JP7644352B2 - Methods for estimating the amount of slag in the cohesive zone of a blast furnace and methods for its operation - Google Patents

Description

The present invention relates to a method for estimating the amount of cohesive zone slag, which is an index that accurately represents the furnace conditions in the lower part of a blast furnace, and a method for operating a blast furnace using that index.

Traditionally, sintered ore, pellets, lump ore, etc. have been used as iron-containing charge materials in blast furnace operations. To stabilize blast furnace operations, efforts have been made to improve the particle size distribution, cold strength, reduction characteristics, etc. of these charge materials, and to increase the amount of self-fluxed sintered ore, which has good properties, used. In particular, the reducibility of iron-containing charge materials affects reaction efficiency, aeration stability, thermal stability, etc., so efforts have been made to improve and optimize these influencing factors.

For example, Patent Document 1 discloses that in blast furnace operation with a pulverized coal injection rate of 150 kg/tp (injection rate per ton of pig iron; "/tp" means per ton of pig iron) or more, _high alumina sintered ore containing 3.9 to 4.9 mass% SiO2, 0.5 to less than 1.2 mass% _MgO , 1.8 to 2.5 mass% _Al2O3 , and CaO/ _SiO2 (mass ratio) of 1.9 to 2.5 accounts for 50 to 80 mass% of the charge, thereby using a large amount of high alumina sintered ore and reducing the amount of blast furnace slag. According to the blast furnace operation of Patent Document 1, it is possible to reduce the slag ratio to 290 kg/tp or less.

The slag ratio (amount of slag) means the amount of slag generated per ton of pig iron. Slag is composed of gangue components (CaO, SiO ₂ , Al ₂ O ₃ , MgO) other than iron and carbon contained in the blast furnace charge and the injected pulverized coal, and the amount is approximately 250 to 320 kg/tp. The slag ratio (amount) is one of the controlling factors that govern the permeability of the lower part of the blast furnace.

Patent Document 2 discloses the use of sintered ore (SiO ₂ : 4.0-4.6 mass%, MgO: 1.0-1.4 mass%, FeO: 4.0-7.0 mass%, basicity (CaO/SiO ₂ ) (mass ratio): 2.0-2.3) with a reduction disintegration index RDI of 40% or more in blast furnace operation with a pulverized coal injection rate of 170 kg/tp or more. According to the blast furnace operation of Patent Document 2, it is possible to reduce the slag rate to 280 kg/tp or less.

However, the slag ratio (amount) described in Patent Documents 1 and 2 is the ratio (amount) of the discharged slag after reduction is complete, and does not accurately indicate the amount of molten liquid (which also contains unreduced FeO) that is generated in the blast furnace in an unreduced state.

The actual amount of molten liquid in a blast furnace, especially in the cohesive zone, depends heavily on the permeability of the blast furnace. Therefore, even if the component composition of the charge is designed to reduce the slag ratio, the amount of molten liquid in the cohesive zone may increase if the charge has poor reducibility. For this reason, in blast furnace operation, the slag ratio (amount) and the furnace permeability index often do not match. Therefore, there is a need to find a precise index that can accurately indicate the permeability inside the blast furnace and manage operations.

In addition to sintered ore, several types of iron-containing charges, such as pellets and lump ore, are usually charged into a blast furnace in arbitrary blend ratios. It has been proposed to collectively index these as the characteristics of blast furnace charges and use them to manage blast furnace operation.

Patent Document 3 discloses a method for managing the high-temperature properties of sintered ore, which involves calculating the permeability index at the high-temperature part of the sintered ore using a formula, and estimating and managing the high-temperature properties of the sintered ore from the calculated value. According to the method of Patent Document 3, the high-temperature properties of sintered ore can be estimated from commonly used management indices such as RDI (reduction disintegration index) and RI (reducibility), enabling rapid charge mix design. However, the method of Patent Document 3 is only applicable to sintered ore and cannot be applied to charge mix design including other charges.

Patent Document 4 discloses a method for adjusting the blending of iron-containing raw materials for blast furnace charging, characterized by blending the iron-containing raw materials for blast furnace charging so that the weighted average air permeability index for high-temperature properties at 1000°C or higher of the iron-containing raw materials for blast furnace charging is 5.7 or less. This method makes it possible to perform stable blast furnace operation with a low amount of Si in the molten iron.

However, although the method of Patent Document 4 is effective for selecting lump ores and for blending and adjusting them, it is difficult to apply this method to all charges. In fact, there are cases where blast furnace operation deteriorates even when the average air permeability index of the charge is 5.7 or less.

When measuring the high-temperature properties of a charge, the airflow resistance index is significantly affected by the packing structure (void ratio, etc.), so taking a weighted average of the airflow resistance index of a single brand does not take into account the changes in the packing structure that occur when several charge materials are mixed and charged. Therefore, the method of Patent Document 4 has the problem that its range of application is limited.

