Method for operating a reduction furnace and method for producing reduced iron

Abstract

Provided is a method for operating a reduction furnace whereby it is possible to reduce the amount of natural gas used without significantly modifying existing equipment. In the method, an iron oxide and a solid hydrocarbon are loaded into a reduction furnace.

Description

Technical Field

[0001] The present invention relates to an operating method of a reduction furnace and a method for producing reduced iron.

Background Art

[0002] In recent years, in steelworks, due to global environmental problems and fossil fuel depletion problems, energy conservation has been strongly demanded. The raw material of iron is mainly iron oxide such as iron ore, and in a steelworks, a reduction process for reducing this iron ore is essential. The most common reduction process worldwide is the blast furnace. In a blast furnace, coke and pulverized coal react with oxygen in hot air (air heated to about 1200°C) at the tuyere. By this reaction, CO and H2, which become reducing gases, are generated, and the reducing gases reduce iron ore and the like in the furnace. Due to recent improvements in blast furnace operation technology, the reductant ratio (the amount of coke and pulverized coal used per ton of hot metal produced) has been reduced to about 500 kg / t, and the reductant ratio has already reached almost the lower limit. Therefore, no further significant reduction in the reductant ratio can be expected.

[0003] On the other hand, a method for producing reduced iron by a vertical reduction furnace (hereinafter also referred to as a shaft furnace) is also often used. In this method, the reduction furnace is filled with agglomerated iron ore such as sintered ore and pellets as an iron oxide raw material (hereinafter simply also referred to as iron oxide). Then, a reducing gas containing CO and H2 is blown into the reduction furnace to reduce the iron oxide and produce reduced iron. In this method, natural gas or the like is used as the raw material gas of the reducing gas. This raw material gas is heated and reformed in a reformer together with the top gas. Thereby, a reducing gas is generated. Here, the top gas is the gas after being used for reducing iron oxide in the reduction furnace, and is generally discharged from the top of the reduction furnace. The generated reducing gas is blown into the reduction furnace and reacts with the iron oxide supplied from the upper part of the reduction furnace. Then, the iron oxide is reduced to become reduced iron. Next, the reduced iron is cooled in a region lower than the position where the reducing gas of the reduction furnace is blown, and then discharged from the lower part of the reduction furnace.

[0004] As mentioned above, the top gas, which is the gas remaining after the reduction of iron oxide, is discharged from the top of the reduction furnace, for example. After dust collection and cooling, a portion of the top gas is supplied to the reformer as a raw material for reformed gas. The remaining top gas is used as fuel gas for the reformer. In this method, the top gas used as fuel gas for the reformer is usually discharged outside the system.

[0005] As an example of such a reduced iron production process, Patent Document 1 describes a method in which exhaust gas from a reduction furnace and natural gas are reformed in a reforming device to generate a reducing gas mainly consisting of CO and H2, and this reducing gas is blown into the reduction furnace to reduce the iron oxide inside the furnace and produce reduced iron.

[0006] Furthermore, Patent Document 2 describes a method for producing reduced iron by partially burning a carbonaceous raw material containing either or both biomass and waste plastic in addition to coal, or by partially burning coal (hereinafter also referred to as carbonaceous raw material, etc.) with oxygen to produce a reducing gas, and then blowing the reducing gas into a reduction furnace. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2017-88912 [Patent Document 2] Patent No. 4250472 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The method described in Patent Document 1 uses natural gas supplied from an external source for the production of reducing gas. Natural gas resources vary greatly depending on the region. Furthermore, because natural gas is a gas, transportation costs are higher than those for solids. Therefore, especially in regions with limited natural gas resources, there is a need to reduce the amount of natural gas used from the perspectives of both operational stability and cost reduction.

[0009] Furthermore, the method described in Patent Document 2 requires combustion equipment for partial combustion of carbonaceous raw materials. However, conventional shaft furnaces commonly used do not typically come equipped with such combustion equipment. Therefore, when manufacturing a reduction furnace using the method described in Patent Document 2, significant costs are incurred for additional equipment.

