO2 emissions associated with steel production in China were higher than those in Brazil, India, Mexico and South Africa. Wang et al. (2007) investigated the energy consumption and CO2 emissions from steel industry in China through the generation of three different scenarios using the Long-range Energy Alternative Planning (LEAP) software. These studies applied different GHG accounting methods and various data from literature and carbon emission factors for China in the calculation of CO2 emissions, rendering different outcomes
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for the CO2 emissions from steel production in China. The objective of this paper is to investigate the three different methods in GHG emissions accounting by comparing three methods for calculation of the GHG emissions from steel production in China based on GHG emission factors for China and various expressions of energy consumption data (e.g., consumption of fuel or electricity, embodied energy consumed in the intermediate steel manufacturing process, comprehensive energy consumption). In this study, the first method follows the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories (IPCC, 2006). The GHG emission factors and the energy consumption data from existing steel plants in China are applied to the IPCC method. The second method is the localization of the Ecoinvent database. In this method, the GHG emissions of each individual sub-process of steel production related to energy are calculated based on the embodied energy GHG emission factors for each type of energy used (i.e., coal, coke, electricity, and natural gas). In the third method, the GHG emissions of steel production in China are calculated in reference to comprehensive energy consumption (CEC), the percentage distribution of primary energy used for steel production in China, and the GHG emission factors for stationary combustion for each type of GHG. The results of GHG emissions, data inputs and sources, differences, benefits, and limitations of each method will be discussed. 2. Methodology 2.1. Modeling scope of study and description of steel manufacturing process in China In this study, the system boundary is “Gate-to-Gate”, which covers the manufacturing process from raw materials (factory-entry gate) to the final product (factory-exit gate). The most important assumption in an application of the life cycle inventory localization (LCIL method) is that Mainland China should have similar steel manufacturing processes as described in the life cycle inventory used in this study. Therefore, the typical steel manufacturing process in Mainland China needs to be identified. A typical steel manufacturing process in the Mainland China consists of a blast furnace (BF) process, a basic oxygen furnace (BOF) process and an electric arc furnace (EAF) process. Fig. 1 shows the process flow diagram of steel production in China. Firstly, the raw materials (e.g., iron ore, coal, coke and limestone) are fed into the BF, followed by air injection to the furnace through the openings at the bottom of the shaft above the hearth crucible. With the presence of air, the coke burns along with the injected fuels, such as tar or light oil, to produce the necessary heat and generate reducing gas to remove oxygen from the ore in the reduction process. After the BF process, a portion of the pig iron is sent to the BOF. High purity oxygen is blown through the molten bath of iron in the BOF to reduce the concentration of carbon, silicon, manganese, and phosphorous in pig iron, while various fluxes (i.e., burnt lime or dolomite) are used to reduce the levels of sulfur and phosphorous. The remaining pig iron is sent to the EAF which relies on recycled steel scrap as raw material. Recycled steel scrap is melted and refined using electrical energy imparted to the charge through carbon electrodes and then alloyed to produce the desired grade of steel. In this study, the total GHG emissions are divided into two parts: (1) energy related GHG emissions, which consist of the GHG emissions from the fuel combustion and electricity consumption; (2) non-energy related GHG emissions, which mainly encompass the chemical reactions during the steel production process. The results of the GHG emissions are expressed in terms of carbon dioxide equivalent (CO2-e), with global warming potential (GWP) values over a 100-year time horizon (IPCC, 2007). The GHG
Fig. 1. Process flow diagram of steel production in China.
emission factors used in this study are obtained from the GHG Protocol Tool for Energy Consumption in China in 2011 (WRI, 2013). The GWP values of CO2, CH4 from fossil sources, and N2O are 1, 25, and 298, respectively (IPCC, 2007). The descriptions of the methodological approach and equations used for each method are explained in Section 2.2, 2.3, and 2.4. 2.2. Calculation of GHG emissions using the Intergovernmental Panel on Climate Change guidelines for national greenhouse gas inventories (IPCC method) The GHG emissions from each type of energy are calculated using the Tier 2 method IPCC, with a multiplicative product of the
R. Jing et al. / Journal of Cleaner Production 83 (2014) 165e172
energy consumption and the GHG emission factors for China (IPCC, 2006). Equations (1)e(3) illustrate how the GHG emissions of fuel and electricity are calculated based on the energy consumption and GHG emission factors (WRI, 2013). The total GHG emissions are calculated based on the total energy related GHG emissions and the ratio of energy related CO2 emissions to the total CO2 emissions of the steel industry in China (Shangguan et al., 2010). The total GHG emissions are shown in Equation (4):
ECO2 ¼
4 X Qi EFi;CO2 Qsteel
(1)
i¼1
ECH4 ¼
4 X
Qi EFi;CH4
Qsteel
(2)
database). The Ecoinvent database was applied to this method and the high qualities of the LCI data are based on industrial data and have been compiled by the Swiss Center for Life Cycle Inventories (Frischknecht and Rebitzer, 2005). In this method, the Ecoinvent database v2.1 is localized based on a major assumption that the steel production process in China is similar to that in European countries (Wen et al., 2014; Classen et al., 2009). The major steel manufacturing processes (Pelletizing process, sintering process, blast furnace process, basic oxygen furnace process, electric arc furnace process) in Europe and China are similar, which are highlighted by red lines in Figure B.4, Figure B.5 and Figure B.6. The energy related GHG emissions of each individual subprocess of steel production are calculated based on Equations (5)e(7).
i¼1
Eh;CO2 ¼ EN2 O ¼
4 X
Qi EFi;N2 O
167
4 X
0 Qi;h EFi;CO2
(5)
i¼1
Qsteel
(3)
i¼1
Etotal ¼ ECO2 R1 GWPCO2 þ ECH4 GWPCH4 þ EN2 O GWPN2 O (4) where i (i ¼ 1, 2, 3, 4) denotes the types of energy used, i.e., coal, coke, electricity and natural gas; ECO2 , ECH4 , and EN2 O are the energy related emissions of CO2, CH4, and N2O (kg/kg steel); Qi is the consumption of energy i (kg for fuel or kWh for electricity); EFi, CO2, EFi,CH4, and EFi, N2O are the emission factors of CO2, CH4 and N2O for energy i which are summarized in Table A.1 in supplementary data (kg GHG/kg fuel or kg GHG/kWh); Qsteel is the amount of steel produced (kg); GWPCO2 , GWPCH4 , and GWPN2 O are the global warming potentials for CO2, CH4, and N2O; R1 is the ratio of energy related CO2 emissions to the total CO2 emissions from steel production in China, i.e., R1 ¼ 98.26% (Shangguan et al., 2010). The questionnaire was sent to one of the top three steel manufacturers in Mainland China, which produced more than 40 million tonnes steel in 2012 (WSA, 2013c). The questionnaire was mainly targeted at the energy consumption of the steel manufacturing process and it has been attached to the supplementary data (Appendix C). The plant-specific data of raw materials consumption, intermediate products' production and final products production are shown in Table A.3. The plant-specific data of energy consumption are shown in Table A.4. The energy consumption data collected from the questionnaire were comparable to the energy consumption data from the company's annual report in 2012. In addition, representative of plant-specific data for the IPCC method have been verified. For the CEC method, the 42 steel manufacturers account for 57.4% of the production of the Chinese steel industry in this study. The average CEC value of the 42 Chinese steel manufacturers (standard deviation: 0.073) is 0.618 kg coal equivalent/kg steel. Meanwhile, the CEC value re-calculated based on the plant-specific data is 0.559 kg coal equivalent/kg steel. The results indicate that the re-calculated CEC value based on the plant-specific data is comparable to the average CEC value of the 42 Chinese steel manufacturers. Therefore, data from the steel manufacturers in Mainland China obtained via the questionnaire in the IPCC method are representative of the entire Chinese steel manufacturing industry. 2.3. Calculation of GHG emissions using the life cycle inventory localization (LCIL method)
Eh;CH4 ¼
4 X
0 Qi;h EFi;CH4
(6)
i¼1
Eh;N2 O ¼
4 X
0 Qi;h EFi;N2 O
(7)
i¼1
where h (h ¼ 1, 2, 3, 4, 5) denotes the intermediate product of sintering, pelletizing, BF, BOF and EAF; i (i ¼ 1, 2, 3, 4) denotes the types of energy used (i.e., coal, coke, electricity and natural gas) for individual sub-process of steel production; Eh;CO2 , Eh;CH4 , and Eh;N2 O are the energy related emissions of CO2, CH4, and N2O for process h, 0 respectively (kg/kg intermediate product); Qi;h is the embodied energy consumed in the intermediate steel manufacturing process h (kg fuel/kg intermediate product or kWh/kg intermediate prod1 uct); EFi;CO EF1i;CH4 , and EF1i;N2 O are the GHG emission factors for 2 China for each type of energy i which are summarized in Table A.1 in supplementary data (kg GHG/kg fuel or kg GHG/kWh). The unit of each individual sub-process of steel production is converted to kg CO2-e/kg steel on the basis of the intermediate product to the steel produced. According to the Ecoinvent life cycle inventories report (Classen et al., 2009), 1.05 kg of sinter and 0.4 kg of pellets are needed to produce 1 kg of pig iron. The ratio of pig iron production to crude steel production is 0.9. Therefore, the mass ratio of sinter, pellet, pig iron, liquid steel produced from BOF, and liquid steel produced from EAF to steel are 0.945, 0.36, 0.9, 1, and 1, respectively. According to the data of Ecoinvent database, the percentage of energy related CO2 emissions to the total CO2 emissions of the steel industry is 99.99% (Classen et al., 2009). The total GHG emissions of the steel manufacturing process for each sub-process are calculated using Equations (8)e(10), and the total GHG emissions of steel production are calculated using Equation (11).