Japanese Patent Application Publication No. 11-43710 JP 2002-256312 A Japanese Unexamined Patent Publication No. 60-89525 Japanese Unexamined Patent Publication No. 59-38308

In blast furnace operation, where several types of iron-containing charges, such as sintered ore, pellets, and lump ore, are usually charged at an arbitrary mixing ratio, no index has been proposed to evaluate the furnace conditions, particularly the quality of gas permeability. In blast furnace operation, the quality of gas permeability inside the furnace depends on the amount of molten liquid (amount of slag) present in the cohesive zone formed by melting the iron-containing charges, but even if the slag composition of the entire blast furnace charge is grasped in a comprehensive manner, it is not possible to accurately predict the amount of molten liquid (amount of slag) present in the cohesive zone.

The present invention aims to provide a method for accurately estimating the amount of molten liquid present in the cohesive zone formed by melting iron-containing charges during blast furnace operation, in which several types of iron-containing charges, such as sintered ore, pellets, and lump ore, are typically charged at an arbitrary blend ratio, and to provide a blast furnace operation method that utilizes the estimated value.

Hereinafter, the amount of molten liquid present at the upper surface of the cohesive zone will be referred to as the "cohesive zone slag amount" and abbreviated as "CSV."

The present inventors have intensively studied a method for solving the above problems. As a result, they have found that the amount of slag in the cohesive zone, which is the amount of molten liquid present on the upper surface of the cohesive zone of a blast furnace, can be estimated by the formula (1), and that the furnace condition in the lower part of a blast furnace, in particular, the adequacy of gas permeability, can be appropriately evaluated using the amount of slag in the cohesive zone as an index.
Amount of slag in the cohesive zone = Amount of FeO remaining on the upper surface of the cohesive zone + Amount of gangue in the iron-containing charge (1)
The present invention has been made based on the above findings, and the gist of the present invention is as follows.

According to one aspect of the present invention, in a blast furnace operation in which iron-containing and carbonaceous charges are alternately charged into the blast furnace and the iron-containing charges are heated and reduced to produce pig iron, a method for estimating the amount of cohesive zone slag: CSV (kg/tp), which is the amount of molten liquid present on the upper surface of the cohesive zone formed by melting the iron-containing charges, is provided, characterized in that the method estimates the amount of cohesive zone slag: CSV (kg/tp) as the sum of the amount of FeO remaining on the upper surface of the cohesive zone of the iron-containing charges (kg/tp) and the amount of gangue of the iron-containing charges (kg/tp).

Here, a load-softening test may be performed on the iron-containing charge to determine the reduction rate Rs of the iron-containing charge at the time when the pressure drop starts to increase, and the amount of remaining FeO (kg/tp) may be calculated by the following formula (Ix).
Residual FeO amount (kg/tp) = (1833.236-202.842 x FeO [%] / T.Fe [%]) x (1-Rs/100)... (Ix)
T. Fe: Total iron content (%) in the iron-containing charge
FeO: Amount of FeO in iron-containing charge (%)
Rs: Reduction rate (%) at the time of pressure drop increase measured in a load-softening test on iron-containing charge

In addition, the CSV _T (kg/tp) of the entire burden consisting of a plurality of iron-containing burden materials may be calculated by the following formula (II).
CSV _T (kg/tp) = Σ(CSV _i・_wi・T.Fe _i )/Σ( _wi・T.Fe _i )...(II)
CSV _i : Slag amount of iron-containing charge i (kg/tp)
W _i : The blending ratio (%) of iron-containing charge i, or the blending unit (kg/tp)
T.Fe _i : T.Fe (%) of iron-containing charge i

In addition, a target value for the amount of cohesive zone slag may be set, and at least one of (a) to (d) may be performed so that the estimated amount of cohesive zone slag using the above-mentioned method for estimating the amount of cohesive zone slag is equal to or less than the target value.
(a) Adjustment of the blending ratio of the iron-containing charge charged to the blast furnace; (b) Adjustment of the content of one or _more of CaO, _SiO2 , _Al2O3 , MgO, CaO/ _SiO2 , and FeO in the iron-containing charge charged to the blast furnace; (c) Adjustment of the particle size of the iron-containing charge charged to the blast furnace; (d) Adjustment of the amount of carbonaceous charge mixed into the iron-containing charge layer.

The target amount of slag in the cohesive zone may also be 920 to 980 kg/tp.

The target amount of slag in the cohesive zone may also be 830 to 890 kg/tp.

According to the present invention, the amount of molten liquid in the cohesive zone can be estimated in blast furnace operation in which iron-containing charges such as sintered ore, pellets, and lump ore are mixed and charged. As a result, it becomes possible to accurately evaluate the furnace conditions in the lower part of the blast furnace, in particular, the suitability of the gas permeability. In addition, by using the amount of slag in the cohesive zone as one of the blast furnace operation management indicators, it is possible to suppress the temperature drop in the lower part of the blast furnace and stabilize the operation. Furthermore, it is possible to reduce the reducing agent ratio, thereby saving energy and reducing _CO2 .

