Gas reduction blast furnace and method for operating same

Abstract

The method for operating a blast furnace into which reducing gas preheated to 800°C or more is blown into a furnace from tuyeres (2a, 2b, 2c, 2d) in addition to top-charging coke and tuyere injection fuels, includes controlling a productivity of a shaft so that an inequality (Pd×Mr) / Vsh ≤ 12 is satisfied; and blowing in the reducing gas so that the amount thereof not including the gas blown upward from the middle section of the shaft satisfies the inequality 3.9 ≥ K1 ≥ 3.1 and the formula (Cf+Cg-Ci)+(Hf+Hg) / 2 = K1×(1-Xm) (formula for 1 mole of iron in pig iron). In the inequalities and the formula, Vsh is the effective furnace volume of the shaft (m3), Pd is the pig iron production per day (tp / day), MR is the ratio of top-charging raw materials (t / tp), K1 is a constant for use when determining fuel rate, Cf is the total amount of [C] in the top-charging coke and the tuyere injection fuel(mol-C / mol-Fe), Hf is the total amount of [H] in the top-charging coke and the tuyere injection fuel (mol-H / mol-Fe), Cg is the amount of CO gas in the reducing gas (mol-C / mol-Fe), Hg is the amount of [H] in the reducing gas (mol-H / mol-Fe), Ci is the amount of [C] in the pig iron (mol-C / mol-Fe), and Xm is the ratio of metallic iron (mol-Fe) to total iron (mol-Fe) in the top-charging raw materials.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for reducing the coke rate and reducing agent rate in a blast furnace, and relates to a reduction in CO 2 exhausted from the blast furnace.BACKGROUND ART

[0002] In a blast furnace, coke and iron ore are charged from the top of the furnace, and hot air, high-temperature air of over 1000°C, and fuels, pulverized coal etc., are blown in from the tuyeres at the casting floor. Accordingly, pulverized coal and coke are combusted, producing a large amount of heat and reducing gases such as CO and H 2 . The high-temperature reducing gas generated in this way rises in the furnace, raises the temperature of the descending iron ore, and reduces it.

[0003] There are three types of iron ore reduction reactions; carbon monoxide gas reduction, hydrogen gas reduction, and direct reduction. Among these, direct reduction is a reaction that directly consumes the carbon in coke (FeO+C=Fe+CO) and is a large endothermic reaction. Furthermore, CO 2 and H 2 O generated by combustion and gas reduction cause solution loss reactions (CO 2 +C=2CO) and water gas reactions (H 2 O+C=CO+H 2 ) that also consume carbon in coke at high temperatures. However, these are also large endothermic reactions. (Hereinafter, when solution loss reaction and water gas reaction are not distinguished, they will be referred to as "coke gasification reaction")

[0004] The ratio of carbon monoxide gas reduction, hydrogen gas reduction, and direct reduction is said to be approximately 6:1:3 in typical blast furnaces. The hydrogen that contributes to hydrogen gas reduction is generated from the moisture brought into the furnace or the water vapor (H 2 O) produced by the combustion of the hydrogen component in the fuel, which is converted into hydrogen gas through a water gas reaction. And the carbon monoxide that contributes to carbon monoxide gas reduction is either a by-product gas from direct reduction or the one converted, through a solution loss reaction, from carbon dioxide produced by combustion of carbon components in the fuel. In other words, many of the reduction reactions in the conventional blast furnace depend on coke consumption.

[0005] Pig iron produced in a blast furnace contains carbon, most of which comes from coke and 15 to 20 % of the coke consumed in conventional blast furnaces serves as carburizer.CITATION LISTPATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application No.1995-90034 "Operation for blowing large quantity of pulverized coal in blast furnace" Patent Literature 2: Patent No. 5722867 "Method for recirculating blast furnace gas, and associated device" Patent Literature 3: Patent Application No. 2016-168281 "To provide a method for operating an oxygen blast furnace" NON-PATENT LITERATURE

[0007] Non-Patent Literature 1: "Experimental study on an oxygen blast furnace using a blast furnace test plant" Tetsu-to-Hagane, Vol.77 (1991) No.12, 2099-2106 Non-Patent Literature 2: "Ironmaking technology for the last 100 years: From adopted technologies to a position of leadership in advanced and next-generation technology" Tetsu-to-Hagane, Vol.100 (2014) No.1, 2-30 Non-Patent Literature 3: "Effect of nitrogen-less reducing atmosphere on permeability of cohesive layer in blast furnace" Tetsu-to-Hagane, Vol.104 (2018) No.9, 467-471 Non-Patent Literature 4: "Development of environmentally friendly process technology / Development of process technology such as hydrogen reduction" NEDO Environment Department, 2020 results report meeting materials Non-Patent Literature 5: "Environmental vision 2050" JFE group environmental management vision 2050 briefing materials P14-23 Non-Patent Literature 6: Ironmaking handbook Non-Patent Literature 7: "Steel handbook (4th edition)" (2002) Non-Patent Literature 8: "Steel handbook (5th edition)" (2014) Non-Patent Literature 9: "Development of new ironmaking process comprising shaft-type reduction furnace and cupola-type melting furnace" Tetsu-to-Hagane, Vol.73 (1987) No.15, 2122-2129 Non-Patent Literature 10: "Outlook of pulverized coal injection into a Blast Furnace" Tetsu-to-Hagane,Vol.78(1992)No.7,1187-1197 Non-Patent Literature 11: "Effect of the Structures of injection facilities on combustion characteristic in the pulverized coal injection into a blast furnace" Tetsu-to-Hagane, Vol.82 (1996) No.12, 993-998 Non-Patent Literature 12: "Model experiment on the formation of the cohesive zone in the blast furnace" Tetsu-to-Hagane, Vol.68 (1982) No.15, 2295-2302 Non-Patent Literature 13: "Investigation on behavior of unburnt pulverized coal in blast furnace" Tetsu-to-Hagane,Vol.77(1991)No.1,71-78 Non-Patent Literature 14: "Development of high ratio coke mixed charging technique to the blast furnace" Tetsu-to-Haganen, Vol.92 (2006) No.12, 901-910 SUMMARY OF THE INVENTION

[0008] Conventional blast furnaces rely on so-called direct reduction to some extent, in which carbon in the form of pulverized coal or coke contacts with iron ore and directly reduces it, and therefore consume inevitably some amount of carbon. Although efforts to reduce the carbon consumption per unit of pig iron have been continuously made, such efforts are inevitably limited. The technology disclosed below aims to realize blast furnace operation with low carbon consumption by fundamentally reconsidering the reactions in the furnace.

[0009] In addition to top-charging coke and / or tuyere injection fuels, reducing gas preheated at 800°C or higher is blown into the furnace from tuyeres, in this operating method for a blast furnace. The method for operating a blast furnace includes controlling the productivity of shaft so as to satisfy the inequality (Pd×MR) / Vsh≤12, where Vsh: Effective furnace volume of the shaft(m 3< ), Pd: Pig iron production per day(tp / day), MR: Ratio of top-charging raw materials (t / tp). And above-mentioned reducing gas, not including the gas blown in at and above the middle of shaft, is controlled so as to satisfy the inequality 3.9≥K1≥3.1 and the formula (Cf+Cg-Ci)+(Hf+Hg) / 2=K1x(1-Xm) for 1 mole of iron in pig iron, where K1:constant to determine fuel rate, Cf: total amount of [C] in top-charging coke and the tuyere injection fuels (mol-C / mol-Fe), Hf: total amount of [H] in top-charging coke and the tuyere injection fuels (mol-H / mol-Fe), Cg: amount of CO gas in the reducing gas (mol-C / mol-Fe), Hg: amount of [H] in the reducing gas (mol-H / mol-Fe), Ci: amount of [C] in the pig iron (mol-C / mol-Fe), Xm:Ratio of metallic iron(mol-Fe) to total iron(mol-Fe) in the top-charging raw materials.EFFECT OF THE INVENTION

[0010] By using the above measures, unlike conventional blast furnaces, the role of the lower furnace can be limited to melting the ore and slag, and the role of the shaft can be limited to reducing the ore (100% gas reduction). Therefore, the amount of preheated reducing gas can be freely increased or decreased, i.e. independently from the lower furnace heat balance, according to the shaft conditions such as gas reduction rate, furnace top temperature, and shaft efficiency, while maintaining the required heat amount in the lower furnace (i.e. pig iron temperature) appropriately with the fuels and oxygen blown in through the tuyeres, making the blast furnace operation easier and stabilizing the furnace conditions.

[0011] In addition, since the heat required in the lower furnace is limited to the amount to melt ore and slag, the amount of gas generated in the lower furnace can be reduced to about half that of conventional blast furnaces, which, together with the multi-stage tuyere effect, enhances the gas permeability of the furnace to make it on par with that of conventional blast furnaces even at a very low coke rate.

[0012] According to the present invention, the coke rate in pig iron production can be reduced to 100 kg / tp or less while ensuring the gas permeability of the blast furnace.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig.1 shows an inside diagram of a conventional blast furnace. Fig.2 shows an inside view of the blast furnace of this embodiment. Fig.3 shows the temperature distribution in the blast furnace of this embodiment when three-stage tuyeres are used. Fig.4 shows the arrangement of control equipment in the blast furnace of this embodiment. Fig.5 shows a flow diagram and the main unit consumptions of a conventional blast furnace Fig.6 shows a flow diagram and the main unit consumptions of Example 1. Fig.7 shows a flow diagram and the main unit consumptions of Example 1-2. Fig.8 shows a flow diagram and the main unit consumptions of Example 2. Fig.9 shows a flow diagram and the main unit consumptions of Example 3. Fig.10 shows a flow diagram and the main unit consumptions of Example 4. Fig.11 shows a flow diagram and the main unit consumptions of Example 5. Fig.12 shows a flow diagram and the main unit consumptions of Examples 6. Fig.13 shows a flow diagram and the main unit consumptions of Example 8. Fig.14 shows heat input and output in the lower furnace. Fig.15 shows the heat balance in the lower furnace (conventional blast furnace). Fig.16 shows a comparison of heat balance in the lower furnace (conventional blast furnace vs. this invention). Fig.17 shows a heat transfer diagram of the lower furnace (this invention). Fig.18 shows a comparison between the required / consumed energy in the lower furnace and the amount of gas passing through the cohesive zone (conventional blast furnace vs. this invention). Fig.19 shows the relationship between bosh gas rate and ore temperature in this invention. Fig.20 shows a Rist model diagram of a conventional blast furnace example. Fig.21 shows a Rist model diagram of Example 1. Fig.22 shows a heat transfer diagram of a conventional blast furnace example. Fig.23 shows a heat transfer diagram of Example 1 and Example 1-2 (gas). DESCRIPTION OF EMBODIMENTS

[0014] Several exemplary embodiments are described below with reference to the accompanying drawings, in which it is to be specifically noted that the drawings are not necessarily drawn to scale and therefore the dimensional relationships between them are not limited to those shown.

[0015] Although each term is used throughout the following description and the appended claims to have a meaning consistent with definitions well known to those skilled in the art, we caution that certain terms have the following meanings: "The lower furnace" means the area of and below the cohesive zone. The part of the blast furnace body that bulges in the radial direction is called the "belly", and the "shaft" refers to the part of the furnace body that is above the belly and below the top of the furnace. The term "middle" of shaft is specifically defined and used to mean not only the center of the shaft in the height direction, but also a region that includes one-sixth of the height of the shaft above and below the center. The "effective furnace volume (m 3< )" of the shaft means, for example, the internal furnace volume between the lower end of the shaft and the height up to the stock line, which is the furnace top raw material level "Partial combustion" means combustion that is not a complete combustion. "Primary combustion" refers to the reaction of C+ 0.5·O 2 = CO, as well as the partial combustion that produces CO, H 2 and H 2 S from coke and / or tuyere injection fuels. The heat generated by this is called "primary combustion heat." "Secondary combustion" means the reaction of CO + 0.5·O 2 =CO 2 and H 2 +0.5·O 2 =H 2 O, and CO 2 and H 2 O are called "secondary combustion gas". The "fuel rate" is the total weight (kg / tp) of coke and tuyere injection fuels to produce 1 ton of pig iron, and is often referred to as the reducing agent rate these days. Unless otherwise specified, the fuel rate does not include reducing gas (CO,H 2 ) blown in from tuyeres by top gas recycling etc. but includes hydrocarbon fuels(CiHjOk; Components display excluding ash component).

[0016] In the research on the oxygen blast furnace, attempts have been made to reduce the coke rate and fuel rate using top gas, and it is also recognized that the use of top gas (reducing gas) reduces the direct reduction ratio as a secondary effect. However, research on the use of reducing gas has mainly focused on top gas from an economic perspective, and it is also believed that there is a limit (about 200 kg) to reduce the coke rate and fuel rate due to the tuyere flame temperature and the heat balance in the lower furnace. Furthermore, even if the coke rate can be reduced in terms of process, it unavoidably brings about operational problems such as the poor gaseous paths in the cohesive zone, which significantly impedes gas permeability in the furnace, and it has been though unrealistic. The operating method disclosed below has been devised in violation of the common general knowledge of those skilled in the art.

[0017] The method to operate a blast furnace, disclosed below, is generally directed to blow a sufficient amount of reducing gas in the blast furnace to substantially complete the reduction reaction of the iron ore above the cohesive zone. Such conditions are achieved by blowing in a reducing gas in the amount, per mole of pig iron produced, to satisfy Cf + Cg − Ci + Hf + Hg / 2 = 1.5 / ηg where Cf: Tota amount of [C] in top-charging coke and tuyere injection fuels (mol-C / mol-Fe) Hf: Total amount of [H] in top-charging coke and tuyere injection fuels (mol-H / mol-Fe) Cg: [CO] amount in preheated reducing gas(mol-C / mol-Fe) Hg: [H] amount in preheated reducing gas(mol-H / mol-Fe) Ci: [C] amount in pig iron (mol-C / mol-Fe) ηg: Gas utilization ratio(%) or secondary combustion ratio(%) of furnace top gas Each symbol listed here and the symbols Xm, K1 in the following paragraphs represent the moles per mole of iron (Fe) in pig iron.

[0018] However, since reduced iron such as DRI(direct reduced iron) or ferrous scrap may be charged from the top of the furnace, the above formula is modified as Cf + Cg − Ci + Hf + Hg / 2 = 1.5 / η g × 1 − Xm where Xm: Ratio of metallic iron (mol-Fe) to total iron(mol-Fe) in the top charging raw materials

[0019] Replacing 1.5 / ηg on the right side with the parameter K1, and having found the appropriate range of K1 from various examples shown in Tables 4 to 7, whose results are shown below. Cf + Cg − Ci + Hf + Hg / 2 = K 1 × 1 − Xm 3.9 ≥ K 1 ≥ 3.1 where: K1: Constant for determining fuel rate

[0020] The present invention will be explained in more detail below.

[0021] As a measure against global warming, one of the most important issues is to reduce the fossil fuels, which are the top-charging coke (hereinafter referred to as coke) and the tuyere injection fuels such as pulverized coal, heavy oil, natural gas, etc. It is well known that the top gas recirculation, in which the top gas is dehumidified (removing water vapor in the gas) and decarbonated (removing carbon dioxide in the gas) and then blown into the blast furnace again, can decrease reducing agent rate (= coke rate + tuyere injection fuel rate), which is the unit consumption of reducing agent to produce one ton of pig iron (Patent Documents 2 and 3). In addition, by replacing the tuyere injection fuels such as pulverized coal with renewable energy fuels (biofuels, etc.) and / or carbon recycle fuels (hydrocarbon fuels converted from CO 2 by green fuels), there is the possibility to effectively reduce CO 2 emissions.

