JP2006291301A - Method for operating blast furnace at initial firing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a blast furnace at the initial firing with which at the initial stage of firing in the blast furnace, the formation of a local portion with a high basicity at the upper part of the furnace (in the furnace) caused by lime stone as auxiliary raw material charged before firing thereof, is prevented and the good gas permeability is kept by restraining the consumption of the auxiliary raw material. <P>SOLUTION: In the method for operating the blast furnace at the initial firing, with which the firing is performed under state of filling up cross tie and coke in order and alternately, filling up sintered ore and the coke on the above layer, particularly, lime stone is mixed in the coke alternately charged with the sintered ore; as the coke, the coke containing ≤11.0 mass% ash is used, and the basicity of a slag at the lower part of the blast furnace, is kept to 1.2-0.9. As the other way, the coke containing ≤3.2 mass% alumina, is used and the alumina in the slag at the lower part of the blast furnace is kept to ≤16 mass%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for maintaining good air permeability in a furnace in a blast furnace operation.

When firing a blast furnace, as described in, for example, Patent Document 1, in order to heat and dissolve the sintered ore initially charged, first, sleepers, coke, auxiliary materials (limestone, ballast, silica stone) Etc.), and then fired with the sinter and coke alternately charged.
At the time of this firing, the amount of coke charged is very large, so the slag collected at the bottom of the blast furnace has a low basicity and a high alumina content. However, the air permeability sometimes deteriorated at the beginning of the burning operation.

As a countermeasure, in order to lower the melting point of the slag and improve the viscosity, auxiliary materials such as limestone, silica, and ballast are mixed with the sintered ore and charged in large quantities.
However, after firing, the temperature of the sintered ore gradually increases in the middle of descending the furnace, and finally melts to form a melt. The melting point of the limestone is lowered by this melt and the limestone is also melted, thereby causing problems such as locally forming an enlarged portion of the cohesive zone and inducing deterioration of air permeability.
In addition, a large amount of secondary raw material leads to an increase in the amount of slag at the lower part of the furnace, so if this slag is not extracted accurately, the amount of output will be increased, causing the air permeability to deteriorate. This is an obstacle.
Japanese Examined Patent Publication No. 61-6122

  The present invention prevents the formation of local high basicity sites in the upper part of the furnace (inside the furnace) caused by limestone, which is an auxiliary material to be charged before the blast furnace, in the initial stage of the blast furnace firing operation, and the amount of the auxiliary material used It is intended to provide a blast furnace firing operation method that suppresses the above and maintains good air permeability in the furnace.

The present invention has been made in order to advantageously solve the above-mentioned problems. The means (1) is to sequentially fill sleepers and coke in a blast furnace furnace, and alternately load sintered ore and coke thereon. In the blast furnace operation method of performing blasting in a charged state, limestone is mixed in coke charged and charged alternately with the sintered ore.
As for the mixing method of coke and limestone, in the case of a bell-type blast furnace, after charging coke on a large bell, charging limestone, temporarily storing and mixing on the large bell, It is preferable to mix coke and limestone in the furnace by charging into the furnace. In the case of a bell-less blast furnace, it is preferable that coke and limestone are stored in a mixed state in a charging hopper and then charged via a turning chute.

  Means (2) is characterized in that the basic slag at the lower part of the blast furnace is maintained at 1.2 to 0.9 by using the coke having a ash content of 11.0% by mass or less. It is the blast furnace burning operation method as described in said means (1).

  Means (3) is characterized in that the alumina in the slag at the lower part of the blast furnace furnace is maintained at 16% by mass or less by using, as the coke, containing alumina of 3.2% by mass or less. It is a blast furnace burning operation method described in 1) or (2).

