Mathematical Modeling of the Energy Consumption and Carbon Emission for the Oxygen Blast Furnace with Top Gas Recycling

The ironmaking process is the most significant source of CO₂ emission in the iron and steel industry, which generates large quantities of greenhouse gases. Recently, oxygen blast and top gas recycling have been applied to the blast furnace to improve the energy efficiency and reduce the pollution from the ironmaking process. However, as a new ironmaking technology, the oxygen blast furnace with top gas recycling (TGR‐OBF) is still under development. This paper focuses on the investigation of the energy consumption and carbon emission for the TGR‐OBF process by modeling the stack, the bosh, the combustion zone, and the gas recycling system. Effects of the key parameters in the TGR‐OBF process on the carbon consumption of reactions and the energy consumption of the system are investigated by orthogonal experiments. Our results indicate that the TGR‐OBF process has the advantages of reducing energy consumption and CO₂ emission. The low temperature and high reducing environment in the new furnace is favorable to lower the coke gasification and increase the reaction rate of iron oxide. The recycling of the top gas can significantly reduce CO₂ emission, and the main advantage comes when the stripped CO₂ is stored.     

Fuel enhancement by conversion of hotter waste CO2 in flue gas with coke

Considering the huge losses of high-temperature metallurgical waste heat and gases in steel works and the energy crisis on a worldwide scale, particularly the waste hotter gases in the flue of a converter that are emitted into air. A novel concept where coke is injected into the hotter gases for enhancement of fuel gas and reduction of CO₂ emissions into air is proposed. Numerical, experimental and industrial investigations are carried out in this work. The effects of injecting mass rate and inserted depth on the mixed state of coke in the flue were numerically evaluated and the effect of the surface structure of coke on the reactions of gas–solid phases was analysed using the t-plot method, and the transient gas products were described during coke injection. The energy change of the flue gas under various injecting schemes was discussed during the tests. The results show that an injecting scheme comprising an injecting pressure of 1.0?MPa, an inserted depth of 500?mm and an injecting mass rate of 18?kg?min^?1 seems to be better. The value of the specific surface area of coke was 8.36?m²?g^?1, while the coal was 20.59?m²?g^?1. With the inserted depth at 400 and 500?mm, the recovery time of the flue gas was 545 and 565?s and the total calorific value accounted for 48.47 and 51.53%, respectively. Without injection, the average contents of CO, O₂ and CO₂ were 48.1, 1.01 and 23.3, whereas after injection the average contents of CO, O₂ and CO₂ were 56, 0.5 and 10.1%, respectively. As a result, this process reduces CO₂ emissions and increases energy of the flue gas.     

Application of the triad of blast furnace,oxygen converter,and electric arc furnace for reducing of carbon footprint

Carbon footprint is the mass of carbon formed in the full cycle of manufacturing one kind or another product. This carbon is included in greenhouse gases. During production of iron and steel are generated carbon monoxide and greenhouse gases: methane, and carbon dioxide. Methane and carbon monoxide burn to carbon dioxide by secondary energy resources. By this means, the carbon footprint by the production of iron and steel has determined by the weight of carbon dioxide formed in this production. As results of analysis of the processes of manufacture of iron and steel, it has revealed that the tandem of blast furnace with electric arc furnace is characterized by a lower value of integrated emissions of CO₂ than the tandem of blast furnace with an oxygen converter. It was proposed to process of the cast iron made by one blast furnace, then in the oxygen converter, and, at last, in one or more electric arc furnaces. Moreover, the electric arc furnace is loaded by 30% of iron produced in blast furnace, and the remaining 70% are complemented by metal scrap. In the oxygen converter is loaded, the part of cast iron (75–85%), that remained after processing in the arc furnace. The converter is applied the metal scrap for full loading. Calculations of total emission of carbon dioxide for different triads of these units are made. Simultaneous use of oxygen converter with electric arc furnaces for cast iron smelting (obtained from one blast furnace) helps to reduce reliably the emission of carbon dioxide to 20% as it is follows from these calculations. This suggests that such a triad of used units conforms to green technology. Example of the use of mentioned triad is for a full load of the converter applied to metal scrap. The calculations total emissions of carbon dioxide for different triads of these units were performed. From these calculations it follows that the simultaneous use of oxygen converters after electric arc furnaces for smelting iron (obtained from one blast furnace), it helps to reduce the emission of carbon dioxide to 20%. This suggests that this triad of used units conforms to green technology. An example of using this triad is in the Magnitogorsk Iron and Steel Works, where along with the oxygen converter, electric arc furnaces with the use of locally produced electricity at burning fuel of secondary energy resources from units, in which the fuel is burnt. This practice can be recommended for a number of other metallurgical enterprises.     

