JP3450168B2 - Blast furnace pulverized coal injection operation method - Google Patents

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 furnace pressure that rises during pulverized coal injection is reduced to improve air permeability. Is.

[0002]

2. Description of the Related Art In recent years, the operation of a blast furnace is a conventional all coke operation (all reducing materials are inserted as coke from the top of the furnace for the purpose of drastically reducing fuel costs, reducing the burden on the coke oven, and extending the life of the furnace. Method)
The amount of coke charged from the top of the furnace is being reduced and a large amount of auxiliary fuel such as pulverized coal, which is inexpensive, is blown from the tuyere of the blast furnace as a substitute for coke, and the operation is being shifted to.

The pulverized coal blowing operation is a technique established as one of the powder blowing operation techniques for the blast furnace, and is 200 k
Stable operation began to be carried out when the amount of pulverized coal injected was g / t-pig iron or more. However, when the amount of pulverized coal blown in is increased in this way, a phenomenon called a shell (or bird's nest) occurs around the raceway, and this shell grows and the gas flow in the lower part of the blast furnace is There is a problem that it often happens when it is mobilized.

First, the mechanism generated by the shell will be described. In the pulverized coal blowing operation, as shown in FIG. 4, the pulverized coal 4 is fed from the tuyere 7 provided on the blast furnace furnace wall 9 to the blast gas 5
At the same time, a large amount is blown into the coke layer 8 through the lance 1. At the time of blowing the pulverized coal, a shell generated by blowing the pulverized coal 4 around (race) the raceway 2 (the combustion space where the coke is thin and exists inside the furnace at the tuyere tip).
(High melting point slag wall) 3 is generated.

The shell 3 is derived from the ash 11 of the pulverized coal produced by burning at high speed in the raceway 2. That is, the pulverized coal 4 blown into the blast furnace contains about 8 to 10% of ash content, and the ash content is SiO 2.
₂ 50-60%, Al ₂ O ₃ 20-30%, other Fe
It is composed 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 the combustion of the pulverized coal is generated.
The acid component slag mainly composed of iO ₂ and Al ₂ O ₃ increases, and the viscosity and melting point of the slag generated around the raceway (in the back of the raceway) increase. Therefore, the slag generated around the raceway is a dripping slag 6 derived from iron ore mainly composed of sinter that descends from the upper part of the blast furnace.
As a result, coke generated in the raceway and ash of pulverized coal generated in the raceway will be delayed appropriately in the raceway. As a result, around the raceway, the slag whose slag has been delayed is thickly accumulated and a thick shell 3 is formed.

When the amount of pulverized coal blown in is increased to increase the pulverized coal ratio, the amount of coke charged to iron ore decreases, and the coke in the furnace core tends to have a smaller particle size or to be easily pulverized. , The porosity of the furnace core decreases. Therefore, the powder blown from the tuyere easily accumulates on the surface of the furnace core. Furthermore, as described above, due to the increase in the amount of pulverized coal blown, strong acidic ash content (ash content) is likely to accumulate in the depths of the raceway or the shell 3, so both of them are affected at the same time and the shell is synergistically. 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 toward the upper part of the furnace, and the generated high-temperature gas flows along the blast furnace wall 9 Flow (flow around the gas flow).
Then, the peripheral flow of the gas flow causes the temperature rise and the reduction of the ore to be stagnant and hinders the molten dropping. This tendency is promoted not only by the thickening of the ore in the pulverized coal blowing blast furnace operation but also by the decrease in the ascending gas flow accompanying the decrease in the coke layer thickness. Further, the flow of gas around the periphery causes an increase in the fuel ratio (an increase in fuel cost) due to an increase in heat loss from the furnace wall 9. In addition, the flow of the hot gas produced along the furnace wall also leads 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, raises the blast pressure and increases the pressure fluctuation, so that a large amount of pulverized coal is blown in and a large amount of pulverized coal is blown in itself. It also makes it difficult to continue for a long time. Therefore, shell formation by blowing pulverized coal can be a serious problem that causes operational problems in the blast furnace and hinders productivity.

