Representativeness of CO2 emissions and energy consumption of steel in construction in Brazil

Transcription

1 Representativeness of CO2 emissions and energy consumption of steel in construction in Brazil Bruna V. da Silva (1), Vanderley M. John (2), Sergio A. Pacca (1) (1) PPGE Programa de Pós Graduação em Energia, USP, Brasil (2) EP Escola Politécnica, USP, Brasil Bruna V. da Silva, Vanderley M. John and Sergio A. Pacca Abstract Steel is a crucial input to construction, and its supply chain is responsible for considerable CO 2 emissions and primary energy consumption. However, the production processes of steel mills vary, depending on the technology and the primary energy source used. Such differences affect the emission factor and the embodied energy content of steel used in construction activities. This work evaluates the effect of steel made in Brazil on CO 2 and primary energy intensities. Results show that emissions and energy consumption due to steel consumption significantly contribute to the environmental burden of construction activities. Accordingly, in Brazil the use of steel production technologies that are based on electricity consumption favors the mitigation of CO 2 emissions and primary energy reduction. Among the steel production technologies employed in Brazil the CO 2 emission factor of a specific company is 37% lower than the Brazilian average industry. In terms of embodied energy, the specific energy values are 87% smaller than values of the Brazilian average industry. The choice of appropriate steel reinforcing bar supplier is fundamental to mitigate CO 2 emissions of the Brazilian construction sector. 1. INTRODUCTION The current market share of the construction sector, which is already considerable, is expected to increase over the next years [1]. Currently, the sector is responsible for 24% of the global raw materials consumption. In addition, energy consumption along the construction supply chain, which encloses manufacturing, construction, and installation of materials, such as steel, concrete, and glass, stands out [2]. In 2010, per capita crude steel consumption in Brazil was 152 kg/habitant and the construction sector was the largest consumer, followed by automotive, capital goods, machinery and equipment (including agricultural) industries, household, and commercial sectors [3]. In 2007, only 5 companies were responsible for 93% of the domestic steel production. This group comprises Arcelormittal Brasil, Companhia Siderurgica Nacional, Companhia Siderurgica de Tubarão, Gerdau, and Usiminas/Cosipa [4]. 240

2 According to Bribián et al 2010, the contribution of steel manufacturing to the primary energy demanded to build 1 m 2 of building floor area is 26%. In comparison to other energy intensive materials, steel is responsible for the largest contribution. Ceramics and cement are responsible for 22% and 11% respectively. However, the contribution of steel to total emissions of 1 m 2 building floor area is 18.7% whereas the contribution of cement and ceramics are respectively 30 and 20 %. According to Gerdau [5], iron reduction (reaction 1), which takes place in integrated steel mills is responsible for part of the emissions. Thus, independently of the fuel used, CO 2 is released. Besides that, this process takes place in the blast furnace, which usually is powered by coke or charcoal, which are carbon intensive fuels that release CO 2. 1Fe 2 O 3 + 3CO 2Fe + 3CO 2 (1) In contrast, non integrated steel mills are not equipped with blast furnaces because they usually process scrap metal, which is mixed to lime, pig iron, sponge iron, and fed in an electric arc furnace [5]. The use of such type of mills in Brazil contributes to the mitigation of carbon emissions because it usually skips the iron reduction step, and the domestic electricity mix is based on hydropower. In fact, 85% of the electricity consumed in Brazil is generated by hydropower plants, considering the imported energy from Itaipu dam [6]. According to the Energy Research Company (EPE) the energy intensity of the blast furnace process in 2007 was 18 GJ/t, on the other hand, the energy intensity of the electric arc route, which consumes iron scrap in the process, was 4,3 GJ/t [4]. According to IEA [7], average CO 2 emissions in steel production in Brazil is between 1,41 and 1,66 tco 2 /t. This variation is explained by the high share of pig iron to steel production, that raises the emission factor. The low CO 2 emission factor of the Brazilian electricity, and the use of charcoal are responsible for the low emission factor of the steel industry. Considering IEA 2007 data [7], the average energy intensity of steel is 20,2 GJ/tonne. On the other hand, Worrel et al 2007 [16] indicate that the total primary energy based on hot rolling-steel bars is 8 GJ, out of which 5,5 GJ refers to steelmaking, 0,1 to casting and 2,4 to hot rolling. ArcelorMittal, is a large steel company that is present in various countries and detains 30% of the long steel Brazilian market, which is used in construction and other activities. Different forms of long steel are produced by ArcelorMittal: wires, railroad tracks, steel bars, and steel mesh [8]. The objective of this study is determining the contribution of steel to CO 2 emissions and primary energy consumption in the Brazilian construction sector. 2. METHODS 2.1 Determining CO2 emissions and primary energy content of the major fuel inputs in steel production When selecting CO 2 emission factors and embodied primary energy on a mass basis of different fuels it is important to distinguish between factors that consider only emissions from combustion and factors that consider emissions from combustion plus life cycle emissions due to resource extraction and fuel production. We were not able to identify life cycle emissions for some of the fuels used in steel production and we have considered only emissions from combustion. However, such 241

