JP7310858B2 - Blast furnace operation method - Google Patents

Description

The present invention relates to a blast furnace operating method.

In blast furnace operation, iron source materials such as iron ore and sintered ore and coke, which is a reducing agent, are alternately charged from the top of the furnace. is being ventilated. Inside the furnace at the tip of the tuyere, a space called a raceway (hereinafter referred to as RW) with a high porosity is formed in which the coke pushed aside by the air blows and burns while swirling.

Further, in recent years, there are many cases where blast furnace operation is performed while pulverized coal pulverized to about 100 μm is blown from the tuyeres as a reducing agent. Changing the operating conditions at the tuyere is an action at a position close to the molten iron slag and the furnace core, so it is more immediate than changing the charging conditions at the top of the furnace. It can respond to a wide range of changes in furnace conditions. However, there are certain restrictions on changing operating conditions at tuyeres. One of the restrictions is the theoretical combustion temperature (hereinafter referred to as TFT). TFT is the reaction of air blown into the furnace from the tuyere, pulverized coal blown into the furnace, and coke that descends from the furnace top, reacting in RW to form a mixed gas of N ₂ , CO, and H ₂ (Bosch gas). A value calculated as a temperature. Non-Patent Document 1 describes that the TFT is calculated by the following formula (2).

T _tf =(2450+Q _f +Q _b )/(C _g ×V _f −0.3) (2)
In the above formula (2), T _ft is TFT (° C.), Q _f is the heat of combustion gasification reaction of reducing agents other than coke per 1 kg of carbon in coke burning at the tuyere tip (kcal/kg), Q _b is the sensible heat of the blown air per 1 kg of carbon in the coke burning at the tuyere tip (kcal/kg), C _g is the specific heat of the bosh gas (kcal/(Nm ³ × K)), V _f is the coke burning at the tuyere tip is the amount of bosh gas per 1 kg of carbon (Nm ³ /kg).

The values of Q _f , Q _b , C _g , and V _f are values that change depending on the unit consumption and composition of the reducing agent and blast in the operation of the blast furnace, but the values that are generally measured and analyzed during the operation of the blast furnace. can be calculated from For example, _Qf can be calculated from the amount, components, calorific value, tapping amount and coke ratio of the reducing material blown from the tuyere. _Qb can be calculated from the blast volume, blast composition, and blast temperature, and _Cg can be calculated from the blast composition. Furthermore, V _f can also be calculated from the amount of reducing agent used, the reducing agent, and the composition of the blast. If the TFT changes significantly to the high temperature side or the low temperature side, the blast furnace cannot be operated stably. For this reason, in blast furnace operation, the proper range of TFT in RW is empirically determined and managed, and this proper range restricts changes in operating conditions in tuyeres.

When the TFT in RW exceeds the appropriate range to the high temperature side, the decrease in coke strength in RW decreases. Coke pulverizes due to attrition from swirl in the RW and reaction with oxygen, carbon dioxide or water vapor. It is said that most of the coke powder generated in the blast furnace is generated in the RW. Therefore, when the coke strength decreases in the RW, the pulverization of coke is promoted, so the amount of coke powder in the RW increases.

The coke powder generated in the RW enters the interior of the furnace along with the gas rising in the furnace, thereby reducing the porosity of the coke packed bed. A decrease in the porosity of the coke packed bed leads to a decrease in air permeability and commutability in the blast furnace, which causes poor blast furnace operation.

When the TFT in the RW exceeds the appropriate range to the high temperature side, the coke strength in the RW decreases, so the coke powder increases due to swirling and reaction in the RW, which adversely affects the furnace conditions. On the other hand, if the decrease in coke strength of the RW can be suppressed and the generation of coke dust can be suppressed, the upper limit of the appropriate TFT range can be relaxed, and the degree of freedom in changing the operating conditions at the tuyere can be expanded.

As a technique for suppressing the generation of coke powder in the RW, Patent Document 1 discloses charging coke with high reactivity to the furnace wall side of the blast furnace and accelerating the consumption of coke to reduce coke pulverization in the RW. A suppression technique is disclosed.

