Gas reduction blast furnace and method for operating same

Abstract

A method for operating a blast furnace in which a reducing gas preheated to 800 DEG C or more is blown into the furnace from tuyeres (2a, 2b, 2c, 2d) in addition to coke fed from the top of the furnace and fuel blown from the tuyeres, the method comprising: controlling the production efficiency of the shaft furnace so as to satisfy the inequality (Pd * MR) / Vsh < = 12; the reducing gas is blown in such a manner that the amount of the gas blown above the intermediate section of the shaft furnace is not included so as to satisfy the inequality 3.9 > = K1 > = 3.1, the equation (Cf + Cg-Ci) + (Hf + Hg) / 2 = K1 * (1-Xm) (the equation for one mole of iron in pig iron), and the reduction gas is blown in such a manner that the amount does not contain the gas blown above the intermediate section of the shaft furnace is the amount satisfying the inequality 3.9 > = K1 > = 3.1, the equation (Cf + Cg-Ci) + (Hf + Hg) / 2 = K1 * (1-Xm). Vsh is the effective furnace volume (m3) of the shaft furnace; pd is the daily pig iron production (tp / day); mR is the raw material ratio (t / tp) fed from the top of the furnace; k1 is a constant when determining the fuel ratio; cf is the [C] amount (mol-C / mol-Fe) obtained by adding the coke fed from the top of the furnace and the fuel blown from the tuyere; hf is the [H] amount (mol-H / mol-Fe) obtained by adding the coke fed from the top of the furnace and the fuel blown from the tuyere; 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 [C] amount (mol-C / mol-Fe) in the pig iron; xm is the ratio of metallic iron (mol-Fe) relative to all iron components (mol-Fe) in the feedstock fed from the top of the furnace.

Description

Technical Field

[0001] The present invention relates to a method for reducing the coke ratio and the reducing material ratio in a blast furnace, and also to a method for reducing CO2 emitted from the blast furnace. Background Art

[0002] The blast furnace method is to put coke and iron ore from the top of the furnace, and blow hot air (high temperature air above 1000℃) and fuel (such as pulverized coal) as a reducing material from the blower tuyere (flow tuyere) of the flow channel (casting bed). At the same time, the combustion of pulverized coal and coke not only generates huge heat, but also generates reducing gases such as CO and H2. The high-temperature reducing gas generated in the above manner rises in the furnace, while heating up and reducing the iron ore that is gradually descending.

[0003] There are three types of reduction reactions of iron ore (carbon monoxide gas reduction, hydrogen reduction, and direct reduction). Among them, direct reduction is a reaction that directly consumes carbon in coke (FeO+C=Fe+CO), which is a significant endothermic reaction. In addition, CO2 and H2O produced by combustion and gas reduction will cause dissolution reactions (CO2+C=2CO) and water gas reactions (H2O+C=CO+H2) that also consume carbon in coke at high temperatures, which are also significant endothermic reactions (hereinafter, it is referred to as "coke gasification reaction" when dissolution reactions or water gas reactions are not distinguished).

[0004] The ratio of carbon monoxide gas reduction, hydrogen reduction, and direct reduction in a general blast furnace is about 6:1:3. The hydrogen that contributes to hydrogen reduction is the gas converted to hydrogen by the water vapor (H2O) produced by the combustion of water or hydrogen components in the fuel through the water gas reaction, and the carbon monoxide that contributes to carbon monoxide gas reduction is also the gas converted to carbon monoxide by the byproduct gas from direct reduction or carbon components in the fuel through the dissolution reaction. That is, the reduction reaction of the conventional blast furnace method mostly relies on the consumption of coke.

[0005] Pig iron produced in a blast furnace contains carbon, which is mostly derived from coke, and 15% to 20% of the coke consumption in a conventional blast furnace process serves as a carburizing material.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application No. 7-90034 "A method for large-scale blowing of pulverized coal in a blast furnace"

[0009] Patent Document 2: Japanese Patent No. 5722867 “Method and related device for recycling blast furnace gas”

[0010] Patent Document 3: Japanese Patent Application No. 2016-168281 “Operation Method of Oxygen Blast Furnace”

[0011] Non-patent literature

[0012] Non-patent document 1: "Review of the oxygen blast furnace process based on a small-scale experimental blast furnace", Iron and Steel, Vol. 77 (1991) No. 12

[0013] Non-patent document 2: “100 Years of Ironmaking Technology - From Technology Introduction to Development of Advanced Technology to Next-Generation Technology”, Iron and Steel, Vol. 100 (2014) No. 1, p. 2-30

[0014] Non-patent document 3: “Effect of nitrogen-free reducing atmosphere on the permeability of blast furnace soft melt layer”, Iron and Steel, Vol. 104 (2018) No. 9

[0015] Non-Patent Literature 4: “Development of Environmentally Friendly Process Technologies / Development of Hydrogen Reduction and Other Process Technologies”, NEDO Environment Department 2020 Annual Results Report

[0016] Non-Patent Document 5: “Environmental Vision 2050”, JFE Group Environmental Management Vision 2050 Presentation Materials, pp. 1-23 (URL: https: / / www.jfe-holdings.co.jp / investor / zaimu / g-data / jfe / 2020-environmental-management-vision210525-01.pdf)

[0017] Non-patent document 6: "Ironmaking Manual" by Akitoshi Shigemune, Jijin Shukan (1979)

[0018] Non-patent document 7: "Steel Handbook (4th edition)" (2002)

[0019] Non-Patent Document 8: “Steel Handbook (5th Edition)” (2014)

[0020] Non-Patent Document 9: "Development of an Ironmaking Method Based on a Combination of a Shaft-Type Reduction Furnace and a Dome-Type Melting Furnace", Iron and Steel, Vol. 73 (1987) No. 15

[0021] Non-patent document 10: "Current Status of Pulverized Coal Blowing Technology for Blast Furnaces", Iron and Steel, Vol. 78 (1992) No. 7

[0022] Non-Patent Document 11: "Structure and Combustion Characteristics of a Blowing Unit for Blowing Pulverized Coal into a Blast Furnace", Iron and Steel, Vol. 82 (1996) No. 12

[0023] Non-patent document 12: "Study on the formation behavior of soft melting zone through model experiment", Iron and Steel, Vol. 68 (1982) No. 15

[0024] Non-Patent Document 13: "Fundamental Review of the Behavior of Unburned Pulverized Coal in Blast Furnaces", Iron and Steel, Vol. 77 (1991) No. 1

[0025] Non-patent document 14: "Development of technology for large-volume mixed feeding of ore and coke into blast furnaces", Iron and Steel, Vol. 92 (2006) No. 12 Summary of the invention

[0026] Conventional blast furnaces rely heavily on so-called direct reduction, i.e., direct reduction of iron ore by contacting carbon in the form of pulverized coal or coke. This necessarily consumes a large amount of carbon. While efforts are ongoing to reduce carbon consumption per unit of pig iron, such efforts have their limits. The purpose of the technology disclosed below is to thoroughly review the reactions within the furnace and achieve blast furnace operation with low carbon consumption.

[0027] A method for operating a blast furnace in which, in addition to coke fed from a furnace top or fuel blown from a tuyere or both, reducing gas preheated to 800° C. or higher is blown from a tuyere into the furnace, the method comprising controlling the production efficiency ((Pd×MR) / Vsh) of the shaft furnace to satisfy the inequality ((Pd×MR) / Vsh≦12), and blowing the reducing gas in such a manner that the amount of gas not including gas blown toward a middle portion of the shaft furnace and above thereof satisfies the inequality 3.9≧K1≧3.1; wherein Vsh: effective furnace volume (m 3 ), Pd: daily pig iron production (tp / day), MR: raw material ratio fed from the furnace top (t / tp); and, for one mole of iron in the pig iron, the formula is satisfied: (Cf+Cg-Ci)+(Hf+Hg) / 2=K1×(1-Xm); K1: constant for determining the fuel ratio, Cf: the sum of the [C] amount of the coke fed from the furnace top and the fuel blown from the tuyere (mol-C / mol-Fe), Hf: the sum of the coke fed from the furnace top and the fuel blown from the tuyere wherein: Cg: the amount of [H] in the aforementioned fuel blown from the tuyere (mol-H / mol-Fe), Cg: the amount of CO gas in the aforementioned reducing gas (mol-C / mol-Fe), Hg: the amount of [H] in the aforementioned reducing gas (mol-H / mol-Fe), Ci: the amount of [C] in the aforementioned pig iron (mol-C / mol-Fe), Xm: the ratio of metallic iron (mol-Fe) to all iron components (mol-Fe) in the raw materials fed from the furnace top.

[0028] Effects of the Invention

[0029] Through the above method, unlike the conventional blast furnace, the function of the lower part of the furnace can be limited to the melting of ore and slag, and the function of the vertical furnace can be limited to the reduction of ore (gas reduction 100%). Therefore, the required heat of the lower part of the furnace (that is, the temperature of pig iron) can be appropriately maintained by the amount of fuel and oxygen blown from the tuyere of the furnace, and the amount of preheated reducing gas can be freely increased or decreased according to the condition of the vertical furnace (gas reduction rate, furnace top temperature, vertical furnace efficiency) (that is, independent of the heat balance of the lower part of the furnace), thereby making the blast furnace easy to operate and the furnace condition stable.

[0030] Furthermore, since the heat required in the lower part of the furnace is limited to that required for melting the ore and slag, the amount of gas generated in the lower part of the furnace can be reduced to about half of that in a conventional blast furnace. Therefore, together with the multi-stage tuyere effect, even at a low coke ratio, the air permeability in the furnace can be ensured to be comparable to that of a conventional blast furnace.

[0031] According to the present invention, the coke ratio in pig iron production can be reduced to 100 kg / tp or less while ensuring the air permeability of the blast furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a diagram showing the interior of a conventional blast furnace.

[0033] Figure 2 This is a diagram showing the interior of a blast furnace according to the present embodiment.

[0034] Figure 3 The figure shows the temperature distribution in the furnace when the blast furnace of the present embodiment has three tuyere stages.

[0035] Figure 4 FIG. 1 shows the arrangement of control items in the blast furnace according to the present embodiment.

[0036] Figure 5 This is a flow chart showing an example of a conventional blast furnace, and the main basic units are also described in the attached figure.

[0037] Figure 6 This is a flow chart showing the first embodiment, and main basic units are also described in the drawing.

[0038] Figure 7 It is a flow chart showing Example 1-2, and main basic units are recorded together in the figure.

[0039] Figure 8 This is a flow chart showing the second embodiment, and the main basic units are also described in the figure.

[0040] Fig. 9 This is a flow chart showing the third embodiment, and the main basic units are also described in the figure.

[0041] Fig.10This is a flow chart showing the fourth embodiment, and the main basic units are also described in the figure.

[0042] Fig.11 This is a flow chart showing the fifth embodiment, and the main basic units are also described in the figure.

[0043] Fig.12 It is a flow chart showing the sixth and seventh embodiments, and the main basic units are also recorded in the drawings.

[0044] Fig.13 This is a flow chart showing the eighth embodiment, and the main basic units are also described in the figure.

[0045] Fig.14 It shows the heat input and heat output of the lower part of the furnace.

[0046] Fig.15 It shows the heat balance in the lower part of the furnace (conventional blast furnace).

[0047] Fig.16 It shows the heat balance comparison of the lower part of the furnace (conventional blast furnace and the present invention).

[0048] Fig.17 It is a heat line diagram showing the lower part of the furnace (the present invention).

[0049] Fig.18 It shows the comparison of the necessary / consumed energy in the lower part of the furnace vs. the amount of gas passing through the soft melting zone (conventional blast furnace and the present invention).

[0050] Fig.19 It shows the basic unit of the gas in the lower part of the furnace and the temperature change of the ore according to the present invention.

[0051] Fig. 20 This is a Rist model diagram showing an example of a conventional blast furnace.

[0052] Fig.21 It is a Rist pattern diagram showing Example 1.

[0053] Fig. 22 This is a heat map showing an example of a conventional blast furnace.

[0054] Fig.23 This is a heat map showing Example 1, and also shows a heat map (gas) of Example 1-2. DETAILED DESCRIPTION

[0055] Several exemplary embodiments are described below with reference to the accompanying drawings. The accompanying drawings are not necessarily shown to scale, so it should be noted that the dimensional relationships between the two are not limited to those shown in the drawings.

[0056] In the following description and the appended claims, the meaning of the use of each term is consistent with the definition known to those skilled in the art, but it should be noted that several terms have the following meanings. The so-called "lower part of the furnace" refers to the soft melt zone and the area below it. The radially bulging portion of the furnace body of a blast furnace is called the "bowel", and the "vertical furnace" means the portion of the furnace body above the aforementioned bowel and below the furnace roof, but the so-called "middle part" of the vertical furnace is a term specially defined as a region representing one-sixth of the height of the vertical furnace from the center upward to downward, in addition to the center of the vertical furnace in the height direction. The so-called "effective furnace volume (m 3 )" refers to, for example, the raw material level between the lower end of a vertical furnace and the top of the furnace, that is, the furnace volume between the heights of the storage line. The so-called "partial combustion" means combustion that does not reach complete combustion. The so-called "primary combustion" means the partial combustion of CO, H2, and H2S generated from the reaction of C+0.5·O2=CO and from coke and fuel blown from the tuyere, and the heat generated by the primary combustion is called "primary combustion heat". The so-called "secondary combustion" means the reaction of CO+0.5·O2=CO2, H2+0.5·O2=H2O, and CO2 or H2O is called "secondary combustion gas". The so-called "fuel ratio" is the total weight (kg / tp) of coke and fuel blown from the tuyere required to produce 1 ton of pig iron, and it is also commonly referred to as the reducing material ratio recently. Unless otherwise specified, the fuel ratio does not include the reducing gas (CO, H2) blown from the tuyere in the furnace top gas circulation, etc., but includes hydrocarbon fuel (CiHjOk; indicating the component after removing ash (Ash)).

[0057] In the research of oxygen blast furnace method, attempts have been made to use top gas to reduce the coke ratio and fuel ratio in the past. It is also known that the use of top gas (reducing gas) will reduce the direct reduction rate. However, from an economic point of view, the use of reducing gas is mainly carried out with top gas as the main body. It is found that there is a limit (about 200 kg) to reduce the coke ratio and fuel ratio from the combustion temperature at the front end of the tuyere and the heat balance in the lower part of the furnace. It is also considered that, for example, even if the coke ratio is reduced in the process, there will inevitably be operational problems such as the air permeability path of the soft melt zone becoming insufficient, which will significantly hinder the air permeability in the furnace. Therefore, it is not practical. The operating method disclosed below is conceived by reversely considering the technical bias of technicians in this field.

