Primary steelmaking in blast and basic oxygen furnaces is inherently carbon-intensive. Partial capture, i.e., capturing only a share of the CO2, is discussed as an option to reduce the cost of carbon capture and storage (CCS) and to realize a near-term reduction in emissions from the steel industry. This work presents a techno-economic assessment of partial capture based on amine absorption of CO2. The cost of steam from excess heat is assessed in detail. Using this steam to drive the capture process yields costs of 28–50 €/t CO2-captured. Capture of CO2 from the blast furnace gas outperforms end-of-pipe capture from the combined-heat-and-power plant or hot stove flue gases onsite by 3–5 €/t CO2-captured. The study shows that partial capture driven exclusively by excess heat represents a lower cost for a steel mill owner, estimated in the range of 15–30 €/t CO2-captured, as compared to full capture driven by the combustion of extra fuel. In addition, the full-chain CCS cost (capture, transport and storage) for partial capture is discussed in light of future carbon prices. We conclude that implementation of partial capture in the steel industry in the 2020s is possible and economically viable if policymakers ensure long-term regulation of carbon prices in line with agreed emission reduction targets beyond Year 2030.

The main objective has been to describe different cases of the methanol production from steel-work off gases (Coke oven gas and Basic oxygen furnace gas) and biomass based synthesis gas. The SSAB steel mill in the town of Luleå, Sweden has been used as a basis to analyze four different methanol production cases.The studied biomass gasification technology is based on a fluidized bed gasifier unit, where the production capacity is determined from case to case coupled to the heat production required to satisfy the local district heating demand. Critical factors are the integration of the gases with availability to the synthesis unit, to balance the steam system of the biorefinery and to meet the district heat demand of Luleå.For each case, the annual production potential of methanol, the overall production efficiencies and the effects on the total steel plant have been estimated.

The energy network in Luleå consists of the steel plant, heat and power production and district heating. Global system studies are necessary to avoid sub-optimization and to deliver energy and/or material efficiency. SSAB began work with global simulation models in 1978. After that several more specialized process integration tools have been tested and used: Mathematical programming using a MILP method, exergy analysis and Pinch analysis. Experiences and examples of results with the different methods are given and discussed. Mathematical programming has been useful to study problems involving the total system with streams of different types of energy and material and reaction between them. Exergy is useful to describe energy problems involving different types of energy, e.g. systematic analysis of rest energies. Pinch analysis has been used especially on local systems with streams of heat energy and heat exchange between them.

The process industries stand for a substantial part of the energy used in Sweden. Industrial systems, such as an integrated steel plant, involve large interchange of energy between various processes and process streams. A major task for the steel industry is to minimize environmental impact, the consumption of energy and raw materials. A natural step is to improve the efficiency of the individual processes. However, since the processes within the steel plant system are connected to each other, energy savings in one individual unit does not necessarily lead to an energy saving for the total system. According to the Swedish National Energy Administration and Statistics, the steel industry used approximately 17.1 % of all industry related energy use the year 2001. Thus will small efficiency changes will result in large absolute energy savings. In order to make a successful energy saving one must understand the interactions between different processes. Methods are needed to optimize the consumption of energy and raw materials for the total system. The purpose of this thesis is to develop and implement such methods. The main method used in the analysis is based on mathematical optimisation. A steel mill in north of Sweden is used as case study, when actual processes and steel plant system are analysed. It is shown that the method used is appropriate for analysing the material and energy system in a steel plant.

Process Integration is a common name for system oriented methods and integrated approaches to complex industrial process plant design. In Process Integration, interactions in the industrial system are taken into account during process design and optimization via their material and energy flows. The use of systematic methodologies is a very effective approach to improve the energy and material efficiency of large and complex industrial facilities. In this paper an analysis of an integrated steel plant together with a new methodology to represent the resource efficiency is presented. The paper shows the importance of process integration as a methodology for the industry in their continued strive to strengthen its long-term sustainability

