The steel industry is considered an important basic sector of the national economy, and its high energy consumption and carbon emissions make it a major contributor to climate change, especially in China. The majority of crude steel in China is produced via the energy- and carbon-intensive blast furnace-basic oxygen furnace (BF-BOF) route, which greatly relies on coking coal. In recent years, China’s steel sector has made significant progress in energy conservation and emission reduction, driven by decarbonization policies and regulations. However, due to the huge output of crude steel, the steel sector still produces 15% of the total national CO2 emissions. The direct reduced iron (DRI) plus scrap-electric arc furnace (EAF) process is currently considered a good alternative to the conventional route as a means of reducing CO2 emissions and the steel industry’s reliance on iron ore and coking coal, since the gas-based DRI plus scrap-EAF route is expected to be more promising than the coal-based one. Unfortunately, almost no DRI is produced in China, seriously restricting the development of the EAF route. Here, we highlight the challenges and pathways of the future development of DRI, with a focus on China. In the short term, replacing natural gas with coke oven gas (COG) and byproduct gas from the integrated refining and chemical sector is a more economically feasible and cleaner way to develop a gas-based route in China. As the energy revolution proceeds, using fossil fuels in combination with carbon capture, utilization, and storage (CCUS) and hydrogen will be a good alternative due to the relatively low cost. In the long term, DRI is expected to be produced using 100% hydrogen from renewable energy. Both the development of deep processing technologies and the invention of a novel binder are required to prepare high-quality pellets for direct reduction (DR), and further research on the one-step gas-based process is necessary.
Chengzhi Wei, Xin Zhang, Jin Zhang, Liangping Xu, Guanghui Li, Tao Jiang.
Development of Direct Reduced Iron in China: Challenges and Pathways.
Engineering, 2024, 41(10): 98-115 DOI:10.1016/j.eng.2024.04.025
To achieve carbon neutrality, policymakers worldwide have imposed limits on energy consumption and CO2 emissions. According to recent estimates, the global steel industry emitted approximately 3.60 billion tonnes (Gt) of CO2 in 2022, with an emissions intensity of 1.91 t CO2 per tonne of crude steel [1], [2]. These emissions are 1.5 times higher than those recorded over the past three decades. As a major energy consumer and greenhouse-gas emitter, the steel industry continues to contribute a large proportion of CO2 emissions. Therefore, effective policies and measures aimed at mitigating the carbon footprint of the steel industry are imperative, especially in China, where the steel sector produces over 60% of all CO2 emissions from the global steel industry and approximately 15% of all domestic CO2 emissions [3].
Crude-steel production factors will account for an estimated 45% of the cumulative reduction in CO2 emissions from the steel industry over the 2021-2060 period. Other reductions will be contributed by full-scrap-electric arc furnace (EAF) processing factors (∼39%), and hydrogen metallurgy factors (∼9%), as well as energy conservation, interface technology, smart improvements, and other factors (∼7%) [4]. In short, achieving carbon neutrality for the steel industry in China requires a reduction in the total output of crude steel, decarbonization of resources and energy, and restructuring of the steel manufacturing process [4], [5], [6].
Ironmaking technologies can be broadly divided into blast furnace (BF) ironmaking and non-BF ironmaking. The latter category is subdivided into two technologies yielding different product states: direct reduction (DR) and smelting reduction. The majority of crude steel in China is produced via the BF-basic oxygen furnace (BOF) route [2]. The BF ironmaking process accounts for approximately 70%-90% of the total carbon emissions of the entire BF-BOF route; therefore, it is under severe pressure to reduce its carbon emissions [7]. However, the current BF-BOF steelmaking process is mature enough to produce at conditions close to the theoretical thermodynamic limit, so it is difficult to achieve further emission reductions of more than 15%-20% through process improvements alone [8].
As shown in Table 1 [9], [10], [11], [12], the traditional BF-BOF steelmaking process generates large amounts of CO2 (2.0-2.2 t per tonne of crude steel produced). In contrast, the gas-based direct reduced iron (DRI)-EAF process, which employs natural gas (NG) as its energy source, emits only 1.3-1.4 t of CO2 per tonne of crude steel. Although the emissions from coal- and gas-based DRI smelting processes are comparable, the iron-production process associated with coal-based DR ironmaking emits twice as much CO2 as NG-based processes, confirming a low emissions-reduction potential. The electric-furnace smelting process, which uses scrap-only as the charge, decreases the carbon footprint to 0.3-0.8 t per tonne of crude steel. The emissions of this process are dominated by indirect emissions from electricity consumption. However, electric furnace smelting presents challenges such as poor scrap quality and limited availability. DRI is a high-purity product with a stable chemical composition, so it is suitable for producing most high-grade steels and special steels [13]. The increasing expansion of EAF steel and the shortfall of scrap in China will stimulate the production of DRI to grow further.
The Ministry of Industry and Information Technology of the People’s Republic of China, the National Development and Reform Commission, and the Ministry of Ecology and Environment of the People’s Republic of China jointly issued a document titled Guidance on Promoting the High-Quality Development of the Steel Industry, in which the electric-furnace-steel share in China is targeted to exceed 15% by 2025. Based on an annual electric-furnace-steel output of 150 million tonnes (Mt) and assuming a DRI ratio of 30% in the electric furnace charge, the projected total DRI demand in China in 2025 is approximately 45 Mt. Such measures are imperative for acceptably developing the steel industry and ensuring China’s long-term competitiveness in the global market.
Low-carbon ironmaking and steelmaking can be achieved via hydrogen-based ironmaking technologies and electric furnace melting processes. However, BFs require the use of coke in BF ironmaking and are not easily adaptable to 100% hydrogen operation [14], [15], [16]. Meanwhile, hydrogen-based smelting reduction technologies are not yet fully developed [17]. DR is an environmentally friendly ironmaking technology with a shorter process compared with traditional methods. Corresponding reductions are expected in greenhouse-gas emissions. The hydrogen content of reductants for gas-based DR can exceed 60% and can even reach 100% [18]. Moreover, DR technology has matured over its long history of over 50 years. At present, hydrogen-based DR is the most feasible means of transitioning from carbon-based to hydrogen metallurgy.
The transition of China’s steel industry toward low-carbon and high-quality development will depend on further enhancements of DR technology. However, these enhancements are limited by the availability of reductants, such as NG, green hydrogen, or green ammonia [19], by the renewable electrical energy required to generate these reductants, and by a lack of high-quality feedstock materials. Fortunately, the availability of green electricity is currently growing fast, offering an opportunity for the direct use of green electricity in iron and steel production [20]. This article introduces DR technology from the perspective of product applications, the global status of DRI production, and prospects for DRI development. It then analyzes the challenges presented by DR development in China, including energy options, raw materials preparation, and DR process optimization. Pathways for developing DR in China are also discussed.
2. Applications of DRI
DRI, which is also known as “sponge iron,” is produced via the reduction of iron ore using energy sourced from gas or non-coking coal at temperatures below the softening point of the ore. Owing to the low reduction temperatures, the carbon content in DRI products is typically below 2%, with a total residual gangue content (e.g., SiO2, CaO, MgO, and Al2O3) below 5%.
2.1. High-quality feedstock for electric-furnace steelmaking
The EAF process, with its low dependence on iron ores, is more energy efficient and environmentally friendly than BF-BOF steelmaking. However, scrap smelted in an electric furnace contains large proportions of residual impurity elements. DRI is chemically pure and stable and can effectively dilute the impurity elements of scrap in electric-furnace steelmaking. It requires raw material with a small acidic gangue content (typically less than 3% and no more than 5%) to reduce the power consumption, improve the productivity, and lengthen the furnace lining life of steel electro-smelting. As shown in Fig. 1(a), adding 30% DRI with a 5% gangue content maximizes the electric-furnace productivity. To decrease the energy consumption of an EAF, when the gangue content is 4% in DRI, the percentage of DRI in the charge is allowed to be as highest as 85%, but the acceptable proportion decreases with increasing gangue content (Fig. 1(b) [13]). Most DRI products (95%) are utilized in electric-furnace steelmaking.
2.2. Applications to the BF-BOF steelmaking process
The oxidation of heat-generating elements (e.g., Si and C) in molten iron often generates excess heat that must be removed by a coolant in order to maintain a suitable steel temperature. The cooling effect of DRI is 1.2-2.0 times greater than that of returned scrap, but the cooling efficiency of DRI decreases with increasing metallization rate. At a metallization rate of 85%, the cooling efficiency of DRI decreases to 30% above that of scrap. Further increase of the metallization rate to 95% induces an additional 10% drop in cooling efficiency [21]. In BF ironmaking, DRI was historically utilized as the charge component to enhance the overall metallization degree of the BF burden, thereby reducing coke consumption and increasing the pig-iron output. However, the economic efficiency of DRI utilization in BF smelting is suboptimal because DR consumes many reductants that increase the cost.
