Method for operating 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

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

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

[0002] In recent years, steelworks have been strongly required to save energy against the backdrop of global environmental issues and the depletion of fossil fuels. The raw material for iron is mainly iron oxide such as iron ore, and a reduction process to reduce this iron ore is essential in steelworks. The most common reduction process that is widespread worldwide is the blast furnace. In a blast furnace, coke or pulverized coal reacts with oxygen in hot air (air heated to about 1200°C) in the tuyere. This reaction produces CO and H, which become reducing gases. ２ These reducing gases reduce iron ore and other materials in the furnace. Thanks to recent improvements in blast furnace operation technology, the reducing agent rate (the amount of coke and pulverized coal used to produce 1 ton of molten iron) has been reduced to about 500 kg / t, which is already at its lower limit. Therefore, a further significant reduction in the reducing agent rate cannot be expected.

[0003] On the other hand, a method of producing reduced iron using a vertical reduction furnace (hereinafter also referred to as a shaft furnace) is also commonly used. In this method, a reduction furnace is filled with iron ore agglomerates such as sintered ore or pellets as an iron oxide raw material (hereinafter also simply referred to as iron oxide). Then, CO and H are added to the reduction furnace. ２ A reducing gas containing the above is injected to reduce iron oxide, thereby producing reduced iron. In this method, natural gas or the like is used as the raw material gas for the reducing gas. This raw material gas is heated and reformed together with the top gas in a reformer. This generates a reducing gas. Here, the top gas is the gas remaining after the reduction of iron oxide in the reduction furnace and is generally discharged from the top of the reduction furnace. The generated reducing gas is injected into the reduction furnace and reacts with iron oxide supplied from the top of the reduction furnace. The iron oxide is then reduced to produce reduced iron. The reduced iron is then cooled in a region of the reduction furnace below the position where the reducing gas is injected and is then discharged from the bottom of the reduction furnace.

[0004] As described above, the furnace gas remaining after the reduction of iron oxide is discharged from the reduction furnace, for example, from the furnace top. After dust collection and cooling, the furnace gas is partially fed to a reformer as a raw material for reformed gas. The remaining furnace gas is used as fuel gas for the reformer. In this method, the furnace 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 discloses a process in which exhaust gas from a reduction furnace and natural gas are reformed in a reformer to produce mainly CO and H. ２ and a method for producing reduced iron by blowing the reducing gas into a reduction furnace to reduce iron oxide therein.

[0006] Furthermore, Patent Document 2 describes a method for producing reduced iron by partially combusting a carbonaceous raw material containing, in addition to coal, one or both of biomass and waste plastics, or coal (hereinafter also referred to as the carbonaceous raw material) with oxygen to produce a reducing gas, and then blowing the reducing gas into a reducing furnace.

[0007] JP 2017-88912 A Patent No. 4250472

[0008] The method described in Patent Document 1 uses natural gas supplied from an external source to produce the reducing gas. Natural gas reserves vary greatly from region to region. Furthermore, because natural gas is a gas, the transportation costs are higher than those for solid natural gas. Therefore, particularly in regions with low reserves of natural gas, there is a demand 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 partially combusting the carbonaceous raw material, etc. However, existing shaft furnaces that are commonly used are usually not equipped with such combustion equipment. Therefore, when a reducing furnace is manufactured using the method described in Patent Document 2, a large amount of cost is incurred for expansion.

[0010] The present invention has been developed in view of the above-described current situation, and aims to provide a method for operating a reducing furnace that can reduce the amount of natural gas used without requiring major modifications to existing facilities. Another object of the present invention is to provide a method for producing reduced iron by using the above-described method for operating a reducing furnace. In this disclosure, any numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively.

[0011] The inventors conducted extensive studies to solve the above-mentioned problems and discovered the following: Namely, by simultaneously charging solid hydrocarbons, particularly solid hydrocarbons having a volatile content of 40 mass% or more, in addition to iron oxide into a reducing furnace, and preferably by appropriately controlling the mass ratio of the solid hydrocarbons to the iron oxide charged into the reducing furnace, it is possible to reduce the amount of natural gas used without requiring major modifications to existing facilities. The present invention was completed based on the above-mentioned findings and through further studies.

[0012] That is, the gist and configuration of the present invention are as follows.

[0013] 1. A method for operating a reduction furnace, comprising: a charging step of charging iron oxide and solid hydrocarbons into the reduction furnace; ２ and a reduction step of reducing the iron oxide in the reducing furnace to obtain reduced iron.

[0014] 2. The method for operating a reducing furnace according to 1 above, wherein the solid hydrocarbons are charged into the reducing furnace from the top of the furnace together with the iron oxide.

