JPH11152508A - Operation of injecting pulverized fine coal in blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blast furnace operating method which can improve the ventilation even in the case of operating extremely large quantity of injected pulverized fine coal, in the blast furnace operating method for injecting the pulverized fine coal. SOLUTION: At the time of injecting the pulverized fine coal together with blasting gas from a tuyere part of the blast furnace, a reached highest temp. Tmax is controlled while containing the control of gas temp. distribution in a raceway from the tuyere of the blast furnace to the deep position of the raceway so that a ratio Tmax /THT of the reached max. temp. Tmax ( deg.C) of the gas in the raceway and the m.p. THT ( deg.C) of ash of the pulverized fine coal becomes in the range of 1.0-1.5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blast furnace pulverized coal blowing operation method, and more particularly to an improvement in a blast furnace pulverized coal blowing operation method in which the pressure inside the furnace, which rises when pulverized coal is blown, is reduced to improve air permeability. It is.

[0002]

2. Description of the Related Art In recent years, the operation of a blast furnace has been carried out in order to greatly reduce fuel costs, reduce the burden on a coke oven, and extend the life of the furnace. How to)
The coke charge from the top of the furnace is being reduced, and operations are beginning to be carried out in which a large amount of inexpensive auxiliary fuel such as pulverized coal is blown from the tuyere of the blast furnace as an alternative to coke.

[0003] The pulverized coal injection operation is a technology that has been established as one of the powder injection operation technologies for a blast furnace.
Stable operation with pulverized coal injection amount of g / t-pig iron or more has been implemented. However, when the amount of pulverized coal injected is increased in this way, a phenomenon called a shell (or bird's nest) occurs around the raceway, and this shell grows and reduces the gas flow in the lower part of the blast furnace. There is a problem that the flow is often caused.

[0004] First, a mechanism generated by the shell will be described. As shown in FIG. 4, the pulverized coal is blown into the pulverized coal 4 from a tuyere 7 provided on a blast furnace
At the same time, a large amount is blown into the coke layer 8 through the lance 1. At the time of the pulverized coal injection, a shell formed by the injection of the pulverized coal 4 around (inside) the raceway 2 (the lean combustion space of coke existing inside the furnace at the tuyere tip).
(High melting point slag wall) 3 is generated.

[0005] The shell 3 is derived from pulverized coal ash 11 generated by burning at high speed in the raceway 2. That is, the pulverized coal 4 blown into the blast furnace contains ash of about 8 to 10%,
₂ 50-60%, Al ₂ O ₃ 20-30%, other Fe
It consists of ₂ O ₃ , CaO, etc., and is mainly composed of acidic components. Therefore, when the blowing amount of the pulverized coal 4 increases, S from the ash 11 generated by burning the pulverized coal
Acid component slag mainly composed of iO ₂ and Al ₂ O ₃ increases, and the viscosity and melting point of slag generated around the raceway (at the back of the raceway) increase. For this reason, the slag generated around the raceway is dripping slag 6 derived from iron ores mainly composed of sinter which descends from the upper part of the blast furnace.
As a result, the coke and pulverized coal ash generated in the raceway are not properly slagmed in the raceway. As a result, the slag whose slag is delayed accumulates thickly around the raceway to form a thick shell 3.

[0006] When the pulverized coal ratio is increased by increasing the amount of pulverized coal to be blown, the amount of coke charged to iron ores decreases, and the coke in the furnace core tends to be reduced in particle size and pulverized. In addition, the porosity of the furnace core decreases. Therefore, the powder blown from the tuyere tends to accumulate on the surface of the furnace core. Further, as described above, the strong acid ash (ash content) is likely to accumulate in the back of the raceway or in the shell 3 due to an increase in the amount of pulverized coal injected. 3 will grow more.

The presence of the shell 3 changes the flow direction of the gas (Bosch gas) generated at the tuyere from the center of the furnace to the upper part of the furnace, and the generated high-temperature gas flows along the blast furnace wall 9. Flow (peripheral flow of gas flow).
The peripheral flow of the gas flow causes a rise in the temperature of the ore and a stagnation of the reduction, and also hinders the dripping of the melt. This tendency is fueled by the increase in ore thickness in the pulverized coal-blown blast furnace operation, as well as by the decrease in ascending gas flow with decreasing coke layer thickness. Further, the peripheral flow of gas causes an increase in the fuel ratio (increase in fuel cost) due to an increase in heat loss from the furnace wall 9. In addition, the flow of the generated hot gas along the furnace wall can lead to damage to the furnace wall refractory / cooling system.