The results of a heating reduction test using samples prepared by sintering sintered ore produced in a sintering machine to a particle size of 10 to 15 mm and the analysis results are shown in Fig. 1. (a) shows the transition of the reduction rate (%) and the change in pressure drop (mmAQ), and (b) shows the results of analyzing the heating reduction test results using the index of the present invention. FIG. 1 is a diagram showing the state of the cohesive zone and a comparison of the index of the present invention and the index of the prior art. 1 shows the analysis results of the lower K value in blast furnace operation. (a) shows the relationship between SV and the lower K value, and (b) shows the relationship between CSV and the lower K value. This is a diagram showing that the index "CSV _T " effectively functions as a management index by analyzing data in blast furnace operation. The left diagram shows the relationship between the lower K value and the CSV amount of slag in the cohesive zone, and the right diagram shows the relationship between the productivity and the CSV amount of slag in the cohesive zone. FIG. 1 is a graph showing the particle size dependence of CSV of sintered ore and lump ore. FIG. 13 is a diagram showing the CSV measured by mixing a carbon-containing material into a single layer of sintered ore. 1 is a diagram showing the operation results of Example 1. (a) shows the operation results when evaluated using the "amount of slag in the cohesive zone" of the present invention, and (b) shows the operation results when evaluated using the conventional "amount of slag." 1 is a diagram showing the operation results of Example 2. (a) shows the operation results when evaluated using the "amount of slag in the cohesive zone" of the present invention, and (b) shows the operation results when evaluated using the conventional "amount of slag."

<Background to the Invention>
First, the background to the present invention will be described.
(Cohesive zone and breathability)
Iron-containing charges (sinter, pellets, lump ore, etc.) charged from the top of the blast furnace are heated and reduced by reducing gas (CO, _H2 ) generated by the reaction of hot air blown in from the tuyeres with coke as they descend through the furnace, forming a cohesive zone in the shaft of the blast furnace. The permeability of the furnace is affected by the permeability of this cohesive zone, which in turn depends on the amount of molten liquid (amount of slag) present in the cohesive zone. (Figure 2, diagram of the cohesive zone)

(Load softening test)
In order to investigate the formation behavior of the cohesive zone, a load-softening test (high-temperature property test) was conducted using a load-softening test device. The load-softening test is a test in which a packed bed in which an iron-containing charge is sandwiched between coke layers on the top and bottom is reduced in an electric furnace, and the reduction, softening, and fusion behavior of the iron-containing charge are reproduced by applying conditions simulating the load, temperature rise, and concentration change of the reducing gas in a blast furnace to the iron-containing charge. The change in the reduction rate of the iron-containing charge is measured from the analysis of the exhaust gas, and the change in the air resistance of the packed bed is measured from the pressure change of the reducing gas passing through the packed bed. The load-softening test method was performed according to the method described in Non-Patent Document: Iron and Steel 83 (1997) 97.

(Load-softening behavior of sintered ore)
Figure 1 shows the results of a load-softening test using a sample prepared by sintering sintered ore produced in a sintering machine to a size of 10-15 mm, and the analysis results. Figure 1(a) shows the change in reduction ratio (%) and pressure drop (mmAQ). Here, the reduction ratio is defined as the ratio of the amount of oxygen removed by reduction to the amount of oxygen to be reduced. Figure 1(b) shows the analysis results of the heating reduction test. The horizontal axis of Figures 1(a) and (b) is the temperature (°C) of the iron-containing charge (sintered ore in this case). The calculation method for FeO + gangue (kg/tp) on the vertical axis of Figure 1(b) will be described later.

Figure 1 (a) shows that the reduction rate increases with an increase in heating temperature, and Figure 1 (b) shows that the amount of molten liquid (remaining FeO + gangue) decreases as the reduction rate increases, until finally only the gangue remains. It also shows that the amount of remaining FeO is greater than the amount of gangue, and that it is essential to take the amount of remaining FeO into account when calculating the amount of molten liquid coexisting inside the cohesive zone.

At around 1250°C, the airflow resistance rises sharply and the pressure drop increases sharply. This is because the gaps between the sintered ore particles that make up the sample are almost completely filled with molten liquid (strictly speaking, molten liquid with suspended solids). Here, the point at which the pressure drop rises sharply (the rate of increase in pressure drop with temperature rise is 10 (mmAQ/°C) or more) is defined as the "softening and fusion point," and the reduction rate at which the pressure drop rises sharply is defined as "Rs" (see Figure 1(a)). The softening and fusion point is essentially the threshold value that distinguishes the indirect reduction zone from the molten reduction zone, and in a blast furnace, it corresponds to the upper surface of the fusion zone (the reduction rate and temperature at that point).

