A Brief Overview of Low CO2 Emission Technologies for Iron & Steel Making

 The global steel production has been growing for the last 50 years, from 200 million metric tons in 1950s to 1,240 million metric tons in 2006. Iron and steelmaking industry is one of the most energy-intensive industries, with an annual energy consumption of about 24 EJ, 5% of the world's total energy consumption. The steel industry accounts for 3-4% of total world greenhouse gas emissions. While enhancing energy efficiency could be a short-term approach for the steel industry to reduce greenhouse gas emission, the long-term approaches to achieve a significant reduction in CO2 emissions from the steel industry would be through (1) developing and applying CO2 breakthrough technologies for iron and steelmaking, and (2) increasing use of renewable energy (in particular, bio-energy) for iron and steelmaking. This paper presents an overview of new CO2 breakthrough technologies for iron and steelmaking, and the current research and development for the use of biomass and bio-fuels as substitutes for coke, coal and natural gas in various iron and steelmaking processes including iron-ore sintering, blast furnace operations, and new iron and steelmaking processes. The key challenges for utilization of bio-energy on a large scale for iron and steelmaking are also discussed in this paper.     

Analysis of CO2 emission and mitigation methods in integrated iron and steel works

CO2 emission of the steel industry takes up a great proportion of the total emission of the world.It is necessary to reduce the CO2 intensity of steel products in order to save energy,protect the environment and keep a sustainable development in the steel industry.Based on the research of steel products’ life cycle inventory,those who conducted this research have focused on the analysis of CO2 emission factors and measures.Adopting the life cycle inventory model of a certain steelmaking site,together with the Tornado Chart,the researchers have identified significant factors,provided some explanation,and suggested some possible measures to reduce CO2 emission.The results have shown that the most important factors are the CO2 intensity of blast furnace gas (BFG), hot metal ratio of basic oxygen furnace (BOF) and the material utilization efficiency.Accordingly,some measures such as removing CO2 in BFG,decreasing the hot metal proportion in BOF,and improve material utilization efficiency in each process,may be taken to decrease CO2 emission.     

The Contribution of Niobium Bearing Steels and Enhanced Sustainability

With the growing concern for the environmental impact of greenhouse gases and the rapid depletion of important resources,the use of Nb-bearing steels for advanced high strength steel applications can reduce raw material usage and the carbon footprint.The conservation and more efficient use of ironmaking and steelmaking raw materials is an urgent issue for steel producers globally.Recently-developed Nb-microalloyed steel applications provide a more effective product design and reduce CO 2 emissions and energy consumption per tonne of steel.A sustainability structural steelstudy presents the positive cost and reduced environmental impact of Nb-microalloyed steels.This analysis compares the CO 2 emission reduction and energy savings in the steelmaking process melted in both the Basic Oxygen Furnace (BOF) and the Electric Arc Furnace (EAF).Nb-microalloyed structural steels offer the opportunity to reduce the total weight of a given structure compared to a non-microalloyed steel construction.Generally,one considers the savings associated with less material and lower construction costs.In addition,there is an environmental benefit in the reduction in emissions (kilograms of CO 2) and less energy consumption (GJ) due to the fact that less steel is melted.Plus,there are lighter sections and less material weight in the final end user design which reduces transportation and fabrication costs.A forecasted trend is presented which introduces an increased usage of microalloyed steel grades to replace traditional commodity-type non-alloyed higher carbon-manganese grades for environmental benefits and significant cost reduction.     

Present situation and development of saving energy and reducing emission technology in iron ore sintering process

The energy consumption of iron ore sintering process is about 10%- 15%of the total of iron and steel industry.Therefore,it is of great significance to take effective measures to reduce the energy consumption in the iron ore sintering process to reduce the costs of sintering product and cut down the emissions of harmful gases,such as CO₂ and SO₂.In this study,the technology development of saving energy and reducing emission in iron ore sintering process was reviewed and discussed;some new directions and measures of saving energy were presented for the sintering process in the future.     

