Process Integration and mathematical programming are useful method to effectively approach large-scale industrial problems. This paper describes some of the most recent methods which have been developed and evaluated at the PRISMA - Centre for Process Integration in Steelmaking in Sweden. The tools described can be; i) used for optimization and/or simulation of integrated iron- and steelmaking systems, ii) used to manage complexity, to manage changes, to manage decisions faster. Examples on studies covering costs, energy and Environmental aspects of steelmaking will be given.

Currently, the blast furnace (BF) to basic oxygen furnace (BOF) is the dominant steel production route in the steel industry. The direct CO2 emission in this process system exceeds 1 t of CO2/t of crude steel produced. Different ferrous burden materials, for instance iron ore and scrap, can be used in various proportions in this steelmaking route. This paper analyses how energy use, conversion costs, and CO2 emissions can be influenced by the use of different ferrous burden materials when producing crude steel. An optimisation mixed integer linear programming (MILP) model has been applied for analysis. By the use of the optimisation model, it is possible to highlight some issues of special importance, such as best practices to increase production at low conversion cost, or best practices to increase production at low CO2 emission. It is found out that more benefits will be gained when using the system-oriented analysis to the steelmaking process. Furthermore, a comprehensive view of the trade-offs between the objectives of Cost and CO2 can provide useful information for decision makers to generate strategies under the future emission trading.

The iron and steel industry is a large energy user in the manufacturing sector. Carbon dioxide from the steel industry accounts for about 5-7% of the total anthropogenic CO2 emission. Concerns about energy consumption and climate change have been growing on the sustainability agenda of the steel industry. The CO2 emission will be heavily influenced with increasing steel production in the world. It is of great interest to evaluate and decrease the specific CO2 emission and to find out feasible solutions for its reduction. In this work, a process integration method focusing on the integrated steel plant system has been applied. In this paper, an optimization model, which can be used to evaluate CO2 emission for the integrated steel plant system, is presented. Two application cases of analysing CO2 emission reduction possibilities are included in the paper. Furthermore, the possibility to apply the model for a specific integrated steel plant has been discussed. The research work on the optimization of energy and CO2 emission has shown that it is possible to create a combined optimization tool that is powerful to assess the system performance from several aspects for the steel plant.

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 methods to analyse the trade-offs between two or more objectives, i.e. costs and emissions, energy utilisation, material efficiency, and other resources. Process Integration is a common name for system oriented methods and integrated approaches to complex industrial process plant design. It is a multi disciplinary approach which consists of mathematical, thermodynamic and economic models and methods.Eco-Efficiency is a concept which brings together economic and environmental progress by consideration of on one side the product value and on the other side the environmental influence in the product manufacture. In this paper a general Process Integration model for iron- and steelmaking to be used for evaluation of the Eco-Efficiency in steelmaking is proposed. The Process Integration model is a Mixed Integer Linear Programming (MILP) model which covers different production routes.

The complex structure of the energy and mass flows in steelmaking has resulted in many attempts to describe the process dynamics by models. Swedish steelmaker SSAB Tunnplåt is one of Europe´s leading manufacturers of high-strength strip steels. The company has orebased steel production in Luleå and strip steel manufacture in Borlänge. SSAB has a long practical experience on how to use optimisation models for planning and decision-making related to energy and material utilisation.Sustainable development is development aimed at improving the quality of life for everyone, and is a factor of increasing importance in the industry. The International Iron and Steel Institute (IISI) have suggested a number of sustainability indicators to measure economic, environmental and social performance for steelmaking. This paper exemplifies how the sustainability indicators; i) material efficiency, ii) energy intensity, and iii) greenhouse gas emissions, can be used as objectives for systematic analysis and optimisation of the industrial system. It is then possible to study possible conflicts or correlations between the different sustainability indicators. A MILP-based process integration model including cokemaking, blast furnace ironmaking, basic oxygen steelmaking, and continuous casting for the production of steel slabs has been adopted for this task.

There are strong associations between standard of living, and energy and material use in the society. In fact, a higher "consumption" of energy and materials is often regarded as synonymous with human wellbeing. To make this fit in with the ideas of the sustainable society, it is important to assure that the industrial systems are designed in an energy and material efficient way, and to enhance the understanding of which barriers or bottlenecks we must do something about to become even more efficient in the future.The MIND method (Method for analysis of INDustrial energy systems) has been developed to model different types of industrial energy systems. The method can also be used to model and analyse other aspects of industrial systems, not only the energy issues. The system to be analysed with the method is represented as a network of process nodes, and nodes representing auxiliary units, connected by energy and material flows. The MIND method is based on Mixed Integer Linear Programming (MILP), meaning that relationships in the system are normally described as linear functions. The potential of the MIND method is that it enables a simultaneous representation of the total industrial system, a production site, or several aggregated production sites. By focusing on the larger system, the centre of attention can be drawn from optimisation of the production processes one by one, as in traditional process development. Instead, it is possible to focus the analysis on the flexibility and the most favourable interactions between different parts of the system.Examples on industrial systems for material production, which have been modelled using the MIND method, are pulp and paper production and steelmaking. Both types of material production involve several processing steps with a high degree of heat and material management. Another likeness is that both materials can be produced from recycled materials and that the recycling rates from the society are among the highest, compared to other materials. The MIND method has shown grand potentials for analysis of these productions system, and also for other systems, such as food manufacturing and chemical industries. It can also be used for analysis of possible synergies between neighbouring industries, or between an industry and the nearby society. In this paper the methodology will be described and references will be made to projects where MIND has been used in pulp and paper production and steelmaking.

The structure of the energy and mass flows in steelmaking is rather complex with a lot of connections between the unit processes. A further developed optimisation model for integrated steelmaking based on mixed integer linear programming (MILP) is described. The system includes today's dominating steel production route, basic oxygen steelmaking, based on iron ore, steel scrap, and carbonaceous reducing agents. Multi or single objective minimisation problems in steelmaking are represented by energy use, CO2 emissions and raw material cost to produce steel slabs. Finally the paper briefly discusses the effects of process and product related constraints on the modelling results.

The complex structure of the energy and mass flows in steelmaking has resulted in many attempts to describe the process dynamics by models. Swedish steelmaker SSAB Tunnplåt has long practical experience on how to use optimisation models for planning and decision-making related to energy and material utilisation. Sustainable development is development aimed at improving the quality of life for everyone, and is a factor of increasing importance in the industry. This paper exemplifies how optimisation models can be used for systematic analysis, design and balancing of steelmaking systems, and how it can be used for optimisation of sustainability indicators such as energy efficiency, greenhouse gas emissions and material utilisation with a limited effort and time. The methodology can also be extended to include cost optimisation

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.