2.3. Other utilizations
DRI can partially replace pig iron during the casting process. However, as DRI can reduce the Si and C contents of cast iron, its acceptable dosage is limited. In addition, the DRI used for pig-iron casting demands a high metallization rate to minimize the additional capacity required for supplementary FeO reduction in the furnace, whereas the gangue content of the DRI employed in pig-iron casting is not strictly regulated.
DRI powder with a high iron grade (TFe > 98.5%) has emerged as a critical industrial raw material in powder metallurgy, soft magnetic materials, wastewater treatment, and other industries. In recent years, the thriving automotive and lithium battery industries have escalated the demand for high-purity reduced iron powder [22].
3. Status of world DRI production
The global DRI output has trended upward since the 1970s, with remarkable annual surges between 2016 and 2019 and an excess of 100 Mt in 2018. This upward trend was interrupted by a minor decline in 2020 due to the coronavirus disease 2019 (COVID-19) pandemic (Fig. 2). In 2021, the global DRI output recovered to 119.2 Mt, indicating a year-on-year growth of 13.7%. The global DRI output then grew rapidly to 127.4 Mt in 2022 and reached an unprecedented level of 135.7 Mt in 2023 [2], [23].
The major DRI production processes are gas-based and coal-based, respectively represented by the Midrex and HYL-III/Energiron processes and rotary kilns (RKs) processes. Gas-based processes account for approximately 70% of the global DRI production because they can be used to operate large-capacity single reactors (Figs. 3(a) and (b)).
As shown in Table 2 and Fig. 4 [23], the global output of DRI is unevenly distributed, being concentrated in regions or countries where NG or non-coking coal is available at economically viable prices. For example, the Middle East, South Africa, and India collectively contribute over 70% of the global DRI production.
India, which is abundant in non-coking coal, produces most of its DRI in coal-based RKs. This nation continued its trend as the top DRI producer in 2023, outputting 49.33 Mt (an 13.3% increase from the previous year) of DRI in that year. Of the total yield, 81% (39.9 Mt) was produced via the coal-based RK method. In contrast, Iran’s total DRI yield in 2023 (33.45 Mt) was produced via gas-based methods, with a 90% contribution from the Midrex process, while PERED plants produced an estimated 2.8 Mt.
In 2023, Russia was the third-highest DRI-producing nation, with a DRI yield of 7.76 Mt. The high productivity of the Midrex hot briquetted iron (HBI) plants in Russia was sustained by captive iron ore, low NG prices, and continuous demand for DRI. The DRI yields in Saudi Arabia have grown relatively slowly, with outputs of 6.68 in 2023. Egypt have surpassed Mexico for 5th place with 6.42 Mt DRI output, while the DRI yields in Mexico was 5.92 Mt in 2023. The DRI production in the US reached its highest production at 5.48 Mt. Other Middle Eastern and North African countries have improved their DRI outputs after the COVID-19 pandemic and installed new DRI-producing plants. For example, Algeria’s DRI output surged almost two times that of 2020 and reached 4.17 Mt in 2023.
The short supply of NG in China has restricted the domestic development of gas-based DR processes. Consequently, coal-based methods have dominated DRI development in China over the past two decades. Scholars in China have focused on increasing the efficiency and cost effectiveness of coal-based RKs rather than improving their cleanliness [21], [24], [25], [26], [27], [28], [29], [30], [31]. Several RK-based DRI plants have been constructed for commercial production in Beijing, Shandong, Xinjiang, and other regions of China (Table 3). However, the operation of coal-based RKs in these plants has been hindered by unsatisfactory economic returns and the impact of increasingly strict environmental policies. Therefore, many of these facilities lie idle.
In 2020, Jiuquan Iron & Steel proposed a novel coal-based DR process to improve the efficiency of RK. This process generates H2 via the gasification and pyrolysis of non-coking coals enriched in volatile components, thereby achieving the fast reduction of iron ore. Nevertheless, this technology is currently in the pilot-scale experimental stage and is mainly applied to solid-waste disposal.
Coal gasification shaft-furnace DR is cleaner and more efficient than coal-based processes [32], [33], [34], [35], [36], [37], [38], [39], [40]. Because it reduces NG consumption, this process is considered a suitable developmental route for DRI production in China. Despite improving the energy efficiency and reducing the greenhouse gas emissions of DRI production, this technology has not been widely taken up, because its high investment precludes its competitive profit in comparison with conventional BFs.
Fortunately, gas-based DR processes in China have advanced in recent years. These developments are primarily driven by policies and regulations aimed at achieving a carbon emissions peak and carbon neutrality. One notable development is the gas-based shaft-furnace reduction line constructed by Taihang Mining Co., Ltd. (Shanxi Province, China), with an annual DRI capacity of 300 kt. This facility adopts a derivative of PERED technology—China Shanxi DRI (CSDRI) technology for DRI production. The reducing gases are generated via coke oven gas (COG) reforming, which reduces or eliminates the need for NG. However, this facility is currently being renovated and has not run smoothly. Two other hydrogen-based facilities have been constructed in Hebei Province, China, by Hebei Iron & Steel Group Co., Ltd. Each facility can produce 550 kt of DRI per annum. One facility using COG-zero reforming (ZR) technology has begun operation in May 2023. The H2 content in the reducing gas at this facility reportedly reaches 80%, approximately eight times the CO content. The other facility, which is still under construction, utilizes H2 generated from renewable resources as the reducing gas.
Sinosteel Engineering & Technology Co., Ltd. (Beijing, China) has contracted Tenova HYL to design and supply a hydrogen-based 1.0 Mt·a−1 Energiron plant, which will be installed at Baosteel Zhanjiang Iron & Steel Co., Ltd. (Guangdong Province, China). This facility can accept various types of feed gases, such as COG, NG, and H2. Several trials have been conducted with different gases composition in early 2024. Once it is fully functional, the facility is expected to produce relatively low greenhouse gas emissions. Several hydrogen-based shaft-furnace production lines are also underway. Despite these recent advancements, the progress of gas-based processes in China remains sluggish, hindering prospects for DRI development. DRI production in China has never reportedly been over 1 Mt·a−1 since 2000, and it has been nearly at zero in recent years (Fig. 5 [23]).
According to data from the World Steel Association, global crude steel production reached approximately 1892 Mt in 2023, including a 541 Mt (28.6%) contribution from electric furnace steelmaking. In contrast, China’s total crude-steel production in 2023 was 1019 Mt, of which only 100.9 Mt (9.9%) was produced in electric furnaces [2]. This data suggests that China produces a much lower proportion of electric-furnace steel than the global average. Short-process electric-furnace steelmaking has been extensively developed in developed countries with abundantly available scrap resources and is now viable in China due to increasing scrap resources [41] (Fig. 6). Nevertheless, the scarcity of domestic DRI necessitates a heavy reliance on imports. Midrex Technologies, Inc. reported that China imported 1.5 Mt of DRI and HBI in 2021 and 0.8 Mt in 2022, respectively [23], ranking China among the top three importers globally. The insufficient availability of DRI is emerging as a crucial constraint on electric-furnace-produced steel in China, warranting urgent attention.
4. Overview of DRI production technologies
As a seminal method in the evolution of ironmaking, the DR of iron has been continuously refined since the first DR patent was issued in the late 18th century. Some of the numerous historical DR processes have been replaced by innovations of industrial technology. DR methods are typically classified as gas-based, coal-based, and electrothermal, depending on their primary energy source (i.e., gases, non-coking coal, and electricity, respectively). DR methods can also be secondarily classified based on their reactor type, such as shaft furnace, fluidized bed, RK, and rotary hearth furnace (RHF; Fig. 7) [13], [18], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53].
4.1. Gas-based DR methods
Most gas-based DR methods are carried out in shaft furnaces, fluidized beds, and fixed-bed reactors. Fixed-bed reactor processes, represented by HYL-I and HYL-II processes, have become obsolete owing to their discontinuous operation mode, while fluidized-bed techniques are too immature for widespread industrial adoption at present. Consequently, the gas-based shaft furnace is the preferred choice for DRI production. Because of their maturity and broad applicability, the Midrex and HYL-III/Energiron processes are commonly employed, outputting over 70% of the global DRI yield.