JP-A-7-278624

Written by Akitoshi Shigemi, Ironmaking Handbook, Chijin Shokan, P217

However, it is known that there is a strong negative correlation between coke reactivity and coke strength, and the higher the reactivity, the lower the coke strength of coke. For this reason, in the technology disclosed in Patent Document 1, even if coke pulverization in the RW can be suppressed by charging highly reactive coke, the coke strength is low, so when descending in the furnace There was a problem that the coke pulverization became severe and the gas flow in the furnace changed, and as a result, the blast furnace operation could not be stabilized. The present invention has been made in view of such problems of the prior art, and its object is to suppress adverse effects on the furnace conditions even if the theoretical combustion temperature in the RW exceeds the upper limit of the appropriate range. It is to provide a method of operation.

Means for solving the above problems are as follows.
[1] A blast furnace operating method in which coke and iron source material are alternately charged from the top of the furnace and pulverized coal is blown in with hot air from tuyeres provided at the bottom of the furnace, wherein the coke is burned in the raceway. If the upper limit temperature of the theoretical combustion temperature at which the amount of decrease in coke strength does not change is the reference theoretical combustion temperature, the theoretical combustion temperature in the raceway obtained from the blowing conditions from the tuyere, and the theoretical combustion temperature and the raceway Using the correspondence relationship between the coke strength of coke burned at the theoretical combustion temperature and the amount of decrease from the reference coke strength, which is the coke strength of coke burned at the reference theoretical combustion temperature, A method of operating a blast furnace, in which coke having a higher coke strength than the coke charged during operation at a temperature equal to or lower than the reference theoretical combustion temperature is charged into the blast furnace.
[2] The method of operating a blast furnace according to [1], wherein the coke with increased coke strength is charged into at least a dimensionless radius of the blast furnace of 0.3 or more and 1.0 or less.
[3] The method for operating a blast furnace according to [1] or [2], wherein the correspondence relationship is the following formula (1).
ΔI=A×(T _tf −B) (1)
In the above formula (1), ΔI is the amount of decrease, _Ttf is the theoretical combustion temperature (° C.) on the raceway, B is the reference theoretical combustion temperature (° C.), and A is a constant determined from the above correspondence. is.

By using the blast furnace operating method according to the present invention, even if the theoretical combustion temperature exceeds the upper limit of the appropriate range, it is possible to suppress the increase of coke powder in the RW and suppress the adverse effect on the furnace conditions. This increases the degree of freedom in changing operating conditions at the tuyeres, contributing to stable operation of the blast furnace.

1 is a schematic cross-sectional view of a blast furnace 10; FIG. 1 is a schematic cross-sectional view showing an example of an experimental furnace 20 used for a coke combustion test; FIG. 4 is a graph showing the relationship between TFT and coke strength.

FIG. 1 is a schematic cross-sectional view of a blast furnace 10. FIG. First, blast furnace operation will be described with reference to FIG. In blast furnace operation, ore and coke are alternately and layeredly charged into the blast furnace from the top of the blast furnace 10, and hot air and a reducing agent such as pulverized coal are emitted from the tuyere 16 provided at the bottom of the blast furnace. sent and implemented. In blast furnace operation, the gas flow 18 in the blast furnace is controlled by adjusting the distribution of the shape and thickness of the ore layer 12 and the coke layer 14 after deposition in the furnace radial direction (furnace caliber direction). Here, the ore is an example of the iron source raw material, and as the iron source raw material, in addition to iron ore (ore), for example, sintered ore, pellets, scrap, and reduced iron are used.

In such a blast furnace operation, since the tuyere 16 is close to the molten iron slag and the furnace core, changing the blowing conditions at the tuyere 16 has a faster effect than changing the charging conditions at the furnace top, and the ventilation inside the furnace is improved. It can quickly respond to a wide range of changes in furnace conditions, including heat level fluctuations. For example, when the temperature of the pig iron tapped from the blast furnace 10 is lowered, the temperature of the hot air blown from the tuyere 16 is increased. As a result, the pig iron temperature of the pig iron to be tapped can be rapidly increased.