[0058] In short, the method for operating a blast furnace disclosed below is to blow a sufficient amount of reducing gas into the blast furnace, thereby substantially completing the reduction reaction of the iron ore above the soft melting zone. The above conditions are achieved by blowing a sufficient amount of reducing gas to be equivalent to one mole of pig iron produced.

[0059] (Cf+Cg-Ci)+(Hf+Hg) / 2=1.5 / ηg…(1)

[0060] And achieved.

[0061] in,

[0062] Cf: The total amount of [C] (mol-C / mol-Fe) of coke fed from the furnace top and fuel blown from the tuyere

[0063] Hf: The total amount of H (mol-H / mol-Fe) from the coke fed from the furnace top and the fuel blown from the tuyere

[0064] Cg: CO gas amount in preheated reducing gas (mol-C / mol-Fe)

[0065] Hg: Amount of [H] in the preheated reducing gas (mol-H / mol-Fe)

[0066] Ci: Amount of [C] in pig iron (mol-C / mol-Fe)

[0067] ηg: Gas utilization rate (%) or secondary combustion rate of furnace top gas (%).

[0068] Each symbol cited here and the symbols Xm and K1 in the following paragraphs represent the number of moles per mole of iron (Fe) in the pig iron.

[0069] However, sometimes reduced iron such as reduced iron and iron scrap (scrap) is fed from the furnace top, so the above formula will be modified to:

[0070] (Cf+Cg-Ci)+(Hf+Hg) / 2=1.5 / ηg×(1-Xm)…(2)

[0071] in,

[0072] Xm: The ratio of metallic iron (mol-Fe) to all iron components (mol-Fe) in the raw materials fed from the furnace top

[0073] The result of replacing 1.5 / ηg on the right side with the parameter K1 and finding the appropriate range of K1 from various embodiments shown in Tables 4 to 7 is:

[0074] (Cf+Cg-Ci)+(Hf+Hg) / 2=K1×(1-Xm)…(3)

[0075] 3.9≧K1≧3.1…(4)

[0076] in,

[0077] K1: Constant that determines the fuel ratio.

[0078] The present invention is described in further detail below.

[0079] As a countermeasure to global warming, reducing the fossil fuels such as coke (hereinafter referred to as coke) fed from the top of the blast furnace and pulverized coal, heavy oil, and natural gas blown from the tuyere in the blast furnace process has become the most important issue. It is known that the top gas circulation method, which dehumidifies the top gas (removes water vapor in the gas) and decarbonates it (removes carbon dioxide in the gas) and then blows it back to the blast furnace, can reduce the reducing material ratio (= coke ratio + fuel ratio blown from the tuyere) of the basic unit (original unit) of reducing materials required to produce 1 ton of pig iron (Patent Documents 2, 3). In addition, with regard to the fuel blown from the tuyere such as pulverized coal, by replacing the fuel with renewable energy fuel (biofuel, etc.) and carbon recovery fuel (hydrocarbon fuel converted from CO2 using environmentally friendly fuel), there is also the possibility of effectively reducing CO2 emissions.

[0080] However, regarding coke, the use of metallurgical coke (made from limited coal) is inevitable due to its functions of 1) ensuring the permeability of the furnace (the role of the grate) and 2) serving as a carburizing material, and therefore the reduction of the coke ratio (the basic unit of coke per ton of pig iron) is the key to CO2 reduction in the blast furnace process.

[0081] Coke is relatively more expensive than the fuel blown from the tuyere, so the goal has always been to operate at a low coke ratio. The coke ratio in a conventional blast furnace using hot air is generally about 350 (300 to 370) kg / tp (tp: means ton of pig iron. The same applies hereinafter), and even the lower limit of the world's overall operation record is about 250 kg / tp.

[0082] As a characteristic of the oxygen blast furnace method, on the one hand, the combustion efficiency of pulverized coal is improved by utilizing oxygen, and on the other hand, pure oxygen is blown from the tuyere to make it burn directly with the hot coke, so there is a problem that the temperature at the front end of the tuyere (the highest temperature point in the raceway) becomes abnormally high. As a countermeasure, in order to suppress the abnormally high temperature at the front end of the tuyere, a method of blowing water vapor (H2O), a furnace top gas containing H2O and CO2, and a method of blowing iron ore have been proposed (Patent Document 3), but it can be inferred that the lower part of the furnace will be cooled by these endothermic reactions, so a large amount of pulverized coal must be blown, and the lower limit of the coke ratio is still 200 to 250 kg / tp (at this time, the pulverized coal ratio = 300 kg / tp, the reducing material ratio = 500 kg / tp).

[0083] The ULCOS-NBF method developed in Europe is a blast furnace method that combines the oxygen blast furnace method and the top gas circulation method. Like other top gas circulation methods, it is a quasi-closed circulation method (semi-closed circulation method) in which the reducing gas blown into the furnace is limited to the top gas derived from the reducing materials (coke and fuel blown from the tuyere), and a part of the top gas is discharged to the outside of the system as residual gas. The input carbon amount (the carbon amount in the reducing materials including coke and fuel blown from the tuyere) is only reduced by about 24% compared with the conventional blast furnace method (Non-Patent Document 2).

[0084] As a countermeasure to global warming, in the two latest blast furnace methods being developed in Japan (non-patent documents 4 and 5), even with the use of CCUS (Carbon Capture, Usage and Storage), the CO2 reduction is still only about 30% compared to the conventional blast furnace method. If the CCUS effect is removed, the reduction is about 10%, and the coke ratio is within the operating range of the conventional blast furnace, about 300 to 350 kg / tp.

[0085] As mentioned above, in order to reduce the coke ratio and reduce CO2, methods have been developed in the past to improve the operation of the traditional blast furnace method and to replace the traditional blast furnace method with an oxygen blast furnace method or a top circulation method. However, there is still no reasonable process proposal that can reduce the coke ratio to below 200kg / tp (in terms of thermal material balance and Rist model), which is the biggest issue of the blast furnace method.

[0086] The operational issue in reducing the coke ratio is the gas permeability in the furnace. Figure 1 As shown, the blast furnace includes a furnace body 1 and a tuyere 2, and ore and coke as raw materials are alternately fed into the furnace to form a block belt 8 in which ore layers 8a and coke layers 8b are stacked in layers. Hot air and fuel are blown from the tuyere 2 to form a wind path zone (hereinafter also referred to as RW) 3, and gas 3a derived from RW generated while reacting with coke rises in the lower part 11 of the furnace. As the raw material descends in the vertical furnace 12, the temperature continues to rise, and the ore is reduced. When it reaches about 1100°C, the ore begins to soften. When it reaches about 1200°C, the ore further softens and begins to melt. Finally, it melts at 1400 to 1500°C to form a liquid flow 5 that drips in the dripping zone 10 and the furnace core 6, and comes to the hearth 15 as slag and molten pig iron 7 (refer to Figure 2). The soft melt layer 9a, which is a collection of softened and molten ores, has poorer air permeability than the ore layer 8a, but the coke (coke slits 9b) sandwiched between the soft melt layers functions as a grate to form a flow path for the gas 3a from the RW, thereby maintaining the air permeability of the soft melt zone 9 (the collection of the soft melt layer 9a and the coke slits 9b). Moreover, the center-feed coke 8c is actively fed to the center of the furnace, thereby ensuring the airflow 4c at the center of the furnace and maintaining the shape of the soft melt zone in an inverted V shape.

[0087] In low coke ratio operation, as the ore / coke ratio (O / C ratio) increases, the thickness ratio of the soft melt layer in the soft melt zone increases, and the thickness ratio of the coke opening decreases. Therefore, the reduction of the permeability of the soft melt zone is a major issue.

[0088] The problems of the present invention can be solved by the following means.

[0089] In an apparatus that effectively ensures the residence time (reaction time) of the raw materials in the vertical furnace, in addition to the coke fed from the furnace top or the fuel blown from the tuyere or both, reducing gas (CO, H2) preheated to above 800°C is blown into the lower part of the vertical furnace and the furnace below it in an amount that satisfies equations (3) and (4) per mole of iron (Fe) in the pig iron, so that the reduction rate of the ore just above the soft melting zone approaches 100%.

[0090] It should be noted that the preheated reducing gas calculated above does not include the preheated reducing gas to be blown to the middle part of the shaft furnace and above it. In addition, the required residence time in the shaft furnace is expressed by the so-called shaft furnace production efficiency Psh (t raw material / day·m 3 ; When arranging the indicators of raw material processing capacity per unit vertical furnace volume), the following formula must be satisfied.

[0091] Psh=(Pd×MR) / Vsh≦12(tRaw material / day·m 3 )…(5)

[0092] Vsh: Effective furnace volume of vertical furnace (m 3 )

[0093] Pd: Daily pig iron production (tp / day)

[0094] MR: Raw material ratio fed from the furnace top (t / tp)

[0095] Even if the residence time and the amount of reducing gas are sufficient, the actual gas reduction rate may still vary due to the reducibility of the ore, the gas permeability of the shaft furnace, etc. Therefore, in order to manage the gas reduction rate, the amount of reducing gas is adjusted so that the total gas amount of CO2 and H2O in the furnace top gas per ton of iron (Fe) in pig iron is Vpc (Nm3 / t-Fe) is within the range of the following formula (range of K value).

[0096] Vpc=K2×Gy / 1.5+Xf×22.4+Xo…(6)

[0097] 610≧K2≧560…(7)

[0098] K2: A constant determined by the direct reduction rate and the iron ratio in pig iron

[0099] Gy: The ratio of oxygen (mol-O) to the iron content (mol-Fe) of the feed ore and the feed metallic iron (mol-O / mol-Fe)

[0100] Xf: Total molar ratio of CaCO3 and MgCO3 contained in the feed raw materials per ton of pig iron (kmol / tp)

[0101] Xo: The amount of secondary combustion gas (CO2, H2O) supplied to the furnace above the 2 / 3 height from the top (1 / 3 height from the bottom) of the vertical furnace (Nm 3 / tp)

[0102] The reducing gas may be recycled after dust removal, H2O removal and CO2 removal from the blast furnace top gas, or may be introduced from outside the system without recycling hydrogen, carbon monoxide, etc. The present invention is characterized in that, since the fuel ratio in the lower part of the furnace is low and in order to prevent nitrogen (N2) from being concentrated due to circulation, in addition to the top gas, reducing gas (including reducing gas produced from combustible fuel) from outside the system is also actively utilized.

[0103] These reducing gases (hereinafter also referred to as gases blown from the tuyere) are preheated to a high temperature of 1200 to 1350°C and blown into the furnace from the tuyere. However, due to the high blowing temperature, in the high temperature area of ​​the heater that preheats the gases blown from the tuyere, part of the combustible fuel such as methane is burned (CH4+0.5O2=CO+H2), or part of the furnace top gas (CO2, H2O) is subjected to gas reforming (CH4+CO2=2CO+2H2, CH4+H2O=CO+3H2), thereby also achieving an improvement in the reduction degree and increase in the amount of the reducing gas.

[0104] By the above method, the gas reduction rate can be made close to 100%, and the energy required for the lower part of the furnace will be reduced. However, in order to further reduce the coke ratio and fuel ratio, the key points are: suppressing the reaction heat (coke gasification reaction) of the lower part of the furnace, the input of cooling fuel such as methane, and reducing the gas generation amount in the lower part of the furnace. As an indicator, it is important to set the total heat of the primary combustion heat in the lower part of the furnace (the heat of CO and H2 formation from coke and fuel blown from the tuyere) and the sensible heat of the gas blown from the tuyere (that is, the total heat supplied to the lower part of the furnace) to 2.4GJ / tp or less (preferably 2.2GJ / tp or less) per ton of pig iron. The specific method is listed below.

[0105] Two or more tuyere groups are arranged in the height direction of the furnace body, and the total amount of oxygen (O2) and secondary combustion gas (CO2, H2O) blown from (at least) the lowest tuyere is 200Nm 3 / tp or less oxygen-containing gas, and blow 500×(1-Xm) from the lower part of the vertical furnace and the tuyere below it 1.3 Nm 3 / tp or more reducing gas (total amount of CO and H2), and the total amount of CO and H2 containing the aforementioned reducing gas and the hydrogen component in the fuel blown from the tuyere is 800×(1-Xm) 1.3 Nm 3 Wherein, Xm: the ratio of metallic iron (mol-Fe) to all iron components (mol-Fe) in the raw materials fed from the furnace top.

[0106] As the fuel blown from the tuyere, "hydrocarbon fuel (CiHjOk; representing the components excluding ash (Ash)) in all forms (gas, liquid, solid) that satisfy the following formula" or "fuel composed of metal monomers (Si, Ca, Al, Mg, Fe, Si, Mn, C) or their alloy irons that constitute pig iron and slag" is used alone or as a mixture of two or more types together with oxygen.

[0107] j / i≦2.3…(8)

[0108] (16×k) / (12×i+j+16×k)≦10%...(9)

[0109] When combustible fuel (fuel blown from the tuyere) and preheated reducing gas (gas blown from the tuyere) are blown together from the blast furnace tuyere, an amount of oxygen in the range of more than (Vo2-1)(O2-kmol / tp) and less than (Vo2+0.2)(O2-kmol / tp) molar amount calculated by the following formula for each ton of pig iron is supplied as pure oxygen (or oxygen with a purity of more than 90%).

[0110] Vo2=0.5×(C1+C2-C3-C4+S1+S2-O1-O2)+S3+1.5×S4…(10)

[0111] C1: The amount of C component in the fuel blown from the tuyere (C-kmol / tp)

[0112] C2: carbon molar amount in coke (C-kmol / tp)

[0113] C3: carbon molar amount in pig iron (C-kmol / tp)

[0114] C4: The carbon molar amount required to reduce metals other than iron in pig iron (C-kmol / tp)

[0115] O1: The amount of O in the fuel blown from the tuyere (O-kmol / tp)

[0116] O2: The molar amount of CO2 and H2O in the preheated reducing gas (kmol / tp)

[0117] S1: Mg component not combined with oxygen in the fuel blown from the tuyere (Mg-kmol / tp)

[0118] S2: Ca component that is not combined with oxygen in the fuel blown from the tuyere (Ca-kmol / tp)

[0119] S3: Si component that is not combined with oxygen in the fuel blown from the tuyere (Si-kmol / tp)

[0120] S4: Al component not combined with oxygen in the fuel blown from the tuyere (Al-kmol / tp)

[0121] It should be noted that the amount of oxygen is set to a range of -1 (O2-kmol / tp) to +0.2 (O2-kmol / tp) relative to the molar amount Vo2 (O2-kmol / tp) calculated according to the formula (10) in order to adjust Vo2 according to the gas reduction rate and the carburizing condition. The amount is set to be greater than -1 (O2-kmol / tp) because the gas reduction rate is assumed to be 100% to 92%, and the amount is set to be less than +0.2 (O2-kmol / tp) to prevent excess oxygen from worsening the carburizing of pig iron.

[0122] Hereinafter, embodiments of the present invention will be described.