4.1.1. The Midrex process
Fig. 8 and Table 4 [13] show the typical flow and operating indices of the Midrex process, respectively. Iron ores are introduced from the top of the shaft furnace, while reducing gas is injected at 800-900 °C from the middle of the furnace. As it moves against the rising, hot reducing gas, the iron oxide is heated and reduced to metallic iron. The discharged DRI can be cooled and passivated for storage and shipping, briquetted as HBI while still hot, or directly fed to an EAF for steelmaking. Any off-gas at the top of the shaft furnace passes through a scrubber, which increases its H2 + CO content to approximately 70%. Around 30%-40% of this gas is combusted for heating the cracking furnace (reformer), and the remainder (60%-70%) enters the compressor, where it is evenly mixed with NG in a specific ratio. The mixture is then catalytically reformed in the reformer and converted into a reducing gas containing approximately 95% CO + H2 and 5% CO2 + H2O. The catalytic reforming process of NG occurs via Eqs. (1), (2) at 850-900 °C. During this process, the off-gas behaves as a cracking agent in the reformer, and the H2 content in the reformed reducing gas is generally about 1.5 times the CO content.
CH4 + CO2 → 2CO + 2H2
CH4 + H2O → CO + 3H2
During reduction, sulfur (S) elements are transferred from feedstock to the off-gas, causing nickel-based catalyst poisoning and failure when entering the reformer. For this reason, the S content in raw materials should be strictly limited to 0.01% or lower. Midrex Technologies Inc. has devised a novel process that permits iron ores with higher S content. Unlike the standard process, most of the scrubbed off-gas is passed to the cooling section and is desulfurized by the hot DRI before being discharged as the cracking agent to the reformer. Nickel-based catalyst poisoning is avoided because off-gas with a high S content does not come into direct contact with the catalyst. Consequently, the allowable S content in the ore is higher, at 0.02%.
In terms of efficiency, output, and product quality, the Midrex process is the most sophisticated DR process available. At present, approximately 100 Midrex-based facilities are operating worldwide, and various derivatives of the normal Midrex process are implemented. For example, the MxCol, Midrex Flex, and Midrex H2 processes employ syngases [44], [45], [48], mixed H2 and NG in a specific ratio [46], [50], and pure H2 [18], [42], [49] as the reductants, respectively. Furthermore, it is planned for the Midrex H2 process to generate green H2 via water electrolysis, thereby converting carbon-based metallurgy into hydrogen-based metallurgy. In Sweden, Midrex has contracted Paul Wurth to build a Midrex H2 plant with an annual capacity of 2.1 Mt of DRI, which is expected to be commissioned by 2025.
4.1.2. The HYL-III/Energiron process
Fig. 9 shows a schematic of another important gas-based DR process: namely, the HYL-III process [13], [18], [47], pioneered by Hojalata Y Lamina S.A., in Monterrey, Mexico, in 1980. In terms of application scale, the HYL-III process is preceded only by the Midrex process. The HYL-III technology operates similarly to the Midrex process, albeit with some differences. For example, the Midrex reformer operates on mixed cleaned off-gas and NG, with no steam necessary [46]. The temperature and composition of the reformed gas is then adjusted as needed. In contrast, the off-gas does not need to be reformed in HYL-III, and the reformer operates on NG using externally generated steam as the cracking agent. This process increases the H2 content of the reductants and requires cooling of the reformed gas to remove water. The reformed gas is then combined with off-gas (with most of its CO2 removed), and the mixture is heated to approximately 900-960 °C, which possibly modifies its chemistry [52], [53]. Unlike the Midrex process, HYL-III feeds NG and steam to its reformers, reducing the burden of the reformers and remarkably shrinking the investment cost. Moreover, as the off-gas is not recirculated back to the reformers feed, the gas phase cannot transfer S from the ores to the reformer, so nickel-based catalyst poisoning is avoided.
The higher H2-to-CO ratio of the feed gas necessitates a higher temperature (typically 930 °C) to overcome the endothermic nature of the HYL-III reduction reactions. Furthermore, HYL-III reactors require a high pressure (∼0.55 MPa) to overcome the increased consumption of reducing gases caused by the fast escape of low-molecular-mass H2, whereas the Midrex process usually runs at approximately 0.2 MPa [52], [53].
The capacity of HYL-III reactors has expanded over time, and the modern HYL-III reactors usually produce more DRI than the Midrex reactors in a single module. Exploiting the well-known catalytic ability of the hot-state DRI in the shaft furnace, Energiron has recently achieved internal reforming. Also known as the Energiron-ZR technology (Fig. 10), this process avoids the need for an external reformer. In other words, Energiron-ZR is an innovative DR technology that can utilize various types of reducing gas sources, such as COG, syngas, or even pure H2, thereby enabling gas-based DRI production in NG-deficient areas [42], [45], [48], [49].
By 2022, 23 DR plants worldwide had adopted the HYL-III/Energiron process for DRI production, and 17 shaft furnaces were in operation [23]. The gas-based shaft furnaces currently operating in the Hebei and Guangdong Provinces in China adopt the Energiron production process as well.
4.1.3. The fluidized-bed process
Fine ores must be agglomerated before entering Midrex or HYL-III shaft furnaces, which results in extra investment and energy consumption. The fluidized-bed process is designed to utilize fine ores directly [52], and the reduction of iron oxides typically occurs in multiple reactors, as shown in Fig. 11. Iron oxides first pass through a preheater, as does the reducing gas, ensuring that the reactants are at the required temperatures when they enter the first reduction chamber [53]. Fluidized beds utilize the same thermodynamic principles as shaft furnaces, but the ores are typically well mixed. Thus, iron oxides can be reduced faster via fluidized-bed reactors than through shaft furnaces. The main issue for a fluidized-bed process is to keep the fluidization stable during the transformation of the iron oxide phases to metallic iron [54], [55], especially when operating with ultra-fine ores [56], [57]. Another issue is the constant conflict between the need for high temperatures (to enhance the reaction kinetics and counteract endothermic reactions) and lower temperatures (to avoid particles sticking) [13]. De-fluidization can be avoided by means of various modification methods [56], [58], and the fluidization state during reduction can also be monitored [55], permitting the process conditions to be changed in time.
Fluidized-bed technology is promising, thanks to the steadily increasing amount of ultra-fines resulting from the intensified beneficiation of low-grade ore [59]. However, this technology is too immature for widespread industrial adoption at present and is typically used as the pre-reduction segment in smelting reduction processes.
4.2. Coal-based DR methods
4.2.1. The two-step process
Gas-based DR methods are more efficient than coal-based methods, allowing greater capacity within a single module. However, coal-based methods are preferred in regions or countries with low NG resources but abundant iron-ore resources and non-coking coals. Moreover, most coal-based DR methods adopt the RK as a reactor.
As most RKs operate on similar basic principles, we provide a general description, referring to the SL-RN flowchart in Fig. 12 [53]. The main components of an RK system are the RK and a product cooler. Oxidation-roasted pellets are conventionally used as feed in RK plants. However, there are some drawbacks to the use of roasted pellets: ① A two-step high-temperature treatment is needed to obtain DRI from iron ore concentrates, resulting in great investment and energy consumption; ② the use of roasted pellets results in poor reducibility and high reduction disintegration; and ③ the resulting DRI has a low iron grade due to the dosage of bentonite during the making of pellets. Different types of highly reactive non-coking coals, such as lignite, sub-bituminous coal, and bituminous coal, can be used as reductants. The RK inclines at 3°-4° from the horizontal plane. Coarser reductants and iron ores enter the upper zone of the kiln, where the ores are preheated and the coals are pyrolyzed. The finer coals are sprayed as fuel into the kiln from the discharge end, where they are combusted for heat generation. As the kiln spins, the feeds move forward and are reduced to metallic iron by the coals and volatiles. The final products are cooled in a rotary cooler and separated from the char and gangue when discharged. The char is recycled, while the products are briquetted or directly used in steelmaking.
Coal-based RKs, in which iron oxide reduction co-occurs with coal chemical processes, allow DR development in countries and regions with limited NG resources and abundant high-quality ores. However, coal-based RK technologies are inefficient, are difficult to scale up, consume high energy, and frequently form rings. Further improvement of RKs is therefore demanded.
4.2.2. The one-step process
A DR method invented by Central South University (Hunan Province, China) increases the efficiency and decreases the energy consumption of RKs by feeding composite binder pellets (CBPs) to kilns (Fig. 13) [28], [30], [31]. The composite binder contains numerous organic components extracted from low-rank coals (e.g., lignite) and performs multiple roles, including binding, reduction, catalysis, and heating. In addition to improving the pelletability, strength, and reducibility of the pellets, the binder enhances the quality of the products and enables a one-step CBP process. In this process, the green pellets are dried and preheated (850-950 °C) before reduction roasting, and DRI is produced after the one-step high-temperature processing of the iron-ore concentrates. In contrast, the green pellets in the two-step process must be oxidized at high temperatures (1200-1300 °C). Compared with conventional two-step processes, the one-step CBP process shortens the process flow, lowers the investment cost, reduces the energy consumption, and improves the efficiency.
