THE APPLICATION OF LIFE-CYCLE ASSESSMENT TO THE ENVIRONMENTAL IMPACTS IN THE PRODUCTION AND USE OF CASTINGS

Transcription

1 5/13 Archives of Foundry, Year 2004, Volume 4, 13 Archiwum Odlewnictwa, Rok 2004, Rocznik 4, Nr 13 PAN Katowice PL ISSN THE APPLICATION OF LIFE-CYCLE ASSESSMENT TO THE ENVIRONMENTAL IMPACTS IN THE PRODUCTION AND USE OF CASTINGS A.J. CLEGG 1 Wolfson School of Mechanical and Manufacturing Engineering Loughborough University, Loughborough, Leics, LE11 3TU, UK SUMMARY The paper considers the foundry industry s opportunities for reducing life-cycle environmental impacts. It relates to EU funded research to produce an improved ductile iron (DILIGHT) to enable component weight reduction. These lighter components could environmentally outperform aluminium alloy components when the whole life-cycle impact of the casting is considered. Key words: cast iron, aluminium alloy, environment, automotive, life-cycle assessment. 1. INTRODUCTION Casting production has environmental implications that extend beyond the foundry s premises. By taking a life-cycle approach the impacts upstream (supply side) and downstream (customer/user side) can be identified. The benefits of a foundry s actions to reduce an environmental impact might be leveraged to reduce impacts at other stages in the life-cycle. However, as a minor player in the supply chain a foundry s influence in reducing life-cycle environmental impacts is limited. This influence can be strengthened if the foundry works in partnership with its customers. A good example of this is a partnership between a foundry and an automotive industry customer. The automotive industry is under continuing pressure to reduce the environmental impacts of the car. Improvements in fuel efficiency are one manifestation of this pressure. A contributing factor to improved fuel efficiency is a reduction in the 1 Dr, BSc, MSc, PhD, MBA, CEng FIMMM, A.J.Clegg@lboro.ac.uk

2 40 vehicle s weight. From a foundry perspective we have seen a progressive substitution of aluminium alloys for ferrous alloys to support this vehicle weight reduction. However, from a life-cycle perspective the environmental benefit of substituting aluminium for iron is not so clear-cut. The production of primary aluminium is extremely energy-intensive and carbon dioxide generating. These effects are so great that it could take the whole life of the car for the environment to benefit from the fuel efficiency improvements achieved through reduced car weight. The paper reports a LCA study to compare and contrast three different material groups namely aluminium alloys, cast iron and the new DILIGHT option. The objective was to assess selected environmental impacts for cast automotive components and to identify the best material choice in terms of energy consumption and global warming potential. 2. REVIEW 2.1 The environmental impacts of the UK foundry industry The foundry industry is already quite effective in its recovery, reuse and recycling of two of its principal inputs: metal and sand. Nevertheless, solid waste, which represents about 14% of the output side of the mass balance, is dominated by waste sand. Most of this waste sand goes to landfill. A number of successful initiatives have been introduced to stimulate the beneficial reuse of foundry wastes. For examples, waste sand may be used as a concrete additive, for road bedding or for mixing with asphalt for road surfacing. However, in the context of this paper it is the issue of energy consumption and its impact on carbon dioxide generation and global warming that is of most interest. It was estimated [1] that the UK foundry industry consumed approximately 3.5 million MWh of energy in the year This produced 1.12 million tones of carbon dioxide, of which about 40% was produced directly by the foundry industry with the balance being output from electricity generation. 2.2 Foundries and energy consumption The industry is a significant user of energy and, not surprisingly, melting and holding of metal is the major consumer of energy in the iron sector which accounts for 80% of the foundry sector s use [2]. Whilst melting and holding account for the major part of consumption, between 20 and 50% (average 35%) of a foundry s energy consumption is related to services. These services comprise motors and drives, compressed air, lighting, space heating etc. Whilst it always makes sense to target the major consumption of energy first in the drive to reduce consumption, oth er areas should not be neglected. In 1996 it was estimated that the UK non-ferrous casting sector produced 210,000 tones of castings of which 150,000 tones were of aluminum alloys [3]. It was

