JP2011144442A - Method for blow-down operation of blast furnace - Google Patents

Abstract

[PROBLEMS] To improve the coke consumption rate and charge reduction rate by suppressing air blow-off and coke fluidization, and to reduce the time required for blow-off operation from a conventional blast furnace. Provide operating methods.
In a blowout operation method of a blast furnace in which a blast furnace 10 is blown off, air is blown from a tuyere 11 of the blast furnace 10 and a charge 12 in the blast furnace 10 is reduced, the blast furnace 10 is blown from a tuyere 11. A limit air flow rate that can prevent air from being blown through the blast furnace 10 is obtained in advance using the flow start speed of the charge 12, and the upper surface of the charge 12 to be scaled down is the furnace belly portion 17 of the blast furnace 10. The amount of air blown from the tuyere 11 when reaching the upper region of the morning glory part 15 from the lower part of the airflow is obtained from the balance between the buoyancy of the air blown from the tuyere 11 and the weight of the charge 12 To below the limit air flow.
[Selection] Figure 1

Description

The present invention relates to a blast furnace blow-off operation method for reducing the charge in a blast furnace in advance when renovating or constructing the blast furnace.

Conventionally, when refurbishing or constructing a blast furnace, a blow-off operation that reduces (reduces) the height level of the charges in the blast furnace (the ore and coke charged in layers in the furnace) in advance Is going. When performing this blow-off operation, since the decrease in the weight of the charged material in the furnace and the change in the pressure loss state in the furnace (such as the disappearance of the cohesive zone) occur at the same time, The phenomenon that the air sent from the tuyere blows through to the top of the blast furnace is easily generated.
For this reason, it is common to determine the amount of air blown with a sufficient safety factor from the past operational results and reduce the charge in the furnace with this amount of blown air.

In particular, at the end of scale reduction, coke is supplied to the tuyere while the core coke in the furnace (inclination angle: usually 60 degrees) collapses to the repose angle (usually 20 to 30 degrees). If the air volume is set incorrectly, the above-described air blow-through and coke fluidization occur, resulting in the following problems.
1) The contact rate between the air blown from the tuyere and the charge is reduced, so that the consumption rate of coke in the charge is delayed.
2) The blown up charge is supplied again to the raceway area in front of the tuyere and the reduction speed of the charge is delayed.
Therefore, for example, as shown in Patent Document 1, the ratio between the buoyancy caused by gas (ΔP × cross-sectional area, ΔP is pressure loss in the furnace) and the charge weight (also referred to as charge load) is calculated. A method has been proposed in which the amount of air blown from the tuyere is determined based on threshold values obtained from actual results.

JP 2007-254897 A

However, the conventional method requires that the cross-sectional area in the blast furnace and the gas flow distribution be constant, so if the ratio of the buoyancy due to gas and the weight of the charge is 1, blow-through occurs. However, at the end of the scale reduction, air blow-through and coke fluidization occurred unless the air flow rate was set to a value that allowed for a safety factor based on the results of normal operation. This is because the charge weight and gas flow distribution are different in the radial direction in the blast furnace.
Furthermore, at the end of the scale reduction, the charge is reduced to the morning glory of the blast furnace, but this morning glory is shaped like a mortar, and the cross-sectional area of the gas flow path is reduced due to the presence of the furnace core coke. Therefore, the flow rate of the in-furnace gas increases, and air blow-out and coke fluidization often occur.

The present invention has been made in view of such circumstances, and suppresses air blow-through and coke fluidization to improve the consumption speed of coke and the reduction speed of charges, and to reduce the time required for blow-off operation. An object is to provide a blast furnace blow-off operation method that can be shortened as compared with the prior art.

The gist of the present invention made to solve the above problems is as follows.
(1) In a blast furnace blow-off operation method in which the blast furnace is blown off, air is blown from the tuyere of the blast furnace, and the charge in the blast furnace is reduced.
The upper limit of the charge to be reduced is determined in advance by using a flow start speed of the charge, and a limit air flow rate that can prevent the air blown from the tuyere from blowing through the blast furnace furnace, The amount of air blown from the tuyere when reaching the upper region of the morning glory part from the lower part of the blast furnace belly part, from the balance between the buoyancy of the air blown from the tuyere and the weight of the charge A blast furnace blow-off operation method characterized by switching from the obtained air blowing amount to the limit air blowing amount or less.