In order to solve such a problem, conventionally, together with pulverized coal, a high basicity medium solvent is blown from the tuyere to raise the basicity of the high melting point slag existing around the raceway to lower the viscosity. (Increases fluidity) and assimilate it with the dropping slag that descends from the upper part of the blast furnace to promote the proper slag formation of the ash content of the pulverized coal within the raceway, so that when pulverized coal is injected into the front tuyere raceway part Various techniques for improving breathability have been proposed.

For example, in Japanese Patent Laid-Open No. 3-291313, the high basicity solvent is CaO, MgO, SiO _{2 or the like.}
The use of a system flux is disclosed. Further, in Japanese Examined Patent Publication No. 6-89382, a basic fine powder medium solvent such as fine dolomite, serpentine, olivine, and limestone is blown at the same time as the fine coal, and the blowing amount is determined by mixing the medium solvent and the ash content in the fine coal. The ash content of pulverized coal and dolomite are assimilated in the raceway so that the basicity (basic component amount / acidic component amount) of 0.5 to 1.3 is formed to form a low-viscosity slag. It is disclosed that the high melting point slag wall (bird's nest) is thinned.

According to these techniques, as shown in FIG. 3 having the same structure as FIG. 4, the high basicity solvent 10 is blown into the coke layer 8 at the same time as the pulverized coal 4 and the blown gas 5 through the lance 1. As a result, the ash content 11 of the pulverized coal and the high basicity medium solvent 10 are assimilated inside the raceway 2 to form a low-viscosity slag, which easily becomes assimilated with the dripping slag descending from the upper part of the blast furnace. It becomes a slag drop and drops inside the blast furnace. As a result, generation of the high melting point slag layer 3 is suppressed, the thickness of the high melting point slag layer 3 is reduced, and a stable raceway shape is maintained, as compared with the case of only blowing pulverized coal as shown in FIG. It is said that it is possible to improve the breathability.

In addition to blowing these high basicity solvent, in Japanese Patent Laid-Open No. 9-176706, the amount of pulverized coal blown to all tuyere is kept constant, and then the pulverized coal is blown at each tuyere. It is disclosed that the generation of the shell is suppressed by controlling the amount to be increased or decreased.

[0013]

However, in the prior art in which the high basicity solvent is blown from the tuyere together with the pulverized coal, the ash content of the pulverized coal and the high basicity solvent are assimilated inside the raceway. The mechanism has not been sufficiently clarified, and as a result, in the operation in which the amount of pulverized coal blown into the blast furnace is extremely large, the amount of the high basicity solvent to be blown is increased correspondingly. As a result, there is a drawback that the blown high basicity medium solvent itself is delayed in melting and slagging inside the tuyere, and is not sufficiently assimilated and melted inside the raceway.

In particular, dolomite, serpentine, olivine,
High basicity medium solvents for ores such as limestone have a high melting point of themselves, at a temperature of about 2000 ° C, and inside the raceway for a limited time for assimilation with ash of pulverized coal particles. It does not melt, and as a result remains in the solid state, does not assimilate with the pulverized coal particles, and easily reaches the back of the raceway.

If the high basicity medium solvent reaches the inner part of the raceway without being melted, it will be taken into the coke bed (furnace core) at the inner part of the temperature far below the flame temperature. It remains molten in the core. Therefore, in the worst case, the high basicity solvent added to improve the air permeability rather deteriorates the air permeability. Further, this also leads to increasing the amount of the high basicity medium solvent blown in more than the amount required for assimilation with the ash content of the pulverized coal particles.

Further, when a highly basic solvent such as limestone accompanied by an endothermic reaction is used, limestone deprives heat of decomposition when decomposing in front of the tuyere, and extra coke is required for this heat compensation. The ratio increases. Along with this, more gas is generated, and the cost of gas recovery increases.