Parameters Affecting Energy Consumption for Producing High Carbon Ferromanganese in a Closed Submerged Arc Furnace

The power consumption is considered to be the most important factor affecting the production cost of fer romanganese alloy. Different parameters affecting the energy consumption for industrial production of high carbon ferromanganese HCFeMn were investigated in a closed submerged arc furnace. The analysis of industrial data revealed that the most energy consumed factors were the direct reduction by solid carbon, Boudouard reaction, metal and slag formation, and decomposition of fluxing materials （limestone and dolomite）. To reduce the energy con- sumption and minimize the energy losses in the production process of HCFeMn, it was recommended to use Mn blend with minimum Mn to Fe ratio of 6 and lower SiO2 content or higher basicity. The added coke must be adjusted according to the material balance to prevent the over-coke and to minimize the highly endothermic ＂Boudouard reac tion＂. In addition, it was recommended to work at basic slags with the ratio of （CaO＋MgO） to Si（）2 equal to 1.0- 1.2 instead of much higher slag basicity. Furthermore, the mass losses had to be minimized through adjusting the handling and charging process and to take care of all metal produced.     

Modeling and Optimization for Piercing Energy Consumption

 Energy consumption is an important quality index in the production of seamless tubes. The complex factors affecting energy consumption make it difficult to build its mechanism model, and optimization is also very difficult, if not impossible. The piercing process was divided into three parts based on the production process, and an energy consumption prediction model was proposed based on the step mean value staged multiway partial least square method. On the basis of the batch process prediction model, a genetic algorithm was adopted to calculate the optimum mean value of each process parameter and the minimum piercing energy consumption. Simulation proves that the optimization method based on the energy consumption prediction model can obtain the optimum process parameters effectively and also provide reliable evidences for practical production.     

Heat Transfer and Energy Analysis of a Pusher Type Reheating Furnace Using Oxygen Enhanced Air for Combustion

 Oxy-fuel firing is more energy efficient and environmental friendly than conventional air-fuel firing and its application for reheating furnaces has begun since 90s. In this study, a computational methodology is presented to predict the steady heat transfer to the billets and temperature distribution in a continuous Pusher type reheating furnace which combustion air is enhanced by oxygen. The furnace is modeled as 2D radiating medium and Weighted Sum of Gray Gases model is used for absorption coefficient. The billets are moved in constant speed through zones of furnace. Radiative heat flux calculated from the radiative heat exchange within the furnace is modeled using the FVM considering the effects of furnace walls and billets. Energy consumption per ton of steel, production rate and thermal efficiency of furnace, and trend of NOx emission in various levels of oxygen enrichment is investigated by comparison with baseline furnace (21% O2 in air).     

Calculating Method for Influence of Material Flow on Energy Consumption in Steel Manufacturing Process

 From the viewpoint of systems energy conservation, the influences of material flow on its energy consumption in a steel manufacturing process is an important subject. The quantitative analysis of the relationship between material flow and the energy intensity is useful to save energy in steel industry. Based on the concept of standard material flow diagram, all possible situations of ferric material flow in steel manufacturing process are analyzed. The expressions of the influence of material flow deviated from standard material flow diagram on energy consumption are put forward.     

Simulation of Thermal Insulation of Top-Surface Slag Layers in Continuous Casting Mold

 A computational model of thermal behavior of the top-surface slag layers in continuous casting mold was applied to interpret the thermal insulation of mold powder. The temperature drop of liquid steel caused by heat removal at the interface of molten steel and slag in mold was proposed to evaluate the thermal insulation of mold slag. The calculation results show that slag consumption is one of important factor influencing the temperature drop, while the casting speed has no obvious effect on it. With the increase of slag consumption, the temperature drop is increased.     

