JPH10204511A - Operation of blast furnace for powder blowing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the lowering of ventilation even in the case of being a large blowing quantity of pulverized fine coal by regulating the m.p. of basic slag blown together with the pulverized fine coal to the temp. of a raceway or lower and the content of phosphorus to a specific ratio or lower and adjusting basicity at the time of mixing of the blowing slag with ash content in the pulverized fine coal in specific range. SOLUTION: In a blast furnace operational method for blowing the pulverized fine coal and the basic slag into the blast furnace, as the blowing slag, a pre- molted slag having the m.p. of the temp. of the raceway or lower, is used. The pre-melted slag is the slag once melted, and converter slag or blast furnace slag are suitable. The content of phosphorus in this basic slag is made to <=1.0%. The slag blowing quantity is adjusted so that the basicity at the time of mixing the blowing slag with the ash content in the pulverized fine coal becomes 0.5-1.3. By this method, even in the case of being much blowing quantity of the pulverized fine coal such as 100kg/t-pig iron, the slag surely becomes the melting or the semi-melting condition in the inner part of the raceway.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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)
In addition to charging coke from the top of the furnace, operations are beginning to blow large amounts of inexpensive pulverized coal from the blast furnace tuyeres.

[0003] The pulverized coal injection operation is a technology established as one of the powder injection operation technologies for a blast furnace.
Stable operation is performed at a pulverized coal injection amount of 〜100 kg / t-pig iron. However, if the amount of pulverized coal injected is larger than the above amount, a phenomenon called a bird's nest occurs around the raceway, and this often grows and causes poor gas flow at the lower part of the blast furnace. There is a problem that happens.

[0004] More specifically, the pulverized coal injection operation comprises:
As shown in FIG. 4, a large amount of pulverized coal 4 is blown into the coke layer 8 from the tuyere 7 provided on the blast furnace wall 9 together with the blowing gas 5 through the lance 1. Therefore, inside the tuyere,
This causes an increase in blast pressure due to pulverized coal combustion. A high melting point slag wall 3 (commonly referred to as a bird's nest) formed by blowing pulverized coal 4 around the raceway 2 (a lean combustion space of coke existing inside the furnace at the tuyere tip). The phenomenon that the property is reduced occurs.

[0005] The high melting point slag wall 3 is
Ash content of pulverized coal generated by burning at high speed within
1 is its origin. That is, it is blown into the blast furnace
Pulverized coal 4 contains about 8 to 10% of ash, and this ash
Is SiO 2 as shown in Table 1 below._Two50-60%, Al
_TwoO_Three20-30%, other Fe_TwoO_Three, CaO, etc.
And is mainly composed of acidic components. Accordingly
When the amount of pulverized coal 4 blows up, pulverized coal burns
From ash 11 generated by_Two, Al _TwoO_ThreeTo
Acid component slag, which is the main component, increased,
The viscosity and melting point of the slag generated in the enclosure (back) increase. This
The slag generated around the raceway is
Does not assimilate with the dripping slag 6 descending from the top of the
Of pulverized coal ash in the raceway is delayed
Will be. As a result, around the raceway,
Slag wall with high melting point due to thick accumulation of slag delayed in formation
3 will be formed.

On the other hand, the production of slag in the blast furnace is important for the stable operation of the blast furnace, and the dripping slag 6 generated from the sinter is assimilated with the slag from the ash of coke and pulverized coal generated in the raceway. It needs to be changed to a stable final slag.

Nevertheless, as described above, if the high melting point slag wall 3 which does not change to a stable final slag and does not become a dripping slag 6 around the raceway exists, the lower part of the blast furnace lowers. Reduces air permeability. This decrease in air permeability causes an increase in the blowing pressure and an increase in pressure fluctuation, and makes it difficult to blow a large amount of pulverized coal and continue the operation of blowing a large amount of pulverized coal for a long time.

[0008] When the pulverized coal ratio is increased by increasing the amount of pulverized coal to be blown, coke in the furnace core tends to be easily pulverized, and 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) is likely to accumulate in the back of the raceway (bird's nest) due to an increase in the amount of pulverized coal injected. Then, the slag wall 3 (bird's nest) having a high melting point grows.

Normally, the porosity ε of the blast furnace core and the pulverized coal injection amount a have the relationship shown in FIG. 5, and the porosity ε of the blast furnace core and the high melting point slag wall The thickness t is
The relationship is as shown in FIG. That is, as described above, as the pulverized coal injection amount a increases, the slag wall thickness t of the high melting point increases, the porosity ε of the furnace core of the blast furnace decreases, and the air permeability decreases.

