Development of Low Carbon Blast Furnace Operation Technology by using Experimental Blast Furnace

Abstract

CO₂ Ultimate Reduction System for Cool Earth 50 (COURSE50) successfully carried out operational trials with an experimental blast furnace in which the effect of the reaction-control by COG injection, top gas recycling, and use of high reducibility sinter on the carbon rate were determined. The conditions of the operational trials were designed by applying the mathematical blast furnace model that was developed. The results obtained in the operational trials indicate that the proportion of carbon direct reduction can be decreased while maintaining that of CO reduction, by the reaction-control by COG injection, top gas recycling, and use of high reducibility sinter. A reduction in the carbon rate of approximately 10% was achieved as predicted by the mathematical blast furnace model.

1. Introduction

The steel industry is one of the industrial sectors that emit a large amount of CO₂. In the steelmaking process, two different major process routes are available, namely the blast furnace with basic oxygen furnace (BF-BOF) route and the electric arc furnace (EAF) route. The global crude steel production from BF-BOF route accounted for 74%¹⁾ in 2016. The amount of CO₂ emissions from BF-BOF route is approximately 1.8–2.0 tons per ton of crude steel, which is approximately three times larger than that from EAF route¹⁾ because the steelmaking process with EAF does not need energy for reduction of iron oxides. However, there is currently not enough amount of scrap to meet global steel demand. Moreover, the steelmaking process from scrap containing tramp elements has not been industrially and economically established. Therefore, it is urgent need to develop CO₂ reduction technology in the blast furnace process.

In order to develop technologies for mitigation of CO₂ emissions from blast furnace process, many projects and researches have ever been made.^{2,3,4,5,6,7,8,9,10,11)} In Japan, a national project named CO₂ Ultimate Reduction System for Cool Earth 50 (COURSE50^2,3)) has been commissioned since 2008 by New Energy and Industrial Technology Development Organization (NEDO). COURSE50 is aimed at developing technologies to reduce CO₂ emissions by 30% from an integrated steel plant through the followings: 1) Approximately 10% mitigation by lowering CO₂ emissions from the blast furnace; 2) Approximately 20% mitigation through the sequestration of CO₂ in BFG. The Japan Iron and Steel Federation announced the “Commitment to a Low Carbon Society Phase II” with the target year of 2030. The first commercial plant based on COURSE50 will be operational by the year. This plan is also reflected in Japan’s Nationally Determined Contribution (NDC) (deadline: 2030) based on the Paris Agreement.

In COURSE50 project, experimental blast furnaces have been used for verification tests. Many studies on the ironmaking process using experimental blast furnaces such as those of U.S. Bureau of Mines.,¹²⁾ Tokyo University,¹³⁾ NKK,^14,15) Sumitomo Metals,^{16,17,18,19,20)} and LKAB^21,22) have been conducted to evaluate raw materials, optimize the operational parameters, and explore new technologies for the blast furnace ironmaking process. In the Ultra-Low CO₂ Steelmaking project in the European Union, nitrogen-free blast furnace processes (ULCOS-NBF) and top gas recycled blast furnace (TGRBF) with the combined implementation of CO₂ capture and storage were suggested and several trials have been conducted using LKAB’s experimental blast furnace.^4,5,6) Top gas recycling utilization of unreacted CO and H₂ in BFG is considered to be effective for reducing the carbon rate as suggested in the ULCOS project. However, the technical details of the effect of top gas recycling on the carbon rate have not been disclosed and clear.