Heat recovery from hot blast furnace slag granulates by pyrolysis of printed circuit boards

Abstract

Heat recovery from hot blast furnace (BF) slag is difficult to achieve but has great potential to recover energy and thereby reduce CO₂ emissions. The objective of this work is to utilise the heat of hot BF slag granulates to generate combustible gas from printed circuit boards. The results showed that this is a possible process and that, after cleaning, the combustible gas could be injected into the BF as a fuel and reducing agent. The new process has advantages over the traditional process in energy saving and pollution emissions.     

Rate of reactions between carbon dioxide and graphite

Solid graphite rods have been oxidized at temperatures between 1020 and 1510 °C using CO₂ containing gases. The activation energy was found to be 270 kJ/mol in the temperature range from 1020 to 1170 °C where the reaction is chemically controlled. At higher temperatures the reaction is controlled by external mass transfer of CO₂ with an activation energy of 86 kJ/mol. The shift from chemical to mass transfer control depends on the CO₂ pressure and the gas flow behaviour. Since per mol of carbon consumed one net mol of gas is produced, there is a net gas flow away from the graphite surface. This makes the transport of CO₂ to the surface more difficult, retarding the rate at high temperatures.     

Smelting‐Reduction Export Gas as Syngas in the Chemical Industry

Export gases from iron‐making processes are typically used as an energy source for heat and power generation within the iron and steel industry, although their calorific value is comparatively low. The fact that COREX® and FINEX® smelting‐reduction export gases typically consist of the major syngas‐components CO and H₂ (approx. 50% of gas composition), makes them attractive for utilization in the direct reduction of iron ores and in the chemical synthesis industry. This paper will discuss the required process steps for converting smelting‐reduction export gases into synthesis gas (syngas) using the example of methanol production. The calculated CO₂‐balance shows promising results for chemical utilization of COREX® export gas compared to energy utilization in conventional or combined power plants.     

Control of greenhouse gas emissions from electric arc furnace steelmaking: evaluation methodology with case studies

Abstract

The energy intensive nature of electric arc furnace (EAF) steelmaking necessitates that efforts to reduce greenhouse gas (GHG) emissions will affect steelmakers directly and/or through electric power producers. A model of GHG emissions from an EAF meltshop has been developed using the life cycle assessment approach. Direct and indirect sources of GHG gas emissions are estimated and ranked. Furnace combustion optimisation was evaluated in case studies conducted on a Canadian conventional EAF and a British scrap preheating `shaft' furnace. The analysis assumed 32 and 68% fossil fuel electricity generation, respectively. These case studies show that indirect GHG emission sources, in particular electricity generation, are more significant than direct emissions from the EAF. For the conventional EAF, offgas analysis and improved combustion control reduced electricity consumption by 40 kWh t^-1, costs by US$1·05/t, and GHG emissions by 20 kg CO₂-eq./t. For the shaft EAF, real time offgas monitoring and closed loop burner control reduced electricity consumption by 25 kWh t^-1, costs by US$3·6/t, and GHG emissions by 15 kg CO₂-eq./t. The case studies show that combustion optimisation using an EAF offgas analysis and combustion control system provides greater electricity, cost, and GHG reductions than previously reported in the literature.     

Cost and Life Cycle Analysis for Deep CO2 Emissions Reduction for Steel Making: Direct Reduced Iron Technologies

Among heavy industrial sectors worldwide, the steel industry ranks first in carbon dioxide (CO₂) emissions. Technologies that produce direct reduced iron (DRI) enable the industry to reduce emissions or even approach net-zero CO₂ emissions for steel production. Herein, comprehensive cradle-to-gate (CTG) life cycle analysis (LCA) and techno-economic analysis (TEA) are used to evaluate the CO₂ emissions of three DRI technologies. Compared to the baseline of blast furnace and basic oxygen furnace (BF–BOF) technology for steel making, using natural gas (NG) to produce DRI has the potential to reduce CTG CO₂ emissions by 33%. When 83% or 100% renewable H₂ is used for DRI production, DRI technologies can potentially reduce CO₂ emissions by 57% and 67%, respectively, compared to baseline BF–BOF technology. However, the renewable H₂ application for DRI increases the levelized cost of steel (LCOS). When renewable natural gas (RNG) and clean electricity are used for steel production, the CTG CO₂ emissions of all the DRI technologies can potentially be reduced by more than 90% compared to the baseline BF–BOF technology, although the LCOS depends largely on the cost of RNG and clean electricity.     