Further, the presence of the shell 3 lowers the air permeability of the lower part of the blast furnace, increases the blowing pressure and increases the pressure fluctuation, and makes it possible to blow a large amount of pulverized coal and to operate the large amount of pulverized coal itself. It makes it difficult to continue for a long time. Therefore, shell formation by pulverized coal injection can be a serious problem that causes operational troubles in blast furnaces and impairs productivity.

In order to solve such a problem, conventionally, a high basicity solvent is blown from a tuyere together with pulverized coal to increase the basicity of the high melting point slag existing around the raceway to lower the viscosity. (Increases fluidity), assimilate with the dripping slag descending from the upper part of the blast furnace, and promote appropriate slagging of pulverized coal ash in the raceway. Various techniques for improving air permeability have been proposed.

For example, in Japanese Patent Application Laid-Open No. 3-291313, CaO-based, MgO-based, SiO ₂
It is disclosed to use a system flux. In Japanese Patent Publication No. 6-89382, a basic pulverizing medium solvent such as pulverized dolomite, serpentine, olivine and limestone is blown simultaneously with pulverized coal, and the amount of blowing is determined by mixing the medium solvent and ash in the pulverized coal. So that the ash of pulverized coal and dolomite are assimilated in the raceway to form a low-viscosity slag. Discloses that the high melting point slag wall (bird nest) is made thinner.

According to these techniques, as shown in FIG. 3 having the same configuration as FIG. 4, a high basicity solvent 10 is blown into the coke layer 8 together with the pulverized coal 4 together with the blowing gas 5 through the lance 1. As a result, the ash 11 of the pulverized coal and the high basicity solvent 10 are assimilated inside the raceway 2 to form a low-viscosity slag, which is easily assimilated with the dripping slag falling from the upper part of the blast furnace. The slag is dropped in the blast furnace. As a result, the formation of the high-melting-point slag layer 3 is suppressed as compared with the case where only the pulverized coal is blown in FIG. 4, and the thickness of the high-melting-point slag layer 3 is reduced, and a stable raceway shape is maintained. It is said that the air permeability can be improved.

In addition to the blowing of these high basicity solvents, Japanese Unexamined Patent Publication No. 9-176706 discloses a method of blowing pulverized coal into each tuyere while keeping the amount of pulverized coal blown into all tuyeres. It is disclosed that the generation of the shell is suppressed by performing control such as increasing or decreasing the amount.

[0013]

However, according to the prior art in which a high basicity solvent is blown together with pulverized coal from a tuyere, the ash of the pulverized coal and the high basicity solvent are assimilated inside the raceway. The mechanism has not yet been sufficiently elucidated, and as a result, in operations where the amount of pulverized coal injected into the blast furnace is extremely large, the amount of high basicity solvent injected is increased accordingly. As a result, melting and slagging of the injected high basicity solvent solvent inside the tuyere are delayed, and there is a drawback that assimilation and melting do not sufficiently occur inside the raceway.

In particular, dolomite, serpentine, olivine,
The high basicity medium solvent of ores such as limestone has a high melting point itself, and is sufficient at a temperature of about 2000 ° C. and within a raceway where there is only a limited time for assimilation with pulverized coal particle ash. It does not melt, and as a result, remains in a solid state, does not assimilate with the pulverized coal particles, and easily reaches the interior of the raceway.

If the high basicity medium solvent reaches the inside of the raceway without melting, it will be taken into a coke bed (furnace core) at a temperature far below the flame temperature, and will not be melted. It remains in the furnace core as it is melted. For this reason, in the worst case, a high basicity solvent to be introduced for improving the air permeability results in impaired air permeability. This also leads to an increase in the amount of the high basicity solvent blown in more than is required for assimilation with the pulverized coal particle ash.

Further, when a high basicity solvent which involves an endothermic reaction such as limestone is used, limestone decomposes heat when decomposed in front of the tuyere, and extra coke is required to compensate for this heat. The ratio goes up. Along with this, the amount of generated gas also increases, and the cost of gas recovery increases.

Further, the control of the amount of pulverized coal blown in each tuyere as disclosed in Japanese Patent Application Laid-Open No. Hei 9-176706 merely temporarily controls (increases or decreases) the rate of shell formation. To prevent deterioration of the air permeability of the lower part of the blast furnace due to
Not considered at all.

Therefore, in these prior arts, when a high basicity medium solvent is used, there is an unavoidable possibility that a new harm may occur. Even when controlling the amount of pulverized coal to be blown into each tuyere, there is a basic problem. Cannot suppress shell creation. For this reason, at present, there is a limit to the amount of pulverized coal blown, and even with the current amount of pulverized coal blown, by improving the permeability of the blast furnace by complicated control of other blast furnace operating conditions, The fact is that pulverized coal injection is maintained.