In a blast furnace process, carbon consumption can be roughly summarized in the following three reactions: carbon combustion in raceway which provides CO gas for reduction and heat for ironmaking process; carbon direct reduction of iron oxides which is referred to as solution-loss carbon; reduction of other materials such as silicon, manganese, and phosphorous oxides; and carburizing into hot metal. Here, the carbon direct reduction of iron oxides includes smelting reduction of iron oxides, carbon gasification by CO₂ and H₂O which is generated by reduction of iron oxides by CO and H₂. The amount of heat required to reduce iron oxides depends on the proportions of reduction reactions, i.e., CO reduction, H₂ reduction, and carbon direct reduction. The latter two reactions are endothermic. In particular, carbon direct reduction requires an enormous amount of heat, which has to be provided by carbon combustion in raceway. Therefore, decreasing the proportion of carbon direct reduction (i.e., replacing carbon direct reduction with indirect reduction (CO reduction or H₂ reduction)) is an effective method for decreasing the heat required for reducing iron ore in the blast furnace process. Figure 1 shows the concept of reducing the carbon rate in a COURSE50 blast furnace. In a current blast furnace, the reaction proportions of CO reduction, H₂ reduction, and carbon direct reduction are approximately 60%, 10%, and 30%,¹⁾ respectively. There is significant scope for increasing the proportion of H₂ reduction because it is relatively low at present. Promotion of H₂ reduction in a blast furnace by use of hydrogenous gas can decrease the proportion of carbon direct reduction, which enables the carbon rate to decrease in blast furnace process.

Fig. 1.

Concept of reaction-control in COURSE50 blast furnace.

In COURSE50, Watakabe et al. carried out an operational trial²³⁾ of hydrogenous gas injection using LKAB’s experimental blast furnace in Lulea in collaboration with LKAB and Swerea MEFOS. In this trial, synthetic COG (57%H₂-31.3%CH₄-11.7%N₂) and two kinds of synthetic reformed COG (RCOG) (77.9%H₂-22.1%N₂ and 77.9%H₂-10%CO-12.1%N₂) were tested for evaluating the effects of H₂ reaction. Their results of the trial verified that the hydrogenous gas injection increased the proportion of H₂ reduction and decreased the proportion of carbon direct reduction, and decreased the carbon rate. However, their results indicated that hydrogenous gas injection into the experimental blast furnace decreased the proportion of CO reduction. Furthermore, RCOG injection from shaft tuyeres caused a low penetration depth of RCOG and deteriorated the utilization efficiency of H₂ gas. From the results, COURSE50 considered that hydrogenous gas injection from ordinary tuyeres is better than that from shaft tuyeres. Moreover, the top gas recycling is thought to be one of the countermeasures to the suppression of CO reduction because a part of unreacted CO gas from BFG can contribute to CO reduction of iron oxides. Therefore, the top gas recycling was attempted to prevent the proportion of CO reduction from decreasing while promoting H₂ reduction by injecting hydrogenous gas through ordinary tuyeres. Furthermore, the application of high reducibility sinter was also attempted to promote indirect reduction.

The aim of a COURSE50 blast furnace is to reduce the carbon rate by approximately 10% through the reaction-control by hydrogenous gas injection, top gas recycling, and use of high reducibility sinter. In order to determine the effect of the reaction-control on the reduction of the carbon rate, the COURSE50 project constructed an experimental blast furnace and conducted several operational trials. This paper presents the results of the verification tests on the effect of the reaction-control by COG injection, top gas recycling, and use of high reducibility sinter on the reduction of the carbon rate in a blast furnace ironmaking process.

2. Experimental

2.1. Experimental Blast Furnace

An experimental blast furnace with a volume of 12 m³ was constructed in Kimitsu Steel Works near a pilot test plant for capturing CO₂ from BFG which has a capacity of 30 t-CO₂/d (CAT30²⁴⁾) to carry out top gas recycling test in which BFG from the experimental blast furnace were sent to CAT30. Figure 2 shows a diagram of the experimental blast furnace. Its fundamental specifications are listed in Table 1. The hearth diameter of the furnace is 1.2 m, and the height from tuyeres to the stock level of the burden is 6.5 m. This furnace is equipped with a rotating chute as the charging device. It has a tap hole, three ordinary tuyeres, and three shaft tuyeres which are installed 1700 mm above the ordinary tuyeres. Horizontal sampling probes are installed at three levels (2059 mm, 3902 mm, and 5503 mm above the tuyeres). During the furnace’s operation, horizontal sampling probes are inserted into the furnace to measure the temperatures and gas compositions in the horizontal direction and to sample the burden materials inside the furnace.