3 emissions are usually greater than the remainder life cycle emissions. In the case of diesel, gasoline and ethanol, life cycle emissions, excluding emissions from combustion, are responsible for 4.7%, 7.3%, and 0.88% respectively. The method employed in our calculations uses the National Energy Balance [6] as the major information source for the heat content and the fuel densities considered. Similarly, we use the Second National Greenhouse Gas Inventory [9] to calculate CO 2 emissions due to fuel combustion. Because information regarding life cycle emissions in Brazil is scarce, in the case of refinery products, we used information from other countries because the technology in place in Brazil is similar to the technology abroad. In summary, we believe that the accuracy of our analysis in this case is not jeopardized. Besides that, in the case of fuels for which national emission factors are not available, emission factors from the Intergovernmental Panel on Climate Change [10] were adopted. Determining fuel emission factors representing Brazilian conditions is a crucial step to calculate the overall emissions of steel production. Moreover, even fuels that are not directly used in steel production, such as ethanol and gasoline, might be relevant because they fuel transportation activities are also part of the supply chain. The functional unit for steel was 1 metric ton of nonspecific finished products, such as: reinforcing bars, heavy plates, strips, wire rods, railroad rails, and pipes. However different functional units were used in the calculation of fuel emission factors that were used in the assessment. In the case of gasoline and diesel, the functional unit was 1kg. In the case of other liquid fuels the functional unit was 1 liter. In the case of electricity the functional unit was 1kWh and in the case of solid fuels, the functional unit was 1 metric ton. Finally, the functional unit of natural gas was 1m Liquid fuels Gasoline and diesel Common gasoline, which is sold at the pumps in Brazil, contains 22% of ethanol and 78% of gasoline [11]. In order to determine emissions associated with gasoline consumption we need to account for life cycle emissions beginning with oil extraction up to the commercialization stage (well to pump) and include emissions from fuel combustion. The same approach is used to determine life cycle emissions of diesel. Although we have not found emission inventories for fuels produced in Brazil, we believe that the technology present in refineries throughout the world is similar. Therefore, we used life cycle emission inventories of gasoline and diesel fuel for the US market (table 1). Table 1: Life cycle emissions of gasoline and diesel (kg/kg). Adapted from EPA 2010 [12]. CO 2 CH 4 N 2 O CO 2eq gasoline diesel According to Macedo et al. [13], life cycle emissions of anhydrous ethanol, which is mixed to gasoline, are 0.55 kgco 2eq /kg. Thus, life cycle emissions of the common gasoline sold at the pump are 0.70 kgco 2eq /kg. 242

4 Table 2 presents CO 2 emissions due to combustion of fuels commercialized in Brazil [11]. Table 2: CO 2 emissions from combustion Combustível kg/kg gasoline 2.93 diesel 3,16 Finally, total gasoline and diesel emissions are respectively 3,72 e 3,9 kgco 2eq /kg. The same approach was used to find out the embodied energy per mass unit of fuels, consequently, we added life cycle energy inputs to the energy released during fuel combustion. Table 3 shows the life cycle energy of fuels. Table 3: Life cycle energy of fuels (adapted from [14]). Fuel kj/kg Diesel 2,074 Gasoline 3,404 In order to determine the energy released during combustion we relied on information from the Brazilian Energy Balance (BEN), which considers the low heating value as the specific energy of fuels. Table 4 presents the energy released during combustion of 1 kg of either diesel or gasoline. Table 4: Energy released during combustion of 1 kg of fuel [6]. Fuel PCI - kj/kg Diesel 42,287 Gasoline 43,543 Trough the tables 3 and 4 it is possible calculating the total embodied energy in diesel and gasoline that is respectively 31, kj/kg e 25, kj/kg Oil coke and fuel oil Although it is possible to calculate life cycle emissions and primary energy inputs for oil coke based on assessments of refineries abroad, we have decided to take into account only direct emissions and energy released during coke combustion. Emissions from coke combustion equal to 3.56 kg/l [10]. Whereas, according to [6], the heating value of coke is 36,567 kj/l. The same rationale and data sources were used to determine energy from fuel oil combustion and its emissions, which are respectively 40,151kJ/l and 3.11 kgco 2 /l. 2.3 Solid fuels Coal and charcoal According to the Second Greenhouse Gas National Inventory, 80% of the coal consumed by steel mills in Brazil in 2005 was imported [9]. The CO 2 emission factor was determined 243