In the heating temperature range above 1250° C., gas reduction does not proceed, and melt reduction due to contact between the molten liquid and carbon proceeds primarily. At this time, the components of the molten liquid are gangue components (CaO+SiO ₂ +Al ₂ O ₃ +MgO) and unreduced FeO (wustite phase).

Therefore, the inventors of the present invention have considered that the factor governing the ventilation resistance in the lower part of a blast furnace is not the conventional amount of slag, which is the sum of _the CaO, _SiO2 , _Al2O3 and MgO components of all the charges, but is essentially the temperature at which the pressure drop starts to increase, that is, the amount of molten liquid present at the upper surface of the cohesive zone. However, no means for directly measuring the amount of molten liquid or indirectly evaluating it has been proposed so far.

<Method for estimating the amount of slag in the cohesive zone>
The inventors came up with the idea of estimating the cohesive zone slag volume (CSV) as the sum of the amount of remaining FeO (wüstite phase) and the amount of gangue in the iron-containing burden (Equation (1)). The cohesive zone slag volume is a new index defined by the inventors in order to properly maintain the furnace conditions, particularly the furnace gas permeability, of the blast furnace, and is a fundamental feature of the present invention.

Amount of slag in the cohesive zone = Amount of FeO remaining on the upper surface of the cohesive zone + Amount of gangue in the iron-containing charge (1)
FIG. 2 shows a comparison between the index proposed by the present inventors and a conventional index, and a method for estimating the amount of melt present in the cohesive zone will be described with reference to FIG.

(Amount of gangue in iron-containing charge)
The gangue amount of the iron-containing charge is the total amount of components other than iron in the iron-containing charge (see FIG. 2). The gangue amount can be calculated by formula (2) using T.Fe, FeO, and _{Fe2O 3} mass% as the chemical components of the charge. In the formula, "950" is the iron content per ton of molten iron (kg/tp) determined based on the assumption that the pig iron contains 5 mass% C. Hereinafter, "%" means "mass%".
Gangue amount (kg/tp) = {(100-Fe ₂ O ₃ [%] - FeO [%]) / T. Fe[%]}・950...(2)

Fe ₂ O ₃ [%] can be calculated from T.Fe [%] and FeO [%] by the formula (3).

Fe ₂ O ₃ [%] = {(55.85×2+16×3)/55.85×2}×{T. Fe[%]-55.85/(55.85+16)×FeO[%] } ...(3)
From equations (2) and (3), equation (4) for calculating the amount of gangue can be obtained.

Amount of gangue (kg/tp) = {100-{(55.85×2+16×3)/55.85×2}×{T. Fe[%]-55.85/(55.85+16)×FeO[%] }-FeO[%] }/T. Fe[%]・950
=(100-1.4297×T.Fe[%]+0.1113×FeO[%])/T. Fe[%]・950...(4)

The amount of gangue is uniquely determined from the T.Fe (mass%) and FeO (mass%) determined from chemical analysis of the charge, and is constant regardless of the progress of reduction (see "Gangue" in Figure 2).

(Charge material unit (ore ratio))
If the ore ratio OR (mass of iron-containing charge (kg)/mass of pig iron (t)) is known, the amount of gangue may be estimated using formula (5) instead of formula (4) from a chemical analysis of the iron-containing charge.
Gangue amount (kg/tp) = OR (kg/tp)/0.95-1000 ... (5)

(Residual FeO content)
Next, the calculation of the amount of remaining FeO, which is the amount of the wustite phase remaining at the time when the pressure drop begins to increase, i.e., at the upper surface of the cohesive zone, will be described.

The reduction rate is defined as the ratio of the amount of oxygen removed by reduction to the amount of oxygen to be reduced. When the reduction rate Rs at the time when the pressure drop starts to increase is used, the following formula (6) is obtained.
Rs (%) = {(Oi-Or)/Oi}・100...(6)
From equation (6), equation (7) is obtained.
Or(kg/tp)=(1-Rs/100)・Oi...(7)

Here, Oi is the amount of oxygen to be reduced before the reduction of the charge (kg/tp), and Or is the amount of oxygen remaining at the reduction rate Rs (see Figure 2 for O in the charge and O remaining during reduction).

Oi is calculated using equation (8).
Oi (kg/tp)={16×1.5/55.85×{T. Fe[%]-55.85/(55.85+16)×FeO[%]}+16/55.85×FeO[%]}/T. Fe[%]・950...(8)

Therefore, from equation (7), equation (9) is obtained.
Or(kg/tp)={16×1.5/55.85×{T. Fe[%]-55.85/(55.85+16)×FeO[%]}+16/55.85×FeO[%]}/T. Fe [%]・950×(1-Rs/100)...(9)

The amount of remaining oxygen Or exists as wustite (FeO) in a furnace at 1000°C or higher, so the amount of remaining FeO can be expressed by formula (10). That is, the amount of remaining FeO decreases linearly as reduction progresses (see Figure 2).

