This article discusses the essential issues of CO2 emission reduction in iron and steel technology and the future technological prospects. In addition, reducing CO2 is related to development trends at home and abroad, and is a common problem faced by the global steel industry. Based on future measures, technology development from a new perspective has begun, such as CCU technology (CO2 capture and utilization) using CO2, and decarbonized hydrogen ironmaking related to renewable energy. This article discusses its development trends.
Steel technology and CO2 production
In order to understand the future development direction of CO2 emission reduction and the existing problems, we must first understand the current production trends and steel technology. Although it is said that there is a surplus of steel production facilities, East Asia is building new steel plants one after another, and crude steel production is increasing year by year to meet the strong demand for steel in Asia in recent years. In 2018, the world’s crude steel production reached 1.808 billion tons. In 2018, the output of crude steel produced by the blast furnace-converter method accounted for 71% of the total crude steel output. In Japan, 75% of crude steel is produced by the blast furnace-converter method. The electric furnace method consists of an electric furnace based on the direct reduction process of natural gas or using scrap steel as an iron source
Combination process of electric furnace. The CO2 emissions of crude steel produced by various processes are compared: using the blast furnace-converter method, the CO2 emissions per ton of crude steel is about 1.8-2.0t; the direct reduction method uses reducing gas obtained by reforming natural gas, so, CO2 emissions are about 70% of the blast furnace-converter method using coal; the scrap-electric furnace method does not require reduction, so it is about 30% of the blast furnace-converter method. Both are dependent on the CO2 emission factor of electricity, which is lower than the blast furnace-converter method.
On the other hand, the blast furnace-converter method can produce all steel products including high-grade steel, which is suitable for mass production. Recently, newly-built steel plants in Asia have adopted the blast furnace-converter method. From the perspective of strong manufacturing technology, it will continue to be positioned as the mainstream process in the future. The maximum scale of the direct reduction process is about 2 million tons/year, and the location of the plant is limited to natural gas extraction areas, which used to be small plants. But recently the site selection conditions are expanding, and the United States is The construction of a large-scale direct reduction process facility with a capacity of 2 to 2.5 million tons per year that utilizes shale gas, the price of natural gas is also changing, and this usage requires attention. From the viewpoint of suppressing CO2 emissions, scrap steel is preferably used. However, urban steel scrap and internally generated steel scrap are used as iron sources. The former is used as an iron source that has been adjusted in composition. Due to the problem of element loss, it is limited to the manufacture of ordinary steel. In addition, the amount of scrap steel itself is limited by the amount of steel accumulated, and the stability is difficult to determine. Therefore, it cannot be the main source of iron.
In order to cope with the future growth of steel demand and to supply high-quality steel products steadily, in response to the current CO2 emission reduction requirements, it is first necessary to consider how to improve the blast furnace-converter method, or flexibly apply the characteristics of other methods, and explore the best of the composite production structure. Good form, as a candidate method. Pay attention to the direct reduction method, not only consider natural gas, but also need to expand the thinking, flexibly use the coke oven gas (COG) produced by the iron plant as the reducing gas process, and combine with the blast furnace-converter method to form a composite process.
Figure 1 shows the macro process of carbon and energy in an integrated steel plant composed of the blast furnace-converter method, as well as the basic measures for low carbon and decarbonization. The integrated steel plant is mainly composed of ironmaking processes and downstream processes, and 22-24GJ/t of energy composed of coal etc. needs to be input into the ironmaking process. In the ironmaking process, in addition to the production of molten iron, the energy self-sufficiency of the integrated steel plant is realized by supplying the gas produced in blast furnaces and coke ovens to the downstream process equivalent to 4 to 5GJ/t.
Figure 1 also shows the boundaries of CO2 reduction. The steel industry is a major energy consumer. Considering energy self-sufficiency, it is necessary to control CO2 emission reduction within the boundaries shown in Figure 1. Measures include reducing carbon demand and decarbonization in blast furnaces, separating, transporting and storing CO2 on the export side of CCS (CO2 capture and storage), and reusing CO2 CCU (CO2 capture and utilization). However, CCS, including transportation and storage, largely depends on the surrounding geographical conditions, and its applicability is difficult to predict. Therefore, the entry-side low-carbon, decarbonization technology and COz reuse technology CCU will become the main development targets in the steel industry.
Figure 2 shows the overall CO2 reduction process centered on the blast furnace. The left side of the figure shows the method of reducing input carbon based on the current blast furnace starting from the raw material side. Enumerated methods such as increasing the carbon utilization rate in the blast furnace, lowering the furnace temperature, controlling the reduction balance, or reducing the reduction load by adding metallic iron. Metal iron is produced by reduction of natural gas or COG. As a means to control the reduction balance, highly reactive coke is a specific form. In Japan, the NEDO-supported ferro-coke project is under development. Through a 30t/d pilot plant, JFE Fukuyama is building a 300t/d intermediate plant. The input of metallic iron into the blast furnace is related to the direct reduction process. Although both require additional equipment, the existing blast furnace can be used directly. The right side of Fig. 4 shows the reconstruction of the reducing gas stream and the method of using the blowing hydrogen reducing material.
