JP6167837B2 - Direct reduction method - Google Patents

Description

A direct reduction method is known as another reduction method different from the blast furnace reduction method. The direct reduction method is a process in which iron ore and pellets agglomerated from it are reduced with CO gas or H ₂ gas to obtain solid reduced iron. Popularization is progressing due to features such as few resource constraints such as caking coal necessary for production. The direct reduction method has been researched and developed for further improvement, and in particular, a technique for utilizing hydrogen as a reducing agent as a countermeasure against global warming is being studied.

  The purpose of process analysis of the blast furnace is to predict changes in the furnace operation index in response to changes or fluctuations in the blast furnace operation factors, and take appropriate measures based on that to improve the operation results while ensuring stable operation of the furnace. It is to measure. In order to ensure stable operation of the blast furnace, it is necessary to have a thermal balance in each part of the furnace, that is, to satisfy the heat balance conditions, and the theory of process analysis is also classified according to the heat balance method. can do.

As a process analysis theory of a blast furnace, a list operation diagram is known (for example, see Non-Patent Document 1). The list operation diagram is one of the process analysis methods that makes it possible to graph the relationship between various operation factors of the blast furnace and the operation index in a simple manner and enable quantitative calculation. The list operation diagram is an extension of the oxygen exchange diagram for the shaft part where indirect reduction mainly proceeds so as to take into account the smelting reduction reaction in the lower part of the furnace. Here, the part corresponding to the oxygen exchange diagram Is outlined. The graph of FIG. 1 schematically shows an oxygen exchange diagram of a blast furnace, the vertical axis corresponds to O / Fe that is the reduction degree of the raw material, and the horizontal axis is the gas utilization rate of the reducing gas (in other words, This corresponds to (CO ₂ + H ₂ O / (CO + CO ₂ + H ₂ + H ₂ O)), which is the oxidation degree of the reducing gas, but since the reducing gas of the blast furnace is mainly CO, there is only a few percent. H ₂ is neglected here, while the denominator value is constant because CO decreases as the reduction proceeds, while CO ₂ increases, and the numerator value does not change, and the CO ₂ concentration increases as the reduction proceeds. Increase.

The solid line in FIG. 1 indicates the operation line, and the broken line indicates the equilibrium constraint for reduction. The point A in the solid line corresponds to the top of the blast furnace and the charge charged from the top of the blast furnace is Fe ₂ O ₃ (hereinafter referred to as “hematite”). .5, and the gas utilization rate of the reducing gas is maximum at the top of the blast furnace furnace, and is about 0.45 in this example. Point B in the solid line corresponds to the raw material after indirect reduction at the shaft portion (hereinafter sometimes referred to as reduced iron) and the gas utilization rate of the reducing gas flowing from the lower part of the furnace.

The reduction equilibrium constraint point of hematite → Fe ₃ O ₄ (hereinafter referred to as “magnetite”) corresponding to the point A is expressed as Heq after the initial of hematite. The reductive equilibrium constraint point of magnetite → FeO _1.05 (hereinafter referred to as “wustite”) is expressed as Meq after the initial of magnetite. The wustite → iron reduction equilibrium constraint point is expressed as Weq after the acronym of wustite. The operation line is created by connecting points A and B with a straight line. The point at which O / Fe = 1.333 on the operation line is indicated as M point from the initial of magnetite, and the point at which O / Fe = 1.05 is indicated as W point from the initial of wustite. In the broken line indicating the equilibrium constraint of reduction, the broken line connecting the Heq point and the Meq point corresponds to the equilibrium gas composition when changing from hematite to magnetite, and the broken line connecting the Meq point and the Weq point is from magnetite to wustite. The broken line extending downward from the Weq point corresponds to the equilibrium gas composition when changing from wustite to the iron raw material. In addition, although the broken line extended horizontally does not actually exist, it is common technical knowledge to draw between those skilled in the art for convenience.

By using the oxygen exchange diagram of this blast furnace, it is possible to grasp the gas utilization rate and the like in magnetite and wustite. In addition, as shown in FIG. 2, an operation state in which the operation line passes on the right side of the Weq point (a state in which the CO ₂ concentration of the reducing gas becomes higher) cannot be performed in reality because the reduction cannot proceed. Absent. Therefore, in order to perform reduction in blast furnace operation, it is necessary to perform an action such that at least the operation line passes on the left side of the Weq point. On the other hand, since the slope of this straight line represents the amount of carbon consumed in the reaction, it is considered that the above-mentioned slope is preferably small from the viewpoint of reducing energy consumption and carbon dioxide emission. Therefore, assuming that it is desirable to make the operation line as close as possible to the Weq point, an oxygen exchange diagram and a list diagram have been conventionally used in the operation design of the blast furnace.

Japanese Patent Laid-Open No. 61-253309 JP-A-5-156335 European Patent Application No. 0207779

Iron and steel, Vol. 79 (1993) No. 9, N618.

  When the present inventors examined improvement of the operation of the direct reduction furnace, a situation in which the descending of the charge and the gas permeability became unstable. As a result of the investigation, it was confirmed that the pellets which are considered to be difficult to reduce by the blast furnace method are reduced. Reduction powdering is triggered by a decrease in strength due to the phase change from hematite to magnetite, which suggests that a stagnant region of magnetite is generated in the direct reduction furnace.