Amount of residual FeO (kg/tp) = {16×1.5/55.85×{T. Fe[%]-55.85/(55.85+16)×FeO[%]}+16/55.85×FeO[%]}/T. Fe [%]・950×(1-Rs/100)×{(55.85+16)/16}
= (1833.236-202.842×FeO[%]/T.Fe[%])×(1-Rs/100) ... (10)

(Cohesive zone slag amount CSV)
From equations (4) and (10), the amount of slag in the cohesive zone can be expressed by equation (11).
Amount of cohesive zone slag (kg/tp) = Amount of remaining FeO (kg/tp) + Amount of gangue (kg/tp)
= (1833.236-202.842×FeO[%]/T.Fe[%])×(1-Rs/100)+(100-1.4297×T.Fe[%]+0.1113×FeO[%] }/T.Fe[%]・950...(11)

In reality, not all of the slag in the cohesive zone is liquid at the point when the pressure drop in the furnace suddenly rises, but rather it gradually becomes liquid in the high temperature region after that point. Therefore, the "cohesive zone slag volume" (CSV), a newly defined indicator by the inventors, precisely means the "amount of slag that can become liquid" that exists inside the cohesive zone.

(Method of determining Rs)
Rs required for estimating the amount of remaining FeO can be obtained as the reduction rate at the softening and fusion point (the point at which pressure loss begins to increase) by carrying out the above-mentioned load-softening test on the iron-containing charge.

It may also be estimated by computer simulation using a mathematical model of the blast furnace.

In addition, in load-softening tests, even when the same sample is used, Rs may change depending on the reduction conditions and equipment characteristics. However, since the main focus of this invention is to relatively evaluate the suitability of the furnace conditions, changes in Rs do not pose a problem.

(When the iron-containing charge is composed of multiple raw materials)
The CSV of the entire burden consisting of various iron-containing burden materials such as sinter, lump ore, and pellets (hereinafter referred to as "CSV _T ") can be calculated as the mass-weighted arithmetic average of the CSVs (CSVi) of the individual iron-containing burden materials. That is, CSV _T can be calculated by the formula (12).

CSV _T (kg/tp) = Σ(CSV _i・_wi・T.Fe _i )/Σ( _wi・T.Fe _i )...(12)

Here, CSV _i : CSV of charge i (kg/tp)
W _i : Blending ratio (mass%) of charge i (The blending unit (kg/tp) may be used instead of the blending ratio. However, the calculation should be unified to either one.)
T.Fe _i : T.Fe (mass%) of charge i

The index "CSV _T " is an index that collectively indicates the characteristics of a burden composed of various iron-containing burdens. The index "CSV _T " can also be applied to the case where a plurality of sintered ores with different characteristics are used.
(Comparison with conventional indicators: CSV)

Table 1 shows the T.Fe (%), FeO (%), and gangue volume (SV) determined by chemical analysis for various iron-containing charges with particle sizes of 10 to 15 mm, the reduction rate Rs (%) at the softening and fusion point measured in a load-softening test, the CSV (kg/tp) calculated using formula (11), and the S value, which is the temperature integral of the airflow resistance. Here, the T.Fe amount of the lump ore is the value after calcination. Note that the hearth slag volume (SV) used in normal operation management includes not only gangue derived from the iron-containing charges, but also auxiliary materials for adjusting the composition, coke, and ash in the pulverized coal, and is therefore about 50 kg/tp more than the gangue volume derived from the iron-containing charges.

As shown in Table 1, the S value simulating the permeability inside a blast furnace does not correspond to the amount of gangue in the iron-containing charge, but corresponds well to the CSV of the present invention. This is because the CSV of the present invention takes into account not only the amount of gangue, but also the amount of unreduced FeO, which changes as reduction progresses.

(Comparison with conventional indicators: CSV _T )
In actual blast furnace operation, multiple iron-containing charges are mixed and used. In that case, CSV _T is used as the amount of slag in the cohesive zone. Next, an example comparing SV and CSV _T is shown.

The change in the lower K value when 15% of the sintered ore was replaced with pellets while keeping the iron production rate constant is shown in Figure 3. The lower K value is an index for evaluating the air flow resistance in the lower part of the blast furnace and is calculated by the following formula.
For a given height from the tuyere, K = (P1 ² - ^{P2 2} )/G ^1.7
Where P1: Air pressure (MPa)
P2: Pressure at a specific part of the blast furnace (MPa)
G: Amount of bosh gas in the blast furnace ( ^Nm3 /min)
In this case, the values were corrected for the coke properties, the properties of the iron-containing charge, and other operational factors. By replacing sintered ore with pellets, the hearth slag volume (SV) was reduced from 290 to 265 kg/tp, but the lower K value showed the opposite trend, worsening from 1.8 to 1.9 (Figure 3(a)). On the other hand, when the change at this time was shown in CSV _T , which takes into account the high-temperature reducibility of pellets, the average CSV _T of the charge was reduced from 910 to 895 kg/tp, which could reasonably explain the change in permeability of the blast furnace (Figure 3(b)).