Specifically, it is a method of CO2 separation on the top gas discharged from the blast furnace, and the separated gas is recycled as a reducing gas and recycled to the blast furnace to reduce the amount of carbon input. Or it can be converted into reducing gas through COG and natural gas reforming and recycled to the blast furnace. In both cases, by enhancing the gas reduction function in the blast furnace, the direct reduction reaction in the blast furnace that consumes coke can be suppressed, and the coke ratio as input carbon can be reduced. Gas reforming can be through dry reforming of CO2 in top gas, or steam reforming. The former is also a carbon cycle. In addition, a method of using a hydrogen-based reducing agent such as natural gas or biomass to be sprayed from a tuyere is cited.
As a basic technology, there is an all-oxygen blast furnace process, which can improve the reduction efficiency by removing nitrogen unnecessary for reduction from the air supply, and increase the freedom of decarbonization by blowing a large amount of hydrogen-based reducing agent. In the early 1970s, Japan developed the technology to inject reducing gas to the bottom of the blast furnace. At that time, Nippon Steel Hirosō conducted some commercial furnace tests. The COG dry reforming method has been verified by NKK (now JFE Steel) as NKGI in the experimental blast furnace. The basis of low-carbon blast furnace-nitrogen-free oxygen blast furnace was tested in a pilot blast furnace in 1980. Currently, Japan is implementing the national project COURSE50. The 50 in COURSE50 refers to the target year 2050. The goal is to reduce CO2 emissions by 10% by injecting reducing gas after steam reforming into COG, and to reduce CO2 emissions by 30% by adding CCS. Currently, tests are being carried out in the test blast furnace constructed by Nippon Steel Junjin Steel Works, and commercial blast furnace verification tests are expected to be carried out in fiscal year 2022 and commercialization will be achieved in 2030.
With the support of the European Union, European steel companies including engineering companies began research and development in 2004. On the basis of a full-oxygen blast furnace, ULCOS (ultra-low CO2) is used to recycle the reducing gas from the top gas of the blast furnace after CO2 separation. Emissions ironmaking project. The separated CO2 is isolated by CCS. The ULCOS project also includes the development of the HIsarna smelting reduction process. The main body of the ULCOS project is the circulation of blast furnace top gas. It has been verified in the pilot blast furnace of the Swedish Luki Mining Company. According to reports, the carbon input in the blast furnace stage has been reduced by 25%. Although the project received attention shortly after its implementation, the next step after the commercial furnace test of the blast furnace top gas cycle was not implemented and was interrupted. It is speculated that the problem of test costs is the root cause, but it also has an impact on the judgment of future development potential and ripple effects. For large projects, the sustainability of participating organizations is also an important factor.
Figure 3 shows a comparison between the CO2 reduction potential of these traditional proposed technologies and the long-term goals. Various technical proposals have been put forward and an initial technical framework has been formed, and the evaluation work is in progress. On the other hand, we will see deviations from the energy integrity of integrated steel plants and theoretical quantitative restrictions on carbon efficiency. As the gas circulation at the top of the blast furnace leads to insufficient energy supply to downstream processes, its supplement must also be evaluated. Based on hot coils, ULCOS’s top gas circulation is reduced by 15%.
Except for CCS, the basic improvement technology of blast furnace shown in Figure 2 can reduce CO2 emissions by only 10%-15%. It is difficult to establish the additivity of various technologies due to repeated principles. Through the advancement of existing process technology improvements, there is a big gap in achieving the long-term goal of 2050. Although the goal setting adopts retrospective thinking, it is also necessary to conduct predictive discussions in materials industries that already have large facilities like steel. As shown in Figure 3, not only need to determine the priority of the target slogan, but also need to propose a technologically promising process plan, and look forward to the emergence of innovative technologies that can bridge this gap.
In response to the 2050 target, EUROFER (European Iron and Steel Institute) put forward its views in 2013 based on the degree to which the accumulation of new technologies can reduce CO2. A hypothetical process study shows that the effective use of reduced iron technology can reduce CO2 emissions by up to 40%, while the combination of blast furnace top gas circulation and CCS can reduce CO2 emissions by 57%. At the same time, cost estimates were carried out. With the introduction of CO2 emission reduction equipment such as equipment modification and conversion, the cost has risen sharply. The specific figures are shown by CAPEX (capital expenditure) and OPEX (operating expenditure). Cost estimates show that the implementation of CO2 emission reduction in a specific area lacks uniformity due to product price gaps, etc. Therefore, the implementation of CO2 emission reduction needs to be carried out globally. In addition, although CCS has a very good effect, due to factors such as geographical environment, the social acceptance of CCS is problematic, and large-scale investment increases the burden, and its feasibility has been questioned. This not only affects the setting of response goals, but also involves the formulation of roadmaps for future topics and arguments.