[0022] However, regarding the coke, using metallurgical coke (produced from limited coal) is considered inevitable due to its roles as 1) ensuring the permeability inside the furnace (role of fire grate) and 2) acting as a carburizer. Therefore, reducing the coke rate (coke consumption per ton of pig iron) is the key to reduce CO 2 emissions in the blast furnace.

[0023] Because coke is more expensive than tuyere injection fuels, there is a history always aiming for lower coke rate operations. The coke rate in hot-air conventional blast furnaces is generally about 350(300-370) kg / tp (tp; means ton of pig iron, the same applies hereinafter), or about 250 kg / tp at the lowest operation record.

[0024] As a feature of the oxygen blast furnace process, using pure oxygen increases the combustion efficiency of pulverized coal. However, the tuyere front temperature (the hottest point in the raceway) becomes abnormally high, because pure oxygen is blown in from the tuyere to directly combust the red-hot coke. As a countermeasure, a method of blowing in steam (H 2 O), top gas containing H 2 O and CO 2 , or iron ore has been devised to prevent the tuyere front from becoming abnormally high temperature (Patent Literature 3). But, since the endothermic reactions also cool the lower furnace, a large amount of pulverized coal must be blown in and the coke rate is considered 200 to 250 kg / tp at the lowest, where pulverized coal ratio =300 kg / tp, reducing agent rate =500 kg / tp.

[0025] The ULCOS-NBF process developed in Europe is a blast furnace process that combines the oxygen blast furnace process and the top gas recirculation (TGR). As with other TGR processes at that time, the reducing gas injected into the furnace is limited to the top gas which is derived from the reducing agent (coke and tuyere injection fuels), and it is a semi-closed circulation system in which some of top gas is discharged outside the system as surplus gas. Carbon charge amount (carbon amount in the reducing agent including coke and tuyere injection fuels) is reduced by only about 24% compared to the conventional blast furnaces (Non-patent Literature 2).

[0026] In the two latest blast furnace processes, being developed in Japan as measures against global warming (Non-patent Literatures 4 and 5), CO 2 will be reduced only by round 30% from conventional blast furnaces even when CCUS (Carbon Capture, Usage and Storage) is used. It will be by about 10% if excluding the CCUS effect. The coke rate is about 300 to 350 kg / tp, which is within the range of conventional blast furnaces.

[0027] As described above, with the aim to reduce the coke rate and CO 2 emissions, improvements have been made to the operation of conventional blast furnaces. And the oxygen blast furnace and the top gas recirculation have been developed as an alternative to the conventional blast furnace process. However, the biggest issue for blast furnaces is that there have been no reasonable process proposals (based on heat and mass balance and / or the Rist model) that would reduce the coke rate below 200 kg / tp.

[0028] An operational issue in reducing the coke rate is gas permeability within the furnace. As shown in Fig.1, the blast furnace is equipped with a furnace body 1 and tuyeres 2, and raw materials such as ore and coke are alternately charged into the furnace, and ore layer 8a and coke layer 8b are stacked in layers to form lumpy zone 8. Hot air and fuels are blown in through the tuyere 2 to form raceway (hereinafter also referred to as RW) 3, which also reacts with coke to generate RW-derived gas 3a, which rises in the lower furnace 11. As the raw material descends in the shaft 12, the temperature rises and the ore reduction proceeds, and when it reaches around 1100 °C, the ore begins to soften, and when it reaches around 1200 °C, the ore begins to further soften and melt, and eventually melts at 1400 to 1500 °C. Liquid stream 5 drips down drip zone 10 and deadman 6 and reaches the bottom of the hearth 15 (see Fig.2) as pig slag bath 7. The permeability of the cohesive layer 9a which is an aggregate of softened or molten ore is poorer than that of the ore layer 8a, but the coke (coke slit 9b) sandwiched between the cohesive layers plays a role of fire-grate, serving as a flow path for the RW-derived gas 3a, to keep the permeability of the cohesive zone 9 (an aggregate of the cohesive layer 9a and the coke slit 9b). In addition, by actively charging the center coke 8c into the center of the furnace, the center gas flow 4c is ensured and the cohesive zone shape is maintained in an inverted V shape.

[0029] In low coke rate operation, as the ore / coke rate (O / C ratio) increases, the thickness ratio of the cohesive layer to the cohesive zone increases and the thickness ratio of the coke slit decreases, a major problem was the decrease in the gas permeability of the cohesive zone.

[0030] The problems of the present invention are solved by the following means.

[0031] In equipment where the raw material residence time (reaction time) in the shaft is effectively ensured, other than the top-charging coke and / or tuyere injection fuels, reducing gas preheated to 800°C or higher is supplied into the furnace in order to make the ore reduction ratio close to 100% above the cohesive zone. The reducing gas is supplied at and below the lower shaft in an amount that satisfies equations (3) and (4) per mole of iron (Fe) in the pig iron,

[0032] It does not include the gas blown in at and above the middle of shaft. Also, the required residence time in the shaft is calculated based on the shaft productivity index Psh (t RM / day·m 3< ; raw material processing volume per shaft volume) to satisfy the following formula. Psh = Pd × MR / Vsh ≤ 12 t RM / day ⋅ m 3

[0033] Vsh: Effective furnace volume of shaft (m 3< ) Pd: Pig iron production per day (tp / day) MR: Ratio of top-charging raw materials (t RM / tp)

[0034] Even if the residence time and amount of reducing gas are sufficient, the actual gas reduction rate may vary depending on the reducibility of the ore, the gas permeability conditions in the shaft, etc. Therefore, to control the gas reduction ratio, the amount of reducing gas is adjusted so that the total gas amount of CO 2 and H 2 O in the top gas per ton of iron (Fe) in the pig iron, Vpc (Nm 3< / t-Fe), is within the range of the following formula (within K range). Vpc = K 2 × Gy / 1.5 + Xf × 22.4 + Xo 610 ≥ K 2 ≥ 560

[0035] K2: Constant determined by the direct reduction ratio and the iron ratio in pig iron Gy: The ratio of oxygen (mol-O) to iron (mol-Fe) in the charged ore and charged metallic iron (mol-O / mol-Fe) Xf: Total molar ratio of CaCOs and MgCO contained in the charged raw materials per ton of pig iron (kmol / tp) Xo: The amount of secondary combustion gas (CO 2 ,H 2 O) supplied to the furnace above 2 / 3 height from the top of the shaft (1 / 3 height from the bottom) (Nm 3< / tp)

[0036] For the above reducing gas, blast furnace top gas that is subjected to dust removal, H 2 O and CO 2 removal may be recycled, or hydrogen, carbon monoxide, etc. may be introduced from outside the recycle system. In the present invention, since the fuel rate in the lower furnace is quite low and to prevent nitrogen gas (N 2 ) from concentrating due to circulation, reducing gas from outside the system, including it made from combustible fuels, is actively used in addition to the top gas.

[0037] These reducing gases (hereinafter also referred to as tuyere blown-in gas) are preheated to a high temperature of 1200 to 1350°C before being blown into the furnace through the tuyeres. Since the blown-in temperature is high, accordingly in the high-temperature zone of the heater that preheats the tuyere blown-in gas, it is possible to increase the reduction degree and the amount by partially burning combustible fuels such as methane (CH 4 +0.502 =CO+H 2 ) and / or by gas-reforming some(CO 2 and H 2 O) of the top gas (CH 4 +CO 2 = 2CO+2H 2 , CH 4 +H 2 O= CO+3H 2 ).

[0038] By the above method, the gas reduction ratio can be brought close to 100%, and the amount of energy required in the lower furnace is reduced. But at the same time, for further reducing the coke rate and fuel rate it is important to reduce the reaction heat (coke gasification) and the fuels such as methane to be cooling heat sources in the lower furnace, which also reduces the amount of gas generated in the lower furnace. As a guideline, it is important to reduce the total amount of heat of primary combustion in the lower furnace (heat of CO and H 2 formation from coke and tuyere injection fuels) and sensible heat of the tuyere blown-in gas (i.e., the total amount of heat supplied to the lower furnace) up to 2.4 GJ / tp or less (preferably 2.2 GJ / tp or less) per ton of pig iron. The specific measures are listed below.

[0039] Two or more stages of tuyeres are arranged in the height direction of the furnace body. And oxygen-containing gas of 200 Nm 3< / tp or less is blown in as the total amount of oxygen(Oz) and secondary combustion gases(CO 2 and H 2 O) from at least the lowest tuyeres, and reducing gas (CO and H 2 ) of 500 × (1-Xm) 1.3< Nm 3< / tp or more is blown in from the tuyeres of and below the lower shaft, so that the total amount of CO and H 2 including the said reducing gas and the hydrogen content in the tuyere injection fuels is 800×(1-Xm) 1.3< Nm 3< / tp or more, where Xm is the ratio of metallic iron (mol-Fe) to total iron (mol-Fe) in the top-charging raw materials.

[0040] As tuyere injection fuel, "hydrocarbon fuel of CiHjOk (composition display excluding ash component) in any form of gas / liquid / solid that satisfies the following formula" or "any fuel consisting of metallic element (Si,Ca,Al,Mg,Fe,Si,Mn,C) or its ferroalloy constituting pig iron or slag" is used alone or in a mixture of two or more fuels together with oxygen. j / i ≤ 2.3 , 16 × k / 12 × i + j + 16 × k ≤ 10 %

[0041] When injecting combustible fuel (tuyere injection fuel) and / or preheated reducing gas (tuyere blown-in gas) from the blast furnace tuyeres, for 1 ton of pig iron, pure oxygen (or oxygen with a purity of 90% or more) is supplied together in the molar amount of "Vo 2 -1"(O 2 -kmol / tp) or more but "Vo 2 +0.2"(O 2 -kmol / tp) or less, where Vo 2 is calculated by the following formula: Vo 2 = 0.5 × C 1 + C 2 − C 3 − C 4 + S 1 + S 2 − O 1 − O 2 + S 3 + 1.5 × S 4

[0042] C1: Amount of C component in tuyere injection fuel (C-kmol / tp) C2: Molar amount of carbon in coke (C-kmol / tp) C3: Molar amount of carbon in pig iron (C-kmol / tp) C4: Molar amount of carbon required to reduce metals other than iron in pig iron (C-kmol / tp) O1: Amount of O component in tuyere injection fuel (O-kmol / tp) O2: Molar amount of CO 2 and H 2 O in the preheated reducing gas (kmol / tp) S1: Mg component not combined with oxygen in tuyere injection fuel (Mg-kmol / tp) S2: Ca component not combined with oxygen in tuyere injection fuel (Ca-kmol / tp) S3: Si components not combined with oxygen in tuyere injection fuel (Si-kmol / tp) S4: Al component not combined with oxygen in tuyere injection fuel (Al-kmol / tp)

[0043] The deviation between actual amount of oxygen and the molar amount Vo 2 (O 2 -kmol / tp) calculated by formula (10) is given here in a range of -1 (O 2 -kmol / tp) to + 0.2(O 2 -kmol / tp) for adjusting Voz according to the gas reduction ratio and carburization situations. It is set to -1 (O 2 -kmol / tp) or more because a gas reduction ratio of 100 % to 92 % is assumed, and it is set to + 0.2 (O 2 -kmol / tp) or less in order to prevent an excess of oxygen that would deteriorate the carburization of the pig iron.

[0044] Embodiments of the present invention will be described below.

[0045] As mentioned in the technical background, in a typical blast furnace, about 30 % of the coke is consumed by a direct reduction reaction, and about 40% is by a reaction with H 2 O or CO 2 . In order to reduce coke consumption, therefore, it is important (1)to increase the gas reduction reaction (to reduce the direct reduction reaction), (2)not to add H 2 O or CO 2 from the outside to the high temperature area of 900 to 1000 °C or higher in the furnace, furthermore (3)to make the amount of heat and gas that are supplied to and generated in the lower furnace necessary and sufficient for the external heat output (pig iron heat, slag heat, heat loss) from the lower furnace (the cohesive zone and below it). The reason why the temperature is set at 900 to 1000 °C or higher is that the coke gasification reaction with carbon (C) substantially starts at about 900 °C and becomes especially active at 1000 °C or higher.

[0046] Incidentally, the relationship between gas-reduction / direct-reduction and fuel is easily understood from the Rist operating diagram, which is one of the most reliable equilibrium diagrams in the blast furnace operation. The Rist operating diagrams of a conventional blast furnace (example) and Example 1 of the present invention described in the Examples section below are shown in Figs. 20 and 21, respectively. Note that in the operating diagrams, CO and H 2 in the tuyere blown-in gas are included on the Y axis (O+H 2 ) as tuyere injection fuel.

[0047] The direct reduction ratio (Yd) of a conventional blast furnace (example) is 30%, but to reduce it to 0%, if point W (the point where reduction of FeO begins) is kept constant, the operating line shown by the dashed line in Fig.20 will be obtained. The slope of the operating line indicates the moles of [C+H 2 ] per mole of [Fe], so in a conventional blast furnace (example) that does not use reducing gas, it is an index proportional to the fuel rate. Therefore, it requires to significantly increase the fuel rate (coke and / or PCI) from the current situation (Yd=30%), which is counterproductive from the standpoint of economy and reducing the fuel rate, and lowering the direct reduction ratio itself could not be an objective of conventional operation.

[0048] The top gas recirculation method based on oxygen blast furnaces expands the degree of freedom of the operating line by compensating for the slope of the operating line not only with the extra fuel rate but also with the top gas (reducing gas). If the fuel rate is the same, the operating line will rise by the amount of top gas blown into the furnace, and the direct reduction ratio (Yd) will decrease. However, since the aim of the development is to lower the fuel rate, the fuel rate should be reduced as the top gas blown-in amount increases (increase in Yd), which will lead to the decrease in the top gas recirculation amount (increase in Yd) due to the fuel rate reduction, and so on. The optimal point was fluid.

[0049] Although a wide variety of research has been conducted into the optimum operating line from the viewpoints of fuel rate reduction, tuyere protection under oxyfuel combustion, top gas temperature, and economic efficiency, there has been no research (literature) to date that aims or measures to achieve Yd = 0% (including conventional methods).

[0050] The operating line of the present invention (Fig.21) passes through Yd = 0%, and has the "maximum slope (fuel rate + reducing gas rate)" when point W and shaft efficiency are constant. The fuel rate of the present invention (see Tables 4 to 7) is significantly lower than any of the previous methods, so the "maximum slope" means that for the same fuel type, the reducing gas rate (unit consumption of tuyere blown-in gas) is greater than any of the other methods.

[0051] This tendency can be also confirmed with the tuyere blown-in gas (V13) in Tables 4 to 7, which show many examples of the present invention. The amount of gas blown in is 700 Nm 3< / tp or more. The reason why the value in Example 7 is as low as 564 Nm 3< / tp is because ethylene (C 2 H 4 ) containing a large amount of H 2 is used as the fuel, which is substantially similar to blowing the H 2 into the lower furnace. And, considering the H 2 component in the tuyere injection fuel as a will-be-reducing gas and converting it to "V13 + tuyere injection fuel [H 2 ]", it corresponds to a reducing gas of 890 Nm 3< / tp, which is 8 times that of a conventional blast furnace (example). In addition, including the metallic iron charging example (metal charge ratio Xm), all of Examples 1 to 8 have equivalent values of 800×(1- Xm) 1.3< Nm 3< / tp or more.

