JP2011190471A - Method for operating blast furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a blast furnace, in which a good operational condition can be obtained for fine powdery coal injecting operation under condition of extremely low molten pig iron tapping-off ratio. <P>SOLUTION: In the case of performing the operation with the extremely low molten pig iron tapping-off ratio, such as ≤1.6t-pig/d/m<SP>3</SP>one day molten pig iron tapping-off ratio, in order to keep the conductivity of the fine powdery coal blown as auxiliary reducing material from a tuyere, the oxygen-enriched ratio during the blasting is set to be 0.4-0.8 and the fine powdery coal-injection is performed at fine powdery coal ratio of 100-130 kg/t-pig, thereby the combustibility of the fine powdery coal under condition of shrinking a race-way as the blowing air flow rate is reduced, can be improved and the deterioration of a furnace-core gas permeability and a molten material permeability, is prevented and thus, the stable operation can be kept and the producing cost of the pig iron can be decreased by changing the coke into the inexpensive fine powdery coal. Further, the combustibility of the fine powdery coal is improved, and because of generating into the space of the permeability, the raw fuel having smaller granular diameter and lower strength can be used at more than the conventional operation, and such operation can be contributed to the rationalization of the blast furnace operation. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a blast furnace operation method performed by injecting pulverized coal as an auxiliary reducing material from a tuyere, and in particular, the operation is performed at an extremely low output ratio where a sunrise sunrise ratio is 1.6 t-pig / d / m ³ or less. It is suitable for the case.

  The pulverized coal injection into the blast furnace is carried out in many blast furnaces because of the great cost merit due to the price difference with the coke, and greatly contributes to the economic improvement of blast furnace operation. In recent years, the price of coking coal has been increasing rapidly, and this trend is expected to remain unchanged over the long term, and the importance of injecting pulverized coal that is cheaper than coke is increasing. . Against this background, active technological development has been carried out on the injection of a large amount of pulverized coal. For example, Patent Document 1 below discloses a technique for stably continuing a large amount of pulverized coal injection by setting operation conditions so that an index of pulverized coal combustion rate satisfies a certain range. In this prior document, an oxygen excess coefficient indicating the excess or deficiency of oxygen with respect to the theoretical oxygen amount necessary for combustion of pulverized coal is used as one of the operating conditions for determining the pulverized coal combustion rate.

On the other hand, the output of the blast furnace is greatly influenced by the economy and the economic situation, and when the pig iron production is reduced, the flow rate of air blown from the blower tuyeres at the bottom of the blast furnace is reduced. In order to continue stable operation at a low output ratio, it is important to ensure core core permeability and liquid permeability and to prevent core deactivation. Specific means include reducing the amount of powder brought into the furnace by reducing the amount of pulverized coal injection (all coke operation), maintaining the amount of gas passing through the furnace by increasing the reducing material ratio (operation with a high reducing material ratio), and burning the tuyere Measures have been taken, such as securing a raceway as a space. To secure the raceway, for example, increase the air flow relatively by reducing the oxygen enrichment rate, adjust the furnace pressure to increase the raceway by reducing the furnace top pressure, or reduce the tuyere diameter. Measures are taken to increase the air blowing speed. In particular, when operating at an extremely low output ratio where the ratio of sunrise per day is 1.6 t-pig / d / m ³ or less, it is common to operate at a high reducing material ratio and all coke.

Japanese Patent No. 3562506

In the situation where coke prices are soaring as in recent years, all-coke operations like the conventional one cause a significant cost deterioration, so pulverized coal injection continues even under extremely low output ratios, resulting in cost deterioration. It is required to control. However, the conventional research on pulverized coal injection mainly focuses on high-volume injection assuming a high output ratio. The low output ratio, that is, the flammability of pulverized coal when the raceway is reduced. However, it was necessary to search for good operating conditions in the operation of pulverized coal injection under extremely low output ratio.
The present invention has been made paying attention to the above problems, and an object thereof is to provide a blast furnace operating method that provides favorable operating conditions in a pulverized coal blowing operation under an extremely low output ratio. To do.