[0010] The present invention was developed in view of the above-mentioned circumstances and aims to provide a method for operating a reduction furnace that can reduce the amount of natural gas used without making significant modifications to existing equipment. The present invention also aims to provide a method for producing reduced iron by producing reduced iron using the above-mentioned method for operating a reduction furnace. In this disclosure, any numerical range expressed using "~" means a range that includes the numerical values ​​written before and after "~" as the lower limit and upper limit, respectively. [Means for solving the problem]

[0011] The inventors conducted various studies to solve the above problems and obtained the following findings. Specifically, by simultaneously charging solid hydrocarbons, particularly solid hydrocarbons with a volatile content of 40% by mass or more, into the reduction furnace in addition to iron oxide, and preferably by appropriately controlling the mass ratio of solid hydrocarbons to iron oxide charged into the reduction furnace, it becomes possible to reduce the amount of natural gas used without making significant modifications to existing equipment. The present invention was completed based on the above findings and further studies.

[0012] In other words, the gist of the present invention is as follows:

[0013] 1. A method for operating a reduction furnace, A charging step involves charging iron oxide and solid hydrocarbons into the aforementioned reduction furnace. A blowing step involves blowing a reducing gas containing CO and H2 into the aforementioned reduction furnace. In the reduction furnace, a reduction step is performed in which the iron oxide is reduced to obtain reduced iron, A method for operating a reduction furnace, comprising [a specific feature / function].

[0014] 2. The operation method of the reduction furnace according to claim 1, wherein the solid hydrocarbon is charged together with the iron oxide from the top of the reduction furnace.

[0015] 3. The operation method of the reduction furnace according to claim 1 or 2, wherein the mass ratio of the solid hydrocarbon to the iron oxide charged into the reduction furnace is 0.010 to 0.050.

[0016] 4. The operation method of the reduction furnace according to any one of claims 1 to 3, wherein at least one of biomass and plastic is used as the solid hydrocarbon.

[0017] 5. The operation method of the reduction furnace according to any one of claims 1 to 4, wherein a solid hydrocarbon having a volatile content of 40% by mass or more is used as the solid hydrocarbon.

[0018] 6. The operation method of the reduction furnace according to any one of claims 1 to 4, wherein a solid hydrocarbon having a volatile content of 40% by mass or more is used as the solid hydrocarbon, and the mass ratio of the solid hydrocarbon to the iron oxide charged into the reduction furnace is 0.020 to 0.045.

[0019] 7. A distribution step of distributing the top gas discharged from the reduction furnace into a first top gas and a second top gas, and A reforming step of obtaining the reducing gas from the raw material gas using the first top gas and the methane-containing gas as the raw material gas, and The operation method of the reduction furnace according to any one of claims 1 to 6, further comprising the above steps.

[0020] 8. A method for producing reduced iron by the operation method of the reduction furnace according to any one of claims 1 to 7.

Advantages of the Invention

[0021] According to the present invention, it is possible to reduce the amount of natural gas used without significantly modifying existing equipment.

Brief Description of the Drawings

[0022] [Figure 1] It is a schematic diagram showing an example of a manufacturing process of reduced iron.

Mode for Carrying Out the Invention

[0023] Hereinafter, an operation method of a reduction furnace according to an embodiment of the present invention will be described.

[0024] The operation method of a reduction furnace according to an embodiment of the present invention is a charging step of charging iron oxide and solid hydrocarbon into the reduction furnace, a blowing step of blowing a reducing gas containing CO and H2 into the reduction furnace, a reduction step of reducing the iron oxide in the reduction furnace to obtain reduced iron, and has Furthermore, optionally, a distribution step of distributing the top gas discharged from the reduction furnace into a first top gas and a second top gas, and a reforming step of obtaining the reducing gas from the raw material gas using the first top gas and the methane-containing gas as the raw material gas.

[0025] FIG. 1 is a schematic diagram showing an example of a manufacturing process of reduced iron to which the operation method of a reduction furnace according to an embodiment of the present invention can be applied. In the figure, reference numeral 1 is a reduction furnace, 1a is iron oxide, 1b is reduced iron, 3 is a dust removal device, 4 is a dehydration device, 5 is a methane-containing gas supply unit, 6 is an air supply unit, and 7 is a reforming device.