Further, the control of the amount of pulverized coal blown in each tuyere as in Japanese Patent Laid-Open No. 9-176706 is merely to temporarily control (increase / decrease) the generation rate of the shell. To prevent the deterioration of air permeability at the bottom of the blast furnace due to
Not considered at all.

Therefore, in these prior arts, when a high basicity solvent is used, it is unavoidable that a new harmful effect may be caused, and even when controlling the blowing amount of pulverized coal at each tuyere, it is basically necessary. Therefore, the shell generation cannot be suppressed. Therefore, at present, there is a limit to the amount of pulverized coal blown, and even with the current amount of pulverized coal blown, the complicated control of other blast furnace operating conditions improves the air permeability in the blast furnace, The reality is that pulverized coal injection is maintained.

The present invention has been made in view of these problems of the prior art.
In a blast furnace operation method that blows pulverized coal, even if the amount of pulverized coal blown is extremely large, it is possible to suppress shell formation and improve the air permeability when blowing pulverized coal in the front tuyere raceway section. The purpose is to provide a method.

[0020]

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention sequentially charges iron-making raw material powder such as ore into the blast furnace from the furnace top, and at the same time, blows 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 Melting point of ash T _HT (℃)
The maximum reached temperature T _max is controlled so that the ratio T _max / T _HT is in the range of 1.0 to 1.5, and the growth of the high melting point slag layer generated inside the raceway is suppressed, and the furnace during pulverized coal injection is controlled. The main point is to improve the internal air permeability.

The present inventors have examined the relationship between the temperature distribution in the raceway at the time when a high amount of pulverized coal was blown, the combustion ash of pulverized coal and the state of ash melting, and the formation of shells. The temperature distribution inside the raceway when the amount of pulverized coal injected was high.The maximum temperature reached in the raceway increased as the pulverized coal rapidly burned compared to during all coke operation, while the temperature inside the raceway On the contrary, it decreases. Figure 2 shows the relationship between the distance from the tuyere tip inside the raceway and the temperature distribution inside the raceway. As is clear from Fig. 2, both at the time of all coke operation B and at the time of blowing 200 kg / t of pulverized coal A at a distance of 100 to 300 mm from the tuyere tip,
The temperature inside the raceway is the highest (highest temperature reached).
However, in the case of high pulverized coal injection A, the highest temperature reached itself became higher, and the highest temperature reached the tip of the tuyere. Moreover, the temperature at the back of the raceway is lower in case A when blowing high pulverized coal.

Therefore, according to the temperature distribution in the raceway when the amount of high pulverized coal is blown, the ash of the pulverized coal which is blown from the tuyere tip and burned rapidly is melted at an early stage and in a large amount. Become. On the other hand, since the temperature inside the raceway is decreasing, the ash of the pulverized coal, which is melted in a large amount, easily aggregates in the coke gaps and the surface layer inside the raceway, and the coke powder is also easily incorporated due to the crosslinking effect. Therefore, the thickness of the generation shell is increased.

When blowing high pulverized coal, the ash of pulverized coal which is blown from the tuyere tip and rapidly burned is more easily melted than the ash of coke in the raceway. The reason for this is that the coke charged from the top of the blast furnace and supplied into the raceway is
Since gasification of SiO ₂ in the ash occurs in the blast furnace, Al ₂ O ₃ / SiO _{2 can} be used in comparison with pulverized coal blown from tuyere.
This is because the melting point of coke ash is higher than that of pulverized coal ash. Therefore, ash of pulverized coal preferentially melts over ash of coke within the raceway.

From the relationship between the temperature distribution in the raceway when the amount of high pulverized coal is blown, the combustion ash of pulverized coal and the ash melting state, and the formation of the shell, the race during high pulverized coal injection It can be seen that in order to suppress the formation of shells at the back of the way, it is effective to lower the temperature inside the raceway, in particular, the maximum reached temperature, to lower the melting amount of ash of pulverized coal.