Sulfur Flow Analysis for New Generation Steel Manufacturing Process

Sulfur flow for new generation steel manufacturing process is analyzed by the method of material flow analysis, and measures for SO2 emission reduction are put forward as assessment and target intervention of the results. The results of sulfur flow analysis indicate that 90 % of sulfur comes from fuels. Sulfur finally discharges from the steel manufacturing route in various steps, and the main point is BF and BOF slag desulfurization. In sintering process, the sulfur is removed by gasification, and sintering process is the main source of SO2 emission. The sulfur content of coke oven gas （COG） is an important factor affecting SO2 emission. Therefore, SO2 emission reduction should be started from the optimization and integration of steel manufacturing route, sulfur burden should be reduced through energy saving and consumption reduction, and the sulfur content of fuel should be controlled. At the same time, BF and BOF slag desulfurization should be optimized further and coke oven gas and sintering exhausted gas desulfurization should be adopted for SO2 emission reduction and reuse of resource, to achieve harmonic coordination of economic, social, and environmental effects for sustainable development.     

A Novel Method of Recycling CO_2 for Slag Splashing in Converter

 Converter off gas, an important energy resource for steel enterprises is one of the weak points in the recovery and utilization of secondary energy resources. To improve the level of recycling converter off gas in steel plants, a novel approach to recycle CO2 separated from converter off gas or other off gas for the green slag splashing technique was developed, and the CO2 equilibrium conversion ratio of the green CO2 slag splashing in different technological conditions was calculated by HSC software. Furthermore, the experiments of CO2 injected into melting converter slag were carried out, and the influence factors of the green CO2 slag splashing technique were analyzed. The results showed that the carbon amount for smoothly CO2 slag splashing was about 4.0%.     

Relationship Between Grain Boundary Segregation of Antimony and Temper Embrittlement in TitaniumDoped Nickel-Chromium Steel

 The observations given by Ohtani et al are analyzed in the present paper and it is concluded that the kinetics of temper embrittlement in titanium-doped low carbon NiCr steel agree well with those of non-equilibrium grain-boundary segregation of Sb. Besides, the mechanism of non-equilibrium grain-boundary segregation of Sb is determined to be the most satisfactory one among the existed mechanisms in the literature to interpret the Sb-induced embrittlement kinetics in the NiCr steel. Based on the conclusion and the determination, the activation energy and frequency factor of diffusion of Sb-vacancy complexes are obtained for the first time according to the concept of critical time in non-equilibrium grain-boundary segregation theory. The calculated results can give theoretical basis for predicting and controlling over the Sb-induced embrittlement in steels.     

A novel process of preparing glass-ceramics directly from molten steel slag

A novel process technology to prepare glass-ceramics directly from molten steel slag(MSS) is proposed in the study.The liquid-solid mixing method was used to adjust the components of the MSS and glass-ceramics was obtained.The effects of heat-treatment conditions on the microstructure,physical and mechanical properties of samples were studied.Economical benefits of the novel process were analyzed.The results show that heat-treatment is a very effective approach to achieving crystallization.The dominant crystal phase in products is diopside [(Mg6Al2Fe2)Ca(Si1.5Al5)O2].The shape of the crystallization is like a granule.The glass-ceramic samples exhibited good mechanical properties and presented chemical stability.The economic benefits of the process are remarkable due to less energy consumption compared with conventional glass-ceramics production methods.     

Application of the DHCR technology in Ningbo Steel

This paper presented the application of the direct hot charge rolling (DHCR) technology in Ningbo Steel.Five aspects have been systematically addressed and analyzed,which include sales order,production schedule programming,steelmaking,continuous casting and hot-rolling.The average DHCR product rate has reached 55% and the average slab charging temperature 699℃.As a result,the production cost,the energy consumption and the CO2emission have been significantly reduced.It is concluded that a breakthrough in application of the DHCR technology has been achieved at Ningbo Steel.     

Final Temperature Prediction Model of Molten Steel in RH-TOP Refining Process for IF Steel Production

 In order to precisely control the final temperature of molten steel in RH (Ruhrstahl Heraeus)-TOP blowing refining, the final temperature prediction models of molten steel in RH-TOP blowing refining process for Interstitial Free (IF) steel production were established under the condition of oxygen blowing and non-oxygen blowing respectively. The results show that the beginning molten steel temperature of refining and the amount of added scrap were influential factors, the baking temperature in vacuum chamber was a factor that had small influence. When the model was operated, the hitting probability was above 95% (under the condition of both oxygen blowing and non-oxygen blowing) of prediction deviation of ±10 ℃. The accuracy is analyzed.     