(Correspondence with productivity)
Figure 4 shows an example of the correlation between the productivity and the amount of pig iron produced during one year of operation of a blast furnace in which the productivity changed between 1.9 and 2.2. Figure 4(a) shows the relationship between the lower K value and the amount of cohesive zone slag (CSV _T ), and Figure 4(b) shows the relationship between the productivity and the amount of cohesive zone slag (CSV _T ). As shown in Figure 5, the correlation between the lower K value and the amount of cohesive zone slag (CSV _T ), and the correlation between the productivity and the amount of cohesive zone slag (CSV _T ) are extremely good.

From the above, it can be seen that the use of the newly defined indicators "cohesive zone slag amount", "CSV" or "CSV _T " in the present invention makes it possible to more accurately evaluate the furnace conditions in the lower furnace, particularly the quality of gas permeability, than the conventional indicator (SV). Furthermore, "CSV" or "CSV _T " is an indicator that directly evaluates the amount of FeO-containing molten liquid at the upper surface of the cohesive zone, and the magnitude of the indicator affects the thermal conditions in the lower furnace, which in turn affects the reducing agent rate, and in conjunction with the relationship with furnace gas permeability, it shows a good correlation with the iron production rate.

<Blast furnace operation method>
The method of operating a blast furnace of the present invention uses the amount of cohesive zone slag ( _CSVT ) as one of the operational management indexes. Specifically, the method of operating a blast furnace is characterized in that a target value of _CSVT is set, and at least one of (a) to (d) is carried out so that the estimated value of _CSVT based on the above-mentioned estimation method is equal to or less than the target value.

(a) Adjustment of the blending ratio of the iron-containing charge charged to the blast furnace; (b) Adjustment of the content of one or _more of CaO, _SiO2 , _Al2O3 , MgO, CaO/ _SiO2 , and FeO in the iron-containing charge charged to the blast furnace; (c) Adjustment of the particle size of the iron-containing charge charged to the blast furnace; (d) Adjustment of the amount of carbonaceous charge mixed into the iron-containing charge layer.

Here, the target value of CSV _T may be set to 920 to 980 kg/tp. As described later in Example 1, by setting CSV _T in the range of 920 to 980 kg/tp, the permeability of the blast furnace is significantly improved.
Furthermore, it is preferable to set the target value of CSV _T to 830 to 890 kg/tp. As will be described later in Example 2, by setting CSV _T in the range of 830 to 890 kg/tp, not only the air permeability can be improved but also the reducing agent rate can be reduced. The details of the adjustments (a) to (d) will be explained below in order.

(Adjustment of the blending ratio of iron-containing charge to be charged into the blast furnace)
A method for adjusting the blending ratio of the iron-containing charge will be described with reference to Table 2. The specifications of sinter A, lump ore B, and pellets C are shown in Table 1.
The mill is operating with a sinter ratio of 70%, lump ore ratio of 15%, and pellet ratio of 15%, and the CSV _T at this time is 1035 kg/tp (operation 1). If ventilation becomes unstable for some reason, the CSV _T target value is reduced by, for example, 30 kg. To achieve this target value, for example, 10% of the lump ore can be replaced with 10% of the sinter. This reduces the CSV _T from 1035 kg/tp to 1004 kg/tp (operation 2).

Furthermore, the lower K value is expected to decrease from 2.3 to 2.2 based on the correlation equation (K value=0.0031×CSV _T −0.9) obtained in FIG. 3( b ).

(Adjustment of chemical composition of iron-containing charge to be charged into blast furnace)
A method for adjusting the chemical composition of the iron-containing charge will be described with reference to Table 2. The specifications of sintered ore B are shown in Table 1.

It is also possible to switch to Operation 3, in which sintered ore B with high T.Fe is used in place of sintered ore A, in comparison with Operation 1. At this time, it is expected that the CSV _T will decrease from 1035 kg/tp to 958 kg/tp, and the lower K value will decrease from 2.3 to 2.1 (Operation 3).

(Adjustment by controlling particle size of charge)
The reactivity of the blast furnace burden is determined mainly by solid-gas reactions, and is therefore highly dependent on particle size. Therefore, it is preferable to use the CSV'' that takes into account the effect of the particle size of the burden as described below for the indicator "CSV" or "CSV _T ."

