Environmental Assessment of Biomass Options for Iron Making

摘要

Aiming at reducing CO2 emissions for ironmaking, we consider and evaluate in this paper the possibility to replace a part of the fossil fuel – coal – usually used to produce pig iron with a renewable one – biomass. Our approach combines life cycle assessment and systems modeling. Steel industry is responsible for more than 6% of the anthropogenic CO2 emissions and reducing the carbon footprint is today a matter of prime importance for iron and steelmakers. Since most of CO2 emissions result from using fossil coal as a fuel and a reductant for ironmaking, using renewable biomass instead looks attractive. Many scenarios (according to the biomass type, the biomass treatment process, the type of injection) are possible and have to be evaluated from environmental, economical and technical feasibility points of view, so that the best option could be identified. First, to check the relevance of a biomass option for an actual pig iron plant located North East of France, the local availability of the biomass was verified and quantified. Then, life cycle assessment (LCA) was used to evaluate the environmental and economical feasibility of the different scenarios. Results of a screening LCA allowed us to proceed to a first selection of scenarios and to determine the hot spots of the whole route, i.e. from raw materials extraction to liquid pig iron. We found that replacing 20 % of the coke with biomass could save around 200 kg of CO2 per metric ton of pig iron produced, which represents a reduction of 10% of the total CO2 emissions of the whole route. Thus, we have already shown that a small substitution of biomass for coke can have a noticeable impact on CO2 footprint. To go further towards an accurate LCA, we are improving the life cycle inventory, through the use of calculated data that precisely respect mass and heat balances. For that purpose, we are currently building mathematical models of the key unit processes (biomass transformation, iron ore sintering, blast furnace) using commercial flowsheeting software.