According to the present invention, by mixing limestone in the coke alternately charged with sinter before blast furnace firing, local enlargement of the cohesive zone after firing due to limestone is prevented, It is possible to maintain good ventilation in the furnace.
In addition, since the contained ash in the coke to be charged is 11.0% by mass or less and the contained alumina is 3.2% by mass or less, it becomes possible to maintain the basicity of the slag to be produced and the amount of alumina appropriately. The amount of auxiliary materials such as limestone, silica, and ballast can be suppressed, and the air permeability can be improved by reducing the amount of slag in the lower part of the furnace.

The present inventors examined a method of charging limestone charged and charged before firing in order to adjust the basicity of the slag at the bottom of the furnace so as not to impair the air permeability in the furnace after the firing. .
Before firing, as shown in FIG. 3, coke C1 is charged onto sleepers M placed in a blast furnace BF, and further, coke C1, a mixture of coke C1 and auxiliary materials (silica stone + limestone + ballast) ) When F is charged to 50-60% in the blast furnace height direction, and then sinter ore and coke C2 are alternately charged into the stock line L in layers, the limestone is mixed into the sintered ore O. The difference in pressure loss, which is an index of air permeability after firing, when limestone was mixed with coke C2 and charged was investigated using a high-temperature property testing apparatus.

In the test using this high-temperature property testing apparatus, a mixture in which coke and limestone were mixed at a mass ratio of 1: 1 and a sintered ore were alternately filled with a height of 80 mm, and the mixture was sequentially heated by a heater from its surroundings. Increase the temperature. Then, during this temperature increase, reducing gas heated to 1500 ° C. is supplied from the lower part of the mixture, and the pressure difference is measured by measuring the pressure difference between the reducing gas above and below the mixture. The measurement result of this pressure loss is shown in FIG.
Further, a mixture of sintered ore and limestone and coke were alternately charged, and the pressure loss was measured in the same manner as described above. In this case, the ratio of the mixed mass of the sintered ore and limestone was 5: 1. The measurement result of this pressure loss is shown in FIG.

Comparing FIG. 1 and FIG. 2, it can be seen that the temperature range in the state where pressure loss is high (for example, 2000 mmAq or more) is narrower when limestone is mixed with coke than when mixed with sintered ore. .
In other words, in the blast furnace furnace, it is presumed that when limestone is mixed with coke, the thickness of the cohesive zone (ventilation resistance zone) is thinner and the air permeability is better than when it is mixed with sintered ore. The
This is because even if the coke descends in the furnace, the limestone does not melt and maintains a solid state in the cohesive zone, so the melting point of limestone is not lowered and is surrounded by coke. Therefore, it is presumed that the influence of the sintered ore can be eliminated even if it melts because there are few opportunities to contact the sintered ore.

  As limestone mixed with coke, those having an average particle size of about 17 mm (about 30 to 10 mm) are good in both mixing and melting. About 1 to 15% of the limestone is preferably mixed for each charge of coke. Moreover, it is preferable to charge another auxiliary | assistant raw material (silica stone, ballast) separately with a sintered ore like the past.

In addition, since the amount of coke charged (filled) at the time of blast furnace firing is very large, 30-50% by mass, reducing the ash content and alumina content of the coke can reduce the amount of auxiliary material charged. It becomes possible to reduce (about 20-30 mass% reduction), and it is effective in maintaining appropriately the basicity of the slag collected in the furnace lower part, and the amount of alumina.
It is preferable to use a coke having an ash content of 11.0% by mass or less to maintain the basicity of the slag accumulated in the lower part of the furnace at 1.2 to 0.9.
The slag basicity in the range of 1.2 to 0.9 is a range in which the slag extractability can be satisfactorily maintained even when the slag temperature varies slightly.

Further, by using a coke having an alumina content of 3.2% by mass or less, it is possible to easily maintain the alumina content of the slag at the lower part of the blast furnace furnace to 16% by mass or less.
In addition, the alumina amount of 16 mass% or less of slag is a range in which the extractability of slag can be maintained satisfactorily.
Furthermore, it is preferable to use a sintered ore containing 1.1% by mass or less of the sintered ore because the amount of the auxiliary raw material can be further reduced.