5 based inventory data, by dividing the total fuel CO 2 emission by the total coal consumed in Brazil, based on 2005 data, the result obtained was 3.59 kgco 2 /t. According to the Brazilian Energy Balance [6], the primary energy associated with the combustion of 1 kg of fuel is 31kJ/t. The same rationale was used to determine the emission factor for charcoal and its energy content. According to [9], emissions from combustion and from production of this fuel equal to 2.83 kgco2/t. However, this result ignores the embodied carbon due to photosynthesis, and does not take into account the timber source. If the timber source is a native forest, CO 2 emissions might be worse. The primary energy, based on the low heating value from BEN 2010 is 27 kj/t. 2.4 Gaseous fuel Natural gas According to [6], the low heating value of natural gas is 36,844 kj/m 3(1). The emission factor was determined based on information from [9] using the ratio between the total emission associated with this fuel and its final consumption on an energy basis. Therefore, the emission factor is 2.27 kgco 2 /m Electricity According to [15], the electricity emission factor in 2010, based on the average of monthly values is kgco 2 /kwh, and the physical relationship (3,600 kj/kwh) was applied to determine the primary energy required to produce 1 kwh. This differs from electricity produced by thermal power plants, in which the primary energy corresponds to the secondary energy divided by the conversion efficiency. For that reason, the primary energy input of steel products from electric arc furnaces is lower than the primary energy input of products from blast furnaces. All emission factors and primary energy contents are used in the calculation of the steel emission factor and its primary energy content. 2.6 Steel emission factor calculation Based on the sustainability report of the steel company it was possible to obtain the list of the main energy sources that are used in steel production. Accordingly, based on inputs' mass it was possible to calculate the emission factor and the primary energy due to steel production. It is important to highlight that steel emission factors account for emissions due to energy consumption in steel mills, and ignore emissions and energy consumption during mining, and transportation. The average emission factor of a specific Brazilian steel company was 1, kgco 2 /t, whereas its primary energy consumption is MJ/t. Another calculation was based on data provided by [6], in which information on the main energy sources consumed by the steel industry is provided. In the next section, results are presented and discussed. Next, we present the methods used to find out life cycle emission factors and the embodied primary energy per mass unit of each fuel. 244

6 3. RESULTS AND DISCUSSION 3.1 Primary energy and CO2 emissions from steel production Analyzing the energy source mix used in steel production, it is possible to realize that ArcelorMittal's production process demands a distinct mix than the average mix of the Brazilian industry. Figure 1 compares the energy mix demanded by ArcelorMittal to the mix of the Brazilian industry. GJ/t Figure 1: Energy profile of 1 metric ton of ArcelorMitall steel versus steel based on the average Brazilian industry (based on [8] and [6]). Figure 1 shows that the studied company uses basically 2 energy sources, coal and electricity. On the other hand, the Brazilian industry generally relies on different sources, including several fossil fuels. Differences related to energy sources used in steel production affect its CO 2 emission factor. Figure 2 shows CO 2 emissions due to major energy inputs in steel manufacturing. kgco 2 /t Figure 2: CO 2 emissions associated with ArcelorMittal1s steel and average emissions of the Brazilian steel industry (Based on [8] and [6]). Coal remains a fundamental input in steel production and this fuel is a major carbon dioxide source in comparison to other inputs used by the industry. 245

