Life Cycle Inventory (LCI) analysis of structural steel members for the environmental impact assessment of steel buildings

Transcription

1 Chapter 5: Monitoring and evaluation Life Cycle Inventory (LCI) analysis of structural steel members for the environmental impact assessment of steel buildings I. Zygomalas, E. Efthymiou & C.C. Baniotopoulos Institute of Metal Structures, Department of Civil Engineering, Aristotle University of Thessaloniki, Greece ABSTRACT: Sustainable building can be achieved with the use of specific methodologies and tools that aim at optimizing the design stage of a building project according to the principles of sustainable development. One of the most widely acknowledged and used sustainability evaluation method is Life Cycle Assessment (LCA), which is based on the collection and management of environmental impact data most often drawn from available Life Cycle Inventory (LCI) databases. The present research forms the basis of a newly developed LCI database focusing on steel structures. Hot rolled structural steel members are used as a reference point in order to collect the required data, through contact with one of the leading steel producing companies in Greece and detailed literature research. Data is analyzed and categorized with regard to the stages of the manufacturing process for hot rolled steel sections, from raw material acquisition to the storage of products ready for use (cradle-to-gate) and then transferred to computer software for processing and results interpretation. The outcome is presented in this paper, both as an available tool within the scope of LCA studies regarding steel structures and also as a framework which can be applied within other geographic regions for similar purposes. 1 INTRODUCTION The evaluation of the sustainability of a building project can be conducted with the help of a number of tools that have been developed over the last few years. One of the most complete and detailed analysis methodologies, based on the concept of the life cycle, is Life Cycle Assessment (LCA). LCA considers the entire life cycle of a product or system, from raw material extraction, through material production and energy requirements, to use and end of life treatment (ISO, 2006). Through such a systematic overview, environmental burdens are identified and possibly avoided. LCA can assist in identifying opportunities to improve the environmental performance of building projects at various points in their life cycle. In order to conduct an LCA analysis, certain stages have to be executed, ranging from goal/scope definition and Life Cycle Inventory (LCI) to Life Cycle Impact Assessment (LCIA) and results interpretation. During the Life Cycle Inventory stage, a list of raw material requirements and environmental emissions is drawn that forms the basis on which the final impact is calculated. As this is a crucial issue with an immediate effect on the validity of the study, it is necessary to examine the data used in detail (Zygomalas et al, 2009). In most cases, it is not recommended to use already available data as found in existing databases, because of 655

2 Portugal SB10: Sustainable Building Affordable to All substantial differences in factors such as geographic range, technology level, time period etc. (Bragança et al, 2007). It is therefore necessary to create new, better suited LCI databases according to the particular properties of projects or -as a more tangible starting point- countries. The current research concerns the development of such a LCI database for Greece, with particular focus on steel structures, a widely acknowledged building technology with significant environmental sustainability potential. 1.1 Research Methodology Since there are two major categories of steel making processes, the first being the blast furnace route with requirements of raw material quantities and the second the electric arc furnace route that produces steel from used scrap, the initial part of the research focuses on allocating the LCI data requirements between the two routes. According to statistical data, the steel manufacturing companies in Greece produce steel with the electric arc furnace (EAF) route, based on the recycling of iron and steel scrap rather than the extraction of raw materials. For year 2006, the total annual production of steel in Greece was approximately thousand metric tones (World Steel Association, 2009), with all of the quantity being produced with the EAF route. Since the EAF route is the only steel manufacturing method used in Greece, it can be assumed that an LCI database based on its detailed examination is representative of the country s steel producing market and can be used for LCA studies within its geographic limits. In order to obtain the data required for the development of the LCI database, the only structural steel member manufacturing company in Greece was contacted and informed of the research purpose and methodology. The data received in reply covered the majority of the manufacturing process for hot rolled structural steel members in detail. Where necessary, data was added as a result of literature research (Athena Sustainable Materials Institute, 2002). After the completion of the collection and categorization of the data, it was entered into the SimaPro software for management and analysis purposes. 2 LIFE CYCLE INVENTORY OF STRUCTURAL STEEL MEMBERS 2.1 Analysis goal The goal of the analysis is to create a new Life Cycle Inventory (LCI) database, which will contain the raw material requirements and environmental impact (emissions to air, water and soil) associated with the production of one (1) kg of hot-rolled structural steel members (steel quality Fe360, equivalent to S235JR or RSt 37-2). Based on the results, it will be possible to calculate raw material requirements and environmental emissions for all similar type structural steel members, according to their weight. 2.2 Data collection and organization The data received from the Greek manufacturing company was examined in detail and organised according to the flow of the manufacturing process for hot-rolled structural steel sections, from scrap assembly to storage of finished products (cradle-to-gate). The main manufacturing stages are presented in Figure