(2) The region is a range of not less than −0.1 times and not more than 0.1 times a distance D from the blast furnace outlet to the tuyere, based on the upper end position of the morning glory portion. (1) The blast furnace blow-off operation method according to (1).

In the blast furnace blow-off operation method according to the present invention, the limit blast volume that can prevent the air blown from the tuyeres from blowing through the blast furnace furnace is obtained in advance using the flow start speed of the charge. The amount of air blown in consideration of the charge weight, gas flow distribution, and cross-sectional area in the furnace, which are different in the radial direction, can be obtained. Here, since the cross-sectional area in the furnace decreases in the area of the morning glory portion of the blast furnace, when the upper surface of the charge to be reduced reaches the area of the upper portion of the morning glory part from the lower part of the furnace belly of the blast furnace, The air blowing amount is switched from the blowing amount obtained from the balance between the buoyancy of the air blown from the tuyere and the weight of the charged material to the limit blowing amount or less.
As a result, air blow-off and coke fluidization can be suppressed, the coke consumption rate and the charge reduction rate can be improved, and the time required for the blow-off operation can be shortened compared to the prior art.

(A)-(D) is explanatory drawing which shows the in-furnace condition of the blast furnace to which the blow-off operation method of the blast furnace which concerns on one embodiment of this invention is applied. It is explanatory drawing which shows transition of the ventilation volume of the air which applied the blow-off operation method of the same blast furnace. It is explanatory drawing of the in-furnace condition in the morning glory part of a blast furnace. It is explanatory drawing which shows the relationship between the reduction rate of a charging thing, and CO production | generation rate. It is explanatory drawing which shows the ventilation volume transition of the air which applied the blow-off operation method of the blast furnace which concerns on an Example.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
As shown in FIGS. 1 (A) to 1 (D) and FIG. 2, the blast furnace blow-off operation method according to an embodiment of the present invention stops the operation of the blast furnace 10 (blowing), and This is a reduction method for reducing the height level of charges 12 in the blast furnace 10, that is, ore and coke charged in layers, by blowing air from the mouth 11. This is a method in which the blow-through to the top and the fluidization of coke are suppressed to improve the consumption speed of coke and the reduction speed of charge 12. This will be described in detail below.

When refurbishing or constructing the blast furnace 10, as shown in FIG. 1 (A), the blow-off operation is started.
First, a larger amount of coke is charged on the ore and coke charged in the blast furnace 10 furnace. In addition, the charge 12 is comprised by the ore and coke charged in layers, and the coke further charged.
Next, during the unwinding shown in FIG. 1 (B), the height level of the charge 12 is measured using a differential finger (pending type level detector) 13 that measures the surface height position of the charge 12. The height level of the charge 12 is reduced by adjusting the amount of air blown from the tuyere 11 in accordance with the height level of the charge 12 while measuring. When the height level of the charge 12 is reduced, the cohesive zone 14 is partially collapsed as shown in FIG. 1C, and the pressure loss in the blast furnace 10 is reduced. .

In the blow-off operation shown in FIGS. 1 (A) to 1 (C), the amount of air blown from the tuyere 11, the buoyancy of the air blown from the tuyere 11 shown below, and the weight of the charge 12 Find from the balance.
ΔP × S = W (1)
Here, ΔP: pressure loss in the furnace (kg / m ² ), S: cross-sectional area in the furnace of the blast furnace (m ² ), and W: charge weight (kg). The pressure loss in the furnace is determined by {(air blowing pressure) − (furnace top pressure)}.
This formula (1) is represented by formula (2), where F is the ratio between the weight of the charge 12 and air buoyancy.
F = W / (ΔP × S) (2)

The above-mentioned charge weight W is expressed by the formula (3).
W = WV × (1 + α) × (O / C + 1) / {(O / C) / _ρore + 1 / _ρcoke } (3)
Where WV: furnace volume (m ³ ), α: compressibility of charge (eg, 0.1), O / C: {(ore weight) / (coke weight)}, ρ _ore : of ore Density (kg / m ³ ), ρ _coke : density of coke (kg / m ³ ).

Then, the charge weight W and the F value obtained from the above equation (3) are substituted into the above equation (2), respectively, and the inside of the furnace at each reduced level (residue height level). The pressure loss ΔP is calculated. The charge weight W is obtained by substituting the value determined by the specifications of the blast furnace and the quality of the ore and coke to be used into Equation (3). The F value may be set to “1” based on the balance between the buoyancy of the air blown from the tuyere and the weight of the charged material. Since there is an O / C difference or the like, it is necessary to set a value including a safety factor (for example, about 2 to 3).