[0052] In the present invention, fuels (external fuels) and oxygen are added to each 1 Nm 3< of top gas in the amount corresponding to the following formula, which are heated to a high temperature. It allows the CO 2 and H 2 O remaining in the gas to be reformed (converted to CO and / or H 2 ), and it also allows to arbitrarily increase the amount of tuyere blown-in gas (CO, H 2 ) without being limited by the top gas amount thanks to the primary combustion (partial oxidation) of the external fuels. O 2 kmol / Nm 3 = FRh / 2 × C − CO 2 − H 2 O − FRh × O

[0053] FRh(kg / Nm 3< ) :Fuel rate added to 1 Nm 3< of furnace gas [CO 2 ](kmol / Nm 3< ) :CO 2 content in the top gas [H 2 O](kmol / Nm 3< ) :H 2 O content in top gas [C] (kmol / kg) :C component in fuels [O] (kmol / kg) :O component in fuels

[0054] When hydrogen or carbon monoxide is used as the external fuel, no oxygen is required according to formula (11). It is also possible to change the entire amount of top gas to an external fuel such as hydrogen.

[0055] Regardless of the amount or composition of the top gas (including cases where the top gas is not used), high-quality reducing gas can be supplied into the furnace in the required amount at any time, so the gas reduction ratio in shaft can be increased ultimately (up to 100%) in terms of equilibrium theory, which is a major feature of the present invention.

[0056] Regarding the amount of blown-in gas (reducing gas) to bring the gas reduction ratio close to 100%, after repeated case studies such as those shown in the examples described below, it was found that, regardless of the CO / H 2 ratio of the reducing gas or the type of fuel, the appropriate amount of reducing gas (CO,H 2 ) for each mole of iron (Fe) in the pig iron, expressed by the following formula, should be blown in and below the lower shaft at a temperature of 800°C or higher in addition to the top-charging coke or tuyere injection fuel.

[0057] The preheated reducing gas that satisfies formulas (3) and (4) does not include the preheated reducing gas blown in and above the middle of the shaft because preheating or reduction to FeO is taking place in and above the middle of the shaft, which is a region where the gas has already passed point W (the pinch point of gas reduction) on the Rist model. The reason for specifying 800°C or higher is that the temperature of point W (the point at which reduction of FeO begins) is determined by the heat balance of the counterflow of gas and ore, and it moves to the lower temperature side with the oxygen blast furnace (high heat flow ratio) or with higher hydrogen reduction (endothermic reaction) ratio, which makes the gas blown in at 800 °C still effective depending on the its location.

[0058] In order for the above formula to be valid, it is of course necessary to ensure the required residence time (reaction time) of the raw materials. Shaft productivity Psh (t RM / day·m 3< ; raw material throughput per shaft volume) should at least satisfy formula (5).

[0059] Psh≤12 is an index value derived by the inventor based on the productivity of general direct reduction furnaces, and the shaft residence time (day) is obtained by multiplying the inverse number by the bulk density of raw materials. Psh of a conventional blast furnace is about 6 to 8 (t RM / day·m 3< ), and there is no problem in productivity (residence time) in comparison with direct reduction furnace. In the present invention, since the coke rate is significantly lower than in conventional blast furnaces, the shaft productivity per pig iron production can be greatly reduced (that is, the ore residence time and reduction time are increased). This means that the preset invention gives more room for productivity improvement in the blast furnace already having the shaft productivity of around 6 to 8 (t RM / day·m 3< ), and that there is no problem with shaft productivity (residence time) itself.

[0060] As a method to produce tuyere blown-in gas from fuel, for example, a synthesis gas production technology from methane is already in a practical use as a steam reforming method to reform H 2 O, a dry reforming method to reform CO 2 , and a partial oxidation method (primary combustion of methane). These are classified to methods for reacting at 600-900 °C using catalyst (catalytic partial oxidation) and methods for reacting at 1200-1300 °C or higher without catalyst (thermal partial oxidation). In the present invention, since the reducing gas is finally blown into the furnace at a high temperature, there are advantages in reacting at high temperatures, in terms of thermal efficiency and equipment, and a non-catalytic method is preferable from the viewpoint of catalyst cost and maintenance. In either case, the generation of soot due from methane can be an issue, but by adopting a regenerative heater such as a blast furnace hot stove (alternating cycle of a heat storage process by combustion exhaust gas and a heat release process by preheating another gas), the removal of soot becomes easier with the oxidizing gas (CO 2 ,H 2 O,O 2 ) in the combustion exhaust gas.

[0061] Regarding the timing of fuel injection into the gas, there are no process restrictions when the fuel is CO or H 2 , but when the fuel is hydrocarbon gas, liquid fuel, or solid fuel, the reducing gas should be preheated to 600 °C or higher before being injected in order to promote primary combustion and gas reforming while suppressing soot generation. Furthermore, in the case of non-catalytic fuels, it is desirable to inject the fuel at 1000 to 1200 °C or higher from the viewpoint of combustion efficiency (prevention of soot generation). However, in order to enhance the preheating effect and enable soot cleaning by the combustion exhaust gas, it is necessary to inject the fuel well before the heater outlet.

[0062] As for the type of heater, in order to preheat the reducing gas to 1000°C or higher, the contact surface of a regenerative heater (regenerative furnace) is preferable to be made of refractory, such as a blast furnace hot stove. After converting a conventional hot-air blast furnace into an oxygen blast furnace, the hot stove is no longer required and it is easy to convert it into a reducing gas heater in respects of gas throughput and processing temperature, which is another advantage of the present invention.

[0063] As the fuel for the heater of the present invention, it is preferable to use blast furnace top gas as used in conventional hot stoves. Even in a pure oxygen blast furnace, the top gas contains N 2 (derived from raw fuel and utilities), and it will become concentrated if the top gas is recycled. So, such a mechanism as to actively extract it outside the circulation system is required. There is another conventional method of sending whole top gas to equipment outside the system as surplus gas, but since it contains CO and requires distribution of CO 2 , it is optimal to use it as fuel for gas heating in the hot stove, ancillary equipment to the blast furnace. When the exhaust gas is used as a heating fuel, if it is separated before the CO 2 separator, combusted with oxygen at an oxygen excess ratio of about 1(complete combustion) and dehumidified, then the CO 2 concentration in the gas can be close to 100% without going through a CO 2 separator, which reduces the capacity and operating load of the CO 2 separator.

[0064] Incidentally, it has been common practice to directly inject fuel such as natural gas into the furnace as tuyere injection fuel without converting it into reducing gas. However, when lowering the coke rate, handling of hydrogen components in the injected fuel becomes an issue. For example, methane emits 35.8 MJ / Nm 3< of heat when completely combusted, but it generates H 2 O and consumes coke around the raceway through a water gasification reaction (H 2 O + C =CO+H 2 ). If the amount of oxygen is lowered to keep it at primary combustion (CH 4 +0.5×O 2 =CO+2H 2 ), the calorific value will drop to 1.6 MJ / Nm 3< and the combustion temperature will only be around 400 °C. In other words, the reducing gases(CO, H 2 ) generated by the primary combustion of methane and oxygen become powerful cooling gases at raceway temperatures of 2000°C or higher, and the coke rate and / or tuyere injection fuel rate (pulverized coal, etc.) worsens (increases). If methane is preheated as a countermeasure, troublesome soot is generated above 600°C due to the cracking phenomenon (CH 4 →C+2H 2 ).

[0065] Not only methane, but any fuel (gas or liquid) with low primary combustion heat (calorific value to generate CO and H 2 ) has the same problem and is not suitable as tuyere injection fuel in the era of CO 2 reduction. Room temperature hydrogen is similar in that it acts as a strong cooling gas for the raceway temperature. In order to utilize such fuels for blast furnace in the era of CO 2 reduction, the fuel supply method described above is the most effective. And since the thermal issues of such fuels can be supplemented (additional heat can be provided) by heaters, it has an advantage in terms of heat balance in the lower furnace.

[0066] Gas reforming technology is a conventional technology, and heating the reducing gas in a hot stove is not a new idea either. However, the features of this invention are that it clarifies and integrates the roles of top gas, external fuel, and gas heating fuel, and supplies a sufficient amount of high-quality reducing gas as tuyere blown-in gas to achieve 100% gas reduction.

[0067] From the above, the means and methods for ensuring the gas quantity and gas quality required to bring the gas reduction rate in the furnace close to 100% were clarified.

[0068] Next, the method of burning fuel and coke in the high temperature region below the cohesive zone will be described.

[0069] In conventional tuyere fuel injection, oxygen is injected for near complete combustion, and CO 2 and H 2 O derived from secondary combustion are actively reacted with the coke around the raceway to generate reducing gas, and Patent Literature 1 recommends an excess oxygen ratio of 1 or more for pulverized coal injection of 170 kg / tp or less. Here, excess oxygen ratio is defined as (excess oxygen ratio) = (total amount of oxygen actually injected from the tuyere as air, pure oxygen, and pulverized coal) / (total amount of oxygen required to burn carbon and hydrogen in pulverized coal to CO 2 and H 2 O).

[0070] When using pure oxygen instead of hot air, it must be noted that the combustion temperature tends to become abnormally high due to the absence of N 2 . Abnormal flame temperatures in front of the tuyere are unavoidable with the same excess oxygen ratio as in conventional blast furnaces. And as the countermeasures, such as "injecting H 2 O, CO 2 and / or iron ores through the tuyere at the same time in order to lower the abnormally high temperature of the flame and tuyere tip by oxygen combustion" (Patent Literature 3). However, the injection of H 2 O and CO 2 causes a coke gasification reaction (endothermic reaction) and leads to increased coke consumption and heat consumption in the lower furnace, so it is a measure to avoid.

[0071] The present invention, the details of which will be described later, is characterized by the fact that the combustion temperature is significantly reduced even in pure oxygen operation by limiting fuel combustion in the raceway to primary combustion (i.e. reducing the rate of excess oxidation). Furthermore, by injecting an appropriate amount of tuyere blown-in gas (reducing gas such as CO or H 2 ) at 1200-1350 °C, which is not a combustion fuel in the raceway, together with the tuyere injection fuel, it is possible to properly control the maximum flame temperature and to increase the ignitability of pulverized coal and / or carbonaceous fuels.

[0072] It is known that the combustion efficiency of pulverized coal decreases when the excess oxygen rate is lowered, but the combustion efficiency increases dramatically when the oxygen concentration (oxygen partial pressure) is increased (Non-patent Literature 1, Non-patent Literature 9). Furthermore, in the oxygen combustion of pulverized coal in the raceway, turbulent diffusion, rather than chemical reaction or gas boundary film diffusion, becomes rate-determining, and 100% primary combustion is possible by strengthening the agitation of pulverized coal and oxygen. Patent Literature 11). In other words, under oxy-fuel combustion, it is fully possible to increase the combustion efficiency of the primary combustion of pulverized coal in the raceway space to at least the same level (50-70%) as that of a conventional blast furnace (hot air).

[0073] On the other hand, as is the case with conventional blast furnaces, even if the combustion efficiency of pulverized coal in the raceway is far from 100%, there is virtually no problem with operation. In other words, "pulverized coal combustion efficiency <100% in the raceway" means the outflow of unburnt char, CO 2 and H 2 O to the outside of the raceway. But the reaction rate of CO 2 and H 2 O with unburnt char is faster than that with coke (Non-patent Literature 13), and the reaction rate with dissolved carbon in the dropped metal is several times faster (Non-patent Literatures 6, 7). In the presence of them (unburnt char and / or dissolved carbon), coke consumption can be effectively suppressed.

[0074] While the unburnt char in bosh gas moves up through the dripping zone, it is washed in a volumetric volume of metal / slag that falls more intensely than any heavy rain on Earth (scrubber effect), then passes through the narrow pores of cohesive zone (filter effect). In these processes, unburnt char is captured and returned to the lower furnace, either carburized or entrained in the metal drops. Non-patent Literature 10 states that "Unburnt char is consumed in carburization and / or coke gasification reactions, and the carburizing rate becomes rate-limiting in the unburnt char supply, and injection rate of pulverized coal of about 200kg / tp does not reach the rate-limiting in carburizing." So, it functions as a reducing agent for CO 2 and H 2 O. In other words, by recycling unburnt char in the lower furnace, coke consumption is suppressed, and the combustion efficiency there approaches 100%.

[0075] The above phenomenon (in-furnace capture and consumption phenomenon of unburnt char) has been confirmed in conventional blast furnaces. But in the present invention, as described later, "The scrubber effect increases since the amount of bosh gas is 1 / 2 to 1 / 3 compared to conventional blast furnace." and "The proportion of gas passing through the coke slit (coarse filter) in the cohesive zone has been reduced from approximately 90% (Table 2) in conventional blast furnaces to approximately 40% (Table 2) to 0% (when all coke is charged mixed with ore)." Therefore, it can be reasonably expected that the char flowing out from the raceway will be further captured and consumed, and the combustion efficiency in the entire lower furnace can be higher than that of a conventional blast furnace.

[0076] The above is not limited to pulverized coal, but is common to other tuyere injection fuels. Specifically, by injecting high-temperature reducing gas and / or ignition materials (metal powders such as Mg, Ca, Si, Al, and / or deoxidizers such as CaC2 and FeSi) together with the fuel and oxygen, the atmospheric temperature before the fuels ignite increases, further increasing ignitability and combustion speed.

[0077] Here, the concept of "heat balance in the lower furnace (from the cohesive zone to the hearth)", which is one of the important elements of the present invention, will be explained.

[0078] Fig.14 shows the heat input and heat output in the lower furnace, including the cohesive zone, of the blast furnace. The heat input includes heat Qm1 of raw materials (ore, coke, etc.) entering from the shaft, heat Qgr of RW gas (gas derived from raceway), and primary combustion heat Qk of coke with solid oxygen in the raw materials. The heat output includes heat Qmt of tapping pig slag, heat Qcg of the gas flowing out from the cohesive zone, and heat Qm3 such as reactions and heat loss consumed in the lower furnace. From their balance, 0= Qm1+Qcg-Qmt-Qgr-Qm3. Regarding FeO reduction (direct reduction) in the lower furnace, it is decided by the following two reactions to consider the heat balance.

[0079] FeO=Fe+0.5×O 2 ; reaction heat (endotherm) is included in Qm3 C+0.5×O 2 =CO; reaction heat (exothermic heat) is included in Qk

[0080] Next, heat exchange between the gas and the raw materials in the lower furnace will be explained with reference to Fig.15. The vertical axis shows the temperature, the width shows the heat capacity rate (kJ / K·tp), and the area in the figure (=temperature × heat capacity ratio) shows the heat capacity rate (kJ / tp). Note that metals other than iron (metalloids) are also reduced in the lower furnace, but the heat of reaction per ton of pig iron is small compared to other heat, so it will be ignored in the heat balance explanation (Fig.14 to 17). In addition, gas specific heat (kJ / Nm 3< K) is assumed to be constant at Cg because the influence of gas component fluctuations is not so large.

[0081] Qgr and Qk are supplied to the lower furnace, and the amount of heat (Qg2+Qg3+Qk2) other than the amount of heat Qcg (=Qg1+Qk) discharged to the shaft together with the gas at temperature Teg becomes net effective heat in the lower furnace. The effective heat is used as heat Qm2 to heat the ore from the cohesive zone entrance temperature Tcs to the tapping pig-slag temperature Ti, and as heat consumption Qm3 (heat of FeO decomposition, heat of dissolution, carburization heat, heat loss) in the lower furnace. Qm2, together with the raw material heat Qm1 brought to the cohesive zone, becomes the heat Qmt of molten pig slag.

