Blast Furnace Operation Law

Abstract

Since blast furnace gas discharged from a blast furnace contains a large amount of CO gas that did not contribute to ore reduction, blast furnace gas containing unused CO gas is again blown into the blast furnace through blast furnace tuyeres to reduce carbon oxides discharged from the blast furnace. If CO2 is removed from the blast furnace gas containing unused CO gas, and CO gas removed of CO2 is blown into the blast furnace again, nitrogen accumulates in the blast furnace, and O2 should be blown in instead of air blowing. Then, since there is no nitrogen in front of the tuyeres, the amount of gas generated in front of the tuyeres is insufficient, the temperature in front of the tuyeres rises, and it becomes difficult to operate the blast furnace. According to the present invention, N2 gas or CO2 gas is blown and circulated along with CO gas blown from the tuyeres.

Description

[Technical Field]

[0001] The present invention relates to a method for operating a blast furnace. [Background technology]

[0002] There is a strong demand for a reduction in CO2 emissions in order to curb global warming caused by increases in CO2 emissions. The steel industry generates a large amount of CO2, making the reduction of CO2 emissions a major issue. CO2 emissions from steelworks are mainly emitted from blast furnaces, and there is a demand for a reduction in CO2 emissions from blast furnaces. One method for reducing CO2 emissions from a blast furnace is to inject blast furnace gas into the blast furnace. Patent Document 1 discloses a blast furnace operation method in which CO2 is separated and removed from at least a portion of the blast furnace gas discharged from the top of the blast furnace, and after heating and raising the temperature, the gas is injected through gas injection port A in the blast furnace shaft, and preheated gas is injected into the furnace through gas injection port B located above A. Patent Document 2 also describes the following problems with oxygen blast furnaces: (1) the temperature before the tuyere, Tf, becomes too high, and (2) the heat flow ratio becomes too high, resulting in reduced heat transfer of the burden. To address (1), the patent discloses a blast furnace operation method in which CO, H, O, etc. are injected through the tuyere to maintain the temperature before the tuyere, Tf, at 2000°C to 2600°C, and to address (2), preheating gas is injected from the middle of the shaft. Patent Document 3 also discloses a blast furnace operation method that includes the steps of generating steam-reformed gas using steam and pyrolysis gas generated by the thermal decomposition of waste plastics, generating regenerated methane gas using blast furnace gas and hydrogen gas supplied from the steam-reformed gas, and injecting blast gas and a reducing agent into the blast furnace through the tuyeres of the blast furnace, and using oxygen gas as the blast gas and regenerated methane gas as at least a part of the reducing agent. Furthermore, Non-Patent Document 1 investigates the penetration of top gas into a blast furnace when it is injected into the blast furnace. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-70952 A [Patent Document 2] Japanese Patent Application Publication No. 159104 / 1983 [Patent Document 3] Japanese Patent Publication No. 2021-152212 [Non-patent literature]

[0004] [Non-Patent Document 1] Nishio et al.: Consideration of the Effect of Reducing Gas Injection into Blast Furnace by Furnace Top Gas Circulation Method and its Distribution in the Furnace, Iron and Steel, No. 12, 1973 (59th year) Summary of the Invention [Problem to be solved by the invention]

[0005] There have been attempts to reduce CO2 emissions by injecting blast furnace gas into a blast furnace. In Patent Document 1 and Non-Patent Document 1, blast furnace gas is injected into the blast furnace from the bottom of the shaft, but there is a problem with penetration into the furnace interior. When injecting blast furnace gas into a blast furnace, it is desirable to inject it from the blast furnace tuyere. Furthermore, Patent Document 2 raises the issue of oxygen blast furnaces, namely, that the temperature before the tuyere Tf becomes too high, and that the heat flow ratio becomes too high due to a decrease in the amount of gas before the tuyere, resulting in insufficient heat transfer of the burden. As a countermeasure against the heat flow ratio, it is necessary to inject preheating gas into the shaft. In addition, in Patent Document 3, CO2 and CO gas in blast furnace gas are converted to CH4 using hydrogen and then blown into the blast furnace tuyere. Blowing in a large amount of CH4 reduces the temperature before the tuyere. Therefore, if oxygen is blown in instead of hot air (air), a large amount of CH4 can be blown in without reducing the temperature before the tuyere. In other words, blast furnace gas can be blown into the blast furnace tuyere. In this case, instead of using hydrogen purchased from an external source, hydrogen is synthesized from waste plastics. When injecting reducing gas from the blast furnace tuyere, it is necessary to prevent a drop in the temperature before the tuyere while also paying attention to changes in the amount of gas in the raceway before the tuyere. This is because changes in the amount of gas inside the blast furnace change the heat flow ratio (the ratio of the heat capacity of the solid to the heat capacity of the gas). Another issue is how much it will cost to produce hydrogen from waste plastics.

[0006] The present invention aims to prevent an increase in the raceway temperature Tf in front of the tuyere and a decrease in the amount of gas in the lower part of the furnace during blast furnace operation in which oxygen and blast furnace gas (CO gas obtained by removing CO from the furnace top gas) are injected through the tuyere, thereby reducing CO emitted from the blast furnace under operating conditions similar to those of normal operation. [Means for solving the problem]

[0007] The present invention provides the following. (1) A blast furnace operation method in which O2 gas is injected through the blast furnace tuyere, CO2 is separated and removed from the blast furnace gas discharged from the top of the blast furnace, and all of the CO gas after CO2 removal is injected through the blast furnace tuyere, characterized in that N2 gas is injected through the blast furnace tuyere together with the CO gas after CO2 removal, and all of the N2 gas discharged from the furnace top is recycled and reused in the blast furnace. (2) A blast furnace operation method in which O2 gas is injected through the blast furnace tuyere, CO2 is separated and removed from the blast furnace gas discharged from the top of the blast furnace, and a portion of the CO gas after CO2 removal is injected through the blast furnace tuyere, characterized in that N2 gas is injected through the blast furnace tuyere together with the CO gas after CO2 removal, and a portion of the N2 gas discharged from the furnace top is recycled and reused in the blast furnace. (3) A method for operating a blast furnace according to (1) or (2), characterized in that H2 gas is blown into the blast furnace through the tuyere, and the CO gas after the CO2 removal contains H2 gas. (4) A blast furnace operation method characterized by injecting O2 gas into the blast furnace tuyere, separating and removing CO2 from a portion of the blast furnace gas discharged from the top of the blast furnace, and combining all of the CO2-removed CO2 with the remaining blast furnace gas discharged from the top of the blast furnace from which CO2 has not been separated and removed, and injecting the resulting gas into the blast furnace tuyere. (5) A blast furnace operation method characterized by injecting O2 gas into the blast furnace tuyere, separating and removing CO2 from a portion of the blast furnace gas discharged from the top of the blast furnace, combining the portion of the CO gas after CO2 removal with the remaining blast furnace gas discharged from the top of the blast furnace from which CO2 has not been separated and removed, and injecting the resulting mixture into the blast furnace tuyere. (6) A method for operating a blast furnace according to (4) or (5), characterized in that H2 gas is blown into the blast furnace through the tuyere, and the CO gas after the CO2 removal contains H2 gas.

[0008] Hereinafter, "injecting N2 gas into the blast furnace tuyere together with CO gas after CO2 removal, and circulating the N2 gas discharged from the furnace top back into the blast furnace" may be referred to as "N2 gas circulation." Also, "injecting all of the CO gas after CO2 removal, together with the remaining blast furnace gas from which CO2 has not been separated and removed, into the blast furnace tuyere" may be referred to as "CO2 gas circulation."

[0009] This invention is a blast furnace operation method in which CO2 is separated and removed from blast furnace gas and then entirely injected into the blast furnace tuyere. Using CCS technology (CO2 removal and fixation), CO2 can be removed from the furnace top gas. However, if CO2 is removed alone, the blast furnace gas contains a large amount of N2. If the entire amount of blast furnace gas is injected into the tuyere, N2 will accumulate in the blast furnace, making continuous operation impossible. To prevent N2 accumulation, oxygen injection is required instead of air injection from the tuyere. However, with oxygen injection, the lack of N2 reduces the amount of gas generated in the raceway before the tuyere, changing the heat flow ratio and raising the raceway temperature before the tuyere, making blast furnace operation difficult. The present invention solves this problem.

