Method for operating shaft furnace and method for producing reduced iron

Abstract

A method of operating a shaft furnace capable of producing reduced iron using the shaft furnace while suppressing CO2 emissions and without preheating the raw materials. A method of operating a shaft furnace in which, at the same time as charging lump ore into the shaft furnace, a reducing gas having H2 as the main component is introduced into the shaft furnace, and the iron oxide contained in the lump ore is reduced to obtain reduced iron, wherein a heated gas containing H2O, which is heated to 800°C or higher by burning H2 and O2, is blown into the shaft furnace from a position above the introduction of the reducing gas in the height direction of the shaft furnace.

Description

Technology Field

[0001] The present invention relates to a method of operating a shaft furnace and a method of producing reduced iron. Background Technology

[0002] Methods for producing reduced iron by reducing raw materials containing iron oxide include the blast furnace method, which produces hot metal using coke as a reducing agent; a method in which a reducing gas is used as a reducing agent and blown into a vertical furnace (hereinafter referred to as a "shaft furnace"); a method in which fine ore is reduced in a fluidized bed using the same reducing gas; and a method in which the agglomeration and reduction of the raw material are integrated (rotary kiln method).

[0003] Among these, in the methods for producing reduced iron excluding the blast furnace method, a reducing gas consisting mainly of carbon monoxide (CO) or hydrogen (H2) produced by reforming natural gas or coal is used as a reducing agent. The raw material charged into the furnace is heated by convection heat transfer with the reducing gas, reduced, and then discharged out of the furnace. Oxidized gases such as water (H2O) or carbon dioxide (CO2), as well as H2 gas or CO gas that did not contribute to the reduction reaction, are discharged from the furnace.

[0004] The raw material (mainly Fe2O3) charged into the furnace undergoes a reduction reaction as shown in the following equations (2) and (3) from a reducing gas, such as CO gas or H2 gas.

[0005] Fe2O3+3CO→2Fe+3CO2… (2)

[0006] Fe2O3+3H2→2Fe+3H2O... (3)

[0007] That is, in the reduction by CO gas shown in Equation (2), CO2 is emitted as the exhaust gas after reduction. On the other hand, in the reduction by H2 gas shown in Equation (3), H2O is emitted as the exhaust gas after reduction.

[0008] Currently, global warming caused by the increase in CO2 emissions is becoming a problem. In order to suppress the emission of CO2, which is one of the greenhouse gases considered to be a factor in global warming, it is desirable to increase the amount of reduction reaction by H2 shown in Equation (3). In the reduction reactions by CO and H2, the amount of heat that is exothermic or endothermic accompanying the reaction is different. That is, while the heat of reduction reaction by CO is +6710 kcal / kmol (Fe2O3), the heat of reduction reaction by H2 is -22800 kcal / kmol (Fe2O3). In other words, the former is a reaction that involves exothermic reaction, while the latter is a reaction that involves endothermic reaction. Therefore, if the intention is to increase the amount of reaction in Equation (3) by increasing the concentration of H2 in the reduction gas, a significant endothermic reaction occurs, causing the temperature inside the furnace to drop and potentially leading to stagnation of the reduction reaction. For this reason, it is necessary to compensate for the insufficient heat by some method.

[0009] As a technique to compensate for insufficient heat, Patent Document 1 discloses a method of preheating raw iron oxide charged from the top to a temperature of 100°C or higher and 627°C or lower. Prior art literature

[0010] Japanese Patent Publication No. 5630222 The problem to be solved

[0011] However, in the technology described in Patent Document 1, equipment for preheating the raw materials was required.

[0012] The present invention is made in consideration of these circumstances and aims to provide a method of operating a shaft furnace that can produce reduced iron using the shaft furnace while suppressing CO2 emissions and without preheating the raw materials. means of solving the problem

[0013] In order to achieve the above-mentioned objective, the inventors, through repeated examinations, discovered that as a heat compensation for the reduction reaction by H2 in a reduction furnace, a combustion gas containing H2O generated by burning H2 and O2 can be blown into the upper shaft to suppress the temperature drop at the top of the furnace.