Further, the presence of the slag wall 3 changes the flow direction of the gas (Bosch gas) generated at the tuyere from the center of the furnace toward the upper part of the furnace. This change in the gas flow causes the generated high-temperature gas to flow along the blast furnace wall 9 (peripheral flow), and further increases the fuel ratio (fuel Cost increase). In addition, the generated hot gas flows along the furnace wall,
It can also cause damage to the furnace wall refractory / cooling system.

In order to solve such a problem, a high basicity solvent has been 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 JP-A-3-291313, CaO-based, MgO-based,
It is disclosed that an SiO-based flux is used.
In Japanese Patent Publication No. 6-89382, a basic pulverizing medium solvent such as pulverized dolomite, serpentine, olivine and limestone is blown at the same time as 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. , High melting point slag wall (bird nest)
Is disclosed.

According to these techniques, as shown in FIG. 3 having the same configuration as FIG. 4, a high basicity medium solvent 10 is blown into the coke layer 8 together with the pulverized coal 4 and 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 to form a low-viscosity slag, which is easily assimilated with the dripping slag falling from the upper part of the blast furnace. Drops are 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 possible to improve the air permeability.

[0014]

However, in these prior arts, the mechanism by which the ash of the pulverized coal and the high basicity solvent are assimilated inside the raceway has not yet been sufficiently elucidated. In operations where the amount of pulverized coal injected 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 is taken into a coke bed (furnace core) at a temperature much lower than the flame temperature, and is not melted. It remains in the 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.

In the case of using a high basicity solvent having an endothermic reaction, such as limestone, limestone decomposes heat of decomposition when decomposing in front of the tuyere, and requires extra coke for heat compensation. The ratio goes up. Along with this, the amount of generated gas also increases, and the cost of gas recovery increases.

Therefore, in these prior arts, when a high basicity medium solvent is used, the possibility of producing the above-mentioned adverse effects is inevitable. This high basicity medium solvent injection technique guarantees a high pulverized coal injection amount. I am worried about going. For this reason, the current amount of pulverized coal to be blown is limited, and even with the current amount of pulverized coal to be blown, the air permeability in the blast furnace is improved by complicated control of other blast furnace operating conditions, and pulverized coal is blown. The fact is that it is maintained.

The present invention has been made in view of these problems of the prior art,
In the blast furnace operating method in which pulverized coal is blown, even in the operation where the amount of pulverized coal blown is extremely large, the permeability at the time of blowing the pulverized coal in the tuyere in front of the tuyere can be improved. It is an object of the present invention to provide a blast furnace operating method in which the amount of slag is small and a decrease in air permeability caused by excessive blowing of basic slag is prevented.

[0020]

In order to achieve the above object, a method for operating a blast furnace according to the present invention is characterized in that, when pulverized coal is blown from a blast furnace tuyere with blowing gas, basic slag is blown together with the pulverized coal. By assimilating slag with pulverized coal ash, the growth of the high melting point slag layer (commonly called bird's nest) generated behind the raceway due to pulverized coal ash is improved, and the air permeability in the furnace when pulverized coal is injected is improved. In the blast furnace operating method (reducing furnace pressure), the blowing slag has a melting point equal to or lower than the temperature of the raceway,
The one having a phosphorus content of 1.0% or less is used, and the basicity (basic component amount / acid component amount) when the blown slag and ash in pulverized coal are mixed is 0.5 to 1. The amount of the blown slag is adjusted so as to be 3.

In the present invention, as the slag having a high basicity, a premelt slag having a melting point lower than the temperature of the raceway is used. Premelt slag means slag that has already been dissolved once. For example, converter slag, blast furnace slag, etc. are generated during the iron making and steel making processes, and have already been melted once in this process, compared to raw ores that have not been melted once, such as the dolomite and CaO-based flux. Very good solubility and slagging properties. Further, as shown in Table 1 below, converter slag, blast furnace slag, and the like also have a high basicity, and thus are suitable as the high basicity slag of the present invention.

By using a high basicity premelt slag having a melting point below the temperature of the raceway, the slag is sufficiently melted inside the raceway and assimilated with the ash of pulverized coal particles. In other words, as in the prior art, the amount of pulverized coal blown is reduced without melting inside the raceway and reaching the inner part of the raceway without assimilating with the pulverized coal particle ash, without impairing the air permeability. Is possible.