[0010] (1) In blast furnace operation, O2 gas is injected into the tuyere, and all of the CO gas after CO2 removal is injected through the tuyere, but this operation is not possible because the raceway temperature before the tuyere, Tf, becomes too high. By circulating N2 gas or CO2 gas along with CO gas, the raceway temperature before the tuyere, Tf, can be made the same level as in normal operation. (2) If the amount of gas generated in the raceway in front of the tuyere of a blast furnace were to change significantly from the normal operation of a current large blast furnace, blast furnace operation would become difficult. By circulating N2 gas or CO2 gas, the amount of gas generated in the raceway in front of the tuyere can be made almost the same as in normal operation. (3) The N2 gas circulation or CO2 gas circulation according to the present invention can maintain the heat flow ratio and the raceway temperature Tf in front of the tuyere almost the same as those in base operation (normal operation), and it is possible to reduce CO2 gas emissions using existing blast furnace operation technology. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a conceptual diagram illustrating a blast furnace operation method related to N2 gas circulation. [Figure 2] FIG. 1 is a diagram showing base operation. [Figure 3] This is a diagram showing the flow of a blast furnace operation method in which CO gas after CO2 removal is injected from the blast furnace tuyeres without N2 gas circulation. [Figure 4] FIG. 1 is a flow diagram of a blast furnace operation method for N2 gas circulation. [Figure 5] This is a diagram explaining that when 1 mole of carbon is charged into a blast furnace, 1 mole of CO gas is blown in from the blast furnace tuyere. [Figure 6] FIG. 1 is a diagram showing that a part of the CO gas or a part of the H gas after CO removal is injected from the blast furnace tuyere. [Figure 7] This is a diagram showing CO2 gas circulation in which all of the CO2 gas after CO2 removal and part of the blast furnace gas discharged from the furnace top are injected through the blast furnace tuyere. [Figure 8] This is a diagram showing CO2 gas circulation in which part of the CO gas after CO2 removal and part of the blast furnace gas discharged from the furnace top are injected into the blast furnace tuyere. DETAILED DESCRIPTION OF THE INVENTION

[0012] As a measure to prevent global warming, reduction of carbon dioxide gas emissions is required. In the steel industry, blast furnaces 1 are the main carbon dioxide gas emitting facilities. N2 gas circulation or CO2 gas circulation according to the present invention can maintain the heat flow ratio and the raceway temperature Tf in front of the tuyere almost the same as those in base operation (normal operation), and it is possible to reduce CO2 gas emissions using existing blast furnace operation technology.

[0013] (Base operation) → Comparative Example 1 (Table 1) First, the base operation will be explained. The base operation is the blast furnace operation that was normally carried out before the present invention. The assumptions for the base operation are as follows: (1-1) For ease of understanding, the air flow rate per unit time is 100 Nm in all-coke operation. 3 (N2 is 79Nm 3 , O2 is 21Nm 3 ) and consider blast furnace 1 with a blast temperature of 1000°C. (1-2) The indirect reduction rate in the blast furnace is 70%. The direct reduction rate is 30%. (1-3) The gas utilization rate (ηCO) of the blast furnace is set to 50%. (1-4) All ore to be charged shall be Fe2O3. (1-5) Although some of the charged carbon enters the pig iron, it is not directly involved in the reactions in the blast furnace. Therefore, in this study, we will discuss the iron content without carbon.

[0014] Figure 2 shows the internal condition of blast furnace 1 during base operation. Airflow rate 100Nm 3 and N2 is 79 Nm 3 , O2 is 21Nm 3 The gas composition in the raceway before the tuyere is that N2 remains the same, O2 is reacted with C + O2 → 2CO, and CO is 42Nm 3 becomes. The composition of the lower shaft is as follows: Part of the carbon charge is obtained by direct reduction of FeO+C→Fe+CO, with CO being XNm 3 The amount of CO generated by direct reduction is XNm 3 is 42Nm before the tuyere 3This contributes to indirect reduction together with the CO generated in the lower furnace. Since the gas utilization rate is 50%, only half of the CO generated in the lower furnace contributes. The direct reduction rate is assumed to be 30%, and the following formula holds:

[0015]

number

[0016] Here, the numerator is the amount of oxygen taken by direct reduction. The denominator is the sum of the CO generated before the tuyere and the CO (X) generated by direct reduction, which is half (gas utilization rate 50%) of the total, which is the oxygen taken by indirect reduction, and the oxygen taken by direct reduction. From this formula, X = 11.45, and the CO at the bottom of the shaft is 42 + 11.45 = 53.45 Nm 3 This becomes: The furnace gas composition is as follows: The blast furnace gas utilization rate (ηCO) is 50%, so 53.45 Nm of CO generated at the bottom of the shaft 3 In the furnace gas, half of the CO2 is 26.73 Nm 3 , remaining CO is 26.73Nm 3 This becomes: Since all of the charged carbon becomes CO or CO2 contained in the furnace gas, the amount of charged carbon is 53.45 / 22.4 = 2.386 moles, or 2.386 x 12 = 28.63 kg.

[0017] Iron production can be calculated from the oxygen balance. The oxygen from the airflow is 21 Nm 3 / 22.4 × 32 kg = 30 kg. The oxygen content of the furnace gas is 26.73 Nm 3 / 22.4×16kg+26.73Nm 3 / 22.4×32kg=57.27kg. The oxygen removed from the iron ore is 57.27-30=27.27kg. Therefore, the iron production is 27.27×112 / 48=63.62kg. Here, 112 / 48 is the ratio of iron to oxygen in Fe2O3 (56×2 / 16×3). The amount of pig iron produced is 63.62 / 0.955 = 66.62 kg, assuming that the carbon content of the pig iron is 4.5%. The amount of coke charged is 28.63 / 0.9 = 31.81 kg, assuming that the carbon in the coke is 90%. 28.63 is the amount of carbon charged. As mentioned above, all of the charged carbon becomes CO or CO2 contained in the furnace gas, so the amount of carbon charged is 53.45 / 22.4 = 2.386 moles, or 2.386 x 12 = 28.63 kg. The coke ratio is 31.81 kg / 66.62 kg = 477 kg / tpig.

[0018] (Heat input during base operation) Next, the heat input during base operation is calculated. In Figure 2, the heat input sources to blast furnace 1 are the charged carbon and the sensible heat of the blast heated by hot stove 2. The charged carbon reacts with oxygen in the blast furnace and oxidizes to become CO2 and CO, which are released as furnace top gas. The combustion heat of C is the heat of production of CO2 and CO. Therefore, the heat input to blast furnace 1 is the sum of the heat of production of CO2 and CO in the furnace top gas and the sensible heat of the blast.

[0019] (2-1) The heat input from the reaction of charged carbon to CO2 is 1.193 kmol, half of the charged carbon (2.386 kmol) converted to CO2 in Figure 2. The calorific value is 1.193 kmol × 393.5 kJ / mol × 0.239 cal / J × 10 3 =112.2×10 3 According to Basic Chemistry 21st Edition (Shokabo), p.132, the standard heat of gas formation during the oxidation of C to CO2 (C + O2 = CO2) is ΔH = -393.5 kJ / mol.

[0020] (2-2) The reaction heat of the charged carbon to CO is 1.193 kmol, which is half of the charged carbon (2.386 kmol) in Figure 2. Therefore, the calorific value is 1.193 kmol × 110.5 kJ / mol × 0.239 cal / J × 10 3 =31.51×10 3 The heat of formation of CO gas is ΔH = -110.5 kJ / mol.

[0021] (2-3) The temperature of the blast is 1000°C. The sensible heat of the blast is 26.37 x 103 kcal, O2 is 7.41 x 10 3 kcal, totaling 33.78 x 10 3 kcal. The sensible heat of N2 is 26.37 x 10 3 kcal is (79Nm 3 / 22.4) × 28 kg × 0.267 cal / kg, and the sensible heat of O2 is 7.41 × 10 3 kcal (21Nm 3 / 22.4) × 32 kg × 0.247 cal / kg, where the specific heats of N2 and O2 at 1000°C are 0.267 cal / kg and 0.247 cal / kg, respectively.

[0022] (2-4) The total heat input is 177.5 × 10 3 kcal (Breakdown: 112.2 x 10 3 kcal+31.5×10 3 kcal+33.78×10 3 kcal). In Figure 2, 177.5 x 10 3 kcal of heat is required. This heat includes the heat of iron reduction, the heat carried away by pig iron and slag, heat dissipated from the furnace body, and others. The breakdown is as follows: heat of iron reduction (67.6%), sensible heat of molten iron and slag (17.2%), sensible heat of furnace top gas (6.2%), heat loss from the furnace body, etc. (Ironmaking and Steelmaking (Asakura Publishing), p. 22).