The amount of air blown from the tuyere 11 (F value constraint) shown in FIG. 2 is obtained using the pressure loss ΔP in the furnace obtained by the above method as a limit pressure. In addition, when calculating | requiring this blast volume of air, it calculates | requires by substituting in the relational expression (past performance) of the limit pressure and blast volume computed beforehand (it may obtain | require with a comparison table).
The calculation of the air blowing amount shown above is performed using a conventionally known arithmetic unit (that is, a computer) provided with a RAM, a CPU, a ROM, an I / O, and a bus connecting these elements. It is not limited to.

With the above blast volume, air is blown into the blast furnace 10 and the charge 12 is reduced. After the fusion zone 14 disappears, the pressure loss in the blast furnace 10 furnace is greatly reduced, and the above-mentioned Since the limit pressure is calculated to be large, the risk of air blow-out increases. In particular, when the scale 12 ends, that is, when the charge 12 is reduced to the morning glory portion 15 of the blast furnace 10, the coke in the blast furnace 10 is fluidized. In the morning glory portion 15 and below, the tuyere 11 is caused by the taper (inclination angle: about 70 to 85 degrees) of the morning glory portion 15 that is reduced in diameter and the core coke 16 (air cannot pass through). This is because the flow path (cross-sectional area) of the air blown from the inside is reduced, and with the above-described air blowing amount, the gas flow rate in the furnace is increased and the coke is easily fluidized.

Therefore, when the upper surface of the charge 12 to be reduced reaches the upper region of the morning glory portion 15 from the lower portion of the furnace belly portion 17 of the blast furnace 10, the amount of air blown from the tuyere 11 is set as described above. From the blast volume determined in step 1, the blast volume is switched to the blast volume that can prevent the air blown from the tuyere 11 from being blown through the blast furnace 10, that is, the limit blast volume or less. In addition, the furnace belly part 17 is a part where the lower end part is connected to the upper end part of the morning glory part 15, and the cross-sectional area thereof is substantially the same from the upper end to the lower end of the furnace belly part 17.
Specifically, the above-described air flow rate switching region is based on the upper end position X of the morning glory portion 15 and is a distance D from the upper end position of the blast furnace 10 (stock line position) to the upper end position of the tuyere 11. It is in the range of not less than 0.1 times and not more than 0.1 times (see FIG. 1A).

In this way, by setting the switching position of the blowing amount within the range of ± 10% of the distance D with the upper end position X of the morning glory portion 15 as a reference, the blowing amount of air within a range that does not adversely affect the blow-off operation. However, preferably, the upper limit is 0.05 times the distance D, and the upper end position X and the lower limit of the morning glory portion 15 are -0.05 times the distance D. In addition, although the upper surface position of the charging material 12 is detected with the pointing finger 13, if the upper surface position of the charging material 12 can be detected, it will not be limited to this.
The above-described limit air blowing amount is obtained in advance using the flow start speed U _mf of the charge 12. Hereinafter, a method for calculating the flow start speed U _mf will be described.

The flow start speed U _mf can be theoretically calculated by the formula (4) by powder engineering. However, the shape factor and porosity used in equation (4) are determined based on the blast furnace demolition investigation (actual value).
U _mf = {D _pi (ρ _i −ρ _gas ) × g / 24.5 / ρ _gas } ^1/2 (4)
Here, U _mf : Flow start speed (m / sec), D _pi : Particle size (m), ρ _i and ρ _gas : Density (kg / m ³ ), g: Gravitational acceleration (m / sec ² ) is there.
Note that ρ _i is a density based on coke, and ρ _gas is H ₂ (8 mass%), H ₂ O (3 mass%), N ₂ (56 mass%), CO (25 mass%). , And a density based on a gas composed of CO ₂ (8% by mass).