In order for the injected slag and fine coal ash to meet and assimilate during the flight in the raceway, the present inventors have already produced the injected slag and the back of the raceway. In order to assimilate with the high melting point slag layer, it has been found that it is important that the injected slag is in a molten or semi-molten state before encountering with fine coal ash. That is, at a temperature of about 1700 to 2000 ° C. and inside the raceway where space is limited, the blown slag is made of a pre-melt slag having a melting point equal to or lower than the temperature of the raceway, thereby increasing the blowing amount. Even if the operating conditions such as the slag are changed, the slag to be blown can be reliably melted or semi-melted.

Incidentally, the melting point of the ore, which is a basic medium solvent in the prior art, varies depending on the composition, but dolomite: about 2450 ° C., serpentine: about 1800 ° C., olivine: about 1500 to 1900 ° C., limestone: About 2570
° C, which is equal to or higher than the raceway internal temperature of about 1700-2000 ° C. On the other hand, the melting point of the converter slag is about 1450 ° C. and the melting point of the blast furnace slag is about 1300 ° C., which is sufficiently lower than the raceway internal temperature. Therefore, by the synergistic effect of the low melting point and the premelt, in the present invention, the blown slag is reliably melted or semi-melted inside the raceway.

Therefore, in the present invention, in particular, the amount of pulverized coal blown is set to 100 kg / t-pig iron or more,
0 kg / t-pig iron or more, even if it is a long-time pulverized coal blowing operation, and if the amount of basic slag to be blown is increased correspondingly, Thus, a molten or semi-melted state is ensured inside the raceway. The basic slag, which has been melted or semi-molten in the raceway, encounters and assimilates with the pulverized coal ash during the flight in the raceway. The assimilation of the melting point with the slag layer is not delayed, and as a result,
A low melting point slag is generated and assimilated and melted sufficiently inside the raceway with the dripping slag in the furnace.

It should be noted that Japanese Patent Publication No. 6-89382 describes the above.
In addition to dolomite, as a high basicity solvent,
There is an example of using a lug. However, in general
The converter slag is the No. 4 high phosphorus converter in Table 1 described below.
As slag, P content is P _TwoO_FiveWith 2-3% (P
1.0 to 1.3%). This high phosphorus converter slag
Is injected into the blast furnace as high basicity slag,
Phosphorus in the furnace rises and the process below the blast furnace (hot metal pretreatment
Dephosphorization treatment to remove phosphorus in steel
However, the improvement of the source unit by pulverized coal injection in the blast furnace
Is also very expensive and not a realistic ironmaking method.
You.

The upper limit of the phosphorus content of the basic slag of the present invention, such as converter slag, is 1.0% so that the dephosphorization operation in steel in the lower step does not increase the cost. Therefore, in the present invention, for example, when a converter slag is used, a low-phosphorus converter slag generated after blowing dephosphorized hot metal, which also has a phosphorus content of 1.0% or less. The fractionated slag is crushed and used.

When using converter slag,
If it is not possible for the converter equipment to separate low phosphorus converter slag, it contains a relatively large amount of CaO (about 40%).
%) It is preferable to pulverize a basic blast furnace slag, mix it with the converter slag, and blow it in.

Further, even when blast furnace slag is used, since the basicity of the blast furnace slag is lower than that of the converter slag, the amount required for blowing is larger than that of the converter slag alone in order to secure the required basicity. I do. Therefore, in order to reduce the amount of slag to be blown, it is preferable in terms of efficiency to use the slag mixed with the converter slag.

The basic slag of the present invention is preferably in the form of fine powder similar to pulverized coal and has a particle size of 200 mesh or less. Larger lumps have a slower action and may not be molten or semi-molten inside the raceway.

As a means for pulverizing the basic slag for pulverization, a predetermined amount of raw material slag may be charged into a blast furnace pulverized coal production mill before blowing into the blast furnace, and mixed and pulverized with coal. Yes, it is also possible to pulverize the converter slag separately with a special mill and then mix it with pulverized coal and blow it.

The amount of basic slag to be blown into the basic slag of the present invention is also considered in consideration of the amount of ash in pulverized coal, and the basicity (basic component) when the slag is mixed with the ash in pulverized coal. (Amount / acid component amount) of 0.5 to 1.3. If the basicity is less than 0.5, the effect of blowing the basic slag of the present invention cannot be expected, and if the basicity exceeds 1.3, there is almost no effect of lowering the basicity.