There is a growing awareness of serious problems associated with the use of energy. These problems include local and global environmental degradation associated with energy use and depletion of resources. The awareness of the problems associated with energy use increased as a consequence of the two oil crises in the 70s which led to rising costs for energy. Today, it is environmental issues that are becoming increasingly important, and it is primarily concern for a higher concentration of greenhouse gases in the atmosphere and the effect this has on climate that are highly prioritised. Analysing the potential for improving the specific energy use and environmental performance in a steel mill can be difficult due to the interactions between the many sub-systems. Changes in one unit may lead to a chain of changes throughout the system and the overall effect may not necessarily be improved performance. This thesis addresses the issue of evaluating and analysing an industrial material and energy system with regard to energy use, and economic and environmental performance, through a systematic approach. The main emphasis is on the development of analysis methods and tools for an integrated steel mill. Several applied studies of the integrated steel mill of SSAB Tunnplåt AB have been carried out. The results show that large savings in energy, cost, and emissions to the environment can be achieved using the analysis methods developed. From the analysis of energy use, a potential reduction of up to ~17% could be identified within the existing system, e.g. through more planning and control, less volatile matter in the coking coal mix, and by increasing the scrap rate in the BOF. From a cost perspective, the method showed that significant savings could be achieved through using a wide system boundary when performing the analysis. In the existing steel making system, the CO2 emission proved to be among the lowest compared to similar systems. Improvements could be taken even further using the optimising methodology proposed. A method for analysing the trade-offs between different objectives is also proposed. The process integration model is a good tool providing new insights into the material and energy system. It can serve as a benchmark for different steel making operations and constitute the basis for continued work on improving material and energy efficiency. Implementing such a tool in the industry is a good complement to the existing analysis tools in order to assess the effect of energy saving measures and can be used together with an energy management system.

This prestudy is the first project of two where the overal aim is to develop techniques for process integration in the steel industry. This industry consumes a lot of energy and a tool for integration is of great importance for process optimazion and energy conservation in steel plants. This projekt involvs first an investigation of what kind of tool the Swedish steel industry needs for process integration (energy conservation, enviromental aspects). The second part contains data recording of relevant process parameters connected to the blast furnace at SSAB Luleå. The third part is a theoretical study of transient process parameters and how they affects the plant and surounding industries such as power plant Lulekraft.

Analysing the potential for improving the specific energy use in a steel mill can be difficult due to the interactions between the different subsystems. Changes in one unit can lead to several changes throughout the system. A process integration model taking into account the different interactions within the system is presented. The model is based on an optimising routine, making it a total analysis method for the steel plant system including the surroundings. The model is used to analyse the different possibilities for energy savings and practice changes within the system. The effect of optimising the total system versus separate optimisation of the different sub-processes is illustrated. The method development can serve as a benchmark for different steelmaking operations and constitute a basis for the continuous work involved in energy, material or economic analyses for the steel production system.

During the years 2001-2002, a comprehensive study regarding CO2 emissions related to the steel production for the integrated steel making production route, was carried out. The study was financed by SSAB and carried out by a research group with members from SSAB, MEFOS and LTV. The aim was to study the emissions from the existing system and how these could be influenced by process changes and by process modifications. The calculations were made using a global spreadsheet model for calculating the CO2 emissions, developed from an existing energy and process integration model of the same system. The calculated cases included the existing BF/BOF route as well as integration of other processes, e.g., an electric arc furnace, DR processes, COREX and a new future smelting reduction process concept (Sidcomet). All new existing alternative ore based process technologies would increase the specific CO2 emission from the system. A technology transfer to scrap based metallurgy would significantly decrease the emission level, but is not feasible for SSAB, due to the future product mix and the structure of scrap availability. In a 5-20 year perspective, the existing steel making process route with the use of magnetite ore for pellet production has the lowest specific CO2 emission. In a long-term perspective, 20-50 years, alternative process routes, e.g., based on H2 and DRI, could be of interest. Studies on such changes are, however, big projects and should be carried out as joint European and/or international efforts

The coke oven plant has a central role in the iron and steel making process in an integrated steel plant. The subject of this research is to study how the production and energy system at the steel industry, with a connected combined heat and power plant, is affected by renovation of the coke oven. The aim is to investigate the interaction between the different processes and how the choice of system boundary affects the operation practice for the steel plant. MILP-based optimization models have been developed and used for the evaluation. The analysis shows that it is very important to take the interactions between the different production units in the system into consideration when making the analysis. A system optimization with a boundary including the whole system has a greater potential for minimizing the total system cost than one that only includes the processes where the actual changes are made. Conclusions are also drawn regarding the production practice for the specific system

The steel industry has faced several challenges during the years. There has always been an aspiration towards higher economic profitability for the system. During the mid 1970s and 1980s the energy crises caused a dramatic rise in energy costs, which led to an increased awareness in energy conservation. In recent years, climate change issues have become more important for the industry. The operating practises for an industrial system are often affected by external restrictions concerning the economical, energy and environmental efficiency of the system. There are a large number of ways to increase the system efficiency, e.g. installation of new process equipment, and practice changes. However, industrial systems such as an integrated steel plant consist of a system of several processes connected together with product and by-product interactions, where changes in one unit may result in changes throughout the total system. A process integration method focusing on the total integrated steel plant system by a simultaneous approach is adopted. An optimisation model is developed and used to study the effect of changes in the existing material and energy system. Applications of the model on the energy and material system have been made. The model can be used to analyse energy, environmental and economic aspects making it a powerful complement as a decision making tool. Conclusions about energy, environmental and economic effects are presented.