3 41 also estimated that the output of aluminum alloy castings was increasing at the rate of 5 to 6 % per annum. This was partly due to the substitution of iron castings in automotive applications. It was estimated that melting and holding each accounted for 30% of the energy consumed with the balance for support services. 3. LIFE-CYCLE ASSESSMENT AND METHODOLOGY The Boustead LCA Model software was chosen for the project. The ISO14040, 1997 LCA framework was adhered to. For the purpose of this analysis a fictive automobile suspension component was chosen as the functional unit and allocated a weight of 3.5 kg in aluminum alloy. The equivalent weight of this component in cast iron was assumed to be 5 kg. A base case and four different life cycle scenarios were considered. In the base case scenario it was assumed that the metal to be converted into castings was primary material, i.e. pig iron from the blast furnace for the cast iron and aluminium ingot from the smelter for the aluminium castings. In the four scenarios it was assumed that the metal converted into castings comprised from 75% to 0% primary and 25% to 100% secondary material. The term secondary material is used here to denote recovered and recycled material. The LCA analysis provided output data on selected air emissions, energy consumption and global warming potential and selected output is presented in the results. The life cycle of the product system was assumed to consist of five life cycle stages: Material production (primary and secondary); Foundry processing; Manufacturing and assembly; Automobile use phas e; and End-of-life management. However, the LCA was restricted to the three life-cycle stages considered to have the most impact on the environment, namely the Material production, Foundry process ing and Automobile use stages. Data for the LCA studies was derived from literature sources and research partners. 4. RESULTS The relative values for global warming potential (GWP), assuming 100% primary material inputs, are shown in Fig. 1. The output from the LCA model produced a total life-cycle inventory of greenhouse gases of kg (CO 2 equivalents) for the aluminum suspension arm. This figure was dominated by the intensive consumption of gasoline in the automobile use phase that contributed kg (CO 2 equivalents). Consequently, the automobile use phase accounts for 52% of the global warming potential. The material production phase contributes 34% and the foundry processes the remaining 14% over the life cycle of the product system. For the equivalent cast iron component the total greenhouse gases are kg of which the foundry process contributes 5%, the material production 6% and the use phase 89%. Similar data were generated for the other life cycle scenarios and, as would be expected, the values for material production, the auto use phase and the total life cycle were reduced.

4 Kg CO 2 Equivalents 42 The LCA data was used to construct graphs that related the GWP of the alternative materials to the distance travelled by a car in the use phase. An example for primary materials is shown in Fig. 2. Such graphs enable a break-even point to be identified. This break-even point shows how far the car must travel before the beneficial effects of lower mass compensate for the energy expended in primary production and foundry processing. Global Warming Potential Aluminium Cast Iron DILIGHT 20 0 Material Production Foundry Process Manufacturing and Assembly Auto Use Phase End-of-Life Management Total Life -Cycle Rys. 1. Fig. 1. Porównanie globalnego efektu cieplarnianego (wyrażonego w kg ekwiwalentnej emisji CO 2 ) *. Comparative global warming potential. 5. DISCUSSION The validity of the assumption that aluminium is a better alternative to a ferrous alloy must be questioned because the reduction in fuel consumption may be achieved at the expense of other environmental impacts. Although aluminium is about one-third the density of iron, the actual weight saving is more likely to be 30% rather than 67%, because of the difference in mechanical properties it is rarely possible to realize the full potential for weight saving [4]. Furthermore, the energy consumed in the production of primary aluminium, foundry processing and recycling exceeds that for an equivalent amount of iron and the latter is not subject to the deterioration associated with multiple recycling of aluminium alloys. The issue was demonstrated by the LCA results. When the life cycle effects of using primary materials are considered, see Fig. 2, we can see that the benefit of reduced fuel consumption when using aluminium is not realised until a distance of 250,000 km has been exceeded. This demonstrates the very significant influence that * Efekt cieplarniany związany z uwzględnieniem wszystkich etapów procesu technologicznego i eksploatacyjnego wyrobu.