The present invention has been made in view of these problems of the prior art,
In the blast furnace operation method in which pulverized coal is injected, even in an operation in which the amount of pulverized coal injected is extremely large, the formation of shells can be suppressed and the blast furnace pulverized coal injection operation that can improve air permeability when pulverized coal is injected in the tuyere in front of the tuyere is improved. The aim is to provide a method.

[0020]

In order to achieve the above object, the present invention provides a method of charging iron ore and other raw materials of iron ore into a blast furnace from the top of the blast furnace together with the blowing gas from the tuyere of the blast furnace. in blast furnace operation method of blowing pulverized coal includes controlling the gas temperature distribution in the race in the way from the blast furnace tuyeres until raceway back, the highest temperature of the gas in the raceway T _{ma x} (℃) and pulverized coal Ash melting point T _HT (° C)
The maximum temperature T _max is controlled so that the ratio T _max / T _HT is in the range of 1.0 to 1.5, the growth of the high-melting slag layer generated at the back of the raceway is suppressed, and the furnace at the time of pulverized coal injection is controlled. The main point is to improve internal ventilation.

The present inventors have studied the relationship between the temperature distribution in the raceway at the time of high pulverized coal injection, the combustion ash of pulverized coal and the melting state of ash, and the formation of a shell. The temperature distribution in the raceway at the time of high pulverized coal injection shows that the maximum temperature in the raceway is higher than that during all-coke operation due to the rapid combustion of pulverized coal. On the contrary, it decreases. Figure 2 shows the relationship between the distance from the tuyere tip in the raceway and the temperature distribution in the raceway. As is evident from Fig. 2, both at the time of all coke operation B and at the time of injection of high pulverized coal at 200 kg / t A, the distance from the tuyere tip was 100 to 300 mm.
The temperature inside the raceway is the highest (maximum temperature reached).
However, in the case of high pulverized coal injection A, the maximum temperature itself is higher and the maximum temperature shifts to the tuyere tip side. In addition, the temperature at the back of the raceway is lower in A when high pulverized coal is injected.

Therefore, according to the temperature distribution in the raceway at the time of blowing the high pulverized coal, the ash of the pulverized coal blown from the tip of the tuyere and rapidly burned is melted quickly and in a large amount. Become. On the other hand, since the temperature at the back of the raceway is low, the ash of the pulverized coal that has been melted in large quantities tends to agglomerate in the coke gap and surface layer at the back of the raceway, and it is easy to take in coke powder due to the crosslinking effect. Therefore, the thickness of the generated shell is further increased.

When high-pulverized coal is injected, pulverized coal ash blown from the tuyere tip and rapidly burned is more easily melted than coke ash in the raceway. The reason is that the coke charged from the blast furnace top and supplied into the raceway must be
Since gasification of SiO ₂ in ash occurs in the blast furnace, Al ₂ O ₃ / SiO ₂ is compared with pulverized coal blown from tuyeres.
This is because the melting point of ash of coke is higher than the melting point of ash of pulverized coal. Therefore, in the raceway, the pulverized coal ash is preferentially melted rather than the coke ash.

In view of the relationship between the temperature distribution in the raceway at the time of high pulverized coal injection, the state of incineration and ash melting of pulverized coal, and the formation of a shell, it is clear that the race It can be seen that in order to suppress shell formation at the back of the way, it is effective to lower the temperature in the raceway, particularly the maximum temperature, to reduce the amount of ash of the pulverized coal.