The technology of CO2 sequestration by mineral carbonation: current status and future prospects

Mineral carbonation (MC) has been extensively researched all over the world since it was found as a naturally exothermic process to permanently sequester CO₂. In order to accelerate the natural process, various methods for carbonation of Mg-/Ca- silicate minerals have been studied. It has been found that the MC efficiency will increase with an increase in CO₂ pressure, retention time, temperature, mass ratio of Mg/Ca to Si in minerals, specific surface area, and the slurry concentration in a specific range, and with the introduction of NaCl and NaHCO₃ or carbonic anhydrase. However, there is still no successful industrial application because of high economic costs and slow reaction rate. It is not economic to exploit Mg-/Ca- silicate minerals deposits or tailings to sequester CO₂ by the MC due to the cost of grinding and heat pre-treatment. In some cases, the whole sequestration process may result in more CO₂ emissions than the sequestered CO₂ due to the requirements of energy inputs. The process, however, may be profitable as a whole (with carbon credits). It is suggested to combine the MC with valuable metals recovery from ore deposits in order to reduce the cost of the MC by cost sharing for mineral recovery.     

基于分析的钢铁企业热电联产碳排放研究

热电厂是钢铁企业重要的能源生产部门,热电联产的碳排放量关系到整个企业碳减排成效。采用单位能源产品碳排放量指标,结合分析来评价热电厂的碳排放量,将单位能源产品碳排放量分解成最小排放量和附加排放量进行研究。研究结果表明：热电联产通过能源梯级利用,提高能源转换效率,减少化石能源使用,有利于实现钢铁企业减少碳排放。     

Evaluation of a New Process for Ironmaking: a Productivity Model for the Rotary Hearth Furnace

In order to address the key issues of capital costs and CO₂ emissions in ironmaking operations, a new process was proposed combining a Rotary Hearth Furnace (RHF) and a Bath Smelter. This paper describes the construction of a productivity model for the RHF based on previous studies concerning the reduction behaviour of pellets of carbon and iron oxides. The model was used to estimate changes in RHF productivity according to the type of carbon used in the RHF pellets, numbers of layers of pellets, final metallization degree of the direct reduced iron (DRI) produced, and initial sizes of the pellets. The results indicate that productivity gains between 33 and 46% can be achieved replacing coal with wood charcoal, a carbon source virtually free of net CO₂ emissions. Also, the productivity of the RHF can be doubled by reducing the charge only up to 70% metallization. The model allows the study of changes in overall energy consumption due to changes in the extent of primary oxidation of the gas at the pellet level showing that the use of wood charcoal increases the total amount of carbon consumed by less than five percent relative to operations with coal.     

Oxidation of molten impurities in converters by means of combustion flames: Thermodynamic principles. 1. Thermodynamic analysis of processes in natural-gas combustion

In the production of steel, as the productivity rises and the resource and energy consumption declines, improvements in converter design are required to ensure preliminary scrap and batch heating and to intensify redox processes in the liquid bath and exhaust-gas combustion above the bath, without impairing the durability of the injection systems and the converter lining. The use of fuel–oxygen combustion flames in the converter resolves numerous technological problems. The hydrodynamics in the reaction zones and in the liquid bath may be greatly changed by fuel combustion in the converter’s working space with jet formation or by means of submersible combustion flames. In the present work, thermodynamic methods are used to analyze the dynamics of gaseous-fuel combustion and the oxidation of elements in the converter bath on interaction with high-temperature combustion products. The interaction of the combustion flame and chemical elements in the converter bath is calculated for equilibrium conditions. The use of the combustion flames is found to change the composition of the gas phase in the converter’s working space (above the bath), which contains H₂ and H₂O in addition to the traditional components associated with oxygen injection: O₂, CO, CO₂. The presence of H₂ and H₂O changes the thermal conditions and oxidative properties of the gas phase. In the combustion of gas–oxygen fuel, the optimal composition of the initial gas mixture (natural gas + oxygen) must correspond to the ratio 100% CH₄ + 69% O₂. The oxidation product is gaseous phase consisting of 40% CO₂ + 60% H₂O. The total enthalpy of combustion of the gas–oxygen fuel at converter temperatures, with an oxygen excess greater than 1.0 (up to 2.0), is about 200 kJ per mole of the initial reagents. In the oxidation of methane by carbon dioxide, the total enthalpy of combustion is between–7 and–14.5 kJ/mol of initial reagents at 1800 K. The process becomes endothermal at temperatures above 2000 K: ΔH ₂₂₀₀ = 7.7–15.4 kJ/mol. In the oxidation of natural gas by water vapor, ΔH ₁₈₀₀–2200 = 19.5–70 kJ/mol. Thus, flame temperatures above 1800 K may only be attained in the oxidation of methane by oxygen. The use of air, carbon dioxide, or water vapor as the oxidant does not yield the required thermal effect.     

