JP2007046145A - Method for operating blast furnace with little variation of furnace heat - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a blast furnace with which the variation of furnace heat is restrained as less as possible by enlarging a dropping range of charged material at the lower part of the furnace without enlarging a raceway shape. <P>SOLUTION: The method for operating the blast furnace having little variation of the furnace heat, has the peculiarity, in which in the blast furnace operational method, the outstanding length L<SB>OT</SB>(m) of a tuyere is set to the length from more than 0.4m to permissible range of the tuyere strength, and the raceway position is shifted to the furnace center side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a blast furnace operating method that expands a descending region of a charge and suppresses furnace heat fluctuation.

  In blast furnace operation, it is usual to use a large blast furnace and perform a high pulverized coal ratio operation or a high tapping ratio operation.

  However, in the operation with high pulverized coal ratio, the increase in the amount of coke powder in the raceway deteriorates the air permeability in the lower part of the furnace, and the amount of gas flowing into the furnace core decreases, as shown in FIG. In addition, it is expected that the raceway is reduced and lengthened from R to R ′ accompanied by the accumulation of coke powder, and the raceway depth is reduced.

  When the above phenomenon occurs in the blast furnace, the descending area in the lower part of the furnace is reduced, and the residence time in the lower part of the cohesive zone is shortened. As a result, undissolved material flows into the raceway and the inside of the furnace core The temperature of the furnace decreases (furnace heat fluctuation).

  Similarly, in high-power ratio operation, the raceway depth also decreases (shrinks and lengthens), and the residence time of the cohesive zone at the bottom of the furnace is shortened. The temperature in the furnace core decreases (furnace heat fluctuation).

  Thus, in blast furnace operation, the depth of the raceway formed at the tip of the tuyere is an important operating factor.

  Normally, in operation of a large blast furnace, the hearth effective cross-sectional area ratio EAH represented by the following formula is used as an index indicating the area occupied by the high-temperature area raceway space at the tuyere center level.

FIG. 2 shows the relationship between the internal volume of the blast furnace and the hearth effective sectional area ratio EAH. As shown in FIG. 2, calculated from the following equation in the case of the 1.2~1.5m the raceway depth _{D R EAH (L OT = 0.4m} [ conventional value (0.4~0.55m)] ) Decreases as the blast furnace volume increases. That is, when the size of the blast furnace is increased (increase in the volume inside the blast furnace), the ratio of the core area occupied at the tuyere level (1-EAH) increases.

EAH = [π · (H _D / 2) ² −π · {H _D / 2− (D _R + L _OT )} ² ] / π · (H _D / 2) ² H _D : hearth diameter (m), D _R : Raceway depth (m), L _OT : Feather overhang length

  When the blast furnace becomes larger and the ratio of the occupied area of the core increases, the lowering of the charge drop area at the lower part of the furnace, the lack of heat transfer due to the shortened residence time of the cohesive zone, and the melting capacity are reduced. Reduction in can be inactive.

  In order to prevent the furnace core from being deactivated, the lowering area of the charge at the lower part of the furnace is expanded to ensure the heat transfer time of the charge, and at the same time, the low temperature furnace core area is as much as possible. As is clear from FIG. 2, as the raceway depth is increased, EAH increases. Therefore, as one of the inactivation prevention measures, the tuyere wind speed is increased and the raceway is increased. It is conceivable to increase the depth.

  Attempts to increase the tuyere wind speed and expand the raceway depth have been made in blast furnaces of various companies (see Non-Patent Document 1, Patent Documents 1 and 2).

  Non-Patent Document 1 proposes an attempt to increase the tuyere wind speed and increase the raceway depth as a countermeasure for expanding the descending region. However, the increase in tuyere wind speed promotes the coke pulverization in the raceway, and the powder accumulates in the coke packed bed near the raceway. There is a possibility that the descending area of the narrower.

  Patent Document 1 proposes a method for controlling the tuyere wind speed so that the raceway depth is equal to or less than the set value. Patent Document 2 controls the tuyere diameter so that the raceway depth is equal to or less than the set value. Although methods have been proposed, both methods have the potential to narrow the charge drop area.