The way of blowing the basic slag from the tuyere
Although it may be mixed with pulverized coal or blown into it with another pipe, it is preferable to blow into the blast furnace at the same time as pulverized coal with the best reaction efficiency.

[0034]

Next, an embodiment of the present invention will be described.
You. FIGS. 1A to 1C show an inner volume of 4550 m. ^ThreeBlast furnace
In Table 1, the No. 1 pulverized coal with ash shown in Table 1 was fixed
When the amount (200 kg / t-hot metal) is injected, different salt
Time of blast pressure when basic slag is blown simultaneously
Changes. 1 (a) to 1 (c).
The vertical axis indicates the blowing pressure, and the horizontal axis indicates the time. Ma
The operating conditions were as follows: air flow: 6000 Nm^Three/ Hr, blast
Temperature: 1100 ° C, wind speed in front of tuyere: 230m / s, tuyere
Diameter: 135 mmφ.

FIG. 1 (a) shows the above-mentioned Japanese Patent Publication No. 6-89382.
No. 2 dolomite having a composition of No. 2 shown in Table 1 (10 kg / t-
(Hot metal) is mixed with pulverized coal and blown.
FIG. 1 (b) shows the method of the present invention, in which the N
5% pulverized low phosphorus converter slag with a composition of o.5 (10kg
/ T-hot metal) is mixed with pulverized coal and blown. FIG. 1 (c) shows a comparative method of the present invention, in which 5% of crushed blast furnace slag having a composition of No. 6 shown in Table 1 (10 kg /
(t-hot metal) is mixed with pulverized coal and blown. The basicity (basic component amount / acid component amount) is 0.4 in FIG. 1 (a), 0.5 in FIG. 1 (b), and 0.4 in FIG. 1 (c).

In FIG. 1A, the fluctuation of the wind pressure level after 0:00 after the start of the dolomite blowing indicated by the arrow S is smaller than before the blowing. This can be said to be the air permeability improvement effect of dolomite. However, the effect is about 2% of the blowing pressure, and the efficiency of the effect is low in view of the large addition ratio (5%) of the blown dolomite to the total pulverized coal amount. This is the above-mentioned Japanese Patent Publication No. 6-89382.
As described as a problem of the technology disclosed in Japanese Unexamined Patent Application Publication No. 10-209, it is presumed that the dolomite is taken into the coke bed (core) without being melted, and remains in the core unmelted, thereby impairing air permeability.

On the other hand, in FIG. 1 (b) of the present invention, pulverized coal and pulverized converter slag 5% are added and blown, and after 2 o.m. The fluctuation of the wind pressure level is smaller than before, and it can be seen that the converter slag is effective in improving the air permeability. The effect is about 6% of the blowing pressure, and the effect of blowing 5% of the whole pulverized coal is highly efficient and satisfactory.

FIG. 1 (c) shows the change in the blowing pressure when 5% of crushed blast furnace slag, which is also a slag (flux) of a pre-melt product, is blown in with the method of the present invention. It can be seen that the fluctuation of the wind pressure level is decreasing after 3:00 after the start of the blast furnace slag blowing indicated by the arrow S. Also, the effect was a decrease of about 3% of the blowing pressure. Therefore, blast furnace slag also has the effect of melting and slagging the high melting point slag layer in front of the tuyere,
Since the composition is lower in basicity than converter slag, more slag must be blown in to obtain the same effect as converter slag.

However, since the blown blast furnace slag does not remain in the furnace core, long-term stable blow is possible. Therefore, it is effective to use the converter slag together with the converter slag when a sufficient amount of low phosphorus converter slag cannot be secured.

FIGS. 2A and 2B show the pulverized coal and dolomite injection shown in FIG. 1A (prior art) and FIG.
After the pulverized coal and converter slag blowing (the present invention) were continued for one week each, the coke and slag in the furnace were sampled during scheduled outage, and the results of investigation of the slag composition are shown.

The Mg in the non-dimensional radius in the furnace shown in FIG.
From the distribution of the amount of O, the prior art (△) shows the present invention example (□
Mark) and the base operation without pulverized coal operation (marked with で), especially in the core part (around the dimensionless radius 0.5 in the furnace)
It can be seen that the amount of MgO in the slag has increased sharply, and that MgO, the main component of dolomite, has accumulated in the back of the tuyere unmelted.