On the other hand, if the blowing conditions at the tuyere 16 are greatly changed, the TFT in RW may exceed the appropriate range. If the coke strength of the RW coke burned in the TFT is taken as the reference coke strength when the TFT is within the proper range, the coke strength is lower than the reference coke strength when the TFT exceeds the proper range. This decrease in coke strength causes an increase in coke powder in the RW, and this increase in coke powder reduces the porosity of the coke packed bed, which deteriorates the air permeability and commutability in the blast furnace, causing deterioration of the furnace conditions. Become. Since changing the blowing conditions of the tuyere 16 rather deteriorates the furnace condition, the change of the blowing conditions of the tuyeres 16 is limited to the range in which the TFT in the RW is within the proper range.

On the other hand, in the blast furnace operating method according to the present embodiment, when changing the blowing conditions from the tuyeres 16, the TFT in the RW is obtained from the blowing conditions, and the TFT and the coke strength of the coke burned in the TFT in the RW Using the corresponding relationship, the amount of decrease in coke strength that decreases below the standard coke strength when burned in the TFT is obtained, and corresponding to the amount of decrease, in operation at the standard theoretical combustion temperature or less Coke having higher coke strength than the coke that has been charged is charged into a blast furnace 10. - 特許庁As a result, even if the TFT exceeds the appropriate range due to a change in the operating conditions of the tuyere 16 and the coke strength in the RW falls below the standard coke strength, coke whose coke strength is increased by more than the increase is used. , RW is prevented from increasing, and adverse effects on furnace conditions can be prevented.

Next, the correspondence relationship between the RW TFT and the coke strength of the coke burned in the TFT will be described. The correspondence relationship between the RW TFT and the coke strength of the coke burned in the TFT is obtained by conducting a coke burning test. FIG. 2 is a cross-sectional schematic diagram showing an example of an experimental furnace 20 used for a coke combustion test.

The experimental furnace 20 is a device that simulates the vicinity of the tuyere of a blast furnace, and includes a pulverized coal hopper 22, a pulverized coal conveying pipe 32, a pulverized coal injection lance 34, a coke hopper 24, a blow pipe 36, and a combustion furnace main body. 40. The combustion furnace main body 40 has a rectangular parallelepiped coke filling area of 400 mm×1000 mm×1100 mm, and a tuyere 42 having an inner diameter of 65 mm is provided on one side surface thereof. The blow pipe 36 is connected to one side surface of the combustion furnace main body 40 where the tuyere 42 is provided. An exhaust port 44 is provided on the upper surface of the combustion furnace main body 40 .

The coke hopper 24 has a feeder 28 and a conveying pipe 30 at its bottom. The conveying pipe 30 is connected to the upper surface of the combustion furnace main body 40 . The coke 60 stored in the coke hopper 24 is fed quantitatively by the feeder 28 and fed into the combustion furnace main body 40 through the carrier pipe 30 . Thereby, the combustion furnace main body 40 is filled with the coke 60 .

The pulverized coal hopper 22 has a feeder 26 at its bottom. Further, the pulverized coal injection lance 34 penetrates the blow pipe 36, and the tip of the pulverized coal injection lance 34 protrudes inside the blow pipe 36 and is connected.

The pulverized coal stored in the pulverized coal hopper 22 is fed quantitatively by the feeder 26 , passes through the pulverized coal conveying pipe 32 and the pulverized coal injection lance 34 and is fed into the blow pipe 36 . Hot air 38 is blown into the blow pipe 36 , and pulverized coal blown from the pulverized coal blowing lance 34 is blown into the combustion furnace main body 40 filled with coke 60 from the tuyeres 42 together with the hot air 38 . A RW 50 is formed in the vicinity of the tip of the tuyere 42 by the hot air blown into the combustion furnace main body 40 .

The experimental furnace 20 shown in FIG. 2 was filled with coke having an average particle size of 15 to 25 mm and an I-drum strength of 85.1, and a coke 60 combustion test was performed. The TFT was adjusted by changing the blowing conditions of the hot air 38 blown from the blow pipe 36 and the pulverized coal. After changing the blowing conditions from the blow pipe 36, the coke 60 was burned by blowing hot air and pulverized coal for 3 hours under the blowing conditions. After 3 hours, the coke 60 in the RW was sampled and the I-type drum strength of the coke 60 was measured.