7 In the case of the steel industry, emissions due to coal combustion are responsible for 97% of the total, whereas emissions due to electricity, which is responsible for 49% of the energy input in the production process, are negligible. However, BEN 2010 data [6] shows that CO 2 emissions are associated primarily with coal, and although electricity is also frequently employed by the Brazilian industry, its CO2 emission factor is small. There is a considerable difference between emission factors obtained based on data from a specific company (1,257 kgco 2 /t) and BEN 2010 data [6] (1,789 kgco 2 /t), which reflects the industry average. In addition, the specific primary energy consumption calculated for the specific steel company was 314 MJ/t, whereas the result obtained based on BEN 2010 data [6] was 2348 MJ/t. Finally, steel manufacturing technology choices impact both the CO 2 emission factor and the embodied energy of 1 metric ton of nonspecific finished steel products, which in the case of ArcelorMittal s technology were respectively 30% and 87% smaller in comparison to the average Brazilian steel industry technology. Therefore it is possible to considerably reduce emissions in the construction sector if we choose suppliers with a specific steel production technology. 4. CONCLUSIONS Based on previous studies steel is a major contributor to CO 2 emissions and primary energy consumption associated with construction in Brazil. In addition, CO 2 emissions from construction are small compared to indirect emissions associated with the supply chain of the industry. Emissions and energy consumption due to embodied steel in buildings are mitigated only if recycling, energy efficiency measures and fuel choices are implemented in the steel production process. The use of steel production technologies in Brazil that are based on recycling and electricity consumption favors the mitigation of CO 2 emissions and primary energy consumption REFERENCES [1] CHANG, Y.; RIES, J. R.; WANG, Y. The embodied energy and environmental emissions of construction projects in China: An economic input-output LCA model. Energy Policy, 38 (2010), , [2] Bribrián I. Z., Capilla A. V., Usón A. A., Life Cycle Assesment of building materials: Comparative analysis of energy and environmental impacts and evaluation of the eco-efficiency improvement potential. Building and Environment, 46 (2011) [3] Dados de Mercado. Disponível em: < Acesso em: 07 nov [4] EPE 2009 Caracterização do uso da Energia no Setor Siderúrgico Brasileiro; Rio de Janeiro. Empresa de Pesquisa Energética Ministério de Minas e Energia. [5] Processo de Produção do Aço. Disponível em: Acesso em 27 abr [6] MINISTÉRIO DE MINAS E ENERGIA. Balanço Energético Nacional Disponível em: < Acesso em 18 out [7] IEA 2007 Tracking Industrial Energy Efficiency and CO 2 Emissions; France. International Energy Agency. 246

8 [8] ArcelorMittal Brasil, Relatório de Sustentabilidade Disponível em: < /pdf/relatorio_sust_2009.pdf>. Acesso em: 27 jul [9] MINISTÉRIO DE CIÊNCIAS E TECNOLOGIA. Segundo Inventário Nacional de Gases do Efeito Estufa Disponível em:< Acesso em: 12 nov [10] IPCC 2006 Guidelines for National Greenhouse Gas Inventories; Volume 2, Energy. Disponível em: < Acesso em 30 set [11] CETESB 2010 Relatório de qualidade do ar no estado de São Paulo 2009 / CETESB. - - São Paulo: CETESB, p. : il. color. - - (Série Relatórios / CETESB, ISSN ) [12] EPA 2010 Renewable Fuel Standard Program (RFS2) Regulatory Impact Analysis Assessment and Standards Division; Office of Transportation and Air Quality; U.S. Environmental Protection Agency EPA-420-R ; February 2010 [13] Macedo, I.C., Seabra, J.E.A. & Silva, J.E.A.R., Green house gases emissions in the production and use of ethanol from sugarcane in Brazil: The 2005/2006 averages and a prediction for Biomass and Bioenergy, 32(7), pp [14] Wang, M; Lee, H; Moulburg, J. Allocation of Energy Use in Petroleum Refineries to Petroleum Products Implications for Life-Cycle Energy Use and Emission Inventory of Petroleum Transportation Fuels. LCA Case Studies, 9 (1), 34-44, [15] MINISTÉRIO DE CIÊNCIAS E TECNOLOGIA. Arquivos dos Fatores de emissão. Disponível em: < Acesso em: 05 out [16] Worrel, E; et al. World Best Practice Energy Intensity Values for Selected Industrial Sectors. Berkeley Lab, june