[0014] The present invention is based on the above understanding. That is, the gist of the present invention is as follows.

[0015] [1] A method of operating a shaft furnace, wherein a reducing gas with a main component of H2 is introduced into the shaft furnace while agglomerated ore is charged into the shaft furnace, and the iron oxide contained in the agglomerated ore is reduced to obtain reduced iron,

[0016] A method of operating a shaft, wherein a heated gas containing H2O heated to 800°C or higher by burning H2 and O2 is blown into the shaft from an inlet position above the introduction position of the reducing gas in the height direction of the shaft.

[0017] [2] A method of operation to the shaft described in [1], wherein the H2O content of the heating gas is 67 volume% or more and 98 volume% or less.

[0018] [3] The above-mentioned heating gas is 1000°C or lower, and the method of operation to the shaft described in [1] or [2] above.

[0019] [4] A method of operating a shaft described in any one of [1] to [3], wherein the distance L in the height direction to the shaft from the charging position of the lump ore to the introduction position of the reducing gas and the distance l in the height direction to the shaft from the charging position of the lump ore to the introduction position of the heating gas satisfy the following formula (1).

[0020] L / 4≤l≤L / 2 … (1)

[0021] [5] A method for producing reduced iron using the method of operating a shaft described in any one of [1] to [4] above. Effects of the invention

[0022] According to the present invention, a method of operating a shaft furnace can be provided to produce reduced iron using the shaft furnace while suppressing CO2 emissions and without preheating the raw materials. Brief explanation of the drawing

[0023] Figure 1 is a diagram showing a schematic of a conventional shaft operation method. FIG. 2 is a diagram showing a schematic of a method of operation to a shaft according to one embodiment of the present invention. Figure 3 is a diagram showing the temperature distribution of agglomerate ore in the height direction of the shaft, calculated by a mathematical model for the operation method of the shaft according to the present embodiment and comparative example. Specific details for implementing the invention

[0024] (Form for carrying out the invention)

[0025] Hereinafter, an embodiment for carrying out the present invention is described. Furthermore, as long as it does not deviate from the gist of the present invention, the embodiments of the present invention are not limited to the following embodiments.

[0026] One embodiment for carrying out the present invention is described. FIG. 1 shows a schematic of a conventional shaft furnace operation method. A surge bin (2) for storing lump ore is installed at the top of the shaft furnace (1). The surge bin (2) supplies lump ore to the top of the furnace. In the conventional shaft furnace operation method, CO and H2 produced by reforming natural gas are blown in from the middle of the furnace. After being charged into the furnace, the lump ore is heated by heat exchange with these reducing gases, and the iron oxide contained in the lump ore is reduced to reduced iron. The reduced lump ore is discharged from the bottom of the furnace to the outside of the furnace.

[0027] [Reducing Gas]

[0028] In the method of operating a shaft according to the present embodiment, a reducing gas having H2 as its main component is introduced into the furnace. Here, having H2 as the main component means that the H2 content contained in the reducing gas is 60% or more by volume. The H2 content contained in the reducing gas is preferably 100%. As described above, by performing a reduction reaction using a reducing gas having H2 as its main component, the emission of CO2 can be suppressed compared to the case where a reduction reaction is performed using a reducing gas having CO as its main component. In order to reduce the amount of CO2 emitted, it is desirable to reduce the CO content in the reducing gas as much as possible. The CO content in the reducing gas is preferably 40% by volume or less, and more preferably 0% by volume.

[0029] The amount of reducing gas introduced into the shaft is not particularly limited, but for the reason that it smoothly lowers lump ore within the furnace while maintaining the production of reduced iron, 1500 Nm 3 It is desirable that / t-DRI or higher, and also 3500 Nm 3 It is desirable that / t-DRI is less than or equal to

[0030] The temperature of the reducing gas is not specifically limited, but it is preferable to set it to 800°C or higher for the reason of maintaining a predetermined reduction rate of the lump ore. In addition, the temperature of the reducing gas is measured by a thermometer installed at the reducing gas inlet. By setting the temperature of the reducing gas to 800°C or higher, a predetermined reduction rate is maintained, and the reduction rate of the lump ore reached until it is discharged from the bottom of the shaft can be 90% or higher.