  Therefore, when adopting a method for increasing or controlling the tuyere wind speed, it is necessary to simultaneously increase the quality of the coke, in particular the strength. Is actually a tricky practice.

  In addition, if the coke strength is increased and the raceway shape is increased in order to suppress the generation of coke powder, the instability of the raceway shape increases and unmelted material flows into the raceway, causing May be reduced.

JP-A-62-1808 JP-A-62-1809 CAMP-ISIJ, 12 (1999), 632

  In view of the above problems in the prior art, the present invention expands the descending region of the charge in the lower part of the furnace without increasing the raceway shape, and suppresses as much as possible the furnace heat fluctuation and the disturbance of the circumferential balance of various operation indices. An object is to provide a method for operating a blast furnace.

  The starting point of the core that defines the descending region at the bottom of the furnace and consequently affects the effective area ratio of the hearth is determined by the position of the raceway.

  The present inventor pays attention to this point, and if the tuyere protruding length is increased, the raceway position, that is, the charging at the lower part of the furnace is maintained without increasing the raceway depth while maintaining substantially the same shape. The rise start point of the furnace core that defines the descending region of the object can be shifted to the furnace center side, and as a result, the idea has been reached that the descending region can be expanded.

  Conventionally, the tuyere overhang length is usually about 0.4 m regardless of the size of the hearth diameter of the blast furnace. Protruding beyond 0.4m, I studied earnestly.

As a result, as shown in FIG. 3, the present inventor, without projecting the tuyere beyond the normal about 0.4 m (L in the figure) (L _{0 in the} figure), does not increase the raceway depth. The raceway position can be shifted to the furnace center side (see Ro in the figure) while maintaining almost the same shape, and the descending area of the charge in the lower part of the furnace is expanded and the raceway is moved into the raceway. It has been found that the inflow of unmelted material can be suppressed, and the furnace heat fluctuation in the lower part of the furnace can be reduced.

  Basically, the above knowledge is premised on the application to all tuyere, but if the above knowledge can be applied to at least 70% of the tuyere, it can be applied to all tuyere. Almost the same effect can be expressed. And under the above tuyere protruding condition, the rising angle of the stagnant layer formed just above the tuyere becomes smaller, so that the root of the cohesive zone falls off and the descent behavior at the morning glory is stable. I found it.

  Further, the inventor of the present invention, the tuyere protrusion based on the above knowledge is the circumferential direction of the blower branch air volume, the amount of molten iron, the hot metal temperature, the hot metal quality, the hearth side wall brick temperature generated due to the enlargement of the core of the blast furnace It was found that it is also effective as a measure to eliminate imbalance.

Further, the present inventor defines the area of the fan-shaped cross section (center angle θ) including the target tuyere when projecting the tuyere for a predetermined length as a local hearth effective cross-sectional area LEAH by the following formula: It has been found that the furnace heat fluctuation can be controlled to be smaller if the tuyere protrusion length is set so that is equal to or greater than a predetermined value.
LEAH = EAH · θ / 360

  The above knowledge will be described later in detail.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

(1) In the blast furnace operation method, the tuyere protrusion length L _OT (m) is set to a length exceeding 0.4 m and within the possible range for the tuyere strength, and the raceway position is on the furnace center side. A method for operating a blast furnace with small fluctuations in furnace heat, characterized in that

  (2) The blast furnace operating method with a small furnace heat fluctuation according to (1), wherein the raceway shape is maintained without increasing the raceway depth when the raceway position is shifted.

(3) The protrusion length L _OT (m) is set so that the hearth effective cross-sectional area ratio EAH represented by the following formula is 0.50 or more and 0.95 or less. Or the blast furnace operating method with small furnace heat fluctuation | variation as described in (2).

EAH = [π · (H _D / 2) ² −π · {H _D / 2− (D _R + L _OT )} ² ] / π · (H _D / 2) ²
Where H _D : hearth diameter (m), D _R : raceway depth (m)

(4) When the number of tuyere whose blowing air flow is less than 90% of the average value exceeds 25% of the total tuyere, the protruding length L _OT (m) is expressed as the effective hearth sectional area represented by the above formula. The blast furnace operating method with small fluctuation in furnace heat according to (1) or (2), wherein the ratio EAH is set to a value of 0.50 or more.

