Free Access
Issue
Metall. Res. Technol.
Volume 117, Number 3, 2020
Article Number 305
Number of page(s) 8
DOI https://doi.org/10.1051/metal/2020026
Published online 13 May 2020

© EDP Sciences, 2020

1 Introduction

The development of iron and steel industry in China has been unprecedented and spectacular since the policy of reform and opening-up in 1978. Figure 1 presents the crude steel production in China from 1978 to 2019 [1]. The crude steel production in 2019 has reached up to 996.3 million tons, which means 31.5 times that of 1978 and 53.3% of the whole world in the same year.

Large blast furnace (BF) technology has played a very important role in the development of Chinese iron-making industry [2,3]. According to Chinese iron-making industry standards, the BFs whose effective volume equals to or is larger than 4000 m3 are classified as large BF or super-large BF. With the constructions of Shougang Jingtang No. 3 BF and Baosteel Zhan Jiang No. 3 BF, the number of large BFs has been to 26 (Tab. 1) in China [4,5]. Although the number of large BFs in China continues to increase, however, the average volume of whole Chinese BFs in service is still significant smaller than that of Western Europe and Japan [68]. Moreover, the technological level and economical indexes of Chinese large BFs are still at a moderate level besides Baosteel and Shougang group [9,10].

The development and production of large blast furnaces from 2015 to 2016 in China has been reviewed [11], in order to elucidate the further production status of large BFs in China for the last three or four years, the production indexes of large BFs between the first half of 2019 and 2015–2016 has been reviewed and compared, including the production status, reductant consumption, raw materials and operation conditions. Furthermore, a detailed discussion has been made on various affecting factors in the development of large BFs and the corresponding optimization advice.

thumbnail Fig. 1

Crude steel production in China from 1978 to 2019.

Table 1

Effective volume over 4000 m3 BFs in China.

2 Production status

2.1 Utilization coefficient and reductant consumption

Figure 2 shows the utilization coefficient and reductant consumption of 23 large BFs in the first half of 2019 with an average effective volume of 4608.91 m3, which is 22.32 m3 larger than that of the 22 large BFs in 2015–2016. The average utilization coefficient is 2.11 t · m−3 · d−1, which is 0.05 t · m−3 · d−1 higher than that of 2015–2016 [11]. So there is no significant increasing in hot metal output, indicating that the development concept of BF ironmaking in China is sticking to the stable production, long life and high quality rather than blind efficiency. It is so farsighted and advisable that BF operators insisted on the long-term benefits together with stable operation, high quality of hot metal and long-term campaign of BF in the last few years. Since the 19th National Congress of the Communist Party of China (CPC), it has become a strategic thinking to promote ecological progress and balance the relationship between environmental protection and economic development, so “clear water and green mountains are mountains of gold and silver”. For further realizing energy-saving and low-carbon of ironmaking, the reductant consumption of large BFs insists on low coke ratio, high coal ratio and low reductant ratio. The average coke ratio, coal ratio and reductant ratio of 23 BFs are 355.26 kg · t−1, 155.65 kg · t−1 and 510.91 kg · t−1 respectively, so the reductant ratio of the first half of 2019 was 2.84 kg · t−1 lower than that of 2015–2016 [11]. Among all the BFs, 2 BFs from Baosteel Zhan Jiang that has surpassed 4 BFs from Baosteel have the lowest reductant ratio, the average is 494.64 kg · t−1, which could represent the advanced level of the world. On the other hand, statistics in Figure 2 reveal that the other large BFs in China are also in progress.

thumbnail Fig. 2

Utilization coefficient and reductant consumption of large BFs.

2.2 Raw materials

The raw materials with high quality and low cost is always not only a focus of attention of the BF operators [12,13], but also a lasting challenge for ironmaking.