[0031] As mentioned above, the reduction reaction of iron oxide by H2 is an endothermic reaction. Therefore, if the reduction of iron oxide is carried out using a reducing gas with H2 as the main component, the temperature inside the furnace is lowered, and there is a risk that the reduction rate will decrease.

[0032] Therefore, in this embodiment, in order to suppress a decrease in temperature inside the furnace, as shown in FIG. 2, a heating gas of 800°C or higher is blown into the shaft furnace from a blowing position located above the introduction position of the reducing gas in the height direction of the shaft furnace, thereby suppressing a decrease in temperature inside the furnace. As shown in FIG. 2, when the reducing gas is introduced from a position in the middle of the height direction of the shaft furnace, the reducing gas flows toward the upper direction of the shaft furnace. Therefore, by blowing a high-temperature heating gas from a blowing position located even higher than the introduction position of the reducing gas, it is possible to secure a reduction zone and suppress a decrease in temperature inside the furnace.

[0033] As the heating gas, a gas containing H2O obtained by burning H2 and O2 is used. Conventionally, a high-temperature gas containing CO2 obtained by burning hydrocarbons is blown in. In contrast, in the present embodiment, by blowing in a heating gas containing H2O obtained by burning H2 and O2, the amount of CO2 emissions can be reduced while suppressing the drop in temperature inside the furnace.

[0034] [Heating Gas]

[0035] The heating gas contains H2O. The heating gas preferably contains 67 volume% or more of H2O. It is preferable that the content of H2O in the heating gas be 98 volume% or less. If the total amount of the heating gas is H2O, the agglomerate reduced above the heating gas injection position is reoxidized by said heating gas. For this reason, it is desirable to add a small amount of H2 to the heating gas to suppress said reoxidation, and therefore, it is preferable that the upper limit of the H2O content in the heating gas be 98 volume%.

[0036] The heating gas contains H2O obtained by burning H2 and O2. The fact that the heating gas contains H2O obtained by burning H2 and O2 leads to the suppression of CO2 emissions. Additionally, to suppress CO2 emissions, it is desirable to use electricity generated by suppressing CO2 emissions for the H2 used in combustion, and in one example, to produce it by electrolyzing water.

[0037] The heating gas may contain components other than H2O. In one example, the heating gas may contain N2, H2, O2, CO2, and CO. To reduce CO2 emissions, it is preferable that the CO2 content in the heating gas be 28 volume% or less. To reduce CO2 emissions, it is preferable that the CO content in the heating gas be 19 volume% or less.

[0038] In addition, generally, in the operation of the shaft, the gas discharged from the furnace top is recovered and reused as a reducing gas. In order to have sufficient reducing ability when reused as a reducing gas, it is desirable that the gas discharged from the furnace top does not contain inert gas (N2). Accordingly, it is desirable to reduce the content of inert gas in the heating gas. Preferably, the content of inert gas in the heating gas is 50 volume% or less.

[0039] The temperature of the heating gas is 800°C or higher. In addition, the temperature of the heating gas is measured, for example, by a thermometer installed at the heating gas inlet. By setting the temperature of the heating gas to 800°C or higher, the decrease in the furnace temperature accompanying the reduction reaction by hydrogen can be effectively suppressed. Although the upper limit of the heating gas temperature is not particularly limited, it is preferable that it be 1000°C or lower. By setting the temperature of the heating gas to 1000°C or lower, the occurrence of clustering, where raw materials stick together, can be more appropriately suppressed. The temperature of the heating gas is preferably 900°C or higher. In addition, the temperature of the heating gas is more preferably 950°C or lower.