[0082] Reducing the coke rate or fuel rate means reducing the RW gas heat rate, which in Fig.15 means 1) reducing the heat consumption in the lower furnace Qm3, 2) increasing the heat of raw materials brought into the lower furnace Qm1 (temperature Tcs), and 3) reducing the heat of the gas flowing out from the lower furnace Qcg (=Qg1+Qk1). Qcg (=Cg·Vg·Tcg) is the ineffective heat (i.e. Heat that cannot be used) in the lower furnace, and it is effective to reduce the cohesive zone passing gas rate Vg (= RW gas rate Vgr + gas rate derived from direct reduction). Effective methods to reduce Vgr (=Qgr / Tg) are to reduce the RW gas heat Qgr and / or to increase the RW gas temperature Tg.

[0083] Fig.16 shows the heat balance in the lower furnace of a conventional blast furnace and that of the present invention.

[0084] In the present invention, where the gas reduction ratio is close to 100%, there is no need for the heat of FeO decomposition (FeO=Fe+0.5×O 2 ) in the lower furnace or the heat of primary coke combustion with solid oxygen Qk' (with 'is for the present invention). Therefore, regarding the heat consumption in the lower furnace (reaction heat, heat loss, etc.), Qm3 =Qg3+Qk2 >> Qm'3 =Qg'3+Qk'3. The ore softening temperature of the present invention is about 100°C higher than that of a conventional blast furnace, Tcs < Tcs', so the heat required in the lower furnace Qmr =Qm2+Qm3, is significantly lower in the present invention.

[0085] Furthermore, since the cohesive zone passing gas rates are Vg >> Vg', the outflowing heats by the gas from the lower furnace are Qcg = Qg1+Qk1 » Qcg'=Qg'1+Qk'1. In the end, the total heat of the primary combustion heat Qk by solid oxygen and the RW gas heat Qgr (sensible heat brought in and primary combustion heat) is significantly lower in the present invention. That is, in the present invention, the fuel rate in the lower furnace can be significantly reduced.

[0086] Here, we will consider the change in the heat balance in the lower furnace (the heat transfer amount Q in the lower furnace) when tuyere injection fuel is mixed with tuyere blown-in gas (CO, H 2 , etc.) of gas amount V and temperature T. Assuming that the temperature Tcg of the gas flowing out from the lower furnace remains unchanged before and after mixed with the blown-in gas, the heat transfer amount Q in the lower furnace increases by ΔQ =(T-Tcg)×V due to gas mixing. If T < Tcg, ΔQ becomes negative (fuel increase factor), which is not desirable.

[0087] Even if T ≥ Tcg, the RW gas temperature (Tg) will decrease, so care must be taken. Fig.17 shows the Reichardt diagram of the lower furnace of the present invention with a solid line. If the RW gas temperature Tg' decreases while the effective heat transfer amount (Qg'2 + Qg'3) to the lower furnace remains constant, the gas operation line moves from the solid line to the two-dot chain line, and the ineffective heat Qg'1 increases. Therefore, for the same effective heat transfer amount, a higher RW temperature Tg' (i.e., a smaller RW gas amount Vg') is more advantageous in terms of reducing the coke rate and fuel rate. If Tg' further decreases and the gas operation line becomes less steep than the two-dot chain line and falls below point A in the figure, the raw materials can no longer be heated to the tapping pig-slag temperature Ti', which will cause problems in operation. The operational lower limit of the RW temperature Tg' when the slag temperature Ti'= 1500°C is approximately 2000°C, depending on the heat loss in the lower furnace.

[0088] The amount of heat required in the lower furnace Qh(=Qm2+Qm3) is the heat required for raw material heating, melting, reaction, carburization, and heat loss, as mentioned above. In the present invention, the iron ore is reduced nearly 100% in the shaft, so the reduction reaction in the lower furnace is limited to metals other than iron (P, Si, Mn, etc.). Therefore, the amount of heat required in the lower furnace Qh varies depending on the slag ratio, pig iron temperature, pig slag composition, and furnace body heat loss, but is 700 to 1200 MJ / tp (650 to 950 MJ / tp excluding heat loss), which is about 1 / 3 of the 2500 to 3500 MJ / tp of conventional blast furnaces.

[0089] As mentioned above, from the perspective of heat balance in the lower furnace, the major advantage of the present invention is that the process has been improved to significantly reduce the required heat in the lower furnace and the amount of gas passing through the cohesive zone compared to conventional blast furnaces. This feature has made it possible to significantly reduce the coke rate and fuel rate.

[0090] Next, in Fig.19 (calculation results as coke rate ≈ 60 kg), the temperature distribution of the gas and raw material in the cohesive zone is summarized from the perspective of heat flow ratio. When V, the amount of gas passing through the cohesive zone, is V=750Nm 3< / tp, the heat flow ratio is 1, and the temperatures of the gas and the raw material shift in parallel lines separated by about 25°C. When V=500Nm 3< / tp, the heat flow ratio is >1, the temperatures shift convexly downward, and the gas and ore temperatures match on the low temperature side (just above the cohesive zone). On the other hand, when V=1000Nm 3< / tp, the heat flow ratio is <1, resulting in upwardly convex temperature shifts, and the temperatures of the gas and ore differ by approximately 50°C on the low temperature side (just above the cohesive zone).

[0091] The temperature difference between the gas and ore on the low temperature side means the temperature difference between Tcg and Tcs explained in Figs. 15 and 16, and becomes invalid heat of the heat input to the lower furnace. Therefore, in Fig.19, in order to reduce the heat input into the lower furnace, V=500Nm 3< / tp is better, and it is preferable to be V≤750Nm 3< / tp. Furthermore, as the coke rate increases, the heat capacity rate (heat flow) of the raw material (kJ / tp·K) increases accordingly. So, the amount of gas V with which the heat flow ratio is balanced also increases, and it will be V=900Nm 3< / tp at a coke rate of 200kg / tp.

[0092] In addition, when the ore becomes hot, it softens and its porosity decreases to increase permeability resistance. If the softening point of 100% gas-reduced ore is 1350°C and its melting point is 1450°C, the longer the residence time between them and the higher the average temperature per residence time, the worse its permeability becomes. Therefore, from the viewpoint of permeability of the cohesive layer, it is preferable for the heat flow ratio to be ≥ 1, which can shorten the residence time at high temperatures.

[0093] In relation to the above characteristics, Fig.18 shows the relationship between the amount of heat input to the lower furnace other than the sensible heat of the ore, (Qk+Qgr) for the conventional blast furnace and the present invention. Regarding the present invention, the region with a 100% gas reduction ratio is shown as a dotted line and the region with 95% gas reduction ratio is shown as a solid line, where the effect of present invention to reduce the heat supply to the lower furnace (Qk+Qgr) is fully enjoyable. The amount of heat input into the lower furnace (Qk+Qgr) and the amount of gas from the lower furnace usually have a strong correlation with the fuel rate in the lower furnace, but they are significantly reduced in the present invention. Examples 1 to 8 of the present invention, which will be described later, have a wide variety of fuels and reducing gas compositions, but all of them are in the region within the dotted line.

[0094] The heat transfer diagrams of a conventional blast furnace (example) and the present invention (Example 1) are shown in Fig.22 and 23, respectively. The vertical axis represents the amount of heat (GJ / tp), which shows the enthalpy change of the raw material and gas in the furnace (i.e., the amount of heat transferred between the two). The horizontal axis represents their respective temperatures. From these comparisons, it can be seen that the amount of heat transferred in the lower furnace is far less in the present invention than in the conventional blast furnace.

[0095] As mentioned above, in the present invention, it appropriately suppresses the combustion temperature even in pure oxygen operation by suppressing the secondary combustion of C in the fuel, while it is required to ensure the raceway (RW) temperature at 2000°C or higher. In other words, it is necessary to select the fuel used in the lower furnace that has a primary combustion temperature of 2000°C or higher when using oxygen. For example, as mentioned above, methane is not suitable as a tuyere injection fuel because its primary combustion temperature is only about 400°C. Coal that has a lot of hidden moisture or attached water is not suitable as a fuel for the lower furnace as well because the decomposition heat of the moisture lowers the primary combustion temperature.

[0096] If the fuel used in the lower furnace is a hydrocarbon fuel (CiHjOk; composition display excluding ash), it must satisfy formulas (8) and (9). Note that it is preferable that both j / i in equation (8) and (16×k) / (12×i+j+16×k) in equation (9) are both lower.

[0097] In other words, in order to reduce the coke rate and fuel rate, it is effective to use fuels with a high carbon content as the hydrocarbon fuels for the lower furnace, which is paradoxical to the recent term hydrogen reduction blast furnace (blast furnace using hydrogen as reductant to decrease CO 2 ). This is simply because they can provide a significantly higher primary combustion heat. Using fuel with higher primary combustion heat, we purposely reduce secondary combustion and keep primary combustion as the main combustion, thereby efficiently increasing the amount of effective heat transfer in the lower furnace while avoiding abnormally high flame temperature in front of the tuyere caused by pure oxygen. This is a feature of the combustion in the lower furnace of the present invention.

[0098] As fuels in the lower furnace, other than hydrocarbon fuels, it is also very beneficial to use "metal elements (Si, Ca, Al, Mg, Fe, Si, Mn) that make up pig iron and slag, or their alloys." Since no by-product gases are produced with the combustion, RW gas at any desired temperature can be produced by co-injecting an appropriate amount of tuyere blown-in gas. Needless to say, the reason to select these fuels is that the by-products of these fuels are pig slag components, and do not affect pig slag quality.

[0099] Depending on the components of the fuel injected through the tuyere, necessary and sufficient amount of oxygen to burn hydrocarbon fuel to CO (primary combustion) and / or to burn metallic fuel is injected simultaneously with the fuels. In other words, the system is characterized by injecting the following amount of oxygen per ton of pig iron depending on the components of the fuel injected through the tuyere. O 2 f = 0.5 × C 1 + S 1 + S 2 − O 1 + S 3 + 1.5 × S 4 [O 2 ]f: Amount of oxygen injected through the tuyere (O 2 -kmol / tp) C1: Amount of C component in tuyere injection fuel (C-kmol / tp) O1: Amount of O component in tuyere injection fuel (O-kmol / tp) S1: Metallic Mg component in tuyere injection fuel (Mg-kmol / tp) S2: Metallic Ca component in tuyere injection fuel (Ca-kmol / tp) S3: Metallic Si component in tuyere injection fuel (Si-kmol / tp) S4: Metallic Al component in tuyere injection fuel (Al-kmol / tp)

[0100] Iron ore contains about 300 Nm 3< of oxygen (O 2 ) per ton of Fe in the case of hematite (Fe 2 O 3 ), and in a conventional blast furnace (direct reduction ratio is about 30%), about 85 Nm 3< / tp of solid oxygen is consumed by direct reduction. In the present invention, the gas reduction ratio can be stably brought close to 100% as described above, so no coke is consumed by direct reduction. Therefore, the oxygen required to burn coke in the lower furnace can be calculated by simply removing the carbon required for carburizing pig iron and reducing metal components other than iron in pig iron (Si, Mn, P, etc.) from the coke rate as shown in the following formula. O 2 c = 0.5 × C 2 − C 3 − C 4 [O 2 ]c: Molar amount of oxygen injected according to the coke (O 2 -kmol / tp) C2: Molar amount of carbon in coke (C-kmol / tp) C3: Molar amount of carbon in pig iron (C-kmol / tp) C4: Molar amount of carbon to reduce metals other than iron in pig iron (C-kmol / tp)

[0101] Therefore, the amount of oxygen Vo 2 (O 2 -kmol / tp) blown into the lower furnace from the tuyere in the present invention is expressed by the following equation as the sum of both equations ([O 2 ]f+[O 2 ]c). V O 2 = 0.5 × C 1 + C 2 − C 3 − C 4 + S 1 + S 2 − O 1 + S 3 + 1.5 × S 3

[0102] A feature of the present invention is that the calculation does not need to take the consumption of carbonaceous material and oxygen due to the direct reduction of iron (the oxidation reaction of carbonaceous material by the solid oxygen in the ore) into account, which is essential in conventional blast furnaces. Furthermore, since the coke rate is extremely low compared to conventional blast furnaces, [O 2 ]f >> [O 2 ]c. In the examples described below, [O 2 ]c = 0 in Examples 1 and 4 to 8, except for Examples 2 and 3, in which no tuyere injection fuel is injected.

[0103] It is not easy to control the quality of the tuyere blown-in gas as a reducing gas to 100%, and as a result, some H 2 O and CO 2 may remain in the tuyere blown-in gas. If H 2 O or CO 2 (assuming a total of O2 kmol / tp) is injected from the tuyere, the same molar amount (O2 kmol / tp) of coke will be consumed, and the carbon content in the pig iron will also decrease. So, the following measures are to be taken.

[0104] 1) Similar to O1 in equation (14), reduce the tuyere blown-in oxygen by O2 / 2 (kmol / tp). 2) Increase tuyere injection fuel by O2 (kmol / tp) as carbon content in the fuel.

[0105] In either case, CO 2 and H 2 O are reformed into CO and H 2 in a high temperature atmosphere (≥2000°C) due to carbon in the tuyere injection fuel, so coke consumption can be suppressed. Also, in either case, the equation (14) can be changed to the following equation. Vo 2 = O 2 f + O 2 c O 2 f = 0.5 × C 1 + S 1 + S 2 − O 1 − O 2 + S 3 + 1.5 × S 4 O 2 c = 0.5 × C 2 − C 3 − C 4

[0106] As mentioned above, it is necessary to suppress the abnormal temperature rise at the tip of the tuyere in an oxygen blast furnace while maintaining the raceway (RW) temperature at an appropriately high temperature. The RW temperature here means an equilibrium gas temperature that includes not only the combustion of the tuyere injection fuel but also cooling by the tuyere blown-in gas and combustion / gasification reaction with surrounding coke.

[0107] The gas discharged from RW has the role to transfer high-temperature heat (high-grade heat) to the material to generate and retain the heat of pig iron and slag, and the heat transfer rate is proportional to the temperature difference between the gas and the material (pig iron, slag, coke). Therefore, the gas temperature from the RW needs to be at least higher than the material temperature there. And in the present invention, as explained in Fig.17, it is controlled at about 2000°C or higher (assuming the tapping pig-slag temperature is 1500°C), so the tuyere blown-in gas preheated to 1300°C still functions as a cooling gas relative to the RW temperature. Therefore, similar to the explanation of Fig.17, there is a restriction on the amount of gas blown into the lower furnace.

[0108] A method to solve the seemingly contradictory phenomena of the need to increase the amount of tuyere blown-in gas to promote gas reduction and decrease the reducing agent rate and the need to restrict the amount of RW gas is to install multi-stage tuyeres in the height direction.

[0109] For example, Fig.2 shows an example in which the tuyeres are installed in two or more stages in the height direction. Fuel and oxygen are injected from the first-stage tuyere (bottom tuyere) 2a. Preheated reducing gas is blown into the first-stage tuyere 2a, installed below the cohesive zone 9, by amount to keep the RW at an appropriate temperature, and the remaining amount of reducing gas, is blown into the second and higher tuyeres 2b to 2e installed above the cohesive zone 9. It is a revolutionary method to enable not only to maintain the RW temperature at an appropriate temperature (2000 to 2600°C), but also to change the reducing gas distribution ratio between the "first-stage tuyere" and "second and higher stage tuyeres" while keeping the temperature of the reducing gas constant, which allows you to adjust the RW temperature and RW gas rate, which are important factors in adjusting the furnace condition, without changing the heat and mass balance of the entire system (including the reducing agent rate). Note that the temperature of the preheated reducing gas is preferably the ore temperature directly above the cohesive zone (1200 to 1350°C or higher) as explained in Fig.14 to 16.