[0026] In the example of the reduced iron production process shown in Figure 1, iron oxide 1a is charged into the reduction furnace 1 from the top and gradually lowered. High-temperature reducing gas is then blown into the middle of the reduction furnace 1 to reduce the iron oxide 1a. Reduced iron 1b is then discharged from the bottom of the reduction furnace 1. At this time, top gas mainly containing CO, CO2, H2, and H2O is discharged from the top of the reduction furnace 1. This top gas is dust-removed by a dust removal device 3. Next, the top gas has its moisture content adjusted by a dewatering device 4, and a portion of it is sent to the reformer 7 as the first top gas. Along with the first top gas, methane-containing gas, such as natural gas, is supplied to the reformer 7. Next, the supplied gas is heated in the reformer 7. A reforming reaction occurs, and high-temperature reducing gas mainly containing CO and H2 is generated. This reducing gas is then blown into the reduction furnace. Furthermore, the remaining portion of the furnace top gas is used as a second furnace top gas, for example, as a heating fuel in the combustion chamber of the reformer 7. The second furnace top gas, after being burned as a heating fuel, is usually discharged outside the system while still containing CO2. Incidentally, when reduced iron is produced using this example of the previous manufacturing process, approximately 1 ton of CO2 is discharged outside the circulation system for every 1 ton of reduced iron produced.

[0027] Furthermore, in the operation method of a reduction furnace according to one embodiment of the present invention, it is important to charge the reduction furnace with solid hydrocarbons in addition to iron oxide. The charging process for simultaneously charging solid hydrocarbons in addition to iron oxide into this reduction furnace will be described below. The distribution process and the reforming process can be carried out according to conventional methods, for example, in the same manner as the manufacturing process described above, so their explanation will be omitted here.

[0028] ·Charging process In a method of operating a reduction furnace according to one embodiment of the present invention, solid hydrocarbons are simultaneously charged into the reduction furnace in addition to iron oxide. The solid hydrocarbons charged into the reduction furnace are heated as they descend within the furnace. In this process, the solid hydrocarbons undergo thermal decomposition or react with CO2 and H2O in the reduction furnace to become gaseous hydrocarbons, CO, H2 (hereinafter also referred to as gaseous hydrocarbons, etc.). The gaseous hydrocarbons, etc. are consumed in the reduction reaction of iron oxide within the reduction furnace. The gaseous hydrocarbons, etc. are also discharged as top gas and supplied to a reformer, for example, as a raw material for reducing gas or as a heating fuel. In other words, by reducing the amount of gaseous hydrocarbons, etc. generated from solid hydrocarbons within the reduction furnace, it becomes possible to reduce the amount of methane-containing gas, specifically natural gas, used as a raw material for reducing gas.

[0029] Here, the mass ratio of solid hydrocarbons to iron oxide charged into the reduction furnace ([solid hydrocarbons (kg / t-DRI)] / [iron oxide (kg / t-DRI)], hereinafter also referred to as solid hydrocarbons / iron oxide) is preferably 0.010 to 0.050. Here, kg / t-DRI is the unit consumption per ton of reduced iron produced. By setting the solid hydrocarbon / iron oxide ratio to 0.010 or higher, the effect of reducing the amount of natural gas used as a raw material for the reducing gas is enhanced. On the other hand, charging solid hydrocarbons into the reduction furnace may generate unreacted residue. Most of the small-sized residue is pushed out of the furnace by the rising gas inside the reduction furnace. In addition, some of the residue remains at the bottom of the reduction furnace and contributes to the carburization of the reduced iron. However, if a large amount of residue remains at the bottom of the reduction furnace, the discharge port for reduced iron from the reduction furnace may become clogged, which may reduce the reaction efficiency. Furthermore, if the reduced iron discharged from the reduction furnace contains a large amount of residue, a process to separate the reduced iron from the residue may be necessary. For this reason, it is preferable that the solid hydrocarbon / iron oxide ratio be 0.050 or less. More preferably, the solid hydrocarbon / iron oxide ratio is 0.015 or higher. More preferably, the solid hydrocarbon / iron oxide ratio is 0.045 or lower. In particular, when using solid hydrocarbons with a volatile content of 40% by mass or more, as described later, a solid hydrocarbon / iron oxide ratio of 0.020 to 0.045 is more preferable. The higher the volatile content of a solid hydrocarbon, the lower its specific gravity. Therefore, when using solid hydrocarbons with a volatile content of 40% by mass or more, setting the solid hydrocarbon / iron oxide ratio to 0.020 or higher can further enhance the effect of reducing the amount of natural gas used. On the other hand, solid hydrocarbons with high volatile content have a high water content, and excessive use of such solid hydrocarbons may hinder the heating of the raw materials charged into the reduction furnace at the top of the furnace. Therefore, when using solid hydrocarbons with a volatile content of 40% by mass or more, it is preferable to set the solid hydrocarbon / iron oxide ratio to 0.045 or less.