[0040] The amount of heating gas blown into the shaft is 200 Nm 3 It is desirable that / t-DRI or higher, and also 400 Nm 3 It is desirable that the value be less than or equal to / t-DRI. Here, DRI refers to Direct Reduced Iron. In addition, the amount of heating gas injected is measured, for example, by a gas flow meter installed at the heating gas injection port. The amount of heating gas injected is 200 Nm 3 By setting the / t-DRI to be greater than or equal to , the drop in furnace temperature accompanying hydrogen reduction can be efficiently suppressed. In addition, the amount of heating gas injected is 400 Nm³ 3 By keeping the t-DRI below 1 / t-DRI, the blowing out of the heating gas is suppressed, thereby increasing the heat generation efficiency. More preferably, the amount of heating gas blown in is 250 Nm³ 3 It shall be greater than / t-DRI. In addition, the amount of heating gas blown in is more preferably 350 Nm 3 Keep it below / t-DRI.

[0041] The injection location for the heating gas is installed at a position higher in the height direction of the shaft relative to the introduction location of the reducing gas. By injecting the heating gas from a position higher than the introduction location of the reducing gas in the height direction of the shaft, a reduction zone can be secured. The injection location for the heating gas is not limited to a single location and may be installed in multiple locations around the shaft.

[0042] In order to more efficiently suppress the temperature drop inside the shaft, as shown in FIG. 2, the distance in the height direction of the shaft from the charging position of the lump ore to the introduction position of the reducing gas is set to L, and the distance in the height direction of the shaft from the charging position of the lump ore to the injection position of the heating gas is set to l, and it is desirable that L and l satisfy the following equation (1).

[0043] L / 4≤l≤L / 2 … (1)

[0044] That is, it is preferable to blow a heating gas into the shaft from a position where the distance l in the height direction from the charging position of the lump ore to the shaft is between L / 4 and L / 2. By blowing a gas containing H2O from a position where the distance l from the charging position of the lump ore is between L / 4 and L / 2, the drop in temperature inside the furnace accompanying hydrogen reduction can be suppressed more efficiently. Furthermore, the reduction of the lump ore stagnates at the position where the heating gas containing H2O is blown in. Therefore, by blowing a heating gas containing H2O from a position where the distance l from the charging position of the lump ore is between L / 2 and L / 2, an area for reducing iron oxide contained in the lump ore can be secured inside the furnace, thereby further improving the reduction rate. Here, the charging position of the lump ore refers to the surface of the lump ore packing layer inside the shaft. Also, the introduction position of the reducing gas refers to the height of the introduction port of the reducing gas. The location of the heat-raising gas injection refers to the location of the heat-raising gas injection port.

[0045] The introduction location of the reducing gas does not need to be specifically limited as long as it is lower than the injection location of the heating gas. The introduction location of the reducing gas is not limited to a single location and may be installed in multiple places around the shaft.

[0046] The lump ore charged into the shaft furnace may be, in addition to fine ore, pellets formed by baking fine ore into a spherical shape and solidifying it. The lump ore may also be sintered ore formed by calcining raw materials containing iron oxide. In this specification, fine ore, pellets, and sintered ore are collectively referred to as "lump ore."

[0047] In addition, other than the aforementioned conditions, the Commercial Act may apply.

[0048] By reducing the iron oxide contained in the lump ore using the aforementioned shaft furnace operation method, reduced iron can be produced using the shaft furnace while suppressing CO2 emissions and without preheating the raw material.

[0049] Examples

[0050] Using a mathematical model regarding one-dimensional heat transfer and reaction, the temperature distribution inside the furnace was calculated for a shaft furnace operated according to the operation method of the shaft furnace according to the present embodiment. Table 1 shows the various values ​​used in the calculation. In Table 1, Comparative Example 1 assumes the operating conditions of a typical shaft furnace currently in use. More specifically, Comparative Example 1 assumes that the gas composition of the reducing gas is 60% CO by volume and 40% H2, and that no heating gas is injected. Comparative Example 2 assumes that the reducing gas is entirely H2 and that no heating gas is injected. Example 1 assumes the case where a heating gas of entirely H2O is injected compared to Comparative Example 2. In addition, the introduction position of the reducing gas was set to the center in the height direction of the shaft, and the injection position of the heating gas was set to the center between the introduction position of the reducing gas and the top of the shaft.