Further, the gas flow rate U _i in the blast furnace 10 is calculated by the equation (5).
U _i = {V _bosh / (60 × ε × S _i )} × {(T _i +273) / 273} × {1.033 / (P _i +1.033)} (5)
Here, U _i : gas flow rate (m / sec), V _bosh : Bosch gas amount (Nm ³ / min), ε: porosity of charge (−), S _i : cross-sectional area (m ² ), T _i : Gas temperature (° C.), P _i : Pressure (kg / m ² ) obtained by subtracting the pipe pressure loss of the blower pipe from the blower pressure. In the left side of the above formula (5), since the Bosch gas amount V _bosh is divided by “60”, the units of the left side and the right side are balanced.
Therefore, after _obtaining the flow start speed U _mf from the formula (4), U _{i that is} less than the flow start speed U _mf (for example, 80% or more and less than 100% of the flow start speed U _mf ) is _expressed by the formula (5). And the Bosch gas amount V _bosh is obtained, and the limit air blowing amount is determined by the equation (6).
V _bosh = BV × 1.21 + (FVO ₂ /60)×2+BV×BM×(22.4/18)×2 (6)
Here, BV: limit blowing amount (Nm ³ / min), FVO ₂ : oxygen enrichment amount (Nm ³ / hour), BM: blowing moisture addition rate (g / Nm ³ ).

Note that the cross-sectional area S _i of a furnace into equation (5) described above, it can be used cross-sectional area S1 shown in FIG. This is because the inclination angle of the morning glory portion 15 of the blast furnace 10 is set so that the charge 12 (here, coke) in the furnace can be reduced in a horizontal state.
However, the cross-sectional area S _i in the furnace may be a value that takes into account the inclination angle of the morning glory portion 15 and the furnace core coke 16. In this case, the coke tends to increase in height position (inclination angle increases) as it approaches the morning glory portion 15 and the furnace core coke 16, but the repose angle of the coke is 30 degrees. It does not increase beyond this tilt angle. Therefore, the horizontal cross-sectional area S2 at the position where the position of the differential finger 13 is the starting point and the morning glory portion 15 is contacted at an inclination angle of 30 degrees is obtained, and the cross-sectional area S2 and the cross-sectional area S1 of the position of the differential finger 13 are obtained. Substituting each into equation (5), the limit air flow rate is determined and the average value is determined. The position of the finger 13 in the furnace radial direction is within the range of 0.4R to 0.7R from the furnace center, where R is the radius of the furnace belly.

Based on the limit air flow obtained in advance by the above-described method, that is, the air limit air flow ( _Umf constraint) shown in FIG. 2 (for example, 70% or more of the limit air flow, further 90% or more, 100% or less Air is blown into the blast furnace 10 furnace. Note that the limit air flow rate can also be obtained in advance by the above-described calculator.
Here, when performing blow-off operation using a 5,000 m class ³ blast furnace, the relationship between the consumption rate of coke in the charge and the reduction speed of the charge is examined, and the time required for blow-off operation is examined. The investigation results will be described with reference to FIG.
In addition, the invention example in FIG. 4 is a result of switching the air blowing amount to the limit blowing amount or less at the upper end position of the morning glory portion of the blast furnace, and the conventional examples 1 and 2 are 5000 m ³ although the internal volume is slightly different. It is the result of having performed based on F value to the last like the conventional method, without switching the ventilation volume of air about two blast furnaces of each grade.

Here, the calculation of the air blowing amount before switching the blowing amount of the invention example and the air blowing amount of the conventional examples 1 and 2 uses the equations (1) to (3), and the same method as the conventional method. I went there.
Further, in calculating the air blowing amount after switching in the inventive example, the above-described formulas (4) and (5) are used, and the particle diameter D _pi in formula (4) is 0.05. (M), 550 (kg / m ³ ) for coke density ρ _i , and 1.201 (kg / m ³ ) for gas density ρ _gas , respectively, and the porosity ε of the charge in formula (5) 0.55 was used.
In addition, the ventilation volume was measured with the flowmeter provided in the ventilation main pipe or the ventilation branch.

The vertical axis ηCO (%) in FIG. 4 is expressed by the following equation.
ηCO = (furnace top gas CO ₂ concentration) / {(furnace top gas CO concentration) + (furnace top gas CO ₂ concentration)} × 100
The unit of the concentration of the furnace top gas CO ₂ and the furnace top gas CO in the above formula is volume%.
Reduction combustion (C + 1 / 2O ₂ → CO) can consume twice the amount of coke (carbon C) with respect to the same amount of oxygen as compared to oxidation combustion (C + O ₂ → CO ₂ ). (Reduction) is possible. That is, if ηCO is a low value, the reduction combustion of coke increases, the consumption rate of coke and the reduction rate can be improved, and as a result, the time required for blow-off operation can be shortened. In addition, each component density | concentration of gas was measured with the gas chromatography installed in the furnace top.