[0015] 3. The method for operating a reducing furnace according to 1 or 2 above, wherein a mass ratio of the solid hydrocarbon to the iron oxide charged into the reducing furnace is 0.010 to 0.050.

[0016] 4. The method for operating a reducing furnace according to any one of 1 to 3 above, wherein at least one of biomass and plastic is used as the solid hydrocarbon.

[0017] 5. The method for operating a reducing furnace according to any one of 1 to 4 above, wherein the solid hydrocarbons used have a volatile content of 40 mass % or more.

[0018] 6. The method for operating a reducing furnace according to any one of 1 to 4 above, wherein the solid hydrocarbons used have a volatile content of 40 mass% or more, and the mass ratio of the solid hydrocarbons to the iron oxide charged into the reducing furnace is 0.020 to 0.045.

[0019] 7. The method for operating a reducing furnace according to any one of 1 to 6 above, further comprising: a distribution step of distributing a furnace top gas discharged from the reducing furnace into a first furnace top gas and a second furnace top gas; and a reforming step of using the first furnace top gas and a methane-containing gas as raw material gases to obtain the reducing gas from the raw material gases.

[0020] 8. A method for producing reduced iron, comprising producing reduced iron by the method for operating a reduction furnace according to any one of 1 to 7 above.

[0021] According to the present invention, it is possible to reduce the amount of natural gas used without making major modifications to existing facilities.

[0022] FIG. 1 is a schematic diagram showing an example of a process for producing reduced iron.

[0023] A method for operating a reducing furnace according to one embodiment of the present invention will now be described.

[0024] A method for operating a reduction furnace according to one embodiment of the present invention includes: a charging step of charging iron oxide and solid hydrocarbons into the reduction furnace; ２ a reduction step of reducing the iron oxide in the reducing furnace to obtain reduced iron, and optionally further comprising a distribution step of distributing a furnace top gas discharged from the reducing furnace into a first furnace top gas and a second furnace top gas, and a reforming step of using the first furnace top gas and a methane-containing gas as raw material gases to obtain the reducing gas from the raw material gases.

[0025] 1 is a schematic diagram showing an example of a process for producing reduced iron to which a method for operating a reducing furnace according to one embodiment of the present invention can be applied. In the figure, reference numeral 1 denotes a reducing furnace, 1a denotes iron oxide, 1b denotes reduced iron, 3 denotes a dust remover, 4 denotes a dehydration device, 5 denotes a methane-containing gas supply section, 6 denotes an air supply section, and 7 denotes a reformer.

[0026] In one example of a reduced iron production process shown in Figure 1, iron oxide 1a is charged from the top of a reduction furnace 1 and gradually lowered. High-temperature reducing gas is blown into the furnace from the middle to reduce the iron oxide 1a. Reduced iron 1b is then discharged from the bottom of the reduction furnace 1. At this time, mainly CO, CO ２ , H ２ , H ２ A furnace top gas containing O is discharged. This furnace top gas is subjected to dust removal in a dust removal device 3. Next, the moisture content of the furnace top gas is adjusted in a dehydration device 4, and a portion of the top gas is sent to a reformer 7 as a first furnace top gas. A methane-containing gas, for example, natural gas, is supplied to the reformer 7 together with the first furnace top gas. Next, the supplied gas is heated in the reformer 7. Then, a reforming reaction occurs, and mainly CO and H are produced. ２ A high-temperature reducing gas containing CO is generated. This reducing gas is then blown into the reducing furnace. The remaining part 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 combusted as a heating fuel usually contains CO ２ When reduced iron is produced by this example of the conventional production process, approximately 1 ton of CO is produced per ton of reduced iron. ２ is excreted from the circulatory system.

[0027] In the method for operating a reducing furnace according to one embodiment of the present invention, it is important to simultaneously charge solid hydrocarbons in addition to iron oxide into the reducing furnace. Hereinafter, the charging step of simultaneously charging solid hydrocarbons in addition to iron oxide into the reducing furnace will be described. The distribution step and the reforming step may be performed in accordance with conventional methods, for example, in the same manner as in the above-described production process, and therefore, a description thereof will be omitted here.

[0028] Charging Step In a method for operating a reducing furnace according to one embodiment of the present invention, solid hydrocarbons are simultaneously charged into the reducing furnace in addition to iron oxide. The solid hydrocarbons charged into the reducing furnace are heated as they descend through the reducing furnace. During this process, the solid hydrocarbons are thermally decomposed or decomposed into CO ２ and H ２ Reacts with O to produce gaseous hydrocarbons, CO, and H ２ (Hereinafter, also referred to as gaseous hydrocarbons, etc.) The gaseous hydrocarbons, etc. are consumed in the reduction reaction of iron oxide in the reducing furnace. The gaseous hydrocarbons, etc. are also discharged as furnace top gas and supplied to a reformer, for example, as a raw material for reducing gas or as a heating fuel. In other words, it is possible to reduce the amount of methane-containing gas, specifically natural gas, used as a raw material for reducing gas by the amount of gaseous hydrocarbons, etc., generated from solid hydrocarbons in the reducing furnace.

