Developpement d'une methode d'analyse du cycle de vie prospective appliquee a la siderurgie

The steel industry is currently one of the most important industrial greenhouse gas (GHG) emitters in the world. Since the demand for steel is continuously increasing due to all potential applications in our everyday lives, we have to find solutions to tackle environmental issues and to get prepared for forthcoming regulations in this field. This master thesis focuses on the assessment of the environmental performance of different existing and developing steel production technologies. In order to reach this purpose, the life cycle assessment (LCA) methodology has been chosen, which allows evaluating the potential impacts of a product through its different life cycle stages. Nevertheless, most of the studied technologies are currently in development and will only be implemented at the industrial scale in years or decades. The influence of time on the results becomes critical in this study and has therefore to be considered. This is why a special declination of the LCA methodology is used: the prospective life cycle assessment approach.;The aim of this master thesis is to develop a prospective life cycle assessment approach for the steel industry. To achieve this goal, an innovative method is developed to integrate the influence of technological changes on inventory data. The proposed approach uses projected environmental policies to predict future emissions. The integration of the effect of future regulations on inventory data is done using time-dependent reduction factors. The applicability of this methodology is tested on a case study specific to the steel industry, the ULCOS (Ultra-Low Carbon dioxyde Steelmaking) programme.;An attributional life cycle assessment is first carried out in order to identify which parts of the system should be involved in a prospective development. This LCA also enables to compare the potential impacts of different technologies using current data. The results of this preliminary assessment indicate that the new technologies studied have a lower potential impact on climate change compared to the traditional blast furnace production chain, used as the reference technology. Regarding other impact categories (namely acidification, eutrophication, photochemical ozone creation potential, and depletion of abiotic resources), conclusions are mixed. Some technologies have indeed higher impacts for some categories compared to the reference technology. This has to be kept in mind before future implementation of these technologies in order to prevent shifting of impacts.;Subsequently, prospective developments of this study are carried out. In this prospective study, two potential perspectives of the future are compared: a “business as usual” scenario and a scenario in which GHG emissions are more strictly regulated. This part of the assessment focuses at first on the future evolution of some assumptions related to electricity sources and transportation. The influence of variations in electricity sources is particularly important. The influence of future environmental policies on inventory data is then developed. It is shown to have a major impact on the results. Finally, the different prospective aspects are simultaneously applied to the case study, and the steel production technologies are compared for the year 2050.;For these two scenarios, impacts associated to each technology decrease with time over the period considered (2000-2050). Depending on both technologies and scenarios, potential impacts decrease for instance in 2050 between 15% and 86% for climate change and between 74% and 89% for acidification, compared to initial results without prospective aspects. Therefore, the results of the study are greatly influenced by the prospective approach. Impacts of the whole European steel industry are also modeled using the results obtained for each current and future steel production technology. These results show that a GHG emission reduction of 50% associated to steel production is possible through the development of new technologies. Impacts in other categories would also decrease.;The work presented in this master thesis was carried out for our specific case study. However, the methodology developed is easily adaptable and could be applied and extended to other types of assessment. Nevertheless, its application has highlighted some limits and several recommendations have been addressed in order to improve the approach:;• To refine reduction factors with for instance a regionalisation of reduction objectives;;• To extend the methodology to all the substances of the inventory and to process input data;;• To implement the methodology into databases in order to facilitate its use and to improve precision.