As described above, when a medium solvent such as dolomite having a high melting point is blown from the tuyere, it is clear that melting and slagging do not proceed and accumulate in the furnace core. This core accumulation results in poor air permeability of the core when the mixing and blowing of pulverized coal and flux is continued for a long time. Therefore, operations such as melting the unslag slag of the furnace core, for example,
An action such as temporarily stopping the blowing of pulverized coal or a solvent is required, which results in an increase in wind pressure again.

Also, in the case of the CaO distribution at the non-dimensional radius in the furnace shown in FIG. 2B, in the present invention example using the converter slag (indicated by □), the base without pulverized coal operation is used. Compared to the operation (marked with 内), Ca
The amount of O does not change much, and C, the main component of converter slag,
It can be seen that aO is not accumulated deeper than the tuyere. As described above, when the converter slag is blown from the tuyere, melting and slagging progress rapidly, and assimilate with the slag derived from pulverized coal in front of the raceway, and it is apparent that the slag does not accumulate in the furnace core. .

As a result, even if the mixing and blowing of the pulverized coal and the flux are continued for a long period of time, poor air permeability of the core does not occur. For this reason, such operations as dissolving the unslag flux in the furnace core, such as mixing and blowing of flux,
In other words, there is no need to temporarily stop the mixing of the flux, and stable operation with a reduced wind pressure level can be continued.

Further, it is possible to reduce the blowing power by reducing the blowing pressure, to suppress the peripheral flow of Bosch gas (furnace gas), and to increase the amount of pulverized coal injected by using the reduced blowing pressure. Then, by replacing the auxiliary raw material inserted from the furnace top with slag, which is a recycled raw material from the tuyere, the auxiliary raw material cost can be reduced.

Further, by suppressing the insertion of limestone and dolomite from the furnace top, the heat energy consumed when these decompose and generate CO ₂ can be reduced.

[0047]

[Table 1]

[0048]

As described above, the method for operating a blast furnace according to the present invention can provide a high basicity medium even in an operation in which the amount of pulverized coal injected is extremely large and the amount of the high basicity medium solvent blown is increased accordingly. The melting and slagging of the solvent is delayed and does not remain in the core unmelted. In addition, when the high basicity solvent decomposes, it takes away the heat of decomposition, and this heat compensation does not cause adverse effects such as an increase in the fuel ratio or gas recovery cost. It is possible to improve the air permeability when pulverized coal is blown and to enable long-time operation of pulverized coal blown. In addition, the effect is industrially significant in that the effect can be achieved without greatly changing the conventional method.

[Brief description of the drawings]

FIG. 1 shows the time-dependent change of the blowing pressure in a blast furnace when pulverized coal and various basic slags are blown simultaneously.
1A is an explanatory diagram of a conventional technique, and FIGS. 1B and 1C are explanatory diagrams of an example of the present invention.

FIG. 2 shows the slag composition in the furnace of the prior art and the example of the present invention after the simultaneous injection of pulverized coal and various basic slags for one week, FIG. 2 (a) shows MgO, FIG. ) Is Ca
It is explanatory drawing regarding O.

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 when only pulverized coal is blown according to a conventional method.

FIG. 5 (a) shows the relationship between the amount of pulverized coal injected and the blast furnace porosity, and FIG. 5 (b) is an explanatory diagram showing the relationship between the high melting point slag wall thickness and the blast furnace porosity.

[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

Claims (3)

[Claims] When a pulverized coal is blown together with a blowing gas from a blast furnace tuyere, a basic slag is blown together with the pulverized coal, the slag is assimilated with the pulverized coal ash, and a high melting point formed in the back of the raceway by the pulverized coal ash. In the blast furnace operating method for suppressing the growth of a slag layer (commonly known as a bird's nest) and improving the air permeability in the furnace when pulverized coal is injected, the blown slag may be a premelt slag having a melting point equal to or lower than a raceway temperature. The basicity (the amount of basic component / the amount of acidic component) when the slag in the blown slag and the ash in the pulverized coal are mixed is 0.5% or less. The method of operating a powder-blasting blast furnace, comprising adjusting the amount of the blowing slag so as to be 1.3. 2. The blowing amount of the pulverized coal is 100 kg.
2. The method for operating a powder-blasted blast furnace according to claim 1, wherein the blast furnace is not less than / t-pig iron. 3. A converter slag and / or a blast furnace slag as the premelt slag.
2. The method for operating a powder-blasted blast furnace according to item 1.