Therefore, when the evaluation by the oxygen exchange diagram was applied to the direct reduction furnace operation, (1) the oxygen exchange diagram of the direct reduction furnace that blows high H ₂ gas is different from the oxygen exchange diagram of the blast furnace operation, It was found that the Meq point in the equilibrium constraint region greatly protruded toward the low gas utilization rate side, and (2) that the operation line and the Meq point were close to each other under the condition that reduced powdering of the pellet was confirmed. . Further studies were made on this, and the following findings were obtained.

The direct reduction method is different from the blast furnace reduction method in which CO is used as the reducing gas in that a gas mainly composed of H ₂ such as a reformed gas obtained by reforming natural gas is used as the reducing gas. That is, since the Meq point is sensitively influenced by the operating condition and the in-furnace condition, it is necessary to appropriately consider the influence. Therefore, the theory based on the oxygen exchange diagram of the blast furnace reduction method cannot be directly applied to the direct reduction method. Therefore, the present invention aims to create an oxygen exchange diagram suitable for the direct reduction method, and to stabilize the direct reduction operation based on the oxygen exchange diagram.

In order to solve the above problems, the present invention provides, as one aspect, (1) a shaft furnace type direct reduction method for producing reduced iron using a reducing gas mainly composed of hydrogen, and the reducing gas to be blown in The operating line information on the oxygen exchange diagram determined by the material balance of the raw material to be charged, the point A specified from the gas composition of the hematite O / Fe and the reducing gas at the gas outlet, and the reduced iron Based on the reduced iron composition at the discharge outlet and the B point specified from the gas composition at the gas inlet of the reducing gas, and based on the operating line, all the hematite contained in the raw material is converted into magnetite. a second step of estimating the gas utilization rate eta _T at point M which varies, for the reduction gas and the raw material, amount of material balance and heat between the said point M, and the point a and the point B By taking the supporting, gas temperature T _g of the reducing gas at the point _M, with estimates of the _M, the estimates of the gas temperature T _g, based on _M, the following equilibrium gas utilization ratio eta _E from the equation A 3 and steps of, if the equilibrium gas utilization ratio eta _E minus the gas utilization rate eta _T △ eta is smaller than a first predetermined value determined from the viewpoint of reduction degradation suppressing, the said △ eta first And a fourth step of performing an action of increasing than 1.
[Formula A]

Where K _CO (T) is an equilibrium constant of (1 / 0.85) Fe ₃ O ₄ + CO = (3 / 0.85) FeO _1.05 + CO ₂ corresponding to the gas temperature T _{g, M} ,
K _H2 (T): (1 / 0.85) Fe ₃ O ₄ + H ₂ = (3 / 0.85) FeO _1.05 + H ₂ O corresponding to the gas temperature T _{g, M}
V _{g1, M} : the flow rate of CO contained in the reducing gas at the point M ,
V _{g2, M} : the flow rate of CO ₂ contained in the reducing gas at the M point ,
V _{g3, M} is the flow rate of H ₂ contained in the reducing gas at point M ,
V _{g4, M} : the flow rate of H ₂ O contained in the reducing gas at the M point ,
T _{s, M} : The temperature of the raw material at the M point, which is the same as the T _{g, M.}

  (2) In the configuration of (1), when Δη is larger than a second predetermined value that is larger than the first predetermined value, the Δη is reduced by performing an action to decrease the Δη. The first predetermined value may be approached. According to the structure of (2), the energy efficiency of reducing gas can be improved, suppressing reduction | restoration powdering.

  (3) In the fourth step in the configuration of (1) above, a first action for increasing the CO concentration of the reducing gas blown from the gas inlet, and the temperature of the reducing gas blown from the gas inlet is increased. A second action for reducing the discharge speed of the reduced iron, or a third action for increasing the blowing speed of the reducing gas blown from the gas inlet, and the blowing speed and reduction of the reducing gas blown from the gas inlet You may implement at least 1 action among 4th actions which increase the discharge | emission speed | rate of iron by equal ratio.

The present invention has, as another aspect, (4) a shaft furnace type in which raw material is lowered in a shaft furnace and a reduction gas mainly composed of hydrogen is used to sequentially reduce hematite to magnetite and magnetite to reduced iron. A first reduction method for obtaining a gas temperature of a reducing gas, a flow rate for each gas composition of the reducing gas, a temperature of the raw material, and a weight ratio for each raw material composition at a first position corresponding to hematite. And a second step for obtaining a gas temperature of the reducing gas, a flow rate for each gas composition of the reducing gas, a temperature of the raw material and a weight ratio for each raw material composition at a second position corresponding to the reduced iron, and a reducing gas For the raw material, a balance between the amount of material and a heat balance is obtained between the first and second positions and the third position where all the hematite contained in the raw material changes to magnetite. It makes the gas temperature T _g of the reducing gas in the third _position, with estimates of _M, and a third step of estimating the gas utilization rate eta _T in the third position from the formula B below, Based on the estimated gas temperature T _{g, M} , the fourth step of estimating the equilibrium gas utilization rate η _E from the following equation C, and Δη obtained by subtracting the gas utilization rate η _T from the equilibrium gas utilization rate η _E is And a fifth step of performing an action of increasing Δη above the first predetermined value when it is smaller than a first predetermined value determined from the viewpoint of reducing powder reduction. And
[Formula B]

[Formula C]