2.2.1 Coke

The inferior coke with small CSR and M40, high CRI and M10 will destroy the stable running of BF due to the decrease in coke size from furnace hearth and the breathability and permeability of BF [14]. The larger BF volume, the higher coke standard. However, the resource of good coking coal are decreasing day by day, so it is more difficult to produce high quality coke by the inferior coking coal. Figure 3 shows the main indexes of coke fed into large BFs in the first half of 2019. The average ash is 12.22% and sulfur is 0.74% in the first half of 2019, on the other hand, the average ash is 11.94% and sulfur is 0.69% in 2015–2016 [11], which means the quality of coking coal is getting worse in 2019 than 2015–2016. But for all this, with the continuous improvement of coking technology in China, the quality of coke is not only undiminished but also a little elevated. The average M40 is 89.65%, M10 is 5.50%, CSR is 69.46%, CRI is 21.89%, particle size is 51.24 mm and nut coke ratio is 32.29 kg · t−1 in the first half of 2019, which are a little better than those of 2015–2016 whose M40 is 89.58%, M10 is 5.67%, CSR is 69.11%, CRI is 22.67%, particle size is 51.38 mm and nut coke ratio is 35.64 kg · t−1 [11]. Even now, the indexes above have been obviously better than before [15] and still satisfy the requirements for large BFs. But if the quality of coking coal continued to decline, so would the quality of coke, which means the stability of BF would be seriously threatened at the same time.

thumbnail Fig. 3

Main coke indexes of large BFs.

2.2.2 Coal

The quality of pulverized coal affects the thermal status and reductant ratio of BF. As shown in Figure 4, the pulverized coal’s average C, volatile, ash, sulfur are 71.57%, 17.98%, 9.48%, 0.49% respectively in 2015–2016 and are 70.52%, 18.11%, 9.58%, 0.52% respectively in the first half of 2019. So the quality of pulverized coal that is the same to the coke is getting worse too. In order to maintain a higher theoretical combustion temperature and increase the combustion rate of pulverized coal and the quality of hot metal, large BFs need to use pulverized coal with higher C, lower ash, volatile and sulfur.

thumbnail Fig. 4

Main pulverized coal indexes of large BFs.

2.2.3 Burden structure and Fe content

BF burden structure is generally composed of basicity sinters, acid pellets and lump ore [16]. Figure 5 shows the burden structure of large BFs. The average proportions of sinter, pellet and lump ore are 71.98%, 19.56% and 8.46% respectively in 2015–2016 [11], the average proportions of sinter, pellet and lump ore are 72.92%, 17.01% and 10.07% respectively in the first half of 2019, so there is no significant change by the average. But if deeply comparing the data of every BF, it is easy to find that 4 BFs of Baosteel have increased the proportions of sinter and lump ore, decreased the proportions of pellet. On the other hand, 2 BFs of Shougang Jingtang and 2 BFs of Taiyuan Steel have increased the proportions of pellet, decreased the proportions of sinter and lump ore. The belt type roasting machine has been used to produce pellet in Shougang Jingtang, which is a more economical, efficient and environmental way to prepare high-quality raw materials for BF. Thus, the burden structure of different BFs should be adjusted according to its own situation within a reasonable range.

The average Fe content of sinter is 57.38% and comprehensive Fe content is 58.99% in the first half of 2019. Compared with 2015–2016 [11], although the average Fe content of sinter is improved slightly, the comprehensive Fe content is declined by 0.17%, which indicates that the quality of iron ore used in large BFs is not only still inferior to that of large BFs from developed countries [8] but also presenting the tendency of decreasing.

thumbnail Fig. 5

Burden structure and Fe content of large BFs.

2.3 Operation condition

2.3.1 Operation level

Operation levels of large BFs could be reflected by the indexes shown in Figure 6. The large BFs in the first half of 2019 have the average air consumption of 1013.63 m3 · t−1, gas utilization rate of 47.72%, coke load of 4.45, first-grade hot metal of 72.03% and precipitator dust ratio 15.05 kg · t−1. On the other hand, the indexes in 2015–2016 are 1066.47 m3 · t−1, 48.53%, 5.1, 76.07% and 14.49 kg · t−1 respectively [11], so besides the air consumption, the other indexes look worse than before. These indexes embody that the average operating level of Chinese large BFs still falls behind America, Europe, Japan and South Korea [17,18]. Specifically, both the air consumption and precipitator dust ratio are higher, however, gas utilization, coke load and first-grade product are lower. Compared Figure 2 with Figure 6, there is a strong correlation between reductant ratio and gas utilization rate, reductant ratio decreases with the increase of gas utilization rate [19]. Taking the 4 BFs from Baosteel and 2 BFs from Baosteel Zhan Jiang as example, their average gas utilization rate of 50.43% is the highest, while their average reductant ratio of 495.75 kg · t−1 is the lowest, which represents the highest level in China.

thumbnail Fig. 6

Main operation level indexes of large BFs.