The reduction of CO2 emissions is a common problem faced by global steel producing countries. The steel products of bulk commodities are international commodities, and CO2 emissions reductions are only implemented in specific countries, with little effect. The steel industry is a growth industry. The developed process will only appear when it is applied to production equipment. Therefore, as a material industry with production facilities that meet customer needs, it is difficult to develop an execution plan. The effect will only be apparent when companies engaged in steel production adopt the new technology in unison. In addition, reducing COz is not a pursuit of profit. The development of CO2 emission reduction has been well received, and it is very important to establish a fair social system equivalent to the incremental cost burden of CO2 emission reduction. It is necessary for all countries engaged in steel production to deploy technology globally with the same values, otherwise it will not be effective.
If the long-term goal of a large amount of CO2 reduction is implemented in existing steel plants, various forms will be considered, such as major changes in production processes and equipment to keep them away from coal, or isolation of CO2 emissions, but this is difficult Imagine. Japanese steel plants have promoted complete energy conservation. Although they rely on coal, they have formed a complete energy cycle chain.
On the other hand, the life span of blast furnaces exceeds 20 years. From the perspective of equipment renewal in iron and steel plants, although it will be 2050, it is not a distant future. Even with a long-term goal and an ideal prospect, the steel industry, as a raw material industry, is the source of Japan’s vitality. While taking on the responsibility of supplying high-quality steel products to users steadily, how to change the large steel mills seen in reality, The road to the future is not easy. It also involves future equipment update plans. Compare this sense of reality with the future It is a challenge to imagine linking up, but it is a key step beyond the traditional steel technology framework, including expanding horizons, establishing links with surrounding industries, and energy use throughout the country. From a holistic perspective, the key to building future prospects seems to be achieving long-term goals.
Currently, a new process for technological development that is different from the past has begun to sprout. The new trend in the world is shifting from improving the use of carbon in blast furnaces to converting to CCU that reuses CO2 and to using hydrogen without CO2 for decarbonization.
The concept of future development believes that CO2 is not a waste, but a valuable resource. As one of the raw materials of chemical products, CCU is integrated with thinking and according to the use of renewable energy, clean hydrogen is produced through water electrolysis, which is used as a reducing material and an energy source. CDA (Direct Carbon Avoidance) to achieve the decarbonization target is a project implemented to increase the potential for reducing CO2 emissions.
ThyssenKrupp of Germany has launched a CCU project called Carbon2Chem. Carbon refers to CO2, and Chem refers to chemical products. The current chemical industry relies on fossil raw materials. The idea is to use CO2-containing waste gas discharged from steel plants as raw materials to produce various chemical products such as methanol. This is an inter-industry alliance, including the chemical industry, and a cross-industry network. It is the concept of reducing CO2 emissions across the entire industry, which is called integrated CO2 capture. The addition of hydrogen in Carbon2Chem’s chemical conversion is essential.
The Power to Gas initiative of Germany is also related to this, which converts unstable and unstorable renewable energy into storable hydrogen or methane and supplies it to the domestic market stably. With the support of the state, ThyssenKrupp established a research center in the Duisburg ironworks to develop key Carbon2Chem technologies. In addition, the company also announced a specific plan to commercialize the technology in 2030. In 2050, the use of hydrogen will reduce CO2 emissions by 80%. The hydrogen production research will be carried out in cooperation with Air Liquide.
ArcelorMittal has launched a project called Steelanol, which uses biotechnology to convert waste gas from steel plants into synthetic fuels such as ethanol. The fermentation technology of Lance Technology Corporation of the United States is the core technology, using fermentation bacteria improved through gene conversion. The company’s Ghent Steel Plant is building a 47,000-ton/year medium ethanol production plant. All of these require LCA assessment. The new development trend is to flexibly utilize the power development system technology of existing steel plants, and use the waste gas of steel plants to produce fuels and chemicals produced from fossil raw materials in the current chemical industry. Made products instead.
In Sweden, Austria, and Germany, as a method of deep decarbonization, a hydrogen ironmaking process using electricity derived from renewable energy without CO2 to produce hydrogen through water electrolysis, and using hydrogen as a reducing agent to reduce iron ore has been proposed. The reduction uses a shaft furnace direct reduction process.