However, d0: The amount of oxygen per ton of reduced iron is converted to the gas volume in the standard state (0 ° C., 1 atm),
V _{g1, i} is the flow rate of CO contained in the reducing gas at the second position,
V _{g2, i} : the flow rate of CO ₂ contained in the reducing gas at the second position ,
V _{g3, i} is the flow rate of H ₂ contained in the reducing gas at the second position ,
V _{g4, i} is the flow rate of H ₂ O contained in the reducing gas at the second position ,
K _CO (T): Equilibrium constant of (1 / 0.85) Fe ₃ O ₄ + CO = (3 / 0.85) FeO _1.05 + CO ₂ corresponding to gas temperature T _{g, M}
K _H2 (T): (1 / 0.85) Fe ₃ O ₄ + H ₂ = (3 / 0.85) FeO _1.05 + H ₂ O corresponding to the gas temperature T _{g, M}
V _{g1, M} is the flow rate of CO contained in the reducing gas at the third position ,
V _{g2, M} : the flow rate of CO ₂ contained in the reducing gas at the third position ,
V _{g3, M} is the flow rate of H ₂ contained in the reducing gas at the third position ,
V _{g4, M} : the flow rate of H ₂ O contained in the reducing gas at the third position ,
T _{s, M} : The temperature of the raw material at the third position ( M point ) , which is the same as T _{g, M.}

  (5) In the configuration of (4), when Δη is larger than a second predetermined value that is larger than the first predetermined value, an action for decreasing Δη is performed, whereby Δη May be brought close to the first predetermined value. According to the structure of (5), the energy efficiency of reducing gas can be improved, suppressing reduction | restoration powdering.

  (6) In the fifth step in the configuration of (4), the first action for increasing the CO concentration of the reducing gas blown from the gas inlet, and the temperature of the reducing gas blown from the gas inlet is increased. A second action for reducing the discharge speed of the reduced iron, or a third action for increasing the blowing speed of the reducing gas blown from the gas inlet, and the blowing speed and reduction of the reducing gas blown from the gas inlet You may implement at least 1 action among 4th actions which increase the discharge | emission speed | rate of iron by equal ratio.

  According to the present invention, since direct reduction is performed based on an oxygen exchange diagram suitable for the direct reduction method, the operation can be stabilized.

It is an oxygen exchange diagram of a blast furnace. It is an oxygen exchange diagram of a blast furnace (when reduction is impossible). Temperature is a graph showing the relationship between _CO 2 / corresponds to the equilibrium gas utilization rate (CO + CO _2). Temperature is a graph showing the relationship between the equilibrium gas utilization _H 2 corresponding to the ratio _{O / (H 2 + H 2} O). It is a schematic block diagram of a shaft furnace. It is the flowchart which showed the preparation method of an oxygen exchange diagram. It is an oxygen exchange diagram of a shaft furnace (corresponding to step S1). It is an oxygen exchange diagram of a shaft furnace (corresponding to step S2). It is an oxygen exchange diagram of a shaft furnace (corresponding to step S4). These are the amount of gas and raw material at point A, point M and point C, temperature, and the like. It is a flowchart of a 2nd embodiment. It is an oxygen exchange diagram which showed quantitatively the effect by CO concentration increase. It is the oxygen exchange diagram which showed quantitatively the effect by blast temperature increase (+ 100K). It is the oxygen exchange diagram which showed quantitatively the effect by ventilation temperature increase (+ 150K). It is the oxygen exchange diagram which showed quantitatively the effect by the ventilation volume increase. It is the oxygen exchange diagram which showed quantitatively the effect when increasing a ventilation speed and a product discharge speed by equal ratio. It is the oxygen exchange diagram which showed quantitatively the effect when both a ventilation speed and a product discharge speed were increased.

(Reduced powder in the direct reduction method)
The reason why reduced powdering is important in the direct reduction method will be described. This is the basis of the present invention. FIG. 3 is a graph showing the relationship between temperature and CO ₂ / (CO + CO ₂ ) corresponding to the equilibrium gas utilization rate. FIG. 4 is a graph showing the relationship between temperature and H ₂ O / (H ₂ + H ₂ O) corresponding to the equilibrium gas utilization rate. The gas utilization factor in these reduction equilibria can be determined by temperature from a thermodynamic technique.

  Referring to FIG. 3, in the reduction method using mainly CO gas as in the blast furnace, the equilibrium gas utilization rate when reducing from magnetite to wustite is 0.56 or more. In normal blast furnace operation, this equilibrium constraint is not a problem. That is, in the case of a blast furnace, theoretically, the reduction reaction from magnetite to wustite can be continued if the gas utilization rate is smaller than 0.56 regardless of the gas temperature. In other words, considering the general operating conditions of the blast furnace, the Meq point moves almost without affecting the operation regardless of the in-furnace conditions.

Referring to FIG. 4, in the reduction method using mainly H ₂ gas as in the direct reduction furnace, the equilibrium gas utilization rate decreases as the temperature decreases. Reduction by H ₂ gas is generally an endothermic reaction, and the temperature in the furnace is also lower than that of CO reduction, which promotes this tendency. Therefore, in direct reduction, the Meq point moves depending on the operating conditions and in-furnace conditions, and the equilibrium limitation of the reduction becomes an important operational problem. It is known that the temperature at which the reduction to wustite actively proceeds in a direct reduction furnace is about 600 to 800 ° C. In particular, from the results of experiments, model analysis, and the like, under conditions where the composition of the reducing gas is H ₂ / CO> 1 (when the blowing gas contains H ₂ O and CO ₂ , (H ₂ + H ₂ O) / (CO + CO ₂ )> 1), this tendency was found to be significant. Furthermore, it is known that the reduction reaction rate is generally proportional to the difference between the reducing gas concentration C _i of the atmosphere and the reducing gas concentration Ce in the equilibrium reached by the reducing gas (Shiro Sugaya: Introduction to Metal Chemistry Series 2 Steel Smelting, Japan Institute of Metals (2000), p. 54).