Therefore, in the present invention, the operating temperature and the pulverized coal conditions are controlled so that the temperature inside the raceway, particularly the maximum reaching temperature, is controlled, and the maximum reaching temperature T _max (° C) of the gas inside the raceway is controlled. And melting point of ash of pulverized coal T _HT (
C) ratio T _max / T _HT is controlled to be in the range of 1.0 to 1.5. The operating conditions and pulverized coal conditions to be controlled are preferably methods such as increasing or decreasing the enriched oxygen amount or adjusting the composition and particle size of the pulverized coal to make it more difficult to burn.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the melting point T _HT (° C.) of the ash of pulverized coal is determined by the properties and composition of the pulverized coal blown from the tuyere, and the pulverized coal used is combusted and ashed. It can be 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. Therefore, with these means, it is quite difficult to perform direct measurement with high local accuracy. Therefore, since it is difficult to actually measure during operation of the blast furnace by these ordinary temperature measuring means, various methods of mass balance and heat balance in the blast furnace or simulation based on operational experience values, known methods using numerical analysis (For example, “Iron and Steel”, Vol 78, 1992, pages 1230 to 1237).
Alternatively, it is preferable to actually measure with an optical fiber.
This optical fiber is consumable, and even if the tip melts at a high temperature in the raceway, a long optical fiber is sent from outside the blast furnace one after another through the water-cooled probe provided on the blast furnace furnace wall, and the instantaneous It is possible to measure the temperature of the target site by receiving such an optical signal. Therefore, the relationship between the distance from the tuyere tip in the raceway and the temperature distribution in the raceway as shown in FIG. 2 can be obtained using this optical fiber. Further, the value of T _max obtained by these calculation formulas and the optical fiber may be verified by the conventional thermometer.

Further, as another embodiment of the present invention, in addition to controlling the maximum temperature of gas in the raceway of the present invention, when blowing pulverized coal with blast gas from the tuyere of the blast furnace,
A method of blowing basic slag together with the pulverized coal, assimilating the slag with the pulverized coal ash content, and suppressing the growth of the shell generated in the depth of the raceway by the pulverized coal ash content may be used together. As the basic slag to be blown, for example, Japanese Patent Laid-Open No.
CaO-based, Mg as described in 3-291313
O-based and SiO-based fluxes, and fine dolomite, serpentine, as described in JP-B-6-89382.
Although olivine and limestone may be used, they have a melting point below the raceway temperature and a phosphorus content of 1.0, as described in Japanese Patent Application No. 9-4745 previously filed by the present applicant. % Or less of the basic premelt slag is preferably used. In addition, when the basic premelt slag is blown, the basicity (the amount of basic component / the amount of acidic component) when mixing the blown slag and the ash in the pulverized coal is 0.5 to 1.
It is preferable to adjust the amount of the blown-in slag so that it becomes 3.

The premelt slag means slag that has already been melted, and corresponds to, for example, converter slag and blast furnace slag. These slags are generated during the ironmaking and steelmaking processes, and have already been melted once in this process, and are more soluble and slag than the undissolved raw ores such as dolomite and CaO-based flux. Very good chemability. Further, converter slag, blast furnace slag, and the like have high basicity, and are suitable as the blown-in slag.
Thus, by using a high basicity pre-melt slag having a melting point below the raceway temperature, the slag is sufficiently molten or semi-molten inside the raceway,
Assimilate with ash of pulverized coal particles. When used in combination with the method of the present invention, a synergistic effect of exhibiting an effect of improving air permeability even when the amount of blowing is small is exhibited.

[0029]