[0110] Furthermore, the multi-stage tuyere system of the present invention has the effect of ensuring a cohesive zone in an inverted V-shaped like the center coke charging method, and is characterized in that it is possible to ensure good permeability inside the furnace.

[0111] The principle is in the configuration that, as shown in Fig.2, high temperature gas (2000-2600°C) is generated from the raceway(RW) 3 formed by the first-stage tuyere 2a, medium temperature gas (1200-1350°C) is blown in from the second-stage tuyere 2b, and medium-low temperature gas (800-1100°C) is blown in from the third-stage tuyere 2c, so that the gas 3a originating from the RW formed by the first-stage tuyere rises up the furnace center, the gas 3c originating from the third-stage tuyere flows at the furnace wall side, and the gas 3b originating from the second-stage tuyere flows in between in the shaft. In other words, the gas temperature difference between the first-stage tuyere, second-stage tuyere, and third-stage tuyere is transferred to a temperature difference in the furnace radial direction.

[0112] A higher gas temperature with the same gas components leads to a higher reduction reaction rate and a higher temperature rise rate, so the ore near the center of the furnace, which is relatively hot, reaches its melting point at the earlier timing than the ore near the wall, which is cooler. Any ore descent speed in radial direction is roughly the same, so an earlier timing means a higher position in the furnace (closer to the charging port). Conversely, the ore near the wall reaches its melting point at the later timing, that is, at a lower position in the furnace (farther from the charging port). Accordingly, the cohesive zone forms an inverted V-shape with excellent permeability. Therefore, the shape of the inverted V-shape and the temperature distribution inside the furnace are determined by the temperature and blown-in rate of each tuyere, as well as the blown-in rate ratios and / or temperature ratios of the first tuyere / second tuyere / third tuyere, and / or the distances between the tuyeres (see Fig.3).

[0113] Since a cohesive zone is formed between the first-stage tuyere (lowest stage tuyere) and the second-stage tuyere, the cohesive zone position can be fixed at the lower part of the furnace by placing the second-stage tuyere and the first-stage tuyere close to each other, which enables to reduce the furnace height. On the other hand, if the furnace height is the same, the preheat zone and / or reduction zone becomes longer, so the productivity can be increased. In this respect, the location of the second-stage tuyere 2b is preferably in the "2b installation recommended range" shown in Fig.2, that is, from the middle position of bosh 14 to the upper end of the belly 13. On the other hand, the third-stage tuyere is preferably installed in the "2c installation recommended range" shown in Fig.2 , which is located above the "2b installation recommended range" at the bottom (below the middle) of the shaft, in order to extend the gas reduction time (residence time) at temperatures below 1000°C (preferably below 900°C), as mentioned above.

[0114] The above explanation is for a three-stage tuyere, but it is clear from the gist of the explanation that the same effect can be obtained with a two-stage tuyere (even if there is a slight difference in effectiveness). Next, we will explain from the perspective of heat balance the cases in which it is rational to intentionally adopt a three-stage tuyere, which becomes complex in terms of equipment.

[0115] First, the reason why the blowing temperature of the second-stage tuyere is set at 1200 to 1350°C (higher is preferable) is to reduce the heat consumption in the lower furnace by raising the ore temperature similar to the cohesive zone temperature. Next, it is preferable for the top gas temperature to be as low as possible unless condensing the gas, in terms of energy consumption, and many blast furnaces operate at 120 to 180 °C.

[0116] Now, in an operation with a gas reduction ratio of 100%, when the tuyere injection fuel and coke rates are determined, the cohesive zone passing gas rate Vg (Nm 3< / tp) is incidentally determined. From the Rist model operating line, the amount of reducing gas (V23) to be blown in from the second and higher tuyeres is uniquely determined with the assumed shaft efficiency.

[0117] Even if the best temperature for the second-stage tuyere blown-in gas seems 1300-1350°C from the viewpoint of heat balance in the lower furnace, there are cases where it is desirable to blow in gas at a temperature (T23) below 1200°C in order to control the top gas temperature, point W temperature (Tr), and / or gas reduction-end temperature (Examples 1 and 8 described below). In such cases, a three-stage tuyere is effective, in which a gas amount V2 is blown in from the second-stage tuyere in the bosh section at 1300°C(T2), while a gas amount V3 is blown in from the third-stage tuyere installed at the bottom of the shaft at a gas temperature (T3) of 1100°C or less. If the specific heat is constant, the relationship between these gas amounts and temperatures is expressed by the following equations. V 23 = V 2 + V 3 T 23 × V 23 = T 2 × V 2 + T 3 × V 3

[0118] However, it is preferable to control the gas volume V2 from the second-stage tuyere so that the total gas volume with the cohesive zone passing gas rate Vg, (Vg+V2), is about 750 to 1000 Nm 3< / tp depending on the coke rate. This is related to the heat flow ratio as explained above in Fig.19, and if the heat flow ratio is > 1 (the heat flow of gas to the raw materials is low), the raw materials cannot be heated to the second-stage tuyere gas temperature and the heat required in the lower furnace increases. And even if the heat flow ratio is ≤ 1, it is better to lower a second-stage tuyere flow rate in order to lower the point W temperature (Tr) and the gas reduction-end temperature.

[0119] Unlike the gas reduction by CO, the gas reduction by H 2 is an endothermic reaction, so when the hydrogen content in the fuel or gas injected through the tuyere is high (endothermic reduction) or when the coke rate is high (increase in heat flow ratio), the top gas temperature drops. In the case of such a fuel combination (Examples 2, 4 to 7), the injection amount of the first-stage and second-stage tuyeres is increased to raise the top gas temperature (as a result, the shaft efficiency decreases because the reducing gas increases), or the ore is heated using the pre-reduction tuyere 2d or the raw material preheating tuyere 2e shown in Fig.2.

[0120] The pre-reduction tuyere 2d is the tuyere that is installed between point M (the start point of magnetite reduction) and point W (the start point of Wustite reduction) on the Rist model, and is installed within the range of ± 1 / 6 of the shaft height from the middle of the shaft, which is the "recommended installation range for 2d" shown in Fig.2. Since hydrogen reduction is an endothermic reaction and its heat is provided by the gas itself, the temperature difference between the top temperature and point W temperature (Tr) becomes large with hydrogen-rich fuel. In order to suppress the rise in Tr, the pre-reduction tuyere is effective as tuyeres that supply reaction heat and heating heat.

[0121] The pre-reduction tuyere only need to be able to perform pre-reduction up to point W, so the degree of reduction of the gas needs to be equal to or above the magnetite reduction equilibrium. In hydrogen-rich operation, the moisture content of the top gas increases, so if the top gas is washed and cooled in the same way as in conventional blast furnaces, it can be easily roughly dehydrated and the degree of gas reduction can be increased. Therefore, the gas after washing and cooling is recycled and injected from the same tuyeres after partially combusted with oxygen. To prevent coke gasification, the gas temperature at the pre-reduction tuyere should be 1000°C or lower (preferably 900°C or lower).

[0122] The advantage of the multi-stage tuyeres is that not only the top temperature but also the point W temperature (Tr) and / or gas reduction-end temperature can be intentionally adjusted, which is a noteworthy point in the process. In Example 1, which will be described later, by using the third tuyere, the reduction-end temperature could be suppressed to 918°C at which the coke gasification reaction is difficult to occur (see Fig. 23). Furthermore, in Example 1-2, by also using the pre-reduction tuyere, the blowing amount of the first / second stage tuyeres 2a, 2b was reduced to a heat flow ratio of 1 (the same amount was increased by the third-stage tuyere), which could lower the point W temperature (Tr) and the reduction-end temperature by 100°C or more while keeping the top temperature the same as in Example 1 (dotted chain line in Fig.23).

[0123] As described above, it is possible to lower the point W temperature (Tr) and the gas reduction-end temperature as shown in the Example 1, by controlling the gas flows so as to reduce the amount of gas blown-in from the first-stage tuyere 2a and the second-stage tuyere 2b and increase the amount of gas blown-in from the third-stage tuyere 2c, and by controlling the gas temperature and the fuel supply amount. Furthermore, as shown in Example 1-2, by lowering the gas temperature at the third-stage tuyere 2c and by blowing in gas from the pre-reduction tuyere 2d and controlling the amount of the gas, it is possible to further reduce the point W temperature (Tr) and gas reduction-end temperature.

[0124] The operation system of this embodiment is equipped with a tuyere blown-in gas flow rate controlling system composed of a plurality of tuyeres 2 configured to blow reducing gas into the inside of blast a furnace body 1, which are made up of tuyere groups 2a, 2b, 2c, and / or 2d each of which are arranged at intervals in the circumferential direction of the furnace body 1, and three or more tuyere groups 2a, 2b, 2c, and / or 2d arranged apart in the height direction of the furnace body 1 (the up and down direction in Fig.2), flow rate measuring devices for each tuyere group and flow rate adjusting devices for each tuyere group, and the control system configured to control an external fuel supply system that supplies the required amount of fuel and oxygen O 2 by measuring the top gas flow rate with flow meter FI7, measuring the top gas oxidation degree with component measuring system (except H 2 O) CA8, flow meter FI8, thermometer TI8 and pressure gage PI8, measuring top gas temperature with thermometer TI7, measuring the temperature of the middle of the shaft with thermometer TI5 , and measuring, as shown in Fig.4, the gas components CA9 and gas flow rate FI9 at the heater inlet and the gas components CA11 and gas flow rate FI11 at the heater outlet, a heating system including a heater 24, and aforesaid tuyere blown-in gas flow rate controlling system. With this operation system, the gas reduction ratio can be increased to nearly 100%, and also, by controlling the gas rate, temperature, and / or fuel rate blown from the third-stage tuyere 2c and / or the pre-reduction tuyere 2d can be controlled to control the temperatures of the point W temperature (Tr) and the gas reduction-end temperature in the range of 600°C to 1000°C while appropriately keeping the top temperature.

[0125] Note that the flow rate measuring devices for each tuyere group that composes the tuyere blown-in gas flow rate controlling system are respectively the flow meter FI12 to measure the flowrate to the tuyere group 2b shown in Fig.4, flow meter FI13 and flow meter FI14 to measure the flowrate to the tuyere group 2c, flow meter FI11 (minus FI12 and FI13) to measure the flowrate to the tuyere group 2a, flow meter FI5, flow meter FI6 and mass flowmeter WI6 to measure the flowrate to tuyere group 2d.

[0126] Also, the flow rate adjusting devices for each tuyere group in the tuyere blown-in gas flow rate controlling system are flow rate adjusting valves provided in the downstream of each flow meter, as shown in Fig.4.

[0127] The reason why the lower limit of the temperature range is 600°C or more is that the reduction reaction does not proceed effectively unless the ore temperature is 600°C or more, and the reason why the upper limit of the temperature range is 1000°C or less is that the coke gasification reaction becomes active at temperatures above that, and the temperature should be controlled within this temperature range.

[0128] The raw material preheating tuyere 2e is a tuyere installed in the upper 1 / 3 of the shaft, higher up the shaft than the pre-reduction tuyere 2d, and is not expected to perform pre-reduction but is for the purpose of raw material preheating and top gas temperature control. Since gas reduction is not expected, it has the advantage that the gas reduction degree of the gas used can be low. In addition, the pre-reduction tuyere functionally includes the raw material preheating tuyere, and the use of the pre-reduction tuyere is particularly advantageous in hydrogen-rich operation as mentioned above.

[0129] In conventional blast furnaces, direct reduction in and below the cohesive zone (the lower furnace) is of course unavoidable, but the presence of FeO in the lower furnace means that gas reduction also occurs in the same region to inevitably lead to a coke gasification reaction, which are exactly the same as direct reduction in terms of heat and mass balance. Since the coke gasification reaction occurs inside the coke, it is known that it significantly deteriorates the coke strength, which is important in the lower furnace, and has a greater effect on coke deterioration than direct reduction. Despite this, none of the many oxygen blast furnaces that have been proposed so far have a direct reduction ratio of 0%, nor has there been any suggestion of a method to suppress coke gasification during or after gas reduction.

[0130] As explained above, the major feature of the present invention is that the gas reduction ratio can approach 100% by controlling the fuel and reducing gas injections and the furnace top gas so that the gas reduction is completed at a temperature (approximately 900 to 1000°C or less) at which the coke gasification reaction can be substantially kinetically suppressed .

[0131] Next, the permeability in the furnace (cohesive zone, bosh to bottom of the hearth, lumpy zone) in the present invention will be explained.

[0132] The gas permeability (gas pressure loss) of the cohesive zone is determined by the amount of gas passing through the cohesive zone and the permeability resistance of the cohesive zone in addition to the shape of the cohesive zone described above. In other words, reducing the amount of gas passing through the cohesive zone can lower the gas pressure loss, and by reducing the permeability resistance of the cohesive zone, the gas pressure loss can be lowered even with the same amount of gas.

[0133] It has already been explained in Figs.14 to 16 that the amount of gas passing through the cohesive zone can be significantly reduced by the present invention compared to the conventional methods. On the other hand, regarding the permeability resistance of the cohesive zone, Non-patent Literature 3 states, "(1) The temperature at which the pressure drop starts to increase due to the softening and shrinkage phenomenon of the ore layer depends largely on the ore reduction ratio (it will be >1300°C when the ore reduction ratio approaches 100%), (2) The pressure drop gradient (gas pressure drop per unit thickness) of the cohesive layer is largely different between in the conventional blast furnace with the ore reduction ratio of around 70% and in the oxygen blast furnace with the gas reduction ratio of near 100% (the pressure drop gradient increases by 100 times that of the ore layer in the former, but it increases by only 10 times that of the ore layer in the latter).

[0134] Because of (1), in an oxygen blast furnace equipped with multiple stage tuyeres, if a raceway of 2000 - 2600 °C is formed in front of the first-stage tuyere and the amount of gas required for 100% gas reduction is blown from the second-stage tuyere at 1200 - 1350 °C, a cohesive zone containing the ore softening point (about 1350°C) is stably formed between the first-stage and second-stage tuyeres.

[0135] Because of its thermal formation conditions, the gas from the second-stage tuyere does not pass through the cohesive zone, and only the gas derived from the first-stage tuyere (raceway) flows. Furthermore, since the oxygen blast furnace is nitrogen-free, the amount of gas in the furnace is reduced and, for example, in the case of Example 1 shown in Table 4 and Fig.6 below, the amount of gas passing through the cohesive zone is around 500 Nm 3< / tp, which is about 30% of the conventional blast furnace (example) in the same table. On the other hand, the coke rate in Example 1 (the theoretical limit coke rate required for carburizing pig iron and reducing metals other than iron) is about 20% of that of a conventional blast furnace, and the proportion of coke slits in the cohesive zone is reduced in proportion to it.