3 Chapter 5: Monitoring and evaluation 1. Transport of scrap Inland /Foreign suppliers 2. Scrap inspection All inspection procedures at steel factory gate 3. Processing & storage of scrap 4. Loading of EAF with scrap baskets A large percentage of scrap must be processed before used for steel production. 1 EAF operation requires 70 t of scrap (3 basket fills of usually 35, 20 & 15 t). 5. Electric Arc Furnace operation 6. Ladle Furnace operation 7. Continuous casting 8. Reheating furnace 9. Hot-rolling 10. Storage of finished products Scrap melting and first processing of the liquid metal. Final processing of the liquid metal in the ladle furnace. Casting of the liquid metal into steel billets. Reheating of the steel billets before hotrolling (preheating, heating and soaking). Process of the desired steel section formation from the steel billets. Packaged structural steel members are stored before sent for use. Figure 1. Main manufacturing stages for hot-rolled structural steel sections. Based on this analysis, each main manufacturing stage is further analysed into processes and sub-processes, so that the environmental inputs and outputs can be documented in detail (Gulyj et al, 1996). As a representative example, the input requirements for the electric arc furnace are presented in Table 1. Table 1. Required environmental inputs for the electric arc furnace stage. Manufacturing stage Process Required data Data for Life Cycle Inventory (LCI) Comments Operation Scrap melting and first of electric arc furnace liquid processing of metal. - Materials added to the furnace. - Power consumption (kwh). Per billet t: kwh (average=415) - infusion of 0-5 kg magnesium oxide MgO (average=2,5) kg graphite C (average=25) Nm3 oxygen (average =37,5*1,4291=53,6 kg) - 10 MJ natural gas from the urban network. - Coal kg petroleum coke (average=5) kg quicklime CaO (average=45) Each operational circle with 70 t of scrap produces: 62,9 (84,8%) t steel, 0,593 t (0,8%) scrap, 3,11 t waste (4,2%) & 7,49 t nonmetallic waste (10,1%). 657

4 Portugal SB10: Sustainable Building Affordable to All 3 ENVIRONMENTAL IMPACT OF HOT-ROLLED STRUCTURAL STEEL MEMBERS Based on the documentation of the manufacturing processes for hot-rolled structural steel members, corresponding process entries were created within the SimaPro software, thus allowing for the evaluation of the associated environmental impact. Results are calculated on the basis of 1 kg of manufactured product, so that they can be easily compared to similar studies findings and also used within the scope of similar future studies. In order to assess the environmental impact, the Eco-Indicator method was used (Eco-Indicator 99 (E), Europe EI 99 E/E). The results obtained contain 766 entries in total, referring to the environmental inputs (raw material requirements) and outputs (emissions to air, water and soil) associated with the manufacture of 1 kg of hot-rolled structural steel section members according to the Greek conditions. Table 2 contains the most important substances according to input and output category, whereas Figure 2 presents the environmental impact of each main manufacturing stage according to the Eco-Indicator impact categories. Table 2. Life Cycle Inventory (LCI) data for the production of 1 kg of hot-rolled structural steel section member in Greece. Substance Category Unit Amount Inputs: Coal (brown, in ground) Raw material kg 0,9302 Dolomite (CaCO 3, in ground) Raw material kg 1,6727 E-04 Iron (46% in ore, 25% in crude ore, in ground) Raw material kg 0,0713 Manganese (Mn, in ground) Raw material kg 5,1938 E-08 Natural gas (in ground) Raw material m 3 0,1010 Oil (crude, in ground) Raw material kg 0,0627 Steel scrap Raw material kg 1,3132 Water (unspecified natural origin) Raw material lt 7,4807 Zinc (Zn, in ground) Raw material kg 2,5301 E-09 Outputs: Carbon dioxide (CO 2 ) Air emission kg 0,2672 Carbon dioxide, fossil (CO 2 ) Air emission kg 1,0898 Carbon monoxide (CO) Air emission kg 3,6529 E-03 Dinitrogen monoxide (N 2 O) Air emission kg 2,1935 E-05 Hydrogen Chloride (HCl) Air emission kg 2,2360 E-04 Hydrogen Sulphide (H 2 S) Air emission kg 5,2839 E-06 Lead (Pb) Air emission kg 4,5187 E-07 Mercury (Hg) Air emission kg 5,3244 E-08 Methane (CH 4 ) Air emission kg 4,0908 E-04 Nitrogen oxides (NO x ) Air emission kg 1,7179 E-03 Non-methane volatile organic compounds (NMVOC) Air emission kg 6,1780 E-04 Particulates, < 2.5 um (PM 2,5 ) Air emission kg 5,4259 E-04 Particulates, < 10 um, mobile & stationery (PM 10 ) Air emission kg 4,1696 E-06 Sulfur dioxide (SO 2 ) Air emission kg 4,0054 E-03 Sulfur oxides (SO x ) Air emission kg 9,8143 E-05 Zinc (Zn) Air emission kg 5,6612 E-07 Ammonia, as N (Ν) Water emission kg 1,4202 E-07 Cadmium, ion Water emission kg 6,0885 E-07 Chemical Oxygen Demand (COD) Water emission kg 0,0014 Chromium, ion Water emission kg 6,5059 E-07 Iron Water emission kg 4,6990 E-06 Lead (Pb) Water emission kg 3,2072 E-06 Nickel, ion Water emission kg 4,6555 E-05 Suspended solids Water emission kg 2,9094 E-04 Zinc, ion Water emission kg 2,1268 E-05 Calcium Soil emission kg 1,5291 E-05 Heat, waste Soil emission MJ 0,0100 Iron Soil emission kg 1,4020 E-05 Oils, unspecified Soil emission kg 2,4071 E-04 Steel waste Waste kg 0,0620 Waste, unspecified Waste kg 0,