[0023] (Tf: Raceway temperature before tuyere during base operation) (Heat input to the raceway in front of the tuyere) (3-1) Sensible heat of ventilation: 33.78 x 10 3 kcal See (2-3) above (3-2) Carbon combustion heat: 49.53 x 10 3 kcal (1.875 kmol x 110.5 kJ / mol x 0.239 Cal / J) (3-3) Heat capacity of carbon entering the raceway before the tuyere: 20.25×10 3 kcal If the temperature of the raceway before the tuyere is 2400°C, the temperature of the carbon entering the raceway before the tuyere is 0.75 times the temperature of the raceway before the tuyere, and the specific heat of carbon at 2400°C is 6 cal / kmol, then (42 / 22.4) kmol × 6 cal / kmol × (2400°C × 0.75) = 20.25 × 10 3 kcal. (3-4) Total heat input to the raceway in front of the tuyere: 103.6 x 10 3 kcal

[0024] (Calculation of the raceway temperature Tf before the tuyere) (4-1) Gas volume in the raceway N279Nm 3 Heat capacity: 79 / 22.4 x 28 x 0.29 x Tf = 28.64 Tf CO4 2Nm 3 Heat capacity: 42 / 22.4×28×0.292×Tf=15.33Tf 28 is the molecular weight of N2 and CO, and 0.29 and 0.292 are the specific heats of N2 and CO when Tf is assumed to be 2300°C. (4-2) Raceway temperature Tf 103.6×10 3 kcal = (28.64Tf + 15.33Tf) × 10 3 kcal From this, we obtain Tf = 2356°C. (4-3) In all-coke operation, the raceway temperature in front of the tuyere reaches a high temperature of 2356°C, but in actual operation, it is thought to reach around 2100°C due to the injection of pulverized coal.

[0025] (A blast furnace operation method in which all CO gas after CO2 removal is injected through the blast furnace tuyere) → Comparative Example 2 (Table 1) This is a blast furnace operation method in which O2 is injected into the tuyere of blast furnace 1, CO2 is separated and removed from the blast furnace gas discharged from the top of the blast furnace, and all of the CO2 gas after CO2 removal is injected into the blast furnace tuyere without circulating N2 gas (Figure 3).

[0026] CO gas injected through the blast furnace tuyere is hereafter referred to as "tuyere-injected CO gas." After the CO2 is removed using a CCS (carbon capture and storage) system, all of the CO gas that did not contribute to ore reduction is again injected through the tuyere. With tuyere-injected CO gas, all of the CO gas emitted from the furnace top is repeatedly injected through the tuyere, so all of it becomes CO2 and contributes to ore reduction, which reduces the coke rate and is expected to reduce CO2 emissions.

[0027] (Prerequisite for blast furnace operation method in which all blast furnace gas after CO2 removal is injected through the blast furnace tuyere) (5-1) In normal blast furnace operation, air is blown in through the tuyere to burn the coke inside the furnace, so the blast furnace gas contains nitrogen. Here, in blast furnace operation where all of the blast furnace gas after CO2 removal is blown in through the tuyere, the blast furnace gas is not discharged to the outside, so if air is blown in through the tuyere, N2 is continuously sent into the blast furnace and accumulates. Therefore, in blast furnace operation where all of the blast furnace gas after CO2 removal is blown in through the tuyere, it is assumed that operation will involve blowing in O2, which does not contain N2, instead of air. (5-2) In blast furnace operation, oxygen is blown through the blast furnace tuyere, and all of the CO gas after CO2 removal is blown through the blast furnace tuyere. Since there is no N2 blown through the tuyere and the amount of gas in the raceway before the tuyere is small, the raceway temperature before the tuyere, Tf, becomes high. If Tf becomes too high, blast furnace operation becomes difficult, so the raceway temperature before the tuyere, Tf, must be kept at the same level as in normal operation. (5-3) In blast furnace operation, in which all of the CO gas after CO2 removal is injected through the blast furnace tuyere, there is no N2 injection from the tuyere, so the amount of gas in the raceway in front of the tuyere is less than in current large blast furnace operation, the heat flow ratio (ratio of the heat capacity of the solid to the heat capacity of the gas) becomes larger, the heat transfer from the furnace gas to the burden decreases, and blast furnace operation becomes difficult. It is necessary to make the amount of gas in the raceway in front of the tuyere the same level as in normal operation.

[0028] (Overall heat balance of a blast furnace in which CO gas after CO2 removal is injected through the blast furnace tuyeres) In Figure 3, the iron production volume is 63.62 kg, the same as in base operation. The entire amount of CO removed from the furnace top gas is stored in the tuyere gas relay tank 4, heated to 1200°C in the hot stove 2, and then blown into the blast furnace through the blast furnace tuyere.

[0029] (Heat input) The amount of carbon required to produce 63.62 kg of iron, the same as in base operation, is assumed to be Yk moles.

[0030] (6-1) The heat input from the combustion of C to CO2 is 94.05Y x 10 3 kcal. This is the heat of CO2 formation when C is burned to CO2 in the blast furnace (calculation breakdown: Y x 393.5 kJ / mol x 0.239 Cal / J x 10 3 ) CO gas is repeatedly blown into the tuyere to become CO2, so all the carbon charged becomes CO2. According to Basic Chemistry 21st Edition (Shokabo), p. 132, the standard heat of gas formation during the oxidation of C to CO2 (C + O2 = CO2) is ΔH = -393.5 kJ / mol. Also, 1 J = 0.239 cal.

[0031] (6-2) The sensible heat of CO gas injected through the tuyere is 9.24Y x 10 3 kcal. The calculation is (Y x 28 kg x 0.275 kcal / kg x 1200°C). The amount of CO gas injected through the tuyere is Yk moles (explained below). It is heated to 1200°C. 28 kg is the molecular weight of CO (kg / k mole), and 0.275 kcal / kg is the specific heat of CO at 1200°C.

[0032] Here, the amount of CO gas injected through the tuyere will be explained. When the amount of carbon charged into the blast furnace is Yk moles, the amount of CO gas injected through the tuyere-blown gas relay tank 4 will be Yk moles. Assuming that the CO gas utilization rate ηCO is 50%, 0.5Yk moles of CO2 are generated from the Yk moles of charged carbon, and 0.5Yk moles of CO2 are generated from the amount of CO gas blown through the tuyere, Yk moles, for a total of Yk moles of CO2.

[0033] FIG. 5 is a diagram illustrating that when 1 mole of carbon is charged into the blast furnace 1, the amount of CO gas blown into the tuyere is 1 mole. When 1 mole of carbon is charged into the blast furnace 1, at an indirect reduction rate of 50%, (1) 0.5 moles of CO2 and 0.5 moles of CO are produced in the furnace top gas. Next, when 0.5 moles of CO (1) is blown into the tuyere via the tuyere CO gas relay tank 4, (2) 0.25 moles of CO2 and 0.25 moles of CO are produced in the furnace top gas. When 0.25 moles of CO (2) is blown into the tuyere, (3) 0.125 moles of CO2 and 0.125 moles of CO are produced in the furnace top gas. Similarly, 0.063 moles, 0.031 moles, etc. of CO are blown into the tuyere, and by charging 1 mole of carbon into the blast furnace, 1 mole of CO (0.5 + 0.25 + 0.063 + 0.031) is ultimately blown into the tuyere. When there is a tank in the middle and 1 mole of carbon is charged into the blast furnace, 1 mole of CO generated beforehand and stored in the tank is blown into the tuyeres. Therefore, when charging Yk moles of carbon into the blast furnace, Yk moles of CO are blown into the tuyeres from the tank.

[0034] (6-3) The total input is 103.3Y x 10 3 kcal. The calculation breakdown is 94.05Y x 10 3 kcal+9.24Y×10 3 kcal.

[0035] To produce 63.62 kg of iron, 177.5 x 10 3 kcal is required (see (2-4) above). Therefore, 103.3Y x 10 3 kcal=177.5×10 3 From kcal, Y=1.718 kmol, and 1.718 kmol of carbon is required.

[0036] (Raceway temperature before tuyere Tf) In the blast furnace 1, iron ore is charged from the top of the furnace and is heated and reduced as it descends through the furnace, and finally, high-temperature molten iron is discharged from the bottom of the furnace. In this case, the heat balance of the lower part of the furnace as well as the heat balance of the entire furnace are important. In tuyere-injected CO gas operation, in which all blast furnace gas after CO2 removal is injected through the blast furnace tuyere, full oxygen injection is required to prevent N2 accumulation in the blast furnace. This results in a lack of N2 in the tuyere raceway, reducing the amount of gas in the tuyere raceway, which is expected to increase the tuyere raceway temperature, Tf. In normal operation, the tuyere raceway temperature, Tf, is approximately 2100°C. In addition, since there is no N2, the amount of gas coming out of the raceway in front of the tuyere is less than that in normal operation, resulting in an excessive heat flow ratio. Therefore, the tuyere raceway temperature Tf and the amount of gas exiting the tuyere raceway during tuyere-injected CO gas operation are calculated.