(5) When the difference between the spouts of the spout amount is 500 t or more, the protruding length L _OT (m) is set so that the EAH represented by the above formula is 0.50 or more. The method for operating a blast furnace according to (1) or (2), wherein the furnace heat fluctuation is small.

(6) When the difference between the hot metal temperature outlets is 50 ° C. or more, the protruding length L _OT (m) is set so that the EAH represented by the above formula is 0.50 or more. The method for operating a blast furnace according to (1) or (2), wherein the furnace heat fluctuation is small.

(7) When the difference between the spouts of the Si value in the hot metal is 0.50% or more, the EAH shown by the above formula is a value of 0.50 or more for the protruding length L _OT (m). The blast furnace operating method with a small furnace heat fluctuation according to the above (1) or (2), characterized in that it is set as follows.

(8) When the temperature of one or more hearth side wall bricks exceeds 10% of the average value of the hearth side wall brick temperature, the protrusion length L _OT (m) of the tuyere in the vicinity of the temperature rising portion is set to A method of operating a blast furnace with a small furnace heat fluctuation, characterized in that the length of the tuyere is set to a length that exceeds 0.4 m and within the possible range of the tuyere strength, and the raceway position is shifted to the furnace center side.

  (9) The blast furnace operating method with small furnace heat fluctuation according to (8), wherein the raceway shape is maintained without increasing the raceway depth when the raceway position is shifted.

(10) The protruding length L _OT (m) is set so that the local hearth effective cross-sectional area ratio LEAH represented by the following formula is a value of 0.50 or more. 9) A method for operating a blast furnace with a small furnace heat fluctuation.

LEAH = [π · (H _D / 2) ² −π · {H _D / 2− (D _R + L _OT )} ² ] / π · (H _D / 2) ² · θ / 360
Here, H _D : hearth diameter (m), D _R : raceway depth (m), θ: central angle of fan-shaped cross section including protruding tuyere (deg)

  According to the present invention, it is possible to increase the descending region of the charge in the lower part of the furnace without increasing the raceway shape and to suppress the furnace heat fluctuation, thereby improving the productivity of the blast furnace.

  In addition, it eliminates the circumferential imbalance between the blower branch air volume, the amount of hot metal, the hot metal temperature, the hot metal quality, and the hearth side wall brick temperature generated due to the furnace core enlargement, thereby suppressing the fluctuation of the furnace heat to a small level. As a result, the productivity of the blast furnace can be increased.

  Furthermore, according to the present invention, the dropout of the root of the cohesive zone is reduced in the furnace, and the descent behavior at the morning glory can be stabilized.

  In order to confirm the probability of the above idea, the present inventor first charged a pseudo ore with a melting point of 120 ° C. and coke from the top of the furnace, and blown hot air of 180 ° C. from the two left and right tuyere. The experiment was conducted. The results are shown in FIGS.

FIG. 4 shows the tuyere overhang length L _OT ((1): 25 mm (actual furnace conversion value 225 mm), (2): 45 mm (actual furnace conversion value 405 mm [conventional value]) affecting the time line and furnace bottom temperature distribution. , (3): 65 mm (actual furnace conversion value 585 mm)).

  In FIG. 4, the horizontal axis indicates the distance (mm) from the furnace center (C) to the furnace wall (W) direction, and the vertical axis indicates the height level from the tuyere to the furnace top direction. Moreover, the lower figure (b) of FIG. 4 shows the isotherm of a 10 degreeC space | interval from 100-160 degreeC.

Further, FIG. 5, protrudes tuyere on "drop width / Royuka径" in morning glory bottom shows the effect of length L _OT.

4 (1) and FIG. 5, the length L _OT is 25mm protruding tuyere (actual furnace converted value 225 mm), is shorter than the normal 45 mm (actual furnace converted value 405mm) is the bosh section In the morning glory area just above the raceway, the repeated phenomenon of coke arch formation and collapse was observed, the raceway shape became vertically long, and the charge slipped near the furnace wall. Descent.