That is, when the reduction of the Meq point becomes a restriction, the reduction of the magnetite stagnates, and the region expands in the furnace, and this is pulverized due to the impact accompanying the lowering of the charge (that is, , Reduction powdering occurs), gas flow is obstructed, and operation becomes unstable. Reduction powdering is known to be a destruction of connective tissue based on volume expansion accompanying the reduction from hematite to magnetite in a low temperature region, and reduction powdering occurs when the reduction stagnates in the state of magnetite.
(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a schematic configuration diagram of a shaft furnace (corresponding to a reduction furnace) for effectively carrying out the direct reduction method. The shaft furnace 1 is a vertical shaft furnace and includes a gas discharge port 11, a gas blowing port 12, and a reduced iron discharge port 13, and reduces the raw material. The gas blowing port 12 is formed in a substantially middle stage of the shaft furnace 1 and supplies a reducing gas into the shaft furnace 1. As the reducing gas, natural gas or a reformed gas mainly composed of H ₂ obtained by reforming natural gas can be used.

  The reducing gas is exhausted as exhaust gas from the gas outlet 11 provided at the top of the furnace after reducing the raw material charged from the top of the shaft furnace 1. The reduced raw material, that is, reduced iron, is cooled by a cooling gas (not shown) circulating in the lower part of the furnace, and then discharged from a reduced iron discharge port 13 provided in the lower part of the furnace.

As the raw material, iron ore mainly composed of Fe ₂ O ₃ and processed products thereof can be used. As the processed product, pellets or briquettes obtained by agglomerating massive iron ore, sintered ore, and powdered iron ore can be used.

  The flowchart in FIG. 6 shows a procedure for creating an oxygen exchange diagram. 7A corresponds to step S1 in FIG. 6, FIG. 7B corresponds to step S2 in FIG. 6, and FIG. 7C corresponds to step S4 in FIG. .

In step S1, points A and B are obtained. The point A can be specified from the O / Fe of hematite and the gas utilization rate of the reducing gas at the gas outlet 11. Since O / Fe of hematite is 1.5, the value of the vertical axis at point A is 1.5. The gas utilization rate (value on the horizontal axis) of the reducing gas at point A is determined by examining the gas composition of the reducing gas discharged from the gas outlet 11 and (CO ₂ + H ₂ O) / (CO + CO ₂ + H ₂ + H ₂ O). ). The gas composition can be measured, for example, by an infrared gas analysis method as defined in JIS K2301. The point B can be specified from the reduced iron O / Fe discharged from the reduced iron discharge port 13 and the gas utilization rate of the reducing gas blown from the gas blowing port 12. O / Fe of reduced iron is, for example, a composition measured by JIS M8212 (total iron amount), M8213 (iron (ii) amount), ISO 5416 (metal iron amount), or metallization measured by JP-A-2002-88417. It can be evaluated from the rate. That is, as illustrated in FIG. 7A, according to an increase in the gas utilization rate of the reducing gas based on the O / Fe at the inlet and outlet of the raw material and the gas composition at the reducing gas inlet and outlet. Operation line information in which O / Fe of the raw material gradually increases can be acquired.

In step S2, M point on the operation line is obtained. Here, since the point M corresponds to magnetite as described in the background art, it is plotted at a point on the operation line where O / Fe is 1.33 (see FIG. 7B). As a result, the gas utilization rate η _T at the point M can be obtained.

In step S3, the gas temperature _{Tg, M} of the reducing gas at point _M is estimated. The method for estimating the gas temperatures _{Tg, M} will be described in detail with reference to FIG. The composition of the metal contained in the raw material is shown inside the dotted line indicated as the raw material, and corresponds to the point A in FIG. In this embodiment, a general iron-making raw material is used as a raw material. Hematite is G _{s1, i} (kg / t-DRI), magnetite is G _{s2, i} (kg / t-DRI), and wustite is G _{s3, i} ( kg / t-DRI), Fe is _{G s4, i (kg / t} -DRI), s5 CaO is _{G, i (kg / t-} DRI), SiO 2 is _{G s6, i (kg / t} -DRI), Al ₂ O ₃ is contained in G _{s7, i} (kg / t-DRI), and MgO is contained in G _{s8, i} (kg / t-DRI). “I” is an abbreviation for “input”.

T _{s, i} (K) is the temperature of the raw material. The composition of the metal contained in the raw material at the point M is shown inside the dotted line indicated as the M point raw material, which corresponds to the point M in FIG. The composition of the metal contained in the reduced iron is shown on the inner side of the dotted line indicated as the product, and corresponds to the point B in FIG. 7B. “O” is an abbreviation for “output”.

The composition of the reducing gas blown from the gas blowing port 12 is shown inside the dotted line indicated as the blown gas. In this embodiment, a gas generally used in the direct reduction method is used as a reducing gas, and the gas composition is such that the CO gas flow rate is V _{g1, i} (Nm ³ / t-DRI), and the CO ₂ gas flow rate. Is V _{g2, i} (Nm ³ / t-DRI), the gas flow rate of H ₂ is V _{g3, i} (Nm ³ / t-DRI), and the gas flow rate of H ₂ O is V _{g4, i} (Nm ³ / t- DRI), the gas flow rate of N ₂ is V _{g5, i} (Nm ³ / t-DRI).