As mentioned earlier, to improve the efficiency of coal-based RKs, Jiuquan Iron & Steel (Gansu Province, China) proposed a novel coal-based DR process in 2020 that generates a large number of H2 and CO molecules via the pyrolysis and gasification of non-coking coals with a high content of volatile components. The process is schematized in Fig. 14.
Feedstock and recycled semi-coke are loaded into the upper zone of the kiln. After moving against the hot flue gas, they are dried and preheated in the drying and preheating zone. As they move forward, the feeds are heated to 600 °C, and the iron oxide is pre-reduced by the pyrolysis gas released from the highly reactive coals. After entering the 800-1000 °C zone, the feeds are further reduced with carbon, and the reducing gas is primarily generated via coal gasification using CO2, enriching its CO content. The highly reactive coals are sprayed from the discharge end into the > 1000 °C zone, where they are fully pyrolyzed and gasified by steam. The feeds are further reduced by H2-enriched gas and gradually cooled. The discharged final products are cooled and separated from char and gangue.
4.2.3. Other coal-based methods
Other coal-based DR methods include the RHF process [60], [61] and the tunnel kiln process [62], [63]. The former is fed with carbon-bearing pellets or briquettes and offers high reproducibility. However, the low thermal efficiency of RHFs limits the height of the pellet layers on the rotary hearth to 1-3 pellets. Moreover, the thermal system and atmosphere of a rotary hearth are difficult to control. Disposing of valuable byproducts in RHFs is more economical than producing DRI because the high residual ash content raises the gangue content of DRI, thereby harming the productivity of the EAFs. The tunnel kiln process is disadvantaged by low thermal efficiency, high energy consumption, and notable pollution. Furthermore, this process is unsuitable for large-scale production and cannot fulfill the current requirements of the steel industry. Its primary application is producing reduced iron powder for powder metallurgy.
Because of the small capacity of single kilns and its high energy consumption, the RK process cannot comply with the increasingly strict environmental policies of DRI development in China, nor can the DRI shortage in China be alleviated by tunnel kilns and RHFs, which have a small capacity and deliver unstable product quality. Therefore, exploring a suitable route for large-scale DRI production is vital.
5. Challenges and pathways for developing DR in China
A scarcity of scrap, insufficient DRI output, and the difficulty of supplying cheap green electricity have slowed the development of short-process electric furnace steelmaking in China. Recycled scrap importation has increased in recent years, and the rising accumulation of scrap will alleviate the charge shortage for EAFs. Advances in ultrahigh-voltage and long-distance transmission techniques, along with the start-up of large-scale green-power plants, will enable economic green-power generation. Cleaner steelmaking will increasingly rely on DRI, a high-quality alternative to scrap in EAFs. The following analysis discusses energy options, raw material preparation, and the optimization of DR processes in DRI development in China.
5.1. Energy source options
5.1.1. Use of NG
As is well known, recoverable NG resources in China are low, accounting for only 4.5% of the global reserves in 2021 (Fig. 15) and only 5.2% (207.58 billion m3) of the overall global output [64], [65]. However, China is a large NG consumer, with an apparent consumption of 378.7 billion m3. Approximately 44% of China’s consumed NG is imported, mainly from Central Asia, Russia, and Australia [64], [65]. The huge demand and scarcity of NG resources in China has raised the cost of NG in gas-based DR processes.
NG-based DRI production in China could be promoted by exploring and developing NG resources abroad, strengthening collaborations with overseas gas businesses, promoting NG exploration, integrating China’s interests with those of neighboring regions or countries, and improving the coordination between captive and imported resources [66], [67].
Approximately 12.5% of China’s total resources are unconventional-gas resources, such as coalbed methane and shale gas (Fig. 16). Coalbed methane, shale gas, and gas in tight sand, which have total recoverable reserves of 12.5, 21.8, and 11.3 billion m3 [65], [68], [69], respectively, have huge potential for utilization. Hydrogen production from unconventional gas is another potential technological pathway to gas-based DRI in China.
However, NG in China is mainly supplied downstream for industrial fuel gas and civilian use (where civilian use takes the first priority). Meanwhile, the unsteady supply of NG in Russia has led to fluctuations in NG prices, continued volatility in energy prices, and potential rises in international gas prices [66], [67]. Consequently, the cost of NG usage in China may also increase. In this scenario, the large-scale utilization of NG for DRI production in China is neither resource-advantageous nor sufficiently economical. Moreover, unconventional-gas usage is prohibited by the high cost of unconventional-gas separation and concentration technologies. Thus, unlike countries and regions with low NG prices, China cannot utilize conventional or unconventional-gas resources for large-scale DRI production.
5.1.2. Utilization of COG
As a high-calorie byproduct of the coking process, COG typically contains 55%-60% H2 and 24%-30% CH4. In China, COG is cheaper and more plentiful than NG and can be modified for DRI production. Therefore, replacing NG with COG can feasibly promote the development of gas-based DR processes in China [32], [70], [71].
Currently, most of the COG from integrated iron and steel works is used for sintering ignition, pellets roasting, and heating during rolling or other processes. Surplus COG is used in civilian applications, power generation, and the production of chemical products such as methanol and ammonia. Recently, COG has also been applied to liquefied NG and hydrogen production. Although it is more valuable to use COG as feed for H2 generation than as fuel, the COG from independent coking plants is typically discharged after combustion, preventing its full exploitation as a reductant [72]. The viability of COG for DRI production has increased with the maturation of COG-based shaft-furnace DR technology. COG-based DRI production would not only ease the shortage of domestic DRI but also utilize surplus COG from the BF-BOF steelmaking route, enabling the effective combination of the BF-BOF and the EAF steelmaking routes.
In 2021, China’s coke oven production capacity was approximately 460 Mt, implying an approximate COG production of 138-161 billion m3. Fig. 17 analyzes the potential of COG-based DRI production [72]. Even after consumption in the BF-BOF steelmaking process, approximately 90.2-113.2 billion m3 of COG remain in surplus. Based on current operating data from the coal-gasification-shaft-furnace installation of Taihang Mining Co., such surplus COG could produce 110-140 Mt of DRI.
Although the reforming principles and setups of COG-based DR are similar to those of NG-based DR, COG purification is more complicated and expensive than NG purification. Moreover, COG-based DR essentially draws on fossil-fuel energy, with inevitably high CO2 emissions. COG utilization is further restricted by low reforming efficiency and limited supply. Thus, COG-based DRI production is viable only when the BF-BOF steelmaking process dominates in China.
5.1.3. Hydrogen production via the gasification of low-rank coals or biomass
Coal gasification converts solids that are difficult to process and purify into gases that are easily purified and applied. Coal gasification is a clean coal technology that continues to dominate hydrogen production in China. As previously noted, China has scarce NG resources but abundant coal reserves. In fact, China owns 13% (143.2 Gt) of the overall global coal reserves. Approximately 58% of China’s coal reserves are low-rank coals with high moisture content and low calorific value. Such low-rank coals are difficult to transport and utilize, and their fuel value is poor; however, their high hydrogen content secures them as major feeds for coal gasification. Accordingly, low-rank coal is a suitable NG substitute in DRI production. As the cheapest hydrogen source, coal gasification gas can realize economical gas-based DRI production in China.
Prior to purification, non-coking coals are usually gasified in a gasifier, where the resulting reducing gases enrich the H2 and CO contents. The purified gases are then evenly mixed with the clean off-gases from the top of the shaft furnace before being fed into the furnace. After increasing the H2 content via the water-gas shift reaction, the reducing gases can be purified and decarbonized for DR individually, as shown in Fig. 18 [33], [34], [35], [36], [37].
The gases generated by pyrolyzing hydrocarbon compounds in low-rank coals can also be harnessed for DRI production. Low-rank coal-derived modified coking gasification technology integrates the technologies of low-rank coal modification, coking, and gasification [70]. First, low-rank coals are washed to obtain clean coals. Next, the unbonded clean coals undergo blending modification with caking coals to prepare modified coals with certain caking properties. The modified products are mixed with clean coals at a specific ratio and pyrolyzed via high-temperature pyrolysis to create volatiles and modified pyrolysis chars. The volatiles typically consist of H2-enriched gases, which are the critical feeds of gas-based DR. The modified char gasification gases can be directly injected into the shaft along with the volatiles or further reformed to increase their H2 content before charging. In addition to alleviating the shortage of high-quality coking coal in China, this technology enables the development of gas-based DR processes in China, although the carbon emission coefficient remains high.