On the other hand, as shown in FIG. 4 (3) and 5, the protruding tuyere length L _OT is 65 mm (actual furnace converted value 585 mm), when longer than normal 45 mm (actual furnace converted value 405mm) is morning glory The area of charge drop at the club was expanded, and the charge drop just above the raceway was smooth.

Then, as shown in FIG. 6, the pressure loss (ΔP) in the furnace decreased as the tuyere protruding length _LOT increased. This is due to the increase in length L _OT protruding tuyere is because the drop region of the charge of the bosh section is expanded.

When tuyere protrusion length _LOT is 45mm (actual furnace equivalent value 405mm), without changing tuyere protrusion length _LOT , the tuyere diameter is reduced to increase tuyere wind speed, and the raceway depth is increased. by expanding, if the length L _OT protruding tuyere securing the same drop width as that of 65 mm (actual furnace converted value 585 mm) (in FIG. 5 × marks, reference), as shown in FIG. 6, the furnace The pressure loss (ΔP) increased significantly (see x in the figure), the gas flow fluctuated, and the material slipped and dropped frequently.

That is, by increasing the tuyere overhang length _LOT to a value greater than the conventional value (about 0.4 m), the furnace pressure loss (ΔP) is reduced in the morning glory portion, and the charge descending region is expanded. be able to.

  The knowledge that is obtained from the above experimental results and forms the basis of the present invention will be described with reference to FIG.

When the tuyere protruding length is a normal length (about 0.4 m) (L in the figure), the raceway R is formed, and the descending width of the charge descending region is W. In this case, if the tuyere wind speed is increased, the raceway depth is increased, and the raceway R ′ is formed, the furnace core rising start point moves to the furnace center side, so the descending width W increases to W _0. On the other hand, coke pulverization inside the raceway increases, and air permeability in the lower part of the furnace deteriorates.

  When the air permeability in the lower part of the furnace deteriorates, the raceway shape becomes unstable, the unmelted material flows into the raceway, and the furnace heat greatly fluctuates in the lower part of the furnace.

On the other hand, when the tuyere overhang length exceeds the normal length (about 0.4 m) (L _{0 in the} figure), the tuyere overhang length is the normal length (about 0.4 m), Since the raceway R ₀ having the same shape as the raceway R formed when the tuyere wind speed is not increased is formed and the furnace core rising start point moves to the furnace center side, the fall width of the charge lowering region is W From W to W ₀ , and the hearth effective area EAH is improved.

FIG. 7 shows the relationship between the hearth effective sectional area EAH and the internal volume (m ³ ) of the blast furnace when the raceway depth is maintained at 1.2 m and the tuyere protruding length is increased. FIG. 8 shows the relationship between the hearth effective area EAH and the tuyere overhang length L _OT (m).

  From FIGS. 7 and 8, it is possible to maintain the hearth effective sectional area EAH at 0.50 or more by setting the protruding length of the tuyere to a length exceeding the normal length (about 0.4 m). I understand.

  In this case, since the tuyere wind speed is not increased, coke pulverization in the raceway is low, air permeability in the lower part of the furnace is maintained well, the raceway shape is maintained stably, and Since the descending area of the entry is enlarged, the unmelted material does not flow into the raceway, and the furnace heat in the lower part of the furnace is stabilized.

  Furthermore, according to the observation results, since the rising angle of the stagnant layer formed just above the tuyere is small, the dropout of the root of the cohesive zone is reduced, the descent behavior at the morning glory is stable, and the furnace at the bottom of the furnace Contributes to heat stabilization.

  Based on the above findings, the present invention is characterized in that the tuyere protruding length is longer than the normal length (about 0.4 m). However, since there is a limit to the tuyere's strength, the tuyere protrusion length should be within the possible range for the tuyere's strength.

  In the present invention, it is not always necessary that the protruding length of all tuyere be longer than the normal length (about 0.4 m).

