JP5630223B2 - Operation method of direct reduction furnace with circulating top gas - Google Patents

Description

  The present invention relates to a method for operating a direct reduction furnace in which a top gas is circulated.

  The production of reduced iron, which reduces iron from raw materials containing iron oxide, has continued to expand against the background of the fact that the plant is inexpensive, easy to operate, and can be located even on a small scale. In particular, the shaft furnace type direct reduction furnace has been improved in various ways because it can effectively use the reducing gas in the furnace.

As a reducing gas source, there is a method in which natural gas is reformed with H ₂ O or CO ₂ to produce synthesis gas, and raw iron oxide is reduced using this synthesis gas. There is also a method of using gas.

In general, a reducing gas using natural gas as a raw material has a H ₂ fraction higher than a CO fraction due to the natural gas composition. On the other hand, the reducing gas derived from coal has a CO fraction exceeding the H ₂ fraction.

Reducing gas with a high CO fraction emits more carbon dioxide as exhaust gas, while reducing exhaust gas with a reducing gas with a high H ₂ fraction becomes H ₂ O and emits less carbon dioxide. In recent years, reducing gas mainly composed of hydrogen has attracted attention because of the necessity of reducing carbon dioxide emissions.

In the direct reduction furnace of the shaft furnace type, the raw iron oxide charged from the top of the furnace is reduced by the reducing gas rising from the lower part of the furnace as it descends in the shaft furnace. The reduction of iron from raw iron oxide proceeds in the order of hematite (Fe ₂ O ₃ ) → magnetite (Fe ₃ O ₄ ) → vustite (FeO) → iron (Fe), but it is reduced by CO gas and by H ₂ gas. In the reduction, the heat of reaction is greatly different.

The reduction reaction formula of iron oxide by CO gas or H ₂ gas is represented by the following formulas (1) to (4) or formulas (5) to (8) (Non-patent Document 1).

The reaction formula for reduction with CO gas is shown below.
3Fe ₂ O ₃ + CO = 2Fe ₃ O ₄ + CO ₂ ΔH ₂₉₈ = −52965 kJ / Kg mol CO (1)
Fe ₃ O ₄ + CO = 3FeO + CO ₂ ΔH ₂₉₈ = + 26 168 kJ / Kg mol CO (2)
FeO + CO = Fe + CO ₂ ΔH ₂₉₈ = −13943 kJ / Kg mol CO (3)
Fe ₂ O ₃ + 3CO = 2Fe + 3CO ₂ ΔH ₂₉₈ = −28096 kJ / Kg mol CO (4)
The heat of reaction ΔH ₂₉₈ is the heat of reaction at 298 ° C., and the minus sign represents an exotherm.

The reaction formula for reduction with H ₂ gas is shown below.
_{3Fe 2 O 3 + H 2 =} 2Fe 3 O 4 + H 2 O ΔH 298 = -11724kJ / Kg molH 2 ... (5)
Fe ₃ O ₄ + H ₂ = 3FeO + H ₂ O ΔH ₂₉₈ = + 67411 kJ / Kg molH ₂ (6)
FeO + H ₂ = Fe + H ₂ O ΔH ₂₉₈ = + 27215 kJ / Kg molH ₂ (7)
Fe ₂ O ₃ + 3H ₂ = 2Fe + 3H ₂ ΔH ₂₉₈ = + 95462 kJ / Kg molH ₂ (8)
The heat of reaction ΔH ₂₉₈ is the heat of reaction at 298 ° C., and the plus sign represents endotherm.

The reduction of iron oxide with CO gas is exothermic, while the reduction of iron oxide with H ₂ is a large endotherm. Therefore, the gas mainly composed of H ₂ in the reducing gas, i.e., a process using a modified natural gas or the like as a reducing gas, under the condition where volume% H ₂ increases, is accompanied endotherm in H ₂ reduction Since the reaction is stagnant due to a decrease in temperature that exceeds the amount of heat generated by CO reduction, it is an important issue to supply the shaft furnace with sufficient heat to compensate the endotherm.