Coke I-drum strength is measured by the following procedure. First, 75 g of coke with a particle size of 20±1 mm is put into an I-shaped drum (cylinder of φ132 mm×700 mm). The I-shaped drum is then rotated 600 times at 20 rpm. The coke recovered from the I-shaped drum after the rotation is classified by a sieve with an opening of 10 mm, and the ratio (percentage) of the mass on the sieve with an opening of 10 mm to the initial input mass is calculated. This mass ratio is the I-type drum strength. In this embodiment and later-described examples, the I-type drum strength measured by the above procedure was used as the coke strength of coke.

The coke strength used in carrying out the present invention is not limited to the I-drum strength. As the coke strength, in addition to the I-type drum strength, the strength defined by the drum method or the tumbler method specified in the Japanese Industrial Standard "JIS K 2151 cokes-test method" may be used. Both the drum method and the tumbler method are indices indicating that the higher the numerical value is, the higher the strength is, similarly to the I-shaped drum strength.

FIG. 3 is a graph showing the relationship between TFT and coke intensity burned in the TFT. The horizontal axis of FIG. 3 is TFT (° C.), and the vertical axis is the I-type drum strength of coke after combustion. The TFT was calculated using the blowing conditions of the hot air 38 and pulverized coal blown from the blow pipe 36 and the above formula (2).

As shown in FIG. 3, when the TFT was 2300° C. or lower, even if coke was burned in the TFT, the reduction in coke strength did not change. Assuming that 2300° C., which is the upper limit temperature of the TFT at which the amount of decrease in coke strength does not change, is the reference TFT and that the coke strength of coke burned in the reference TFT is the reference coke strength, when the TFT becomes higher than the reference TFT, the The coke strength of coke in RW fired at temperature decreased significantly from the baseline coke strength. The following formula (3) for calculating the amount of decrease in coke strength from the reference coke strength is obtained from the plot of the coke strength at which the TFT in FIG. 3 becomes equal to or higher than the reference TFT.

ΔI=0.00795×(T _tf −2300) (3)
In the above equation (3), ΔI is the amount of decrease in coke strength from the reference coke strength, _Ttf is TFT (°C), and 2300 is the reference TFT (°C). Assuming that 0.00795 in the above equation (3) is a constant A and the reference TFT is B (° C.), the above equation (3) can be expressed by the following equation (1).

ΔI=A×(T _tf −B) (1)
ΔI in the above formula (1) is the amount of decrease in coke strength from the reference coke strength, _Ttf is the TFT (° C.), B is the reference TFT (° C.), and A is the TFT shown in FIG. and the coke strength of the coke burned in the TFT in RW. The above formulas (3) and (1) determined in this manner are specific examples of the corresponding relationship between the TFT and the coke intensity of the coke burned in the TFT in the RW. In addition, the "decrease amount" calculated as ΔI means that there was no decrease in coke strength when it was calculated as a negative value or 0 (zero), and when it was calculated as a positive value, the coke strength means that the

In this way, if the corresponding relationship between the TFT and the coke intensity of the coke burned in the TFT in the RW is obtained, in changing the blowing conditions at the tuyere 16, the above equation (2) is used to By calculating the TFT after the blowing condition is changed in , and using the calculated TFT and the above equation (3), the amount of decrease in coke strength from the reference coke strength can be obtained. If the amount of decrease in coke strength from the reference coke strength is obtained, the coke strength of coke corresponding to the amount of decrease, that is, the coke strength of coke whose coke strength has been increased by the amount of decrease or more can be specified. When changing the blowing conditions at the tuyeres 16, the blast furnace can be operated by charging coke with increased strength to the coke strength. As a result, even if the TFT exceeds the upper limit of the appropriate range due to a change in the blowing conditions at the tuyere 16, it is possible to prevent an increase in coke powder in the RW and to prevent adverse effects on the furnace conditions.