ECO2 ¼
5 X
Kh Eh;CO2
(8)
h¼1
ECH4 ¼
5 X Kh Eh;CH4
(9)
h¼1
EN2 O ¼
5 X Kh Eh;N2 O
(10)
h¼1
The LCIL method evaluates the GHG emission based on the embodied energy of the individual sub-process of steel production provided in the existing life cycle inventory (i.e., Ecoinvent
Etotal ¼ ECO2 GWPCO2 R2 þ ECH4 GWPCH4 þ EN2 O GWPN2 O (11)
168
R. Jing et al. / Journal of Cleaner Production 83 (2014) 165e172
where h (h ¼ 1, 2, 3, 4, 5) denotes the intermediate product of sintering, pelletizing, BF, BOF and EAF; Kh is the mass ratio of intermediate product of each process h to steel (e.g., 0.945 kg sinter/ kg steel); Eh,CO2, Eh,CH4, and Eh,N2O are the energy related emissions of CO2, CH4, and N2O for process h, respectively (kg/kg intermediate product); ECO2 , ECH4 , and EN2 O stand for the total CO2, CH4, and N2O emissions of steel production (kg/kg steel); R2 is the ratio of energy related CO2 emissions to the total CO2 emissions of steel production obtained from Ecoinvent database, i.e., R2 ¼ 99.99% (Classen et al., 2009); Etotal is the total GHG emissions of steel production (kg); GWPCO2 , GWPCH4 , and GWPN2 O are the global warming potentials for CO2, CH4, and N2O. The GHG emissions related to energy can be corrected by the ratio of the intermediate steel product to the final steel produced. The total GHG emissions are derived using the percentage of energy related CO2 emissions to the total CO2 emissions of the steel industry obtained from the Ecoinvent database. 2.4. Calculation of GHG emissions using the comprehensive energy consumption (CEC method) 2.4.1. Definition of comprehensive energy consumption Comprehensive energy consumption (CEC) is defined as the sum of all the physical energy consumed by the energy consumption unit within the production process. The measurement system boundary of the comprehensive energy consumption is the total energy used by an enterprise's main production system, auxiliary production system and subsidiary production system within the production process (AQSIQ, 2008). The unit used for the calculation of the comprehensive energy consumption converted to primary energy is called the standard coal equivalent (as shown in Equation (12)).
CEC ¼
4 X ðei pi Þ=Qsteel
(12)
i¼1
where i (i ¼ 1, 2, 3, 4) denotes the types of energy used (i.e., coal, coke, electricity, and natural gas) for calculation of the comprehensive energy consumption; ei refers to the amount of energy i consumed during steel production (kg); pi stands for the conversion factor for each energy i used (kg coal equivalent/kg energy), which is summarized in Table A.2 in supplementary data; Qsteel is the quantity of total steel produced (kg). 2.4.2. Calculation of GHG emissions of steel production in China using the CEC method In this study, the CEC method utilizes the comprehensive energy consumption of 42 steel producers in China. The 42 steel manufacturers account for 57.4% (China's Steel Prices, 2012) of the production of the Chinese steel industry (203 steel manufacturers). The comprehensive energy consumption is calculated based on the general principles defined in GB/T 2589-2008. Out of 203 steel manufacturers in China, the comprehensive energy consumptions of 42 manufacturers were obtained from annual reports, company websites, and literature reviews. Figure B.2 shows the comprehensive energy consumption in kg coal equivalent/kg steel in 42 steel manufacturers. In order to calculate the GHG emissions, the energy sources of each company are calculated in regard to the comprehensive energy consumption, the percentage distribution of primary energy used by the steel producers in China, and the energy conversion factors of each type of energy. Four primary energy sources, which are coal, coke, electricity, and natural gas, with mix percentages of 49.9%, 41.5%, 6.67%, and 0.45%, contribute to the energy consumption distribution of steel production in China (LBNL, 2011). In addition, the energy conversion factors of each
energy source, provided by the Chinese National Statistics Bureau (AQSIQ, 2008), are shown in Table A.2. Equation (13) shows the calculation of the primary energy consumed by each steel company in China.
AFi ¼ CEC ki =pi
(13)
where i stands for the type of energy used (i.e., coal, coke, electricity, and natural gas); AFi stands for the consumption of energy i calculated based on comprehensive energy consumption of steel production (kg energy used/kg steel); ki is the percentage of energy i that contributes to the distribution of energy consumption for steel production in China; CEC is the comprehensive energy consumption for steel production (kg coal equivalent/kg steel); pi is the conversion factor of the coal equivalent for each type of energy i used (kg coal equivalent/kg energy used). Equation (14) shows that the total GHG emissions for 1 kg steel production can be calculated based on the energy consumption, the GHG emission factors (EFi;CO2 , EFi;CH4 , and EFi;N2 O ) and the ratio of energy related CO2 to total GHG emissions (R3).
Etotal ¼
4 X AFi EFi;CH4 GWPCO2 R3 i¼1
þ
4 X AFi EFi;CH4 GWPCH4
(14)
i¼1
þ
4 X AFi EFi;N2 O GWPN2 O i¼1
where i (i ¼ 1, 2, 3, 4) denotes the type of energy (i.e., coal, coke, electricity, and natural gas); AFi stands for the consumption of energy i calculated based on the comprehensive energy consumption in steel production (kg energy used/kg steel); EFi;CO2 , EFi;CH4 , and EFi;N2 O are the GHG emission factors for energy i (kg GHG/kg fuel or kg GHG/kWh); R3 stands for the ratio of energy related CO2 emission to the total CO2 emission, i.e., R3 ¼ 98.26%; (Shangguan et al., 2010); GWPCO2 , GWPCH4 , and GWPN2 O are the global warming potentials for CO2, CH4, and N2O. 3. Results and discussion 3.1. The results of GHG emissions calculated using the IPCC, LCIL, and CEC methods As shown in Table 1, the total GHG emissions from the steel production plant in China calculated using the IPCC method are 1.717 kg CO2-e/kg steel, with an amount of 1.687 kg CO2-e/kg steel for total energy related GHG emissions. Among the four types of energy, the combustion of coke and coal account for the highest GHG emissions in the steel production, in which the combustion of coke and coal generate 0.785 kg CO2-e/kg steel (46.6%) and 0.735 kg CO2-e/kg steel (43.6%) of the total energy related GHG emissions, respectively. For the LCIL method, the total energy related and total GHG emissions are 1.7150 and 1.7152 CO2-e/kg steel, respectively. Figure B.3 shows that the energy related GHG emissions are mainly contributed by coke combustion (59.3%), followed by coal combustion (24.2%). This is mainly attributed to the fact that coke and coal are highly consumed during the production of pig iron in the BF process, rendering a high GHG release during the combustion of coke and coal. As shown in Table 2, the combustion of coke in the BF process generates 0.884 kg CO2-e/kg steel, in which it accounts for 51.4% of the total energy related GHG emissions. The results of GHG emissions calculated using the CEC method are shown in Table 3. The total energy related and total GHG
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169
Table 1 Results of GHG emissions using the IPCC method (Tier 2). Types of energy
Quantitya (million tonnes/year)
Coal 16.2 Coke 12.0 Electricity 7.01 Natural gas 0.38 Total energy related GHG emissions Total GHG emissionsd a b c d
CO2 emission factorb (kg CO2/kg fuel or kg CO2/kwh)
CH4 emission factorb (kg CH4/kg fuel or kg CH4/kwh)
N2O emission factorb (kg N2O/kg fuel or kg N2O/kwh)
Energy related GHG emissionsc (kg CO2-e/kg steel)
Percentage of total energy related GHG emissions (%)
1.981 2.860 0.873 3.088
0.00021 0.00028 0.00001 0.00019
0.000031 0.000043 0.000013 0.000004
0.735 0.785 0.140 0.027 1.687 1.717
43.6 46.6 8.29 1.60
Based on the plant specific data provided by one of the biggest steel manufacturers in China. Obtained from GHG Protocol Tool for Energy Consumption in China in 2011 (WRI, 2013). Calculated based on the results of Equations (1)e(3) and global warming potentials. The steel production is 44 million tonnes in 2012. Calculated based on Equation (4).