2.3.2 Blast air condition

Figure 7, the average oxygen-rich and blast air temperature of the first half of 2019 are 3.8% and 1205.15 °C respectively, 2015–2016 are 1206.24 °C and 3.4% respectively [11]. Although that oxygen-rich has just increased 0.4% is not as high as abroad [20], which is conducive to the safety and longevity of BF [21]. There is only one reasonable position of tuyere raceway for each BF according to the actual smelting situation [22]. Blast air speed is one of the most important factors on the position of tuyere raceway [23]. The average blast air speed of large BFs is 249.58 m · s−1 in the first half of 2019 and 265 m · s−1 in 2015–2016. For large BF whose hearth diameter is over 10 m, blast air speed should be in a range of 260–280 m · s−1 to blow through BF hearth center, so the blast air speed presents an unreasonable trend. The problem is not only that, but also the average pressure difference of 178 kpa in the first half of 2019 is higher than that of 160 kpa in 2015–2016 [11], which indicates that the stable production of large BFs faced some difficulties and challenges in the first half of 2019.

thumbnail Fig. 7

Main blast air condition indexes of large BFs.

2.3.3 Thermal condition

Thermal condition signifying the temperature and heat level of BF hearth regulates the equilibrium state of heat income and expense [24]. Either too low or too high heat of hearth will cause BF fluctuations. Hearth heat as the main thermal condition index consists of chemical heat determined by silicon content in hot metal and physical heat related to the temperature of hot metal. As shown in Figure 8, the average silicon content and temperature of hot metal are 0.41% and 1505.10 °C respectively in the first half of 2019, are 0.43% and 1502.38 °C respectively in 2015–2016 [11]. Thus, thermal condition of most BFs in China has walked a big step toward low-silicon smelting. But the hot metal temperatures of some BFs are even less than 1500 °C, which are needed to increase 10 °C at least.

thumbnail Fig. 8

Main thermal condition indexes of large BFs.

2.3.4 Slag condition

In general, slag condition that decided by raw materials and hot metal composition has an effect on slag fluidity, slag stability, slag sulphide capacity [25,26]. As the other one main product from BF, slag is more important than hot metal in BF stability and hot metal quality [27]. The slag condition indexes of large BFs are presented in Figure 9. The average slag ratio, basicity, MgO content, Al2O3 content, MgO/Al2O3 are 298.08 kg · t−1, 1.19, 7.51%, 14.27% and 0.53 in the first half of 2019 respectively, so the slag condition is relatively stable comparing with 2015–2016 [11].

thumbnail Fig. 9

Main slag condition indexes of large BFs.

2.3.5 Charging condition

In previous study, the two charging modes for bell-less BFs in China have been introduced, including non-central coke charging and central coke charging [2831]. Table 2 shows the distribution matrices of 5 large BFs with non-center coke charging, the average effective volume of 5 large BFs is 4530.6 m3, the average gas utilization rate and reductant consumption are 50.10% and 498.01 kg · t−1 respectively. Table 3 shows the distribution matrices of 3 large BFs with center coke charging, the average effective volume of 3 large BFs is 4510.7 m3, the average gas utilization rate and reductant consumption are 44.55% and 533.54 kg · t−1 respectively. So there are 5.55% and 35.53 kg · t−1 difference in gas utilization rate and reductant consumption between non-central coke charging and central coke charging of the total eight BFs samples, which means 1% of gas utilization rate corresponds to 6.4 kg · t−1 reductant consumption.

In fact, the similarity between the two modes is to maintain central gas flow by placing some coke in BF center indirectly or directly. The reason why non-central coke charging is unsuitable to every BF is that the raw materials quality fed into the BF does not meet the corresponding requirements [11]. For the BF with raw materials of poor quality, central coke charging is “providing timely help”, however non-central coke charging is “icing on the cake”, so optimizing the charging principle by combining the characteristics of the two modes is the right way to improve BF performance. Herein, there are 2 successful cases in Table 4, the new charging mode is temporarily defined as“Hybrid”in order to explain better.