[0123] As described in the background art, in a general blast furnace, about 30% of coke consumption is related to direct reduction reactions, and about 40% is related to the reaction of H2O and CO2. Therefore, the key points to reduce coke consumption are: (1) increasing gas reduction reactions (reducing direct reduction reactions); (2) preventing H2O and CO2 from being mixed from the outside into the high-temperature area of ​​900 to 1000°C or above in the furnace; and (3) ensuring that the amount of heat and gas supplied to and generated in the lower part of the furnace is sufficient relative to the external heat output (pig iron heat, slag heat, heat loss) from the lower part of the furnace (soft melting zone and below). Here, 900 to 1000°C or above is set because it is a temperature at which the coke gasification reaction with carbon (C) is particularly active from about 900°C to above 1000°C.

[0124] Incidentally, the relationship between gas reduction, direct reduction and fuel can be easily determined by the Rist operation diagram, which is one of the most reliable equilibrium diagrams in blast furnace operation. The Rist operation diagrams of the conventional blast furnace (example) described in the following examples and the Rist operation diagrams of Example 1 of the present invention are shown in FIG. Fig. 20 and Fig.21 It should be noted that, on the operation line diagram, CO and H2 in the gas blown from the tuyere are counted as fuel blown from the tuyere on the Y axis (O+H2).

[0125] The direct reduction rate (Yd) of a conventional blast furnace (for example) is 30%. To reduce it to 0%, the W point (the point where FeO reduction starts) is fixed, and the Fig. 20 The operating line is shown by the dotted chain line in the middle. The slope of the operating line shows the mole of [C+H2] per mole of [Fe], so the conventional blast furnace (example) that does not use reducing gas is an indicator proportional to the fuel ratio. Therefore, compared with the current situation (Yd = 30%), the fuel ratio (coke, PCI) must be greatly increased, which is counterproductive from the perspective of economic efficiency and fuel ratio reduction. Reducing the direct reduction rate itself cannot achieve the goal of conventional operation.

[0126] The top gas circulation method based on the oxygen blast furnace corrects the inclination of the operating line not only by the fuel ratio but also by the top gas (reducing gas), thereby increasing the degree of freedom of the operating line. If the fuel ratio is the same, the operating line will rise according to the amount of top gas blowing, which will reduce the direct reduction rate (Yd). However, since the development goal is to reduce the fuel ratio, and since the fuel ratio will decrease as the top gas blowing increases (Yd increases), the top gas circulation amount will also decrease due to the reduction in the fuel ratio (Yd increases), and its optimal point will change.

[0127] From the perspectives of fuel ratio reduction, tuyere protection under oxygen combustion, furnace top temperature, economy, etc., the optimal operating line has undergone various studies, but to date (including conventional methods) there is still no actual research report (literature) with Yd=0% as the goal and method.

[0128] The operating line of the present invention ( Fig.21 ) is the "maximum slope (fuel ratio + reducing gas ratio)" when Yd = 0% is used to make the W point and the vertical furnace efficiency fixed. The fuel ratio of the present invention (see Tables 4 to 7) is much lower than any previous method, so the so-called "maximum slope" is greater than any other method in the same type of fuel in terms of reducing gas ratio (basic unit of gas blown from the tuyere).

[0129] This tendency is also confirmed in the gas (V13) blown from the tuyere in Tables 4 to 7 showing many examples of the present invention. In Examples 1 to 8 without metallic iron feed, the amount of gas blown from the tuyere is 700 Nm 3 / tp or more. The reason why Example 7 is as low as 564Nm 3 / tp is because ethylene (C2H4) containing a large amount of H2 is used as fuel, and H2 is blown to the lower part of the furnace in a simulated manner. Therefore, the H2 component in the fuel blown from the tuyere is regarded as reducing gas, and when converted as "V13 + fuel blown from the tuyere [H2]", 890Nm 3 / tp of reducing gas, which is more than 8 times that of the conventional blast furnace (example). It should be noted that all Examples 1 to 8, including the example of metal iron input (metal input rate Xm), have a conversion value of 800×(1-Xm) 1.3 Nm 3 / tp and above.

[0130] In the present invention, for every 1Nm 3 The top gas of the furnace is heated to a high temperature by adding fuel (external fuel) and oxygen that match the following formula. This allows the CO2 and H2O remaining in the gas to be reformed (converted into CO and H2), and the amount of gas (CO and H2) blown from the tuyere can be increased arbitrarily by primary combustion (partial oxidation) of the external fuel without being limited by the amount of top gas.

[0131] [O2](kmol / Nm 3 )=FRh / 2×([C]-[CO2]-[H2O]-FRh×[0])…(11)

[0132] FRh(kg / Nm 3 ): for 1Nm 3 Fuel ratio of top gas added

[0133] [CO2](kmol / Nm 3 ): CO2 composition in top gas

[0134] [H2O](kmol / Nm 3 ): H2O composition in the furnace top gas

[0135] [C] (kmol / kg): C content in fuel

[0136] [O] (kmol / kg): O content in fuel

[0137] It should be noted that when hydrogen or carbon monoxide is used as the external fuel, oxygen is not required at all according to equation (11). Alternatively, all of the furnace top gas may be an external fuel mainly composed of hydrogen.

[0138] A major feature of the present invention is that regardless of the amount and composition of the top gas (including the case where no top gas is used), high-quality reducing gas can be supplied to the furnace in the required amount at any time, thereby greatly improving the gas reduction rate in the vertical furnace (maximum 100%) in equilibrium theory.

[0139] As a result of repeated case studies as shown in the embodiments described below regarding the amount of gas (reducing gas) blown from the tuyere to bring the gas reduction rate close to 100%, it was found that the appropriate amount is: regardless of the CO / H2 ratio of the reducing gas and the type of fuel, "for one mole of iron (Fe) in the pig iron, in addition to the coke fed from the furnace top or the fuel blown from the tuyere, or both, the reducing gas (CO, H2) in the amount shown in the following formula is blown to the lower part of the vertical furnace and below it at a temperature of 800°C or above."

[0140] It should be noted that the preheated reducing gas that satisfies equations (3) and (4) does not include the preheated reducing gas blown to the middle part of the shaft furnace and above it. This is because preheating or reduction of FeO is carried out in the furnace in the middle part of the shaft furnace and above it, and it is a region exceeding the W point (rate control point of gas reduction) on the Rist model. It is set to be above 800°C because although the W point (the point where FeO reduction starts) temperature is determined by the heat balance between gas and ore under countercurrent, when the ratio of oxygen blast furnace (high heat flux ratio) and hydrogen reduction (endothermic reaction) increases, the W point moves to the low temperature side, so the gas temperature of 800°C is still effective depending on the blowing position.

[0141] In order for the above formula to hold, it is necessary to ensure the required raw material residence time (reaction time). 3 ; The raw material processing capacity per unit vertical furnace volume) must at least satisfy formula (5).

[0142] Psh≤12 is an index value derived by the inventor of this case based on the production efficiency of general direct reduction equipment. Its reciprocal multiplied by the bulk density of raw materials is the residence time of the shaft furnace. The Psh of a traditional blast furnace is 6 to 8 (t raw material / day·m 3 ) or so, compared with direct reduction equipment, the production efficiency (residence time) itself has no problem. In the present invention, the coke ratio is much smaller than that of the traditional blast furnace, and the vertical furnace production efficiency per unit of pig iron production is greatly reduced (i.e., the ore residence time and reduction time are prolonged). Therefore, if the present invention is applied to the traditional blast furnace, the vertical furnace production efficiency is 6 to 8 (t raw material / day·m 3 ) of the conventional blast furnace, there is room for increasing production, and the production efficiency (residence time) itself is not a problem. In the present invention, the coke ratio is much smaller than that of the conventional blast furnace, and the ore residence time (i.e., reduction time) in the same furnace volume is also greatly extended, so there is room for increasing production when the present invention is applied to the conventional blast furnace.

[0143] As for the method of producing the gas blown from the tuyere from the fuel, for example, as a synthesis gas production technology for methane, the steam reforming method for gas reforming H2O, the dry reforming method for gas reforming CO2, and the partial oxidation method of methane (primary combustion) have also been put into practical use. Among these, there are methods of reacting at 600 to 900°C using a catalyst (catalytic partial oxidation) and methods of reacting at 1200 to 1300°C or above using a catalyst-free method (thermal partial oxidation). In the present invention, the reducing gas is finally blown to the tuyere at high temperature, so there are advantages in thermal efficiency and equipment for reacting at high temperature. From the perspective of catalyst cost and maintenance, it is better to use a catalyst-free method. In any case, there is the problem of coal ash generation caused by methane, but by using a regenerative furnace such as a blast furnace hot blast furnace (using the alternating cycle of the heat storage process of the combustion exhaust gas and the gas preheating process), it is easy to remove the coal ash through the oxidizing gas (CO2, H2O, O2) in the combustion exhaust gas.

[0144] Regarding the time point of blowing the fuel into the gas, there is no process restriction when the fuel is CO or H2, but when the fuel is hydrocarbon gas, liquid fuel, or solid fuel, in order to suppress the generation of coal ash and promote primary combustion and gas reforming, the reducing gas will be heated to above 600°C before blowing. Furthermore, in the absence of a catalyst, from the perspective of combustion efficiency (preventing the generation of coal ash), it is better to blow at 1000 to 1200°C or above. However, in order to improve the preheating effect, the coal ash can be removed by using the combustion exhaust gas, so the fuel must be blown before it is sufficiently close to the heater outlet.

[0145] As for the form of heater, in order to preheat the reducing gas to above 1000°C, a regenerative heater (regenerative furnace) whose gas contact surface is made of refractory is preferred, such as a blast furnace hot blast furnace. When a hot blast furnace is converted to an oxygen blast furnace, since a hot blast furnace is not required, it is easy to convert the hot blast furnace to a reducing gas heater in terms of gas processing volume and processing temperature, which is also an advantage of improving the process of the traditional blast furnace method.

[0146] The fuel of the heater of the present invention is the same as that of the conventional hot blast furnace, and it is preferred to utilize the blast furnace top gas. Even in the case of a pure oxygen blast furnace, since the top gas contains N2 (derived from the raw fuel and facilities), it will be concentrated if the top gas is recycled, so a structure is required to actively extract it to the outside of the circulation system. Although there is also a method of sending it to equipment outside the system in the form of residual gas as in the past, it will contain CO and the CO2 must be dispersed, so it is most appropriate to use the gas heating fuel in the heater that is ancillary equipment of the blast furnace. When used as a heating fuel, as long as it is separated before the CO2 separation equipment, for example, and the exhaust gas is dehumidified after the oxygen combustion near the oxygen excess rate 1 (complete combustion), the CO2 concentration can be close to 100% even without passing through the CO2 separator, and the capacity burden and operation burden of the CO2 separation equipment can be reduced.

[0147] By the way, it is common to blow natural gas or other fuel directly into the furnace as fuel from the tuyere without converting it into reducing gas. However, when reducing the coke ratio, the treatment of the hydrogen component in the blown fuel becomes a problem. For example, methane will produce 35.8MJ / Nm due to complete combustion. 3 The heat generated by the combustion will be reduced to 1.6MJ / Nm. 3 , and the combustion temperature is only about 400°C. That is, the reducing gas (CO, H2) produced by the primary combustion of methane and oxygen forms a strong cooling gas relative to the wind path temperature above 2000°C, which will deteriorate (increase) the coke ratio and the fuel ratio (fine pulverized coal, etc.) blown from the tuyere. When preheating methane as a countermeasure, coal ash will be generated at above 600°C due to the cracking phenomenon (CH4→C+2H2) and cause problems.

[0148] The same problem applies not only to methane, but also to fuels (gas, liquid) with low primary combustion heat (heat generation when generating CO and H2), and are not suitable for fuels blown from the tuyere in the CO2 reduction era (carbon reduction trend). The same is true for room temperature hydrogen, which acts as a strong cooling gas for the temperature of the wind path area. In order to use these fuels as blast furnace fuels in the CO2 reduction era, the fuel addition method described above is the most effective. Since the heat of these fuels can be supplemented (additional heating can be performed) by the heater, the heat balance of the lower part of the furnace is quite excellent.

[0149] Gas reforming technology is a well-known technology, and using a hot blast furnace to heat reducing gas is not a new concept. However, the present invention is characterized in that it clearly integrates the roles of furnace top gas, fuel outside the system, and fuel for gas heating, and is a system that supplies high-quality and sufficient reducing gas for achieving 100% gas reduction as gas blown from the tuyere.

[0150] Based on the above, methods and strategies for ensuring the gas quantity and gas quality required to make the gas reduction rate in the furnace close to 100% are further explained.

[0151] Next, a method for burning fuel and coke in a high-temperature region below the soft melting zone will be described.

[0152] The conventional tuyere fuel blowing is to blow oxygen that is close to complete combustion, so that CO2 and H2O from secondary combustion actively react with coke around the wind path area to produce reducing gas. Patent document 1 recommends that when pulverized coal is blown at a rate of less than 170 kg / tp, the excess oxygen rate should be greater than 1. Here, it is defined as: (excess oxygen rate) = (the amount of oxygen in the air, pure oxygen, and pulverized coal blown from the tuyere) / (the amount of oxygen required to burn carbon and hydrogen in the pulverized coal into CO2 and H2O).

[0153] When pure oxygen is used instead of hot air, it is also necessary to pay attention to the fact that the combustion temperature is prone to abnormally high temperatures due to the absence of N2. Under the same oxygen excess rate as in conventional blast furnaces, abnormal flame temperatures at the front end of the tuyere are inevitable. For example, countermeasures such as "blowing H2O, CO2, and iron ore from the tuyere at the same time to reduce the temperature at the front end of the tuyere that is abnormally high due to oxygen combustion" have been reviewed (Patent Document 3). However, blowing H2O and CO2 will cause coke gasification reaction (endothermic reaction), which will lead to increased coke consumption and increased heat consumption in the lower part of the furnace, so it should be avoided strategically.

[0154] The strategy of the present invention will be described in detail later, but the feature of the present invention is that the combustion of fuel in the wind path area is suppressed to primary combustion (= reducing the excess oxidation rate), so that the combustion temperature can be greatly suppressed even in pure oxygen operation. Furthermore, the gas (reducing gas of CO, H2) blown from the tuyere at 1200 to 1250°C that is not burned in the wind path area is blown in an appropriate amount together with the fuel blown from the tuyere, so that the ignition property of pulverized coal and carbon fuel can be improved, and its maximum combustion temperature can be appropriately managed.