Residue materials generated in the metallurgical industry have gained an increasing importance, both from the points of view of energy and material supply. A joint process integration model for the integrated steel plant system is developed and used in this paper. It takes into account both residue materials and energy recirculation for the system. The potential for increased recirculation and the effect on the system from an environmental point of view is presented, and implementations and practical experiences are discussed. The model developed can serve as a benchmark for different steelmaking operations and constitute a basis for the continuous work involved in material, energy, environment or economic analyses for the steel production system.

One third of the total steel production in the world today is produced by electrical steel making and is supposed to increase. It is a very energy intense process but for the production costs the scrap mix is nowadays clearly the most dominating cost factor. Because the ingoing raw material mix affects the energy consumption and the chemistry of the final product it is an important factor to control. A system optimization model for a generalized electric steelmaking plant has been developed. The vision has been to include a planned production sequence and a dynamic scrap stock level along with a full material- and energy balance connected to the processes. This gives the opportunity to run optimizations with restrictions similar to real production conditions. The generalized steelmaking plant produces hot rolled coils and five main processes are included in the model; a material pre-treatment process, an electric arc furnace, a ladle furnace, a continuous casting process and a hot rolling mill process. To estimate the chemical composition of the ingoing scrap grades, a regression model has been made based on process data from a Höganäs Sweden AB plant. Mixed Integer Linear Programming (MILP) has been used as the method for modeling the production system. Simulations and optimizations have been focused on changes in the chemical composition of certain scrap grades, restrictions of the availability of scrap grades and restrictions regarding the forecasted production sequence. The objectives used for the optimizations are production costs and total energy consumption. The model deliveries results in form of optimal raw-material mixes for the different steel grades defined in the model, optimal energy mix and optimal target temperatures for the sub-processes. Further it shows the effect on process parameters such as energy consumption, slag amount, off gas generation, injected carbon and oxygen etc. The model makes it possible to simulate scenarios that are expected for the future regarding new steel grades, availability of raw-materials and changed amount of tramp elements in the raw material used today. It is a good tool to find an optimal solution not only for a single heat but for a sequence of heats with varying chemical specifications

Residual steel work gases are often utilised internally at the steel plant as a fuel and as well as for heat- and power production in heat recovery steam boilers located near the steel mill. This study aims to investigate the technical and economic consequences to use the coke oven gas (COG) to produce methanol (MeOH) to be used as automotive fuel. In a case study of a steel mill located in the northern Sweden, SSAB Tunnplåt AB in the town of Luleå, four different production processes have been studied. Two of them only use COG as a fuel, while the other two systems also use biomass based synthesis gas to blend with the COG. The results show that nearly 300 GWh of MeOH could be produced annually from COG only to a production cost in the range of €0.13 to €0.26 per litre MeOH. If also 420 GWh per year of biomass for synthesis gas production is supplied and the gas blended with the COG totally 570 GWh of MeOH can be produced annually to a similar production cost range. The main conclusion is that MeOH can be produced to a competitive cost independent of production system. Turning a steel mill into a refinery may also result in other benefits, such as better energy storage possibilities and increased incentives to utilise residual heat currently not motivated to make use of.

Off-gases generated during steelmaking are to a large extent used as fuels in process units within the plant. The surplus gases are commonly supplied to a plant for combined heat and power production. The main objective of this study has been to techno-economically investigate the feasibility of an innovative way of producing methanol from these off-gases, thereby upgrading the economic value of the gases. Cases analyzed have included both off-gases only and mixes with synthesis gas, based on 300 MWth of biomass. The SSAB steel plant in the town of Luleå, Sweden has been used as a basis. The studied biomass gasification technology is based on a fluidized-bed gasification technology, where the production capacity is determined from case to case coupled to the heat production required to satisfy the local district heating demand. Critical factors are the integration of the gases with availability to the synthesis unit, to balance the steam system of the biorefinery and to meet the district heat demand of Luleå. The annual production potential of methanol, the overall energy efficiency, the methanol production cost and the environmental effect have been assessed for each case. Depending on case, in the range of 102,000–287,000 ton of methanol can be produced per year at production costs in the range of 0.80–1.1 EUR per liter petrol equivalent at assumed conditions. The overall energy efficiency of the plant increases in all the cases, up to nearly 14%-units on an annual average, due to a more effective utilization of the off-gases. The main conclusion is that integrating methanol production in a steel plant can be made economically feasible and may result in environmental benefits as well as energy efficiency improvements.