Failure Mechanisms in High Chrome Oxide Gasifier Refractories

Gasification is a high-temperature, high-pressure chemical process used to convert a carbon feedstock into CO and H₂ (syngas) for use in power generation and the production of chemicals. It is also a leading candidate as a source of hydrogen in a hydrogen economy and is one of several technologies expected to see increased use in advanced fossil fuel power systems in the future. Gasification is being evaluated because of its high efficiency, its ability to capture CO₂ for sequestration or reuse in other applications, and its potential for carbon feedstock fuel flexibility. At the heart of the gasification process is a gasifier, a high pressure chemical reaction vessel used to contain the interactions between carbon and water in a shortage of oxygen, producing syngas. The gasifier is lined with high chrome oxide materials to protect the containment vessel. Gasifiers are complex systems, and failure of the refractories used to line them was identified by industry as a limitation to their reliability and availability and to their increased use. NETL researchers have examined spent high-Cr₂O₃ (over 90 pct Cr₂O₃) refractories from numerous gasifiers to determine in-service failure mechanisms. This analysis revealed that premature failure of the high chrome oxide refractories was related to ash in the carbon feedstock, which liquefies during gasification and interacts with the refractories, leading to wear by chemical dissolution or spalling (structural and chemical). A discussion of this postmortem wear of spent refractory materials and of thermodynamic modeling used to explain microstructural changes leading to wear are explained in this article. This information will serve the basis to develop improved performance refractory materials.     

Carbonation Behavior Assessment of RH Slag Batch after Aqueous Extraction at Environmental Pressure

In order to assess CO₂ sequestration amount and carbonation degree for RH slag at surrounding pressure, carbonation process of RH slag batch in lab is investigated, and the parameters of carbonation degree and CO₂ sequestration amount are the targets, and the relationship between both and relevant factors, such as CO₂ flow, gas bubble size etc. is originally discussed. The carbonation degree increases when temperature increases before 60 °C, then decreases. Particle size has a positive effect on carbonation degree, and carbonation degree for 0.5 L/min is bigger than those for 0.1 L/min and 1.0 L/min. When small gas bubble generator is adopted, carbonation degree and CO₂ sequestration amount is improved. The maximum carbonation degree and CO₂ sequestration amount is 34% and 178.65 g/kgslag, respectively when 38 μm RH slag batch is carbonated for 90 min at 60 °C under the conditions that CO₂ flow is 0.5 L/min and bubble size equals 5 mm. CaCO₃ and MgCO₃ phases exists through XRD analysis, showing that carbonation process is effective. Carbonation degree model is established assuming carbonation reaction occurs on the active surface of RH slag batch. This model fits very well by comparison between experimental results and model results.     

Integration of the Blast Furnace Route and the FINEX®‐Process for Low CO2 Hot Metal Production

The blast furnace is the most important process for the production of hot metal. An integral part of this process route is the coking of coal and sintering of fine ore. The FINEX®‐process is a new technology for hot metal production which uses untreated fine ores and coal instead of sinter and coke. This paper deals with the investigation of integration concepts of the blast furnace and FINEX®. Low reduced iron (LRI) and/or reducing gas are/is produced in FINEX® and are/is considered as substitute/s of burden and fuel in the blast furnace, respectively. In the article the overall fuel demand and CO₂ emissions for the integration of the blast furnace and FINEX® are shown. For that reason two case studies for the integration are carried out and compared with the base case, that is, the two‐independent processes. The CO₂ emissions are calculated considering the fuel and electric power consumption of the different cases.     