[0030] Furthermore, while there are no particular limitations on the types of solid hydrocarbons, examples include biomass, plastics, and coal. Among these, biomass is particularly advantageous because it is a carbon-neutral raw material, and using biomass as a solid hydrocarbon effectively reduces CO2 emissions from the manufacturing process by the amount used. Plastics can be new or used. Used plastics, conceptually, include waste plastics, plastics not intended for disposal, and factory scraps. Waste plastics, in particular, are a resource that should be actively utilized.

[0031] The properties of the solid hydrocarbon used are preferably such that the volatile content is 40% by mass or more (40-100% by mass). As mentioned above, the amount of natural gas used as a raw material for the reducing gas can be reduced by the amount of gaseous hydrocarbons generated from the solid hydrocarbon in the reduction furnace. Therefore, when the mass ratio of iron oxide to solid hydrocarbon is the same, using a solid hydrocarbon with a higher volatile content will increase the effect of reducing the amount of natural gas used. It is also advantageous in terms of transportation costs. Furthermore, it is advantageous in terms of reducing the residue that accumulates at the bottom of the reduction furnace. Accordingly, it is preferable to use a solid hydrocarbon with a volatile content of 40% by mass or more. It is even more preferable to use a solid hydrocarbon with a volatile content of 70% by mass or more, and even more preferably 85% by mass or more. The upper limit of the volatile content of the solid hydrocarbon is not particularly limited and may be 100% by mass. In addition to volatile content, the solid hydrocarbon contains ash and water, and the remainder is fixed carbon.

[0032] Furthermore, the volatile content of solid hydrocarbons should be measured in accordance with JIS M 8812:2006.

[0033] Furthermore, it is desirable to use solid hydrocarbons with a thermal decomposition temperature of preferably 900°C or lower, more preferably 700°C or lower. In addition, it is desirable to use solid hydrocarbons with a mass fraction of gangue components of preferably 5% or lower, more preferably 3% or lower.

[0034] Furthermore, the properties of biomass, plastics, coal, etc., particularly their volatile content, vary depending on their type and origin. Therefore, it is preferable to select, for example, solid hydrocarbons such as various biomass, plastics, and coal that have a volatile content of 40% by mass or more.

[0035] Furthermore, the method of charging solid hydrocarbons into the reduction furnace is not particularly limited, but for example, solid hydrocarbons can be charged into the reduction furnace simultaneously with iron oxide through the same charging port as iron oxide, preferably a charging port provided at the top of the reduction furnace.

[0036] [Blowing process] A reducing gas containing CO and H2 is blown into the reduction furnace. The gas composition of the reducing gas is, for example, CO: 1-60 volume%, H2: 40-99 volume%, and remainder: 0-30 volume%.

[0037] [Reduction Process] In the reduction process, iron oxide is reduced by a reducing gas to obtain reduced iron. Iron oxide can also be reduced by gaseous hydrocarbons generated from solid hydrocarbons directly charged into the reduction furnace.

[0038] Other than the conditions mentioned above, there are no particular limitations; you may follow the usual law.

[0039] For example, the injection temperature of the reducing gas can be exemplified as 750 to 1100°C.

[0040] Furthermore, the iron oxide used in the operation method of the reduction furnace according to one embodiment of the present invention is, for example, iron ore. Specific examples include lump iron ore (lump ore), iron oxide pellets (powdered iron ore compressed into a spherical shape), etc. The grade of the iron ore used as iron oxide, that is, the iron content, is not particularly limited, but from the viewpoint of reduction in a shaft furnace, it is generally preferable to have 65% by mass or more.

[0041] In the operating method of a reduction furnace according to one embodiment of the present invention, a method using a shaft furnace as the direct reduction ironmaking method was described in particular. However, the type of reduction furnace is not limited to this, and methods using fluidized bed, rotary kiln, rotary hearth furnace (RHF), etc. are also possible. In addition, a shaft furnace is preferred as the reduction furnace because it has high production efficiency, operating rate and operational stability. Furthermore, the majority of direct reduction furnaces operating worldwide are shaft furnace types, such as Midrex® and Hyl®.