emissions of 42 steel manufacturers in China are 1.925 and 1.959 CO2-e/kg steel, respectively. According to Table 3, it can be seen that coal combustion is the largest contributor of total energy related GHG emissions (44.9%) compared to other types of energy. The percentage contribution by coal in the CEC method is higher than that in the IPCC and LCIL methods. The reason is that coal is the largest primary energy used (44.9%) compared to the other energy sources for 42 steel manufacturers. Therefore, coal combustion contributes a large amount of GHG emissions. As shown in Fig. 2, the total GHG emissions of 42 steel manufacturers in China range from 2.27 to 1.05 kg CO2-e/kg steel and the average and variance are 1.96 kg CO2-e/kg steel and 0.053, respectively. It is also worth noting that most of the steel manufacturers in China emit GHG in a range of 1.80e2.00 kg CO2-e/kg steel, in which 16 out of the 42 steel manufacturers in China are within this level (as shown in the histogram diagram in Figure B.1). It is found that the average GHG emissions of the 42 steel manufacturers in China, calculated using the CEC method (i.e., 1.959 kg CO2-e/kg steel), is relatively higher than that of the IPCC
(i.e., 1.717 kg CO2-e/kg steel) and the LCIL methods (i.e., 1.715 kg CO2-e/kg steel). However, the variance of the total GHG emissions in these three methods is 0.019, which is relatively smaller than the variance of the total GHG emissions of the 42 steel manufacturers in China, as abovementioned (i.e., 0.053). On the other hand, it should be highlighted that the non-energy related GHG emissions are insignificant compared to the total energy related GHG emissions. The non-energy related GHG emissions of the IPCC, LCIL and CEC methods are 0.030, 0.002 and 0.034 kg CO2-e/kg steel, respectively. These findings are in line with the results reported by Zhang et al. (2012), in which fossil fuel combustion and electricity consumption are the two major categories of CO2 emissions in a steel production plant. 3.2. Comparison of data input and sources of the IPCC, LCIL, and CEC methods Different sets of data are required for each method in order to account for the GHG emissions from steel production in China. The
Table 2 Results of GHG emissions using the LCIL method (based on the Ecoinvent database). Process
Sintering
Types of energya
Coke Electricity Natural gas Pelletizing Coal Electricity Natural gas Blast furnace process Coal Coke Electricity Natural gas Basic oxygen furnace process Coke Electricity Natural gas Electric arc furnace process Coal Electricity Natural gas Total energy related GHG emissions Total GHG emissionsc
a b c d e f g h
Energy consumptiona (kg fuel/kg intermediate product or kWh/kg intermediate product)
Mass ratio (kg intermediate product/kg steel)
Energy related GHG emissionsb (kg CO2-e/kg steel)
Percentage of total energy related GHG emissions (%)
0.050 0.010 0.0000653d 0.013 0.025 0.001e 0.210 0.340 0.100 0.002f 0.00000874 0.022 0.000674g 0.014 0.120 0.018h
0.945 0.945 0.945 0.360 0.360 0.360 0.900 0.900 0.900 0.900 1.000 1.000 1.000 1.000 1.000 1.000
0.136 0.008 0.000190 0.009 0.008 0.001 0.377 0.881 0.079 0.006 0.0000251 0.019 0.0021 0.028 0.105 0.054 1.715 1.715
7.93 0.48 0.01 0.54 0.46 0.08 22.0 51.4 4.61 0.35 0.00 1.12 0.12 1.63 6.14 3.16
Obtained from the Ecoinvent Life Cycle Inventories of Metals Data v2.1 (Classen et al., 2009). Calculated by Equations (5)e(7). The results are converted by multiplying the mass ratio of each intermediate product to steel produced. Calculated by Equations (8)e(11). Calculated with 0.00363 MJ/kg sinter multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas. Calculated with 0.069 MJ/kg pellet multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas. Calculated with 0.12 MJ/kg pig iron multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas. Calculated with 0.0375 MJ/kg steel multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas. Calculated with 0.975 MJ/kg steel multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas.
Percentage of total energy related GHG emissions of each individual process (%) 8.42
1.08
78.4
1.24
10.9
170
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Table 3 Results of GHG emissions using the CEC method (based on 42 steel companies in China). Types of energy
CO2a (kg CO2/kg steel)
CH4a (kg CH4/kg steel)
N2Oa (kg N2O/kg steel)
Energy related GHG emissions (kg CO2-e/kg steel)
Total GHG emissions (kg CO2-e/kg steel)
Percentage of total energy related GHG emissions (%)
Coal Coke Electricity Natural gas Average GHG emissions of 42 steel manufacturersb Average GHG emissions of 17 steel manufacturersc Average GHG emissions of 25 steel manufacturersd
0.857 0.756 0.293 0.005 1.912
0.000090 0.000075 0.000003 0.0000003 0.00017
0.00001 0.00001 0.000004 0.00000001 0.00003
0.864 0.762 0.295 0.005 1.925
0.879 0.775 0.300 0.0051 1.959
44.9 39.6 15.3 0.26
1.929
0.00017
0.00003
1.942
1.976
1.900
0.00017
0.00003
1.913
1.947
a b c d
Calculated based on the Equation (13) and the GHG emission factors (refer to Table A.1). Calculated based on Equation (13). The production process includes BF, BOF, and EAF processes. The production process includes BF and BOF processes only.
data input are collected from different sources by different approaches. In this study, the energy consumption data of the IPCC method are collected from one of the major steel manufacturers in China by questionnaire survey. The data could represent the most recent energy utilization levels and technologies used by the steel manufacturers in China based on year 2012 as the data provided by one of the biggest steel manufacturers. This steel manufacturer utilizes a number of energy efficient technologies such as efficient power generation, low energy intensive furnaces, and reuse of residual heat; therefore, the GHG emissions are potentially lower. For the LCIL method, the steel production processes in the Ecoinvent database mainly relies on the production and supply situation in Europe in 2000 (Frischknecht and Rebitzer, 2005). One of the caveats when applying the LCIL method is that the manufacturing processes and technologies in the studied countries/regions should be similar to the manufacturing process in life cycle inventory as described in the Ecoinvent. This study assumes that the manufacturing processes and technologies for steel production in Europe and China are similar. Based on this assumption, the data for embodied energy of individual sub-process of steel production from the Ecoinvent database can be applied in the LCIL method. However, for certain countries such as Thailand, the LCIL
method might not be suitable to be applied, due to the fact that the steel production process in Thailand is dramatically different from countries in Europe (Sodsaia and Rachdawong, 2012). For the CEC method, the major data sources for comprehensive energy consumption are based on the annual reports, company websites, statistical yearbooks of steel manufacturers in China, and literature. The production technology levels for the 42 manufacturers are covered from 2000 to 2011. As elucidated in Section 2.4.1, comprehensive energy consumption, which calculated by using GB/ T 2589-2008, is used to reflect the energy consumption among the steel production processes of 42 steel manufacturers in China. However, it should be pointed out that due to the lack of detailed information concerning the steel manufacturing processes in some steel manufacturers in China, it might affect the data quality of the comprehensive energy consumption and comparability among the 42 steel manufacturers. For example, some steel manufacturers in China purchase intermediate products such as sinter or coke instead of producing these intermediate products by their own companies. In these circumstances, the comprehensive energy consumption and the total GHG emissions from these steel manufacturers could be smaller than that the average level of the 42 steel manufacturers in China.
2.5
Total GHG emissions kg CO2-e/ kg steel
2.0
1.5
1.0
0.5
0.0 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
Steel manufacturers in China Fig. 2. Total GHG emissions of 42 steel manufacturers in China determined from the CEC method.