Coal gasification produces approximately 22 kg CO2 per kilogram of H2 production (kg CO2·(kg H2)−1). These emissions far exceed those of steam methane reforming (with a CO2 intensity of 12 kg CO2·(kg H2)−1 (Fig. 19). Combining coal gasification with carbon capture and storage can effectively lessen CO2 emissions but increases the cost of hydrogen generation, thus lowering the cost effectiveness of coal-gasification-based DR [69], [73]. A more viable NG alternative is biomass, which is hydrogen-rich, renewable, and environmentally friendly [74], [75], [76], [77]. Despite these advantages, biomass-integrated techniques have not yet matured in China. Therefore, coal-gasification techniques that lower the cost and CO2 intensity or that utilize biomass for DRI production are expected to popularize gas-based DR while China revolutionizes its energy production.
5.1.4. Application of byproduct gases from integrated refining and chemical plants
Refining and olefin production release large amounts of H2-enriched gases (including dry gas). Regrettably, these gases are usually burned as fuel for traditional steam-cracking technology without fully exploiting their potential chemical energy. As the cost of green electricity decreases, the re-electrification of oil refining and olefin production technology will become inevitable. Once fuel energy is replaced with electrical energy, petrochemical byproducts can be harnessed for DRI production (Fig. 20).
Refining re-electrification and chemical integration will enable the production of approximately 1 m3 of H2 per kilowatt-hour of electricity via direct steam-cracking and dry reforming technologies (Fig. 21) [78]. One tonne of olefin production consumes approximately 1500 kW·h of electricity while generating approximately 1500 m3 of H2 as a byproduct. As noted previously, H2 is a critical feedstock for DR. One tonne of DRI production consumes an estimated 500-550 m3 of H2 [72], indicating that 3 t DRI can be created by harnessing the H2 generated per tonne of olefin production. Traditional steam-cracking technology in China produced approximately 50 Mt of olefin in 2020 and is expected to produce 70 Mt by 2025. If olefin production is completely electrified, the H2 byproduct will realize approximately 210 Mt of DRI in 2025. Moreover, the re-electrification of refineries will generate dry gases for use in hydrogen production. This gas-generation process is more competitive than water electrolysis in the medium term.
5.1.5. Use of green hydrogen produced by renewable sources
Unlike conventional carbon-based metallurgy, hydrogen metallurgy is a fossil fuel-free technology that reduces CO2 emissions at the source. The off-gas of hydrogen metallurgy contains only water. The produced hydrogen is divided into three groups (gray, blue, and green) with different CO2 intensities. Gray hydrogen is produced via carbon-intensive processes such as NG reforming and coal gasification, which use fossil fuels and contribute approximately 96% of the total H2 production. Blue hydrogen is made from industrial byproducts or fossil fuels. Fossil-fuel feeds require CCUS technology for H2 production, which substantially lowers the CO2 intensity from that of gray hydrogen production. Finally, green hydrogen is produced through water electrolysis with electricity generated from renewable resources. As green hydrogen emits no carbon during its entire life cycle, it is regarded as the most effective measure for decreasing CO2 emissions in the steel industry.
Although direct hydrogen reduction is the most promising ironmaking technology, the amount of green hydrogen production and the technological aspects of this process require further discussion. The first problem is maintaining the heat balance [18], [42]. As the hydrogen reduction of iron oxide is highly endothermic, the inlet-gas temperature of a hydrogen-based furnace must be raised to maintain an efficient reduction process. This problem can be overcome in three ways [79], [80], [81]: ① adding nitrogen or an inert gas as a heat carrier; ② injecting NG to release heat while sustaining the carbon content; or ③ overblowing H2 (i.e., allowing a higher H2 flow in the furnace than is required for reduction).
The second problem is the zero carbon of DRI during full-hydrogen practice. Products without carbon are easily re-oxidized and difficult to transport and store. Moreover, an EAF requires DRI with a 1.5%-3.0% carbon content to metalize the iron, supply extra energy for smelting, and ensure the formation of foamy slag. This problem can be overcome by introducing hydrocarbons such as NG in the cooling zone, which would modify the carbon content of DRI.
In addition, full hydrogen reduction requires a high operating pressure to decrease hydrogen consumption and maintain a heat balance in the furnace. To operate at a high pressure, the quality of the reactor and the supporting equipment must be improved. Both the Midrex and Energiron DR processes can easily accommodate hydrogen-enriched gases operation in large-scale shaft furnaces, and a full-H2 fluidized bed was successfully operated in the last century, demonstrating the feasibility of using 100% H2 in the shaft furnace of DR processes. The exergy efficiency also should be fully considered; the exergy efficiency of the green hydrogen generation-shaft furnace-EAF process is only 28%-45% [82].
Table 5 compares the performance of different hydrogen-production technologies [69], [83], [84], [85], [86]. Hydrogen production using the existing techniques is neither large-scale nor economically viable. Therefore, achieving all-hydrogen DR presents major challenges.
Over the short term, DR in China can be most competitively realized through modified COG and coal-gasification gas. Using byproduct gases from refinery or petrochemical plants might also clean the production of iron and steel. However, H2 made from fossil fuels leaves a carbon footprint [69], [81]. Although processes run on industrial byproduct gases have lower CO2 intensity than those run on fossil fuels, they are typically followed by gas purification, which raises their cost. Nuclear energy is a zero-carbon method for large-scale hydrogen production, but its use is limited by the need for waste-material disposal [69]. The electrolysis of water using renewable resources—that is, wind, solar, and tide energy—is the best approach to green hydrogen production; however, due to technical limitations, it is costlier and less efficient than fossil fuels or byproduct gases [83], [87]. To develop direct hydrogen reduction, the evolution of low-cost, large-scale H2 generation techniques is needed.
In summary, fossil fuels will remain China’s primary energy source over the long term. As NG usage in China is economically nonviable, neither conventional- nor unconventional-gas resources can generate reducing gas for large-scale DR facilities. At this stage, more feasible solutions for DRI production include surplus COG from integrated iron and steel plants, all types of syngas, and byproduct gases from integrated refining and chemical plants. However, the available COG will gradually decline as long flow processes are phased out. In addition, methods using the abovementioned gases are carbon-intensive ironmaking processes with high CO2 intensity. Therefore, they are suitable only for short-term applications. As the energy revolution proceeds, the costs of CCUS and electrolyzers are likely to decrease. During the transition period, hydrogen made from fossil fuels can be combined with the CCUS technique for DRI production, and hydrogen can be generated via water electrolysis using grid powder. In the long run, DRI is expected to eventually be produced using 100% green hydrogen derived from renewable sources, thereby realizing carbon-free steelmaking.
5.2. Preparation of high-quality charge for DR
Natural rich lump ores and high-grade pellets are both good feedstocks for DR. To ensure that DRI is accepted as a smelting raw material by EAFs, the iron grade of the ores or pellets should exceed 67%, and the acid gangue content should be below 5%. As shown in Fig. 22(a), China consumes a huge quantity of iron ores annually, of which the majority (∼70%-80%) are imported. The iron ores imported into China are transported through a single pathway, mainly from Australia and Brazil (Fig. 22(b)) [64]. As most of the imported ores are low-iron grade and fluctuate in quality, they fail to meet the requirements for DRI production, so they are typically reserved for sintering.
The average iron grade of the iron ores in China is about 34%; high-grade iron ores are scarce [88]. China contains numerous complex iron-ore resources with fine embedded particle sizes and complex co-associated components. Less than 3% of these iron ores are suitable for DRI production. High-grade concentrates that meet the requirements for DRI production must be obtained through further processing. Such high-grade fine concentrates can either be directly reduced in fluidized beds or pelleted and fed into RKs and shaft furnaces. However, as fluidized-bed processes tend to become sticking and defluidized during reduction, high-quality pellet feeds improve the operability of DR.
According to the International Iron Metallics Association, the global demand for commercial-grade iron-ore pellets for DR could rise from 38 Mt in 2020 to 53 Mt by 2025 and to 81 Mt by 2030. Approximately 28.5 Mt of this demand will come from newly started DRI plants. In the near future, the global demand will likely overtake the supply of pellets for DRI production. China’s DRI demand is estimated at 15-45 Mt by 2025, which also suggests a high demand for iron-ore pellets for DR.