Fig. 2.

Configuration of the experimental blast furnace.

Table 1. Basic specifications of the experimental blast furnace.

Items	Specifications
Inner volume	12 m3
Throat diameter	1.00 m
Height (from tuyere to SL)	6.50 m
Hearth diameter	1.25 m
Number of tuyeres	3
Number of shaft tuyeres	3
Number of tap-holes	1
Top charging device	Rotating chute type

The experimental blast furnace and the peripheral facilities are shown in Fig. 3. Hot air enriched with oxygen is produced by the hot stove. Pulverized coal (PC) is injected through tuyeres from PC feed tanks. The COG that is utilized in the steel works is injected through ordinary tuyeres. As for top gas recycling, BFG from the experimental blast furnace is recycled to the furnace through the shaft tuyeres after removing CO₂ by CAT30 and heating up to approximately 800°C by utilizing electric heaters.

Fig. 3.

Experimental blast furnace and peripheral facilities.

2.2 Operational Methods for Reaction-control with the Experimental Blast Furnace

Figure 4 shows a schematic diagram of blast furnace operations for the reaction-control. The base operation is an ordinary PCI operation, which is a common type of blast furnace operation. Operations A, B, and C inject COG from ordinary tuyeres. Moreover, in Operations B and C, the CO₂ in the top gas from the blast furnace is removed, and the reducing gas containing CO, H₂, and N₂ (hereinafter referred to as RG) is recycled from shaft tuyeres. In addition, in Operation C, the reducibility of sinter is controlled unlike in the other operations.

Fig. 4.

Schematic diagram of blast furnace operations for the reaction-control. (Online version in color.)

The operational conditions of the experimental blast furnace were designed using a mathematical blast furnace model.²⁵⁾ The PC injection rate, COG injection rate, RG injection rate, and JIS-RI of sinter used in each operation are listed in Table 2. The coke rate was estimated by the mathematical blast furnace model for the hot metal to attain a temperature of 1450°C (a designed value) under these conditions. The predicted decrease in carbon rate in each operation is shown in Fig. 5. The calculated results indicate that the carbon rate decreases in the following order: Operation A, Operation B, and Operation C. Furthermore, the carbon rate in Operation C can be decreased by approximately 10% compared with that in the base operation. Operational trials were conducted with the experimental blast furnace to verify the effect of each operation.

Table 2. Basic conditions planned in each operation.

Operation		Base	A	B	C
PC rate	kg/tHM	146	146	146	146
COG rate	Nm3/tHM	0	95	95	95
RG rate	Nm3/tHM	0	0	300	300
JIS-RI (Sinter)	%	64	64	64	72
Sinter ratio	%	75	75	75	75
Lump ore ratio	%	25	25	25	25

Fig. 5.

Decrease in carbon rate predicted by the mathematical blast furnace model. (Online version in color.)

2.3. Operation of the Experimental Blast Furnace

Four campaigns were conducted with the experimental blast furnace, with approximately 30 days for each campaign. In each campaign, the base operation and certain types of operation (Operation A, B, or C (see Fig. 4)) were carried out, and their carbon rate was compared with that of the base operation.

The particle size of the coke used in the operations was 15–25 mm and that of both sinter and lump ore was 10–25 mm. The reducibility of the sinter used in the base operation, Operation A, and Operation B was 64% in JIS-RI, and that in Operation C was 72% in JIS-RI.