Therefore, in the present invention, the operating conditions and pulverized coal conditions are controlled so as to lower the temperature in the raceway, particularly the maximum attainable temperature, so that the maximum attainable temperature T _max (° C.) of the gas in the raceway is attained. And the melting point T _HT (
The ratio T _max / T _HT of ° C.) is controlled to a range of 1.0 to 1.5. As the operating conditions and pulverized coal conditions to be controlled, it is particularly preferable to increase or decrease the oxygen-enriched amount or to adjust the composition and particle size of the pulverized coal to make combustion more difficult.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the melting point T _HT (° C.) of pulverized coal ash is determined by the properties and composition of pulverized coal blown from tuyeres. It is determined by actually measuring the melting point T _HT when melted. The maximum temperature T _max (° C) of the gas in the raceway of the blast furnace may be measured with a normal thermocouple, a two-color thermometer or a radiation thermometer. With these means, direct measurement with high local accuracy is very difficult. Therefore, it is difficult to measure the temperature during operation of the blast furnace with these ordinary temperature measurement means, and a known method using numerical analysis by simulation based on various models of the material balance and heat balance in the blast furnace or operation experience values. (E.g., “Iron and steel”, Vol 78, 1992, pp. 1230-1237) or
Alternatively, it is preferable to actually measure using an optical fiber.
This optical fiber is a consumable type, and even if the tip melts in the high temperature part of the raceway, a long optical fiber is sequentially sent from the outside of the blast furnace through a water-cooled probe provided on the blast furnace furnace wall, and instantaneous By receiving a proper optical signal, it is possible to measure the temperature of the target portion. Therefore, the relationship between the distance from the tip of the tuyere in the raceway and the temperature distribution in the raceway as shown in FIG. 2 can be obtained using this optical fiber. In addition, the value of _Tmax obtained by the above calculation formula or the optical fiber may be verified by the conventional thermometer.

According to another embodiment of the present invention, in addition to controlling the maximum temperature of the gas in the raceway of the present invention, when pulverized coal is blown together with the blowing gas from the blast furnace tuyere,
A method may also be used in which a basic slag is blown together with pulverized coal, the slag is assimilated with pulverized coal ash, and the growth of shells formed in the back of the raceway by the pulverized coal ash is suppressed. As the basic slag to be blown, for example,
CaO-based, Mg as described in 3-291313
O-based and SiO-based fluxes, fine dolomite, serpentinite, and the like as described in JP-B-6-89382.
Olivine, limestone, may be, but as described in Japanese Patent Application No. 9-4745 filed by the present applicant, has a melting point below the temperature of the raceway, the phosphorus content is 1.0 % Or less of a basic premelt slag is preferably used. When the basic premelt slag is blown, the basicity (basic component amount / acid component amount) when the blown slag and the ash in the pulverized coal are mixed is 0.5 to 1.
It is preferable to adjust the amount of the blown slag so as to be 3.

The premelt slag means slag that has already been melted once, and includes, for example, converter slag and blast furnace slag. These slags are generated in the iron making and steel making processes, and have already been melted once in this process, and have higher solubility and slag compared to raw ores that have not been melted, such as the dolomite and CaO-based flux. Very good conversion. Further, converter slag, blast furnace slag, and the like also have a high basicity, and are therefore suitable as the blowing slag.
In this way, by using a high basicity premelt slag having a melting point equal to or lower than the temperature of the raceway, the slag is sufficiently melted or semi-molten inside the raceway,
Assimilate with pulverized coal particle ash. When used in combination with the method of the present invention, a synergistic effect of having an effect of improving air permeability even with a small amount of blowing is exhibited.

[0029]

Next, embodiments of the present invention will be described. Using a coke-filled test combustion furnace simulating a blast furnace, the blast pressure P _B
(kPa) maximum temperature T of gas in raceway
The ratio T _max / T of _{ma x} (℃) and a melting point T _HT ash pulverized coal (℃)
The effect of _HT was evaluated. The test combustion furnace is "iron and steel"
(Vol. 81, 1995, No. 12, pp. 1141-1119) is also disclosed as a means for investigating combustion behavior and gas flow changes in a raceway. More specifically, as shown in FIG. 5, the height 2.5 m, depth 1.9m, with fan-shaped furnace having an inner volume of 4.2 m ^3, has a tuyere 13 having an inner diameter of 0.08m one, as in the blast furnace Hot air is blown into the furnace to burn coke in the furnace. Note that the hot blast stove uses a heat exchange method by electric heating. The test combustion furnace 12 has a packed bed of river sand at the bottom of the furnace.
And a rotary feeder equipped with this sand at the bottom of the furnace.
(Not shown), and a method of lowering the coke 15 (existing on the river sand packed layer 14) of the entire packed bed, which is quantitatively charged by the level meter 17 from the coke hopper 16 at the furnace top. I have. Therefore, this test combustion furnace 12
It has a structure that can simulate the renewal of the core of the blast furnace and the raceway inside the tuyere, that is, the mechanism of supplementing coke consumed by combustion with coke above. In addition, the test combustion furnace is equipped with a water-cooled sampling prog 18 at three levels (from the tuyere center, 0.3 m above the tuyere and 0.6 m above the tuyere) from the tuyere facing side. A sample constituting the raceway 22 can be collected. A thermocouple 19 including an exhaust gas port 21 is installed on the furnace wall side.