The Swedish Steel Company and the Swedish Luki Mining Company have started the HYBRIT (Hydrogen Breakthrough Ironmaking Technology) project, the voestalpine Group and Siemens have jointly started the H2FUTURE project, and the German Salzgitter has started the SALCOS (Salzgitter low CO2 steelmaking) project pilot plant scale research. These are all seeking support from the European Union or government public funds. The direct reduction process uses the existing ENERGIRONI technology of the MIDREX or TENOVA-HYL system and is smelted in an electric furnace.
ArcelorMittal uses the existing MIDREX reduced iron equipment in Hamburg, Germany, in parallel with the CCU to develop 100,000 tons/year of hydrogen iron production. Primetals has started to develop a fluidized bed for reducing iron ore powder with hydrogen, and announced that it will start operation of a pilot plant in 2020. For the water electrolysis process that uses electricity from renewable energy sources to produce hydrogen, solutions such as alkaline electrolysis, PEM (proton exchange membrane), and solid oxide SOEC (solid oxide electrolytic cell) have been proposed.
Building a vision for the future of steel and its future
At present, the main topics of ironmaking, such as resource responsiveness and energy conservation, have been completed within the scope of ironmaking. Regarding the issue of CO2 emission reduction in the iron and steel industry in the future, it is impossible to achieve the goal only through traditional research such as steel process improvement and gradual technological reform. Recognizing the limitations, we are starting from the long-term goal of realizing the global environmental problems, and are changing to expand its framework and technical objects to master the steel process from multiple angles. Converting CO2-containing waste gas emitted by steel plants into chemical raw materials, promoting cooperation between industries to reduce cross-industry CO2 emissions, and considering the design of ironmaking production processes from clean energy production. This is a reorganization, including chemical , Large-scale framework in the energy sector.
SCU (Smart Carbon Utilization) is a new collective term for carbon utilization including CCU, reduced iron utilization, carbon recycling, etc. Renewable energy and hydrogen production by water electrolysis belong to other fields and are separated from steel, but without it, decarbonization of ironmaking cannot be achieved. The current I technology that relies on carbon is to use carbon as a reducing material to form an energy system that supplies energy from iron smelters to downstream processes. It has independent integrity, but it also brings constraints.
Hydrogen production is the conversion of reducing materials and energy itself. It must be noted that the ironmaking process does not have an energy supply function, hydrogen and electricity are consumed, and the use of energy in downstream processes will also change. Although you will think in a larger framework, the degree of freedom will increase. CCU is also useful for the idea of a carbon cycle linked to chemistry, such as recirculating intermediate substances such as synthetic reducing materials produced in the process of converting into chemical products to the steel process, etc., there may be various developments.
Hydrogen is a secondary energy source. The ideal is to use renewable energy to produce CO2-free hydrogen, but the greenness of the whole process of hydrogen production, transportation and storage must be fully evaluated. In Europe, this research is pioneering. The CertifHy project defines a green hydrogen source and proposes a quantitative evaluation method.
Looking at the situation in Japan again, as mentioned above, the steel industry is mainly composed of large steel plants. Considering the role of producing high-quality steel products and providing them to users, the conversion of manufacturing processes is not easy. In particular, the Japanese steel plant was built under the concept of a coastal steel plant in the 1960s. After continuous improvement, it has been in operation for more than 50 years, and the basic infrastructure is aging. In East Asia, large new steel plants are being built one after another, and the form of steel plants is changing. Energy-saving equipment that has not yet been popularized in Japan is being actively adopted in East Asia. Focusing on 2050, global environmental issues are often seen as constraints, but it is also an opportunity to promote the transition to new technologies.
The amount of CO2 emissions produced by steel depends on the production volume and the intensity of CO2 emissions. People often tend to focus only on CO2 emission intensity for future targets. But you can choose in the basic direction, whether to emphasize the significance of adapting to scale, or to pursue an ideal form from the beginning, giving priority to the potential of CO2 reduction. Hydrogen ironmaking is close to the CO2 reduction potential pursued. The crude steel production in Sweden, which is under development, is 4.7 million tons/year, and the crude steel output in Austria is 6.9 million tons/year. Judging from the scale of the two countries, it is not impossible to achieve. Can become a benchmarking existence. SCU is based on current technology and its route is easy to understand. With the development of the technology used, the applicability is also expanding. The best form will vary according to the application area and conditions. Japan is a resource importing country. Due to its geographical conditions, it is difficult to use renewable energy in a wide area like Europe’s “Power to Gas” to achieve mutual use of energy. Japanese iron and steel companies are composed of large-scale integrated steel plants, producing a variety of products. A roadmap for independent development in line with Japan’s national conditions is needed. Although the nature of the various options is different, it is an ideal choice to promote both expansion and reduction potential. CO2 reduction technology is a global problem faced by all industries and the world’s steel industry. In technology development, we hope to achieve cross-industry collaboration, international cooperation and role sharing.