  As a means for promoting the reaction of the shaft furnace, there is generally a method of increasing the temperature of the air blown from the lower part of the furnace. However, when heat is input from the lower part of the furnace, the product (reduced iron) discharged from the lower part of the furnace is excessively heated, and the particles of the reduced iron are fused together and clustering occurs. For this, crushing of the product (reduced iron) with a crusher is conceivable, but if the equipment is blocked at the location where the fused product (reduced iron) is generated, it may cause a serious obstacle to stable operation. is there.

On the other hand, in Patent Document 1, the gas at the top of the furnace is mixed with methane and air, and the mixed gas is blown from the bottom of the furnace after preheating. There is a description of a direct reduction method in which iron oxide is produced at the lower part of the shaft furnace. The reforming of natural gas is performed in the lower part of the furnace to generate a reformed gas, and the product (reduced iron) is prevented from being fused by cooling by an endothermic reaction. This is a technique for omitting the reformed gas production process outside the furnace and preventing the fusion of the product (reduced iron), and is not a technique for dealing with the endotherm due to the reduction of iron oxide by H ₂ .

  Further, Patent Document 2 describes a technique for blowing the furnace top exhaust gas from the middle part of the shaft furnace to suppress a rapid increase in the temperature of the upper part of the shaft and to prevent the strength deterioration of the charged raw material. This technique relates to the case of using a CO rich gas such as coal gasification, and since the heat of reduction reaction is exothermic, the temperature at the upper part of the furnace rapidly increases and the strength of the raw material deteriorates. In order to prevent deterioration of raw material strength, furnace top exhaust gas is blown from the middle part of the furnace. The present application is concerned with heat absorption due to reduction of iron oxide in the case of using a reducing gas mainly composed of hydrogen, and the invention described in Patent Document 2 which is mainly composed of CO and has a problem of rapid temperature rise at the top of the shaft. The problem is quite different.

Japanese Patent Publication No. 7-88525 JP 59-123708 A

Book that understands iron and steel (12th edition), edited by Shin Nippon Steel Co., Ltd., Nippon Jitsugyo Publishing Co., Ltd.

  The present invention eliminates the lack of heat at the upper part of the furnace while suppressing excessive temperature rise and fusion at the lower part in a shaft furnace type direct reduction furnace that produces reduced iron using a gas mainly composed of hydrogen. An object of the present invention is to provide a method for operating a direct reduction furnace that ensures a high product reduction rate.

In the present invention, it is effective to increase the raw material temperature in the upper part of the furnace as a means for supplying heat to achieve the above object, and for that purpose, the sensible heat (temperature and combustible gas components) of the furnace top gas is utilized. Is based on the idea that is the most efficient. That is,
[1] In a method of operating a direct reduction furnace using a shaft furnace method in which reduced iron is produced using a reducing gas containing 50% by volume or more of hydrogen and having a temperature of 900 ° C. or less ,
A method for operating a direct reduction furnace in which a furnace top gas is circulated, wherein a part of the gas discharged from the furnace top is blown from the furnace middle so that the product temperature is less than 800 ° C.
[2] Oite the operation method of the direct reduction furnace according to [1],
The operation method of the direct reduction furnace which circulated the top gas, wherein the gas blown from the intermediate part of the furnace is 20% by volume or more with respect to the gas discharged from the top .
[3] In the method for operating a direct reduction furnace according to [1] or [2],
A method for operating a direct reduction furnace in which a top gas is circulated, wherein oxygen is added to a gas blown into the furnace middle part.
[4] In the method of operating a direct reduction furnace according to any one of [1] to [3],
A method for operating a direct reduction furnace in which a gas at the top of the furnace is circulated, wherein the gas pressure at the top of the furnace is increased.

  In a shaft furnace type direct reduction furnace that produces reduced iron using a gas mainly composed of hydrogen, the furnace top gas was circulated to prevent excessive temperature rise and fusion at the bottom and ensure a high product reduction rate. A method for operating a direct reduction furnace can be provided.