[0136] The pressure drop gradient in the packed bed of the blast furnace can be expressed by the following equation (Non-patent Literatures 6 to 8), and can be applied to ore layers, coke layers, coke slits, and cohesive layers. Δ P / L ∝ ρ − 1 ⋅ K ⋅ G 1.7 ΔP: Pressure loss (Pa / m) L: Layer height or gas passage length (m) ρ: Gas density (kg / m 3< ) G: Superficial mass flow rate (kg / m 2< ·s) K: Permeability resistance index (see the following Table; from Non-patent Literatures 3, 12, 14) [Table 1] Coke layer Ore layer Cohesive layer Coke slit Conv.BF (example) 100 150 15000 100 Example 1 100 150 (170*) 1500 100 * : when mix-charged with about 3% of coke

[0137] According to equation (18), the pressure loss is calculated from the amount of gas passing through the cohesive zone of a conventional blast furnace (example)(the sum of gas 4a passing through the coke slit and gas 4b passing through the cohesive layer in Fig.1), and Table 2 shows the gas flow rate (Nm 3< / tp) passing through the cohesive zone of the present invention (Example 1) which has the same pressure loss. In addition, regarding the thickness L of the cohesive zone, the thickness of the conventional blast furnace is supposed twice that of the present invention in the same thermal calculation as explained in Fig.19. Furthermore, in a conventional blast furnace (example), 30Nm 3< / tp is subtracted from the top gas amount as the gas derived from the coke gasification reaction above the cohesive zone. [Table 2]Cohesive layer Coke slit Total amout Amount from heat-mass balance Conv.BF (example) 140 1450 1590 1590 Example 1 810 560 1370 500

[0138] When the cohesive zone pressure loss is the same as in the conventional blast furnace (example), the coke slit flow rate in Example 1 decreases according to the coke rate, but the cohesive layer flow rate increases significantly, reaching a total of about 2.7 times that of the gas required from the heat mass balance, 500Nm 3< / tp. This means that at the required flow rate, the pressure loss will be reduced to 20% of that of a conventional blast furnace (example) (from equation (18)). Furthermore, since the cohesive layer of the present invention is formed from ore with a reduction ratio close to 100%, it can suppress the phenomena found in conventional blast furnaces that the melt from the cohesive layer (a low melting point compound made of unreduced FeO) droops into the coke slit to block its gas permeability. Therefore, the gas low rates are calculated in proportion to the coke slit thickness ratio.

[0139] As mentioned above, in the present invention, the coke rate is reduced to the maximum, so the ratio of top-charge ore (O) including auxiliary materials and top-charge coke (C) is O / C=28 in Example 1, which is much different from that in a conventional blast furnace (example), O / C = 5. Therefore, the proportion of coke in the whole charging material, C / (O+C), is 3.5 wt% in Example 1, which is within the range of conventional knowledge of mixed charging of ore and coke, and the entire amount of (O+C) can be mixed and charged.

[0140] Ore-coke mixed charging is a widely known method in which small coke (C) is mixed with ore (O) in advance at a ratio of several to 10% for the purpose of improving the permeability of the cohesive zone, etc. Non-patent Literature 14 also shows the physical properties, high-temperature properties, charging method, etc., of the case where lump coke other than small coke is mixed.

[0141] The greatest advantage of the coke slit is that it ensures the permeability of the cohesive zone, allowing the bosh gas (gas flowing into the cohesive zone) to bypass the poorly permeable cohesive layer and pass through the coke slit. On the other hand, since most gas bypasses the cohesive layer, the heat exchange efficiency between the two is poor, resulting in the disadvantages explained in Fig.16 (increase in inefficient heat in the lower furnace). Because of the poor heat exchange, the thickness of the cohesive layer becomes longer and pressure loss increases.

[0142] In the present invention, the coke rate is low and the permeability of the cohesive layer is high, so as shown in Table 2, gas flows thorough the cohesive layer more than the coke slit, brilliantly resolving the disadvantages of conventional blast furnaces. A further development is the entire amount mixing method of the present invention in which the whole amount of bosh gas is passed through the cohesive layer.

[0143] Table 3 shows the pressure distribution (kPa) in the conventional blast furnace (example), and the pressure distributions in the Example 1 for when the raw materials are charged in layers and for when the raw materials are charged entirely mixed (without coke slit). The charged raw material volume per ton of pig iron (m 3< / tp) varies depending on the coke rate. For example, in Example 1, since it is 70% of that of the conventional blast furnace (example), the calculation is done as its lumpy zone height becomes 70% so that the residence times in the lumpy zone are constant. In addition, since it is difficult to accurately calculate the pressure loss in the dripping zone, it is compared with the conventional blast furnace assuming that the pressure loss of the zone in the conventional blast furnace is 60 kPa, the Ergun formula is expandable using the liquid residence rate in the packed bed (Non-patent Literature 7), and the calculation is simplified to only the first power term of the mass velocity. However, the calculation of the pressure loss simplified to only the first power term of the mass velocity shown in Table 3 is the way of calculation to give results more unfavorable to Example 1 than the calculation without simplification. [Table 3]Lumpy zone (height) Cohesive zone Dripping zone to raceway Total Conv.BF (example) 100 (16m) 40 60 200 Example 1 (layers) 46 (11m) 7 22 76 Example 1 (mixed) 53 (11m) 8 22 83

[0144] Although the coke rate in Example 1 is about 1 / 5 of that in a conventional blast furnace (example), the permeabilities are greatly improved in either charging method compared to the conventional blast furnace (example), demonstrating the superiority of the present invention. Decrease in pressure loss and / or increase in residence time mean a room for production increase, if the perspective is turned around. And if the present invention is applied to an existing blast furnace while keeping the pressure and furnace height unchanged, production can be increased by more than 40%. If the production can be increased by 40%, the heat loss (MJ / tp) in the lower furnace can be reduced by 30%, which reduces the same amount of required heat in the lower furnace and makes it possible to further reduce the fuel rate (10kg / tp reducible in Example 1). It also has great benefits from the perspective of reducing CO 2 .

[0145] By the way, regarding gas permeability in the lower furnace, not only pressure loss but also prevention of flooding (liquid blowing up phenomenon) is another important operational guideline. Conventional blast furnaces are operated at points slightly lower than the flooding limit curve (right-hand downward curve, Non-patent Literatures 7 and 8) which is arranged in logarithmic form on the flooding factor (vertical axis) vs. fluid ratio (horizontal axis). If the superficial gas velocity u 0 (∝ cohesive zone passing gas rate) decreases while the superficial liquid velocity v 0 (∝ productivity ratio) remains constant, the fluid ratio (oc v 0 / u 0 ) increases and the flooding factor (∝ u 0 2< ) decreases to the power of 2 , which shifts the operation right-downward twice as sharp as the slope of the flooding limit line of right-hand downward curve, enabling a stable operation.

[0146] In the present invention, the gas flow rate in the lower furnace is reduced to about 1 / 2 to 1 / 3 of that of conventional blast furnaces, so the operation is free from flooding. In conventional blast furnaces, flooding has been a factor that determines the production rate, but in this respect as well, the present invention can increase the production rate more than in conventional blast furnaces.

[0147] Fig.4 shows the means to keep the gas reduction ratio close to 100% and appropriately control fuels and oxygen. The measurement items are as follows. (The numbers in parentheses correspond to the instrument numbers in Fig.4)

[0148] (1) [O] content in iron ore, [CO 2 ] content in auxiliary materials (CA_1) and feeding rate (WI_1) (2) coke components [C][H][O] (CA_2) and charging speed (WI_2) (3) Temperature of pig iron (TI_3) and [C] content (CA_3) (4) Tuyere injection fuel components [C][H][O] (CA_4), fuel rate (WI_4), and oxygen flow rate (FI_4) (5) Temperature in the furnace below the pre-reduction tuyeres (TI_5) and the top gas recirculation flow rate to the same tuyeres (FI_5) (6) Pre-reduction tuyere fuel components[C][H][O](CA_6), fuel rate (WI_6), and oxygen flow rate (FI_6) (7) Top gas flow rate (FI_7), temperature (TI_7), and gas pressure (PI_7) (8) Top gas flow rate (FI_8), temperature (TI_8), gas pressure (PI_8), and gas components (CA_8) after dust removal and dehumidification (9) Top gas flow rate (FI_9) and gas components (CA_9) after CO 2 separation (10) [C][H][O] components of fuel mixed with top gas (C10_10), fuel rate (WI_10), and oxygen flow rate (FI_10) (11) Flow rate (FI_11), temperature (TI_11), pressure (PI_11), and [CO 2 ] content (CA_11) of the heater outlet gas (12) Second-stage tuyere gas flow rate (FI_12) (13) High-temperature gas flow rate sent to the third-stage tuyere (FI_13) and temperature before blown-in (TI_13) (14) Low-temperature gas flow rate sent to the third-stage tuyere (FI_14) and temperature (TI_14) (15) Gas flow rate extracted from the top gas to outside the system (FI_15)

[0149] The H 2 O component in the top gas is difficult to measure directly, but it is calculated as follows. The vapor pressure of the top gas(8) (after dust removal and dehumidification) will give the H 2 O component of (8), and the H 2 O ratio in the top gas(7) can be determined from the molar flow rate of (7) and (8). As a result, in addition to measuring the gas components in (8), it is possible to determine the molar flow rates of CO, CO 2 , H 2 , H 2 O, and N 2 as top gas(7). So, by subtracting the CO 2 and H 2 O produced by combustion(6) and from auxiliary materials(1), the molar flow rate X of CO 2 and H 2 O produced by the in-furnace gas reduction reaction can be determined. On the other hand, a gas reduction ratio of 100% means that CO 2 and H 2 O are produced by reducing iron ore with only CO and H 2 (that is, removing oxygen from the iron ore). Since the O (oxygen) molar flow rate Y in the iron ore can be determined with the information (1), the gas(9) flow rate (FI_9) and the fuel(10) injection rate (WI_10) are adjusted to keep the gas reduction ratio RDg = X / Y = 1, using equations (6) and (7) as feedback guidelines.

[0150] Here, the oxygen(10) flow rate (FI_10) is controlled according to the formula (11) so that the gas quality after heating becomes optimal (composed only of CO and H 2 ) according to both of the molar flow rates of CO 2 and H 2 O in the gas(9) after the CO 2 separator and the molar flow rates of C, H, and O in the fuel(9).

[0151] Direct reduction ironmaking is an ironmaking method that is similar to the gas reduction section of a blast furnace. The reduction ratio of the reduced iron (DRI or HBI) produced by the direct reduction method is not 100% (about 95 to 97%). This is mainly because the ore temperature is kept below about 900°C to prevent sticking, even though the gas reduction rate is faster at higher temperatures. In the present invention, there is no sticking restriction and gas reduction is possible up to the temperature just above the cohesive zone (about 1300°C), so ore with a reduction ratio close to 100% can be supplied to the lower furnace. However, if the final reduction temperature exceeds 1000°C, coke gasification occurs due to CO 2 and H 2 O generated by gas reduction. So, the apparent gas reduction ratio will not reach 100% until the furnace top temperature is adjusted by the second / third stage tuyere flow rates, pre-reduction tuyere, and / or raw material preheating tuyere.

[0152] Furthermore, achieving a gas reduction ratio of 100% is not necessarily the only reasonable operational goal. In particular, if the shaft efficiency decreases, it leads to an increase in the amount of external fuel and circulating gas and a decrease in overall energy efficiency including sensible heat loss of the top gas, heat supply to the heater, and gas processing energy. Therefore, in parallel with the gas reduction ratio RDg, it is important to manage the shaft efficiency. Strict control of the shaft efficiency is not easy. But since the gas reduction ratio is high in the present invention, there is a strong correlation between shaft efficiency and top gas amount, and the top gas flow rate (FI_7) is only required to be watched, which is operationally easy.

[0153] On the other hand, from the top gas(7) molar flow rates of CO, CO 2 , H 2 , H 2 O, N 2 determined above and the top gas temperature (TI_7), the enthalpy flow rate Q7 (sensible heat and latent heat) of the top gas(7) can be calculated. Similarly, the enthalpy flow rate Q11 (sensible heat and latent heat) of the heater outlet gas(11) can be calculated. Since the net energy amount Qnet to produce pig iron in the blast furnace itself including its heat loss is fixed, the total enthalpy flow rate Qfuel of the fuels supplied into the furnace is uniquely determined as "Qfuel = Qnet+Q7-Q11". Here, Qfuel includes the latent heat flow rate Q4 derived from the fuel(4) injection speed (WI_4), the latent heat flow rate Q6 derived from the fuel(6) injection speed (WI_6), and the latent heat flow rate Q23 corresponding to the amount obtained by subtracting the C molar flow rate dissolved in pig iron(3) from the C molar flow rate in coke(2). In other words, "Qfuel = Q4+Q6+Q23".

[0154] The heat required to make pig iron and slag after softening starts must be at a high temperature of 2000°C or higher (high-grade heat) and is provided as the primary combustion of the first-stage tuyere fuel and coke (Q4 + Q23). In addition, the rate of reduction reaction is faster at higher temperatures, and it is virtually difficult for the reaction to proceed unless the ore is preheated to 600°C or higher. Therefore, the coke(2) flow rate (WI_2) and fuel(4) should be adjusted so that the temperature (TI_3) and the carbon content (CA_3) of the pig iron(1), and the temperature (TI_5) below the preheating tuyere(5) are the required values. Adjust the flow rate (WI_4). At this time, adjust the oxygen (4) flow rate (FI_4) as shown in equation (10), and adjust the distribution ratio between the first-stage tuyere and the second-stage tuyeres and above so that the raceway temperature is appropriate.

[0155] Finally, adjust the furnace top gas (7) temperature (TI_7) and the temperature (TI_5) below the pre-reduction tuyere(5) at the required temperatures.

[0156] First, in the case of a combination of raw materials and fuels that causes a high top gas temperature (when carbon content is high), the pre-reduction tuyere 2d is not used in principle. Keep the heater outlet gas(11) temperature (TI_11) at a high temperature, blow only through the first-stage tuyere 2a and second-stage tuyere 2b, and confirm that the furnace top temperature is within the appropriate range. If the temperature at the top or the temperature in the middle of the shaft (TI_5) is high, blow in the gas from the third-stage tuyere 2c at a temperature (TI_13), which is a mixed gas of the heater outlet gas and heater inlet gas as shown in Fig.4 at their respective flow rates (FI_13) and (FI_14). Thereby, the furnace top temperature (∝ sensible heat loss of the top gas) and the temperature below the middle of the shaft (oc Tr temperature and reduction-end temperature) can be lowered while the amount of blown-in reducing gas remains unchanged.

[0157] Next, in the case of a combination of raw materials and fuels that results in a low top gas temperature (when hydrogen component is large), the pre-reduction tuyere 2d is used in place of the third-stage tuyere 2c. After blowing in the required amount of reducing gas from the first-stage tuyere 2a and the second-stage tuyere 2b, the fuel(6) flow rate (WI_6) and oxygen(6) flow rate (FI_6) from the pre-reduction tuyere is adjusted so that the top gas(7) temperature reaches the required temperature and at the same time adjust the top gas recirculation(5) flow rate (FI_5) is adjusted so that the mixed gas temperature from the pre-reduction tuyere is 700 to 900°C. When the shaft gas contains a large amount of hydrogen, additionally supplying raw material preheating heat and / or pre-reduction heat have the effect of shifting not only the top temperature but also the point W (the point where FeO reduction begins) on the Rist model to the right, reducing the amount of reducing gas and lowering reduction-end temperature (suppression of coke gasification reaction).