晋南钢铁高炉喷吹富氢气体工业化实践

 钢铁工业是中国制造业中碳排放量最高的行业,碳排放占全国碳排放总量的15%左右。高炉是钢铁工业碳消耗量最大的工序,碳消耗占钢铁流程总碳消耗的70%以上,减少高炉冶炼碳消耗是降低钢铁工业碳排放的最有效措施。高炉喷吹富氢气体不但可以提高冶炼效率,减少污染物排放,而且可以减少焦炭或煤粉消耗,从源头上降低高炉冶炼碳消耗,从而减少碳排放。以山西晋南钢铁两座1 860 m3高炉风口喷吹富氢气体工业化生产数据为例,详细研究了高炉喷吹富氢气体对燃料比、风口理论燃烧温度、炉腹煤气量、H₂利用率以及CO₂排放量的影响。结果表明,喷吹富氢气体可以显著降低高炉固体燃料消耗,在吨铁富氢气体喷吹量为65 m3条件下,富氢气体与固体燃料的置换比为0.49 kg/m3;风口喷吹富氢气体降低了风口理论燃烧温度,吨铁每喷吹1 m3富氢气体,风口理论燃烧温度降低约1.5 ℃,高炉鼓风量和炉腹煤气量都少量降低;喷吹富氢气体以后,炉内H₂的利用率平均为37.3%,CO的利用率约为43.2%;吨铁CO₂排放量可以降低80 kg左右,高炉CO₂排放降低了5.6%,取得了较好的经济、环境和减污降碳效果。     

黄金企业碳排放核算模型研究

黄金企业是主要的碳排放源，对于碳达峰有重要的意义。从化石燃料燃烧、炸药爆炸过程、脱氰过程、购入电力四个角度构建黄金企业二氧化碳排放核算模型。以内蒙古某金矿为例核算碳排放，电力消耗是主要碳排放源，其次为化石燃料燃烧。过程排放，即炸药爆炸和脱氰过程，不是黄金企业主要碳源，但是不可忽略的重要组成部分。     

Study of the Reduction of Industrial Grade MoO<Subscript>3</Subscript> Powders with CO or CO-CO<Subscript>2</Subscript> Gases to Prepare MoO<Subscript>2</Subscript>

Industrial grade MoO₂ powders have a plenty of advantages relative to MoO₃ in the direct alloying steelmaking processes. In this work, the reduction of industrial grade MoO₃ powder with CO gas or the mixed gases of CO and CO₂ has been investigated in detail in order to prepare industrial grade MoO₂ powder. It is found that reaction temperature has a significant effect on the product composition. Using pure CO as the reducing gas, for temperatures below 868 K (595 °C), the main product is MoO₂ with some whisker carbon; for temperatures above 868 K (595 °C) the main reaction products are MoC and amorphous carbon; as the reaction temperature further increased, the final reaction product is Mo₂C. In addition, Mo₄O₁₁ is always formed as an intermediate product during the reaction processes both at lower and higher temperatures, which is similar to that observed on reduction of MoO₃ by H₂. It is found that adding CO₂ to the reducing gases eliminated carbon formation but still allows the formation of MoO₂ during the reaction process. This method may be applied to produce industrial grade MoO₂.     

Calculation method of equilibrium composition in the carbon-hydrogen-oxygen system and its application to environments of a high-temperature gas-cooled reactor

A simple method for calculation of high-temperature equilibrium composition has been developed for the C-H-O system of the species H₂, H₂O, CO, CO₂, CH₄, O₂, and solid C. The calculation process has been simplified by using the most fundamental equilibria for high-temperature reactions of gaseous species. This method is applied for cases of carbon activity equal to or less than 1 using the identical equilibria. We have also applied the method to two kinds of gases for a high-temperature gas-cooled reactor, which are an impure helium gas for the reactor coolant and a reducing gas for the utility system of the reactor. Characteristics of these gases are discussed from the viewpoint of corrosion and hydrogen permeation of the reactor materials. Formerly with Nuclear Materials Division     

Power increase and metallurgical effects during arc heating of liquid steel due to the addition of molecular gases

Molecular gases were laterally injected into the gas atmosphere of a pilot furnace containing 200 kg of steel melt and heated by two AC argon plasma arcs. The power increase in the arcs obtained by the injection was 12 % for 20 % N₂, 70 % for 20 % CO₂, 32 % for 3 % CH₄, and 62 % for 3 % C₃H₈. Mixtures of CO₂ and hydrocarbons were also tested. CO₂ acted as an oxidizing agent for steel components with oxygen transfer efficiencies of 28 % in the case of slag-free steel melts and of 10 % in the presence of slag, while the addition of CH₄ did not cause any noticeable carbon transfer to the melt.