Coke with increased coke strength may be used for all the coke charged into the blast furnace, or may be used for part of the coke charged into the blast furnace. When coke with increased coke strength is partially used, the coke with increased coke strength is used at least for the coke charged into the blast furnace with a dimensionless radius of 0.3 to 1.0.

Coke charged into the blast furnace with a dimensionless radius of 0.3 or more and 1.0 or less descends in the blast furnace 10 and flows into the RW, but the dimensionless radius is 0.0 or more and less than 0.3 Coke charged within the range forms a coke filling layer in the lower part of the blast furnace 10 and does not flow into the RW, so even if the TFT exceeds the appropriate range, the coke strength does not decrease and the coke does not pulverize. For this reason, coke with increased coke strength may not be used for the coke charged in the range of the dimensionless radius of 0.0 or more and less than 0.3.

As a charging method for charging coke with different coke strengths into the blast furnace 10, coke with different coke strengths is separately charged into a plurality of top hoppers, and coke with different coke strengths is fed from these top hoppers to the blast furnace 10. may be charged in a predetermined charging range. Alternatively, the coke strength of coke charged from one top hopper may be changed between the front and rear halves of charging, thereby charging coke with different coke strengths into a predetermined charging range of the blast furnace 10 .

Since the furnace condition is not adversely affected even if the TFT exceeds the upper limit of the appropriate range by using coke with increased coke strength, in the blast furnace operating method according to the present embodiment, the TFT exceeds the upper limit of the appropriate range. It becomes possible to change the operating conditions at the tuyere 16 up to a range. As a result, the degree of freedom of changing the operating conditions at the tuyere 16 is increased more than before, and it becomes possible to cope with a wide range of furnace condition changes. It can be seen that it can contribute to the stable operation of

In addition, in the blast furnace operating method according to the present embodiment, the example using the above formula (3) as the correspondence relationship between the TFT in the RW and the coke intensity of the coke burned in the TFT in the RW was described, but the present invention is not limited to this. For example, as a correspondence relationship between the TFT in RW and the coke intensity of coke burned in the TFT in RW, an equation for calculating the coke intensity after burning in the TFT from the TFT may be used. The amount of decrease from the standard coke strength may be obtained from the coke strength and the standard coke strength.

Next, an example for confirming the effect of the blast furnace operating method according to the present embodiment will be described. In this example, using the experimental furnace 20 shown in FIG. 2, a combustion test was performed by changing the TFT and coke strength, and the furnace pressure drop during the test, the RW coke strength and the coke fineness after the test were evaluated. bottom. The test conditions of the combustion test were based on the actual blast furnace operation so that the combustion test in the experimental furnace 20 simulated changes in furnace pressure loss, coke strength of RW, and coke fineness due to TFT fluctuations in the actual blast furnace. set as a condition. Table 1 shows the test conditions and test results of the combustion test. In addition, it was confirmed in advance that the furnace condition deteriorates even in the actual blast furnace operation when the pressure loss in the experimental furnace 20 exceeds 4.00 kPa/m. In this example, the reference TFT is 2300° C., and the reference coke strength is 81.2 in I-type drum strength.

In Invention Example 1, the TFT was set at 2200° C. and coke with an I-type drum strength of 85.1 was used as the filling coke. Since the amount of decrease ΔI from the standard coke strength predicted from the TFT (2200 ° C.) and the equation (3) was -0.8, it was judged that there was no need to increase the coke strength of the charged coke. Combustion tests were conducted with the coke strength of the coke set equal to the coke strength of the packed coke. As a result, the pressure drop in the furnace was 3.92 kPa/m, the RW coke strength was 81.1, and the RW coke fineness was 4.55%. Thus, in Invention Example 1, since the pressure loss in the furnace was 4.00 kPa/m or less, it was confirmed that stable operation could be maintained even in an actual blast furnace.