T _{g, i} (K) is the gas temperature of the reducing gas at the gas inlet 12. The composition of the reducing gas at the point M is shown on the inner side of the dotted line indicated as the point M gas. The gas composition of the reducing gas exhausted from the gas discharge port 11 is shown inside the dotted line indicated as the furnace top gas.

  The following conditional expression is derived from the definition of point M (stage where hematite is all reduced to magnetite).

Formula 1

Formula 2

Formula 3

Formula 4

In the above formula (2), “55.85” is the atomic weight of Fe, and “16” is the atomic weight of oxygen. Equation (3) means that the contents of wustite, Fe, CaO, SiO ₂ , Al ₂ O ₃ and MgO do not change when changing from hematite to magnetite. Equation (4) means that the content of N ₂ contained in the reducing gas does not change when changing from hematite to magnetite.

  From the mass balance of C, the following conditional expression is derived.

Formula 5

  From the mass balance of H, the following conditional expression is derived.

Equation 6

  From the mass balance of O,

Equation 7

Then,

Equation 8

That is,

Equation 9

It becomes. d0 (m ³ / t) is obtained by converting the amount of substance per ton of oxygen product into a gas volume in a standard state (0 ° C., 1 atm).

Here, temperature difference between the fixed and the reducing gas at the point M, _{i.e., T} g, M _{-T s, M} may be considered as zero. When the heat loss from the furnace body is evaluated, -Q (J / t-DRI) (Q ≧ 0) as the heat loss is assumed to occur in a portion below the M point. The generation enthalpy of each chemical species is expressed as follows.
(About reducing gas)
CO production enthalpy: ΔHf ⁰ _g1 (J / Nm ³ )
CO ₂ production enthalpy: ΔHf ⁰ _g2 (J / Nm ³ )
H ₂ production enthalpy: ΔHf ⁰ _g3 (J / Nm ³ )
H ₂ O (g) generation enthalpy: ΔHf ⁰ _g4 (J / Nm ³ )
N ₂ generation enthalpy: ΔHf ⁰ _g5 (J / Nm ³ )
(About raw materials)
Fe ₂ O ₃ production enthalpy: ΔHf ⁰ _s1 (J / kg)
Fe ₃ O ₄ production enthalpy: ΔHf ⁰ _s2 (J / kg)
FeO _1.05 formation enthalpy: ΔHf ⁰ _s3 (J / kg)
Fe generation enthalpy: ΔHf ⁰ _s4 (J / kg)
CaO generation enthalpy: ΔHf ⁰ _s5 (J / kg)
SiO ₂ production enthalpy: ΔHf ⁰ _s6 (J / kg)
Al ₂ O ₃ production enthalpy: ΔHf ⁰ _s7 (J / kg)
MgO production enthalpy: ΔHf ⁰ _s8 (J / kg)
Further, the heat capacity (constant pressure specific heat) can be expressed as a function of temperature as follows.
(About reducing gas)
CO heat capacity: Cp _g1 (T) (J / Nm ³ .K)
CO ₂ heat capacity: Cp _g2 (T) (J / Nm ³ .K)
H ₂ heat capacity: Cp _g3 (T) (J / Nm ³ .K)
H ₂ O (g) heat capacity: Cp _g4 (T) (J / Nm ³ .K)
N ₂ heat capacity: Cp _g5 (T) (J / Nm ³ .K)
(About raw materials)
Fe ₂ O ₃ heat capacity: Cp _s1 (T) (J / kg.K)
Fe ₃ O ₄ heat capacity: Cp _s2 (T) (J / kg.K)
FeO _1.05 heat capacity: Cp _s3 (T) (J / kg.K)
Fe heat capacity: Cp _s4 (T) (J / kg.K)
CaO heat capacity: Cp _s5 (T) (J / kg.K)
SiO ₂ heat capacity: Cp _s6 (T) (J / kg.K)
Al ₂ O ₃ heat capacity: Cp _s7 (T) (J / kg.K)
MgO heat capacity: Cp _s8 (T) (J / kg.K)
Here, when the heat balance is taken as (heat input) = (heat output) between the blown gas and the product and the point M, the following equation is obtained.

Equation 10

Here, T ₀ is generally given an arbitrary value at a reference temperature, but here, 298K, which is generally used as a reference state temperature in the field of thermodynamics, is used.

Further, assuming that the equilibrium of the following equation (11) that is a water gas shift reaction is established at the M point, the equilibrium constant Kw = [CO ₂ ] [H ₂ ] / [CO] [H ₂ O] is It can be obtained from the gas temperature Tg _{, M} by a thermodynamic method.

Equation 11

Therefore, the consumption amount of CO and H ₂ O by the water gas shift reaction is equal to the generation amount of CO ₂ and H ₂ , so this is set as dW,

Formula 12

Equation 13

Equation 14

Equation 15

Then, equation (10) and equation (16) below

Equation 16

T _{s, M} and dW may be obtained so as to satisfy the above. For example, it can be obtained by a numerical calculation method such as a Newton-Raphson method or a bisection method.