EXAMPLES Next, examples of the present invention will be described. Blow pressure P _B using a coke filling type test combustion furnace simulating a blast furnace
Maximum reaching temperature T of gas in raceway that affects (kPa)
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"
(Vol81, 1995, No. 12, pages 1114 to 1119) is also disclosed as a means for investigating combustion behavior and gas flow change in a raceway. More specifically, as shown in Fig. 5, it is a fan-shaped furnace with a height of 2.5 m, a depth of 1.9 m, and an internal volume of 4.2 m ³ , and has one tuyere 13 with an inner diameter of 0.08 m, which is the same as the blast furnace. Hot air is blown into the furnace to burn the coke in the furnace. The hot air stove uses a heat exchange method by electric heating. This test combustion furnace 12 has a packed bed of river sand in the lower part of the furnace.
A rotary feeder equipped with 14 and equipped with this sand at the bottom of the furnace
It is cut out with a (not shown), and the coke 15 of the entire packed bed (existing on the packed bed 14 of the river sand), which is quantitatively charged by the level meter 17 from the coke hopper 16 at the top of the furnace, is lowered. There is. Therefore, this test combustion furnace 12
The structure is such that the raceway inside the blast furnace core and tuyeres can be renewed, that is, the mechanism that supplements the coke consumed by combustion with the upper coke can be simulated. Furthermore, the test combustion furnace was equipped with water-cooled sampling prog 18 at three levels from the tuyere facing side (the center of the tuyere, 0.3 m above the tuyere, and 0.6 m). The sample forming the raceway 22 can be collected. Further, a thermocouple 19 including an exhaust gas port 21 is installed on the furnace wall side.

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

FIG. 1 shows the blast pressure P _B (kPa) and T _max / T _HT.
Shows the relationship with. As is clear from Figure 1, T _max / T _HT
Is set in the range of 1.0 to 1.5, the blast pressure P _B (k
Pa) has fallen below 20 kPa. Then, under this blowing pressure, the gas flow in the coke-filled test combustion furnace was stabilized. The reason for this is that when T _max / T _HT is in the range of 1.0 to 1.5, the melting amount of ash of pulverized coal blown from the tuyere tip and burned in the raceway is significantly reduced, and This is because the amount of shell formed by coagulation with coke powder in the coke gap or coke surface layer was reduced, and the air permeability around the raceway was improved. Actually, after the combustion test, the test combustion furnace was disassembled and the raceway was investigated, and as a result, T _max / T
_{If HT} is outside the range of 1.0 to 1.5, it can be distinguished from other parts as white parts 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 as to be indistinguishable 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 when blowing pulverized coal in the front tuyere raceway portion even when the amount of pulverized coal blown is extremely large. In addition, stable operation of the blast furnace can be achieved. Moreover, this remarkable effect is industrially valuable in that it can be achieved without significantly changing the conventional method.

[Brief description of drawings]

FIG. 1 is 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 example of the present invention.
It is explanatory drawing which shows the relationship of _Tmax / _THT .

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

FIG. 3 is an explanatory diagram showing a raceway situation when pulverized coal and a high basicity medium solvent are simultaneously blown in by a conventional method.

FIG. 4 is an explanatory diagram showing a raceway situation when blowing pulverized coal by a conventional method.

FIG. 5 is a 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: Blow gas 6: Metal slag droplets 7: Tuyere 8: Coke layer 9: Blast furnace wall 10: Basic solvent 11: Fine coal ash

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akito Kasai 1 Kanazawa-machi, Kakogawa-shi, Hyogo Kobe Steel Works, Ltd. Kakogawa Works (56) Reference JP-A-58-171507 (JP, A) JP Heihei 9-263807 (JP, A) JP 5-179323 (JP, A) JP 4-21710 (JP, A) JP 3-291315 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21B 5/00 319

Claims (2)

(57) [Claims] 1. A method for operating a blast furnace in which pulverized coal is blown together with blast gas from a blast furnace tuyere, including controlling a gas temperature distribution in the raceway from the blast furnace tuyere to the interior of the raceway. Maximum temperature T _max
(° C) to melting point T _HT (° C) of ash of pulverized coal T _max / T _HT
To control the maximum temperature T _max so that it is in the range of 1.0 to 1.5, and suppress the growth of the high melting point slag layer formed in the interior of the raceway to improve the air permeability in the furnace during the injection of pulverized coal. Blast furnace pulverized coal blowing operation method characterized by. 2. The blast furnace pulverized coal blowing operation method according to claim 1, wherein the amount of the pulverized coal blown in is 200 kg / t-pig iron or more.