In Invention Example 2, the TFT was set at 2300° C. and coke with an I-type drum strength of 85.1 was used as the filling coke. Since the amount of decrease ΔI from the reference coke strength predicted from the TFT (2300 ° C.) and the equation (3) was 0, it was judged that there was no need to increase the coke strength of the charged coke, and the coke of the charged coke A combustion test was conducted with the same strength as the coke strength of the packed coke. As a result, the pressure drop in the furnace was 3.90 kPa/m, the coke strength in the RW was 81.2, and the coke powder rate in the RW was 4.41%. As described above, in Invention Example 2, the in-furnace pressure loss was 4.00 kPa/m or less, so it was confirmed that stable operation could be maintained even in an actual blast furnace.

In Inventive Example 3, the TFT was set at 2450° C. and coke with an I-type drum strength of 85.1 was used as the filling coke. Since the amount of decrease ΔI from the standard coke strength predicted from the TFT (2450 ° C.) and the equation (3) was 1.2, a combustion test was performed using coke with a coke strength of 86.3 as the charged coke. rice field. As a result, the pressure loss in the furnace was 3.94 kPa/m, the RW coke strength was 81.0, and the RW coke powder ratio was 4.71%. Thus, in Invention Example 3, the in-furnace pressure loss was 4.00 kPa/m or less, so it was confirmed that stable operation could be maintained even in an actual blast furnace.

On the other hand, in Comparative Example 1, the TFT was set at 2450° C. and coke with an I-type drum strength of 85.1 was used as the filling coke. The amount of decrease ΔI from the reference coke strength predicted from TFT (2450 ° C.) and equation (3) was 1.2, but the combustion test was conducted with the coke strength of charged coke equal to the coke strength of charged coke. gone. As a result, the pressure loss in the furnace was 4.87 kPa/m, the RW coke strength was 80.2, and the RW coke powder ratio was 5.51%. As described above, in Comparative Example 1, since the pressure loss in the furnace exceeded 4.00 kPa/m, it was confirmed that the furnace condition deteriorated in the actual blast furnace.

From the results of Invention Example 3 and Comparative Example 1, when changing the blowing conditions at the tuyere 16, the TFT after changing the blowing conditions at the tuyere 16 was calculated, and the calculated TFT and the above equation (3) were compared. By obtaining the amount of decrease from the reference coke strength using and charging coke with increased coke strength corresponding to the amount of decrease into the blast furnace, the TFT is within the appropriate range (2200 to 2300 ° C. in the case of this embodiment). It was confirmed that even if the upper limit was exceeded, an increase in coke powder in the RW could be prevented, thereby preventing adverse effects on furnace conditions.

10 blast furnace 12 ore layer 14 coke layer 16 tuyere 18 gas flow 20 experimental furnace 22 pulverized coal hopper 24 coke hopper 26 feeder 28 feeder 30 transfer pipe 32 pulverized coal transfer pipe 34 pulverized coal injection lance 36 blow pipe 38 hot air 40 combustion furnace Body 42 Tuyere 44 Exhaust port 50 RW
60 coke

Claims (2)

A blast furnace operating method in which coke and iron source material are alternately charged from the top of the furnace and pulverized coal is blown in with hot air from tuyeres provided at the bottom of the furnace,
If the upper limit temperature of the theoretical combustion temperature at which the amount of decrease in coke strength does not change even if the coke is burned in the raceway is taken as the reference theoretical combustion temperature,
The theoretical combustion temperature in the raceway obtained from the blowing conditions from the tuyere;
The following formula (1), which is the correspondence relationship between the theoretical combustion temperature and the coke strength of coke burned at the theoretical combustion temperature in the raceway,
to determine the amount of decrease from the standard coke strength, which is the coke strength of coke burned at the standard theoretical combustion temperature,
A method of operating a blast furnace, wherein coke having a higher coke strength than the coke charged during operation at the reference theoretical combustion temperature or lower corresponding to the decrease amount is charged into the blast furnace.
ΔI=A×(T _tf −B) (1)
In the above formula (1), ΔI is the amount of decrease, Ttf _is the theoretical combustion temperature (° C.) on the raceway, B is the reference theoretical combustion temperature (° C.), and A is a constant determined from the above correspondence. is. The blast furnace operating method according to claim 1, wherein the coke with increased coke strength is charged into at least a dimensionless radius of the blast furnace of 0.3 or more and 1.0 or less.

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