In order to solve the above-mentioned problems, the blast furnace operating method of the present invention is a blast furnace operating method in which operation at an extremely low output ratio with a sunrise sunrise ratio of 1.6 t-pig / d / m ³ or less, In order to maintain the combustibility of the pulverized coal injected as an auxiliary reducing material from the mouth, the oxygen enrichment rate during blowing is set to 0.4 to 0.8, and the pulverized coal injection is performed at a pulverized coal ratio of 100 to 130 kg / t-pig. It is characterized by doing.
pig is an abbreviation for pig iron and t-pig means per ton of pig iron. The output ratio is a value obtained by dividing the amount of dredging per day by the blast furnace volume. The pulverized coal ratio indicates the amount of pulverized coal per 1 ton of hot metal.

Thus, according to the blast furnace operating method of the present invention, when operating at an extremely low output ratio where the sunrise ratio is 1.6 t-pig / d / m ³ or less, it is blown from the tuyere as an auxiliary reducing material. In order to maintain the combustibility of the pulverized coal, the oxygen enrichment during blowing is set to 0.4 to 0.8, and the pulverized coal is injected at a pulverized coal ratio of 100 to 130 kg / t-pig. The pulverized coal injection operation under the ratio is good.

It is a longitudinal cross-sectional view which shows one Embodiment of the blast furnace to which the blast furnace operating method of this invention was applied. It is explanatory drawing of a combustion state when pulverized coal is blown in from the lance of FIG. It is explanatory drawing which shows the relationship between a raceway depth and a substitution rate. It is explanatory drawing which shows the relationship between a substitution rate and a reducing material ratio. It is explanatory drawing which shows the relationship between a substitution rate and a furnace condition index.

Next, an embodiment of the blast furnace operating method of the present invention will be described with reference to the drawings.
FIG. 1 is an overall view of a blast furnace to which the blast furnace operating method of the present embodiment is applied. As shown in the figure, a blast pipe 2 for blowing hot air is connected to the tuyere 3 of the blast furnace 1, and a lance 4 is installed through the blast pipe 2. A combustion space called a raceway 5 exists in the coke deposit layer in the hot air blowing direction ahead of the tuyere 3, and coke combustion and gasification (reduction of iron ore, that is, ironmaking) are mainly performed in this combustion space. .

FIG. 2 shows the combustion state when pulverized coal 6 is blown from the lance 4. The pulverized coal 6 that passes through the tuyere 3 from the lance 4 and is blown into the raceway 5, together with the coke 7, combusts its volatile matter and fixed carbon, and remains unburned, generally called char. The aggregate of ash is discharged as unburned char 8 from the raceway 5.
When the flow rate of air blown from the tuyere 3 is decreased in order to reduce the output ratio, the blowing energy of hot air blown from the tuyere is reduced, and the raceway 5 formed at the tip of the tuyere is reduced. For example, if the broken line in FIG. 2 is the normal raceway 5, the raceway 5 when the output ratio is reduced appears as a solid line. The reduction of the raceway 5 is due to the inferior heat transfer to the core due to a decrease in the distance of hot air entering the furnace, the increase in the unburned powder rate due to the shortened residence time of the pulverized coal 6, and the core inactivity in a double sense. It becomes the cause. In order to secure the depth of the raceway 5, it is only necessary to decrease the enriched oxygen amount during the blowing and increase the blowing flow rate. However, the oxygen enrichment rate decreases due to the replacement of the enriched oxygen with the blowing flow rate. As the flow rate increases, the amount of oxygen enrichment becomes insufficient, and as a result, the combustibility of the pulverized coal 6 may be deteriorated.

Table 1 below shows examples and comparative examples of the present invention when the tapping ratio, oxygen enrichment ratio, and pulverized coal ratio are variously changed. This blast furnace has a content seat of 5000 m ³ , has 40 tuyere, and each tuyere has two pulverized coal injection lances. Examples 1 and 2 in the table were subjected to oxygen-enriched ventilation with an oxygen enrichment rate of 0.4 or more in the operation with an extremely low output ratio, and Comparative Example 1 cut the enriched oxygen in the operation with an extremely low output ratio. Comparative Examples 2 and 3 are high output ratio operations.