The campaigns were carried out with the experimental blast furnace according to the following schedule. After the blow-in operation, heating-up operation was conducted for approximately 10 days to attain constant temperatures of the hearth refractory while approaching the base operation. After the heating-up operation, the base operation was continued for approximately four days to determine the material balance, measure the temperatures and gas compositions, and sample the raw materials inside the furnace by using the horizontal sampling probes. After the base operation, the transition to another operation was carried out by stabilizing the state of the reactions inside the furnace and the hot metal temperatures for approximately two days. After the stabilization, the operation was continued for approximately 4–5 days to determine the material balance, measure the temperatures and gas compositions, and sample the raw materials inside the furnace by using the horizontal probes. In addition, the hot metal temperature and components in the hot metal and slag were measured for each tapping. Immediately after the completion of all the test operations planned in each campaign, the burden materials in the furnace were cooled down with cold N₂ from the tuyeres. After the temperatures in the furnace became less than 100°C, the cold N₂ was replaced with cold air, and cooling was continued for approximately two weeks. After the cooling of the experimental blast furnace was completed, a dissection investigation was conducted. The layer structure of the burden was observed. Furthermore, the burden materials were sampled from each layer from the upper part to the lower part of the furnace, and their components were analyzed.

3. Results and Discussion

Four campaigns were successfully carried out to demonstrate the effect of Operation A, B, and C on the carbon rate compared to the base operation. Figure 6 shows an example of the operational transition in the fourth campaign in which base, Operation B, and C were carried out. During the campaigns, the coke rate was adjusted to maintain the hot metal temperature of 1450°C under the constant production rate, the PC rate, the COG rate (Operation A, B, and C), and the RG rate (Operation B and C). Overall, a stable operation was achieved.

Fig. 6.

Example of transition of experimental blast furnace operation (4th campaign).

Table 3 shows representative operational data averaged during the period almost constant for 24 hours continuously in each operation. The overall material balance and heat balance were analyzed from those data to consider the feasibility of the reaction-control and to determine the carbon rate. The proportions of CO reduction, H₂ reduction, and carbon direct reduction of iron ore are calculated by considering material balance based on the boundary mass flow data across the experimental blast furnace which determines the rate of CO reduction, H₂ reduction, and carbon direct reduction of iron ore. Figure 7 shows the variations in the proportions of CO reduction, H₂ reduction, and carbon direct reduction of iron ore as obtained from the experimental results and calculated using the mathematical blast furnace model based on the operational conditions. As for Operation A by COG injection from ordinary tuyeres, it was verified that the proportion of the H₂ reduction increased by approximately 10% compared with that in the base operation and the proportion of carbon direct reduction decreased by approximately 10% although the proportion of CO reduction was slightly decreased. In Operation B by RG injection from shaft tuyeres, the proportion of indirect reduction, which is the sum of the proportion of CO reduction and that of H₂ reduction, increased and that of carbon direct reduction decreased compared with those in Operation A. Moreover, in Operation C by the use of high reducibility sinter, the proportion of indirect reduction slightly increased and that of carbon direct reduction slightly decreased compared with those in Operation B. The CO gas utilization and the H₂ gas utilization in Operation C increased compared with those in Operation B as shown in Table 3. These increases in gas utilizations contributed to the decrease in the proportion of carbon direct reduction from 16.5% to 16.0% in the data obtained by the experiment.

Table 3. Averaged operational results of reference period.

	Unit	Base	A	B	C
Coke rate	kg/tHM	441	395	377	362
PC rate	kg/tHM	136	135	136	132
COG rate	Nm3/tHM	0	93	93	93
RBFG rate	Nm3/tHM	0	0	291	294
Blast volume rate	Nm3/tHM	977	716	682	626
O2 enrichment	%	7.9	15.2	16.0	16.9
Blast temperature	°C	1013	1003	997	996
Blast moisture	g/Nm3	4.0	4.2	3.1	3.8
Temperature of RBFG	°C	–	–	797	802
CO gas utilization, ηCO	%	42.9	44.5	42.5	43.2
H2 gas utilization, ηH2	%	40.6	44.8	45.0	50.3
Top gas temperature	°C	135	101	147	113
Production	t/d	33.0	32.9	32.9	34.7
Hot metal temperature	°C	1453	1441	1462	1457

Fig. 7.