[0037] (Heat input to the raceway in front of the tuyere) (7-1) The heat input from the combustion of C to CO is 45.74 × 10 3 kcal. The calculation is 2 x 0.866 kmol x 110.5 kJ / mol x 0.239 cal / J x 10 3 is. From the oxygen balance, the oxygen blown into the tuyere is calculated, and the amount of C burned is calculated. When 1.718 kmol of carbon is charged, the oxygen discharged from the furnace top is 1.718 kmol (CO2), and the oxygen taken from the ore is 27.27 kg / 32 kg = 0.8522 kmol, so the oxygen blown into the tuyere is 1.718 - 0.8522 = 0.866 kmol. Note that 27.27 kg is the oxygen taken from the iron ore as mentioned above. CO generation is 2 x 0.866 kmol. The heat of CO combustion of C is 110.5 kJ / mol (heat of CO formation is ΔH = -110.5 kJ / mol).

[0038] (7-2) The heat capacity of the carbon entering the raceway before the tuyere is 23.38 × 10 3 kcal. The calculation breakdown is 2 x 0.866 kmol x 6 cal / kmol x (3000°C x 0.75). The carbon that burns with the oxygen (0.866 kmol) blown into the tuyere is 2 x 0.866 kmol. 6 cal / kmol is the specific heat of carbon at 3000°C, and the pre-tuyere raceway temperature Tf is assumed to be 3000°C. Additionally, the carbon temperature entering the pre-tuyere raceway is assumed to be 0.75 times the pre-tuyere raceway temperature Tf.

[0039] (7-3) The sensible heat of CO gas injected through the tuyere is 9.24 × 1.718 = 15.87 × 10 3 kcal. 9.24Y×10 3 Substitute Y=1.718 for kcal (see (6-2) above).

[0040] (7-4) The total heat input to the raceway in front of the tuyere is 84.99 × 10 3 kcal. The calculation breakdown is 45.74 x 10 3 kcal+23.38×10 3 kcal+15.87×10 3 kcal.

[0041] (gas volume coming out of the raceway) The CO emitted from the raceway will be 96.6 kg. CO generation before the tuyere is due to the reaction C + 0.5O2 = CO. For every 0.866 kmol of oxygen blown into the tuyere, 1.732 kmol of CO is generated, which is 1.732 x 28 = 48.50 kg. As mentioned above, when the carbon charged to the blast furnace is Yk moles, the amount of CO gas injected via the tuyere gas relay tank 4 is Yk moles. Yk moles is 1.718 kmol, which is 48.10 kg. The total CO before the tuyere is 96.6 kg. This is 96.6 / 28 = 3.45 kmol, or 22.4 × 3.45 = 77.3 Nm 3 is.

[0042] (Raceway temperature before tuyere Tf) The temperature of the raceway before the tuyere, Tf, is calculated from the heat input to the raceway before the tuyere = heat output. The heat input is 84.99 x 10 3 kcal (see (7-4) above), and the heat output is 96.6 kg × 0.297 kcal / kg × Tf, where 0.297 kcal / kg is the specific heat of CO at 3000°C. 84.99×10 3 kcal=96.6kg×0.297kcal / kg×Tf×10 3 From kcal, the raceway temperature before the tuyere, Tf, is obtained as 2962°C.

[0043] In blast furnace operation where all CO gas is injected through the tuyere, the raceway temperature in front of the tuyere, Tf, reaches a high temperature of 2962°C because N2 is not injected into the tuyere. This is significantly different from normal operation, and damages the refractory and tuyere, making oxygen injection and full blast furnace gas circulation operation impossible. In addition, as mentioned above, the CO emitted from the raceway is 77.3 Nm 3 and normal operation (121Nm 3 ) is less than

[0044] (A blast furnace operation method in which recycled N2 gas is injected into the blast furnace tuyeres along with CO gas after CO2 removal) →Invention Example 1 (Table 1) This is a blast furnace operation method in which O2 is injected through the blast furnace tuyere, CO2 is separated and removed from the blast furnace gas discharged from the top of the blast furnace, and all of the CO gas after CO2 removal is injected through the blast furnace tuyere, and is characterized in that circulating N2 gas is injected through the blast furnace tuyere together with the CO gas after CO2 removal.

[0045] In the blast furnace operation method (Comparative Example 2) in which all of the blast furnace gas after CO2 removal is injected through the blast furnace tuyere as shown in Figure 3, the raceway temperature Tf before the tuyere becomes too high, making operation impossible. Measures for lowering the raceway temperature Tf before the tuyere are considered. Figure 1 shows a conceptual diagram of a blast furnace operation method in which circulating N2 gas is injected into the tuyere of a blast furnace (1) along with CO2-removed blast furnace gas. In this operation, circulating N2 gas is injected through the tuyere. Fifty percent of the CO2 gas in the blast furnace is converted to CO2, and the remaining 50% is converted to CO. However, the CO2-removed CO is repeatedly injected through the tuyere, eventually converting to CO2. Meanwhile, N2 does not undergo chemical reactions within the blast furnace; it simply circulates within the blast furnace gas circulation system, from the furnace interior to the furnace top and from the furnace top to the tuyere. A predetermined amount of N2 is required at the start of operation; it is not continuously added from an external source, as is the case with tuyere airflow. Because N2 does not combust in the raceway before the tuyere, it serves as a coolant for the raceway before the tuyere, which is heated to a high temperature (2962°C) by O2 injection through the tuyere, maintaining the Tf at 2100°C, the same as in base operation. In addition, since N2 is injected into the raceway before the tuyere, the amount of gas generated in the raceway before the tuyere can be kept at a level similar to that in normal operation.

[0046] Figure 4 is a flow diagram of a blast furnace operation method in which recycled nitrogen is injected into the tuyere of blast furnace 1 together with blast furnace gas after CO2 removal. This is the flow when producing the same iron content of 63.62 kg as in base operation. The recycled nitrogen is stored in tuyere-injected gas relay tank 4 together with CO gas after CO2 removal. Thereafter, the N2 and CO gas discharged from the tuyere-blowing gas relay tank 4 are heated to 1000°C to 1200°C in the existing hot stove 2 and then blown into the blast furnace 1 through the blast furnace tuyere. Heating by the hot stove 2 is intended to reduce the amount of carbon charged in order to reduce CO2 emissions, and the heating temperature can be determined according to the amount of circulating N2 and the target Tf.

[0047] (Heat input in blast furnace operation where circulating N2 gas is injected into the blast furnace tuyere) A blast furnace operation method in which N2 is circulated along with tuyere-injected CO gas is considered under the condition of producing the same iron content of 63.62 kg as in base operation. The carbon charged to blast furnace 1 is assumed to be Yk moles.

[0048] (8-1) The heat input from the combustion of C to CO2 is 94.05Y x 103 kcal. The calculation is Y × 393.5 kJ / mol × 0.239 Cal / J × 10 3 (See (6-1) above).

[0049] (8-2) The sensible heat of CO gas injected through the tuyere is 9.24Y x 10 3 kcal. The calculation breakdown is Y x 28 kg x 0.275 kcal / kg x 1200°C (see (6-2) above).

[0050] (8-3) The sensible heat of circulation of N2 is Wk moles × 28 kg × 0.272 kcal / kg × 1200°C = 9.14 W × 10 3 kcal. The amount of N2 circulating in the blast furnace gas circulation system is assumed to be Wk moles. This N2 is added to the blast furnace gas circulation system when the blast furnace begins operation and is not emitted to the outside from the circulation system. Specifically, after switching from normal operation (air blowing) to operation (O2 blowing), the N2 in the blast furnace is adjusted to a specified amount and circulated. 28 kg is the molecular weight of N2 (kg / k mole), and 0.272 kcal / kg is the specific heat of N2 at 1200°C. For safety reasons, the oxygen blown in is not heated, and therefore has no sensible heat.

[0051] (8-4) The total heat input is 103.3Y x 10 3 kcal+9.14W×10 3 kcal. The calculation breakdown is 94.05Y x 10 3 kcal+9.24Y×10 3 kcal+9.14W×10 3 kcal. Since the amount of pig iron produced is the same as that of base operation (63.62 kg), if we assume that the required heat is the same as that of base operation, the following equation (A) holds true. 103.3Y×10 3 kcal+9.14W×10 3 kcal=177.5×10 3 kcal (A)

[0052] (Tf: Raceway temperature before tuyere in blast furnace operation with circulating N2 gas injected through the blast furnace tuyere) The raceway temperature before the tuyere becomes high due to the absence of N2. In normal blast furnace operation, pulverized coal injection is often performed, and the raceway temperature before the tuyere, Tf, is set at 2000°C to 2400°C. Therefore, in Example 1, the target value of the raceway temperature before the tuyere, Tf, is set to 2100°C, and Wk moles of nitrogen are injected as the cooling gas.

[0053] (heat input) (9-1) The heat of carbon combustion before the tuyere is (52.82Y-45.01) x 10 3 kcal. The calculation breakdown is (Y-27.27 / 32) x 2 x 110.5 kJ / mol x 0.239 cal / J. Since the production volume is the same as that of base operation, 63.62 kg of iron, the oxygen contained in the ore is 27.27 kg. The amount of oxygen blown into the raceway before the tuyere is (32Y-27.27) kg, which is the 32Y kg of oxygen contained in the furnace gas minus the 27.27 kg of oxygen taken from the ore, or (Y-27.27 / 32) kmoles. 2 kmol of CO are produced from 1 kmol of oxygen (2C + O2 = 2CO). The heat of formation of CO gas is ΔH = -110.5 kJ / mol.