5 Chapter 5: Monitoring and evaluation As shown in Figure 2, the most environmentally damaging processes are the operation of the electric arc furnace and hot-rolling. The reheating furnace and ladle furnace processes also result in noticeable environmental impacts, while the rest of the processes affect the overall impact at a lower degree. With regard to the environmental impact categories (Figure 3), the categories fossil fuels that refers to natural resources and respiratory-inorganics -associated with negative effects on human health- are mainly burdened. The manufacturing stages primarily responsible for these negative effects are again identified as the operation of the electric arc furnace and hot-rolling. Figure 2. Environmental impact of main manufacturing stages for 1 kg of hot-rolled structural steel section member in Greece. Figure 3. Environmental impact of 1 kg of hot-rolled structural steel section member in Greece according to impact categories. 659

6 Portugal SB10: Sustainable Building Affordable to All In order to identify the sources of environmental burden within the boundary of each manufacturing stage, it is also necessary to examine the network of environmental burden flow for the production of 1 kg of hot-rolled structural steel members, presented in Figure 4. For presentation purposes, this diagram does not contain all of the processes, but only the most influential ones. As the thickness of the arrows indicates the environmental loads, it is evident that electricity requirements are responsible for more than half (55,6%) of the total environmental impact. Figure 4. Environmental burden flow for the manufacturing of 1 kg of hot-rolled structural steel section members in Greece. Further down in the diagram, the lignite burned at the power plant for the production of the electric energy is revealed as the main source of environmental burden. This also explains why the fossil fuels impact category is so heavily affected by the operation of the electric arc furnace and the hot-rolling process, both of which require significant amounts of electricity. On the other hand, natural gas is also used as an energy source, yet its environmental impact is quite lower. 4,33 MJ of natural gas energy required in total for the reheating furnace and the hot-rolling process (2,45 MJ for the reheating furnace and 1,88 MJ for hot-rolling) are responsible for 20,6% of the total environmental burden, as opposed to 55,6% corresponding to 2,73 MJ of electric energy required in total. Regardless of source, energy requirements account for 76,2% of the total environmental load, a figure which leaves little room for doubt that in order for hot-rolled structural steel member manufacturers to improve their products sustainability, they will have to reconsider their current energy strategies. 660