[0155] It is known that the combustion efficiency of pulverized coal will decrease as long as the excess oxygen rate is reduced, but if the oxygen concentration (oxygen partial pressure) is increased, the combustion efficiency will increase significantly (Non-Patent Document 1, Non-Patent Document 9). Furthermore, due to the oxygen combustion of pulverized coal in the air path space, turbulent diffusion becomes the speed control, rather than chemical reaction and gas boundary film diffusion, and it is also possible to achieve 100% primary combustion due to the intensified stirring of pulverized coal and oxygen (Non-Patent Document 11). That is, under oxygen combustion, the combustion efficiency of the primary combustion of pulverized coal in the air path space can be fully set to be equal to or higher than that of a conventional blast furnace (hot air) (50% to 70%).

[0156] In contrast, in conventional blast furnaces, even if the combustion efficiency of pulverized coal in the wind path area is far less than 100%, there is no substantial obstacle in operation. That is, the so-called "combustion efficiency of pulverized coal in the wind path area <100%" means that unburned char, CO2, and H2O flow out of the wind path area, but the gasification reaction rate of unburned char with CO2 and H2O is faster than that of coke (Non-Patent Document 13), and the reaction rate with molten carbon in dripping metal is several times faster (Non-Patent Documents 6, 7), so the presence of these (unburned char, molten carbon) can effectively inhibit the consumption of coke.

[0157] As the unburned carbon in the furnace gas moves forward in the dripping zone, it is washed by the metal / slag that pours down more violently than any heavy rain on the earth in terms of volume conversion (washing effect), and then passes through the soft melting zone with narrow gaps (filtering effect). In these processes, the unburned carbon is captured and carburized in the metal or returns to the lower part of the furnace. Moreover, as stated in non-patent document 10, "the unburned carbon is consumed in the carburizing and coke gasification reactions, and the carburizing rate becomes the speed control of the unburned carbon supply. The pulverized coal blowing of about 200 kg / tp cannot reach the speed control of the carburizing rate", it acts as a reduction reaction material for CO2 and H2O. That is, the consumption of coke is suppressed by the recovery of unburned carbon, and the combustion efficiency of the lower part of the furnace is close to 100%.

[0158] The above phenomenon (capture and consumption of unburned charcoal in the furnace) has also been confirmed in conventional blast furnaces, but in the present invention, as described later, "the amount of gas in the furnace bosh can be reduced to 1 / 2 to 1 / 3 compared with that in conventional blast furnaces, so the washing effect is increased" and "the ratio of the amount of gas passing through the coke openings (large filter mesh) in the soft melt zone is reduced from about 90% (Table 2) in conventional blast furnaces to about 40% (Table 2) to 0% (when all coke is mixed and fed)", so the outflowing char from the wind path area will be captured and consumed again, and the overall combustion efficiency of the lower part of the furnace can reasonably be expected to be higher than that of conventional blast furnaces.

[0159] The above is not limited to pulverized coal, but also common to other fuels blown from the tuyere. By blowing high-temperature reducing gas and ignition materials (metal powders such as Mg, Ca, Si, Al, etc., deoxidizing materials such as CaC2, FeSi, etc.) together with fuel and oxygen, the ambient temperature before the fuel is ignited is increased, which can further improve the ignition performance and combustion speed.

[0160] Here, the concept of "heat balance in the lower part of the furnace (from the soft melting zone to the furnace bottom)", which is one of the important elements of the present invention, will be described.

[0161] Fig.14 The heat input and heat output of the lower part of the blast furnace including the soft melting zone are shown. In terms of heat input, it is: the heat Qm1 of the raw materials (ore, coke, etc.) coming from the vertical furnace, the heat Qgr of the RW gas (gas from the wind path zone), and the heat Qk of the coke primary combustion due to the solid oxygen in the raw materials; in terms of heat output, it is: the heat Qmt of the slag, the heat Qcg of the gas flowing out of the soft melting zone, and the heat Qm3 consumed by the reaction in the lower part of the furnace, heat loss, etc.; 0 = Qm1 + Qcg-Qmt-Qgr-Qm3. It should be noted that regarding the reduction of FeO (direct reduction) in the lower part of the furnace, the heat balance can be considered to be established by the following two reactions.

[0162] FeO = Fe + 0.5 × O2; the heat of reaction (endothermic) is contained in Qm3

[0163] C + 0.5 × O2 = CO; the heat of reaction (heat generation) is included in Qk

[0164] Below, with Fig.15 This figure shows the heat exchange between the gas and the raw material in the lower part of the furnace. The vertical axis represents temperature, the horizontal axis represents heat capacity ratio (kJ / K·tp), and the area (= temperature × heat capacity ratio) in the figure shows the heat ratio (kJ / tp). It should be noted that metals other than iron (metalloids) are also reduced in the lower part of the furnace, but the heat of reaction per ton of pig iron is less than other heat, so it is not necessary to explain the heat balance ( Figures 14 to 17 ) can be ignored. Also, the specific heat of gas (kJ / Nm 3The influence of the gas composition change of (K) is not significant, so Cg is set to be fixed.

[0165] Qgr and Qk are supplied at the lower part of the furnace. Heat other than the heat Qcg (=Qg1 + Qk) discharged together with the gas at temperature Tcg to the shaft furnace, i.e., (Qg2 + Qg3 + Qk2), will be transferred to the lower part of the furnace by heat transfer. The heat transferred by heat transfer is used for the heat Qm2 to heat the ore from the softening zone inlet temperature Tcs to the tapping slag temperature Ti, and the heat consumption Qm3 (FeO decomposition heat, melting heat, carburizing heat, heat loss) at the lower part of the furnace. Qm2 and the raw material heat Qm1 brought into the softening zone together form the iron slag heat Qmt.

[0166] Reducing the coke ratio and fuel ratio aims to reduce the RW gas heat. Among Fig.15 them: 1) reducing the heat consumption Qm3 at the lower part of the furnace; 2) increasing the heat Q1 (temperature Tcs) of the raw materials brought into the lower part of the furnace; 3) reducing the gas outflow heat Qcg (=Qg1 + Qk1) from the lower part of the furnace. Qcg (=Cg·Vg·Tcg) is the ineffective heat at the lower part of the furnace (= the heat that will not be transferred by heat transfer), and it can effectively reduce the softening zone passing gas ratio Vg (= RW gas ratio Vgr + the gas ratio from direct reduction). Regarding the method of reducing Vgr (=Qgr / Tg), it is effective to reduce the RW gas heat Qgr and increase the RW gas temperature Tg.

[0167] Fig.16 Shows the heat balance at the lower part of the traditional blast furnace and the furnace of the present invention.

[0168] In the present invention where the gas reduction rate is close to 100%, since the FeO decomposition heat (FeO = Fe + 0.5×O2) at the lower part of the furnace and the primary combustion heat Qk' of coke due to solid oxygen are not required, the heat consumption (reaction heat, heat loss, etc.) Qm3 = Qg3 + Qk2 >> Qm'3 = Qg'3 + Qk'3 at the lower part of the furnace. Since the ore softening temperature of the present invention is about 100°C higher than that of the traditional blast furnace, i.e., Tcs < Tcs', the heat Qmr = Qm2 + Qm3 required at the lower part of the furnace of the present invention will be significantly reduced.

[0169] Furthermore, since the softening zone passing gas ratio Vg >> Vg', the gas heat carried out from the lower part of the furnace Qcg = Qg1 + Qk1 >> Qcg' = Qg'1 + Qk'1. As a result, the total heat of the primary combustion heat Qk of coke due to solid oxygen and the RW gas heat (inlet sensible heat and primary combustion heat) Qgr of the present invention will be significantly reduced. That is, the present invention can further reduce the fuel ratio at the lower part of the furnace.

[0170] Here, consider the change in the lower furnace heat balance (lower furnace heat transfer amount Q) when the gas (such as CO, H2, etc.) blown from the tuyere with a gas volume V and temperature T is mixed with the fuel blown from the tuyere and blown. Before and after the mixing of the gas blown from the tuyere, if the temperature Tcg of the outflow gas from the lower furnace remains unchanged, the lower furnace heat transfer amount Q will increase by ΔQ = (T - Tcg) × V due to gas mixing. If T < Tcg, ΔQ will be negative (the main reason for fuel increase), so it is not ideal.

[0171] Even if T ≥ Tcg, the RW gas temperature (Tg) will decrease, so attention must be paid. Fig.17 The Reichardt diagram of the lower furnace of the present invention is shown by a solid line. Keeping the effective heat transfer amount (Qg’2 + Qg’3) of the lower furnace fixed, if the RW temperature Tg’ decreases, the gas operating line will move from the solid line to the two-dot chain line, and the ineffective heat Qg’1 will increase. Therefore, for the same effective heat transfer amount, a higher RW temperature Tg’ (that is, a smaller RW gas volume Vg’) is more beneficial for reducing the coke ratio and fuel ratio. Furthermore, if Tg’ decreases and the slope of the gas operating line becomes gentler than the two-dot chain line and lower than point A in the figure, the raw materials cannot be heated up to the tap slag temperature Ti’ anymore, which will hinder the operation. The lower limit of the RW temperature Tg’ during operation when the slag temperature Ti’ = 1500 °C also depends on the lower furnace heat loss and is about 2000 °C.

[0172] The heat Qh required for the lower furnace (=Qm2 + Qm3) is the heat required for raw material heating, melting, reaction, carburization, and heat loss as described above. In the present invention, the iron ore will be reduced by nearly 100% in the shaft furnace, so the reduction reaction in the lower furnace is limited to metals other than iron (such as P, Si, Mn, etc.). Therefore, although the heat Qh required for the lower furnace varies depending on the slag ratio, pig iron temperature, slag composition, and furnace body heat loss, it is still 700 to 1200 MJ / tp (650 to 950 MJ / tp excluding heat loss), which is about 1 / 3 compared with 2500 to 3500 MJ / tp of a traditional blast furnace.

[0173] As described above, from the perspective of the lower furnace heat balance, a major feature of the present invention is also to improve the process so that the heat required for the lower furnace and the gas volume passing through the softening-melting zone are significantly reduced compared with a traditional blast furnace, thereby significantly reducing the coke ratio and fuel ratio.

[0174] Hereinafter, the temperature distribution of the gas and raw materials passing through the softening-melting zone will be sorted out from the perspective of the heat flow ratio and shown in Fig.19 (Calculated value when the coke ratio ≒ 60 kg). In the softening-melting zone, when the gas volume V passing through is 750 Nm 3 / tp, the heat flow ratio = 1, and the temperatures of the gas and raw materials show a parallel line change with a difference of about 25 °C. When V = 500 Nm3 / tp, the heat flow ratio is >1, forming a convex temperature change downward, and the temperature of the gas and the ore are consistent on the low temperature side (just above the soft melting zone). On the other hand, V = 1000Nm 3 / tp, the heat flow ratio is <1, forming a convex temperature change upward. On the low-temperature side (directly above the soft melting zone), the temperature difference between the gas and the ore is about 50°C.

[0175] The temperature difference between the gas and the ore on the low temperature side is Fig.15 , Fig.16 The temperature difference between Tcg and Tcs described above will be ineffective heat as heat input to the lower part of the furnace. Fig.19 In order to reduce the heat input to the lower part of the furnace, V = 500Nm 3 / tp, at least V ≤ 750Nm 3 It should be noted that if the coke ratio increases, the heat capacity ratio (kJ / tp·K) of the raw material will increase by an amount corresponding to the increase in the coke ratio, so the gas volume V that is balanced with the heat flow ratio will also increase. When the coke ratio is 200kg / tp, V = 900Nm 3 / tp.

[0176] In addition, if the ore is heated to high temperature, it will soften, the porosity will decrease, and the air permeability resistance will increase. Assuming that the softening starting point of the 100% gas-reduced ore is 1350°C and the melting point is 1450°C, the longer the residence time and the higher the average temperature per unit residence time, the worse the air permeability will be. Therefore, from the perspective of the air permeability of the so-called soft melting layer, a heat flow ratio of ≧1 is preferred, which can shorten the residence time at high temperature.

[0177] Associated with the above features, Fig.18 The relationship between the input heat (Qk+Qgr) other than the sensible heat of the ore in the lower part of the furnace and the required heat Qh of the lower part of the furnace is shown in the comparison between the conventional blast furnace and the present invention. Regarding the input heat (Qk+Qgr) in the lower part of the furnace, it is assumed that the solid line represents the range in which the effect of the present invention can be fully exerted before the gas reduction rate is about 95%, and the dotted line represents the case where the gas reduction rate is 100%. The input heat and gas amount in the lower part of the furnace are strongly related to the fuel ratio in the lower part of the furnace, but they are greatly reduced in the present invention. Examples 1 to 8 of the present invention described later are various fuel and reducing gas compositions, but all are within the area within the dotted line.

[0178] Fig. 22 and Fig.23Each is a heat diagram comparing a conventional blast furnace (example) and the present invention (Example 1). The heat (GJ / tp) on the vertical axis represents the enthalpy change of the raw material and gas in the furnace (that is, the amount of heat transfer between the two), and the horizontal axis represents the temperature of each. From these comparisons, it can be seen that the amount of heat transfer in the lower part of the furnace in the present invention is much smaller than that in the conventional blast furnace.

[0179] In the present invention, as described above, the combustion temperature is appropriately suppressed in pure oxygen operation by suppressing the primary combustion of the C component in the fuel. On the other hand, the temperature of the wind path zone (RW) must be ensured to be above 2000°C. That is, the fuel used in the lower part of the furnace must be selected as "a fuel that makes the primary combustion temperature due to oxygen reach above 2000°C". As described above, for example, the primary combustion temperature of methane is only about 400°C, so it is not suitable as a fuel blown from the tuyere. Coal also has a large amount of internal water and adsorbed water, and the primary combustion temperature will be lowered by the decomposition heat of water, so it is not suitable as a fuel for the lower part of the furnace.

[0180] If the fuel used in the lower part of the furnace is hydrocarbon fuel (CiHjOk; representing the components without ash (Ash)), equations (8) and (9) must be satisfied. It should be noted that j / i in equation (8) and (16×k) / (12×i+j+16×k) in equation (9) are preferably lower.

[0181] That is, in order to reduce the coke ratio and fuel ratio, hydrocarbon fuels with a high carbon content are effective in the lower part of the furnace. The main reason is that a higher primary combustion heat can be obtained, which contradicts the recent so-called hydrogen reduction blast furnace (a general term for blast furnace methods that mainly use hydrogen to reduce CO2). The combustion in the lower part of the furnace of the present invention is characterized by: by using a fuel with a high primary combustion heat, secondary combustion is deliberately reduced and retained in the primary combustion as the main body, so as to avoid the abnormal combustion temperature at the front end of the tuyere caused by pure oxygen, and at the same time effectively increase the effective heat transfer amount in the lower part of the furnace.

[0182] It should be noted that, in addition to hydrocarbon fuels, it is also extremely beneficial to use oxygen combustion of "metal monomers (Si, Ca, Al, Mg, Fe, Si, Mn) or their alloy irons that constitute pig iron and slag" as the fuel used in the lower part of the furnace. Since no by-product gas accompanying combustion is generated, it can be blown from the tuyere together with an appropriate amount of gas blown from the tuyere to produce RW gas of any desired temperature. Moreover, the by-products of these fuels are iron slag components, which have no effect on the quality of iron slag, which is of course the reason for selecting these fuels.