[0054] (9-2) The sensible heat of CO gas injected through the tuyere is 9.24Y x 10 3 kcal. The calculation breakdown is Yk moles × 28 kg × 0.275 kcal / kg × 1200°C (see (6-2) above).

[0055] (9-3) The sensible heat of circulating N2 is 9.14 W × 10 3 kcal. The calculation breakdown is Wk moles × 28 kg × 0.272 × 1200°C (see (8-3) above).

[0056] (9-4) The heat capacity of the carbon entering the raceway before the tuyere is (18.9Y-16.12) x 10 3 kcal. The calculation breakdown is (Y-27.27 / 32) x 2 kmol x 6 cal / mol x 2100°C x 0.75. (Y-27.27 / 32) × 2 kmol is the amount of carbon entering the raceway before the tuyere. 6 cal / kmol is the specific heat of carbon at 2100°C, and the carbon temperature entering the raceway before the tuyere was set to 0.75 times the temperature before the tuyere.

[0057] (9-5) The total heat input is (80.96Y + 9.14W - 61.13) x 10 3 kcal. The calculation breakdown is (52.82Y-45.01) x 10 3 kcal+9.24Y×10 3 kcal+9.14W×10 3 kcal+(18.9Y-16.12)×10 3 kcal.

[0058] (fever) The carbon charge amount Y and the circulating N2 amount W are determined so that the raceway temperature Tf in front of the tuyere becomes 2100°C.

[0059] (10-1) Heating of CO is (50.98Y-28.96) x 10 3 kcal. The calculation is ((Y-27.27 / 32) x 2 + Y) x 28 kg x 0.289 kcal / kg x 2100°C, where 0.289 kcal / kg is the specific heat of CO at 2100°C.

[0060] (10-2) Heating of N2 is 16.82W x 10 3 kcal. The calculation is Wk moles x 28 kg x 0.286 kcal / kg x 2100°C, where 0.286 kcal / kg is the specific heat of N2 at 2100°C.

[0061] (10-3) The total heat output is (50.98Y-28.96) x 10 3 kcal+16.82W×10 3 kcal.

[0062] (heat balance) Pre-tuyere raceway heat balance: 29.98Y×10 3 kcal-7.68W×10 3 kcal=32.16×10 3 kcal (B) The calculation breakdown is: total heat input = total heat output, (80.96Y + 9.14W - 61.12) x 10 3 kcal = (50.98Y - 28.96) x 10 3 kcal+16.82W×10 3 kcal.

[0063] (Carbon charge amount Y and N2 gas circulation amount W) The above formulas (A) and (B) are solved as two-variable equations to calculate the carbon charge amount Y and the circulating N2 amount W. Carbon charge Y: 1.553 kmol → 34.9% CO2 reduction compared to base operation 2.386 N2 circulation volume W: 1.875 kmol (42 Nm 3 )

[0064] (tuyere raceway composition and gas volume) CO2: 66.2Nm 3 The calculation is ((Y - 27.27 / 32) x 2 + Y) = (3 x Y - 1.7044) kmol. Substituting Y = 1.553 kmol, we get 2.955 kmol = 66.2 Nm 3 becomes. N2: 42.0Nm 3 (1.875 kmol) The total gas volume of CO and N2 was 108.2 Nm 3 becomes.

[0065] (Blast furnace operation method in which circulating N2 gas is injected into the tuyere, maintaining the amount of gas in the raceway in front of the tuyere) →Invention Example 2 (Table 1) In Example 1, the circulating N2 was 42.0 Nm 3 The raceway temperature Tf is 2100°C, and the gas volume in the raceway is 108.2 Nm3 The gas volume in the raceway before the tuyere is 121 Nm3 3 If the amount of gas generated in the raceway before the tuyere is small, the heat flow ratio increases, and there is a possibility that the heat transfer from the furnace gas to the burden may be insufficient. Therefore, in Example 2, the gas volume in the raceway before the tuyere was set to 121 Nm 3 Consider measures to improve the condition to approach this. In order to maintain the gas volume before the tuyere and bring the heat flow ratio to approximately the same level as in base operation, it is sufficient to increase the circulating N2. To ensure that Tf remains at 2100°C even when the N2 is increased, the amount of ore charged is kept constant and the amount of carbon charged is increased to increase the heat input. The amount of gas in the raceway before the tuyere increases due to the increase in N2 and the increase in CO before the tuyere caused by the increase in carbon charged.

[0066] Specifically, due to the increase in charged carbon, the heat input in Example 1 was 177.5 × 10 3 Calculate the heat balance and the raceway temperature Tf before the tuyere when the value of kcal is gradually increased. 3 When the gas volume is calculated as explained below using equations (A') and (B) in which kcal is used, the gas volume in the tuyere raceway is 122 Nm 3 became. 103.3Y×10 3 kcal+9.14W×10 3 kcal=190×10 3 kcal (A') 29.98Y×10 3 kcal-7.68W×10 3 kcal=32.16×10 3 kcal (B)

[0067] (Carbon charge amount Y and N2 gas circulation amount W) The above formulas (A') and (B) are solved as two-dimensional equations to calculate the carbon charging amount Y and the blast furnace gas circulation amount W. Carbon charge Y: 1.643 kmol → 31.1% CO2 reduction compared to base operation 2.386 N2 circulation amount W: 2.224 kmol (49.8 Nm 3 )

[0068] (Gas composition and volume before the tuyere) CO2: 72.2Nm 3 The calculation is (3 x Y - 1.7044) kmol (see calculation in Example 1). Substituting Y = 1.643 kmol, we get 3.225 kmol = 72.2 Nm 3 becomes. N2: 49.8Nm 3 (2.224 kmol) The total gas volume of CO and N2 is 122 Nm 3 becomes.

[0069] (A blast furnace operation method in which blast furnace gas containing CO gas and H2 is injected into the tuyere) → Comparative Example 3 (Table 1) When blast furnace gas is injected into the tuyere, the temperature in the raceway before the tuyere reaches 2962°C because N2 gas is not being injected, making operation impossible. In response to this, we consider the use of hydrogen gas in combination as a cooling gas for the raceway before the tuyere. This is the case when H2 is added and there is no N2 circulation.

[0070] (heat input) The carbon charged to blast furnace 1 is assumed to be Yk moles. (11-1) The heat input from C to CO2 is 94.05Y × 10 3 kcal. The calculation is Y × 393.5 kJ / mol × 0.239 Cal / J × 10 3 kcal (see (6-1) above).

[0071] (11-2) The sensible heat of CO gas injected through the tuyere is 9.24Y×10 3 kcal. The calculation breakdown is Y x 28 kg x 0.275 kcal / kg x 1200°C (see (6-2) above).

[0072] (11-3) The heat input from H2 → H2O is 57.79Z × 10 3 kcal. The calculation breakdown is Z × 241.8 kJ / mol × 0.239 kcal / kJ × 10 3 If Zk moles of hydrogen are blown in, 241.8 kJ / mol is the heat of formation of H2O(g).

[0073] (11-4) The sensible heat of H2 injected through the tuyere is 8.573Z×10 3 kcal. The calculation is Z x 2kg x 3.572kcal / kg x 1200°C, where 3.572kcal / kg is the specific heat of hydrogen at 1200°C.

[0074] (11-5) The total heat input is (103.3Y + 66.36Z) × 10 3 kcal. The calculation breakdown is 94.05Y x 10 3 kcal+9.24Y×10 3 kcal+57.79Z×10 3 kcal+8.573Z×10 3 kcal.

[0075] (11-6) Overall furnace heat balance: The amount of iron produced is the same as that of base operation (63.62 kg), so the calorific value is also the same (177.5 x 10 3 kcal, the following formula (A") holds true because total heat input = total heat output. (103.3Y+66.36Z)×10 3 kcal=177.5×10 3 kcal (A”)

[0076] (Heat balance in the raceway before the tuyere) The temperature of the raceway before the tuyere becomes high due to the lack of N2. Therefore, the target value of the raceway temperature before the tuyere, Tf, is set to 2100°C, and Zk moles of hydrogen are blown into the tuyere as cooling gas.

[0077] (heat input) (12-1) The heat of carbon combustion before the tuyere is (52.82Y + 26.41Z - 45.01) × 10 3 kcal. The calculation breakdown is (Y + 0.5Z - 27.27 / 32) x 2 x 110.5 kJ / mol x 0.239 cal / J x 10 3 kcal. The oxygen contained in the furnace gas is (32Y + 16Z) kg, and the oxygen blown into the raceway in front of the tuyere is (32Y + 16Z - 27.27) kg = (Y + 0.5Z - 27.27 / 32) kmol. 27.27 kg is the oxygen taken from the ore. 2 kmol of CO is produced from 1 kmol of oxygen (2C + O2 = 2CO). The heat of production of CO gas is ΔH = -110.5 kJ / mol.