7 Chapter 5: Monitoring and evaluation Another parameter which was examined was the carbon dioxide emissions to the atmosphere. In this respect, it is both electric energy and also natural gas energy which are responsible for the largest percentage of emissions. It is therefore clear that in order to reduce the total environmental impact, energy requirements -particularly electric energy- will have to be reduced. 4 GLOBAL WARMING POTENTIAL (GWP) ANALYSIS It is also possible to estimate the amount of equivalent carbon dioxide air emissions, by the calculation of the Global Warming Potential (GWP) index (IPCC, 2007). This methodology is based on specific factors with which every substance emission is multiplied and thus translated into equivalent gr of carbon dioxide, which are finally added to a total. In this manner, a single index becomes an immediate depiction of the environmental impact of a product or system, for a time horizon of 20, 100 or 500 years. For 1 kg of hot-rolled structural steel members, the GWP results are presented in Table 3. For a 100-year time horizon the equivalent carbon dioxide emission was calculated at 1,405 kg CO 2 eq. Table 3. GWP index for the production of 1 kg of hot-rolled structural steel members, based on the IPCC GWP 2007 methodology. GWP methodoly Unit Total IPCC GWP 20a (20 έτη) kg CO 2 eq 1,4838 IPCC GWP 100a (100 έτη) kg CO 2 eq 1,4054 IPCC GWP 500a (500 έτη) kg CO 2 eq 1,3732 The contribution of each main manufacturing stage is displayed in Figure 5. As was shown by the Eco-Indicator analysis, the stages which are mainly responsible for the total environmental impact are the electric arc furnace operation, the hot-rolling process and the reheating furnace operation. 0,7 gr CO2 eq. 0,6 0,5 0,4 0,3 0,2 0,1 Scrap transport Scrap processing EAF loading EAF Ladle furnace Continuous casting Reheating furnace Hot-rolling Finished products storage 0 IPCC GWP 20a IPCC GWP 100a IPCC GWP 500a Figure 5. Process contribution to total environmental impact as estimated with the IPCC GWP 2007 methodology. 5 CONCLUSIONS While the Life Cycle Assessment (LCA) methodology provides a detailed approach to calculating the environmental impact of steel structures, it never ceases to associate its validity with the qual- 661

8 Portugal SB10: Sustainable Building Affordable to All ity of the Life Cycle Inventory (LCI) data which is used. The research conducted provides a useful initial attempt at the development of a new LCI database for structural steel elements in Greece. The impact of the manufacturing of hot-rolled structural steel members was estimated, based on data provided by a Greek steel manufacturing company and secondary data found in literature and existing LCI databases as well. It is not possible to claim that any LCI database contains data which represent environmental impacts with total accuracy. However, as is the case with the current newly formed database, they do serve as a reliable estimation which can be used for future decision-making, strategy planning, or in the case of steel structures, optimization of the design processes. With regard to environmental impact, the main source of burden associated with the manufacturing of hot-rolled structural steel members was found to be the energy requirements. While electric energy accounts for more than half of the total environmental impact, natural gas energy is responsible for almost 60% of the total carbon dioxide emissions to the atmosphere. Energy has been an issue within the scope of sustainable development for quite some time now and as was shown by the research undertaken, it must also be integrated into the manufacturing process for steel members in order to ensure a sustainable manufacturing procedure. The analysis described can also be used as a framework which can be applied to other geographic regions for the assessment of the environmental impact of hot-rolled structural steel members. The main manufacturing stages will require minor modifications to fit the specific conditions which apply for each country, with the most significant part of data required remaining the energy requirements. REFERENCES Athena Sustainable Materials Institute Cradle-to-gate Life Cycle Inventory: Canadian and US Steel Production by Mill Type, Ottawa, Canada, March Bragança L., Koukkari H., Blok R., Gervásio H., Veljkovic M., Plewako Z., Landolfo R., Ungureanu V., Silva L.S. (2007), Sustainability of Constructions Integrated Approach to Life-time Structural Engineering, COST Action C25, Proceedings of the first Workshop, Lisbon 13, 14, 15 September Gulyj, V.K., Dmitriev, Yu.V., Kirsanov, V.M., Litvinov, A.A., Petrichenko, A.A., Tyagnij, V.V System for degassing the open hearth steel: from construction to development of technology, Metallurgist (10), pp IPCC Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment, Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp. ISO (International Organization for Standardization) International Standard ISO 14040:2006 Environmental management - Life cycle assessment - Principles and framework, International Organization for Standardization. World Steel Association (Worldsteel) Steel Statistical Yearbook 2008, Worldsteel Committee on Economic Studies Brussels. Zygomalas Ι., Efthymiou Ε. & Baniotopoulos C.C On the Development of a Sustainable Design Framework for Steel Structures, Transactions of FAMENA, issue 2, volume 33, Zagreb