[0183] According to the components of the fuel blown from the tuyere, sufficient oxygen required for combustion to CO (primary combustion) or oxidation combustion of the metal fuel is blown together with the fuel. That is, it is characterized in that according to the components of the fuel blown from the tuyere, oxygen calculated by the following formula is blown per ton of pig iron.

[0184] [O2]f=0.5×(C1+S1+S2-O1)+S3+1.5×S4…(12)

[0185] [O2]f: The amount of oxygen blown by the fuel blown from the tuyere (O2-kmol / tp)

[0186] C1: The amount of C component in the fuel blown from the tuyere (C-kmol / tp)

[0187] O1: The amount of O in the fuel blown from the tuyere (O-kmol / tp)

[0188] S1: Metal Mg content in the fuel blown from the tuyere (Mg-kmol / tp)

[0189] S2: Metal Ca content in the fuel blown from the tuyere (Ca-kmol / tp)

[0190] S3: Metal Si content in the fuel blown from the tuyere (Si-kmol / tp)

[0191] S4: Metal Al content in the fuel blown from the tuyere (Al-kmol / tp)

[0192] In iron ore, in the case of hematite (Fe2O3), each ton of Fe contains about 300 Nm 3 Oxygen (O2), in a conventional blast furnace (direct reduction rate is about 30%), about 85Nm 3 / tp of solid oxygen directly consumes carbon materials by direct reduction. In the present invention, as described above, the gas reduction rate can be stably kept close to 100%, so coke is not consumed by direct reduction. Therefore, as shown in the following formula, the oxygen required for burning coke in the lower part of the furnace can be calculated by deducting the carbon required for carburization of pig iron and reduction of metal components other than iron in pig iron (Si, Mn, P, etc.) from the coke ratio.

[0193] [O2]c=0.5×(C2-C3-C4)…(13)

[0194] [O2]c: The molar amount of oxygen blown corresponding to the coke (O2-kmol / tp)

[0195] C2: carbon molar amount in coke (C-kmol / tp)

[0196] C3: carbon molar amount in pig iron (C-kmol / tp)

[0197] C4: The carbon molar amount required for the reduction of metals other than iron in pig iron (C-kmol / tp)

[0198] Therefore, in the present invention, the amount of oxygen Vo2 (O2-kmol / tp) blown from the tuyere at the bottom of the furnace becomes as shown in the following formula, which is the sum of the two formulas ([O2]f+[O2]c).

[0199] Vo2=0.5×(C1+C2-C3-C4+S1+S2-O1)+S3+1.5×S4…(14)

[0200] The present invention is characterized in that the consumption of carbon materials and oxygen due to the direct reduction of iron, which is necessary in a conventional blast furnace (due to the oxidation reaction of carbon materials by solid oxygen in the ore), is not taken into account in the calculation; furthermore, compared with a conventional blast furnace, the coke ratio is extremely small, so [Q2]f>>[O2]c. In the embodiments described later, in embodiments 1, 4 to 8 other than embodiments 2 and 3 in which fuel is not blown from the tuyere, [O2]c=0.

[0201] It is not easy to 100% manage the quality of the reducing gas blown from the tuyere, and as a result, H2O and CO2 may remain in the gas blown from the tuyere to some extent. Whenever H2O and CO2 (assuming a total of O2 kmol / tp) are blown from the tuyere, a corresponding amount (O2 kmol / tp) of coke is consumed, and the carbon content in the pig iron is reduced, so the following countermeasures are taken.

[0202] 1) Similar to O1 in equation (14), reduce the oxygen blown from the tuyere by O2 / 2 (kmol / tp).

[0203] 2) Increase the O2 (kmol / tp) of the fuel blown from the tuyere in a manner consistent with the carbon content.

[0204] The above measures all use the carbon in the fuel blown from the tuyere to reform CO2 and H2O into CO and H2 in a high temperature furnace (≧2000°C), thereby suppressing coke consumption. In addition, equation (14) can be converted into the following equation to cope with the above measures.

[0205] VO2=[O2]f+[O2]c…(15)

[0206] [O2]f=0.5×(C1+S1+S2-O1-O2)+S3+1.5×S4…(15-1)

[0207] [O2]c=0.5×(C2-C3-C4)…(15-2)

[0208] As mentioned above, the abnormal temperature rise at the front end of the tuyere in the oxygen blast furnace is suppressed, and the wind path (RW) temperature must be maintained at an appropriately high temperature. The RW temperature here refers to not only the combustion of the fuel blown from the tuyere, but also the equilibrium gas temperature including the cooling of the gas blown from the tuyere, the coke gasification reaction with the surrounding coke, and the combustion.

[0209] The gas discharged from the RW has the function of transferring the heat (high-grade heat) required to generate and maintain high temperature of pig iron and slag to the material. 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 must be at least higher than the material temperature; Fig.17 In the present invention, the temperature is controlled at about 2000°C or above (assuming that the slag temperature is 1500°C), so even if the reducing gas at the blowing tuyere is preheated to 1300°C, it will relatively play the role of cooling the gas compared to the RW temperature. Fig.17 Similarly, the amount of gas blown from the tuyere in the lower part of the furnace should be limited.

[0210] A method for resolving the seemingly contradictory phenomenon between the need to increase the amount of gas blown from the tuyere in order to promote gas reduction and reduce the reducing material ratio and the need to limit the amount of RW gas is to set multiple tuyere sections in the height direction.

[0211] For example, Figure 2 An example of an air port divided into two or more sections in the height direction is shown. Fuel and oxygen are blown from the first section air port (the lowest section air port) 2a, and preheated reducing gas is blown from the first section air port 2a disposed below the soft melting zone 9 in an amount that keeps RW at an appropriate temperature, and the remaining amount is blown from the second section air ports 2b to 2e disposed above the soft melting zone 9. This is a groundbreaking method that not only maintains the RW temperature at an appropriate temperature (2000 to 2600°C), but also changes the reducing gas distribution ratio for the "first section air port" to the "second section and above air ports" while maintaining a fixed temperature for the reducing gas, thereby adjusting the RW temperature and RW air volume, which are important factors for adjusting the furnace condition, without changing the thermal material balance (including the reducing material ratio) of the entire system. It should be noted that, if Figures 14 to 16 As explained, the temperature of the preheated reducing gas is preferably the ore temperature just above the soft melting zone (above 1200 to 1350°C).

[0212] Furthermore, the multi-stage tuyere system of the present invention has the effect of ensuring that the soft melting zone is in an inverted V shape like the center coke charging method, and therefore has the characteristic of ensuring the air permeability in the furnace.

[0213] like Figure 2The principle is that a high-temperature gas (2000 to 2600°C) is generated from the wind path area (RW) 3 formed by the first-stage tuyere 2a, a medium-temperature gas (1200 to 1350°C) is blown from the second-stage tuyere 2b, and a medium-low temperature gas (800 to 1100°C) is blown from the third-stage tuyere 2c. Inevitably, the gas 3a from the RW formed by the first-stage tuyere will rise on the furnace center side, and the gas 3c from the third-stage tuyere will flow on the furnace wall side, while the gas 3b from the second-stage tuyere will flow in the middle of the vertical furnace. That is, the gas temperature difference of the first-stage tuyere / second-stage tuyere / third-stage tuyere will be replaced by the temperature difference in the furnace radius direction.

[0214] Under the same gas composition, a higher gas temperature means a faster reduction reaction rate and a faster heating rate. Therefore, the ore on the furnace center side with a relatively higher temperature will reach the melting point at a faster time point than the ore on the furnace wall side with a relatively lower temperature. The ore lowering speed in the radial direction is roughly the same, so a faster time point means a higher position in the furnace (closer to the feed port). Conversely, the furnace wall side reaches the melting point at a slower time point, that is, at a lower position in the furnace (away from the feed port). Therefore, the soft melt zone forms an inverted V shape with excellent air permeability. Therefore, the shape of the inverted V shape and the temperature distribution in the furnace can be determined according to the temperature and air volume of each tuyere, the air volume ratio of the first tuyere / second tuyere / third tuyere, the temperature ratio, and the distance between the tuyere. (Refer to Figure 3 ).

[0215] Since a soft melting zone is to be formed between the first tuyere (the lowest tuyere) and the second tuyere, the second tuyere is placed close to the first tuyere, so that the soft melting zone can be fixed at the bottom of the furnace, thereby reducing the furnace height. On the contrary, under the same furnace height, a longer preheating zone and reduction zone can be obtained, thereby improving production efficiency. Figure 2 The "2b recommended setting range" shown in the figure is preferably from the middle position of the bell-shaped part (furnace belly) 14 to the upper end of the furnace belly "furnace center" 13. On the contrary, as mentioned above, in order to extend the gas reduction time (residence time) below 1000°C (preferably below 900°C), the third stage tuyere should be set at Figure 2 The "2c recommended setting range" shown is located above the "2b recommended setting range" of the lower part of the vertical furnace at the lower side of the middle part.

[0216] The above is an explanation of the three-stage tuyere, but from the main point of the explanation, it is clear that the two-stage tuyere can also achieve the same effect (the effect is somewhat different). The following is an explanation of the rationality of deliberately using the more complex third-stage tuyere on the equipment from the perspective of thermal balance.

[0217] First, the blowing temperature of the second stage tuyere is set to 1200 to 1350°C (preferably higher), because, as mentioned above, in order to reduce the heat consumption of the lower part of the furnace, the ore temperature is raised to a temperature close to the soft melting zone. Secondly, in terms of energy basic units, the furnace top temperature is preferably set as low as possible within the range where the gas does not condense, and most blast furnaces are operated at 120 to 180°C.

[0218] In the operation with 100% gas reduction rate, when the ratio of fuel and coke blown from the tuyere is determined, the soft melting zone passes through the gas ratio Vg (Nm 3 / tp) is also determined accordingly, so the amount of reducing gas (V23) blown from the second and higher tuyere ports can be uniquely determined according to the assumed vertical furnace efficiency from the Rist model operating line of 100% gas reduction rate.

[0219] From the perspective of heat balance in the lower part of the furnace, the best blowing temperature of the second stage tuyere is 1300 to 1350°C. Even so, in terms of the management of the furnace top gas temperature, the W point temperature (Tr), and the gas reduction end temperature, there is still a situation where it is desired to blow at a temperature (T23) lower than 1200°C (described later in Examples 1, 8, etc.). In this case, the three-stage tuyere is effective, and the gas volume V2 is blown at 1300°C (T2) from the second stage tuyere in the belly of the furnace, and the gas volume V3 is blown at a gas temperature (T3) lower than 1100°C from the third stage tuyere located in the lower part of the vertical furnace. The relationship between these gas volumes and temperatures, assuming that the specific heat is constant, is as shown in the following formula.

[0220] V23=V2+V3…(16)

[0221] T23×V23=T2×V2+T3×V3…(17)

[0222] However, the gas volume V2 of the second stage tuyere is managed so that the total gas volume (Vg+V2) with the gas ratio Vg passing through the soft melting zone becomes 750 to 1000 Nm according to the coke ratio. 3 / tp is better. This is because Fig.19 The explanation is also related to the heat flow ratio. If the heat flow ratio>1 (the heat flow of the gas is lower than that of the raw material), the raw material cannot be heated to the gas temperature of the second tuyere and the heat required in the lower part of the furnace will increase. Even if the heat flow ratio is ≦1, in order to lower the W point temperature (Tr) and the gas reduction end temperature, it is still better to have a smaller flow rate in the second tuyere.

[0223] Unlike gas reduction by CO, gas reduction by H2 is an endothermic reaction. Therefore, when the fuel blown from the tuyere or the gas blown from the tuyere contains a large amount of hydrogen (endothermic reduction), or when the coke ratio is high (increased heat flow ratio), the top gas temperature will decrease. In the case of such a fuel combination (Examples 2, 4 to 7), the blowing amount of the first stage / second stage tuyere is increased to increase the temperature of the top gas (as a result, the reducing gas increases, thereby reducing the efficiency of the shaft furnace), or the use of Figure 2 The ore is heated by the pre-reduction tuyere 2d and the raw material preheating tuyere 2e.

[0224] The preliminary reduction tuyere 2d is a tuyere set between point M (the reduction starting point of magnetite) and point W (the reduction starting point of wurtzite) on the Rist model. Figure 2 The "2d recommended setting range" shown is the range of ±1 / 6 of the shaft furnace height from the middle of the shaft furnace. Hydrogen reduction is an endothermic reaction, and the heat is provided by the gas. Therefore, when the fuel is rich in hydrogen, the temperature difference between the furnace top temperature and the W point temperature (Tr) will become larger. In order to suppress the increase of Tr, it is effective to prepare a reduction tuyere as a tuyere for supplying reaction heat and temperature rise heat.

[0225] The preliminary reduction tuyere only needs to be able to be reduced to the W point, so the reduction degree of the gas only needs to be above the magnetite reduction equilibrium. In the case of hydrogen-rich operation, the moisture content in the furnace top gas will increase, so as long as the furnace top gas is cleaned and cooled like a conventional blast furnace, it is easy to preliminarily dehydrate to increase the gas reduction degree. Therefore, the cleaned and cooled gas is recycled, and the gas partially burned by oxygen is blown from the tuyere. From the viewpoint of preventing coke gasification, the gas temperature of the preliminary reduction tuyere is set to be below 1000°C (preferably below 900°C).

[0226] The advantage of multi-stage tuyere is that it can be used in the process in particular: not only the furnace top temperature, but also the W point temperature (Tr) and the gas reduction end temperature can be adjusted specifically. In Example 1 described below, the third stage tuyere is used to suppress the reduction end temperature to 918°C (refer to Fig.23 In addition, in Example 1-2, the preparatory reduction tuyere is also used, so that the blowing amount of the first stage / second stage tuyere 2a, 2b can be reduced to the heat flow ratio 1 (the third stage tuyere is increased accordingly), and the W point temperature (Tr) and the reduction end temperature can be reduced by more than 100°C while maintaining the same furnace top temperature as in Example 1 ( Fig.23 a point chain line).

[0227] As described above, by reducing the blowing amount of gas from the first stage tuyere 2a and the second stage tuyere 2b and increasing the blowing amount of gas from the third stage tuyere 2c, and by controlling the gas flow rate, and the gas temperature and fuel supply amount, as shown in Example 1, the W point temperature (Tr) and the gas reduction end temperature can be reduced. Furthermore, by reducing the gas temperature of the third stage tuyere 2c, blowing gas from the preliminary reduction tuyere 2d, and controlling the blowing amount, as shown in Example 1-2, the W point temperature (Tr) and the gas reduction end temperature can be further reduced.