Table 4 shows the distribution matrices of 2 large BFs with hybrid, the average effective volume of two large BFs is 5275 m3, the average gas utilization rate and reductant consumption are 49.46% and 499.40 kg · t−1 respectively. The new charging mode of hybrid comes from the exploration of practical experiments, the amount of center coke was reduced from 20–30% to 10–15% of coke batch comparing with the traditional center coke charging, and the amount of edge coke was increased appropriately at the same time. Such burden matrices could form two platforms and a funnel on the surface layer. The former inhibited the horizontal movement of ore particles and the latter help large coke particles move to BF center. Consequently, hybrid took the advantages of both central and non-central coke charging and had a great effect on reducing reductant consumption.

Table 2

The distribution matrices of 5 large BFs with non-center coke charging.

Table 3

The distribution matrices of 3 large BFs with center coke charging.

Table 4

The distribution matrices of 2 large BFs with hybrid.

3 Advice for large BF

3.1 Stability

Utilization coefficient, reductant consumption, gas utilization rate and the other production indexes were extremely influenced by the stability of BF which is not only the basic requirement of the production, but also the only way to realize high quality, low consumption and long campaign of large BF. By the comparison, the stability of large BFs in the first half of 2019 is not as well as 2015–2016, so some work should be done to stop and recover the unfavorable situation.

3.2 Raw material

The quality of raw materials used in large BFs in the first half of 2019 witnessed a downward trend, which should be paid morn attention. If not, the unfavorable situation of large BFs would deteriorate further. Especially the coke’s quality must be promoted to the nationwide average level at least, ash should be lower than 12%, sulfur should be lower than 0.7%. The average pellet percent of Chinese large BFs is only 17.01% much lower than that of Europe and America large BFs, which is essential to increase the pellet percent in the burden structure.

3.3 Operation conditions

The operation conditions are listed as follows:

  • blast air condition: blast air speed is in a range of 260–280 m · s−1;

  • thermal condition: low-silicon smelting requires silicon content of 0.15%–0.25% and hot metal temperature of 1500 °C–1520 °C;

  • slag condition: basicity increases to 1.20, slag ratio and Al2O3 content are as low as possible and MgO/Al2O3 is in an appropriate range according to the BF situation;

  • charging condition: practice has proved that hybrid which took the advantages of both central and non-central coke charging and had a great effect on reducing reductant consumption is worth promoting.

4 Summary

In this paper, by comparison the production indexes of large BFs in China between the first half of 2019 and 2015–2016, the developing actuality of Chinese large BFs has been quantitively analyzed and the existing problems have been proposed clearly. In the first half of 2019, Chinese large BFs still had made a lot of achievements, but the stability of large BFs in the first half of 2019 was not as well as 2015–2016, so some work should be done to stop and recover the unfavorable situation. Based on that, the expectations of enhancing the quality of raw materials and improving the operation conditions are suggested. Large BFs make great contributions to energy saving, low-carbon, high automatic, environmental protection and economic development, so there will be more large BFs constructed and put into production in China in the future.

Acknowledgements

The authors would gratefully express their gratitude to the operation indexes of large BFs from China Iron and Steel Association.

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Cite this article as: Bing Dai, Hong-ming Long, Yi-long Ji, Dai-wen Liu, Jia-yong Qiu, Development and production of Chinese large blast furnaces in 2019 compared with 2015–2016, Metall. Res. Technol. 117, 305 (2020)

All Tables

Table 1

Effective volume over 4000 m3 BFs in China.

Table 2

The distribution matrices of 5 large BFs with non-center coke charging.

Table 3

The distribution matrices of 3 large BFs with center coke charging.

Table 4

The distribution matrices of 2 large BFs with hybrid.

All Figures

thumbnail Fig. 1

Crude steel production in China from 1978 to 2019.

In the text
thumbnail Fig. 2

Utilization coefficient and reductant consumption of large BFs.

In the text
thumbnail Fig. 3

Main coke indexes of large BFs.

In the text
thumbnail Fig. 4

Main pulverized coal indexes of large BFs.

In the text
thumbnail Fig. 5

Burden structure and Fe content of large BFs.

In the text
thumbnail Fig. 6

Main operation level indexes of large BFs.

In the text
thumbnail Fig. 7

Main blast air condition indexes of large BFs.

In the text
thumbnail Fig. 8

Main thermal condition indexes of large BFs.

In the text
thumbnail Fig. 9

Main slag condition indexes of large BFs.

In the text

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