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171
Table 4 Comparison of the IPCC, LCIL, and CEC methods in this study. IPCC method
LCIL method
CEC method
1.687
1.715
1.925
0.030
0.002
0.034
1.717 One of the biggest steel manufacturers in China
1.715 Eco-invent database v2.1
Method analysis Data inputs
Energy input-based Energy consumption of plant-specific data
Process-based Embodied energy of individual subprocess Mass ratio of intermediate product of each process to steel
Differences
GHG emissions were estimated based on the real activity data (e.g., coal consumption collected from the questionnaire) Based on different data quality, threetier methods can be used to estimate GHG emissions More time and efforts are needed to collect the first hand data
GHG emissions were estimated based on the statistical data analysis
1.959 Company's annual report Published literature review Chinese statistical yearbook Energy input-based Energy consumption in terms of coal equivalent The percentage of each type of energy that contributes to the distribution of energy consumption for steel production in China GHG emissions were estimated based on statistical data analysis
Energy-related GHG emissions (kg CO2e/kg steel) Non-energy-related GHG emissions (kg CO2-e/kg steel) Total GHG emissions (kg CO2-e/kg steel) Data sources
Advantages
Disadvantages
Benefits
Internationally recognized
Limitations
The results calculated using this method can be improved by applying the IPCC Tier 3
3.3. Comparison of the IPCC, LCIL, and CEC methods based on energy input-based and process-based analysis The IPCC and CEC methods are categorized as energy inputbased analyses. The results of these two methods are calculated by collecting the energy consumption data for the overall steel manufacturing processes. The results provide a valuable reference source for steel manufacturers in China regarding the GHG emissions levels. However, the uncertainty in the collection of energy consumption data could make its results less reliable compared to the LCIL method. Therefore, it requires verification and validation of the energy input in the manufacturing processes to enhance the accuracy and reliability of input data. The LCIL method is a process-based analysis which evaluates the inputs (e.g., embodied energy consumed in the intermediate steel manufacturing process) and the outputs (e.g., GHG emissions to the environment) for each and every process in steel production. By using this method, stakeholders can identify the major subprocesses that contribute to the highest GHG emissions in steel production within the studied system boundary. For example, the results of this study show that the blast furnace process contributes the highest GHG emissions, in which it accounts for 78.4% of the total energy related GHG emissions. Appropriate design and operating improvements, such as efficient power generation, low energy intensive furnaces, and reuse of residual heat, can be applied to the blast furnace processes to reduce the GHG emissions. 3.4. Benefits and limitations of the IPCC, LCIL, and CEC methods Among the three methods used in this study, the IPCC method is the most widely accepted approach for the calculation of GHG emissions in steel production. This method combines activity data with GHG emission factors for China (e.g., kg CO2/kg fuel) which quantify the emissions or removals per unit activity. Tier 2 IPCC
More optional databases can be used for this method (e.g., Chinese Life Cycle Database) Many calculations can be involved when the LCIL method is applied to estimate GHG emissions GHG emissions of individual subprocess can be calculated
Production processes of the countries/ regions should be similar to those in Europe
GHG emissions can be estimated simply based on coal equivalent The system boundaries of energy consumption data of each steel manufacturer are different GHG emissions can be easily calculated on the basis of the distribution of primary energy used for steel production in China CEC value is only developed by steel manufacturers in China
method is used in this study through the application of GHG emission factors of the fuel combustion and electricity consumption for China. The data quality of the results of the GHG emissions could be improved if Tier 3 IPCC method is applied in this study. Nevertheless, more time and efforts would be required during the data collection process as more local specific data are necessary for the calculation of GHG emissions in Tier 3 IPCC method. One of the benefits of the LCIL method is that it provides the GHG emissions from each individual sub-process of steel production, in which the IPCC method and the CEC method could only provide the total GHG emissions within the studied system boundary. However, the LCIL method can be applied only in the situation when the steel manufacturing process of a region is similar to the process as described in Ecoinvent life cycle inventory. Another limitation of applying the LCIL method is that the results of GHG emissions of individual sub-process may change if the energy contents of fuels are different. For example, according to the GHG Protocol Tool for Energy Consumption in China, burning one tonne of Chinese and European coke produce 28,435 and 28,600 MJ of energy, respectively (WRI, 2011; WRI, 2013). Compared to the IPCC and LCIL methods, the benefits of using the CEC method is that the GHG emissions can be simply calculated by multiplying the CEC value with the percentage distribution of primary energy used for steel production in China. However, as far as the authors know, the CEC is mainly developed by the steel manufacturers in China but not in other countries. Therefore, the steel manufacturers in other countries are required to calculate their own the CEC value in order to apply the CEC method for GHG accounting in steel production. It should be noted that the percentage distribution of primary energy used for steel production in China may change over time and it can alter the results of GHG emissions. The Chinese Central Government has set carbon reduction policies to curtail GHG emissions, culminating in a pledge under the 2009 Copenhagen
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accord to achieve a 40e45% reduction in its carbon intensity by 2020 (CRS, 2011). China has taken strong effort to reduce carbon intensity and has enacted progressive policies to promote nuclear energy (Best and Levina, 2012). Therefore, cleaner energy source such as nuclear energy may be applied to steel industry in China to reduce the GHG emissions. A summary of comparison of the IPCC, LCIL, and CEC methods is shown in Table 4. 4. Conclusions This paper presents three accounting methods for the calculation of GHG emissions from steel production in China. On the basis of the data collected and the system boundary defined, the total GHG emissions of these three methods are 1.72, 1.72 and 1.96 kg CO2-e/kg steel, respectively. The IPCC method is based on energy input-based analysis. The GHG emissions were calculated based on the overall energy consumption data collected from one of the top three steel manufacturers in Mainland China. By knowing the various energy contributions to GHG emissions, potential alternatives for energy saving in this industry can be recommended to stakeholders, thereby enabling GHG mitigation. However, it should be noted that the IPCC method is recommended to be used for plant specific GHG emission estimation because the GHG emitted can be widely varied depending on the fuel combustion conditions and facilities operation conditions. The LCIL method is highly recommended to be used, when stakeholders want to calculate the GHG emissions for each individual sub-process in steel production or identify the hotspot areas of GHG emissions so as to facilitate system and process improvement for GHG mitigation. The LCIL method is a process-based analysis which is especially useful for assessing the GHG emissions from steel production based on the generic data without much first-hand data. However, the LCIL method is restricted to being used in regions that have similar major steel manufacturing processes as described in the life cycle inventory, because the embodied energy of each manufacturing process depends on the energy type and operational system boundary. Otherwise, the embodied energy of the manufacturing process used in GHG emissions estimation might not reflect the actual status. The CEC method obtains the comprehensive energy consumption per unit for producing one unit of steel, and the reference unit is kg coal equivalent/kg steel. The CEC value of each steel manufacturer is the total energy used by the steel manufacturer's main production system, auxiliary production system and subsidiary production system. The benefit of applying the CEC method is that GHG emissions can be estimated simply based on a wider range of statistical CEC values (i.e., coal equivalent) and the distribution of primary energy for steel production in China. However, it should be emphasized that the CEC method is mainly proposed for the steel manufacturers in China but is not commonly used in other countries or regions. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jclepro.2014.07.016.
References Asian metallurgy, 2013. Chinese Steel Production in 2012 up by 3.1%. Available from: http://www.steelworld.com/newsletter/2013/jan13/chinacalling0113.html (accessed 25.03.14). AQSIQ (General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China), 2008. General Principles for Calculation of the Comprehensive Energy Consumption, China. Best, D., Levina, E., 2012. Facing China's Coal Future. Available from: http://www.iea. org/publications/insights/chinas_coal_future.pdf (accessed 16.11.13.). Burchart-Korol, D., 2013. Life cycle assessment of steel production in Poland: a case study. J. Clean. Prod. 54, 235e243. China's Steel Prices, 2012. Major Chinese Iron and Steel Corporations Steel Production Statistics in 2011. Available from: http://www.zh818.com/html/2012/2/ 9/html (accessed 25.05.13.). Classen, M., Althaus, H.J., Blaser, S., Scharnhorst, E., 2009. Life Cycle Inventories of Metals Data v2.1. report No. 10. Swiss Centre for Life Cycle Inventories, Dubendorf. CRS (Congressional Research Service), 2011. China’s Greenhouse Gas Emissions and Mitigation Polices (CRS report for congress). Frischknecht, R., Rebitzer, G., 2005. The ecoinvent database system: a comprehensive web-based LCA database. J. Clean. Prod. 13, 1337e1343. IPCC (Intergovernmental Panel on Climate Change), 2006. IPCC Guidelines for National Greenhouse Gas Inventories. Mineral Industry Emissions. In: Energy, 2. IPCC (Intergovernmental Panel on Climate Change), 2007. Climate change 2007: the physical science basis. In: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. LBNL (Lawrence Berkeley National Laboratory), 2011. A Comparison of Iron and Steel Production Energy Use and Energy Intensity in China and the U.S. Price, L., Sinton, J., Worrell, E., Phylipsen, D., Xiulian, H., Ji, L., 2002. Energy use and carbon dioxide emissions from steel production in China. Energy 27, 429e446. Shangguan, F.Q., Zhang, C.X., Hu, C.Q., Li, X.P., Zhou, J.C., 2010. Estimation of CO2 emission in Chinese steel industry. Chin. Metall. 5, 37e42. Sodsaia, P., Rachdawong, P., 2012. The current situation on CO2 emissions from the steel industry in Thailand and mitigation options. Int. J. Greenh. Gas. Control 6, 48e55. Stanway, D., Lian, R., 2012. Analysis: China Steel Mills Too Big to Fail e or Succeed. Available from: http://www.reuters.com/article/2012/05/03/us-china-steelidUSBRE84203620120503 (accessed 16.04.14.). Tian, Y.H., Zhu, Q.H., Geng, Y., 2013. An analysis of energy related greenhouse gas emissions in the Chinese iron and steel industry. Energy Policy 56, 352e361. Wang, K., Wang, C., Lu, X.,D., Chen, J.,N., 2007. Scenario analysis on CO2 emissions reduction potential in China's iron and steel industry. Energy Policy 35, 2320e2335. Wen, Z.G., Meng, F.X., Chen, M., 2014. Estimates of the potential for energy conservation and CO2 emissions mitigation based on Asian-Pacific Integrated Model (AIM): the case of the iron and steel industry in China. J. Clean. Prod. 65, 120e130. WRI (World Resources Institute), 2011. Emission Factors from Cross-sector Tools. Available from: http://www.ghgprotocol.org/calculation-tools/all-tools (accessed 15.11.13.). WRI (World Resources Institute), 2013. GHG Protocol Tool for Energy Consumption in China. Available from: http://www.ghgprotocol.org/calculation-tools/alltools (accessed 15.11.13.). WSA (World Steel Association), 2013a. World Steel Association Steel Statistical Yearbook 2013. Available from: https://www.worldsteel.org/dms/ internetDocumentList/statistics-archive/yearbook-archive/Steel-StatisticalYearbook-2013/document/Steel-Statistical-Yearbook-2012.pdf (accessed 25.03.14.). WSA (World Steel Association), 2013b. World Steel Association Crude Steel Production, 1980e2012. Available from: https://www.worldsteel.org/dms/ internetDocumentList/statistics-archive/production-archive/steel-archive/ steel-annually/steel_yearly_1980 2012/document/Steel%20annual%2019802012.pdf (accessed 25.03.14.). WSA (World Steel Association), 2013c. Top Steel-producing Companies 2012. Available from: https://www.worldsteel.org/statistics/top-producers.html (accessed 14.04.14.). Zeng, S., Lan, Y.L., Huang, J., 2009. Mitigation paths for Chinese iron and steel industry to tackle global climate change. Int. J. Greenh. Gas. Control 3, 675e682. Zhang, B., Wang, Z.H., Yin, J.H., Su, L.X., 2012. CO2 emission reduction within Chinese iron & steel industry: practices, determinants and performance. J. Clean. Prod. 33, 167e178.