[0051]

[0052] For the calculation of direct reduction in the shaft furnace method, a mathematical model was constructed using the approach of a one-dimensional unsteady model (Reference 1) for blast furnaces, and this was used for the shaft furnace calculation. For the reduction reaction model of agglomerate ore, an overall reaction rate equation (References 2, 3) was used, which assumes that the reduction reaction proceeds normally through three processes: diffusion within the gas film on the surface of the ore grains, diffusion within the grains, and chemical reaction at the reaction interface. From these mathematical models, for each example, the temperature of the agglomerate ore and the reduction rate of iron oxide contained in the agglomerate ore were calculated according to the gas blowing conditions. The results are shown in Figure 3 and Table 2.

[0053]

[0054] Figure 3 shows the temperature distribution of agglomerate ore in the furnace in the height direction of the shaft calculated by a mathematical model. In Figure 3, the vertical axis is set to the position in the height direction from the introduction position of the reducing gas. As shown in Figure 3, compared to the temperature distribution of Comparative Example 1, the temperature of the agglomerate ore in Comparative Example 2 is lowered due to the endothermic effect of hydrogen reduction. In contrast, in Example 1, it can be seen that the temperature of the agglomerate ore is increased by blowing H2O as the heating gas.

[0055] In addition, as shown in Table 2, the reduction rate achieved in Comparative Example 2 is significantly lower than that of Comparative Example 1. In contrast, in Example 1, by blowing H2O as the heating gas, the reduction rate is improved and can be seen to be improved to a level equivalent to that of Comparative Example 1.

[0056] [Reference 1] Hideo Kubo, et al., "Equational Model for Examining the Dynamic Characteristics of Blast Furnaces," Kawasaki Steel Technical Report, Vol. 14, 1982, No. 2, pp. 134-144

[0057] [Reference 2] Muchi Iwao, et al., "Reaction Rates Inside the Blast Furnace," Journal of the Japan Institute of Metallurgy, Vol. 30, 1966, No. 9, pp. 826-831

[0058] [Reference 3] Junichiro Yagi et al., "Reactions Involving Hydrogen and Steam in Blast Furnace Models and Application of Stratum Gas Temperature," Journal of the Japan Institute of Metallurgy, Vol. 31, 1697, No. 6, pp. 711-716 Explanation of the symbols

[0059] 1 : With the shaft 2 : Seo Ji Bin

Claims

Claim 1 A method of operating a shaft furnace, wherein a reducing gas having H2 as its main component is introduced into the shaft furnace while charging agglomerated ore into the shaft furnace, and iron oxide contained in the agglomerated ore is reduced to obtain reduced iron, wherein a heating gas containing H2O, which is heated to 800°C or higher by burning H2 and O2, is blown into the shaft furnace from a blowing position above the introduction position of the reducing gas in the height direction of the shaft furnace, and the H2O content of the heating gas is 67 volume% or more. Claim 2 A method of operation to a shaft according to claim 1, wherein the H2O content of the heating gas is 67 volume% or more and 98 volume% or less. Claim 3 A method of operation to a shaft in which the heating gas in paragraph 1 is 1000℃ or lower. Claim 4 In paragraph 2, the above-mentioned heating gas is 1000℃ or lower, a method of operation to a shaft. Claim 5 A method of operation of a shaft according to any one of claims 1 to 4, wherein the distance L in the height direction to the shaft from the charging position of the lump ore to the introduction position of the reducing gas and the distance l in the height direction to the shaft from the charging position of the lump ore to the blowing position of the heating gas satisfy the following formula (1). L / 4 ≤ l ≤ L / 2 … (1) Claim 6 A method for producing reduced iron using a method of operation with a shaft described in any one of paragraphs 1 to 4. Claim 7 A method for producing reduced iron using the method of operating with a shaft as described in paragraph 5.

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