[0078] (12-2) The heat capacity of the carbon entering the raceway before the tuyere is (18.9Y + 9.45Z - 16.11) × 10 3 kcal. The calculation breakdown is (Y + 0.5Z - 27.27 / 32) x 2 kmol x 6 cal / mol x 2100°C x 0.75.

[0079] (12-3) The sensible heat of CO injected through the tuyere is 9.24Y x 10 3 kcal (see (6-2) above).

[0080] (12-4) The sensible heat of H2 injected through the tuyere is 8.573Z×10 3 kcal (see (11-4) above).

[0081] (12-5) The total heat input is (80.96Y + 44.43Z - 61.12) × 10 3 kcal. The calculation breakdown is (52.82Y + 26.41Z - 45.01) x 10 3 kcal + (18.9Y + 9.45Z - 16.11) x 10 3 kcal+9.24Y×10 3 kcal+8.573Z×10 3 kcal.

[0082] (Heat output) Hydrogen is added so that the raceway temperature in front of the tuyere reaches 2100°C.

[0083] (13-1) Heating of CO is (50.98Y + 17.00Z - 28.97) × 10 3 kcal. The calculation breakdown is ((Y + 0.5Z - 27.27 / 32) x 2 + Y) kmol x 28 kg x 0.289 kcal / kg x 2100°C. (Y + 0.5Z - 27.27 / 32) x 2 kmol is the amount of CO moles generated before the tuyere, Y is the amount of CO moles injected into the tuyere, 28 is the molecular weight of CO, and 0.289 kcal / kg is the specific heat of CO at 2100°C.

[0084] (13-2) The heating of H2 injected through the tuyere is 31.62Z x 10 3 kcal. The calculation breakdown is (Z+Z) x 2kg x 3.764kcal / kg x 2100℃ x 10 3 Z+Z is the amount of hydrogen initially injected and the amount of hydrogen injected through the relay tank, and 3.764 kcal / kg is the specific heat of H2 at 2100°C.

[0085] (13-3) The total heat output is (50.98Y + 48.62Z - 28.97) × 10 3 kcal. The calculation breakdown is (50.98Y + 17.00Z - 28.97) x 10 3 kcal+31.62Z×10 3 kcal.

[0086] (Heat balance in the raceway before the tuyere) Pre-tuyere raceway heat balance: 29.98Y-4.19Z=32.15 (B') The calculation breakdown is (80.96Y + 44.43Z - 61.12) x 10 3 kcal=(50.98Y+48.62Z-28.97)×10 3 kcal.

[0087] (Carbon charge amount Y and hydrogen injection amount Z) The above formulas (A") and (B') are solved as two-dimensional equations to calculate the carbon charge amount Y and the hydrogen injection amount Z. Carbon charge Y: 1.188 kmol Hydrogen injection amount Z: 0.826 kmol

[0088] (Gas volume in the raceway before the tuyere) Calculating from Y=1.188 and Z=0.826, CO: 60.2 Nm 3 becomes. The calculation breakdown is: ((Y + 0.5Z - 27.27 / 32) x 2 + Y) kmol = 3Y + Z - 1.704 = 2.686 kmol = 60.2 Nm 3 is. H2:37.0Nm 3 Substituting Z = 0.826 moles into (Z + Z) k moles gives 1.65 k moles = 37 Nm 3 becomes. The total gas volume of CO and H2 is 97.2 Nm 3 becomes.

[0089] (A blast furnace operating method in which N2 is circulated along with blast furnace gas containing CO gas and H2) →Invention Example 3 (Table 1) In the blast furnace operation method in which H2 is injected and CO and H2 are injected through the tuyere (Comparative Example 3), the amount of raceway gas before the tuyere is 97 Nm 3 And the base operation is 121Nm 3 Less than. Therefore, circulating N2 is added to the CO gas and H2 injected through the tuyere, and the amount of gas in the raceway before the tuyere is increased. The amount of N2 added is changed, and the overall heat balance of blast furnace 1 and the Tf of the raceway before the tuyere are calculated. The amount of circulating N2 is set to W = 1 kmole, and the charged carbon is increased to increase the heat input to 200 x 10 3 kcal, the amount of raceway gas before the tuyere is 120 Nm 3 The breakdown of the calculation is shown below.

[0090] (Required heat amount in Example 3) (heat input) The carbon charged to blast furnace 1 is assumed to be Yk moles. (14-1) The heat input from C to CO2 is 94.05Y × 10 3 kcal The calculation is Y × 393.5 kJ / mol × 0.239 Cal / J × 10 3 kcal (see (6-1) above).

[0091] (14-2) The sensible heat of CO gas injected through the tuyere is 9.24Y×10 3 kcal. The calculation breakdown is Y x 28 kg x 0.275 kcal / kg x 1200°C (see (6-2) above).

[0092] (14-3) The heat input from H2 → H2O is 57.79Z × 10 3 kcal. The calculation breakdown is Z × 241.8 kJ / mol × 0.239 kcal / kJ × 10 3 kcal (see (11-3) above).

[0093] (14-4) The sensible heat of H2 injected through the tuyere is 8.573Z×10 3 kcal. The calculation breakdown is Z x 2 kg x 3.572 kcal / kg x 1200°C (see (11-4) above).

[0094] (14-5) The sensible heat of circulation of N2 is 9.14 × 10 3 kcal. 9.14W x 10 3 Substitute W = 1 kmol for kcal (see (8-3) above).

[0095] (14-6) The total heat input is (103.3Y + 66.36Z + 9.14) × 10 3 kcal. The calculation breakdown is 94.05Y x 10 3 kcal+9.24Y×10 3 kcal+57.79Z×10 3 kcal+8.573Z×10 3 kcal+9.14×10 3 kcal. (14-7) Overall furnace heat balance: The amount of iron produced is the same as that of base operation, 63.62 kg, but when circulating N2 is present, the amount of heat required to prevent a drop in the raceway temperature before the tuyere increases, so the amount of charged carbon Y is slightly increased. When the required amount of heat is changed, the required amount of heat in equation (A'''), which is consistent with the above equation (B) that determines the raceway temperature before the tuyere, is 200 x 10 3 kcal. (103.3Y+66.36Z+9.14)×10 3 kcal=200×10 3 kcal (A''') Moving the constant term to the right hand side gives the following equation: (103.3Y+66.36Z)×10 3 kcal = 190.9 × 10 3 kcal

[0096] (Raceway in front of the tuyere) (heat input) (15-1) The heat of carbon combustion before the tuyere is (52.82Y + 26.41Z - 45.01) × 10 3 kcal. The calculation breakdown is (Y + 0.5Z - 27.27 / 32) x 2 x 110.5 kJ / mol x 0.239 cal / J x 10 3 kcal (see (12-1) above).

[0097] (15-2) The heat capacity of the carbon entering the raceway before the tuyere is (18.9Y + 9.45Z - 16.11) × 10 3 kcal. The calculation details are (Y + 0.5Z - 27.27 / 32) x 2 kmol x 6 cal / mol x 2100°C x 0.75 (see (12-2) above).

[0098] (15-3) The sensible heat of CO injected through the tuyere is 9.24Y x 10 3 kcal (see (6-2) above).

[0099] (15-4) The sensible heat of H2 injected through the tuyere is 8.573Z×10 3 kcal (see (11-4) above).

[0100] (15-5) The sensible heat of circulation of N2 is 9.14 × 10 3 kcal. 9.14W x 10 3 Substitute W = 1 kmol for kcal (see (8-3) above).

[0101] (15-6) The total heat input is (80.96Y + 44.43Z - 51.98) × 10 3 kcal. The calculation breakdown is (52.82Y + 26.41Z - 45.01) x 10 3 kcal + (18.9Y + 9.45Z - 16.11) x 10 3 kcal+9.24Y×10 3 kcal+8.573Z×10 3 kcal+9.14×10 3 kcal.

[0102] (fever) (16-1) The heating of CO is (50.98Y + 17.00Z - 28.97) × 10 3 kcal (see (13-1) above).

[0103] (16-2) Heating of H2 is 31.62Z×10 3 kcal (see (13-2) above).

[0104] (16-3) Heating of N2 is 16.82 × 10 3 kcal. 16.82W x 10 3 Substitute W = 1 kmol for kcal (see 10-2 above).

[0105] (16-4) The total heat output is (50.98Y + 48.62Z - 12.15) × 10 3 kcal.

[0106] (Heat balance in the raceway before the tuyere) Pre-tuyere raceway heat balance: 29.98Y-4.19Z=39.83 (B”) The calculation breakdown is (80.96Y + 44.43Z - 51.98) x 10 3 kcal=(50.98Y+48.62Z-12.15)×10 3 kcal.