Comparison of fraction of reduction ratio obtained by experimental blast furnace operation.

Above results indicates that the reaction-control by COG injection, top gas recycling, and use of high reducibility sinter is effective for decreasing the proportion of carbon direct reduction. These experimental results are in good agreement with the calculation results of the mathematical blast furnace model.

Figure 8 shows the effect of the total amount of H₂ input on the proportion of H₂ reduction. Here, the total amount of H₂ input implies the stoichiometric amount of H₂ in all the reducing agents provided to the experimental blast furnace. It includes the H₂ generated after the decomposition of PC, COG, and H₂O in blast air. As a whole, the proportion of H₂ reduction increases with the increase in the H₂ input to the blast furnace. This result indicates that the hydrogen provided to the blast furnace contributes to the H₂ reduction with almost an equal efficiency. On the other hand, the proportion of H₂ reduction in Operation C increased from that in Operation B by use of high reducibility sinter according to the increase in the H₂ gas utilization as shown in Table 3.

Fig. 8.

Effect of total amount of H₂ input on the proportion of H₂ reduction of iron ore.

Figure 9 shows the carbon rate and its components obtained by an analysis of each operation. The following is the decreasing order of the total carbon rate: Operation A, Operation B, and Operation C. This result agrees with that of the previous estimations obtained using the mathematical blast furnace model shown in Fig. 5. This decrease in carbon rate is mainly because of the decrease in solution-loss carbon, which corresponds to a decrease in the proportion of carbon direct reduction (see Fig. 7). Here, solution-loss carbon rate can be calculated by the following expression,   

$${\mathrm{C}}_{\mathrm{s}\mathrm{o}\mathrm{l}}={\mathrm{O}}_{\mathrm{o}\mathrm{r}\mathrm{e}}\cdot {\mathrm{D}}_{\mathrm{R}}\cdot {\mathrm{M}}_{\mathrm{C}}$$(1)

in which C_sol, O_ore, D_R, M_C are the solution-loss carbon rate (kg/tHM), the amount of the atomic oxygen to be reduced from the iron oxides in the iron ore (kmol/tHM), the proportion of carbon direct reduction (-), the atomic weight of carbon (kg/kmol), respectively. Moreover, in Operation C, the carbon consumed in the raceway decreased with the application of high reducibility sinter. This is because the application of high reducibility sinter enables the proportion of carbon direct reduction and amount of heat required in the blast furnace process to decrease as described above.

Fig. 9.

Total carbon consumption and its components.

The carbon rate in Operation C decreased by approximately 10% compared with that in the base operation. Figure 10 shows the decrease in carbon rate in each operation as determined from the experimental results and calculated using the mathematical blast furnace model based on the operational conditions. The decreases in carbon rate in Operations A, B, and C compared with that in the base operation are approximately 4%, 8%, and 10%, respectively. These experimental results are also in good agreement with the calculation results of the mathematical blast furnace model.

Fig. 10.

Decrease in carbon rate in each operation.

Figure 11 shows the heat required for reduction of iron oxides which is denoted by stacking the heat of CO reduction, carbon direct reduction, and H₂ reduction. The heat of CO reduction is extended into negative direction from zero because CO reduction is exothermic. From the bottom of the heat of CO reduction, the heat for carbon direct reduction and H₂ reduction, which are endothermic, are stacked and the top of the bar denotes the total heat consumed in reduction of iron oxides. The total heat of reduction of iron oxides in Operation A decreases compared to that in the base operation because of decrease in the heat of carbon direct reduction although the heat of H₂ reduction increases. Moreover, the total heat of reduction of iron oxides in Operation B decreases compared to that in the Operation A because of further decrease in the heat of carbon direct reduction. On the other hand, the total heat of reduction of iron oxides in Operation C is almost the same level as that in Operation B because the increase in the heat of H₂ reduction and the decrease in the heat of carbon direct reduction are canceled.