For example, during operation, if the number of tuyere whose blast branch airflow is less than 90% of the average value exceeds 25% of the total tuyere, the furnace heat fluctuation will increase, so periodic inspection for equipment inspection and repair On the blast furnace off-air day, the protruding length L _OT (m) of these tuyere may be set so that the hearth effective cross-sectional area ratio EAH represented by the above formula becomes 0.50 or more. By this setting, the furnace heat fluctuation can be suppressed in the subsequent operation.

In addition, the furnace heat fluctuation during blast furnace operation is either (a) the difference in the amount of iron output, (b) the difference between the hot metal temperature outlets, or (c) the output of the Si value in the hot metal. Since it appears as a difference between the mouths, follow these operation indexes, find the timing to change the protrusion length of the tuyere, and change the protrusion length of the tuyere to a predetermined L _OT (m) Also good.

When the amount of tapping is used as a tracking index, when the difference between tapping holes becomes 500 t or more, the protrusion length L _OT (m) of the tuyere is set so that the EAH represented by the above formula is 0.50 or more. It is preferable to set it to be a value.

When the hot metal temperature is used as a tracking index, the protrusion length L _OT (m) of the tuyere when the difference between the spouts becomes 50 ° C. or more, the EAH represented by the above formula is 0.50 or more. It is preferable to set it to be a value.

When the Si value in hot metal is used as the tracking index, when the difference between the spouts becomes 0.50% or more, the protrusion length L _OT (m) of the tuyere is 0 as the EAH shown by the above formula. It is preferable to set the value to be 50 or more.

  Also, the furnace heat fluctuation during blast furnace operation appears directly as (d) hearth side wall brick temperature rise, so by tracking the temperature, find the timing to change the tuyere protrusion length, Change the protruding length of the tuyere.

In this case, when the temperature of one or more hearth side wall bricks exceeds 10% of the average value of the hearth side wall brick temperature, the tuyere protrusion length L _OT (m) near the temperature rising portion is The length is set to a range that exceeds 0.4 m and is possible in the tuyere strength, and the raceway position is shifted to the furnace center side. This setting / transfer eliminates the furnace heat fluctuation in the circumferential direction.

  As a matter of course, it is preferable to maintain the raceway shape without increasing the raceway depth when the raceway position is shifted.

Further, when changing the tuyere protrusion length L _OT (m) in the vicinity of the temperature rise portion, the local hearth effective cross-sectional area ratio LEAH represented by the following formula may be set to a value of 0.50 or more. This is preferable in that the furnace heat fluctuation can be further reduced.
LEAH = EAH · θ / 360
Here, θ is the central angle (deg) of the sector cross section that protrudes and includes the target tuyere.

  As described above, in the present invention, based on changes in various operation indexes, the tuyere protruding length is reset to a predetermined length exceeding the conventional length of about 400 mm, so that Thermal fluctuation can be suppressed as much as possible, and the productivity of the blast furnace can be increased.

  Next, examples of the present invention will be described. The conditions of the examples are one example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. It is not done. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Example 1
Examples in which the present invention is applied to actual blast furnace operation will be described below. Using the present invention, the use of long tuyere with a large protruding length was started in a 5775 m ³ blast furnace. Specifically, during regular blast furnace breaks, for several tuyere, the conventional tuyere with a protruding length of 535 mm was replaced with a long tuyere with a protruding length of 635 mm. The mouth was replaced with a long tuyere.

  Since the start of the replacement to the long tuyere, the solution loss carbon amount SLC, which is an index indicating the pressure loss at the lower part of the furnace and the reduction load at the lower part of the furnace, began to decrease. Table 1 shows the main operational indices before and after the replacement to the long tuyere.

By replacing all tuyere with long tuyere, the pressure loss at the bottom of the furnace, the solution loss carbon amount SLC, the morning glory brick temperature decreased, and the reduction indices η _CO and η _H2 increased.

  The above phenomenon is presumed to be a result of the reduction state being improved and the descent behavior stabilized by securing the cohesive zone residence time by expanding the descending region in the lower part of the furnace.

(Example 2)
Next, the present invention is implemented as a measure to eliminate circumferential imbalances such as the air volume of the blower branch pipe, the amount of molten iron, the hot metal temperature, the hot metal quality, the temperature of the hearth side wall bricks, etc. generated due to the enlargement of the core of the blast furnace did.