In step S4, the equilibrium gas utilization rate η _E at the gas temperature T _{g, M} is estimated. The equilibrium gas utilization rate η _E at the Meq point (M point in the equilibrium constraint) can be obtained from the following calculation formula based on the gas temperature (T _{g, M} or T _{s, M} ) at the M point.

Equation 17

Equilibrium constant K _CO (T) = [CO ₂ ] / [CO]

Equation 18

By substituting the equilibrium constant K _H2 (T) = [H ₂ O] / [H ₂ ] into the following equation (19), the equilibrium gas utilization factor η _E can be obtained.
The coefficient of formula 17 and formula 18, gave _CO, and coefficient of CO 2, _{H 2} and _{H 2} 0 to 1.

Equation 19

Note that the equilibrium constant can be calculated based on the gas temperature Tg, M at the point _M , for example, from thermodynamic data in a known document. FIG. 7C schematically shows the equilibrium gas utilization rate η _E.

Next, a difference Δη between the equilibrium gas utilization rate η _E at the Meq point and the gas utilization rate η _T at the M point is obtained.

Equation 20

Here, Δη is preferably 0.02 or more. If Δη is 0.02 or more, the M point and the Meq point are sufficiently separated from each other, and reduction powdering is reliably suppressed, so that the operation can be stabilized. That is, if the operating line gets too close to the Meq point, the reduction from magnetite to wustite stagnates, and a fragile magnetite region is generated extensively in the furnace. cause. By implementing an action such that Δη is 0.02 or more, such a problem can be suppressed. The upper limit value of Δη is not specified. If Δη becomes too large, the use efficiency of the reducing gas is lowered and the energy efficiency is lowered. However, the improvement of the energy efficiency is not the main problem of the present application, and therefore the upper limit value is not particularly defined.

  Here, the reason why the appropriate value of Δη (corresponding to the first predetermined value) is set to 0.02 or more is that, in the experimental results, the amount of powder generated by reducing powdering was the most intense in the reduction furnace When evaluated by a weight fraction of 3 mm or less in the region (hereinafter, this value is referred to as “powder rate”), Δη was 0.02 while Δη was 0.02 or more, while no significant difference was observed. In the following, it is because the increase in the powder rate became remarkable. The recommended value of the first predetermined value described above is an example based on experimental examination. In carrying out the invention of the present application, it should be appropriately changed according to the reducing powdering characteristics of the raw materials used and the aeration status of the reduction furnace.

(Second Embodiment)
In the above-described embodiment, the point A and the point B are specified and an operation diagram is created, and the gas utilization rate η _T at the point M is obtained from this operation diagram. Without creating a figure, the gas utilization rate η _T at the point M is obtained from the calculation formula. FIG. 9 is a flowchart of the present embodiment, and corresponds to FIG. 6 of the first embodiment.

In step S11, the gas temperature of the reducing gas, the flow rate for each gas composition of the reducing gas, the temperature of the raw material, and the weight ratio for each raw material composition are acquired at the first position corresponding to hematite. Here, the first position corresponds to point A in the first embodiment. Therefore, the gas temperature of the reducing gas corresponds to T _{g, o} (K) of the first embodiment, and the flow rate for each gas composition is V _{g1, o} (Nm ³ / t-DRI) of the first embodiment, V _{g2, o} (Nm ³ / t-DRI), V _{g3, o} (Nm ³ / t-DRI), V _{g4, o} (Nm ³ / t-DRI), V _{g5, o} (Nm ³ / t-DRI) ). Moreover, the temperature of the raw material corresponds to T _{s, i} (K) of the first embodiment, and the weight ratio for each raw material composition is G _{s1, i} (kg / t-DRI), G _{s2 of the} first embodiment. _{, I} (kg / t-DRI), _{Gs3, i} (kg / t-DRI), _{Gs4, i} (kg / t-DRI), _{Gs5, i} (kg / t-DRI), _{Gs6, i} (Kg / t-DRI), G _{s7, i} (kg / t-DRI), and G _{s8, i} (kg / t-DRI).

In step S12, the gas temperature of the reducing gas, the flow rate for each gas composition of the reducing gas, the temperature of the raw material, and the weight ratio for each raw material composition are acquired at the second position corresponding to the reduced iron. Here, the second position corresponds to point B in the first embodiment. Therefore, the gas temperature of the reducing gas corresponds to T _{g, i} (K) of the first embodiment, and the flow rate for each gas composition is V _{g1, i} (Nm ³ / t-DRI) of the first embodiment, V _{g2, i} (Nm ³ / t-DRI), V _{g3, i} (Nm ³ / t-DRI), V _{g4, i} (Nm ³ / t-DRI), V _{g5, i} (Nm ³ / t-DRI) ). Moreover, the temperature of the raw material corresponds to T _{s, o} (K) of the first embodiment, and the weight ratio for each raw material composition is G _{s1, o} (kg / t-DRI), G _{s2 of the} first embodiment. _{, O} (kg / t-DRI), _{Gs3, o} (kg / t-DRI), _{Gs4, o} (kg / t-DRI), _{Gs5, o} (kg / t-DRI), _{Gs6, o} (Kg / t-DRI), _{Gs7, o} (kg / t-DRI), and _{Gs8, o} (kg / t-DRI). However, the order of steps S11 and S12 may be reversed.