Some elements in the raw materials used in iron- and steelmaking make it difficult to maintain or further improve the steel quality, but also adversely affect the composition of generated slags and other materials, thereby reducing their potential for internal recycling and/or other utilisation.A Process Integration (PI) approach was taken to analyse the dependence of the properties of a specific metallurgical slag on individual processes as well as on the interaction between processes. Analyses were made of how to obtain maximum usage of metallurgical slags without compromising the quality of the main product, i.e. crude steel. Based on a real case scenario, a number of approaches were studied with regard to the quality demands for maximised use of slags. The effects of changes in raw materials on blast furnace (BF) and basic oxygen furnace (BOF) processes were investigated. Altered composition of the raw materials affects material and BF reductant rate, generated slag amounts, slag recycling and material compositions, etc. In this study special attention was directed towards the magnesium oxide (MgO) contents in BF and BOF slags and, subsequently, the effects on phosphorus (P) refining in the BOF.The analysis of system effects of changed quality of lime raw material, i.e. limestone and consequently on-site produced burnt lime, show that an increased MgO content raises the MgO level, exceeding the set maximum permissible MgO content in both the BF and the BOF slag. The increased MgO content in burnt lime charged to the BOF will have a strong negative effect on the P refining capacity of the slag; therefore, burnt lime with an increased MgO content cannot be used without taking further measures if maximum P refining is required.Based on the results of the analysis, a number of approaches were further investigated in order to identify methods to preserve or decrease current MgO levels in generated slags and maintain, or further improve, slag utilisation potential without compromising the liquid steel (LS) quality. Analysed strategies were: diluting the MgO content in the BF slag by increased slag rate, decreased BOF slag recycling to the BF, increased P tolerance in BF produced hot metal (HM), lower MgO content in pellet mix or decreased use of dolomitic lime in the BOF. The most efficient approach to markedly increase the BOF slag recycling rate and simultaneously maintain the prerequisite MgO content in BF slag and LS quality is by increasing the tolerance of P in hot metal while at the same time excluding dolomitic lime in the BOF.

Vanadium in raw materials used in iron- and steelmaking, a particular challenge for Nordic steel producers, affects the composition of the generated slag from the steelmaking vessel, i.e. the basic oxygen furnace (BOF) adversely and reduces the potential for recycling and external utilisation. A process concept under development aims to enrich and extract the vanadium content of slag from the BOF, making use of the vanadium in the slag and also increasing the overall slag use potential. Applications of this concept affect slag compositions and internal material flows in the iron and steel production system, especially when recycling BOF slags as flux in the blast furnace (BF). This paper will present a case study, based on a Process Integration (PI) approach, using a designated system model to simulate the steel production system and the implementation of the process concept, thereby analysing how to obtain maximum usage of metallurgical slags without compromising the quality of the main product, i.e. liquid steel. Different approaches were studied to improve the environmental sustainability in the production system by maximising the material efficiency through vanadium recovery (as FeV alloy) and the use of slags, thereby minimising the stored/deposited slag amounts.

This paper focuses on the optimisation of a recovery strategy for waste materials and thereby improved material efficiency in the iron and steel industry. A joint venture between four Nordic steel plants is considered in order to recycle materials otherwise mainly put to landfill, i.e. dusts and sludges from the steel production processes. Process integration (PI) was used to investigate the possibilities for recovering the materials by developing a system optimisation model of the steel plants and integrating a dedicated material upgrading process in the system. This work aims to develop a model suitable for analysing and finding a logistic solution needed to achieve a common recycling system by studying material supply, required material storage, shipping system and shipping frequency. The developed optimisation model is presented, using a case study of the steel production plants with the dedicated upgrading process and the logistics system. The prospect for shipping materials from the steel production sites to the material upgrading process site as well as the material supply to the upgrading unit is essential in the system analysis. A mathematical optimisation model based on mixed-integer linear programming (MILP) for the common system is presented. The integration of the dedicated material upgrading process show a system in balance regarding the materials generated and processed in the upgrading unit. Generated material amounts suitable for the upgrading process can be fully recovered thereby decreasing the landfilled amounts from the four steel production sites.