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Comparison of greenhouse gas emission accounting methods for steel production in China Ran Jing, Jack C.P. Cheng*, Vincent J.L. Gan, Kok Sin Woon, Irene M.C. Lo Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 January 2014 Received in revised form 12 May 2014 Accepted 7 July 2014 Available online 15 July 2014
Steel production is an environmentally sensitive process accounting for 10% of greenhouse gas (GHG) emissions in China, which represents 4e5% of the world's total anthropogenic GHG emissions. This study presents and compares three GHG emissions accounting methods for steel production in China, which are the Intergovernmental Panel on Climate Change (IPCC) method, the Life Cycle Inventory Localization (LCIL) method, and the Comprehensive Energy Consumption (CEC) method. Different criteria such as sources of data, energy input-based and process-based analyses, and benefits and limitations of the three methods are compared and discussed. On the basis of the data collected and system boundary defined in this study, the total GHG emissions of the IPCC, LCIL, and CEC methods are estimated as 1.717, 1.715, and 1.959 kg CO2-e/kg steel, respectively. The results of the IPCC and CEC methods show that the coal and coke combustion contributes 90.2% and 84.5% of total energy related GHG emissions during steel production in China, respectively. For the LCIL method, it quantifies the GHG emissions from each individual sub-processes associated with the sintering process to the electric arc furnace process. The results of the LCIL method indicate that the hotspot area for GHG emissions during steel production is the blast furnace process, which accounts for 78.4% of the total energy related GHG emissions. These three methods can be applied to other countries to investigate their GHG emissions. Moreover, the comparison of these three methods provides insights for adopting appropriate methods to calculate GHG emissions for steel production. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Comprehensive energy consumption Greenhouse gas Intergovernmental panel on climate change Life cycle inventory localization Steel production
1. Introduction In 2012, the world's steel production was 1545.01 million tonnes (WSA, 2013a). China produced 716.54 million tonnes of steel (WSA, 2013b) and it accounted for 3-4 percent of China's GDP in 2012 (Stanway and Lian, 2012). The steel production in China increased by 3.1 percent in 2012 due to the economic growth and demand for road and railway constructions (Asian metallurgy, 2013). According to the Chinese Statistics Bureau, it's the 31st annual increase in steel production and came as the world's second-largest economy expanded 7.8 percent in 2012 (Asian metallurgy, 2013). Steel production is a high energy intensive industry with large emissions of greenhouse gas (GHG) (Burchart-Korol, 2013). According to Tian et al. (2013), steel production accounts for approximately 4e5% of the world's total GHG emissions. In China, steel production is the third largest GHG emissions sector accounting for 10% of total GHG
* Corresponding author. Tel.: þ852 23588186; fax: þ852 23581534. E-mail address: [email protected] (J.C.P. Cheng). http://dx.doi.org/10.1016/j.jclepro.2014.07.016 0959-6526/© 2014 Elsevier Ltd. All rights reserved.
emissions (Zeng et al., 2009). Estimation and assessment methods for GHG emissions from steel production have been developed in China (Price et al., 2002; Wang et al., 2007; Shangguan et al., 2010). Shangguan et al. (2010) calculated the CO2 emissions from steel production in China based on the analysis of carbonaceous flow, in which the CO2 emissions from energy consumption in the steel industry in China accounted for over 90% of the total CO2 emissions. Price et al. (2002) examined the CO2 emissions from the steel industry by modifying the official Chinese energy consumption statistics for steel production in China in order to avoid doublecounting of certain data such as the coal-based energy consumption. Price et al. (2002) found that the energy use and CO2 emissions associated with steel production in China were higher than those in Brazil, India, Mexico and South Africa. Wang et al. (2007) investigated the energy consumption and CO2 emissions from steel industry in China through the generation of three different scenarios using the Long-range Energy Alternative Planning (LEAP) software. These studies applied different GHG accounting methods and various data from literature and carbon emission factors for China in the calculation of CO2 emissions, rendering different outcomes
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for the CO2 emissions from steel production in China. The objective of this paper is to investigate the three different methods in GHG emissions accounting by comparing three methods for calculation of the GHG emissions from steel production in China based on GHG emission factors for China and various expressions of energy consumption data (e.g., consumption of fuel or electricity, embodied energy consumed in the intermediate steel manufacturing process, comprehensive energy consumption). In this study, the first method follows the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories (IPCC, 2006). The GHG emission factors and the energy consumption data from existing steel plants in China are applied to the IPCC method. The second method is the localization of the Ecoinvent database. In this method, the GHG emissions of each individual sub-process of steel production related to energy are calculated based on the embodied energy GHG emission factors for each type of energy used (i.e., coal, coke, electricity, and natural gas). In the third method, the GHG emissions of steel production in China are calculated in reference to comprehensive energy consumption (CEC), the percentage distribution of primary energy used for steel production in China, and the GHG emission factors for stationary combustion for each type of GHG. The results of GHG emissions, data inputs and sources, differences, benefits, and limitations of each method will be discussed. 2. Methodology 2.1. Modeling scope of study and description of steel manufacturing process in China In this study, the system boundary is “Gate-to-Gate”, which covers the manufacturing process from raw materials (factory-entry gate) to the final product (factory-exit gate). The most important assumption in an application of the life cycle inventory localization (LCIL method) is that Mainland China should have similar steel manufacturing processes as described in the life cycle inventory used in this study. Therefore, the typical steel manufacturing process in Mainland China needs to be identified. A typical steel manufacturing process in the Mainland China consists of a blast furnace (BF) process, a basic oxygen furnace (BOF) process and an electric arc furnace (EAF) process. Fig. 1 shows the process flow diagram of steel production in China. Firstly, the raw materials (e.g., iron ore, coal, coke and limestone) are fed into the BF, followed by air injection to the furnace through the openings at the bottom of the shaft above the hearth crucible. With the presence of air, the coke burns along with the injected fuels, such as tar or light oil, to produce the necessary heat and generate reducing gas to remove oxygen from the ore in the reduction process. After the BF process, a portion of the pig iron is sent to the BOF. High purity oxygen is blown through the molten bath of iron in the BOF to reduce the concentration of carbon, silicon, manganese, and phosphorous in pig iron, while various fluxes (i.e., burnt lime or dolomite) are used to reduce the levels of sulfur and phosphorous. The remaining pig iron is sent to the EAF which relies on recycled steel scrap as raw material. Recycled steel scrap is melted and refined using electrical energy imparted to the charge through carbon electrodes and then alloyed to produce the desired grade of steel. In this study, the total GHG emissions are divided into two parts: (1) energy related GHG emissions, which consist of the GHG emissions from the fuel combustion and electricity consumption; (2) non-energy related GHG emissions, which mainly encompass the chemical reactions during the steel production process. The results of the GHG emissions are expressed in terms of carbon dioxide equivalent (CO2-e), with global warming potential (GWP) values over a 100-year time horizon (IPCC, 2007). The GHG
Fig. 1. Process flow diagram of steel production in China.
emission factors used in this study are obtained from the GHG Protocol Tool for Energy Consumption in China in 2011 (WRI, 2013). The GWP values of CO2, CH4 from fossil sources, and N2O are 1, 25, and 298, respectively (IPCC, 2007). The descriptions of the methodological approach and equations used for each method are explained in Section 2.2, 2.3, and 2.4. 2.2. Calculation of GHG emissions using the Intergovernmental Panel on Climate Change guidelines for national greenhouse gas inventories (IPCC method) The GHG emissions from each type of energy are calculated using the Tier 2 method IPCC, with a multiplicative product of the
R. Jing et al. / Journal of Cleaner Production 83 (2014) 165e172
energy consumption and the GHG emission factors for China (IPCC, 2006). Equations (1)e(3) illustrate how the GHG emissions of fuel and electricity are calculated based on the energy consumption and GHG emission factors (WRI, 2013). The total GHG emissions are calculated based on the total energy related GHG emissions and the ratio of energy related CO2 emissions to the total CO2 emissions of the steel industry in China (Shangguan et al., 2010). The total GHG emissions are shown in Equation (4):
ECO2 ¼
4 X Qi EFi;CO2 Qsteel
(1)
i¼1
ECH4 ¼
4 X
Qi EFi;CH4
Qsteel
(2)
database). The Ecoinvent database was applied to this method and the high qualities of the LCI data are based on industrial data and have been compiled by the Swiss Center for Life Cycle Inventories (Frischknecht and Rebitzer, 2005). In this method, the Ecoinvent database v2.1 is localized based on a major assumption that the steel production process in China is similar to that in European countries (Wen et al., 2014; Classen et al., 2009). The major steel manufacturing processes (Pelletizing process, sintering process, blast furnace process, basic oxygen furnace process, electric arc furnace process) in Europe and China are similar, which are highlighted by red lines in Figure B.4, Figure B.5 and Figure B.6. The energy related GHG emissions of each individual subprocess of steel production are calculated based on Equations (5)e(7).