Clearly, innovative deep processing techniques for iron ores with an iron grade below 67% are required. Re-gridding followed by the beneficiation of iron-ore concentrates can yield raw materials with stable quality for DRI production. High-performance, low-cost binders are also essential. The most widely used binder in iron-ore pelletization is bentonite, which mainly consists of SiO2 and Al2O3 and introduces many alumino silicate impurities when applied at high dosage. Therefore, bentonite binder decreases the iron grade of the pellets. In contrast, organic binders contain low residue and can be applied at a low dosage to maintain the iron grade of the pellets. Unfortunately, the usage cost of organic binder is more than double that of bentonite, and the pellets prepared with organic binder have low thermal strength. Composite binders, which typically combine the advantages of both inorganic and organic binders, can realize the requisite low residue, good performance, and low cost of binders for pellet-based DR in China.
5.3. Process and equipment
As mentioned in Section 5.2, pellet-based DR techniques are more operable than techniques using fine-grain concentrates. To obtain DRI from iron-ore concentrates, conventional pellet-based processes require two high-temperature steps (i.e., oxidation roasting at 1200-1300 °C and reduction roasting at 800-1100 °C), which are carried out in different equipments. Hot oxidized balls must be cooled for transportation and then heated to the requisite temperature for reduction; moreover, the low porosity of oxidation-roasted pellets inhibits the reduction reaction, unavoidably increasing the fuel consumption and reducing the production efficiency.
A one-step process would improve the efficiency of DR. In the one-step process, the pellets are subjected only to reduction roasting from concentrates to DRI (high-temperature oxidation roasting is omitted). The feedstocks of one-step processes are pellets containing organic or composite binders. With their higher internal porosity, the pellets are obviously more easily reduced than oxidation-roasted pellets. Consequently, the process flow is shorter, the energy consumption and production cost are lower, and the efficiency is higher in one-step processes than in conventional two-step processes.
The one-step coal-based RK DR technology is mature and has entered industrial production. Coal continues to dominate energy sources in China (Fig. 23) and is expected to maintain this dominance over the long term. Producing DRI via one-step coal-based RKs with higher efficiency and less environmental damage would mitigate the current shortage of DRI in China.
A high-performing, economically feasible novel binder with low residual content is essential for improving the efficiency of RKs in the one-step route. Meanwhile, as demonstrated by the one-step DRI production practices already implemented in China, optimizing the thermal system of the RK is essential for improving the efficiency of coal-based RKs. RKs can be cleaned by substituting non-coking coals with highly reactive renewable biomass. However, biomass-based techniques have not yet matured in China and must be further developed.
The inherent drawbacks of RKs—namely, scale-up difficulty and high CO2 intensity—will limit the wide future application of RK technology in China. For high-grade iron ore (TFe > 67%), the one-step gas-based DR-EAF route, which offers a greater production capacity and lower CO2 intensity than RK-based methods, is the expected direction of DR development; for medium-grade iron ore (TFe = 63%-67%), the gas-based DR-electric furnace smelting-converter steelmaking process would effectively alleviate the shortage of high-quality iron ore in the future.
6. Conclusions
The main points of this review are summarized below.
(1) Hydrogen-based ironmaking technologies and EAF processes can lower the carbon footprint of ironmaking and steelmaking. Hydrogen-based DR is the most promising solution for transitioning from carbon to hydrogen metallurgy because it can operate on any mixture of NG and hydrogen (including pure hydrogen). DRI has emerged as an excellent alternative for scrap in EAF-based steelmaking. In addition, DRI, with its high purity and stable chemical composition, can be applied as a fine charge for producing most high-grade and special steels. However, almost no DRI is produced in China. To promote the low-carbon and high-quality development of the steel industry in China, DR technology must be further developed.
(2) In China, NG is scarce, and the hydrogen derived from existing electrolytic water technologies is prohibitively expensive. Therefore, in the short term, both COG from integrated iron and steel plants and byproduct gases from integrated refining and chemical plants are viable substitutes for NG in DRI production. Our investigation revealed that surplus COG can yield approximately 110-140 Mt of DRI; in other words, surplus COG promises to reduce the carbon emissions of DRI production during the current period, when the conventional BF-BOF route still dominates crude-steel production. If olefin production is completely electrified in China, sufficient hydrogen byproduct for over 200 Mt of DRI is obtainable by 2025. Over the mid-term of the energy revolution, the available COG will gradually decline with the phasing-out of the long flow process. During this period, hydrogen generated from fossil fuels will be combined with the CCUS technique for DRI production, and electrolysis water using grid powder will be employed for hydrogen production. As the energy revolution proceeds, efforts to popularize renewable energy sources must be intensified. Finally, DRI production using 100% green hydrogen derived from renewable sources is expected for carbon-free steelmaking.
(3) High-grade iron ores are the major feeds of DRI production. Steel-industry developments are depleting the global supply of premium iron ores. Most of the iron-ore concentrates produced by existing beneficiation processes are unsuitable for DRI production in China. Further processing technologies of iron-ore concentrates, such as iron enrichment through re-grinding and re-beneficiation, are needed to obtain higher-grade concentrates that meet the requirements for DRI production.
(4) Conventional DRI production from pelleted fine-iron-ore concentrates involves two high-temperature steps: oxidation roasting and DR. Doping with bentonite and lime reduces the iron grade of the products. Moreover, conventional DRI production has a long process flow, consumes a great deal of energy, and requires a large investment. To overcome these problems, China must innovate DR technologies and supporting techniques such as one-step gas-based DR, hot briquetting, and the HYTEMP pneumatic transport system that sends hot DRI from the reduction reactor to the EAF shop. A high-performance, low-cost novel binder with low residual content is essential for preserving the iron grade of the product. One-step high-temperature roasting from iron concentrates is also necessary for efficient DRI production. Technologies for producing DRI from fine concentrates—that is, fluidized-bed processes—should be developed and implemented.
(5) Current attempts to reach carbon neutrality have rapidly increased the global demand for high-quality iron ore. A serious shortage of high-quality iron ore for DR is expected in future. The development of medium-grade iron ore (TFe = 63%-67%) via the DRI-electric furnace smelting process would effectively alleviate the shortage of high-quality iron ore while realizing low-carbon green production. New processes for green H2-based DR-electric-smelting-converter steelmaking and related equipment for utilizing medium-grade iron ore are demanded in future.
Acknowledgments
This work is supported by the Strategic Research and Consulting Project of Chinese Academy of Engineering (2022-XY-91), the Basic Science Center Project for National Natural Science Foundation of China (72088101), and the Key Project of YueLuShan Center Industrial Innovation (2023YCII0105).
Compliance with ethics guidelines
Chengzhi Wei, Xin Zhang, Jin Zhang, Liangping Xu, Guanghui Li, and Tao Jiang declare that they have no conflict of interest or financial conflicts to disclose.
Sustainabilityindicators2022 report. Report. Brussels: World Steel Association; 2022 Dec.
[2]
World steel in figures 2024. Report. Brussels: World Steel Association; 2024 May.
[3]
S.H.Zhang, B.W.Yi, F.Guo, P.Y.Zhu.Exploring selected pathways to low and zero CO2 emissions in China’s iron and steel industry and their impacts on resources and energy. J Clean Prod, 340 (2022), p. 18.
[4]
F.Q.Shangguan, Z.D.Liu, R.Y.Yin. Study on implementation path of “carbon peak” and “carbon neutrality” in steel industry in China. China Metall, 31 (9) (2021), pp. 15-20. Chinese.
[5]
J.L.Shen, Q.Zhang, L.S.Xu, S.S.Tian, P.Wang.Future CO2 emission trends and radical decarbonization path of iron and steel industry in China. J Clean Prod, 326 (2021), p. 14.
[6]
R.Y.An, B.Y.Yu, R.Li, Y.M.Wei. Potential of energy savings and CO2 emission reduction in China’s iron and steel industry. Appl Energy, 226 (2018), pp. 862-880.
[7]
J.Zhao, H.Zuo, Y.Wang, J.Wang, Q.Xue. Review of green and low-carbon ironmaking technology. Ironmaking Steelmaking, 47 (3) (2020), pp. 296-306.
[8]
L.Ren, S.Zhou, X.M.Ou. The carbon reduction potential of hydrogen in the low carbon transition of the iron and steel industry: the case of China. Renew Sustain Energy Rev, 171 (2023), Article 113026.
[9]
J.Perpinan, B.Pena, M.Bailera, V.Eveloy, P.Kannan, A.Raj, et al. Integration of carbon capture technologies in blast furnace based steel making: a comprehensive and systematic review. Fuel, 336 (2023), Article 127074.
