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.
Environmental concerns lead industries to implement gasified biomass (syngas) as a promising fuel in steel reheating furnaces. The impurities of syngas as well as a combination with iron oxide scale form complex mixtures with low melting points, and might cause corrosion on steel slabs. In this paper, the effects of syngas impurities are thermodynamically investigated, when scale formation on the steel slabs surface simultaneously takes place. A steel reheating furnace can be divided into preheating, heating, and soaking zones where the temperature of a steel slab changes respectively. Therefore, the thermodynamic calculation is performed at different temperatures to predict the fate of impurities. Then, the stable species are connected with respective zones in a reheating furnace. It is concluded that reactions due to alkali compounds, chloride, and particulate matter could take place on steel slabs. In the low temperature range, interaction of sodium chloride occured with pure iron prior to scale formation. Then, at high temperature the reactions of impurities are notable with iron oxides due to scale growing. Furthermore, the multicomponent reactions with syngas impurities showed that most of alkali contents evaporate at first stages, and only small amounts of them remain in slag at high temperature.
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.
The hemicelluloses fraction of black liquor is an underutilized resource in many chemical pulp mills. It is possible to extract and separate the lignin and hemicelluloses from the black liquor and use the hemicelluloses for biochemical conversion into biofuels and chemicals. Precipitation of the lignin from the black liquor would consequently decrease the thermal load on the recovery boiler, which is often referred to as a bottleneck for increased pulp production. The objective of this work is to techno-economically evaluate the production of sodium-free lignin as a solid fuel and butanol to be used as fossil gasoline replacement by fractionating black liquor. The hydrolysis and fermentation processes are modeled in Aspen Plus to analyze energy and material balances as well as to evaluate the plant economics. A mathematical model of an existing pulp and paper mill is used to analyze the effects on the energy performance of the mill subprocesses.
The melt stratification phenomenon, which results from the natural convection in ladles holding molten steel, is of fundamental importance for the temperature control in the continuous casting process. The progressively increasing stress on the quality of continuously cast products necessitates much tighter tundish temperature control, which in turn will require a more precise definition of the extent of melt temperature stratification in ladles. For this reason, ladle melt stratification phenomena were studied both by numerical simulations, using the PHOENICS package, and by plant measurements at SSAB Tunnplat AB's steelworks in Lulea. The parameters studied in the numerical simulations were the fluid flow velocity field, the temperature distribution field, ladle initial heat content and height to diameter ratio of ladles. One of the important boundary conditions that was used in these numerical simulations was the time and geometry-dependent heat loss rate through the ladle walls, which is the major cause of the natural convection. This transient boundary condition was obtained from the temperature simulation model TempSim. Steel temperatures measured at different positions along the ladle height are compared in the paper with results from the numerical calculations. The possibility of expressing the stratification with a simple formula was discussed. However, to propose this model for industrial use, experimental verification with prolonged holding time is needed.
The melt stratification phenomenon, which results from the natural convection in ladles holding molten steel, is of fundamental importance for the temperature control in the continuous casting process. The progressively increasing stress on the quality of continuously cast products necessitates much tighter tundish temperature control, which in turn will require a more precise definition of the extent of melt temperature stratification in ladles. For this reason, ladle melt stratification phenomena were studied both by numerical simulations, using the PHOENICS package, and by plant measurements at SSAB Tunnplat AB's steelworks in Lulea. The parameters studied in the numerical simulations were the fluid flow velocity field, the temperature distribution field, ladle initial heat content and height to diameter ratio of ladles. One of the important boundary conditions that was used in these numerical simulations was the time and geometry-dependent heat loss rate through the ladle walls, which is the major cause of the natural convection. This transient boundary condition was obtained from the temperature simulation model TempSim. Steel temperatures measured at different positions along the ladle height are in the paper compared with results from the numerical calculations. The possibility to express the stratification with a simple formula was discussed. However, to propose this model for industrial use, experimental verification with prolonged holding time is needed.
This paper presents a three-dimensional numerical model simulating fluid flow, heat transfer and concentration distribution in 105t steel ladles before and during casting. The model was developed by combined implementation of a numerical simulation package, TEMPSIM, and a computational fluid dynamics (CFD) simulation package, PHOENICS. In this study, TEMPSIM was used to calculate the heat transfer in ladle linings and predict the heat losses from the steel melt to the linings which are transient and sensitive to ladle configurations. These data were used as input into PHOENICS for CFD modeling of fluid flow and heat transfer as well as transport of six tracer elements in steel bath in the ladle. The modeling results were compared with concentrations measured in an industrial experiment where six tracer elements were added at different positions in the ladle and at different times before and during casting. With the use of this model, the stratification phenomenon and the effect of drainage flow, as well as the behavior of added tracer elements, in the steel ladle during the casting period, were described and discussed.
Numerical experiments were performed on fluid flow and heat transfer in 107-tonne steel ladles by 3-step implementations of numerical models. In the first step, a 1-dimensional numerical model was used to predict heat conduction fluxes through the ladle wall, bottom and top slag layer. In the second step, by means of computational fluid dynamics (CFD) modelling and employing the predicted heat loss fluxes as thermal boundary conditions, a 2-dimensional CFD model was applied to simulate natural convection in steel ladles during the holding period before teeming. In the third step, a 3-dimensional CFD model was implemented to further simulate fluid dynamics in the same ladles with drainage flows during teeming. Using these mathematical numerical models, the bulk cooling rate of the steel melt, the extent of thermal stratification during holding and the steel stream temperature during teeming were investigated for 2 types of 107-tonne steel ladles lined, respectively, with alumina and spinel in walls. In these investigations, the following 4 parameters were considered: (i)ladle lining inside surface (hot-face) temperature before tapping, (ii)top slag layer thickness, (iii) holding time and (iv) teeming rate. An important result of these investigations is that the concerned parameters all significantly influence the steel stream temperature during teeming, and the differences in teeming stream temperatures among different ladles, caused by these parameters, can be up to 20 deg C, which may be essential to temperature control in tundishes during continuous casting.
Pinch analysis originated at UMIST in the 1970's. It has since then been used as a method for energy analysis and optimisation of industrial systems. The blast furnace process for reducing iron oxide to molten iron is a very important process unit in the metallurgical industry. It is a counter-current shaft process with a wide temperature range and gaseous, solid and liquid phases present in different zones. Because of this the blast furnace acts as a system of different sub-processes rather than a single process. The analysis tools developed to describe the process are in some respects similar to the tools of pinch analysis. The exchange between the two fields of knowledge has yet been negligible. In this paper the methods are described and compared. Problems, possibilities and advantages with an exchange and synthesis of knowledge are discussed.
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
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 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.
Steel production is one of the energy intensive industries in the world. Energy saving measures are of increasing interest to Chinese steel industry in recent years. One of the technical instruments of energy saving is energy audit. This paper presents the energy audit analysis of integrate steel plants in China as a case study. The analysis is useful to determine the actual consumption, reveal the anomalies and suggest corrective measures. These will provide clear indication on the pattern of energy losses and will aid in decision support for evolution of energy saving measures. The paper will show the achievements of Chinese steel plants during these years of energy saving activities proposed by government and the potential for energy efficient renovation. Some suggestion has been made in order to widely use this analytical diagnostic tool in Chinese steel industry.