[0158] If the raw material preheating tuyere 2e (see Fig.2) is used in combination with or instead of the pre-reduction tuyere 2d and hydrogen is used as fuel to achieve complete combustion, the subsequent dehumidifier (including the gas cleaning cooler) can remove it from the circulating gas as water and the influence of the raw material preheating tuyere fuel can be limited from the furnace top to the dehumidifier. As described above, according to the present invention, stable and easy operation can be realized even with a much lower coke rate and fuel rate than in conventional blast furnaces.EXAMPLES

[0159] Tables 4 to 7 show the unit consumption figures and temperatures of the examples of the present invention in comparison with those of a conventional blast furnace (example). [Table 4]unit Conv. BF(e.g.) Example 1 Example 1-2 Example 1-3 Metal charge ratio Xm % 0 0 0 20% Gas reduction ratio % 70 100 100 100 Hydrogen reduction ratio % 9 49 49 39 Coke ratio kg / tp 320 58 58 58 Fuel ratio (coke+tuyere inj. fuels) kg / tp 510 234 234 188 Slag ratio kg / tp 304 228 228 185 Shaft efficiency kg / tp 90% 95% 95% 95% Top gas Gas ratio(Wet) Vt Nm 3< / tp 1620 1,240 1,438 1,018 H 2 O % 3 22 21 17 N 2 dry% 49 0.1 0.1 0.1 CO dry% 24 25 27 38 CO 2 dry% 22 29 30 32 H 2 dry% 5 45 43 30 Temperature °C 150 120 120 151 Heater Top gas mix ratio Nm 3< / tp N / A 537 531 457 External fuel mix ratio Nm 3< / tp N / A H 2 362 H 2 376 H 2 223 O2 ratio of mixed fuel Nm 3< / tp N / A 0 0 0 Cmbustion fuel Unit / tp 2.0 GJ 1.7 GJ 1.5 GJ 1.4 GJ Tuyere blown-in gas V13=V1+V2+V3 Nm 3< / tp N / A 899 907 680 V13+tuyere inj. fuel[H2] Nm 3< / tp 106 902 911 683 1st-stage tuyere Tuyere blown-in gas V1 Nm 3< / tp 1017(hot blast) 158(red.gas) 408(red.gas) 162(red.gas) Gas temperature °C 1,200 1,300 1,300 1,300 Tuyere injection fuel kg / tp 190;PCI 176;graphite 176;graphite 175;graphite Tuyere blown-in O 2 Nm 3< / tp 43 + Air 974 165 165 163 Raceway temperature °C 2,024 2,345 2,014 2,331 2nd-stage tuyere Tuyere blown-in gas V2 Nm 3< / tp N / A 350 -518 Gas temperature °C N / A 1,300 -1,300 3rd-stage tuyere Tuyere blown-in gas V3 Nm 3< / tp N / A 391 499 -Gas temperature °C N / A 1115 950 -Prereduction tuyere Top gas (cleaned) Nm 3< / tp N / A 0 130 -O 2 for heating Nm 3< / tp N / A -14 -Gas temperature °C N / A -900 -Cohesive zone passing gas ratio Nm 3< / tp 1590 500 500 500 Shaft gas-reduction index Point W temperature Tr °C 914 870 744 988 K 1 / (1-Xm) mol / molFe 2.1 3.3 3.3 3.3 K2 Nm 3< / tp 421 602 602 602 total heat input to lower furnace (gas included) Qgr+Qk GJ / tp 4.4 1.7 2.2 1.7 [Table 5] unit Conv. BF(e.g.) Example 1-4 Example 15 Example 2 Metal charge ratio Xm % 0 20% 36% 0 Gas reduction ratio % 70 100 100 100 Hydrogen reduction ratio % 9 38 25 63 Coke ratio kg / tp 320 58 58 186 Fuel ratio (coke+tuyere inj. fuels) kg / tp 510 232 232 186 Slag ratio kg / tp 304 185 185 232 Shaft efficiency kg / tp 90% 95% 95% 95% Top gas Gas ratio(Wet) Vt Nm 3< / tp 1620 1,103 972 1,499 H 2 O % 3 16 10 25 N 2 dry% 49 0.1 0.1 0.2 CO dry% 24 32 41 17 CO 2 dry% 22 34 39 24 H 2 dry% 5 33 20 59 Temperature °C 150 120 120 120 Heater Top gas mix ratio Nm 3< / tp N / A 430 356 672 External fuel mix ratio Nm 3< / tp N / A H 2 230 H 2 119 H 2 365 O2 ratio of mixed fuel Nm 3< / tp N / A 0 0 0 Cmbustion fuel Unit / tp 2.0 GJ 1.2 GJ 1.0 GJ H 2 190 Nm 3< Tuyere blown-in gas V13=V1+V2+V3 Nm 3< / tp N / A 660 476 1,037 V13+tuyere inj. fuel[H2] Nm 3< / tp 106 663 480 1,048 1st-stage tuyere Tuyere blown-in gas V1 Nm 3< / tp 1017(hot blast) 162(red.gas) 162(red.gas) 273(red.gas) Gas temperature °C 1,200 1,300 1,300 1,300 Tuyere injection fuel kg / tp 190;PCI 175;graphite 175;graphite 0 (Coke) Tuyere blown-in O 2 Nm 3< / tp 43 + Air 974 163 163 103 Raceway temperature °C 2,024 2,332 2,328 2,404 2nd-stage tuyere Tuyere blown-in gas V2 Nm 3< / tp N / A 370 313 764 Gas temperature °C N / A 1,300 1,300 1,300 3rd-stage tuyere Tuyere blown-in gas V3 Nm 3< / tp N / A 128 - - Gas temperature °C N / A 950 - - Prereduction tuyere Top gas (cleaned) Nm 3< / tp N / A 105 160 236 O 2 for heating Nm 3< / tp N / A 8 12 17 Gas temperature °C N / A 900 900 900 Cohesive zone passing gas ratio Nm 3< / tp 1590 500 500 500 Shaft gas-reduction index Point W temperature Tr °C 914 851 887 803 K 1 / (1-Xm) mol / molFe 2.1 3.3 3.3 3.3 K2 Nm 3< / tp 421 602 602 602 total heat input to lower furnace (gas included) Qgr+Qk GJ / tp 4.4 1.7 1.7 1.8 [Table 6] unit Conv. BF(e.g.) Example 3 Example 3-2 Example 4 Metal charge ratio Xm % 0 0 0 0 Gas reduction ratio % 70 100 100 100 Hydrogen reduction ratio % 9 45 45 65 Coke ratio kg / tp 320 186 186 58 Fuel ratio (coke+tuyere inj. fuels) kg / tp 510 186 186 233 Slag ratio kg / tp 304 232 232 200 Shaft efficiency kg / tp 90% 95% 95% 95% Top gas Gas ratio(Wet) Vt Nm 3< / tp 1620 1,251 1,377 1,301 H 2 O % 3 20 19 29 N 2 dry% 49 0.2 0.2 0.1 CO dry% 24 33 30 16 CO 2 dry% 22 30 32 23 H 2 dry% 5 36 38 60 Temperature °C 150 140 150 120 Heater Top gas mix ratio Nm 3< / tp N / A 542 517 0 External fuel mix ratio Nm 3< / tp N / A CH 4 161 CH 4 167 H 2 883 O2 ratio of mixed fuel Nm 3< / tp N / A 81 84 0 Cmbustion fuel Unit / tp 2.0 GJ 1.8 GJ 1.7 GJ 1.7 GJ Tuyere blown-in gas V13=V1+V2+V3 Nm 3< / tp N / A 1,025 1,018 883 V13+tuyere inj. fuel[H2] Nm 3< / tp 106 1,035 1,028 886 1st-stage tuyere Tuyere blown-in gas V1 Nm 3< / tp 1017(hot blast) 273(red.gas) 273(red.gas) 160(red.gas) Gas temperature °C 1,200 1,300 1,300 1,300 Tuyere injection fuel kg / tp 190;PCI 0 (Coke) 0 (Coke) 175;graphite Tuyere blown-in O 2 Nm 3< / tp 43 + Air 974 103 103 164 Raceway temperature °C 2,024 2,392 2,394 2,344 2nd-stage tuyere Tuyere blown-in gas V2 Nm 3< / tp N / A 752 745 723 Gas temperature °C N / A 1,300 1,300 1,300 3rd-stage tuyere Tuyere blown-in gas V3 Nm 3< / tp N / A - - - Gas temperature °C N / A - - - Prereduction tuyere Top gas (cleaned) Nm 3< / tp N / A - 133 78 O 2 for heating Nm 3< / tp N / A - 10 6 Gas temperature °C N / A - 900 900 Cohesive zone passing gas ratio Nm 3< / tp 1590 500 500 500 Shaft gas-reduction index Point W temperature Tr °C 914 966 863 880 K 1 / (1-Xm) mol / molFe 2.1 3.3 3.3 3.2 K2 Nm 3< / tp 421 602 602 602 total heat input to lower furnace (gas included) Qgr+Qk GJ / tp 4.4 1.8 1.8 1.7 [Table 7] unit Conv. BF(e.g.) Example 5 Example 6 Example 7 Example 8 Metal charge ratio Xm % 0 0 0 0 0 Gas reduction ratio % 70 100 100 100 100 Hydrogen reduction ratio % 9 97 61 65 32 Coke ratio kg / tp 320 58 58 58 58 Fuel ratio (coke+tuyere inj. fuels) kg / tp 510 106 307 260 307 Slag ratio kg / tp 304 278 252 200 252 Shaft efficiency kg / tp 90% 85% 95% 95% 95% Top gas Gas ratio(Wet) Vt Nm 3< / tp 1620 1,633 1,307 1,306 1,252 H 2 O % 3 35 27 29 14 N 2 dry% 49 0.1 0.5 0.1 0.5 CO dry% 24 1 19 16 35 CO 2 dry% 22 2 25 23 35 H 2 dry% 5 97 56 61 29 Temperature °C 150 200 120 120 150 Heater Top gas mix ratio Nm 3< / tp N / A 574 0 0 574 External fuel mix ratio Nm 3< / tp N / A CH4 11+H2795 H 2 732 H 2 564 CH. 61 O2 ratio of mixed fuel Nm 3< / tp N / A 0 0 0 31 Cmbustion fuel Unit / tp 2.0 GJ 2.7 GJ 1.4 GJ 1.1 GJ 1.4 GJ Tuyere blown-in gas V13=V1+V2+V3 Nm 3< / tp N / A 1,402 732 564 758 V13+tuyere inj. fuel[H2] Nm 3< / tp 106 1,405 850 890 877 1st-stage tuyere Tuyere blown-in gas V1 Nm 3< / tp 1017(hot blast) 487(red.gas) 50(red.gas) 0(red.gas) 100(red.gas) Gas temperature °C 1,200 1,300 1,300 1,300 1,300 Tuyere injection fuel kg / tp 190;PCI 48;Mg,Ca,Si 249;PCI 202; C2H4 249;PCI Tuyere blown-in O 2 Nm 3< / tp 43+Air 974 22 181 162 181 Raceway temperature °C 2,024 2,383 2,264 2,108 2,184 2nd-stage tuyere Tuyere blown-in gas V2 Nm 3< / tp N / A 915 682 564 230 Gas temperature °C N / A 1,300 1,300 1,300 1,300 3rd-stage tuyere Tuyere blown-in gas V3 Nm 3< / tp N / A ---428 Gas temperature °C N / A ---906 Prereduction tuyere Top gas (cleaned) Nm 3< / tp N / A 218 78 83 0 O 2 for heating Nm 3< / tp N / A 15 6 6 -Gas temperature °C N / A 980 900 900 -Cohesive zone passing gas ratio Nm 3< / tp 1590 500 548 659 598 Shaft gas-reduction index Point W temperature Tr °C 914 860 884 877 843 K 1 / (1-Xm) mol / molFe 2.1 3.7 3.2 3.2 3.3 K2 Nm 3< / tp 421 602 602 602 602 total heat input to lower furnace (gas included) Qgr+Qk GJ / tp 4.4 1.7 1.8 2.0 1.9

[0160] Figs. 5 to 13 show the flow diagrams of the conventional blast furnace example and Examples 1 to 8 in Tables 4 to 7, respectively (Examples 6 and 7 correspond to Fig.12). The values in the figures show the unit consumptions to produce 1 ton (1,000 kg) of pig iron, and some of which are the unit consumptions shown in Tables 4 to 7. Each unit consumption was calculated using the Rist model and / or heat and mass balance model for an each zone including thermal equilibrium calculations. But, regarding the dehumidifier, CO 2 separator, gas reformer, and CO 2 recycling equipment, the unit consumptions were calculated assuming 100% reaction efficiencies.

[0161] Example 1 is an example of the ultimate coke rate in which the amount of coke used is limited to the amount of coke required for carburizing and reducing non-ferrous metals, and is an example of using graphite as a fuel. The top gas is used as the heating fuel in the heater 24 and hydrogen is used for the fuel mixed with the top gas in the heater 24 and preheating raw materials, by which the carbon source that enters the system (= going out from the system) is limited to the minimum necessary coke .

[0162] The top gas, after dust removed, H 2 O removed in a dehumidifier 21, and CO 2 separated in CO 2 separator 22, with the remaining components (CO, H 2 , N 2 ) is sent to a heater 24. CO 2 is sent to a CO 2 recycling facility 25 outside the system and converted to CH 4 by a methanation reaction (CO 2 + 4H 2 = CH 4 + 2H 2 O; exothermic reaction) not shown, and then reconverted to C (graphite) in a graphite conversion facility (e.g., HAZER process) not shown, and then reinjected into the furnace from the first-stage tuyere 2a.

[0163] The heater 24 is a regenerative furnace similar to the hot stove 23 of the conventional blast furnace example (Fig.5), and for its heating fuel, the top gas extracted from the downstream of the dehumidifier 21 is utilized so that the nitrogen, which is contained in coal and coke and / or supplied inside as utility gas, will not be concentrated by the circulation. It is mixed with the combustion exhaust gas for the purpose of adjusting the flame temperature and oxygen combusted in a combustion chamber (not shown). The CO 2 -rich exhaust gas passes thorough the regenerative chamber (not shown), and then sent to a CO 2 recycling facility 25 through a dehumidifier 21 if necessary. Since N 2 which is an impure gas is discharged from the system in the process of carbon dioxide liquefaction (not shown), N 2 is not concentrated in the entire system. The top gas after the CO 2 separator 22 is pressurized by the gas compressor 31, passes through another preheated regenerative chamber (not shown), is preheated to a required temperature, and is supplied to each tuyere.

[0164] As mentioned above, only the minimum amount of coke required is charged as a fossil fuel, and the other fuels are circulating fuel and hydrogen, and This is a system that does not emit CO 2 to the atmosphere if CO 2 recycling equipment installed outside the system is assumed included..

[0165] Example 1-2 is the case that the blowing amount of the third-stage tuyere and the first-stage tuyere are increased, the second-stage tuyere is deleted, and pre-reduction tuyere is installed, which is in order to lower the point W temperature (Tr) and the reduction-end temperature than in Example 1. Although the second-stage tuyere is removed to simplify the equipment, it is also good that the first-stage tuyere is returned to 158 Nm 3< / tp and the second-stage tuyere blows 250 Nm 3< / tp. Since both examples do not assume a coke gasification reaction, the amount of fossil fuels used in Examples 1 is slightly smaller in the calculations, but there is a possibility that Example 1-2 is superior in the actual operation due to the differences of point W temperature (Tr) and / or the reduction-end temperature.

[0166] As a method to lower the third-stage tuyere temperature below the heater outlet temperature, the heater inlet gas and heater outlet gas are mixed in Fig.7, but if the hydrogen supply pressure is high, it is also good to directly mix hydrogen instead of the heater inlet gas.