[0029] Here, the mass ratio of solid hydrocarbons to iron oxide charged into the reducing 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 of production per ton of reduced iron. By setting the solid hydrocarbons / iron oxide ratio to 0.010 or more, 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 reducing furnace may produce unreacted residues. Most of the small-sized residues are pushed out of the furnace by the rising gas inside the reducing furnace. Furthermore, some of the residues remain in the lower part of the reducing furnace and contribute to carburization of the reduced iron. However, if a large amount of residue remains in the lower part of the reducing furnace, the discharge port for reduced iron from the reducing furnace may easily become clogged, which may reduce the reaction efficiency. Furthermore, if the reduced iron discharged from the reducing furnace contains a large amount of residue, a process for separating the reduced iron from the residue may be necessary. Therefore, the solid hydrocarbon / iron oxide ratio is preferably 0.050 or less. The solid hydrocarbon / iron oxide ratio is more preferably 0.015 or more. The solid hydrocarbon / iron oxide ratio is more preferably 0.045 or less. In particular, when using solid hydrocarbons having a volatile content of 40% by mass or more, as described below, the solid hydrocarbon / iron oxide ratio is more preferably 0.020 to 0.045. The higher the volatile content of a solid hydrocarbon, the smaller its specific gravity. Therefore, when using solid hydrocarbons having a volatile content of 40% by mass or more, setting the solid hydrocarbon / iron oxide ratio to 0.020 or more can further enhance the effect of reducing the amount of natural gas used. On the other hand, solid hydrocarbons with a high volatile content have a high moisture content. Using such solid hydrocarbons in excess may hinder the temperature rise of the raw material charged into the reducing furnace at the top of the reducing furnace. Therefore, when using a solid hydrocarbon having a volatile content of 40 mass % or more, it is preferable to set the ratio of solid hydrocarbon / iron oxide to 0.045 or less.

[0030] The type of solid hydrocarbon is not particularly limited, but examples include biomass, plastic, coal, etc. Among them, biomass is a carbon-neutral raw material, so when biomass is used as the solid hydrocarbon, CO2 from the production process is reduced by the amount used. ２ This is particularly advantageous as it allows for a substantial reduction in emissions. The plastic may be virgin or used. The concept of used plastic includes waste plastic, plastic that is not intended to be disposed of, factory offcuts, etc. Waste plastic, in particular, is a resource that should be actively utilized.

[0031] Regarding the properties of the solid hydrocarbons used, those with a volatile content of 40% by mass or more (40 to 100% by mass) are preferred. As described above, it is possible to reduce the amount of natural gas used as a raw material for the reducing gas by the amount of gaseous hydrocarbons generated from the solid hydrocarbons in the reduction furnace. Therefore, when the mass ratio of iron oxide to solid hydrocarbons is the same, using solid hydrocarbons with a higher volatile content is more effective in reducing the amount of natural gas used. This is also advantageous in terms of transportation costs. Furthermore, it is advantageous in terms of reducing residue remaining in the lower part of the reduction furnace. Therefore, it is preferable to use solid hydrocarbons with a volatile content of 40% by mass or more. It is more preferable to use solid hydrocarbons 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 hydrocarbons is not particularly limited and may be 100% by mass. Note that the solid hydrocarbons contain ash and moisture in addition to the volatile content, with the remainder being fixed carbon.

[0032] The volatile content of the solid hydrocarbon may be measured in accordance with JIS M 8812:2006.

[0033] It is also desirable to use solid hydrocarbons whose thermal decomposition temperature is preferably 900° C. or less, more preferably 700° C. or less. Furthermore, it is desirable to use solid hydrocarbons whose mass fraction of gangue components is preferably 5% or less, more preferably 3% or less.

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

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

[0036] [Blow-in process] CO and H are blown into the reduction furnace. ２ The gas composition of the reducing gas is, for example, CO: 1 to 60% by volume, H ２ : 40 to 99 volume %, and the remainder: 0 to 30 volume %.

[0037] [Reduction Step] In the reduction step, iron oxide is reduced with a reducing gas to obtain reduced iron. Iron oxide is also reduced by gaseous hydrocarbons generated from solid hydrocarbons charged into a direct reduction furnace.

[0038] The conditions other than those mentioned above are not particularly limited, and may be those according to conventional methods.

[0039] For example, the temperature at which the reducing gas is blown in can be 750 to 1100°C.