[10]
Iron and steel technology roadmap:part of energy technology perspectives. Report. Paris: International Energy Agency; 2020 Oct.
[11]
Z.Y.Fan, S.J.Friedmann. Low-carbon production of iron and steel: technology options, economic assessment, and policy. Joule, 5 (4) (2021), pp. 829-862.
[12]
T.Wolfinger, D.Spreitzer, H.Zheng, J.Schenk. Influence of a prior oxidation on the reduction behavior of magnetite iron ore ultra-fines using hydrogen. Metall Mater Trans B, 53 (1) (2022), pp. 14-28.
C.Lan, Y.Hao, J.Shao, S.Zhang, R.Liu, Q.Lyu. Effect of H2 on blast furnace ironmaking: a review. Metals, 12 (11) (2022), p. 1864.
[15]
Y.Chen, H.Zuo. Review of hydrogen-rich ironmaking technology in blast furnace. Ironmaking Steelmaking, 48 (6) (2021), pp. 749-768.
[16]
H.Nogami, Y.Kashiwaya, D.Yamada. Simulation of blast furnace operation with intensive hydrogen injection. ISIJ Int, 52 (8) (2012), pp. 1523-1527.
[17]
M.A.Zarl, D.Ernst, J.Cejka, J.Schenk. A new methodological approach to the characterization of optimal charging rates at the hydrogen plasma smelting reduction process part 1: method. Materials, 15 (14) (2022), p. 4767.
[18]
J.Tang, M.S.Chu, F.Li, C.Feng, Z.G.Liu, Y.Zhou. Development and progress on hydrogen metallurgy. Int J Miner Metall Mater, 27 (6) (2020), pp. 713-723.
[19]
Y.Ma, J.W.Bae, S.H.Kim, M.Jovičević-Klug, K.Li, D.Vogel, et al. Reducing iron oxide with ammonia: a sustainable path to green steel. Adv Sci, 10 (16) (2023), Article 2300111.
[20]
D.Raabe. The materials science behind sustainable metals and alloys. Chem Rev, 123 (5) (2023), pp. 2436-2608.
[21]
T.Jang, G.Z.Qiu, J.C.Xu, D.Q.Zhu.Direct reduction of composite binder pellets and use of DRI. Electrotherm (India) Ltd, Ahmedabad (2007).
[22]
G.Z.Yao, Y.L.Li, Q.Guo, T.Qi, Z.C.Guo. Preparation of reduced iron powder for powder metallurgy from magnetite concentrate by direct reduction and wet magnetic separation. Powder Technol, 392 (2021), pp. 344-355.
[23]
World direct reduction statistics 2023. Report. Charlotte: Midrex Technologies Inc; 2023 Sep.
[24]
X.B.Zhang, M.H.Wang, M.Y.Kou. New technology of coal-based hydrogen metallurgy for green and short-flow steelmaking. Mining Metall Eng, 41 (6) (2021), pp. 174-177. Chinese.
[25]
L.K.Hong, H.Y.Qi, C.J.Sun, J.J.Gao, B.Q.Wu. Direct reduction of coal based vanadium-bearing titanomagnetite. Iron Steel, 52 (11) (2017), pp. 15-19. Chinese.
[26]
R.F.Wei, D.Q.Cang, L.L.Zhang, Y.Y.Bai. Staged reaction kinetics and characteristics of iron oxide direct reduction by carbon. Int J Miner Metall Mater, 22 (10) (2015), pp. 1025-1032.
[27]
J.Kou, T.Sun, D.Tao, Y.Cao, C.Xu.Coal-based direct reduction and magnetic separation of lump hematite ore. Miner Metall Process, 31 (3) (2014), pp. 150-161.
[28]
D.Q.Zhu, V.Mendes, T.J.Chun, J.A.Pan, Q.H.Li, J.Li, et al. Direct reduction behaviors of composite binder magnetite pellets in coal-based grate-rotary kiln process. ISIJ Int, 51 (2) (2011), pp. 214-219.
[29]
Z.H.Lu, Y.Chen, D.M.Chen, S.Q.Li. Experimental research on rotary kiln one-step process DRI productions. J Iron Steel Res Int, 23 (5) (2011), pp. 11-14. Chinese.
[30]
J. Li. A study on mechanism and process of direct reduction of pellets made from concentrate and composite binder. Central South University Press, Changsha (2007). Chinese.
[31]
Z.C.Huang. Cold-bonded pellets direct reduction technology of and use of the technology. Central South University Press, Changsha (2002). Chinese.
[32]
S.H.Geng.Fundamental research on gas-based direct reduction of iron ore with reformed coke oven gas. Shanghai University Press, Shanghai (2018). Chinese.
[33]
Y.J.Su, M.X.Cai, Y.H.Du, S.L.Chen.Esitimation of two-section series DRI process using coal gas. China Metall, 27 (5) (2017), pp. 27-32. Chinese.
[34]
Z.C.Wang, S.Y.Chen, M.S.Chu, Z.G.Liu, J.W.Zhang. Tentative study on direct reduction iron production by gasification-shaft furnace. China Metall, 23 (1) (2013), pp. 20-25. Chinese.
[35]
Z.C.Wang. Fundamental study on process of coal gasification-gas based shaft furnace direct reduction. Northeastern University Press, Shenyang (2013). Chinese.
[36]
Y.S.Zhou, H.Qian, H.Y.Qi, D.M.Liu, H.T.Feng, et al. Scheme of direct reduction iron production combined with coal gasification. Iron Steel, 47 (11) (2012), pp. 27-31. Chinese.
[37]
D.G.Yang. A study on process of direct reduction of pellets made from concentrate based on coal gasification. Central South University Press, Changsha (2012). Chinese.
[38]
Y.Q.Li, H.Chen, X.W.Li, Y.S.Zhou, Q.S.Gan. Change of carbon and sulfur contents in the pellets during direct reduction in BL shaft furnace. Baosteel Technol, 5 (2000), pp. 21-24. Chinese.
[39]
Z.T.Feng, H.C.Chu, J.L.Xu. A new use of water gas: production of sponge iron by BL method. Coal Chem Ind, 1 (2000), pp. 51-55. Chinese.
[40]
H.Chen, Y.Q.Li, Y.S.Zhou, B.Q.Chen, X.W.Li, et al. BL shaft furnace direct reduction process. Baosteel Technol, 4 (1999), pp. 25-28. Chinese.
[41]
Z.F.Cui, F.Q.Shangguan, F.J.Wang, J.C.Zhou, A.J.Xu. Analysis and prediction of scrap resources in China from 2022 to 2060. Iron Steel, 58 (6) (2023), pp. 126-133. Chinese.
[42]
R.R.Wang, Y.Q.Zhao, A.Babich, D.Senk, X.Y.Fan. Hydrogen direct reduction (H-DR) in steel industry—an overview of challenges and opportunities. J Clean Prod, 329 (2021), Article 129797.
[43]
F.M.Shen, X.Jiang, Q.J.Gao, G.Wei, H.Y.Zheng. Situation and prospect on production technology of direct reduction iron. Iron Steel, 52 (1) (2017), pp. 7-12. Chinese.
[44]
QianLF. Midrex syngas based direct reduction technology. In: Proceedings of the 10th CSM Steel Congress & the 6th Baosteel Biennial Academic Confrence; 2015 Oct 21-23; Shanghai, China. Beijing: Metallurgical Industry Press; 2015. p. 1257-66. Chinese.
[45]
F.M.Zhang, C.Z.Cao, H.Xu. Current status and prospects of gas-based shaft furnace direct reduction technology. Iron Steel, 49 (3) (2014), pp. 1-10. Chinese.
[46]
L.Y.Yi. Fundamental research on gas-based direct reduction of iron ore pellets with carbon monoxide and hydrogen mixtures. Central South University Press, Changsha (2013). Chinese.
[47]
J.Fang.Non-blast furnace ironmaking process and theory. ( 2nd ed.), Metallurgical Industry Press, Beijing (2012). Chinese.
[48]
H.D.Ye, F.Q.Zheng, B.Hu, W.L.Li, C.Liu. Status and development trend of hydrogen-based fuel non-blast furnace iron-making technology. Sintering Pelletizing, 47 (1) (2022), pp. 10-17. Chinese.
[49]
X.Y.Guo, Y.L.Chen, Q.H.Tian, Q.M.Wang. Research progeress on hydrogen metallurgy theory and method. Chin J Nonferrous Met, 31 (7) (2021), pp. 1891-1906. Chinese.
[50]
L.Y.Yi, Z.C.Huang, H.Peng, T.Jiang. Action rules of H2 and CO in gas-based direct reduction of iron ore pellets. J Cent South Univ, 19 (8) (2012), pp. 2291-2296.