[0107] (Carbon charge amount Y and N2 amount W) The above formulas (A''') and (B'') are solved as two-variable equations to calculate the carbon charge amount Y and N2 amount W. Carbon charge Y: 1.421 kmol → CO2 reduction: 40.4% N2 blowing amount W: 1 kmol Hydrogen injection amount Z: 0.6641 kmol

[0108] (Gas volume in the tuyere raceway) CO2: 72.2Nm 3 The calculation breakdown is: ((Y + 0.5Z - 27.27 / 32) x 2 + Y) kmol = 3Y + Z - 1.704 = 3.223 kmol = 72.2 Nm 3 is. H2: 27.5Nm 3 Substituting Z = 0.6641 kmol for (Z + Z) kmol, → 1.328 kmol = 29.7 Nm 3 becomes. ·N2:1kmol=22.4Nm 3 The total gas volume of CO, H2 and N2 is 124.3Nm 3 becomes.

[0109] (A blast furnace operation method in which a portion of the CO gas after CO2 removal is injected into the blast furnace tuyeres) FIG. 6 shows a blast furnace operation method in which a portion of the blast furnace gas after CO2 removal is injected through the tuyere of the blast furnace 1. The iron ore used in the blast furnace 1 may contain impurities such as Zn and Pb. If the entire blast furnace gas after CO2 removal is continuously injected through the blast furnace tuyere, these impurities may accumulate in the blast furnace 1, hindering operation. These impurities are blown out of the blast furnace 1 by the time the base operation after the blast furnace refueling is switched to the tuyere-injected CO gas operation according to the present invention. However, starting up the blast furnace after the refueling is insufficient, and there may be cases where a portion of the blast furnace gas needs to be blown out regularly. In such cases, a portion of the blast furnace gas can be blown into the blast furnace gas holder 5.

[0110] The operation of blowing a portion of the blast furnace gas as described above can be used as an intermediate step between the base operation and the operation of blowing all of the blast furnace gas through the tuyere. In this case, a portion of the circulating N2 gas is blown together with the blown blast furnace gas, so the circulating N2 gas needs to be replenished. The circulating N2 gas can be replenished by blowing air.

[0111] Although FIG. 6 shows an operation in which CO gas and a portion of N gas are injected from the tuyere, an operation in which a portion of blast furnace gas containing CO gas, H gas, and N gas is injected from the tuyere may also be used.

[0112] (Summary of tuyere injection of blast furnace gas containing N2) The world's population is expected to grow in the future, and if developing countries continue to consume the same amount of steel as developed countries, the demand for steel will increase worldwide. The use of H2 and other measures are being considered to reduce CO2 emissions from blast furnaces1. However, in order to meet future steel demand, the current 4,000m 3 , 5000m 3 The operation of large blast furnaces of this class is essential. In this case, it is desirable to make progress in reducing CO2 emissions by extending current blast furnace technology. The present invention provides blast furnace operation conditions for the amount of gas inside the blast furnace and the raceway temperature Tf before the tuyere that are nearly identical to those of current blast furnaces, and can be used to reduce CO2 emissions.

[0113] [Table 1]

[0114] (A blast furnace operating method in which part of the CO2 gas is recycled back into the blast furnace.) →Invention Example 4 (Table 2) In oxygen injection operation of a blast furnace, CO2, like N2 gas, can prevent an increase in the pre-tuyere raceway temperature Tf and a decrease in the pre-tuyere raceway gas volume by circulating CO2 gas.

[0115] Figure 7 shows an example of a blast furnace operation method in which part of the CO2 gas is recycled back into the blast furnace. O2 gas is injected through the blast furnace tuyere, CO2 is separated and removed from part of the blast furnace gas discharged from the top of the blast furnace, and all of the CO2 gas after CO2 removal is combined with the remaining blast furnace gas discharged from the top of the blast furnace from which CO2 has not been separated and removed, and then injected through the blast furnace tuyere. A portion of the blast furnace gas (CO + CO2) emitted from blast furnace 1 is separated and removed in CCS3 (CO2 removal and fixation equipment), and the remainder is stored in tuyere gas relay tank 4 without passing through CCS3. The CO2 and CO gas emitted from tuyere gas relay tank 4 are then heated to 1000-1200°C in the existing hot stove 2 before being blown into blast furnace 1 through the tuyere. Heating by hot stove 2 is intended to reduce the amount of carbon charged in order to reduce CO2 emissions.

[0116] In Figure 7, all of the CO gas in the top gas is stored in the gas relay tank 4, but by mixing in top gas that does not pass through the CCS 3, the gas stored in the gas relay tank 4 contains a certain amount of CO2. By injecting a certain amount of CO2 gas into the tuyere together with CO gas, it is possible to maintain the pre-tuyere raceway temperature Tf and the pre-tuyere raceway gas volume at approximately the same levels as in base operation, and by reducing the amount of carbon charged, it is possible to reduce CO2 gas emissions from the blast furnace.

[0117] (Heat input in blast furnace operation where recycled CO2 gas is injected into the blast furnace tuyere) A blast furnace operation method in which CO2 gas is circulated along with the tuyere-injected CO gas is considered under the condition of producing the same iron content of 63.62 kg as in base operation. The carbon charged to blast furnace 1 is assumed to be Yk moles.

[0118] (17-1) The heat input from the combustion of C to CO2 is 94.05Y × 10 3 kcal. The calculation is Y × 393.5 kJ / mol × 0.239 Cal / J × 10 3 (See (6-1) above).

[0119] (17-2) The sensible heat of CO gas injected through the tuyere is 9.24Y x 10 3 kcal. The calculation breakdown is Y x 28 kg x 0.275 kcal / kg x 1200°C (see (6-2) above).

[0120] (17-3) The sensible heat of circulating CO2 gas is Wk moles × 44 kg × 0.277 kcal / kg × 1200°C = 14.63 W × 10 3 kcal. Let Wk moles of CO2 circulating in the blast furnace gas circulation system. 44 kg is the molecular weight of CO2 (kg / k mole), and 0.277 kcal / kg is the specific heat of CO2 at 1200°C.

[0121] (17-4) The total heat input is 103.3Y x 10 3 kcal+14.63W×10 3 kcal. The calculation breakdown is 94.05Y x 10 3 kcal+9.24Y×10 3 kcal+14.63W×10 3 kcal. Since the amount of pig iron produced is the same as that of base operation (63.62 kg), if we assume that the required heat is the same as that of base operation, the following equation (C) holds true. 103.3Y×10 3 kcal+14.63W×10 3 kcal=177.5×10 3 kcal (C)

[0122] (Tf, raceway temperature before tuyere in blast furnace operation with circulating CO2 gas injected through the blast furnace tuyere) (heat input) (18-1) The heat of carbon combustion before the tuyere is (52.82Y-45.01) x 10 3 kcal. The calculation breakdown is (Y-27.27 / 32) x 2 x 110.5 kJ / mol x 0.239 cal / J (see (9-1) above).

[0123] (18-2) The sensible heat of CO gas injected through the tuyere is 9.24 Y × 10 3 kcal. The calculation breakdown is Yk moles × 28 kg × 0.275 kcal / kg × 1200°C (see (6-2) above).

[0124] (18-3) The sensible heat of CO2 injected through the tuyere is 14.63W x 10 3 kcal. The calculation breakdown is Wk moles x 44 kg x 0.277 x 1200°C.

[0125] (18-4) The heat of reaction (endothermic) between CO2 and C before the tuyere is -41.22W x 10 3 kcal. In front of the tuyere, CO2 undergoes the following chemical reaction with C: CO2+C=2CO ΔH = +172.5 kJ / kmol CO2 The heat of reaction for Wk moles is 172.5 kJ / k mole × 0.239 cal / J × 10 3 kcal.

[0126] (18-5) The heat capacity of the carbon entering the raceway before the tuyere is (18.9Y + 9.45W - 16.12) × 10 3 kcal. Of these, the heat capacity of C burning with oxygen is (18.9Y-16.12) x 10 3 kcal (see (9-4) above). The heat capacity of C, which reacts with CO2 before the tuyere, is 9.45W×10 3kcal. 1 kmol of CO2 reacts with 1 kmol of C, so the reaction mass is Wk moles × 6 cal / mol × 2100°C × 0.75 (see (9-4) above).

[0127] (18-6) The total heat input to the raceway in front of the tuyere is the sum of the above (18-1) to (18-5), which is (80.96Y - 17.14W - 61.13) x 10 3 kcal.