5 Global Warming Potential 43 primary production has on energy consumption and global warming. In practice, most cast components would be produced using a mixture of primary and secondary materials. In the scenario in which there is an equal proportion of primary and secondary material, the benefit of aluminium is delivered after 150,000 km. Whilst there is a reduction in processing energy for all materials, the effect is most dramatic for aluminium. A more detailed explanation is provided elsewhere [5] Break-Even Point Aluminium Cast Iron DILIGHT Vehicle Use (1,000 km) Rys. 2. Fig. 2. Wpływ przebiegu pojazdu (w tys. km) z odlewami z różnych tworzyw odlewniczych na wartość globalnego efektu cieplarnianego, wyrażonego w kg ekwiwalentnej emisji CO 2. Break-even point for 100% primary materials. 6. CONCLUS IONS 1. For a system in which primary aluminium competes with primary cast iron to generate a mass saving of 23%, the demand for energy for the aluminium product system is 30% higher than it is for the alternative cast iron product system. This in turn generates a global warming potential that is 15% higher. 2. The distance that a car must travel before the reduced mass of aluminium begins to provide a reduction in the life cycle energy consumption is 250,000 km for the scenario in which only primary materials are used. This distance is reduced to 150,000 km when a combination of 50% primary and 50% secondary material is used.

6 44 7. ACKNOWLEDGEMENTS The author acknowledges the support of the European Union through a Fifth Framework Programme (GROWTH) contract to conduct research under the co ntract number: G5RD-CT (acronym: DILIGHT). He also acknowledges the agreement of the partners in the contract to the publication of this paper. REFERENCES [1] Castings Technology International: The Foundry Mass Balance Project, pp72, (2003). [2] Department of the Environment, Energy Saving in Foundry Services, pp45 (1995). [3] Department of the Environment, Transport and the Regions, Non-ferrous Foundries Energy Consumption Guide 38 (2 nd Edition), pp30 (1997). [4] C M Moore, K Rohrig and R Deike, Auto Aluminium, is it really Cost Effective?. Foundry Trade Journal International, 22, 2, p37-42 (1999). [5] C J Backhouse, A J Clegg and T Staikos, Reducing the Environmental Impacts of Castings by Life-cycle Management, To be published in Progress in Industrial Ecology, 1, 1, (2004). ZASTOSOWANIE OCENY CYKLU ŻYCIA DO OKREŚLANIA ODDZIAŁYWANIA NA ŚRODOWISKO PRODUKCJI I EKSPLOATACJI ODLEWÓW STRESZCZENIE W pracy przedstawiono kompleksową ocenę wpływu pełnego cyklu życia odlewów z różnych stopów na otoczenie. Zastosowano metodę analizy oddziaływania na otoczenie wszystkich etapów cyklu produkcyjnego, jak również czasu eksploatacji odlewu z danego stopu, aż do jego pełnego zużycia i recyklingu. Wykazano, że istotny wpływ na środowisko, oceniany za pomocą tzw. ekwiwalentnego efektu cieplarnianego, towarzyszącego danemu etapowi produkcji i eksploatacji odlewu, wywiera faza wytopu i przygotowania danego stopu ze składników pierwotnych. Dominacja tej fazy jest tak znaczna, że efekt zastąpienia stopu o większej gęstości (np. żeliwa) stopem lekkim (np. AlMg) wymagałby wydłużenia przebiegu samochodów do ok km, aby można było skompensować efekt cieplarniany procesu metalurgicznego stopów aluminium. Przedstawiona metoda oceny oddziaływania procesu produkcyjnego odlewów na środowisko, stanowiąca pewną nowość, jest już stosowana w krajach Unii Europejskiej. Recenzent: prof. dr hab. inż. Józef Dańko.