The test conditions were as follows: pulverized coal blowing amount from the tuyere 13 by the lance 20: 72144 kg / hr (200 kg / t-converted hot metal conversion);
Lance position from the tuyere tip: 0.17-0.34m, hot air blowing volume: 560-720 N / mm ³ / hr, blowing temperature: 1050 ° C, oxygen content: 21-27vol%, increase / decrease oxygen enrichment by, when changing the T _max / T _HT, blower pressure P _B (kP
a) was measured. The properties of the pulverized coal used for injection from the tuyere were as follows: VM: 11.2 to 42.3, Ash: 0.5 to 9.8, F.
C .: The range is 54.3-88.3 (each dbmass%).
C .: 73.3-89.3, H: 3.8-5.7, N: 1.0-2.4, S
: 0.4 to 1.6, O: 2.4 to 12.2 (each dbmass%). The melting point T _HT of the ash of this pulverized coal is 1300-1600 ° C
Range. The maximum temperature T _max (° C.) of the gas in the raceway was measured by an optical fiber sequentially sent from the outside of the furnace through a water-cooled probe 18 provided on the furnace wall, and verified by a radiation thermometer.

FIG. 1 shows the blowing pressure P _B (kPa) and T _max / T _HT
The relationship is shown below. As is clear from FIG. 1, T _max / T _HT
Is in the range of 1.0 to 1.5, the blowing pressure P _B (k
Pa) has fallen below 20 kPa. Then, under the blowing pressure, the gas flow in the coke-filled test combustion furnace was stabilized. The reason is that when T _max / T _HT is in the range of 1.0 to 1.5, the amount of ash of the pulverized coal blown from the tuyere tip and burned in the raceway is significantly reduced, This is because, in the coke gap or the coke surface layer, the amount of the shell formed by coagulation with the coke powder is reduced, and the air permeability around the raceway is improved. In fact, after the combustion test, as a result of the investigation of the race way to dismantling the test combustion furnace, T _max / T
_{If the HT} is out of the range of 1.0 to 1.5, it can be distinguished from other parts as a white area around the raceway,
A shell-like shell having a thickness of 60 mm was formed.
On the other hand, when T _max / T _HT was in the range of 1.0 to 1.5, the formation of this shell was so slight that it could not be distinguished from other parts. Therefore, this fact supports the effect of improving the air permeability in the blast furnace of the present invention.

[0032]

As described above, the blast furnace pulverized coal blowing operation method of the present invention improves the air permeability at the time of blowing the pulverized coal in the tuyere front raceway portion even when the pulverized coal blowing amount is extremely large. Thus, stable operation of the blast furnace can be achieved. Moreover, the industrial value is great in that this remarkable effect can be achieved without greatly changing the conventional method.

[Brief description of the drawings]

FIG. 1 shows a ratio of a blowing pressure, a maximum temperature of gas in a raceway, and a melting point of ash of pulverized coal in an embodiment of the present invention.
FIG. 4 is an explanatory diagram illustrating a relationship of T _max / T _HT .

FIG. 2 is an explanatory diagram showing a temperature distribution in a raceway.

FIG. 3 is an explanatory view showing a raceway situation when pulverized coal and a high basicity solvent are simultaneously injected according to a conventional method.

FIG. 4 is an explanatory view showing a raceway situation at the time of pulverized coal injection according to a conventional method.

FIG. 5 is a cross-sectional view showing a test combustion furnace simulating a blast furnace used in an example of the present invention.

[Explanation of symbols]

1: Lance 2: Raceway 3: High melting point slag wall 4: Pulverized coal 5: Blast gas 6: Metal slag drop 7: Tuyere 8: Coke layer 9: Blast furnace wall 10: Basic solvent 11: Pulverized coal ash

Continued on the front page (72) Inventor Akito Kasai 1 Kanazawa-cho, Kakogawa-shi, Hyogo Kobe Steel, Ltd. Inside the Kakogawa Works

Claims (2)

[Claims] A method for operating a blast furnace in which pulverized coal is blown together with blown gas from a blast furnace tuyere includes controlling a gas temperature distribution in the raceway from the blast furnace tuyere to the inside of the raceway. Maximum temperature T _max
(° C) and melting point T _HT (° C) of pulverized coal ash T _max / T _HT
Control the maximum temperature _{Tmax so} that the temperature is in the range of 1.0 to 1.5, suppress the growth of the high melting point slag layer generated at the back of the raceway, and improve the air permeability in the furnace when pulverized coal is injected. Blast furnace pulverized coal injection operation method characterized by the above-mentioned. 2. The blast furnace pulverized coal injection method according to claim 1, wherein the pulverized coal injection amount is 200 kg / t-pig iron or more.