Potentials for Saving Energy and CO2-Emission Through the Use of EPM Technologies

The paper demonstrates how electromagnetic processing of materials(EPM)provides significant opportunities for saving primary energy and reducing carbon emissions in industrial thermal processes.Potentially electricity can replace up to 100%of other energy carriers currently used for process heat.For the time horizon from now to the year2050 a transition scenario is developed and described.In this scenario the industrial processes are gradually switched from the actual situation to a situation with 100%electrically operated industrial processes.The developed scenarios take into account the most energy intensive industrial thermal processes,which could be replaced by electrothermal technologies and offer obviously the biggest future potential in terms of saving of primary energy and reducing of carbon emissions.As the average primary energy factor(PEF)gradually decreases from 2.5 currently,to 1 for a 100%renewable electricity system,the benefits of EPM will gradually increase.For each step in the development of the PEF the annual primary energy savings and annual reductions in greenhouse gas emissions are calculated and described in this paper.     

Steel Temperature Compensating Model With Multi-Factor Coupling Based on Ladle Thermal State

 Combined with the parameters of the production process of a steel factory, numerical simulations for a new ladle from preheating to turnover are conducted using the finite element analysis system software (ANSYS). The measured data proved that the simulated results are reliable. The effects of preheating time, thermal cycling times, and empty package time on steel temperature are calculated, an ideal preheating time is provided, besides, based on the analysis of a single factor and use the nonlinear analysis method, a steel temperature compensating model with diversified coupling factors is proposed, with the largest error of the present coupling model at 1462 ℃, and the errors between actual and target steel temperature in tundish after the model is applied to practical production are basically controlled within ±6 ℃, which can meet the accuracy of the manufacturer and has a practical guiding significance for the production in steelmaking workshops.     

On-line Ladle Lining Temperature Estimation by Using Bounded Jacobian Nonlinear Observer

The knowledge of transient temperature of the ladle wall is a key factor in optimizing energy consumption in steelmaking process.The transient temperature needs to be estimated.A nonlinear lumped parameter model was used to model the thermal dynamics of the ladle.Then,the bounded Jacobian nonlinear observer was utilized to esti-mate the temperature.With this method,the estimation model became a closed-loop model and the observer gains were obtained by solving linear matrix inequalities and simply implemented to the system.Comparison between the simulation and recorded data at a participating steel plant in Thailand showed that the nonlinear observer accurately estimated the temperature of the ladle lining.This estimated temperature was very useful in determining suitable tap-ping temperature for energy conservation and steel quality.     

Multi-Period Optimal Distribution Model of Energy Medium and Its Application

 A mathematical model of optimal energy medium distribution in steelmaking process is formulated. In this model, three kinds of important energy mediums including byproduct gases, steam and electricity are considered, and the objective function accounts for both the change of generation and consumption of the byproduct gases and the demand of low (or middle) pressure steam and electricity for each period to maximize the benefit of products cost and minimize the consumption of energy. The results indicate that the optimal distribution scheme of byproduct gases, middle pressure steam, low pressure steam and electricity is achieved and case study shows that 6% of operation cost is reduced by using the proposed model comparing with the previous model.     

Effect of Heat Input on Fume Generation and Joint Properties of Gas Metal Arc Welded Austenitic Stainless Steel

 The effect of heat input on fume and their compositions during gas metal arc welding (GMAW) of AISI 316 stainless steel plates are investigated. Fume generation rate (FGR) and fume percentage were determined by ANSI/AWS F12 methods. Particle characterization was performed with SEM-XEDS and XRF analysis to reveal the particle morphology and chemical composition of the fume particles. The SEM analysis reveals the morphology of particles having three distinct shapes namely spherical, irregular, and agglomerated. Spherical particles were the most abundant type of individual particle. All the fume particle size falls in the range of less than 100 nm. Mechanical properties (strength, hardness and toughness) and microstructural analysis of the weld deposits were evaluated. It is found that heat input of 115 kJ/mm is beneficial to weld stainless steel by GMAW process due to lower level of welding fume emissions and superior mechanical properties of the joints.