In the operation of the 5775m ³ blast furnace, the number of tuyere whose blast branch air volume was less than 90% of the average value exceeded 25% of the total tuyere. Thus, the tuyere protrusion length L _OT (m) was set by replacing the tuyere with a long tuyere so that the EAH value would be 0.50 or more on the blast furnace resting day. As a result, there was no tuyere in which the air flow from the branch branch was less than 90% of the average value in the operation after the resting wind.

In the operation of the 5775m ³ blast furnace, the difference in the output amount between the outlets became 500t or more. Thus, the tuyere protrusion length L _OT (m) was set by replacing the tuyere with a long tuyere so that the EAH value would be 0.50 or more on the blast furnace resting day. As a result, in the operation after the resting wind, the difference in the amount of output was less than 200 t.

In the operation of the 5775 m ³ blast furnace, the difference between the hot metal outlets was 50 ° C. or more. Thus, the tuyere protrusion length L _OT (m) was set by replacing the tuyere with a long tuyere so that the EAH value would be 0.50 or more on the blast furnace resting day. As a result, the difference between the hot metal outlets was less than 20 ° C. in the operation after resting.

In the operation of the 5775 m ³ blast furnace, the difference between the outlets of the Si value in the hot metal became 0.50% or more. Thus, the tuyere protrusion length L _OT (m) was set by replacing the tuyere with a long tuyere so that the EAH value would be 0.50 or more on the blast furnace resting day. As a result, the difference between the outlets of the Si value in the hot metal was less than 0.20% in the operation after the wind break.

In the operation of the 5775m ³ blast furnace, the temperature of one or more hearth side wall bricks increased to more than 10% of the average value of the hearth side wall brick temperature. Therefore, replace the long tuyere with the protruding length L _OT (m) of the tuyere so that the fan-shaped LEAH including the tuyere has a value of 0.50 or more on the resting day of the blast furnace. Set. As a result, in the operation after the resting wind, the increase in the temperature of one or more hearth side wall bricks that rapidly increased decreased to less than 3% of the average value of the hearth side wall brick temperature.

  As described above, according to the present invention, it is possible to increase the descending region of the charge in the lower part of the furnace without increasing the raceway shape, and to suppress the furnace heat fluctuation, thereby improving the productivity of the blast furnace. it can.

  In addition, it eliminates the circumferential imbalance of the blower branch airflow, hot metal temperature, hot metal temperature, hot metal quality, and hearth side wall brick temperature generated due to the furnace core enlargement, so that the furnace heat fluctuation can be suppressed small. The productivity of the blast furnace can be increased.

  Furthermore, according to the present invention, in the furnace, the rising angle of the stagnant layer formed immediately above the tuyere is reduced, so that the dropout of the root of the cohesive zone is reduced, the descent behavior in the morning glory is stable, The furnace heat at the bottom of the furnace is stabilized. Therefore, the present invention has high applicability in the steel industry.

It is a figure which shows the change of the shape and depth of the conventional raceway. It is a figure which shows the relationship between the hearth effective area cross-sectional area ratio EAH (calculated with the conventional value [0.4m]) and blast furnace volume when raceway depth is enlarged. It is a figure which shows the position, shape, and depth of the raceway by this invention by contrast with the past. It is a figure which shows the result of a two-dimensional warm model experiment (effect of tuyere overhang length on timeline and furnace lower part temperature distribution). (1) shows the case of tuyere protrusion length 25 mm (actual furnace conversion value 225 mm), (2) shows the case of tuyere protrusion length 45 mm (actual furnace conversion value 405 mm [conventional value]), (3) shows a case where the tuyere protrusion length is 65 mm (actual furnace conversion value 585 mm). It is a figure which shows the result of the two-dimensional warm model experiment (effect of tuyere overhang length on "falling width / hearth diameter" at the morning glory lower end). It is a figure which shows the result (effect of a tuyere protrusion length on the pressure loss in a furnace) of a two-dimensional warm model experiment. It is a figure which shows the relationship between the hearth effective cross-sectional area EAH and the internal volume (m < ³ >) of a blast furnace in case a raceway depth is maintained at 1.2 m and tuyere protruding length is increased. Hearth projecting effective area EAH and tuyeres is a diagram showing the relationship between the length L _OT (m).