The figure which shows operation of a direct reduction furnace. The figure which shows the operation which blows a part of furnace top gas in a furnace intermediate part in a direct reduction furnace. The figure which shows the operation which adds oxygen to the gas which blows in the intermediate part of a furnace in a direct reduction furnace. Diagram showing the relationship of the air blowing in H ₂ and finished products discharge temperature and finished product return rate. The figure which shows the in-furnace condition in operation of Case1 (blower temperature of 900 degreeC) of a direct reduction furnace. The figure which shows the in-furnace condition in operation of Case2 (fan temperature of 1000 degreeC) of a direct reduction furnace. The figure which shows the relationship between ventilation temperature, product discharge temperature, and product reduction rate. The figure which shows the in-furnace condition in operation of Case4 (blower temperature of 900 degreeC, 20% of top gas circulation) of a direct reduction furnace. The figure which shows the in-furnace condition in operation of Case5 (Blasting temperature 900 degreeC, furnace top gas 20% circulation, oxygen addition 5%) of a direct reduction furnace. The figure which shows the in-furnace condition in operation of Case6 (Blasting temperature 900 degreeC, furnace top gas 20% circulation, oxygen addition 5%, furnace top pressure 15Mp) of a direct reduction furnace. The figure which shows the relationship between the product reduction | restoration rate and product discharge temperature at the time of changing the amount of furnace top gas circulation on conditions with ventilation temperature of 900 degreeC and oxygen addition 5%. The figure which shows the relationship between the product reduction | restoration rate and product discharge temperature at the time of changing the oxygen addition amount on condition of blast temperature of 900 degreeC and furnace top gas 20% circulation. The figure which shows the relationship between the product reduction | restoration rate and product discharge temperature at the time of changing a furnace top pressure on the conditions of ventilation temperature 900 degreeC, oxygen addition 5%, and furnace top gas 20% circulation amount.

  Embodiments of the present invention will be described below. This is the result of calculation based on “Mathematical model of shaft furnace for iron ore reduction (Yukiaki Hara et al., Iron and Steel, 62 (1976), P.315)” for reduction of shaft furnace type direct reduction furnace. Based.

  The mathematical model of the iron ore reduction shaft furnace uses a multistage sequential reaction as a reduction reaction, and uses a velocity equation based on a multi-interface unreacted nuclear model to reduce one particle, and uses a raw iron oxide, a reducing gas, a blower, etc. This is a model for calculating the product reduction rate, product discharge temperature, etc. according to the conditions.

  The operation of the direct reduction furnace 10 used for the calculation is shown in FIG. The raw iron oxide 1 is charged directly into the reduction furnace 10 from the top of the furnace. The product 2 is discharged from the lower part of the furnace. The reducing gas 3 is blown from the furnace lower part, and the furnace top gas 4 is discharged from the furnace top.

FIG. 2 shows an operation in which a part of the furnace top gas 4 is blown into the furnace intermediate part in the direct reduction furnace 10.
Here, the furnace intermediate portion is a range in which the solid temperature at that position is lower than the circulating gas temperature, a range in which a reduction in the product discharge temperature is suppressed and a reduction rate can be sufficiently improved, It is determined by a calculation method as shown in the following examination example or an experimental method. For example, it is the range of 1m-3m from a ventilation part.

  FIG. 3 shows an operation in which oxygen is added to the gas blown into the middle part of the direct reduction furnace.

  As a calculation premise, a furnace having a furnace height of 4 m and a furnace diameter of 100 mm was used, the blast gas basic unit was 1600 Nm 3 / t-DRI, and the charging temperature was 27 ° C. Here, DRI indicates a product (directly reduced iron). Moreover, the blowing position of the furnace top gas was set to 2 m from the air blowing part (just an intermediate position between the air blowing part and the furnace top part).

FIG. 4 shows the relationship between the product reduction rate and the product discharge temperature when the raw material charging temperature is 27 ° C., the CO ₂ being blown is 10% constant, and the remaining CO and H ₂ are changed. The horizontal axis is indicated by H ₂ volume%.
With only CO and CO ₂ , the reaction rate is slow and the product reduction rate is low. As H ₂ increases, the reaction is accelerated and the product reduction rate is improved. The product discharge temperature rises accordingly. However, when H ₂ becomes excessive, the product reduction rate decreases due to the temperature decrease due to the endothermic reaction and the accompanying reaction suppression. Since the influence of H ₂ exceeds 50%, it becomes a remarkable effect. Therefore, a means for preventing the stagnation of the reaction due to the endothermic reaction when H ₂ is 50% or more is required. The H _{2 at} which this endothermic reaction becomes significant is 50% or more, and the effect of the circulation of a part of the exhaust gas to the intermediate portion increases the effectiveness.