[0167] Examples 1-3 to 1-5 are examples in which a certain proportion of the ore in Example 1 is replaced with metallic iron (DRI or scrap). 20 % metallic iron is used in Examples 1-3 and 1-4, and 36 % for Example 1-5. Since metallic iron does not need reduction and does not contain oxygen, the heat capacity per ton of iron is smaller and the heat flow ratio in the shaft decreases, which has the effect of offsetting the increase in heat flow ratio (shaft) due to oxygen blast furnaces and hydrogen reduction. In addition, it has a feature that the amount of reducing gas in the shaft (lumpy zone) can be reduced because reduction is not required, but the fuel rate remains almost the same because the heat balance in the lower furnace remains unchanged.

[0168] Example 1-3 is a calculation result in which the iron ore of Example 1 is replaced with 20% metallic iron, and is also an example of two stages of tuyere, where the coke gasification reaction (=apparent direct reduction) is unavoidable since the point W temperature (Tr) is high (988°C) and the reduction-end temperature exceeds 1000°C. Example 1-4 is the one that a third-stage tuyeres and a pre-reduction tuyeres are also used in order to suppress the coke gasification reaction, which has realized Tr = 851°C and the reduction-end temperature = 890°C.

[0169] Example 1-5 is an example in which the proportion of metallic iron is further increased. And the pre-reduction tuyere is required, since the lumpy zone is further cooled and the temperature at the top of the furnace also decreases even though all the preheated reducing gas is blown in from the first / second stage tuyeres.

[0170] Example 2 is a case where the tuyere injection fuel (CO 2 recycled fuel) of Example 1 is not used. As with conventional blast furnaces, coke is used as a combustion heat source and a reducing gas source. So, the coke rate is higher than in Example 1, but compared to the conventional blast furnace (example) that uses 190 kg / tp of pulverized coal, the coke rate is reduced to 58% and the fuel rate (reducing agent rate) is reduced to 36%.

[0171] Example 3 is a case in which the fuel in Example 2 is changed from hydrogen to methane. Utilizing hydrogen is essential for reducing CO 2 , but it will be difficult to utilize hydrogen until infrastructure such as hydrogen production equipment and transportation systems are in place. Therefore, a case using methane is shown, which is highly available, including LNG. In conventional blast furnaces and another system (Non-patent Literature 5), methane is directly injected into the furnace as tuyere fuel, which is partially combusted (primary combustion; producing CO and H 2 ) and mixed with the top gas in the example (Fig.9) of the present invention.

[0172] By using methane instead of hydrogen, the endothermic reaction is reduced compared to Example 2, and an appropriate furnace top temperature can be maintained even with two stages of tuyere. But since the point W temperature (Tr) was found to be as high as 966°C, Example 3-2 is shown as a case in which Tr is reduced by 100°C or more by using a pre-reduction tuyere. Coke consumption is lower than in Example 2, and although CO 2 emissions excluding the CO 2 recycling effect are higher than in Example 2 due to the usage of methane instead of hydrogen, it can be reduced by approximately 46% (Example 3-2) compared to the conventional blast furnace example.

[0173] The present invention can also be applied when the top gas is not recirculated. Example 4 (Fig.10) is a case in which external hydrogen is used for all of the tuyere gas in Example 1 without using the top gas. The top gas (main components are H 2 , H 2 O, CO, and CO 2 ) goes through the gas cleaning cooler 21a and is, as a byproduct gas, utilized for a fuel in the power generation equipment 26 outside the system, and is exhausted as H 2 O and / or CO 2 . The exhaust gas becomes CO 2 gas by H 2 O being removed in a dehumidifier 21, and it is converted to graphite (C) in a CO 2 recycling facility 25, which is then reused as tuyere injection fuel. The electric power generated by the power generation equipment 26 is used in a hydrogen / oxygen production equipment 27 that produces H 2 and O 2 necessary for the blast furnace. The system is similar to Example 1 in that it does not emit any CO 2 into the atmosphere, but it is characterized by the fact that CO 2 separator is not necessary neither on the blast furnace side nor outside the system since the top gas is not recirculated within the blast furnace.

[0174] The above examples are just some of examples. Although examples were shown in which hydrogen (H 2 ), methane (CH 4 ), and graphite (C) were used as fuel, any combustible fuel can be used, including biomass fuel, coke gas (COG), converter gas (LDG), COz conversion fuel (gas, liquid, solid), metallic fuel, coke powder, etc.

[0175] Example 5 (Fig.11) shows a case in which metallic fuels (powder) containing metallic magnesium (Mg), metallic calcium (Ca), and metallic silicon (Si) mixed in a slag component ratio are used.

[0176] By blowing an appropriate amount of tuyere blown-in gas together with metal fuels and oxygen from the lowest-stage tuyere, it is possible to supply the necessary heat to the lower furnace (the zone of and below the cohesive zone) while maintaining an appropriate raceway temperature (2383°C in Example 5). Iron ore is reduced by hydrogen supplied from an external source, and the hydrogen reduction ratio is increased to nearly 100% (about 97%), making it a literally hydrogen reduction blast furnace. As no coke or fossil fuels are burned in the furnace, almost no CO or COz is emitted from the top of the furnace (only generated by the reduction of non-ferrous metals), which is an example of the revolutionary system that does not require COz separator or COz recycling equipment.

[0177] In Example 5, in order to prevent the concentration of CO gas generated during the reduction of non-ferrous metals and impurity gases (N 2 , etc.) that enter even in small amounts, some portion of the top gas is extracted as the heater combustion gas as in Examples 1 and 3. In this example, since the COz content in the heater combustion exhaust gas is small (several percent by volume), it is exhausted from the gas chimney 28, but it is also possible to capture COz by installing a dehumidifier. Also, since the top gas contains COz even if only in small amounts, CH 4 is injected into the downstream of the heater to reform the gas, which thereby suppresses the coke gasification reaction, caused by COz, in the lower furnace.

[0178] Because the hydrogen reduction ratio, which is an endothermic reaction, is high at 97%, in order to suppress the temperature drop in the lumpy zone and promote the reduction reaction, the second-stage tuyere blown-in rate is increased (the shaft efficiency decreases), and reducing gas from the pre-reduction tuyere is actively used. This operation reduces the heat flow ratio at the top of the shaft to nearly 0.6 and causes the furnace top temperature to rise slightly, but on a heat and mass balance and equilibrium theory basis, it has been all realized that a reduction-start temperature of 650°C or higher, a reduction-end temperature of 900°C or lower, and a furnace top temperature of 200°C or lower, even with a hydrogen reduction ratio of 97%.

[0179] Examples 6 and 7 are cases in which an open system without top gas recirculation is used. As tuyere injection fuels, they are respectively the case in which biofuel such as bio-coke and / or bio-coal is used, and the case in which E-Fuel converted from COz by green power is used. Since these fuels are considered to have a COz emission coefficient of zero(0), and only the amount for the reduction of non-ferrous metals is counted as COz emissions in the top gas, COz recovery is not necessary when being combusted and exhausted. Because the top gas has an easy-to-use calorific value (8500 to 8700 kJ / Nm 3< in Examples 6 and 7), it can be an alternative energy source and widely utilized through existing gas networks by factories other than the blast furnace, which brings about benefits to significantly reduce COz emissions from the factories.

[0180] Example 8 is a case in which the coke rate and fuel rate are reduced by only the fuels (reducing agents) used in conventional blast furnaces: coke, pulverized coal (PCI), and methane (equivalent to natural gas). Pulverized coal can be mixed with bio-coke and / or bio-coal in any ratio to create a mixed fuel, and if it has become 100% bio-fuel, COz emissions derived from tuyere injected fuel will become zero (0). Also regarding the methane, which is partially combusted in the heater and converted into reducing gas, a similar effect can be achieved by switching it to COz recycled methane. In the figure, the carbon (C) unit consumptions before and after fuel conversion are shown in their respective order.

[0181] Even in the fossil fuel-based Example 8, the amount of carbon discharged from the blast furnace to the outside is 238 kg / tp (excluding the amount for COz recycling), which can reduce COz emissions by round 40% (i.e.38%) even at least in appearance compared with 381 kg / tp of the conventional blast furnace. Furthermore, taking into account that 1.7 to 1.8 kg of coal is required to produce 1 kg of coke, it is possible to substantially reduce COz emissions by half (50%).

[0182] The above examples are merely limited examples, and it is also possible to utilize intermediate raw fuels and / or configure intermediate systems by combining examples 1 to 8. In other words, it is itself a breakthrough that the present invention has infinitely expanded options for raw fuels and system configurations to reduce coke and COz emissions, and it will be possible to revise the heat and mass balances according to future developments in COz storage / utilization technologies as ancillary facilities and adopt the optimal system taking into account economic efficiency.

[0183] The entire contents of Japanese Patent Application No. 2022-68527 (filing date: March 31, 2022) are incorporated herein by reference.

[0184] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.[Industrial applicability]

[0185] The technology according to the present invention can also be applied to reduced iron production equipment and / or cupolas (scrap melting furnaces).

Claims

1. A method of operating a blast furnace, comprising: blowing in reducing gas preheated at 800°C or higher into the furnace in addition to top-charging coke and / or tuyere injection fuels; controlling a productivity of a shaft ((Pd×MR) / Vsh) so that a following inequality is satisfied: Pd × MR / Vsh ≤ 12 , where, Vsh: an effective furnace volume of the shaft (m3), Pd: pig iron production per day (tp / day), and MR: a ratio of top-charging raw materials (t / tp); wherein the reducing gas, not including the gas blown in at and above a middle of shaft, is blown so that a following inequality is satisfied: 3.9 ≥ K1 ≥ 3.1 , and Cf + Cg − Ci + Hf + Hg / 2 = K1 × 1 − Xm for 1 mole of iron in pig iron, where K1: a constant to determine fuel rate, Cf: a total amount of [C] of the top-charging coke and the tuyere injection fuels (mol-C / mol-Fe), Hf: a total amount of [H] of the top-charging coke and the tuyere injection fuels (mol-H / mol-Fe), Cg: an amount of CO gas in the reducing gas (mol-C / mol-Fe), Hg: an amount of [H] in the reducing gas (mol-H / mol-Fe), Ci: an amount of [C] in the pig iron (mol-C / mol-Fe), and Xm: a ratio of metallic iron (mol-Fe) to total iron (mol-Fe) in the top-charging raw materials.

2. The method according to claim 1 further comprising: further adjusting the amount of the reducing gas to satisfy a following inequality in a total amount of COz and H2O in the top gas per ton of iron in the pig iron, Vpc = K2×Gy / 1.5+Xf×22.4+Xo (Nm3 / t-Fe), 610 ≥ K2 ≥ 560 , where K2: a constant determined by the direct reduction ratio and the iron ratio in pig iron, Gy: a ratio of oxygen (mol-O) to iron (mol-Fe) in the charged ore and charged metallic iron (mol-O / mol-Fe), Xf: a total molar ratio of CaCO3 and MgCO3 contained in the charged raw materials per ton of pig iron (kmol / tp), and Xo: an amount of secondary combustion gas (COz, H2O) supplied to the furnace above 2 / 3 height from the top of the shaft (1 / 3 height from the bottom) (Nm3 / tp).

3. The operating method according to claim 1 or 2, further comprising: reducing a total amount of heat of primary combustion in the lower furnace and the sensible heat of the tuyere blown-in gas to 2.4 GJ / tp or less per ton of pig iron.

4. The method according to claim 1 or 2, further comprising: arranging two or more stages of tuyeres, which are arranged in a height direction, to the furnace body including the shaft and the lower furnace; blowing in oxygen-containing gas of 200 Nm3 / tp or less as a total amount of oxygen(Oz) and secondary combustion gas from tuyere at the lowest stage of the tuyeres, and blowing in the reducing gas of 500×(1-Xm)1.3 Nm3 / tp or more from the tuyeres of and below the lower shaft, so that a total amount of CO and H2, included in the reducing gas and a hydrogen content in the tuyere injection fuels, is 800×(1-Xm)1.3 Nm3 / tp or more, where, Xm: a ratio of metallic iron (mol-Fe) to total iron (mol-Fe) in the top-charge raw materials.

5. The method according to claim 3, further comprising: arranging two or more stages of tuyeres, which are arranged in a height direction, to the furnace body including the shaft and the lower furnace, blowing in oxygen-containing gas of 200 Nm3 / tp or less as a total amount of oxygen(Oz) and secondary combustion gas from the tuyere at the lowest stage of the said tuyeres,and blowing in the reducing gas of 500×(1-Xm)1.3 Nm3 / tp or more being blown in from the tuyeres of and below the lower shaft, so that a total amount of CO and Hz, included in the reducing gas and a hydrogen content in the tuyere injection fuels, is 800×(1-Xm)1.3 Nm3 / tp or more, where, Xm: a ratio of metallic iron (mol-Fe) to total iron (mol-Fe) in the top-charge raw materials.

6. The operating method according to any one of claims 1 to 5, further comprising: blowing in at least a portion of the reducing gas through the tuyeres above the cohesive zone and the tuyeres below the cohesive zone at 1200°C or higher.

7. The operating method according to any one of claims 1 to 6, further comprising: using as the tuyere injection fuel, together with oxygen, the tuyere injection fuel being: hydrocarbon fuel being represented by a chemical formula CiHjOk excluding ash component to satisfy j / i ≤ 2 .3 , and 16 × k / 12 × i + j + 16 × k ≤ 10% , ferroalloy containing one or more selected from Si, Ca, Al, Mg, Fe, Si, Mn, and C, or a mixed fuel containing the hydrocarbon fuel and the said ferroalloy.

8. The operating method according to any one of claims 1 to 7, further comprising: blowing in oxygen with a purity of 90% or more into the furnace, together with the tuyere injection fuel and the preheated reducing gas, in an amount ranging from -1(O2-kmol / tp) to +0.2(O2-kmol / tp) with respect to an amount satisfying a following formula: Vo 2 = O 2 f + O 2 c , per ton of pig iron where O 2 f = 0 .5 × C1 + S1 + S2 − O1 − O2 + S3 + 1 .5 × S4 , O 2 c = 0.5 × C2 − C3 − C4 , C1: an amount of C component in the tuyere injection fuel (C-kmol / tp), C2: a molar amount of carbon in coke (C-kmol / tp), C3: a molar amount of carbon in pig iron (C-kmol / tp), C4: a molar amount of carbon required to reduce metals other than iron in pig iron (C-kmol / tp), O1: an amount of O component in the said tuyere injection fuel (O-kmol / tp), O2: a molar amount of COz and H2O in the preheated reducing gas (kmol / tp), S1: Mg component not combined with oxygen in the said tuyere injection fuel (Mg-kmol / tp), S2: Ca component not combined with oxygen in the said tuyere injection fuel (Ca-kmol / tp), S3: Si component not combined with oxygen in the said tuyere injection fuel (Si-kmol / tp), and S4: Al component not combined with oxygen in the said tuyere injection fuel (Al-kmol / tp).

9. The operating method according to any one of claims 1 to 8, further comprising: charging an entire amount of the top-charging coke mixed with ore containing auxiliary materials into the furnace.

10. An operating system for carrying out the operating method according to any one of claims 1 to 9, comprising: a tuyere blown-in gas flow rate controlling system, including; three or more tuyere groups arranged apart in a height direction of the furnace body, each group including a plurality of tuyeres arranged at intervals in a circumferential direction of the furnace body, each tuyere being configured to blow reducing gas into an inside of the furnace body of the blast furnace, a flow rate measuring device for each of the tuyere groups, and a flow rate adjusting device for each of the tuyere groups, and a control system configured to control an external fuel supply system, a heating system, and the tuyere blown-in gas flow rate controlling system, by measuring a top gas flow rate, a top gas oxidation degree, a furnace top temperature, and a temperature at a middle of the shaft.

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