Fig. 11.

Heat required for reduction of iron oxides.

Figure 12 shows the analytical result of heat balance across the boundary of the experimental blast furnace in order to evaluate its properties of the blast furnace process in each operation. The total input heat is the sum of sensible heat of blast and RG and combustion heat of carbon in raceway, which means energy input in the process operation in the experimental blast furnace. On the other hand, the total output heat is the sum of heat for reduction of iron oxides and other materials, sensible heat of top gas, decomposition heat of PC, moisture, and COG, etc., which means energy required in the ironmaking process using the experimental blast furnace. The total input or output heat for Operation A decreases compared with those of the base operation because the heat for reduction of iron oxides decreases. However, RG injection from shaft tuyeres in Operations B increases the sensible heat of top gas and the heat loss compared to that in Operation A although the heat for reduction of iron oxides decreases. Therefore, RG injection does not necessarily contribute to output heat reduction although RG injection from shaft tuyeres contributes to decrease in carbon consumption. The use of high reducibility sinter in Operation C decreases the heat loss compared to that in Operation B because the gas utilization increases and the gas volume in the furnace decreases although RG is injected in the same way as in Operation B and the heat for reduction of iron oxides is almost the same.

Fig. 12.

Heat balance in each operation.

Figure 13 shows the distributions of solid temperature inside the experimental blast furnace on the cross-section in the direction of a tuyere side in each operation calculated using the mathematical blast furnace model. The temperatures in the lumpy zone in Operation A decreases compared with those in the base operation because of the decrease in gas volume owing to higher oxygen enrichment. Meanwhile, the temperatures in the lumpy zone in Operation B are higher than those in Operation A. This is because of the increase in gas volume owing to RG injection. However, the temperatures near the wall and upper side from the shaft tuyere level are below those in Operation A. This is because the temperature of RG (approximately 800°C) is lower than that in front of the shaft tuyeres in Operation A. The temperatures in the lumpy zone in Operation C are lower than those in Operation B. This is because of the decrease in the gas volume from the raceway owing to the decrease in the carbon input rate. The level of cohesive zone in Operation A is higher than that in the base operation notwithstanding the decreasing temperatures in the lumpy zone in Operation A as described above. This is because the increase in the proportion of indirect reduction in Operation A results in the decrease in the apparent specific heat capacity of burdens in the lower part of the furnace and it causes the heat flow ratio in the lower part of the furnace to decrease. Therefore, the thickness of the cohesive zone in Operation A is less than that in the base operation. Meanwhile, the level of cohesive zone in Operation B is lower than that in Operation A. This is because the temperatures in front of the shaft tuyere in Operation A are higher than that of RG (800°C). The level of cohesive zone in Operation C is lower than that in Operation B because of a larger decrease in the gas volume from the raceway owing to the decrease in the carbon input rate.

Fig. 13.

Distribution of solid temperature inside the experimental blast furnace in each operation calculated using the mathematical blast furnace model.

Figure 14 shows the 1-dimensional distributions of the reduction degree of iron ore inside the experimental blast furnace calculated by averaging the values at the same heights in the 3-dimensional calculation results with the mathematical blast furnace model. The reduction degree of iron ore increases with increase in the temperature inside the furnace. The reduction degree of iron ore in Operation A is higher than that in the base operation at all the temperatures because of the contribution of H₂ reduction. Meanwhile, the increase in the reduction degree of iron ore in Operation B accelerates in the temperature region above 800°C in the lumpy zone because of RG injection. It corresponds to the temperatures greater than 800°C in front of the shaft tuyere in Operation B as shown in Fig. 13. RG injection results in the higher reduction degree in the cohesive zone. Operation C shows the highest reduction degree of iron ore at all the temperatures compared with the other operations.