[0228] The operating system of this embodiment has a flow rate adjustment system and a control system for the gas blown from the tuyere. The flow rate adjustment system for the gas blown from the tuyere is composed of a plurality of airflow control units arranged in the height direction ( Figure 2 The control system is composed of three or more tuyere groups 2a, 2b, 2c, 2d which are separated and arranged (in the vertical direction) and flow measurement equipment and flow adjustment equipment of each of the tuyere groups. The tuyere groups 2a, 2b, 2c, 2d are each formed by a plurality of tuyere 2 which are respectively configured to blow reducing gas into the furnace body 1 of the blast furnace and are arranged at intervals in the circumferential direction of the furnace body 1. The control system is configured to measure the flow rate of the furnace top gas with a flow meter FI7, the oxidation degree of the furnace top gas with a component meter CA8 (except H2O) and a flow meter FI8, a thermometer TI8, and a pressure gauge PI8, the furnace top temperature with a thermometer TI7, the temperature of the middle part of the vertical furnace 12 with a thermometer TI5, and measure Figure 4 The gas composition CA9 and gas flow rate FI9 at the inlet of the middle heater and the gas composition CA11 and gas flow rate FI11 at the outlet of the heater are used to control the external fuel supply system for supplying the required amount of fuel and oxygen O2, the heating system including the heater 24, and the flow rate adjustment system of the gas blown from the tuyere. According to this operating system, the gas reduction rate can be increased to nearly 100%, and the gas amount, temperature, and fuel amount blown from the third-stage tuyere 2c and the preliminary reduction tuyere 2d can be controlled to appropriately maintain the furnace top temperature, and at the same time, the temperature control of the above-mentioned W point temperature (Tr) and the gas reduction end temperature is performed in the range of 600°C to 1000°C.

[0229] It should be noted that the flow rate measuring devices of each tuyere group constituting the flow rate adjustment system of the gas blown from the tuyere are respectively: Figure 4 The flow meter shown includes flow meter FI12 for measuring the flow rate of air outlet group 2b, flow meter FI13 for measuring the flow rate of air outlet group 2c, flow meter FI14, flow meter FI11 for measuring the flow rate of air outlet group 2a (excluding FI12 and FI13), flow meter FI5 for measuring the flow rate of air outlet group 2d, flow meter FI6, and mass flow meter WI6.

[0230] In addition, the flow rate adjustment device of each tuyere group of the flow rate adjustment system of the gas blown from the tuyere refers to: Figure 4 As shown, a flow control valve is provided on the downstream side of each flow meter.

[0231] It should be noted that the lower limit of the temperature range is set to above 600°C. This is because if the ore temperature is not above 600°C, it is difficult to substantially carry out the reduction reaction. The upper limit of the temperature range is set to below 1000°C. This is because if the temperature exceeds 1000°C, the coke gasification reaction will become active, so the temperature is controlled within this temperature range.

[0232] The raw material preheating tuyere 2e is a tuyere located at the upper 1 / 3 of the vertical furnace, which is closer to the vertical furnace than the preliminary reduction tuyere 2d, and is a tuyere for unexpected preliminary reduction, and is provided for the purpose of raw material preheating and furnace top temperature management. Since the gas reduction is unexpected, there is an advantage that the gas reduction degree of the gas to be used can be lower. It should be noted that, functionally, the preliminary reduction tuyere includes the raw material preheating tuyere, and particularly in hydrogen-rich operations, as described above, the advantage of using the preliminary reduction tuyere is greater.

[0233] In the conventional blast furnace method, it is self-evident that direct reduction is inevitable in the soft melting zone and below (the lower part of the furnace), but the presence of FeO in the lower part of the furnace means that gas reduction will also occur in this area, and the coke gasification reaction will inevitably occur, which is exactly the same as direct reduction in terms of thermal mass balance. The coke gasification reaction occurs inside the coke, so it is known that the important coke strength will be significantly deteriorated in the lower part of the furnace, and the coke degradation effect is greater than that of direct reduction. In any case, most of the oxygen blast furnace methods proposed so far do not teach a direct reduction rate of 0%, nor do they teach a method to suppress the gasification of coke during and after gas reduction.

[0234] A major feature of the present invention is that, as described above, by blowing fuel and reducing gas and managing furnace top gas, the coke gasification reaction is able to complete gas reduction at a temperature that is actually kinetically suppressible (about 900 to 1000°C or below), thereby making the gas reduction rate extremely close to 100%.

[0235] Hereinafter, the air permeability of the furnace body (soft melt zone, furnace belly to furnace bottom, and block zone) in the present invention will be described.

[0236] The air permeability (air permeation pressure loss) of the soft melting zone is determined by the amount of gas passing through the soft melting zone and the air permeation resistance of the soft melting zone in addition to the shape of the soft melting zone mentioned above. That is, reducing the amount of gas passing through the soft melting zone can reduce the air permeation pressure loss, and by reducing the air permeation resistance of the soft melting zone, the air permeation pressure loss can be reduced at the same gas amount.

[0237] Regarding the amount of gas passing through the soft melting zone, Figures 14 to 16It has been shown that the present invention can significantly reduce the air resistance compared with the conventional method. On the other hand, regarding the air permeability resistance of the soft melt zone, non-patent document 3 reveals that "(1) Due to the softening and shrinkage of the ore layer, the temperature at which the pressure loss begins to rise is greatly related to the ore reduction rate (if the ore reduction rate is close to 100%, it is >1300°C). (2) The pressure loss gradient (air permeability pressure loss per unit thickness) of the soft melt layer is greatly different in a conventional blast furnace with an ore reduction rate of about 70% and an oxygen blast furnace with a gas reduction rate of nearly 100% (the former will rise to 100 times the pressure loss gradient of the ore layer, but the latter will only rise to 10 times the pressure loss gradient of the ore layer)."

[0238] Regarding the above (1), in an oxygen blast furnace with multiple tuyere sections, a wind path zone of 2000 to 2600°C is formed at the front end of the first tuyere section. If the amount of gas required for a 100% gas reduction rate is blown from the second tuyere section at 1200 to 1350°C, a soft melting zone containing the ore softening point (about 1350°C) will be stably formed between the first tuyere section and the second tuyere section.

[0239] For the above-mentioned soft melting zone, due to the formation of temperature, the gas from the second stage tuyere does not pass through, and only the gas from the first stage tuyere (wind path area) flows. Furthermore, there is no nitrogen in the oxygen blast furnace, so the gas volume in the furnace is reduced, so for example, in Table 4, Figure 6 In the case of Example 1 shown in the figure, the amount of gas passing through the soft melting zone is about 500Nm 3 / tp, which is about 30% of the conventional blast furnace (example) in the table. On the other hand, the coke ratio (theoretical limit coke ratio required for carburization of pig iron and reduction of metals other than iron) of Example 1 is about 20% of that of the conventional blast furnace, and the ratio of coke openings in the soft melting zone is proportionally reduced.

[0240] The pressure loss gradient of the blast furnace filling layer can be expressed by the following formula (non-patent documents 6 to 8), which can also be applied to the ore layer, coke layer, coke slit, and soft melt layer.

[0241] ΔP / L∝ρ -1 ·K.G. 1.7 …(18)

[0242] ΔP: Pressure loss (Pa / m)

[0243] L: Layer height or gas passage length (m)

[0244] ρ: gas density (kg / m 3 )

[0245] G: Empty tower mass flow rate (kg / m 2 ·s)

[0246] K: Air permeability resistance index (see the table below; based on non-patent literature 3, 12, 14)

[0247] [Table 1]

[0248] Coke layer Ore Layer Soft melting layer Coke Slit Conventional blast furnace (example) 100 150 15000 100 Example 1 100 150(170*) 1500 100

[0249] *: About 3% coke lump mixed feed

[0250] According to formula (18), based on the gas flow rate of the soft melting zone of the conventional blast furnace (example) Figure 1 The pressure loss is calculated by calculating the sum of the gas 4a passing through the coke opening and the gas 4b passing through the soft melting layer, and the gas flow rate (Nm) passing through the soft melting zone of the present invention (embodiment 1) that will form the same pressure loss is calculated. 3 / tp), the results are shown in Table 2. It should be noted that the thickness L of the soft melting zone is Fig.19 For the same heat calculation, the thickness of the conventional blast furnace is twice that of the present invention. In addition, in the conventional blast furnace (example), 30 Nm is subtracted from the amount of top gas. 3 / tp as the gas originating from the coke gasification reaction above the soft melting zone.

[0251] [Table 2]

[0252] Soft melting layer Coke Slit sum Thermal mass balance Conventional blast furnace (example) 140 1450 1590 1590 Example 1 810 560 1370 500

[0253] When the pressure loss of the soft melt zone is the same as that of the conventional blast furnace (example), the coke opening flow rate of Example 1 will decrease according to the coke ratio, but the soft melt layer flow rate will increase significantly, so the total amount required for the thermal mass balance is 500Nm 3 / tp is about 2.7 times the gas flow. This means that if the required flow rate is achieved, the pressure loss will be reduced to 20% of that of a conventional blast furnace (for example) (according to formula (18)). It should be noted that the soft melt layer of the present invention is formed by ore with a reduction rate close to 100%, so it is possible to suppress the phenomenon that the molten material (low-melting point compounds of unreduced FeO) from the soft melt layer drips into the coke openings and hinders the air permeability, which is observed in conventional blast furnaces. Therefore, the air permeability is calculated using the thickness ratio of the coke openings.

[0254] As described above, the coke ratio is reduced to the limit in the present invention, so the ratio of the feed ore (O) with auxiliary raw materials to the feed coke (C) is O / C=28 in Example 1, which is also greatly different from O / C=5 in the conventional blast furnace (example). Therefore, the ratio of coke in the feed raw material C / (O+C) is 3.5wt% in Example 1, and the whole amount of (O+C) can be mixed and fed within the known range of the conventional mixed feed of ore and coke.

[0255] As is known to all, ore and coke mixed feeding is a method of mixing several % to 10% of small coke (C) in ore (O) in advance for the purpose of improving the permeability of the soft melting zone, etc. Examples of mixing non-small coke lumps are also disclosed in non-patent document 14, including physical properties, high temperature properties, feeding methods, etc.

[0256] The biggest advantage of coke slits is that they ensure the permeability of the soft melt zone, allowing the bosh gas (gas flowing into the soft melt zone) to bypass the soft melt layer with poor permeability and pass through the coke slits. On the other hand, since the main gas bypasses the soft melt layer, the heat exchange efficiency between the two becomes poor, and Fig.16 The disadvantage described above (increase in ineffective heat in the lower part of the furnace) is that the thickness of the soft melt layer increases due to poor heat exchange and increased pressure loss.

[0257] In the present invention, the coke ratio is low and the permeability of the soft melt layer is also high, so as shown in Table 2 described later, there is gas circulation in the soft melt layer with more than coke openings, thus greatly solving the shortcomings of the conventional blast furnace. Further development, so that the entire amount of the bosh gas passes through the soft melt layer becomes the full amount mixing method of the present invention.

[0258] Table 3 shows the pressure distribution (kPa) in the conventional blast furnace (example) and the pressure distribution in the furnace when the raw materials of Example 1 are fed in layers and when the raw materials are fed in full mixed form (without coke slits). It should be noted that the volume of the raw materials fed per ton of pig iron (m 3 / tp) will vary with the coke ratio. For example, Example 1 is 70% of the conventional blast furnace (example). Therefore, in order to fix the residence time of the block band, it is calculated at 70% of the block band height. In addition, it is difficult to correctly calculate the pressure loss in the dripping zone. Therefore, the pressure loss of the same part of the conventional blast furnace is set to 60 kPa, and the liquid retention rate in the packing layer can be used to expand the Ergun equation (non-patent document 7), simplify it to only the first-order term of the mass velocity, and compare the calculation with the conventional blast furnace. However, the calculation result of simplifying the pressure loss to only the first-order term of the mass velocity shown in Table 3 is a calculation method that will produce a calculation result that is more unfavorable to the calculation result of Example 1 compared with the result without simplification under comparative calculation.

[0259] [Table 3]

[0260] Block band (height) Soft melting zone Drip tape~RW total Conventional blast furnace (example) 100(16m) 40 60 200 Example 1 (Layered) 46(11m) 7 22 76 Example 1 (mixing) 53(11m) 8 22 83

[0261] The coke ratio of Example 1 is about 1 / 5 of that of the conventional blast furnace (example), but regardless of the feeding method, the air permeability is greatly improved compared to the conventional blast furnace (example), showing the superiority of the present invention. From another perspective, the reduction in air permeability pressure loss and the increase in residence time mean that there is room for increased production. If the present invention is directly applied to an existing blast furnace without changing the pressure and furnace height, the production can be increased by more than 40%. If the production can be increased by 40%, the heat loss ratio (MJ / tp) in the lower part of the furnace can be reduced by 30%, and the heat required in the lower part of the furnace will be reduced by a corresponding amount, and the fuel ratio can be further reduced (10kg / tp can be reduced in Example 1), which is also a great advantage from the perspective of CO2 reduction.

[0262] Incidentally, regarding the air permeability of the lower part of the furnace, in addition to pressure loss, preventing overflow (liquid splashing) is another important operating indicator. For conventional blast furnaces, the furnace is operated at a point slightly lower than the overflow limit curve (curve with a rightward slope) obtained by logarithmic expression of the overflow factor (vertical axis) and the fluid ratio (horizontal axis) (Non-patent Documents 7 and 8). If the gas superficial flow rate u0 (∝ gas ratio passing through the soft melt zone) decreases and the liquid superficial flow rate v0 (∝ pig iron ratio) is fixed, the fluid ratio (∝v0 / u0) will increase, but the overflow factor (∝u0 2 ) will decrease quadratically, so stable operation can be performed by moving away from the right-sloping overflow limit line at a slope twice as steep as the right-sloping overflow limit line.

[0263] In the present invention, since the gas flow rate in the lower part of the furnace is reduced to about 1 / 2 to 1 / 3 of that in a conventional blast furnace, an overflow-free operation is possible. In a conventional blast furnace, overflow is the main factor determining the iron-out ratio, but in this regard, the present invention can increase the iron-out ratio compared to a conventional blast furnace.

[0264] Figure 4 The method of keeping the gas reduction rate close to 100% and properly controlling the fuel and oxygen is shown. The measurement items are as follows (the numbers in brackets are Figure 4 The measuring instrument number corresponds to the measuring instrument number).

