On the use of process integration methods evaluation of energy and CO2 emission strategies in blast furnace ironmaking and oxygen steelmaking

Abstract: This work deals with sustainable resource utilisation in integrated (iron ore based) steelmaking, with special emphasis on how to analyse process adaptation and developments aiming towards lowering of the emission of greenhouse gases, in particular carbon dioxide (CO2), to the atmosphere. Climate change and management of CO2 are real issues for the steel industry these days. Much of the research and development within the CO2 area take place internationally, often in co-operation between academic and applied research groups at universities, institutes and the industry. This work has therefore been influenced by ongoing national and international research programmes even if it is not always stated in the individual papers. Profitability is one of the foundations for industrial sustainable development. In general, cost and performance have to be balanced in an industrial system. This is one of the incentives for developing systematic and all-embracing methods to analyse the trade-offs between two or more objectives, i.e. emissions and costs, energy utilisation, material efficiency, and other resources. This thesis consists of five papers covering Process Integration aspects of energy, CO2 emission, and cost minimisation in integrated steelmaking. The concept of Process Integration, and the two methods pinch analysis and mathematical programming, are described. A method based on mixed integer linear programming (MILP) and the MIND method has proved to be particularly useful for optimisation and/or simulation of integrated iron- and steelmaking systems. The MIND method (Method for analysis of INDustrial energy systems) represents the industrial system as a network of process nodes, connected by energy and material flows. This type of optimisation models for an industrial system can therefore be used to manage complexity, to manage changes, to facilitate faster decisions, and is a powerful complement to other tools with only a simulation capacity. In this phase of the work, the main process focus has been on the blast furnace ironmaking and oxygen steelmaking processes since these processes in principal are the characteristic processes of integrated steelmaking. The processes are also energy intensive, and well-described in the literature, both with respect to theory and practice. The interaction between these processes, and other parts of the integrated steelmaking system, is however not so much discussed in the literature as one would expect. The Process Integration approaches have been used in several studies of the material and energy utilisation for the integrated steelmaking system. From the modelling results, some conclusions and strategies have been drawn on costs, energy and environmental aspects.