As is clear from FIG. 4, in Conventional Examples 1 and 2, an increase in ηCO was confirmed from a reduction ratio of 80% (a position corresponding to the upper end position X of the morning glory portion). This is because air blow-through and coke fluidization occurred, and the reduction combustion of coke could not be further increased.
On the other hand, in the inventive examples, it was confirmed that ηCO can be continuously reduced to a reduction ratio of 95%. This is because the reduction combustion of coke can be further increased by suppressing air blow-off and coke fluidization. Note that the reduction rate of 100% is a position corresponding to the upper end position of the tuyere.

As a result, it took about 30 to 36 hours in the conventional examples 1 and 2 in the operation of blowing out a 5000 m ³ class blast furnace, but in the example of the invention, it was shortened to about 24 hours.
From the above, by switching the amount of air blown from the tuyere from the value of the F value constraint to the value of the U _mf constraint, air blow-through and coke fluidization (pressure gauges provided on the top and the furnace wall) It was confirmed that the time required for the blow-off operation could be shortened compared to the conventional method by suppressing coke consumption and improving the coke consumption rate and the charge reduction rate.

As a result, as shown in FIG. 1 (D), the surface height position of the charge 12 near the tuyere 11 reaches the height position of the tuyere 11, and part of the core coke 16 also collapses. This completes the blow-off process. At this time, since the coke is not supplied to the tuyere 11, the coke is not scattered at the tip of the tuyere 11 (the tuyere opening). Then, the hot metal 19 and the molten iron (slag) 20 remaining at a height position higher than the tap hole 18 are discharged from the furnace through the tap hole 18.
Since the blow-off operation is completed by the above method, after the furnace is further cooled, the blast furnace is repaired or constructed.

Next, examples carried out for confirming the effects of the present invention will be described.
First, with respect to a 5000 m class ³ blast furnace, the amount of air blown by the F value constraint is obtained using the above-mentioned formulas (1) to (3), and U _mf is used using the above-described formulas (4) to (6). The limit air volume of value constraint was calculated. In calculating the air blowing rate, the same value as that used in FIG. 4 was used.
The result is shown in FIG.
Then, based on the result of FIG. 5 obtained, when the upper surface of the charge to be reduced reaches the upper end of the morning glory portion of the blast furnace (reduction rate of the charge: 80%), from the tuyere The amount of air to be blown was switched from the value of the F value constraint to the limit amount of air flow of the U _mf value constraint.

Specifically, as shown by the Δ mark in FIG. 5, the air flow rate is 85% of the calculated air flow rate in the F-value management area (charge reduction rate: less than 80%) (further, 90%) to 100% or less, and in the U _mf management area (reduction rate of the charge: 80% or more), 70% (and 90%) of the determined critical airflow It adjusted within the range of 100% or less. In addition, in the area | region where the reduction rate of a charge exceeds 90%, in order to reduce gradually the ventilation volume of air, it may be less than an above-described minimum.
This amount of air flow was measured with a flow meter provided in the air main pipe or the air supply branch pipe.
As a result, by applying the blast furnace blow-off operation method of the present invention, air blow-off and coke fluidization can be suppressed, and the coke consumption rate and the charge reduction rate can be improved. It was confirmed that the time required for operation could be shortened compared to the conventional method.

As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the configuration described in the above embodiment, and the matters described in the scope of claims. Other embodiments and modifications conceivable within the scope are also included. For example, a case where the blast furnace blow-off operation method of the present invention is configured by combining some or all of the above-described embodiments and modifications is also included in the scope of the right of the present invention.

10: blast furnace, 11: tuyere, 12: charge, 13: index finger, 14: cohesive zone, 15: morning glory, 16: core coke, 17: furnace belly, 18: taphole, 19: Hot metal, 20: Hot metal

Claims (2)

In the blowout operation method of the blast furnace, which blows off the blast furnace, blows air from the tuyere of the blast furnace, and reduces the charge in the blast furnace,
The upper limit of the charge to be reduced is determined in advance by using a flow start speed of the charge, and a limit air flow rate that can prevent the air blown from the tuyere from blowing through the blast furnace furnace, The amount of air blown from the tuyere when reaching the upper region of the morning glory part from the lower part of the blast furnace belly part, from the balance between the buoyancy of the air blown from the tuyere and the weight of the charge A blast furnace blow-off operation method characterized by switching from the obtained air blowing amount to the limit air blowing amount or less. 2. The blast furnace blow-off operation method according to claim 1, wherein the region is at least −0.1 times a distance D from a furnace outlet of the blast furnace to the tuyere, based on an upper end position of the morning glory portion. Blast furnace blow-off operation method, characterized in that the range is less than double.

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