  In order to prevent the stagnation of the reaction due to the endothermic reaction during the reduction of the raw iron oxide using a gas mainly composed of hydrogen, (1) means for increasing the blowing temperature, and (2) the top gas in the middle of the furnace (3) Means for adding oxygen to the top gas circulated to the middle part of the furnace, and (4) Means for further increasing the top gas pressure.

Calculation of means for preventing stagnation of reaction due to endothermic reaction when reducing raw material iron oxide using a gas mainly composed of hydrogen with a reducing gas composition of CO: CO ₂ : H ₂ and 25:10:65 The results are shown in Table 1.

In Case 1 (fan temperature 900 ° C.), the product reduction rate was 65.5%, and the product discharge temperature was 735 ° C. The product reduction rate is low.
FIG. 5 shows the in-furnace situation in this case. In FIG. 5 and FIGS. 5, 6, 8, 9, and 10 to be described later, the horizontal position of the furnace position on the horizontal axis is 0.0 m for the bottom product reduction side, and 4.0 m is the raw material input side at the top of the furnace. Represents.
In the upper part of the furnace, the reaction of hematite (Fe ₂ O ₃ ) → magnetite (Fe ₃ O ₄ ) → vustite (FeO) proceeds, but the reduction by H ₂ according to the above formula (6) is a significant endothermic reaction. Therefore, the gas and solid temperatures are both low, the progress of the reduction is slow, the solid temperature at the furnace intermediate position (furnace height height position 2 m) is about 460 ° C., and the reduction rate is about 10%. Stay on. The solid rapidly reduces as the furnace descends thereafter, but the final product reduction rate is only 65.5%.

In Case 2 (fan temperature 1000 ° C.), the fan temperature was only raised by 100 ° C. with respect to Case 1, and the other conditions were the same as in Case 1. The product reduction rate is 81.0%, the product discharge temperature is 799 ° C., and the product reduction rate is improved, but the product discharge temperature is increased.
FIG. 6 shows the in-furnace situation in this case. Because of the heat increase from the lower part of the furnace, the temperature rise of the gas and the solid in the upper part of the furnace is small, the solid temperature at the furnace middle position (furnace height height position 2 m) is about 490 ° C., and the reduction rate is 11 It remains at about%. Due to the heat increase from the lower part of the furnace, the reduction at the lower part of the furnace proceeds rapidly and the final product reduction rate rises to 81.0%, but the product discharge temperature becomes as high as 799 ° C.

  In Case 3 (air blowing temperature 1100 ° C.), the air temperature was only increased by 200 ° C. with respect to Case 1, and the other conditions were the same as in Case 1. The product reduction rate is improved to 97.5%, but the product discharge temperature is increased to 875 ° C. When the product discharge temperature is 800 ° C. or higher, fusion of the product (reduced iron) occurs, the equipment is blocked, and becomes a serious obstacle to stable operation.

  FIG. 7 shows the relationship between the blowing temperature, the product discharge temperature, and the product reduction rate. Although the reduction rate is improved with the increase of the blowing temperature, the product discharge temperature is also rising. The rise in product discharge temperature per product reduction rate is 4.38 ° C./%, and the rise in product discharge temperature with respect to product reduction rate is a serious problem.

In Case 4 (fan temperature 900 ° C, furnace top gas 20% circulation), the product discharge temperature increases to 67% without melting at 736 ° C by circulating the furnace top gas 20%. I was able to. Although the effect of improving the product reduction rate is small, the rise in product discharge temperature per product reduction rate is as small as 0.7 ° C./%. FIG. 8 shows the in-furnace situation in this case.
By circulating the top gas to the middle of the furnace, the amount of reducing gas per iron oxide to be reduced is increased by 20%. As a result, the heat absorption at the upper part of the furnace due to hydrogen reduction is covered, and the product reduction rate can be increased without increasing the product discharge temperature.