i¼1
Eh;CO2 ¼ EN2 O ¼
4 X
Qi EFi;N2 O
167
4 X
0 Qi;h EFi;CO2
(5)
i¼1
Qsteel
(3)
i¼1
Etotal ¼ ECO2 R1 GWPCO2 þ ECH4 GWPCH4 þ EN2 O GWPN2 O (4) where i (i ¼ 1, 2, 3, 4) denotes the types of energy used, i.e., coal, coke, electricity and natural gas; ECO2 , ECH4 , and EN2 O are the energy related emissions of CO2, CH4, and N2O (kg/kg steel); Qi is the consumption of energy i (kg for fuel or kWh for electricity); EFi, CO2, EFi,CH4, and EFi, N2O are the emission factors of CO2, CH4 and N2O for energy i which are summarized in Table A.1 in supplementary data (kg GHG/kg fuel or kg GHG/kWh); Qsteel is the amount of steel produced (kg); GWPCO2 , GWPCH4 , and GWPN2 O are the global warming potentials for CO2, CH4, and N2O; R1 is the ratio of energy related CO2 emissions to the total CO2 emissions from steel production in China, i.e., R1 ¼ 98.26% (Shangguan et al., 2010). The questionnaire was sent to one of the top three steel manufacturers in Mainland China, which produced more than 40 million tonnes steel in 2012 (WSA, 2013c). The questionnaire was mainly targeted at the energy consumption of the steel manufacturing process and it has been attached to the supplementary data (Appendix C). The plant-specific data of raw materials consumption, intermediate products' production and final products production are shown in Table A.3. The plant-specific data of energy consumption are shown in Table A.4. The energy consumption data collected from the questionnaire were comparable to the energy consumption data from the company's annual report in 2012. In addition, representative of plant-specific data for the IPCC method have been verified. For the CEC method, the 42 steel manufacturers account for 57.4% of the production of the Chinese steel industry in this study. The average CEC value of the 42 Chinese steel manufacturers (standard deviation: 0.073) is 0.618 kg coal equivalent/kg steel. Meanwhile, the CEC value re-calculated based on the plant-specific data is 0.559 kg coal equivalent/kg steel. The results indicate that the re-calculated CEC value based on the plant-specific data is comparable to the average CEC value of the 42 Chinese steel manufacturers. Therefore, data from the steel manufacturers in Mainland China obtained via the questionnaire in the IPCC method are representative of the entire Chinese steel manufacturing industry. 2.3. Calculation of GHG emissions using the life cycle inventory localization (LCIL method)
Eh;CH4 ¼
4 X
0 Qi;h EFi;CH4
(6)
i¼1
Eh;N2 O ¼
4 X
0 Qi;h EFi;N2 O
(7)
i¼1
where h (h ¼ 1, 2, 3, 4, 5) denotes the intermediate product of sintering, pelletizing, BF, BOF and EAF; i (i ¼ 1, 2, 3, 4) denotes the types of energy used (i.e., coal, coke, electricity and natural gas) for individual sub-process of steel production; Eh;CO2 , Eh;CH4 , and Eh;N2 O are the energy related emissions of CO2, CH4, and N2O for process h, 0 respectively (kg/kg intermediate product); Qi;h is the embodied energy consumed in the intermediate steel manufacturing process h (kg fuel/kg intermediate product or kWh/kg intermediate prod1 uct); EFi;CO EF1i;CH4 , and EF1i;N2 O are the GHG emission factors for 2 China for each type of energy i which are summarized in Table A.1 in supplementary data (kg GHG/kg fuel or kg GHG/kWh). The unit of each individual sub-process of steel production is converted to kg CO2-e/kg steel on the basis of the intermediate product to the steel produced. According to the Ecoinvent life cycle inventories report (Classen et al., 2009), 1.05 kg of sinter and 0.4 kg of pellets are needed to produce 1 kg of pig iron. The ratio of pig iron production to crude steel production is 0.9. Therefore, the mass ratio of sinter, pellet, pig iron, liquid steel produced from BOF, and liquid steel produced from EAF to steel are 0.945, 0.36, 0.9, 1, and 1, respectively. According to the data of Ecoinvent database, the percentage of energy related CO2 emissions to the total CO2 emissions of the steel industry is 99.99% (Classen et al., 2009). The total GHG emissions of the steel manufacturing process for each sub-process are calculated using Equations (8)e(10), and the total GHG emissions of steel production are calculated using Equation (11).
ECO2 ¼
5 X
Kh Eh;CO2
(8)
h¼1
ECH4 ¼
5 X Kh Eh;CH4
(9)
h¼1
EN2 O ¼
5 X Kh Eh;N2 O
(10)
h¼1
The LCIL method evaluates the GHG emission based on the embodied energy of the individual sub-process of steel production provided in the existing life cycle inventory (i.e., Ecoinvent
Etotal ¼ ECO2 GWPCO2 R2 þ ECH4 GWPCH4 þ EN2 O GWPN2 O (11)
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where h (h ¼ 1, 2, 3, 4, 5) denotes the intermediate product of sintering, pelletizing, BF, BOF and EAF; Kh is the mass ratio of intermediate product of each process h to steel (e.g., 0.945 kg sinter/ kg steel); Eh,CO2, Eh,CH4, and Eh,N2O are the energy related emissions of CO2, CH4, and N2O for process h, respectively (kg/kg intermediate product); ECO2 , ECH4 , and EN2 O stand for the total CO2, CH4, and N2O emissions of steel production (kg/kg steel); R2 is the ratio of energy related CO2 emissions to the total CO2 emissions of steel production obtained from Ecoinvent database, i.e., R2 ¼ 99.99% (Classen et al., 2009); Etotal is the total GHG emissions of steel production (kg); GWPCO2 , GWPCH4 , and GWPN2 O are the global warming potentials for CO2, CH4, and N2O. The GHG emissions related to energy can be corrected by the ratio of the intermediate steel product to the final steel produced. The total GHG emissions are derived using the percentage of energy related CO2 emissions to the total CO2 emissions of the steel industry obtained from the Ecoinvent database. 2.4. Calculation of GHG emissions using the comprehensive energy consumption (CEC method) 2.4.1. Definition of comprehensive energy consumption Comprehensive energy consumption (CEC) is defined as the sum of all the physical energy consumed by the energy consumption unit within the production process. The measurement system boundary of the comprehensive energy consumption is the total energy used by an enterprise's main production system, auxiliary production system and subsidiary production system within the production process (AQSIQ, 2008). The unit used for the calculation of the comprehensive energy consumption converted to primary energy is called the standard coal equivalent (as shown in Equation (12)).
CEC ¼
4 X ðei pi Þ=Qsteel
(12)
i¼1
where i (i ¼ 1, 2, 3, 4) denotes the types of energy used (i.e., coal, coke, electricity, and natural gas) for calculation of the comprehensive energy consumption; ei refers to the amount of energy i consumed during steel production (kg); pi stands for the conversion factor for each energy i used (kg coal equivalent/kg energy), which is summarized in Table A.2 in supplementary data; Qsteel is the quantity of total steel produced (kg). 2.4.2. Calculation of GHG emissions of steel production in China using the CEC method In this study, the CEC method utilizes the comprehensive energy consumption of 42 steel producers in China. The 42 steel manufacturers account for 57.4% (China's Steel Prices, 2012) of the production of the Chinese steel industry (203 steel manufacturers). The comprehensive energy consumption is calculated based on the general principles defined in GB/T 2589-2008. Out of 203 steel manufacturers in China, the comprehensive energy consumptions of 42 manufacturers were obtained from annual reports, company websites, and literature reviews. Figure B.2 shows the comprehensive energy consumption in kg coal equivalent/kg steel in 42 steel manufacturers. In order to calculate the GHG emissions, the energy sources of each company are calculated in regard to the comprehensive energy consumption, the percentage distribution of primary energy used by the steel producers in China, and the energy conversion factors of each type of energy. Four primary energy sources, which are coal, coke, electricity, and natural gas, with mix percentages of 49.9%, 41.5%, 6.67%, and 0.45%, contribute to the energy consumption distribution of steel production in China (LBNL, 2011). In addition, the energy conversion factors of each
energy source, provided by the Chinese National Statistics Bureau (AQSIQ, 2008), are shown in Table A.2. Equation (13) shows the calculation of the primary energy consumed by each steel company in China.
AFi ¼ CEC ki =pi
(13)
where i stands for the type of energy used (i.e., coal, coke, electricity, and natural gas); AFi stands for the consumption of energy i calculated based on comprehensive energy consumption of steel production (kg energy used/kg steel); ki is the percentage of energy i that contributes to the distribution of energy consumption for steel production in China; CEC is the comprehensive energy consumption for steel production (kg coal equivalent/kg steel); pi is the conversion factor of the coal equivalent for each type of energy i used (kg coal equivalent/kg energy used). Equation (14) shows that the total GHG emissions for 1 kg steel production can be calculated based on the energy consumption, the GHG emission factors (EFi;CO2 , EFi;CH4 , and EFi;N2 O ) and the ratio of energy related CO2 to total GHG emissions (R3).