An industrial energy system is subject to different regulations and restrictions. Good integration between units within the production chain as well as integration with the community can lead to both environmental and energy savings. Process integration is a system oriented methodology to analyze whole production systems to find optimal system changes. A mathematical programming technique is being developed for the Swedish iron ore producing facility of LKAB in Malmberget. The mathematical model will be based on a mass and energy balance for the facility specified for the different unit operations. The development of a good mathematical model requires a systematic mapping of the energy and material flows within an iron ore producing facility. In this paper a conceptual model for the process integration tool is described.

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

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.

In integrated steelmaking there are a number of means to reduce CO2 emissions. One approach is to increase the metallic Fe input to the production system. A common belief is that scrap works as a CO2 diluent when introduced in iron ore based steelmaking. It is not necessarily so. Scrap is a key supplementary charge material in oxygen steelmaking converters, but scrap can also be utilised in ironmaking where it will decrease the use of reducing agents and with that also the specific CO2 emissions. By the use of a process integration model which basically includes the primary processes of cokemaking, sintering, ironmaking and oxygen steelmaking the overall influence of scrap input on CO2 emissions is demonstrated and commented. The influence of hot metal silicon content is elucidated by calculations with different material and process constraints. The results show that at moderate scrap rates, the reduction of CO2 emissions is favoured by increased scrap additions to the oxygen converter. When the scrap additions to the converter balances the actual heat capacity of the bath, other means to achieve an increased scrap melting capacity can be taken into account. This include combinations of scrap addition to the blast furnace, increased silicon content in tapped hot metal, and/or addition of Ferro-silicon combined with further scrap additions to the oxygen converter. Different strategies for CO2 emission reduction have to be suggested depending on if the objective is to minimise the site (direct) emissions or the global (indirectdirect) emissions.

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.

With oxygen enrichment in hot stoves (HS) the high calorific coke oven gas can be saved due to the possibility of using lower calorific gases which enables replacement of other imported fuels such as oil or LPG. The application of oxygen enrichment in hot stoves or increased O2 content in the blast to the blast furnace (BF), will also potentially lead to lower coke rate. The demand for coke oven gas depends on internal operation logistics and it also has outdoor temperature dependence through a heat and power plant producing district heat to the community. An analysis of the influence of increased oxygen enrichment in HS-BF on the entire energy system has been carried out by using an optimization model. A method of achieving a high time resolution in MILP optimisation is applied in the analysis. Different strategies have been suggested for minimum energy consumption at the studied steel plant and the nearby combined heat and power (CHP) plant. Central to the performance in system optimisation is the ability to analyse and properly describe the system variations.

In this paper a new method for increased time resolution in multi-period Mixed Integer Linear Programming (MILP) optimisation is presented and applied to a district heating system. The proposed method facilitates the analysis of many time periods in multi period MILP optimisation projects. In the paper, a 365 time period model spanning 1 year developed with the novel method is compared to a 12 time period model developed with a more conventional methodology. The new method offers a significant decrease in the amount of input data for multi period models and facilitates changes to the analysed time span or resolution in time. In the application of the new method oil savings of 7% compared to the current operational strategy of the district heating system are revealed.

It is crucial for a steel making production system to operate at the lowest possible production cost, while satisfying stability and reliability conditions. To plan future production strategies, it is therefore important to be able to model the system behaviour when internal and external parameters are changed. In this study the sensitivity and stability of an optimised solution, of an integrated steel plant, have been investigated. The solution's sensitivity has been analysed taking both internal process changes and external price variations into account, through applying both simulation and optimisation. The analysis also includes both costs and environmental issues such as carbon dioxide and sulphur emissions. Based on the methodology suggested, it is possible to determine the stability of the system solution, including both economic and environmental performance.

The implementation of the EU Emission Trading Scheme ( ETS) started on January 1(st) 2005 according to national plans for allocating emissions rights. The steel industry is one of the industrial sectors included in this scheme. The objective of this paper is to investigate and evaluate the optimum solution( s) for European steel plants to meet their emission allowance with low reduction cost. An optimization model based on a Swedish steel plant is developed and used. Three scenarios were created in the model, i. e., internal changes within the steel plant, EU ETS, and the Kyoto Protocol's clean development mechanism ( CDM). For the last scenario, China was selected as a country of the non- Annex I Party for the emission trading by CDM. The modeling results show that the studied plant will face an emission gap between allowed and calculated emissions in the near future. Compared to EU ETS, the implementation of CDM projects will make the plant reduce CO2 emissions at a lower cost. The internal changes within the plant will also play an important role for the solution of low abatement cost. The model developed could serve as a benchmark for the future emission trading simulation's purpose within the European steel industry.