[51]
S.X.Wen. A novel direct reduction technology-energiron. Sintering Pelletizing, 34 (4) (2009), p. 27. Chinese.
[52]
S.K.Dutta, R.Sah. Direct reduced iron:production. Encyclopedia of iron, steel, and their alloys, CRC Press, New York City (2016).
[53]
T.Battle, U.Srivastava, J.Kopfle, R.Hunter, J.McClelland. The direct reduction of iron. Treatise on process metallurgy, Elsevier, Cambridge (2014).
[54]
J.H.Shao, Z.C.Guo, H.Q.Tang.Influence of temperature on sticking behavior of iron powder in fluidized bed. ISIJ Int, 51 (8) (2011), pp. 1290-1295.
[55]
L.Guo, Z.Wang, S.P.Zhong, Q.P.Bao, Z.C.Guo.Fluidization state monitoring using electric current during fluidized bed reduction of iron ore. Powder Technol, 343 (2019), pp. 683-692.
[56]
T.Wolfinger, D.Spreitzer, J.Schenk. Analysis of the usability of iron ore ultra-fines for hydrogen-based fluidized bed direct reduction—a review. Materials, 15 (7) (2022), p. 2687.
[57]
S.Y.He, H.Y.Sun, C.Q.Hu, J.Li, Q.S.Zhu, H.Li.Direct reduction of fine iron ore concentrate in a conical fluidized bed. Powder Technol, 313 (2017), pp. 161-168.
[58]
Z.Du, Y.Ge, F.Liu, C.L.Fan, F.Pan. Effect of different modification methods on fluidized bed hydrogen reduction of cohesive iron ore fines. Powder Technol, 400 (2022), Article 117226.
[59]
A.M.Nyembwe, R.D.Cromarty, A.M.Garbers-Craig. Prediction of the granule size distribution of iron ore sinter feeds that contain concentrate and micropellets. Powder Technol, 295 (2016), pp. 7-15.
[60]
M.K.Sharma, V.Solanki, G.G.Roy, P.K.Sen. Study of reduction behaviour of prefabricated iron ore-graphite/coal composite pellets in rotary hearth furnace. Ironmaking Steelmaking, 40 (8) (2013), pp. 590-597.
[61]
F.M.Zhang. Progress of rotary hearth furnace direct reduction technology. J Iron Steel Res Int, 16 (2009), pp. 1347-1352.
[62]
X.T.Yu. Sponge iron and reduced iron powder produced by Hoganas process. Powder Metall Technol, 3 (1997), pp. 31-39. Chinese.
[63]
S.Y.Wu, N.P.Xu, Y.L.Jin. Recent state of Hoganas process in China. Sintering Pelletizing, 1 (1996), pp. 36-39. Chinese.
[64]
China mineral resources 2022. Report. Beijing: Ministry of Natural Resources of the People’s Republic of China; 2022 Sep. Chinese.
[65]
China natural gas development report 2022. Report. Beijing: Petroleum Industry Press; 2022 Aug. Chinese.
[66]
F.Gao, B.L.Liu, M.L.Li, C.X.Li. Global natural gas development trend and enlightenment. China Pet Explor, 27 (6) (2022), pp. 13-21. Chinese.
[67]
R.Chen, H.Bai. Review of global natural gas market in recent years and prospects for 2025. J China Univ Pet, 35 (5) (2019), pp. 1-7.
[68]
S.W.Zhou, J.L.Zhu, T.W.Shan, Q.Fu, D.Zhang, et al. Development status and outlook of natural gas and LNG industry in China. China Offshore Oil Gas, 34 (1) (2022), pp. 1-8.
[69]
J.W.Cao, W.Q.Zhang, Y.F.Li, C.H.Zhao, Y.Zheng, et al. Current status of hydrogen production in China. Prog Chem, 33 (12) (2021), pp. 2215-2244. Chinese.
[70]
Y.J.Zhao, Q.Yi, T.Wang, J.C.Han, Y.Cui, Q.Liu, et al. Key technologies and strategic thinking for the coal-coking-hydrogen-steel industry chain in China. SSCAE, 23 (5) (2021), pp. 103-115. Chinese.
[71]
Y.Zhou, H.J.Zhou, C.M.Xu. Exploration of hydrogen sources for the low-carbon and green production in the steel industry in China. Chem Ind Eng Prog, 41 (2) (2022), pp. 1073-1077. Chinese.
[72]
Y.X.Dai, J.J.Yu, Z.C.Wang, Y.Chen. Consideration on layout of metallurgical processes of long and short flow based on coke oven gas balance. Sintering Pelletizing, 47 (3) (2022), pp. 66-72. Chinese.
[73]
J.J.Li, W.J.Cheng. Comparative life cycle energy consumption, carbon emissions and economic costs of hydrogen production from coke oven gas and coal gasification. Int J Hydrogen Energy, 45 (51) (2020), pp. 27979-27993.
[74]
I.N.Zaini, A.Nurdiawati, J.Gustavsson, W.J.Wei, H.Thunman, R.Gyllenram, et al. Decarbonising the iron and steel industries: production of carbon-negative direct reduced iron by using biosyngas. Energy Convers Manage, 281 (2023), p. 19.
[75]
A.Nurdiawati, I.N.Zaini, W.J.Wei, R.Gyllenram, W.H.Yang, P.Samuelsson.Towards fossil-free steel: life cycle assessment of biosyngas-based direct reduced iron (DRI) production process. J Clean Prod, 393 (2023), p. 15.
[76]
J.L.Zhang, H.Y.Fu, Y.X.Liu, H.Dang, L.Ye, A.N.Conejio, et al. Review on biomass metallurgy: pretreatment technology, metallurgical mechanism and process design. Int J Miner Metall Mater, 29 (6) (2022), pp. 1133-1149.
[77]
I.Shukla.Potential of renewable agricultural wastes in the smart and sustainable steelmaking process. J Clean Prod, 370 (2022), p. 13.
[78]
H.J.Zhou, Y.Zhou, C.M.Xu. Exploration of refining and chemical integration under China’s dualcarbon target. Chem Ind Eng Prog, 41 (4) (2022), pp. 2226-2230. Chinese.
[79]
F.Patisson, O.Mirgaux. Hydrogen ironmaking: how it works. Metals, 10 (7) (2020), p. 922.
[80]
D.Spreitzer, J.Schenk.Reduction of iron oxides with hydrogen—a review. Steel Res Int, 90 (10) (2019), p. 1900108.
[81]
XuWR, ZhuRL, MaoXM, ChuMS, TangJ. Current status and main problems of hydrogen metallurgy. In: Proceedings of the 13th CSM Steel Congress; 2022 Apr 9-10; Chongqing, China. Beijing: Metallurgical Industry Press; 2022. p. 507-9. Chinese.
[82]
F.Li, M.Chu, J.Tang, Z.Liu, Z.Zhao, P.Liu, et al. Quantifying the energy saving potential and environmental benefit of hydrogen-based steelmaking process: status and future prospect. Appl Therm Eng, 211 (2022), Article 118489.
[83]
Y.Z.Wang, S.Zhou, X.W.Zhou, X.M.Ou. Cost analysis of different hydrogen production methods in China. Energy China, 43 (5) (2021), pp. 29-37. Chinese.
[84]
E.Cetinkaya, I.Dincer, G.F.Naterer. Life cycle assessment of various hydrogen production methods. Int J Hydrogen Energy, 37 (3) (2012), pp. 2071-2080.
[85]
R.Shandarr, C.A.Trudewind, P.Zapp. Life cycle assessment of hydrogen production via electrolysis—a review. J Clean Prod, 85 (2014), pp. 151-163.
[86]
M.D.Ji, J.L.Wang. Review and comparison of various hydrogen production methods based on costs and life cycle impact assessment indicators. Int J Hydrogen Energy, 46 (78) (2021), pp. 38612-38635.
[87]
J.N.Tian, J.Jiang, Y.Luo, X.Ma. Development status and trend of green hydrogen energy technology. Distrib Energy, 6 (02) (2021), pp. 8-13. Chinese.
[88]
Y.X.Han, Q.Zhang, Y.S.Sun, P.Gao, Y.J.Li. Progress in pharse transformation technology for clean and efficient utilization of refractory iron. J Iron Steel Res Int, 34 (12) (2022), pp. 1303-1313.
RIGHTS & PERMISSIONS
THE AUTHOR
AI Summary 中Eng×
Note: Please be aware that the following content is generated by artificial intelligence. This website is not responsible for any consequences arising from the use of this content.
PDF
(4283KB)