Fig. 14.

Distribution of reduction degree of iron ore inside the experimental blast furnace calculated using the mathematical blast furnace model.

Figure 15 shows a comparison between the measurement results (obtained using the horizontal probes) and calculation results (obtained using the mathematical blast furnace model) of the H₂ concentration distribution in Operation A. The measured results show that H₂ reduction occurs almost in the lower region than in the middle level of the horizontal probe. The calculation results obtained using the model reproduce the measured values accurately.

Fig. 15.

Comparison of calculated and measured radial distribution of H₂ concentration in Operation A.

In addition, to evaluate the reduction state of the iron ore in the furnace, the burden materials in the furnace were sampled during the operation or after blow-off, and the reduction degrees were measured and compared. Figure 16 shows a comparison between the calculation results (obtained using the mathematical blast furnace model) and measured results of the reduction degree of iron ore for Operation B. Here, the measured values were determined from samples obtained with the horizontal sampling probes during operation. It is verified that the two are relatively in good agreement. Similarly, Fig. 17 shows a comparison between the calculated and measured results of the reduction degree of iron ore in Operation B. Here, the measured values were obtained by the dissection investigation performed after blowing off and cooling down. The results of the dissection investigation in the upper part of the furnace show higher reduction degrees, and those at the stock level are approximately 10%. It is likely that the reduction degree of iron ore increased by 10% after the last charge until blow-off that took several minutes. Considering this, the measured and calculated results are almost in good agreement. These facts shown in Figs. 16 and 17 that the calculated and measured results show in good agreement indicate that the mathematical blast furnace model can predict the inner state of the furnace with high accuracy under conditions with the COG injection, RG injection.

Fig. 16.

Comparison of calculated and measured reduction degrees during Operation B obtained by horizontal samplers.

Fig. 17.

Comparison of calculated and measured reduction degrees in Operation B in the dissection investigation.

Thus, the effect of the reaction-control on the reduction of the carbon rate in the blast furnace process by COG injection from ordinary tuyeres, RG injection from shaft tuyeres with top gas recycling, and use of high reducibility sinter was demonstrated in the experimental blast furnace operation trials. Furthermore, the change in the inner state of the furnace by the reaction-control was analyzed with the mathematical blast furnace model.

4. Conclusion

Operational trials were successfully carried out with an experimental blast furnace to demonstrate the effect of the reaction-control on the carbon rate by COG injection from ordinary tuyeres, RG injection from shaft tuyeres with top gas recycling, and use of high reducibility sinter. The COG injection from ordinary tuyeres increased the proportion of H₂ reduction by approximately 10% and decreased that of carbon direct reduction by approximately 10% although the proportion of CO reduction was slightly decreased. As a result of it, the decrease in the carbon rate by approximately 4% was confirmed. In addition to the COG injection from ordinary tuyeres, the RG injection from shaft tuyeres with top gas recycling enhanced the decrease in the proportion of carbon direct reduction. As a result of it, the decrease in the carbon rate by approximately 8% was confirmed. Furthermore, the use of high reducibility sinter with the COG injection from ordinary tuyeres and the RG injection from shaft tuyeres with top gas recycling decreased the proportion of carbon direct reduction with the high gas utilizations of CO and H₂ which enabled the amount of carbon combusted in raceway to decrease. As a result of the reaction-control, the reduction in the carbon rate by approximately 10%, which is the target in COURSE50, was achieved. Therefore, it was confirmed that COG injection from ordinary tuyeres, RG injection from shaft tuyeres with top gas recycling, and use of high reducibility sinter are effective measures for the reaction-control and mitigation of CO₂ in the blast furnace process.

Acknowledgments

This paper is based on results obtained from “CO₂ Ultimate Reduction System for Cool Earth 50 (COURSE50) Project” commissioned by New Energy and Industrial Technology Development Organization (NEDO).

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