[0265] (1) [O] content in iron ore, [CO2] content in auxiliary raw materials (CA_1) and input speed (WI_1)

[0266] (2) [C] [H] [O] composition in coke (CA_2) and input speed (WI_2)

[0267] (3) Pig iron temperature (TI_3) and [C] composition (CA_3)

[0268] (4) [C] [H] [O] composition (CA_4) and injection speed (WI_4) of the fuel blown from the tuyere, and oxygen flow rate (FI_4)

[0269] (5) The furnace temperature below the preliminary reduction tuyere (TI_5) and the furnace top gas recirculation flow rate for the tuyere (FI_5)

[0270] (6) Preliminary reduction: [C] [H] [O] composition (CA_6) of the fuel blown from the tuyere, injection speed (WI_6), and oxygen flow rate (FI_6)

[0271] (7) Furnace top gas flow (FI_7) and temperature (TI_7), gas pressure (PI_7)

[0272] (8) Furnace top gas flow (FI_8) and temperature (TI_8), gas pressure (PI_8), and gas composition (CA_8) after dust removal and dehumidification

[0273] (9) Top gas flow (FI_9) and gas composition (CA_9) after CO2 separation

[0274] (10) [C] [H] [O] composition (CI0_10) and injection speed (WI_10) of the fuel mixed in the furnace top gas, and oxygen flow rate (FI_10)

[0275] (11) Heater outlet gas flow rate (FI_11), temperature (TI_11), pressure (PI_11), [CO2] composition (CA_11)

[0276] (12) Gas flow rate blown from the second tuyere (FI_12)

[0277] (13) High-temperature gas flow rate (FI_13) delivered to the third tuyere and temperature before blowing (TI_13)

[0278] (14) Flow rate (FI_14) and temperature (TI_14) of low-temperature gas delivered to the third tuyere

[0279] (15) Gas flow rate extracted from the furnace top to the outside of the system (FI_15)

[0280] Although it is not easy to directly measure the H2O component in the furnace top gas, the H2O component of the gas (8) can be obtained from the vapor pressure of the furnace top gas (after dust removal and dehumidification) (8), and the H2O ratio in the furnace top gas (7) can be determined from the molar flow rates of (7) and (8). As a result, the molar flow rates of CO, CO2, H2, H2O, and N2 to be discharged as the furnace top gas (7) can be determined while measuring the gas composition of (8). Therefore, by subtracting the CO2 and H2O generated from the combustion (6) and the auxiliary raw material (1), the molar flow rate X of CO2 and H2O generated by the reduction reaction of the furnace gas can be determined. On the other hand, the so-called gas reduction rate of 100% means that CO2 and H2O are produced by reducing the iron ore (that is, removing the oxygen in the iron ore) using only CO and H2. Since the molar flow rate Y of O (oxygen) in the iron ore can be determined by (1), the gas (9) flow rate (FI_9) and the fuel (10) injection rate (WI_10) can be adjusted using formulas (6) and (7) as feedback indicators so that the gas reduction rate is close to RDg=X / Y=1.

[0281] Here, the oxygen (10) flow rate (FI_10) is adjusted according to the molar flow rate of CO2 and the molar flow rate of H2O in the gas (9) after the CO2 separation device and the molar flow rates of C, H, and O in the fuel (9) according to formula (11) so that the quality of the gas after heating becomes optimal (consisting only of CO and H2).

[0282] Direct reduction ironmaking is an ironmaking method that only removes the gas reduction part of the blast furnace. The reduction rate of reduced iron (DRI, HBI) produced by the direct reduction method is not 100% (about 95% to 97%). The main reason is that although the gas reduction rate is faster as the temperature is higher, the ore temperature is suppressed to below about 900°C to prevent sticking. The present invention has no sticking limit and can reduce the gas to the temperature just above the soft melting zone (about 1300°C), so the ore with a reduction rate close to 100% can be supplied to the lower part of the furnace. However, if the final reduction is above 1000°C, coke gasification will occur due to CO2 and H2O produced by gas reduction. Therefore, before adjusting the furnace top temperature through the second / third stage tuyere flow rate, preliminary reduction tuyere, and raw material preheating tuyere, the apparent gas reduction rate cannot reach 100%.

[0283] In addition, achieving a gas reduction rate of 100% is not always a reasonable operation target. In particular, if the efficiency of the shaft furnace becomes low, the amount of external fuel and circulating gas increases, which in turn reduces the overall energy efficiency such as the sensible heat loss of the furnace top gas, the input heat of the heater, and the gas processing energy. Therefore, in parallel with the gas reduction rate RDg, the management of the shaft furnace efficiency is extremely important. Strict management of the shaft furnace efficiency is not easy, but the gas reduction rate of the present invention is high, so the shaft furnace efficiency has a strong correlation with the amount of furnace top gas, and in terms of operation, it is only necessary to manage the furnace top gas flow rate (FI_7), which can be easily performed.

[0284] On the other hand, the enthalpy flow rate Q7 (sensible heat and latent heat) of the top gas (7) can be calculated from the molar flow rates of CO, CO2, H2, H2O, and N2 of the top gas (7) and the top gas temperature (TI_7) obtained above. Similarly, the enthalpy flow rate Q11 (sensible heat and latent heat) of the heater outlet gas (11) can be calculated. Since the pig iron production energy amount Qnet of the blast furnace body including heat loss is determined, the required total enthalpy flow rate Qfuel of the fuel introduced into the furnace is uniquely determined as "Qfuel = Qnet + Q7-Q11". Here, Qfuel includes the latent heat flow rate Q4 from the introduction rate (WI_4) of the fuel (4) and the latent heat flow rate Q6 from the introduction rate (WI_6) of the fuel (6), and also includes the latent heat flow rate Q23 equivalent to the amount obtained by subtracting the molar flow rate of C melted in the pig iron (3) from the molar flow rate of C in the coke (2). That is, "Qfuel = Q4 + Q6 + Q23" is formed.

[0285] The heat required from softening to making pig iron and slag must be a high temperature (high-grade heat) of more than 2000°C, and is supplied as the primary combustion (Q4+Q23) of the first-stage tuyere fuel and coke. Moreover, the reduction reaction rate is faster as the temperature is higher. If the ore is not preheated to more than 600°C, it is actually difficult to react. Therefore, the coke (2) flow rate (WI_2) and the fuel (4) flow rate (WI_4) are adjusted so that the temperature (TI_3) of the pig iron (1), the carbon content (CA_3), and the temperature (TI_5) below the preheating tuyere (5) are the required values. At this time, the oxygen (4) flow rate (FI_4) is adjusted as shown in formula (10), and the distribution ratio of the first-stage tuyere to the second-stage tuyere and above is adjusted so that the temperature of the wind path area is appropriate.

[0286] Finally, adjust the temperature (TI_7) of the furnace top gas (7) and the temperature (TI_5) below the preliminary reduction tuyere (5) to the desired temperatures.

[0287] First, in the case of a combination of raw materials and fuels that will increase the furnace top gas temperature (in the case of a high carbon content), the preliminary reduction tuyere 2d is not used in principle. The heater outlet gas (11) temperature (TI_11) is kept at a high temperature, and only the first stage tuyere 2a / second stage tuyere 2b is used for blowing, and it is confirmed that the furnace top temperature is within an appropriate range. If the furnace top temperature and the temperature of the middle part of the vertical furnace (TI_5) are high, then Figure 4 As shown, the heater outlet gas and heater inlet gas are distributed to their respective flow rates (FI_13) and (FI_14) and then mixed and blown from the third stage tuyere 2c at a temperature (TI_13). Thus, the furnace top temperature (∝sensible heat loss of furnace top gas) and the temperature below the middle part of the vertical furnace (∝Tr temperature or final reduction temperature) can be lowered while the amount of blowing reducing gas remains unchanged.

[0288] Next, in the case of a combination of raw materials and fuel that will lower the furnace top temperature (in the case of a high hydrogen content), the preliminary reduction tuyere 2d is used instead of the third stage tuyere 2c. The required amount of reducing gas is blown from the first stage tuyere 2a and the second stage tuyere 2b, and the fuel (6) flow rate (WI_6) and oxygen (6) flow rate (FI_6) of the preliminary reduction tuyere are adjusted so that the furnace top gas (7) temperature becomes the required temperature, and the furnace top recirculation gas (5) flow rate (FI_5) is adjusted so that the mixed gas temperature from the preliminary reduction tuyere becomes 700 to 900°C. In the case of a high hydrogen content in the shaft furnace gas, by additionally supplying raw material preheating and preliminary reduction heat, it is effective to move not only the furnace top temperature but also the W point (the point where FeO reduction starts) on the Rist model to the right, and it helps to reduce the amount of reducing gas and lower the final reduction temperature (suppress the coke gasification reaction).

[0289] If the raw material preheating tuyere 2e is used (refer to Figure 2 ) is used together with the preliminary reduction tuyere 2d or in place of the preliminary reduction tuyere 2d, and hydrogen is used as fuel and is completely burned, and the water can be removed from the circulating gas by the dehumidifier (including the gas scrubbing cooler) in the rear stage, so the influence of the raw material preheating tuyere fuel can be limited to the furnace top to the dehumidifier. As described above, according to the present invention, even with a coke ratio and a fuel ratio far lower than those of conventional blast furnaces, stable and easy operation can be achieved.

[0290] [Example]

[0291] Tables 4 to 7 show the comparison of the basic units and temperatures of the examples of the present invention with those of the conventional blast furnace.

[0292] [Table 4]

[0293]

[0294] [Table 5]

[0295]

[0296] [Table 6]

[0297]

[0298] [Table 7]

[0299]

[0300] Respectively Figures 5 to 13 The conventional blast furnace examples shown in Tables 4 to 7, and the flow charts of Examples 1 to 8 (Examples 6 and 7 correspond to Fig.12 ). The numbers in the attached drawings show the basic units for producing one ton of pig iron (1000 kg), and form part of the basic units shown in Tables 4 to 7. Each basic unit is calculated using a thermal material balance model for each region including a Rist model and a heat balance calculation, but for the dehumidifier, CO2 separation device, gas reforming, and CO2 recovery equipment, the basic unit is calculated by setting the reaction efficiency to 100%.

[0301] Example 1 is an example of a final coke ratio in which the amount of coke used is limited to the amount of coke required for carburization and reduction of non-ferrous metals, and is an example of using graphite as a fuel. The top gas is used as a heating fuel for the heater, and hydrogen is used as a fuel mixed with the top gas in the heater 24 and a fuel for preheating raw materials, so that the carbon source transported into the system (= discharged outside the system) is set to only the minimum required coke.

[0302] After the furnace top gas is dusted, H2O is removed by a dehumidifier 21, CO2 is separated by a CO2 separation device 22, and the remaining components (CO, H2, N2) are sent to a heater 24. CO2 is sent to a CO2 recovery device 25 outside the system, and after being converted into CH4 by a methanation reaction (CO2+4H2=CH4+2H2O; exothermic reaction) not shown in the figure, it is converted into C (graphite) by a graphite conversion device (such as the HAZER process) not shown in the figure, and then fed into the furnace from the first stage tuyere 2a.

[0303] Heater 24 is similar to the conventional blast furnace example ( Figure 5) is a regenerative furnace similar to the hot blast furnace 23. For the heating fuel, in order to prevent the nitrogen contained in the coal and coke and the nitrogen mixed into the facility from being concentrated due to circulation, the top gas extracted from the rear section of the dehumidifier 21 is used. It is mixed with the combustion exhaust gas for the purpose of adjusting the flame temperature and oxygen combustion is carried out in the combustion chamber (not shown). It passes through the regenerative chamber (not shown) as a CO2-rich exhaust gas and passes through the dehumidifier 21 as needed, and is sent to the CO2 recovery equipment 25. N2, as an impurity gas, is discharged to the outside of the system through a carbonation liquefaction process (not shown), so N2 will not be concentrated in the entire system. After the top gas from the CO2 separation device 22 is pressurized by the gas compressor 31, it is preheated to a predetermined temperature through other preheated regenerative chambers (not shown) and supplied to each tuyere.

[0304] In the above, only the minimum necessary coke is input as fossil fuel, but the other fuels are supplied by recycled fuel and hydrogen. As long as the CO2 recovery equipment installed outside the system is included, the system will not emit any CO2 into the atmosphere.

[0305] In order to reduce the W point temperature (Tr) and the reduction end temperature to a lower level than that in Example 1, the blowing amount of the third and first stage tuyere is increased, the second stage tuyere is deleted, and a preliminary reduction tuyere is provided. Although the second stage tuyere is deleted to simplify the equipment, the first stage tuyere can be returned to 158Nm 3 / tp, blowing 250Nm to the second section of the tuyere 3 Since neither of the two examples assumes a coke gasification reaction, the amount of fossil fuel used in Example 1 is slightly lower in calculation, but due to the difference in the W point temperature (Tr) and the reduction end temperature, in actual operation, Example 1-2 may be more excellent.

[0306] As a method to lower the temperature of the third stage tuyere below the heater outlet temperature, Figure 7 The heater inlet gas and the heater outlet gas are mixed in the process, but if the hydrogen supply pressure is high, hydrogen can be directly mixed instead of the heater inlet gas.

[0307] Examples 1-3 to 1-5 are examples in which the fixed ratio of the ore in Example 1 is replaced with metallic iron (DRI, scrap) and the feed is carried out. Examples 1-3 and 1-4 are 20% metallic iron, and Example 1-5 is 36% metallic iron. Metallic iron does not require reduction and does not contain oxygen, so the heat capacity per ton of iron is small, so the heat flow ratio in the vertical furnace is reduced, which has the effect of offsetting the increase in heat flow ratio (vertical furnace) due to oxygen blast furnace and hydrogen reduction. In addition, it has the following characteristics: since reduction is not required, the amount of reducing gas in the vertical furnace (lump belt) can be reduced, but since the heat balance in the lower part of the furnace remains unchanged, the fuel ratio is almost unchanged.

[0308] Example 1-3 is the calculation result of replacing the iron ore of Example 1 with 20% metallic iron, and is also an example of a two-stage tuyere, but the W point temperature (Tr) is high (988°C) and the reduction end temperature exceeds 1000°C, so coke gasification reaction (= apparent direct reduction) is inevitable. In Example 1-4, in order to suppress the coke gasification reaction, the third stage tuyere and the preliminary reduction tuyere are used, and Tr=851°C and the reduction end temperature=890°C are set.

[0309] Embodiment 1-5 is an example of further increasing the metallic iron ratio. Even if the block strip is further cooled and all the preheated reducing gas is blown from the first / second stage tuyere so that Tr reaches the required temperature, the furnace top temperature will also drop, so a preliminary reducing tuyere is necessary.

[0310] Example 2 is an example in which the fuel (CO2 recovery fuel) blown from the tuyere of Example 1 is not used. As with the conventional blast furnace, since coke is used as a combustion heat source and a reducing gas generation source, the coke ratio is higher than that of Example 1, but compared with the conventional blast furnace (example) using 190 kg / tp pulverized coal, the coke ratio is reduced to 58%, and the fuel ratio (reducing material ratio) is reduced to 36%.