Figure 5 shows the results of investigating the particle size dependency of CSV for sintered ore and lump ore. Here, the average particle size MS (mm) is the weight-based average diameter calculated from the following formula:

MS=Σ(Wi・Di)/ΣWi
Wi weight of grain size class i (g)
Di Median of particle size class i (mm)

As shown in FIG. 5, the CSV increased with an increase in the average particle size (MS) of all the iron-containing charges, but the influence coefficient was +28 (kg/tp)/(MS+1 mm) regardless of the type of iron-containing charge.

Using this influence coefficient, the CSV' of the iron-containing charge taking into account the particle size can be defined by equation (13).
CSV' (kg/tp) = Σ(CSV''i・wi・T.Fei)/Σ(wi・T.Fei)...(13)

_CSV''i is the CSV of the iron-containing charge taking into account the particle size, and can be expressed by the following formula:

CSV'' _i (kg/tp)=CSV _i +28×(MS-12.5)
MS (mm): average particle size of charge (mm)
Wi: Blending ratio (mass%) of charge i, or blending unit (kg / tp)
T. Fei: T. of charge i. Fe (mass%)

Conversely, CSV'' can be adjusted by controlling the particle size of the charge materials. Table 2 shows an example of operation 4 in which pellets C are entirely replaced with pellets C'', which have a particle size 5 mm smaller. The CSV'' of pellets C'' is 761, which is 28 x 5 = 140 smaller than the 901 of pellets C. The CSV of the charge material is 1,014 kg/tp, and it is expected that the lower K value will improve from 2.3 to 2.2.

(Adjustment by mixing charcoal)
Figure 6 shows the CSV measured using a load-softening test device when carbon-containing materials were mixed into a layer of pure sintered ore. Sintered ore with a particle size of 10-15 mm, lump coke with a particle size of 15-20 mm, small lump coke with a particle size of 10-15 mm, and unfired carbon-containing pellets (carbon-containing agglomerated ore) containing 20% carbon were used. Although the degree varies depending on the type of carbon-containing material, the CSV decreases as the amount of mixture increases. This is the result of a carbon gasification reaction (CO generation) occurring in the mixed layer, regenerating the reduction potential of the reducing gas. Note that the finer the particle size of the carbon contained, the greater the degree of decrease in CSV.

At this time, the CSV reduction coefficient, "CSV change (kg/tp)/(+1 kg/tp)", is approximately as follows, based on FIG.
Lump coke (particle size: 15-20 mm): -1.0
Small coke (particle size: 10-15 mm): -2.0
Carbon-bearing agglomerate (particle size: 10-15mm): -3.3
Therefore, the CSV value can be controlled by mixing various carbon-containing materials with the iron-containing charge.

Next, an embodiment of the present invention will be described. However, the conditions in the embodiment are merely an example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to this example of conditions. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

Example 1
Sintered ores with different amounts of T.Fe were produced in a sintering machine with a sintering area of 600 ^m2 . At this time, the composition conditions and firing conditions (mainly the firing heat level) were changed to change the texture of the sintered ore. The sintered ores were subjected to a load softening test to measure the softening fusion point reduction rate Rs, and the CSV of each sintered ore was calculated.

In the operation of a 5000 ^m3 blast furnace, 80% of the produced sintered ore was used. The wind pressure fluctuation was maintained at 43 hPa or less, the gas utilization rate ηCO was 50.0% or more, and the molten iron temperature was 1500°C or more.

The results of the operation are shown in Figure 7. Figure 7(a) shows the results of the operation when evaluated using the "amount of slag in the cohesive zone" of the present invention, and Figure 7(b) shows the results of the operation when evaluated using the conventional "amount of slag."
As shown in Fig. 7(a), even if the T.Fe content is different, operation is good if sintered ore with a CSV of 950 kg/tp or less is used. Specifically, operation was possible at a low reducing agent rate without causing large aeration fluctuations.

However, even if the sintered ore has a T.Fe content of 60% and a low gangue content, if the porosity is extremely low due to excessive heat production conditions and the Rs is low, the CSV will exceed 950 kg/tp and operation will deteriorate.

On the other hand, even in the case of sintered ore with a high gangue content of T.Fe of 54.0%, if the charge blending conditions and firing conditions are optimized and Rs is high, the _CSVT can be reduced to 950 kg/tp or less, and operation is good.

In contrast, when using the conventional indicator "slag volume," as shown in Figure 7(b), it is not possible to comprehensively evaluate blast furnace operations that use the above-mentioned sintered ore.

Example 2
Using sintered ores with different _SiO2 contents ranging from 4.2 to 5.1 mass%, load-softening tests and BIS furnace evaluation tests were carried out. The BIS test conditions were as follows: coke with alkali (3 g KOH added per charge), reducing agent ratio of 481 kg/tp, pulverized coal injection of 132 kg/tp (O/C 4.63, sintered ore ratio 100%, bosh gas 1343 ^Nm3 /tp) in order to simulate the improvement in coke reactivity due to alkali circulation in an actual blast furnace.