In step S13, with respect to the reducing gas and the raw material, a material amount balance and a heat balance are obtained between the first and second positions described above and a third position where all the hematite contained in the raw material changes to magnetite. Thus, the gas temperature _{Tg, M} of the reducing gas at the third position is estimated, and the gas utilization rate η _T at the third position is estimated from the following equation (21). The third position corresponds to point M in the first embodiment. Therefore, the gas temperature _{Tg, M} can be calculated by the same method as in the first embodiment.

Equation 21

In step S14, the equilibrium gas utilization rate η _E at the gas temperature T _{g, M} is calculated. Since the calculation method of the equilibrium gas utilization rate η _E is the same as that of the first embodiment, the description will not be repeated.

Since the difference Δη between the equilibrium gas utilization rate η _E and the gas utilization rate η _T is also the same as in the first embodiment, the description will not be repeated.

Next, a method for increasing Δη will be described. In the following, conditions under which trouble due to reduced powdering occurred (blowing temperature: 1000 ° C., total flow rate: 300 NL / min, CO: CO ₂ : H ₂ : H ₂ O = 9.0: 1.0: 81.0: 9.0, discharge conditions: 12 kg / h, Δη = 0) are shown by thin lines for comparison. That is, in the comparative example, the operation is performed under the condition where the M point and the Meq point overlap. Note that the powder ratio under these conditions was 23%.

As actions for increasing Δη, the following means (1) to (4) are conceivable. These means may be implemented alone or in combination.
(1) The gas composition in the blowing gas that increases the CO concentration in the blowing gas,
When CO concentration was increased by changing to CO: CO ₂ : H ₂ : H ₂ O = 18.0: 2.0: 72.0: 8.0, as shown in FIG. The equilibrium constraint shifted from the thin line to the position shown by the solid line. As a result, Δη could be increased to 0.034. In addition, the powder rate decreased to 5.2%. As means for increasing the CO concentration, for example, H ₂ or H ₂ O contained in the blast is reduced, or natural gas with relatively little hydrogen is used (for example, carbon number such as C ₂ H ₆ and C ₃ H _8). A natural gas having a high hydrocarbon concentration and a high hydrocarbon concentration).

(2) Increasing the blowing temperature By raising the blowing temperature, the reduction is promoted and the gas utilization rate η _T is also increased. However, since the increase amount of the equilibrium gas utilization rate η _E is relatively large, as a result, Δη Will increase. In the example of FIG. 11A, Δη increased by 0.008 by increasing the blowing temperature by + 100K. The powder rate at this time was 14.1%. In the example of FIG. 11B, Δη increased by 0.037 by increasing the blowing temperature by + 150K. The powder rate at this time was 5.1%. In the example of FIG. 11C, Δη increased by 0.096 by increasing the blowing temperature by + 200K. The powder rate at this time was 4.6%. The blowing temperature can be raised by increasing the amount of heat for heating the blowing gas.

(3) Decrease product discharge speed or increase air blowing speed.
By reducing the product discharge speed or increasing the air blowing speed, the air blowing basic unit, which is the air blowing amount per reduced iron unit amount, increases and the heat supply amount relatively increases as brought-in sensible heat. Gas utilization rate η _E increases. Furthermore, the slope of the operation line increases and the gas utilization rate η _T decreases. In the example of FIG. 12, Δη increased by 0.037 by increasing only the air blowing speed by 25%. The powder rate at this time decreased to 5.4%. The product discharge rate can be controlled by a known method. Further, the air blowing speed can be increased by performing a process for increasing the air blowing amount.

(4) Increasing the blowing speed and the product discharge speed by an equal ratio By increasing the blowing speed and the product discharge speed by an equal ratio, the product reduction rate decreases, so the ultimate gas utilization rate at point M decreases (gas The utilization factor η _T decreases). In the example of FIG. 13, Δη increased by 0.02 when both the blowing speed and the product discharge speed were increased by 20%. The powder rate at this time was 6.2%.

(Other embodiments)
When Δη is larger than a second predetermined value that is larger than the first predetermined value, an action for decreasing Δη may be performed under the condition that Δη does not become smaller than the first predetermined value. For example, when Δη is 0.1, since the energy efficiency of the blown gas is poor, an action for reducing Δη may be performed. The second predetermined value described above can be set as appropriate based on the target value of energy efficiency. Δη is reduced by performing an action opposite to the actions (1) to (4). Thereby, energy efficiency can be improved, suppressing reduction | restoration powdering.

1 Shaft furnace 11 Gas outlet 12 Gas inlet 13 Reduced iron outlet

Claims (6)