[0042] Furthermore, a method for producing reduced iron according to one embodiment of the present invention involves producing reduced iron by the operation method of the reduction furnace described above. Other conditions are not particularly limited and may be carried out according to conventional methods. [Examples]

[0043] The following describes an example. Using existing equipment with the manufacturing process shown in Figure 1, and according to the conditions described in Table 1, reduced iron was produced by charging solid hydrocarbons into the reduction furnace simultaneously with iron oxide from the iron oxide charging inlet at the top of the reduction furnace. In the comparative example, reduced iron was produced under conditions in which solid hydrocarbons were not charged into the reduction furnace. In both conditions, the operating period was 28 days. Table 1 shows the operating parameters based on the unit cost per ton of reduced iron produced. For example, if 1300 kg of iron oxide pellets are used to produce 1 ton of reduced iron, the amount of iron oxide pellets used is expressed as 1300 kg / t-DRI. If 3000 tons of reduced iron are produced per day, multiplying this amount by 3000 will give the daily parameters.

[0044] Furthermore, under all conditions, the filling process involved filling the reduction furnace with iron oxide pellets, the raw material, at a rate of 1394 kg / t. In the blowing process, reducing gas heated to 980°C was blown into the center of the reduction furnace to reduce the iron oxide pellets and obtain reduced iron. After dust removal and dewatering of the top gas discharged from the reduction furnace, the top gas was divided into a first top gas for use as a raw material for reducing gas and a second top gas for use as heating fuel. Of these, the first top gas was mixed with natural gas, and the resulting mixture was supplied to a reformer to obtain reducing gas containing CO and H2. The second top gas was burned with air in the combustion chamber of the reformer. Conditions other than those described above and in Table 1 followed the standard methods or the general descriptions.

[0045] [Table 1]

[0046] In all of the inventive examples, stable operation of the reduction furnace was possible over the entire 28-day operating period, while reducing natural gas consumption compared to the comparative example (a condition in which reduced iron was produced without charging solid hydrocarbons into the reduction furnace). In particular, the inventive examples using solid hydrocarbons with a volatile content of 40% by mass or more showed an even greater reduction in natural gas consumption. Furthermore, it was advantageous in terms of reducing CO2 emissions. [Explanation of Symbols]

[0047] 1. Reduction furnace 1a Iron oxide 1b Reduced iron 3 Dust removal equipment 4 Dehydration equipment 5. Natural Gas Supply Department 6. Air supply unit 7. Modification device

Claims

1. A method for operating a reduction furnace by direct reduction ironmaking, A charging step involves charging iron oxide and solid hydrocarbons into the aforementioned reduction furnace. CO and H to the reduction furnace ２ A blowing process in which a reducing gas containing is blown in, In the reduction furnace, a reduction step is performed in which the iron oxide is reduced to obtain reduced iron, A distribution step, which divides the top gas discharged from the reduction furnace into a first top gas and a second top gas, The process includes a reforming step in which the first furnace top gas and a methane-containing gas are used as raw material gases, and the reducing gas is obtained from the raw material gases. The mass ratio of the solid hydrocarbon to the iron oxide charged into the reduction furnace is 0.014 to 0.

050. A method for operating a reduction furnace, wherein the solid hydrocarbon used is one in which the volatile content is 50% by mass or more.

2. The method for operating a reduction furnace according to claim 1, wherein the solid hydrocarbon is charged together with the iron oxide from the top of the reduction furnace.

3. The method for operating a reduction furnace according to claim 1, wherein at least one of biomass and plastics is used as the solid hydrocarbon.

4. The method for operating a reduction furnace according to claim 2, wherein at least one of biomass and plastics is used as the solid hydrocarbon.

5. A method for operating a reduction furnace according to any one of claims 1 to 4, wherein the mass ratio of the solid hydrocarbon to the iron oxide charged into the reduction furnace is 0.020 to 0.

045.

6. A method for producing reduced iron, comprising producing reduced iron by operating a reduction furnace according to any one of claims 1 to 4.

7. A method for producing reduced iron, comprising producing reduced iron by the method of operating a reduction furnace as described in claim 5.

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