The BIS furnace is a test method that simulates the countercurrent reaction in the shaft of a blast furnace. Sintered ore and coke are charged in layers into a pre-fixed reaction tube, and the heating electric furnace is moved from the top to the bottom of the reaction tube. The countercurrent reaction in a blast furnace is simulated by circulating reducing gas from the top to the bottom of the reaction tube. The reaction efficiency (shaft efficiency) is evaluated from the component values of the obtained exhaust gas (top gas). Details of the test equipment are described in Utility Model JPU: S59-191597, and the test method is described in Non-Patent Document: Iron and Steel (1986) 1529, so they are omitted here.

The test results are shown in Figure 8. The S value (time integral value of pressure loss) in the load-softening test decreased with decreasing CSV (Figure 8b), and the shaft efficiency in the BIS test also improved (Figure 8a). In particular, sintered ore with a CSV of 860 kg/tp or less showed a high shaft efficiency of over 97% in the BIS furnace.

Example 3
A blast furnace operation test was carried out using two types of sintered ore 1 and sintered ore 2 having different CSVs shown in Table 3.

The reducing agent rate of blast furnace operation during the period when sintered ore 2, whose CSV was 860 kg/tp, was 5 kg lower per ton of molten iron than the reducing agent rate during the period when sintered ore 1, whose CSV was 995 kg/tp, was used.

These results show that by keeping the CSV at 860 kg/tp or less, not only can air permeability be improved but the reducing agent ratio can also be reduced.

As described above, according to the present invention, in blast furnace operation in which a mixture of sintered ore, pellets, lump ore, and other charges is charged, it is possible to carry out an appropriate charge mix design that can improve the permeability inside the furnace, and as a result, it is possible to suppress a temperature drop in the lower part of the blast furnace and stabilize the operation. Furthermore, according to the present invention, it is possible to reduce the reducing agent ratio in blast furnace operation, thereby saving energy and reducing _CO2 .

Therefore, the present invention will make a significant industrial and social contribution and has high industrial applicability.

Claims (6)

In blast furnace operation, in which iron-containing and carbonaceous charges are alternately charged into a blast furnace and the iron-containing charges are heated and reduced to produce pig iron, a method for estimating the amount of cohesive zone slag is characterized in that the amount of molten liquid present on the upper surface of the cohesive zone formed by melting the iron-containing charges, that is, the amount of cohesive zone slag: CSV (kg/tp), is estimated as the sum of the amount of FeO remaining on the upper surface of the cohesive zone of the iron-containing charges (kg/tp) and the amount of gangue of the iron-containing charges (kg/tp). The method for estimating the amount of cohesive zone slag according to claim 1, characterized in that a load-softening test is performed on the iron-containing burden to determine the reduction rate Rs of the iron-containing burden when the rate of increase in pressure drop due to a temperature rise is 10 (mmAQ/℃) or more, and the remaining FeO amount (kg/tp) is calculated by the following formula (Ix).
Residual FeO amount (kg/tp) = (1833.236-202.842 x FeO [%] / T.Fe [%]) x (1-Rs/100)... (Ix)
T. Fe: Total iron content (%) in the iron-containing charge
FeO: Amount of FeO in iron-containing charge (%)
Rs: Reduction rate (%) at the time of pressure drop increase measured in a load-softening test on iron-containing charge The method for estimating the amount of cohesive zone slag according to claim 1 or 2, characterized in that the CSV _T (kg/tp) of the entire burden consisting of a plurality of iron-containing burden materials is calculated by the following formula (II).
CSV _T (kg/tp) = Σ(CSV _i・_wi・T.Fe _i )/Σ( _wi・T.Fe _i )...(II)
CSV _i : Slag amount of iron-containing charge i (kg/tp)
W _i : The blending ratio (%) of iron-containing charge i (The blending unit (kg/tp) may be used instead of the blending ratio. However, the calculation should be unified to either one.)
T. Fe _i : Total iron content (%) of iron-containing charge i A blast furnace operation method, comprising: determining a target value for the amount of cohesive zone slag; and performing at least one of (a) to (d) so that an estimated value of the amount of cohesive zone slag using the method for estimating the amount of cohesive zone slag according to any one of claims 1 to 3 is equal to or less than the target value.
(a) Adjustment of the blending ratio of the iron-containing charge charged to the blast furnace; (b) Adjustment of the content of one or _more of CaO, _SiO2 , _Al2O3 , MgO, CaO/ _SiO2 , and FeO in the iron-containing charge charged to the blast furnace; (c) Adjustment of the particle size of the iron-containing charge charged to the blast furnace; (d) Adjustment of the amount of carbonaceous charge mixed into the iron-containing charge layer. The blast furnace operation method according to claim 4, characterized in that the target value of the cohesive zone slag amount is 920 to 980 kg/tp. The blast furnace operation method according to claim 4, characterized in that the target value of the cohesive zone slag amount is 830 to 890 kg/tp.

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