This study is to investigate different types of biomass products’ injection into the blast furnace (BF) to replace pulverized coal injection (PCI). The biomass products covered in the study are charcoal, torrefied material and wood pellets on the basis of Swedish forests. The modelling work has been performed in a specialized BF model. The modelling results show that charcoal has the significant effects on the BF operation. PCI can be replaced fully by charcoal, and only limited amount of torrefied material and wood pellets can be injected into BF. For the studied BF, the annual CO2 emission reduction potential from the replaced amount of PCI when injecting charcoal, torrefied material and wood pellets are about 1140 kton, 260 kton and 230 kton, respectively. In addition, a possible energy saving can be achieved for charcoal injection. A slightly higher P content in the hot metal may occur when injecting torrefied material

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.

We have investigated and modeled the injection of biomass into blast furnaces (BF), in place of pulverized coal (PC) from fossil sources. This is the easiest way to reduce CO2 emissions, beyond efficiency-improvements. The considered biomass is either pelletized, torrefied or pyrolyzed. It gives us three cases where we have calculated the maximum replacement ratio for each. It was found that charcoal from pyrolysis can fully replace PC, while torrefied material and pelletized wood can replace 22.8% and 20.0% respectively, by weight.Our energy and mass balance model (MASMOD), with metallurgical sub-models for each zone, further indicates that (1) more Blast Furnace Gas (BFG) will be generated resulting in reduced fuel consumption in an integrated plant, (2) lower need of limestone can be expected, (3) lower amount of generated slag as well, and (4) reduced fuel consumption for heating the hot blast is anticipated. Overall, substantial energy savings are possible, which is one of the main findings in this paper.Due to the high usage of PC in Sweden, large amounts of biomass is required if full substitution by charcoal is pursued (6.19 TWh/y). But according to our study, it is likely available in the long term for the blast furnace designated M3 (located in Luleå).Finally, over a year with almost fully used production capacity (2008 used as reference), a 28.1% reduction in on-site emissions is possible by using charcoal. Torrefied material and wood pellets can reduce the emissions by 6.4% and 5.7% respectively. The complete replacement of PC in BF M3 can reduce 17.3% of the total emissions from the Swedish steel industry.

LKAB Malmberget is a Swedish mining site located at Malmberget, Sweden. Seven boiler centers are located in the north part of Malmberget. There are no connections in between these boiler centers, meaning that it is a decentralized heating system. The heat generated is used to heat up buildings and for mine ventilation air mainly during the cold periods. The heat is mainly provided from electric and oil boilers. However, most boilers under use are over 20 years old, and it is time to retrofit the boiler system and infrastructure. The purpose of this work is to design and optimize the heating system by introducing an integrated concept to minimize the heat production cost.An optimization model based on the mixed integer linear programming (MILP) has been developed. Several technical options have been considered in a new centralized heating system. The optimization principle is based on two kinds of perspectives: current price and external costs. With consideration of environmental and health damage from society concerns point of view, instead of environmental taxes in the current price perspective, the monetary values of externalities due to pollutants such as CO2, NOx, SO2 and particulates emitted from the heating system are included. On the basis of data input and assumptions, modeling results indicate that a lower cost could be achieved when a waste heat recovery boiler is installed at the older pelletization plant to recover sensible heat from flue gas. This technical option is the best solution or at least contributes to the best solution in all optimization results. Including the externality cost is useful for making fair evaluation of the social-environmental impacts of the alternatives.

With oxygen enrichment in hot stoves the high calorific coke oven gas can be saved due to the possibility of using lower calorific gases which enables replacement of other imported fuels such as oil or LPG. The application of increased oxygen use in hot stoves or increased O2 in blast, will also potentially lead to lower coke rate. Central to the performance in system optimisation is the ability to analyse and properly describe the system variations. The demand for coke oven gas is depending on both internal operation logistics but it also has outdoor temperature dependence through a heat and power plant producing district heat to the community. An analysis of the influence of increased oxygen enrichment on the entire energy system has been carried out by use of an optimization model. A method of achieving a high time resolution in MILP optimisation is applied in the analysis. Different strategies have been suggested for minimum energy consumption at the studied steel plant and the nearby CHP plant.