Explanation of symbols

L normal tuyere L ₀ tuyere of the present invention R, R 'raceway Ro raceway according to the present invention

Claims (10)

In the blast furnace operation method, the tuyere protrusion length L _OT (m) is set to a length exceeding 0.4 m and within the range possible for the tuyere strength, and the raceway position is shifted to the furnace center side. A method of operating a blast furnace with a small fluctuation in furnace heat.   2. The blast furnace operating method according to claim 1, wherein the raceway shape is maintained without increasing the raceway depth when the raceway position is shifted. The protrusion length L _OT (m) is set so that the hearth effective sectional area ratio EAH represented by the following formula becomes a value of 0.50 or more and 0.95 or less. Blast furnace operation method with small furnace heat fluctuation.
EAH = [π · (H _D / 2) ² −π · {H _D / 2− (D _R + L _OT )} ² ] / π · (H _D / 2) ²
Where H _D : hearth diameter (m), D _R : raceway depth (m) When the number of tuyere whose blast branch airflow is less than 90% of the average value exceeds 25% of the total tuyere, the protruding length L _OT (m) is expressed by the hearth effective area ratio EAH represented by the following formula: The blast furnace operating method with small fluctuation in furnace heat according to claim 1 or 2, characterized in that the value is set to 0.50 or more.
EAH = [π · (H _D / 2) ² −π · {H _D / 2− (D _R + L _OT )} ² ] / π · (H _D / 2) ²
Where H _D : hearth diameter (m), D _R : raceway depth (m) When the difference between the spouts of the spout amount is 500 t or more, the protruding length L _OT (m) is set so that EAH represented by the following formula is a value of 0.50 or more. The blast furnace operating method with small furnace heat fluctuations according to claim 1 or 2.
EAH = [π · (H _D / 2) ² −π · {H _D / 2− (D _R + L _OT )} ² ] / π · (H _D / 2) ²
Where H _D : hearth diameter (m), D _R : raceway depth (m) When the difference between the hot metal outlets is 50 ° C. or more, the protruding length L _OT (m) is set so that the EAH represented by the following formula is 0.50 or more. The blast furnace operating method with small furnace heat fluctuations according to claim 1 or 2.
EAH = [π · (H _D / 2) ² −π · {H _D / 2− (D _R + L _OT )} ² ] / π · (H _D / 2) ²
Where H _D : hearth diameter (m), D _R : raceway depth (m) When the difference between the outlets of the Si value in the hot metal is 0.50% or more, the protruding length L _OT (m) is set so that the EAH represented by the following formula is 0.50 or more. The method of operating a blast furnace according to claim 1 or 2, wherein the furnace heat fluctuation is small.
EAH = [π · (H _D / 2) ² −π · {H _D / 2− (D _R + L _OT )} ² ] / π · (H _D / 2) ²
Where H _D : hearth diameter (m), D _R : raceway depth (m) When the temperature of one or more hearth side wall bricks exceeds 10% of the average value of the hearth side wall brick temperature, the tuyere overhang length L _OT (m) in the vicinity of the temperature rise portion is set to 0. A blast furnace operating method with small fluctuations in furnace heat, characterized in that it is set to a length exceeding 4 m and within the possible range of tuyere strength, and the raceway position is shifted to the furnace center side.   The method of operating a blast furnace according to claim 8, wherein the raceway shape is maintained without increasing the raceway depth when the raceway position is shifted. The furnace according to claim 8 or 9, wherein the protruding length L _OT (m) is set so that a local hearth effective cross-sectional area ratio LEAH represented by the following formula becomes a value of 0.50 or more. Blast furnace operation method with small heat fluctuation.
LEAH = [π · (H _D / 2) ² −π · {H _D / 2− (D _R + L _OT )} ² ] / π · (H _D / 2) ² · θ / 360
Here, H _D : hearth diameter (m), D _R : raceway depth (m), θ: central angle of fan-shaped cross section including protruding tuyere (deg)

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