[0311] Example 3 is an example of changing the fuel in Example 2 from hydrogen to methane. In order to reduce CO2, the use of hydrogen is indispensable, but the use of hydrogen is difficult to carry out before the infrastructure such as hydrogen manufacturing equipment and transportation system is improved. Therefore, an example of using methane that is easily available and includes LNG is illustrated. In conventional blast furnaces and other methods (non-patent document 5), methane is directly blown into the furnace as tuyere fuel, but in this embodiment, it is partially burned in a regenerative heater (primary combustion; CO and H2 are generated) and mixed in the furnace top gas ( Fig. 9 ).

[0312] By using methane instead of hydrogen, the endothermic reaction is reduced more than in Example 2, and even with a two-stage tuyere, an appropriate furnace top temperature can be maintained, but it is found that the W point temperature (Tr) is as high as 966°C, so Example 3-2 shows an example of deliberately using a preliminary reduction tuyere to reduce Tr by more than 100°C. Although the coke consumption is less than that in Example 2, by using methane instead of hydrogen, the CO2 emission that eliminates the CO2 recovery effect is more than in Example 2, and can be reduced by about 46% compared to the conventional blast furnace example (Example 3-2).

[0313] The present invention is also applicable to the case where the furnace top gas is not recycled. Fig.10) is an example in which the tuyere gas of Example 1 does not utilize the top gas, but utilizes all external hydrogen. The top gas (main components are H2, H2O, CO, CO2) is used as a by-product gas via the gas cleaning cooler 21a and is used as a fuel for the power generation equipment 26 outside the system, and is discharged as H2O and CO2. The exhaust gas is removed from H2O by the dehumidifier 21 to form CO2 gas, and is converted into graphite (C) by the CO2 recovery equipment 25, and is reused as a fuel blown from the tuyere. The electricity generated by the aforementioned power generation equipment 26 is used in the hydrogen and oxygen manufacturing equipment 27 for manufacturing H2 and O2 required for the blast furnace. The formation of a system that does not emit all CO2 into the atmosphere is the same as Example 1, but is characterized in that, because the top gas is not recycled in the blast furnace, no CO2 separation equipment is required on the blast furnace side or outside the system.

[0314] The above embodiments are merely illustrative, showing examples of fuels that also utilize hydrogen (H2), methane (CH4), and graphite (C). However, in addition to the heavy oil, pulverized coal, and waste plastics that have been used in the past, it is self-evident that so-called combustible fuels such as biofuels, coke gas (COG), converter gas (LDG), CO2 conversion fuels (gas, liquid, solid), metal-based fuels, and coke powder can also be utilized.

[0315] Example 5 Fig.11 ) shows an example of using a metal fuel (powdered) prepared by blending metal magnesium (Mg), metal calcium (Ca), and metal silicon (Si) in a slag composition ratio.

[0316] An appropriate amount of gas blown from the tuyere is blown together with the metal fuel and oxygen from the lowest tuyere, thereby ensuring an appropriate temperature of the wind path zone (2383°C in Example 5) and supplying the necessary heat to the lower part of the furnace (the soft melting zone and the area below it). The iron ore is reduced by hydrogen supplied from the outside, and the hydrogen reduction rate is increased to nearly 100% (about 97%), becoming a hydrogen reduction blast furnace as described in the text. Since no coke or fossil fuel is burned in the furnace, almost no CO or CO2 is emitted from the top of the furnace (only the amount generated from the reduction of non-ferrous metals), so it is an embodiment of an epoch-making system that does not require CO2 separation equipment or CO2 recovery equipment.

[0317] In Example 5, in order to prevent the concentration of CO gas generated during the reduction of non-ferrous metals and a small amount of impurity gas (N2, etc.), a part of the furnace top gas is extracted as the heater combustion gas in the same way as in Examples 1 and 3. In this embodiment, since the CO2 content in the heater combustion exhaust gas is only a little (a few %vol), the gas will be emitted from the gas chimney 28, but a dehumidification device can also be set to recover CO2. In addition, although the furnace top gas is only a small amount, it still contains CO2, so CH4 is blown in the rear stage of the heater to reform the gas, thereby suppressing the coke gasification reaction based on CO2 in the lower part of the furnace.

[0318] It should be noted that since it is an endothermic reaction, the hydrogen reduction rate is as high as 97%. Therefore, in order to suppress the temperature drop of the block belt to promote the reduction reaction, the blowing amount of the second stage tuyere is increased (the efficiency of the vertical furnace is reduced), and the reducing gas from the preliminary reduction tuyere is further actively used. Through this operation, the heat flow ratio of the upper part of the vertical furnace is reduced to nearly 0.6, and the furnace top temperature will rise to some extent. However, since the hydrogen reduction rate is 97%, the reduction start temperature ≧650℃, the reduction end temperature ≦900℃, and the furnace top temperature ≦200℃ are achieved in terms of thermal material balance and equilibrium theory.

[0319] Examples 6 and 7 are examples of an open system that does not recirculate the top gas. The fuel blown from the tuyere is an example of using biofuel such as biocoke and biocoal, and an example of electronic fuel (E-Fuel) that uses environmentally friendly electricity to fuel CO2. These fuels regard the CO2 emission coefficient as zero (0), so the CO2 emission of the top gas is only calculated as the amount of non-ferrous metal reduction, so there is no need to recover CO2 when it is burned and discharged. The top gas has a calorific value that is easy to use (8500 to 8700 kJ / Nm in Examples 6 and 7). 3 ), so even in factories other than blast furnaces, it can be widely used as an alternative energy source by utilizing the existing gas supply network, which has the advantage of significantly reducing CO2 emissions from these factories.

[0320] Example 8 is an example of reducing the coke ratio and fuel ratio using only fuels (reducing materials) such as coke, pulverized coal (PCI), and methane (equivalent to natural gas) that are used in conventional blast furnaces. Pulverized coal can be mixed with bio-coke and bio-coal in any ratio to form a mixed fuel. If 100% biofuel is finally formed, the CO2 emission from the fuel blown from the tuyere will become zero (0). The same effect can be obtained by replacing the methane that is partially burned in the heater and converted into reducing gas with methane that has been recovered through CO2. The basic units of carbon (C) before and after the fuel conversion are recorded in sequence in the accompanying drawings.

[0321] In the fossil fuel-based embodiment 8, the amount of carbon discharged from the blast furnace to the outside of the system (without CO2 recovery) is 238 kg / tp, which is 381 kg / tp of the conventional blast furnace, and the CO2 emission can be reduced by about 40% (38%). Furthermore, if 1.7 to 1.8 kg of coal required to produce 1 kg of coke is added, the CO2 emission can actually be reduced by half (reduced by 50%).

[0322] The above embodiment is only an example, and the intermediate raw material utilization and system configuration of the embodiments 1 to 8 may also be combined. That is, according to the present invention, the options of raw materials and system configurations for reducing coke and CO2 are expanded without limit, which is a groundbreaking technology in itself, and the most appropriate system can be adopted by correcting the heat balance and material balance and considering the economic efficiency in response to the future development of CO2 storage / utilization technology as ancillary equipment.

[0323] The entire contents of Japanese Patent Application No. 2022-68527 (filing date: March 31, 2022) are cited here.

[0324] Several embodiments of the present invention have been described above, but these embodiments are examples of suggestions 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 changes can be made without departing from the gist of the invention. These embodiments and their variations are included in the scope and gist of the invention, and are also included in the invention described in the scope of the patent application and its equivalent.

[0325] Possibility of Industrial Application

[0326] The technology of the present invention can also be applied to reduced iron manufacturing equipment and iron melting furnaces (waste melting furnaces).

Claims

1. A method for operating a blast furnace in which, in addition to coke fed from a furnace top or fuel blown from a tuyere, or both, reducing gas preheated to 800° C. or higher is blown from a tuyere into the furnace, the method comprising: The production efficiency of the shaft furnace, i.e. (Pd×MR) / Vsh, is controlled to satisfy the inequality (Pd×MR) / Vsh≦12. in, Vsh: the vertical furnace in m 3 The effective furnace volume is Pd: daily pig iron production in tp / day, MR: raw material ratio fed from the furnace top in t / tp, The reducing gas is blown in such a manner that the amount of gas blown toward the middle portion of the shaft furnace and above the shaft furnace is such that the amount satisfies the inequality 3.9≧K1≧3.

1. in, For one mole of iron in pig iron, the formula (Cf+Cg-Ci)+(Hf+Hg) / 2=K1×(1-Xm) is satisfied. K1: constant that determines the fuel ratio, Cf: the amount of [C] in mol-C / mol-Fe calculated by adding the coke fed from the furnace top and the fuel blown from the tuyere, Hf: the amount of [H] in mol-H / mol-Fe calculated by adding the coke fed from the furnace top and the fuel blown from the tuyere, Cg: the amount of CO gas in the reducing gas in terms of mol-C / mol-Fe, Hg: the amount of [H] in the reducing gas in mol-H / mol-Fe, Ci: the amount of [C] in pig iron in mol-C / mol-Fe, Xm: The ratio of metallic iron in mol-Fe to all iron components in mol-Fe in the raw materials fed from the furnace top.

2. The operating method according to claim 1, wherein: Also includes: For each ton of iron in the pig iron, the CO2 and H2O in the top gas are expressed in Nm 3 / t-Fe total gas volume Vpc = K2×Gy / 1.5+Xf×22.4+Xo, The amount of the reducing gas is further adjusted to satisfy the inequality 610≧K2≧560, in, K2: A constant determined by the direct reduction rate and the iron ratio in pig iron. Gy: The ratio of oxygen in mol-O to the iron content in mol-Fe of the feed ore and feed metallic iron, which is expressed as mol-O / mol-Fe. Xf: The total molar ratio of CaCO3 and MgCO3 in kmol / tp contained in the feed raw materials per ton of pig iron, Xo: The secondary combustion gas supplied from outside the furnace at a position higher than 2 / 3 of the height from the top of the vertical furnace, that is, 1 / 3 of the height from the bottom, in Nm 3 / tp metered gas volume.

3. The operating method according to claim 1 or 2, wherein: Also includes: The total heat of the primary combustion heat in the lower part of the furnace and the sensible heat of the gas blown from the tuyere is set to less than 2.4 GJ / tp per ton of pig iron.

4. The operating method according to claim 1 or 2, wherein: Also includes: In the furnace body including the vertical furnace and the lower part of the furnace, more than two stages of the tuyere are arranged along the height direction; From the lowermost tuyere of the tuyere, a total amount of 200 Nm of oxygen and secondary combustion gas is blown. 3 / tp or less oxygen-containing gas; The reducing gas is blown in the following manner: 500×(1-Xm) is blown from the lower part of the vertical furnace and the tuyere below it. 1.3 Nm 3 / tp or more, and the total of CO and H2 including the reducing gas and the hydrogen component in the fuel blown from the tuyere is 800×(1-Xm) 1.3 Nm 3 / tp or above; in, Xm: The ratio of metallic iron in mol-Fe to all iron components in mol-Fe in the raw materials fed from the furnace top.

5. The operating method according to claim 3, wherein: Also includes: In the furnace body including the vertical furnace and the lower part of the furnace, more than two stages of the tuyere are arranged along the height direction; From the lowermost tuyere of the tuyere, a total amount of 200 Nm of oxygen and secondary combustion gas is blown. 3 / tp or less oxygen-containing gas; The reducing gas is blown in the following manner: 500×(1-Xm) is blown from the lower part of the vertical furnace and the tuyere below it. 1.3 Nm 3 / tp or more, and the total of CO and H2 including the reducing gas and the hydrogen component in the fuel blown from the tuyere is 800×(1-Xm) 1.3 Nm 3 / tp or above; in, Xm: The ratio of metallic iron in mol-Fe to all iron components in mol-Fe in the raw materials fed from the furnace top.

6. The operating method according to any one of claims 1 to 5, wherein: Also includes: At least a portion of the reducing gas is blown at 1200° C. or higher through the tuyere above the soft melting zone and the tuyere below the soft melting zone.

7. The operating method according to any one of claims 1 to 6, wherein: Also includes: Using hydrocarbon fuel, alloy iron, or a mixed fuel containing the hydrocarbon fuel and the alloy iron together with oxygen as the fuel blown from the tuyere; The hydrocarbon fuel has a chemical formula of C i H j O k When the ash content is removed, the following conditions are met: j / i≦2.3, (16×k) / (12×i+j+16×k)≦10%; The alloy iron contains one or more selected from Si, Ca, Al, Mg, Fe, Si, Mn, and C.

8. The operating method according to any one of claims 1 to 7, wherein: Also includes: Blowing oxygen into the furnace together with the fuel blown from the tuyere and the preheated reducing gas, The oxygen is oxygen with a purity of 90% or more and is calculated based on the oxygen content of each ton of pig iron. O2 = an amount in the range of -1 in terms of O2-kmol / tp to +0.2 in terms of O2-kmol / tp, in, [O2]f=0.5×(C1+S1+S2-O1-O2)+S3+1.5×S4 [O2]c=0.5×(C2-C3-C4) C1: the amount of C component in the fuel blown from the tuyere in C-kmol / tp, C2: molar amount of carbon in coke in C-kmol / tp, C3: molar amount of carbon in pig iron in C-kmol / tp, C4: The molar amount of carbon in C-kmol / tp required for the reduction of metals other than iron in pig iron, O1: the amount of O component in the fuel blown from the tuyere in terms of O-kmol / tp, O2: the molar amount of CO2 and H2O in the preheated reducing gas in kmol / tp, S1: Mg content in Mg-kmol / tp that is not combined with oxygen in the fuel blown from the tuyere, S2: Ca content in Ca-kmol / tp that is not combined with oxygen in the fuel blown from the tuyere, S3: Si component in Si-kmol / tp that is not combined with oxygen in the fuel blown from the tuyere, S4: Al component not combined with oxygen in the fuel blown from the tuyere, expressed as Al-kmol / tp.

9. The operating method according to any one of claims 1 to 8, wherein: Also includes: The entire amount of the coke fed from the furnace top is mixed with ore containing auxiliary raw materials and fed into the furnace.

10. An operating system for implementing the operating method according to any one of claims 1 to 9, the operating system comprising a flow rate adjustment system and a control system for the gas blown from the tuyere; wherein: The flow rate adjustment system of the gas blown from the tuyere is composed of three or more tuyere groups separated and arranged in the height direction of the furnace body of the blast furnace, flow rate measuring equipment of each tuyere group, and flow rate adjustment equipment of each tuyere group, each of the tuyere groups is composed of a plurality of tuyere respectively configured to blow reducing gas into the furnace body, and the plurality of tuyere are arranged at intervals in the circumferential direction of the furnace body; The control system is configured to control the external fuel supply system, the heating system and the flow rate adjustment system of the gas blown from the tuyere by measuring the furnace top gas flow rate, furnace top gas oxidation degree, furnace top temperature and the temperature of the middle part of the vertical furnace.

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