[0128] (fever) The carbon charge amount Y and the circulating CO2 amount W are determined so that the raceway temperature before the tuyere Tf becomes 2100°C. (19-1) Heating of CO is (50.98Y-28.96) × 10 3 kcal. The calculation breakdown is ((Y-27.27 / 32) x 2 + Y) x 28 kg x 0.289 kcal / kg x 2100°C (see (10-1) above). (19-2) The heating of CO due to the reaction of CO with C is 34.0 W × 10 3 kcal. The calculation breakdown is 2 Wk moles x 28 kg x 0.289 kcal / kg x 2100°C. (19-3) The total heat output is (50.98Y + 34.0W - 28.96) x 10 3 kcal.

[0129] (heat balance) Pre-tuyere raceway heat balance: 29.98Y×10 3 kcal-51.14W×10 3 kcal=32.16×10 3 kcal (D) The calculation breakdown is: total heat input = total heat output, (80.96Y - 17.14W - 61.12) x 10 3 kcal = (50.98Y + 34.0W - 28.96) x 10 3 kcal.

[0130] (Carbon charge amount Y and CO2 gas circulation amount W) The above formulas (C) and (D) are solved as two-dimensional equations to calculate the carbon charge amount Y and the circulating CO2 amount W. Carbon charge Y: 1.669 kmol → 30.0% CO2 reduction compared to base operation 2.386 CO2 circulation volume W: 0.349 kmol

[0131] (tuyere raceway composition and gas volume) CO2:74.0Nm 3 The calculation breakdown is (3 x Y - 1.7044) kmol (see the explanation of Example 1). Substituting Y = 1.669 kmol, we get 3.302 kmol = 73.96 Nm 3 becomes. CO from the reaction of CO2 and C: 15.7 Nm 3 = 2 x 0.349 kmol Total gas volume is 89.7Nm 3 becomes.

[0132] (A blast furnace operation method in which recycled CO2 gas is injected into the blast furnace tuyere, maintaining the amount of gas in the raceway in front of the tuyere) → Invention Example 5 (Table 2) In Example 4, when the circulating CO2 was 0.349 kmol, the raceway temperature Tf was 2100°C and the gas volume in the raceway was 89.7 Nm 3 The gas volume in the raceway before the tuyere is 121 Nm3 3 Therefore, in Example 5, the gas volume in the raceway before the tuyere was set at 121 Nm3 for the base operation. 3 We will consider measures to improve the ratio to approach the standard operating level. In order to maintain the amount of gas before the tuyere and keep the heat flow ratio at approximately the same level as in base operation, it is sufficient to increase the amount of circulating CO2. If the amount of carbon charged is increased to increase the heat input while keeping the amount of ore charged constant, the amount of gas in the raceway before the tuyere will increase due to the increase in CO2 and the increase in CO before the tuyere caused by the increase in carbon charged.

[0133] Specifically, due to the increase in charged carbon, the heat input in Example 4 was 177.5 × 10 3Calculate the heat balance and the raceway temperature Tf before the tuyere when the value of kcal is gradually increased. In the above formula (C), the heat input is 215 × 10 3 When the gas volume is calculated as explained below using equations (C') and (D) in which kcal is used, the gas volume in the tuyere raceway is 121 Nm 3 became. 103.3Y×10 3 kcal+14.63W×10 3 kcal=215×10 3 kcal (C') 29.98Y×10 3 kcal-51.14W×10 3 kcal=32.16×10 3 kcal (D)

[0134] (Carbon charge amount Y and N2 gas circulation amount W) The above equations (C') and (D) are solved as two-dimensional equations to calculate the carbon charge amount Y and the CO2 circulation amount W. Carbon charge Y: 2.004 kmol → 16.0% CO2 reduction compared to base operation 2.386 CO2 circulation volume W: 0.5460 kmol

[0135] (Gas composition and volume before the tuyere) CO2: 96.5Nm 3 The calculation is (3 x Y - 1.7044) kmol (see calculation in Example 1). Substituting Y = 2.004 kmol, we get 4.308 kmol = 96.5 Nm 3 becomes. CO from the reaction of CO2 and C: 24.5 Nm 3 = 2 × 0.5460 kmol Total gas volume is 121Nm 3 becomes.

[0136] (A blast furnace operation method in which part of the CO gas after CO2 removal and part of the blast furnace gas are injected into the blast furnace tuyeres) Figure 8 shows a blast furnace operation method in which part of the CO gas after CO2 removal and part of the blast furnace gas are injected through the blast furnace tuyeres. The significance of this blast furnace operation method is similar to that of blast furnace operation in which part of the CO gas and N2 gas are injected through the tuyeres (see the explanation of the blast furnace operation method shown in Figure 6). Figure 8 shows the flow when αK moles of CO gas after CO2 gas removal in CCS 3 is blown into the blast furnace gas holder 5. The amount of CO2 recovered is (Y-α)K moles, minus the CO blown.

[0137] (A blast furnace operation method in which the CO gas after CO2 removal contains H2 gas, and this gas is injected into the blast furnace tuyeres.) In blast furnace operations where CO gas after CO2 removal and the remaining blast furnace gas discharged from the top of the blast furnace without CO2 separation and removal are combined and injected into the blast furnace tuyeres, if H2 gas is added to the CO gas after CO2 removal, the amount of charged carbon can be further reduced, and further CO2 reductions can be expected. If all of the CO gas after CO2 removal is blown in through the tuyere, the H2 gas blown in through the tuyere will be returned to the blast furnace, just like the CO gas, and will remove oxygen from the ore, resulting in a hydrogen utilization rate ηH2 of 100%, meaning that all of the hydrogen will be utilized.

[0138] (Summary of tuyere injection of blast furnace gas containing CO2 gas) When injecting blast furnace gas (CO) into the tuyere, CO2 gas circulation is a useful method, similar to N2 gas circulation. By utilizing the CO2 gas in the blast furnace, it is possible to utilize 100% of the unused CO gas in the blast furnace gas, and reduce the amount of carbon used in the blast furnace by 16%. If the CO gas after CO2 removal contains H2 gas, further reductions in carbon usage can be expected, leading to further CO2 reductions.

[0139] [Table 2]

[0140] According to the present invention as described above, pig iron can be produced with reduced CO2 emissions under operating conditions that are almost the same as those of existing large blast furnaces. [Explanation of symbols]

[0141] 1 blast furnace 2 hot stove 3 CCS (CO2 removal and fixation equipment) 4 Tuyere injection gas relay tank 5 Blast furnace gas holder

Claims

【Request Item 1】 Instead of air blowing, O is blown from the blast furnace tuyere. ２ The gas is blown into the furnace, and CO is extracted from the blast furnace gas discharged from the top of the blast furnace. ２ is separated and removed, and CO ２ A blast furnace operation method in which all of the removed CO gas is injected through the blast furnace tuyere, The CO ２ The N gas blown into the blast furnace through the tuyere and discharged from the top of the blast furnace together with the removed CO gas. ２ All of the gas is recycled to the blast furnace, and the N ２ A blast furnace operation method characterized by keeping the circulation volume constant. 【Request Item 2】 Instead of air blowing, O is blown from the blast furnace tuyere. ２ The gas is blown into the furnace, and CO is extracted from the blast furnace gas discharged from the top of the blast furnace. ２ is separated and removed, and CO ２ A blast furnace operation method in which a portion of the removed CO gas is injected through the blast furnace tuyere, The CO ２ The N gas blown into the blast furnace through the tuyere and discharged from the top of the blast furnace together with a part of the removed CO gas. ２ The gas is recycled to the blast furnace, and the N ２ A blast furnace operation method characterized by keeping the circulation volume constant. 【Request Item 3】 From the blast furnace tuyere ２ The CO ２ The CO gas after removal is H ２ 3. The method for operating a blast furnace according to claim 1 or claim 2, wherein the blast furnace comprises a gas. 【Request Item 4】 Instead of air blowing, O is blown from the blast furnace tuyere. ２ The gas is blown into the furnace, and CO is extracted from a part of the blast furnace gas discharged from the top of the blast furnace. ２ is separated and removed, and CO ２ All of the CO gas after removal and CO from the blast furnace gas discharged from the top of the blast furnace ２ The remaining blast furnace gas that has not been separated and removed is injected into the blast furnace through the tuyere. ２ A blast furnace operation method characterized by keeping the circulation volume constant. 【Request Item 5】 Instead of air blowing, O is blown from the blast furnace tuyere. ２ The gas is blown into the furnace, and CO is extracted from a part of the blast furnace gas discharged from the top of the blast furnace. ２ is separated and removed, and CO ２ A part of the CO gas after removal and CO from the blast furnace gas discharged from the top of the blast furnace ２ The remaining blast furnace gas that has not been separated and removed is injected into the blast furnace through the tuyere. ２ A blast furnace operation method characterized by keeping the circulation volume constant. 【Request Item 6】 From the blast furnace tuyere ２ The CO ２ The CO gas after removal is H ２ 6. The method for operating a blast furnace according to claim 4 or claim 5, wherein the blast furnace comprises a gas.

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