  In Case 5 (blowing temperature 900 ° C., furnace top gas 20% circulation, oxygen addition 5%), by adding 5% oxygen to the furnace top gas circulation, part of the furnace top circulation gas burns in the middle of the furnace. However, the heat in the furnace rises due to the combustion heat, thereby eliminating the heat shortage in the upper part of the furnace. As a result, it is considered that the product reduction rate could be increased without increasing the product discharge temperature. The rise in product discharge temperature per product reduction rate is 1.6 ° C./%, and the effect of improving the product reduction rate is great. FIG. 9 shows the in-furnace situation in this case. The gas temperature at a height of 2 m in the furnace rises by about 100 ° C. in the oxygen-added furnace top gas circulation and promotes the reduction reaction.

  In Case 6 (air blowing temperature 900 ° C, furnace top gas circulation 20%, oxygen addition 5%, furnace top pressure 5 MPa), the furnace top pressure is further increased to 5 MPa in Case 4, and the reaction in the furnace is promoted, and the product discharge temperature is increased. The product reduction rate could be increased to 91.5% without increasing it. The rise in product discharge temperature per product reduction rate is 0.7 ° C./%, and the effect of improving the product reduction rate is great. FIG. 10 shows the in-furnace situation in this case. Due to the rise in the furnace pressure due to the rise in the furnace top pressure, the solid reduction rate in the furnace is generally increased.

  FIG. 11 shows the relationship between the product reduction rate and the product discharge temperature when the furnace top gas circulation rate is changed under the conditions of a blowing temperature of 900 ° C. and oxygen addition of 5%. The product reduction rate increases as the circulation rate increases, but if the furnace top gas circulation rate exceeds 30%, the product discharge temperature exceeds 800 ° C., which causes a problem of fusion of the product (reduced iron). Therefore, the top gas circulation rate is preferably 30% or less.

  FIG. 12 shows the relationship between the product reduction rate and the product discharge temperature when the oxygen addition amount is changed when the furnace top gas circulation rate is 20%. As the amount of oxygen added increases, the product reduction rate increases. However, when the product reduction rate approaches 95%, the product discharge temperature rises to near 800 ° C., causing a problem of fusion of the product (reduced iron). Therefore, the oxygen addition amount is preferably 10% or less.

  FIG. 13 shows the relationship between the product reduction rate and product discharge temperature when the top of the furnace is changed under the conditions of an air blowing temperature of 900 ° C., oxygen addition of 5% and furnace top gas of 20%. Since the reduction rate reaches 100% at a furnace top pressure of 0.15 MPa, the furnace top pressure is preferably 0.15 MPa or less practically.

  In a shaft furnace type direct reduction furnace that produces reduced iron using a gas mainly composed of hydrogen as a reducing agent, the top gas is circulated to suppress product fusion and secure a high product reduction rate. The direct reduction furnace operating method can be used.

  DESCRIPTION OF SYMBOLS 1 ... Raw iron oxide, 2 ... Product, 3 ... Air blow, 4 ... Furnace top gas, 5 ... Oxygen, 10 ... Direct reduction furnace.

Claims (4)

In a method for operating a direct reduction furnace using a shaft furnace method in which reduced iron is produced using a reducing gas containing 50% by volume or more of hydrogen and having a temperature of 900 ° C. or less ,
A method for operating a direct reduction furnace in which a furnace top gas is circulated, wherein a part of the gas discharged from the furnace top is blown from the furnace middle so that the product temperature is less than 800 ° C. Oite the operation method of the direct reduction furnace according to claim 1, a furnace, characterized in that with respect to gas discharged from the furnace top portion, the gas blown from the furnace middle portion is 20% by volume or more Operation method of direct reduction furnace with circulating top gas. In the operating method of the direct reduction furnace of Claim 1 or Claim 2,
A method for operating a direct reduction furnace in which a top gas is circulated, wherein oxygen is added to a gas blown into the furnace middle part. In the operating method of the direct reduction furnace in any one of Claims 1 thru | or 3,
A method for operating a direct reduction furnace in which a gas at the top of the furnace is circulated, wherein the gas pressure at the top of the furnace is increased.

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