An example of the blast furnace operation of the present invention will be described with reference to FIG. This operation example is a case where it is applied to the burning operation of a super large bell type blast furnace of 5700 m ³ class and the height from the bottom of the furnace to the stock line L is 40 m.

When performing this firing, ash and coal with low Al ₂ O ₃ (alumina) are selected in advance and coke with an ash content of 10.7% by mass and an alumina content of 3.1% by mass in a coke oven. Manufactured and stocked.
Prior to firing after the blast furnace refurbishment, 1300 m ^{3 of} sleepers M were stacked from the bottom of the furnace to a height of 8.0 m, and then coke was filled to about 750 t to form a coke layer C 1, and limestone was further formed thereon. Coke C1 mixed with silica, ballast auxiliary materials was stacked up to 9.5 m in height using 1392 t (corresponding to C1 + F in FIG. 3). The mixing ratio of the auxiliary material to the coke C1 was 10.2% by mass, and the mixing ratio of the auxiliary material, limestone: silica stone: ballast, was 40:30:30.

O / C (O: sintered ore, C: coke) at the lowest position where the sintered ore O and the coke C2 mixed with limestone were alternately laminated on the mixture F of the auxiliary material and coke was 0.20. In the upper layer portion, the amount of sintered ore O was increased so that the O / C of the uppermost layer was 2.20.
Furthermore, the ratio of the limestone blended in the coke C2 gradually decreases from the position where the sinter O and the coke C2 are started to be layered to the middle part in the blast furnace height direction as the upper layer is increased. Lowermost layer: 5% by mass, uppermost layer: 0.5% by mass).
In addition, the ratio of the auxiliary raw materials composed of quartzite, ballast and the like to be mixed in the sinter O is sequentially increased from the position where the sinter O and the coke C2 are started to be layered to the top in the blast furnace height direction. Reduction (lowermost layer: 45% by mass, uppermost layer: 6% by mass).

The fire was put on in this state. And the first dredging after the burning (fired and the molten material first accumulated in the lower part of the furnace was discharged from the vent). At this time, the amount of slag was 101 t and the hot metal temperature was 1472 degrees. The slag was extracted with an extraction amount of 109 t, an estimated temperature of 1606 ° C., a basicity of 1.15, an alumina of 15.7% by mass, a melting point of 1379 ° C., and a viscosity of 6.4 poise (at 1450 ° C.). I was able to maintain sex.
In addition, the pressure loss resistance indicating the air permeability in the furnace from the first firing to the first dredging is 130 kPa or less, which is 34% compared with the conventional method (when sinter is mixed with limestone and the alumina of the sintered ore is high). It is estimated that the degree has been reduced.
The results of this example can be fully evaluated.

The figure which shows the relationship between the heating temperature and pressure loss by the method of this invention in a high-temperature property testing apparatus. The figure which shows the relationship between the heating temperature and pressure loss by the conventional method in a high temperature property testing apparatus. The conceptual diagram which shows the filling state of the furnace interior entry before blast furnace burning.

Explanation of symbols

BF: blast furnace M: sleepers C1, C2: coke F: mixture of coke and auxiliary materials O: sintered ore L: stock line

Claims (3)

  In the blast furnace burning operation method in which the blast furnace furnace is charged with sleepers and coke sequentially, and then the sinter and coke are alternately charged and charged in this state, the blast furnace is charged alternately with the sintered ore. Blast furnace operation method characterized by mixing limestone in coke.   The said coke is a thing containing 11.0 mass% or less as ash, and maintains the basicity of the slag of a blast furnace lower part to 1.2-0.9, It is characterized by the above-mentioned. Blast furnace operation method. The blast furnace according to claim 1 or 2, wherein the coke contains 3.2% by mass or less of alumina and the alumina in the slag at the lower part of the blast furnace is maintained at 16% by mass or less. How to fire.

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