Etotal ¼
4 X AFi EFi;CH4 GWPCO2 R3 i¼1
þ
4 X AFi EFi;CH4 GWPCH4
(14)
i¼1
þ
4 X AFi EFi;N2 O GWPN2 O i¼1
where i (i ¼ 1, 2, 3, 4) denotes the type of energy (i.e., coal, coke, electricity, and natural gas); AFi stands for the consumption of energy i calculated based on the comprehensive energy consumption in steel production (kg energy used/kg steel); EFi;CO2 , EFi;CH4 , and EFi;N2 O are the GHG emission factors for energy i (kg GHG/kg fuel or kg GHG/kWh); R3 stands for the ratio of energy related CO2 emission to the total CO2 emission, i.e., R3 ¼ 98.26%; (Shangguan et al., 2010); GWPCO2 , GWPCH4 , and GWPN2 O are the global warming potentials for CO2, CH4, and N2O. 3. Results and discussion 3.1. The results of GHG emissions calculated using the IPCC, LCIL, and CEC methods As shown in Table 1, the total GHG emissions from the steel production plant in China calculated using the IPCC method are 1.717 kg CO2-e/kg steel, with an amount of 1.687 kg CO2-e/kg steel for total energy related GHG emissions. Among the four types of energy, the combustion of coke and coal account for the highest GHG emissions in the steel production, in which the combustion of coke and coal generate 0.785 kg CO2-e/kg steel (46.6%) and 0.735 kg CO2-e/kg steel (43.6%) of the total energy related GHG emissions, respectively. For the LCIL method, the total energy related and total GHG emissions are 1.7150 and 1.7152 CO2-e/kg steel, respectively. Figure B.3 shows that the energy related GHG emissions are mainly contributed by coke combustion (59.3%), followed by coal combustion (24.2%). This is mainly attributed to the fact that coke and coal are highly consumed during the production of pig iron in the BF process, rendering a high GHG release during the combustion of coke and coal. As shown in Table 2, the combustion of coke in the BF process generates 0.884 kg CO2-e/kg steel, in which it accounts for 51.4% of the total energy related GHG emissions. The results of GHG emissions calculated using the CEC method are shown in Table 3. The total energy related and total GHG
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Table 1 Results of GHG emissions using the IPCC method (Tier 2). Types of energy
Quantitya (million tonnes/year)
Coal 16.2 Coke 12.0 Electricity 7.01 Natural gas 0.38 Total energy related GHG emissions Total GHG emissionsd a b c d
CO2 emission factorb (kg CO2/kg fuel or kg CO2/kwh)
CH4 emission factorb (kg CH4/kg fuel or kg CH4/kwh)
N2O emission factorb (kg N2O/kg fuel or kg N2O/kwh)
Energy related GHG emissionsc (kg CO2-e/kg steel)
Percentage of total energy related GHG emissions (%)
1.981 2.860 0.873 3.088
0.00021 0.00028 0.00001 0.00019
0.000031 0.000043 0.000013 0.000004
0.735 0.785 0.140 0.027 1.687 1.717
43.6 46.6 8.29 1.60
Based on the plant specific data provided by one of the biggest steel manufacturers in China. Obtained from GHG Protocol Tool for Energy Consumption in China in 2011 (WRI, 2013). Calculated based on the results of Equations (1)e(3) and global warming potentials. The steel production is 44 million tonnes in 2012. Calculated based on Equation (4).
emissions of 42 steel manufacturers in China are 1.925 and 1.959 CO2-e/kg steel, respectively. According to Table 3, it can be seen that coal combustion is the largest contributor of total energy related GHG emissions (44.9%) compared to other types of energy. The percentage contribution by coal in the CEC method is higher than that in the IPCC and LCIL methods. The reason is that coal is the largest primary energy used (44.9%) compared to the other energy sources for 42 steel manufacturers. Therefore, coal combustion contributes a large amount of GHG emissions. As shown in Fig. 2, the total GHG emissions of 42 steel manufacturers in China range from 2.27 to 1.05 kg CO2-e/kg steel and the average and variance are 1.96 kg CO2-e/kg steel and 0.053, respectively. It is also worth noting that most of the steel manufacturers in China emit GHG in a range of 1.80e2.00 kg CO2-e/kg steel, in which 16 out of the 42 steel manufacturers in China are within this level (as shown in the histogram diagram in Figure B.1). It is found that the average GHG emissions of the 42 steel manufacturers in China, calculated using the CEC method (i.e., 1.959 kg CO2-e/kg steel), is relatively higher than that of the IPCC
(i.e., 1.717 kg CO2-e/kg steel) and the LCIL methods (i.e., 1.715 kg CO2-e/kg steel). However, the variance of the total GHG emissions in these three methods is 0.019, which is relatively smaller than the variance of the total GHG emissions of the 42 steel manufacturers in China, as abovementioned (i.e., 0.053). On the other hand, it should be highlighted that the non-energy related GHG emissions are insignificant compared to the total energy related GHG emissions. The non-energy related GHG emissions of the IPCC, LCIL and CEC methods are 0.030, 0.002 and 0.034 kg CO2-e/kg steel, respectively. These findings are in line with the results reported by Zhang et al. (2012), in which fossil fuel combustion and electricity consumption are the two major categories of CO2 emissions in a steel production plant. 3.2. Comparison of data input and sources of the IPCC, LCIL, and CEC methods Different sets of data are required for each method in order to account for the GHG emissions from steel production in China. The
Table 2 Results of GHG emissions using the LCIL method (based on the Ecoinvent database). Process
Sintering
Types of energya
Coke Electricity Natural gas Pelletizing Coal Electricity Natural gas Blast furnace process Coal Coke Electricity Natural gas Basic oxygen furnace process Coke Electricity Natural gas Electric arc furnace process Coal Electricity Natural gas Total energy related GHG emissions Total GHG emissionsc
a b c d e f g h
Energy consumptiona (kg fuel/kg intermediate product or kWh/kg intermediate product)
Mass ratio (kg intermediate product/kg steel)
Energy related GHG emissionsb (kg CO2-e/kg steel)
Percentage of total energy related GHG emissions (%)
0.050 0.010 0.0000653d 0.013 0.025 0.001e 0.210 0.340 0.100 0.002f 0.00000874 0.022 0.000674g 0.014 0.120 0.018h
0.945 0.945 0.945 0.360 0.360 0.360 0.900 0.900 0.900 0.900 1.000 1.000 1.000 1.000 1.000 1.000
0.136 0.008 0.000190 0.009 0.008 0.001 0.377 0.881 0.079 0.006 0.0000251 0.019 0.0021 0.028 0.105 0.054 1.715 1.715
7.93 0.48 0.01 0.54 0.46 0.08 22.0 51.4 4.61 0.35 0.00 1.12 0.12 1.63 6.14 3.16
Obtained from the Ecoinvent Life Cycle Inventories of Metals Data v2.1 (Classen et al., 2009). Calculated by Equations (5)e(7). The results are converted by multiplying the mass ratio of each intermediate product to steel produced. Calculated by Equations (8)e(11). Calculated with 0.00363 MJ/kg sinter multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas. Calculated with 0.069 MJ/kg pellet multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas. Calculated with 0.12 MJ/kg pig iron multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas. Calculated with 0.0375 MJ/kg steel multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas. Calculated with 0.975 MJ/kg steel multiplied by 0.7 kg/m3 natural gas and divided by 38.931 MJ/m3 natural gas.
Percentage of total energy related GHG emissions of each individual process (%) 8.42
1.08
78.4
1.24
10.9
170
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Table 3 Results of GHG emissions using the CEC method (based on 42 steel companies in China). Types of energy
CO2a (kg CO2/kg steel)
CH4a (kg CH4/kg steel)
N2Oa (kg N2O/kg steel)
Energy related GHG emissions (kg CO2-e/kg steel)
Total GHG emissions (kg CO2-e/kg steel)
Percentage of total energy related GHG emissions (%)
Coal Coke Electricity Natural gas Average GHG emissions of 42 steel manufacturersb Average GHG emissions of 17 steel manufacturersc Average GHG emissions of 25 steel manufacturersd
0.857 0.756 0.293 0.005 1.912
0.000090 0.000075 0.000003 0.0000003 0.00017
0.00001 0.00001 0.000004 0.00000001 0.00003
0.864 0.762 0.295 0.005 1.925
0.879 0.775 0.300 0.0051 1.959
44.9 39.6 15.3 0.26
1.929
0.00017
0.00003
1.942
1.976
1.900
0.00017
0.00003
1.913
1.947
a b c d
Calculated based on the Equation (13) and the GHG emission factors (refer to Table A.1). Calculated based on Equation (13). The production process includes BF, BOF, and EAF processes. The production process includes BF and BOF processes only.