  In the table, the air volume ratio is the air volume divided by the blast furnace volume. The oxygen enrichment rate indicates the oxygen enrichment rate with respect to the blast. The oxygen excess rate is a value obtained by dividing the amount of oxygen in the blast by the amount of oxygen necessary for complete combustion of coke and pulverized coal. The reducing material ratio indicates the amount of coke per 1 ton of hot metal. Further, the substitution rate is a value obtained by dividing the amount of reduction of the coke ratio (reducing material ratio) by pulverized coal injection by the amount of pulverized coal injection, and is an index of pulverized coal combustibility. Further, the furnace condition index is an index indicating fluctuations in the ventilation of the furnace and abnormalities in the fall of the charge, and here represents the number of abnormal ventilations and drops per 5 days.

  FIG. 3 shows the relationship between the raceway depth and the replacement rate in Table 1. In Comparative Examples 2 and 3, which are high output ratio operations, the raceway depth was around 1.4 m and the replacement rate was around 0.80. However, the operation shifted to extremely low output ratio operation, and the oxygen enrichment rate was zero. In Comparative Example 1, the raceway depth is 1.23 m and the replacement rate is 0.54. On the other hand, in Examples 1 and 2 in which enriched oxygen blowing was performed at an oxygen enrichment rate of 0.4 to 0.8 with an extremely low output ratio substantially similar to that of Comparative Example 1, the raceway was 1.20 to 20. Although 1.23 m and the comparative examples 2 and 3 are significantly reduced, the substitution rate is 0.73, which is only a small decrease compared to the comparative examples 2 and 3 at a high yield ratio. .

  4 shows the relationship between the replacement rate and the reducing material ratio in Table 1, and FIG. 5 shows the relationship between the replacement rate and the furnace condition index. In Comparative Example 1 in which the enriched oxygen was cut under extremely low output ratio operation, the substitution rate decreased, and it was difficult to perform stable operation due to a significant increase in the reducing material ratio and frequent fluctuations in the ventilation of the furnace. On the other hand, in Examples 1 and 2, the substitution rate is improved by the oxygen enrichment blown with an oxygen enrichment rate of 0.4 to 0.8, and the ratio of the reducing material and the ventilation stability from the operation with a high output ratio are deteriorated. I was able to suppress it. Note that the upper limit of the oxygen enrichment rate is desirably 0.8 or less due to the raceway reduction accompanying the above-described delivery flow rate replacement.

As described above, in the operation method of the blast furnace according to the present embodiment, when the operation is performed at an extremely low output ratio where the ratio of sunrise per day is 1.6 t-pig / d / m ³ or less, it is injected from the tuyere as an auxiliary reducing material. In order to maintain the combustibility of pulverized coal, the oxygen enrichment rate during blowing is set to 0.4 to 0.8 and pulverized coal is injected at a pulverized coal ratio of 100 to 130 kg / t-pig, thereby reducing the flow rate of the blast. Along with this, the flammability of pulverized coal under conditions where the raceway is shrinking can be improved, the deterioration of the core breathability and liquid permeability due to unburned char can be prevented, and stable operation can be continued. Can do. As a result, pig iron production costs can be reduced by substituting coke with cheap pulverized coal. In addition, the flammability of pulverized coal is improved, and there is a margin for breathability, so that more raw fuel with a smaller particle size and lower strength can be used than before, which contributes to rationalization of blast furnace operation. it can.

  1 is a blast furnace, 2 is a blow pipe, 3 is a tuyere, 4 is a lance, 5 is a raceway, 6 is pulverized coal, 7 is coke, and 8 is char

Claims (1)

It is a blast furnace operation method that operates at an extremely low output ratio of 1 t / pig / d / m ³ or less per day, and maintains the combustibility of pulverized coal injected as an auxiliary reducing material from the tuyere Therefore, a blast furnace operating method is characterized in that the oxygen enrichment during blowing is 0.4 to 0.8 and pulverized coal is injected at a pulverized coal ratio of 100 to 130 kg / t-pig.

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