[0040] The iron oxide used in the method for operating a reduction furnace according to one embodiment of the present invention is, for example, iron ore. Specific examples include lumpy iron ore (lump ore) and iron oxide pellets (iron ore powder solidified into a spherical shape). The quality of the iron ore used as the iron oxide, i.e., the iron content, is not particularly limited, but is generally preferably 65% ​​by mass or more from the viewpoint of reduction in a shaft furnace.

[0041] In the method for operating a reduction furnace according to one embodiment of the present invention, a method using a shaft furnace as a direct reduction ironmaking process has been described. However, the type of reduction furnace is not limited to this, and methods using a fluidized bed, rotary kiln, rotary hearth furnace (RHF), etc. are also possible. Note that a shaft furnace is preferred as the reduction furnace because of its high production efficiency, availability, and operational stability. Furthermore, the majority of direct reduction furnaces operating around the world are shaft furnace-type Midrex (registered trademark) and Hyl (registered trademark).

[0042] In addition, a method for producing reduced iron according to one embodiment of the present invention produces reduced iron by the above-described method for operating a reduction furnace. Conditions other than those described above are not particularly limited, and may be performed in accordance with conventional methods.

[0043] Examples are described below. Using existing equipment having the production process shown in FIG. 1 , reduced iron was produced by charging solid hydrocarbons into a reducing furnace simultaneously with iron oxide through an iron oxide charging port at the top of the reducing furnace under the conditions shown in Table 1. In a comparative example, reduced iron was produced without charging solid hydrocarbons into the reducing furnace. In all cases, the operation period was 28 days. Table 1 lists the operational specifications in terms of the consumption rate per ton of reduced iron produced. For example, if 1,300 kg of iron oxide pellets are used to produce 1 ton of reduced iron, the amount of iron oxide pellets used is expressed as 1,300 kg / t-DRI. To produce 3,000 t / day of reduced iron, multiply this amount by 3,000 to obtain the daily specifications.

[0044] In addition, under all conditions, in the filling step, the raw material iron oxide pellets were filled into the reducing furnace at a rate of 1,394 kg / t. In the injection step, reducing gas heated to 980°C was injected from the center of the reducing furnace to reduce the iron oxide pellets and obtain reduced iron. The furnace top gas discharged from the reducing furnace was dusted and dehydrated, and then divided into a first furnace top gas used as a reducing gas raw material and a second furnace top gas used as heating fuel. Of these, the first furnace top gas was mixed with natural gas, and the mixed gas was supplied to a reformer to remove CO and H. ２A reducing gas containing the above was obtained. The second furnace gas was combusted with air in the combustion chamber of the reformer. Conditions other than those described above and in Table 1 were the same as those described in the ordinary method or general description section.

[0045]

[0046] In all of the inventive examples, stable operation of the reducing furnace was possible over the entire 28-day operation period while reducing the amount of natural gas consumed compared to the comparative example (conditions under which reduced iron was produced under conditions under which no solid hydrocarbons were charged into the reducing furnace). In particular, in the inventive examples using solid hydrocarbons with a volatile content of 40 mass% or more, a greater effect of reducing the amount of natural gas consumed was achieved. ２ It was also advantageous in terms of reducing emissions.

[0047] REFERENCE SIGNS LIST 1 reduction furnace 1a iron oxide 1b reduced iron 3 dust removal device 4 dehydration device 5 natural gas supply section 6 air supply section 7 reformer

Claims

1. A method for operating a reduction furnace, comprising: a charging step of charging iron oxide and solid hydrocarbons into the reduction furnace; ２ and a reduction step of reducing the iron oxide in the reduction furnace to obtain reduced iron.

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

3. The method for operating a reducing furnace according to claim 1 or 2, wherein a mass ratio of the solid hydrocarbons to the iron oxide charged into the reducing furnace is 0.010 to 0.

050.

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

5. The method for operating a reducing furnace according to any one of claims 1 to 4, wherein the solid hydrocarbons used are solid hydrocarbons having a volatile content of 40 mass% or more.

6. A method for operating a reducing furnace according to any one of claims 1 to 4, wherein as the solid hydrocarbons, solid hydrocarbons having a volatile matter content of 40 mass% or more are used, and a mass ratio of the solid hydrocarbons to the iron oxide charged into the reducing furnace is 0.020 to 0.

045.

7. The method for operating a reducing furnace according to any one of claims 1 to 6, further comprising: a distribution step of distributing a top gas discharged from the reducing furnace into a first top gas and a second top gas; and a reforming step of obtaining the reducing gas from the first top gas and a methane-containing gas as raw material gases.

8. A method for producing reduced iron, comprising producing reduced iron by the method for operating a reduction furnace according to any one of claims 1 to 7.

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