data input are collected from different sources by different approaches. In this study, the energy consumption data of the IPCC method are collected from one of the major steel manufacturers in China by questionnaire survey. The data could represent the most recent energy utilization levels and technologies used by the steel manufacturers in China based on year 2012 as the data provided by one of the biggest steel manufacturers. This steel manufacturer utilizes a number of energy efficient technologies such as efficient power generation, low energy intensive furnaces, and reuse of residual heat; therefore, the GHG emissions are potentially lower. For the LCIL method, the steel production processes in the Ecoinvent database mainly relies on the production and supply situation in Europe in 2000 (Frischknecht and Rebitzer, 2005). One of the caveats when applying the LCIL method is that the manufacturing processes and technologies in the studied countries/regions should be similar to the manufacturing process in life cycle inventory as described in the Ecoinvent. This study assumes that the manufacturing processes and technologies for steel production in Europe and China are similar. Based on this assumption, the data for embodied energy of individual sub-process of steel production from the Ecoinvent database can be applied in the LCIL method. However, for certain countries such as Thailand, the LCIL
method might not be suitable to be applied, due to the fact that the steel production process in Thailand is dramatically different from countries in Europe (Sodsaia and Rachdawong, 2012). For the CEC method, the major data sources for comprehensive energy consumption are based on the annual reports, company websites, statistical yearbooks of steel manufacturers in China, and literature. The production technology levels for the 42 manufacturers are covered from 2000 to 2011. As elucidated in Section 2.4.1, comprehensive energy consumption, which calculated by using GB/ T 2589-2008, is used to reflect the energy consumption among the steel production processes of 42 steel manufacturers in China. However, it should be pointed out that due to the lack of detailed information concerning the steel manufacturing processes in some steel manufacturers in China, it might affect the data quality of the comprehensive energy consumption and comparability among the 42 steel manufacturers. For example, some steel manufacturers in China purchase intermediate products such as sinter or coke instead of producing these intermediate products by their own companies. In these circumstances, the comprehensive energy consumption and the total GHG emissions from these steel manufacturers could be smaller than that the average level of the 42 steel manufacturers in China.
2.5
Total GHG emissions kg CO2-e/ kg steel
2.0
1.5
1.0
0.5
0.0 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
Steel manufacturers in China Fig. 2. Total GHG emissions of 42 steel manufacturers in China determined from the CEC method.
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Table 4 Comparison of the IPCC, LCIL, and CEC methods in this study. IPCC method
LCIL method
CEC method
1.687
1.715
1.925
0.030
0.002
0.034
1.717 One of the biggest steel manufacturers in China
1.715 Eco-invent database v2.1
Method analysis Data inputs
Energy input-based Energy consumption of plant-specific data
Process-based Embodied energy of individual subprocess Mass ratio of intermediate product of each process to steel
Differences
GHG emissions were estimated based on the real activity data (e.g., coal consumption collected from the questionnaire) Based on different data quality, threetier methods can be used to estimate GHG emissions More time and efforts are needed to collect the first hand data
GHG emissions were estimated based on the statistical data analysis
1.959 Company's annual report Published literature review Chinese statistical yearbook Energy input-based Energy consumption in terms of coal equivalent The percentage of each type of energy that contributes to the distribution of energy consumption for steel production in China GHG emissions were estimated based on statistical data analysis
Energy-related GHG emissions (kg CO2e/kg steel) Non-energy-related GHG emissions (kg CO2-e/kg steel) Total GHG emissions (kg CO2-e/kg steel) Data sources
Advantages
Disadvantages
Benefits
Internationally recognized
Limitations
The results calculated using this method can be improved by applying the IPCC Tier 3
3.3. Comparison of the IPCC, LCIL, and CEC methods based on energy input-based and process-based analysis The IPCC and CEC methods are categorized as energy inputbased analyses. The results of these two methods are calculated by collecting the energy consumption data for the overall steel manufacturing processes. The results provide a valuable reference source for steel manufacturers in China regarding the GHG emissions levels. However, the uncertainty in the collection of energy consumption data could make its results less reliable compared to the LCIL method. Therefore, it requires verification and validation of the energy input in the manufacturing processes to enhance the accuracy and reliability of input data. The LCIL method is a process-based analysis which evaluates the inputs (e.g., embodied energy consumed in the intermediate steel manufacturing process) and the outputs (e.g., GHG emissions to the environment) for each and every process in steel production. By using this method, stakeholders can identify the major subprocesses that contribute to the highest GHG emissions in steel production within the studied system boundary. For example, the results of this study show that the blast furnace process contributes the highest GHG emissions, in which it accounts for 78.4% of the total energy related GHG emissions. Appropriate design and operating improvements, such as efficient power generation, low energy intensive furnaces, and reuse of residual heat, can be applied to the blast furnace processes to reduce the GHG emissions. 3.4. Benefits and limitations of the IPCC, LCIL, and CEC methods Among the three methods used in this study, the IPCC method is the most widely accepted approach for the calculation of GHG emissions in steel production. This method combines activity data with GHG emission factors for China (e.g., kg CO2/kg fuel) which quantify the emissions or removals per unit activity. Tier 2 IPCC
More optional databases can be used for this method (e.g., Chinese Life Cycle Database) Many calculations can be involved when the LCIL method is applied to estimate GHG emissions GHG emissions of individual subprocess can be calculated
Production processes of the countries/ regions should be similar to those in Europe
GHG emissions can be estimated simply based on coal equivalent The system boundaries of energy consumption data of each steel manufacturer are different GHG emissions can be easily calculated on the basis of the distribution of primary energy used for steel production in China CEC value is only developed by steel manufacturers in China
method is used in this study through the application of GHG emission factors of the fuel combustion and electricity consumption for China. The data quality of the results of the GHG emissions could be improved if Tier 3 IPCC method is applied in this study. Nevertheless, more time and efforts would be required during the data collection process as more local specific data are necessary for the calculation of GHG emissions in Tier 3 IPCC method. One of the benefits of the LCIL method is that it provides the GHG emissions from each individual sub-process of steel production, in which the IPCC method and the CEC method could only provide the total GHG emissions within the studied system boundary. However, the LCIL method can be applied only in the situation when the steel manufacturing process of a region is similar to the process as described in Ecoinvent life cycle inventory. Another limitation of applying the LCIL method is that the results of GHG emissions of individual sub-process may change if the energy contents of fuels are different. For example, according to the GHG Protocol Tool for Energy Consumption in China, burning one tonne of Chinese and European coke produce 28,435 and 28,600 MJ of energy, respectively (WRI, 2011; WRI, 2013). Compared to the IPCC and LCIL methods, the benefits of using the CEC method is that the GHG emissions can be simply calculated by multiplying the CEC value with the percentage distribution of primary energy used for steel production in China. However, as far as the authors know, the CEC is mainly developed by the steel manufacturers in China but not in other countries. Therefore, the steel manufacturers in other countries are required to calculate their own the CEC value in order to apply the CEC method for GHG accounting in steel production. It should be noted that the percentage distribution of primary energy used for steel production in China may change over time and it can alter the results of GHG emissions. The Chinese Central Government has set carbon reduction policies to curtail GHG emissions, culminating in a pledge under the 2009 Copenhagen
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accord to achieve a 40e45% reduction in its carbon intensity by 2020 (CRS, 2011). China has taken strong effort to reduce carbon intensity and has enacted progressive policies to promote nuclear energy (Best and Levina, 2012). Therefore, cleaner energy source such as nuclear energy may be applied to steel industry in China to reduce the GHG emissions. A summary of comparison of the IPCC, LCIL, and CEC methods is shown in Table 4. 4. Conclusions This paper presents three accounting methods for the calculation of GHG emissions from steel production in China. On the basis of the data collected and the system boundary defined, the total GHG emissions of these three methods are 1.72, 1.72 and 1.96 kg CO2-e/kg steel, respectively. The IPCC method is based on energy input-based analysis. The GHG emissions were calculated based on the overall energy consumption data collected from one of the top three steel manufacturers in Mainland China. By knowing the various energy contributions to GHG emissions, potential alternatives for energy saving in this industry can be recommended to stakeholders, thereby enabling GHG mitigation. However, it should be noted that the IPCC method is recommended to be used for plant specific GHG emission estimation because the GHG emitted can be widely varied depending on the fuel combustion conditions and facilities operation conditions. The LCIL method is highly recommended to be used, when stakeholders want to calculate the GHG emissions for each individual sub-process in steel production or identify the hotspot areas of GHG emissions so as to facilitate system and process improvement for GHG mitigation. The LCIL method is a process-based analysis which is especially useful for assessing the GHG emissions from steel production based on the generic data without much first-hand data. However, the LCIL method is restricted to being used in regions that have similar major steel manufacturing processes as described in the life cycle inventory, because the embodied energy of each manufacturing process depends on the energy type and operational system boundary. Otherwise, the embodied energy of the manufacturing process used in GHG emissions estimation might not reflect the actual status. The CEC method obtains the comprehensive energy consumption per unit for producing one unit of steel, and the reference unit is kg coal equivalent/kg steel. The CEC value of each steel manufacturer is the total energy used by the steel manufacturer's main production system, auxiliary production system and subsidiary production system. The benefit of applying the CEC method is that GHG emissions can be estimated simply based on a wider range of statistical CEC values (i.e., coal equivalent) and the distribution of primary energy for steel production in China. However, it should be emphasized that the CEC method is mainly proposed for the steel manufacturers in China but is not commonly used in other countries or regions. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jclepro.2014.07.016.
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