A shaft furnace type direct reduction method for producing reduced iron using a reducing gas mainly composed of hydrogen,
The operating line information on the oxygen exchange diagram determined by the reducing gas to be blown and the material balance of the raw material charged is point A specified from the O / Fe of hematite and the gas composition of the reducing gas at the gas outlet. A first step of obtaining based on the reduced iron composition at the outlet for discharging reduced iron and the B point specified from the gas composition at the gas inlet of the reducing gas;
A second step of estimating a gas utilization rate η _T at point M where all of the hematite contained in the raw material changes to magnetite based on the operating line;
For the reducing gas and the raw material, the gas temperature Tg, M of the reducing gas at the point _M is estimated by taking the mass balance and the heat balance between the point M and the points A and B. And a third step of estimating the equilibrium gas utilization factor η _E from the following equation A based on the gas temperatures T _{g, M} :
Equilibrium gas utilization ratio eta △ eta minus gas utilization rate eta _T from _E is smaller than the first predetermined value determined from the viewpoint of reduction degradation suppressing, the △ eta than the first predetermined value A fourth step of performing an action that also increases
A direct reduction method comprising:
[Formula A]
・ ・ ・ ・ ・ ・ (Formula A)
Where K _CO (T) is an equilibrium constant of (1 / 0.85) Fe ₃ O ₄ + CO = (3 / 0.85) FeO _1.05 + CO ₂ corresponding to the gas temperature T _{g, M} ,
K _H2 (T): (1 / 0.85) Fe ₃ O ₄ + H ₂ = (3 / 0.85) FeO _1.05 + H ₂ O corresponding to the gas temperature T _{g, M}
V _{g1, M} : the flow rate of CO contained in the reducing gas at the point M ,
V _{g2, M} : the flow rate of CO ₂ contained in the reducing gas at the M point ,
V _{g3, M} is the flow rate of H ₂ contained in the reducing gas at point M ,
V _{g4, M} : the flow rate of H ₂ O contained in the reducing gas at the M point ,
T _{s, M} : The temperature of the raw material at the M point, which is the same as the T _{g, M.}
  When the Δη is larger than a second predetermined value that is larger than the first predetermined value, the Δη is brought closer to the first predetermined value by performing an action to decrease the Δη. The direct reduction method according to claim 1, wherein: In the fourth step,
A first action for increasing the CO concentration of the reducing gas blown from the gas inlet;
A second action for increasing the temperature of the reducing gas blown from the gas inlet, a third action for reducing the reduced iron discharge speed, or increasing the blowing speed of the reducing gas blown from the gas inlet, 2. The direct reduction method according to claim 1, wherein at least one of the fourth actions of increasing the blowing speed of the reducing gas blown from the gas inlet and the discharging speed of the reduced iron at an equal ratio is performed. . It is a direct reduction method of the shaft furnace type in which the raw material is lowered in the shaft furnace, using a reducing gas mainly composed of hydrogen, and sequentially reduced from hematite to magnetite and from magnetite to reduced iron.
In a first position corresponding to hematite, a first step of obtaining a gas temperature of the reducing gas, a flow rate for each gas composition of the reducing gas, a temperature of the raw material, and a weight ratio for each raw material composition;
A second step for obtaining a gas temperature of the reducing gas, a flow rate for each gas composition of the reducing gas, a temperature of the raw material and a weight ratio for each raw material composition at a second position corresponding to the reduced iron;
With respect to the reducing gas and the raw material, the first and second positions and the third position where all the hematite contained in the raw material changes to magnetite are balanced, so that the first A third step of estimating the gas temperature T _{g, M} of the reducing gas at the position 3 and estimating the gas utilization rate η _T at the third position from the following equation B:
A fourth step of estimating an equilibrium gas utilization rate η _E from the following equation C based on the estimated gas temperatures T _{g, M} :
Equilibrium gas utilization ratio eta △ eta minus gas utilization rate eta _T from _E is smaller than the first predetermined value determined from the viewpoint of reduction degradation suppressing, the △ eta than the first predetermined value A fifth step of performing an increasing action,
A direct reduction method comprising:
[Formula B]
η _T = (V _{g2, i} + V _{g4, i} + dO) / (V _{g1, i} + V _{g2, i} + V _{g3, i} + V _{g4, i} ) × 100 (formula B )
[Formula C]
・ ・ ・ ・ ・ ・ (Formula C)
However, d0: The amount of oxygen per ton of reduced iron is converted to the gas volume in the standard state (0 ° C., 1 atm),
V _{g1, i} is the flow rate of CO contained in the reducing gas at the second position,
V _{g2, i} : the flow rate of CO ₂ contained in the reducing gas at the second position ,
V _{g3, i} is the flow rate of H ₂ contained in the reducing gas at the second position ,
V _{g4, i} is the flow rate of H ₂ O contained in the reducing gas at the second position ,
K _CO (T): Equilibrium constant of (1 / 0.85) Fe ₃ O ₄ + CO = (3 / 0.85) FeO _1.05 + CO ₂ corresponding to gas temperature T _{g, M}
K _H2 (T): (1 / 0.85) Fe ₃ O ₄ + H ₂ = (3 / 0.85) FeO _1.05 + H ₂ O corresponding to the gas temperature T _{g, M}
V _{g1, M} is the flow rate of CO contained in the reducing gas at the third position ,
V _{g2, M} : the flow rate of CO ₂ contained in the reducing gas at the third position ,
V _{g3, M} is the flow rate of H ₂ contained in the reducing gas at the third position ,
V _{g4, M} : the flow rate of H ₂ O contained in the reducing gas at the third position ,
T _{s, M} : The temperature of the raw material at the third position ( point M ) , which is the same as T _{g, M.}
  When the Δη is larger than a second predetermined value that is larger than the first predetermined value, the Δη is brought closer to the first predetermined value by performing an action to decrease the Δη. The direct reduction method according to claim 4. In the fifth step,
A first action for increasing the CO concentration of the reducing gas blown from the gas inlet;
A second action for increasing the temperature of the reducing gas blown from the gas inlet, a third action for reducing the reduced iron discharge speed, or increasing the blowing speed of the reducing gas blown from the gas inlet, 5. The direct reduction method according to claim 4, wherein at least one of the fourth actions of increasing the blowing speed of the reducing gas blown from the gas inlet and the discharging speed of the reduced iron at an equal ratio is performed. .