JP2008111172A - Method for operating blast furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a blast furnace, which can inhibit the lowering of the temperature of a blast furnace gas, when operating the blast furnace while charging ferrocoke used as a raw material into the furnace from the top of the furnace. <P>SOLUTION: The method for operating the blast furnace includes controlling the temperature of the blast furnace gas when operating the blast furnace, which uses ferrocoke as a part of raw charging materials, by controlling one or more selected from the factors of: an oxygen-enriched rate in a blast blown from a tuyere; an amount of a reducing material blown from the tuyere; and an amount of enriched nitrogen in the blast blown from the tuyere. It is preferable to determine a relationship between the oxygen-enriched rate and the temperature of the blast furnace gas, so as to raise the temperature of the blast furnace gas by decreasing the oxygen-enriched rate using the relationship, determine a relationship between the amount of the blown reducing material and the temperature of the blast furnace gas, so as to increase the amount of the blown reducing material by using the relationship, and determine a relationship between the amount of the enriched nitrogen and the temperature of the blast furnace gas, so as to raise the temperature of the blast furnace gas by increasing the amount of the enriched nitrogen by using the relationship. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for operating a blast furnace using ferro-coke, which is produced by molding and dry distillation a mixture of coal and iron ore, as a blast furnace raw material.

  In order to lower the reducing material ratio of the blast furnace, a technique using the effect of lowering the temperature of the thermal preservation zone of the blast furnace using ferro-coke is effective (for example, see Patent Document 1). Ferro-coke produced by dry distillation of a molded product formed by mixing coal and iron ore promotes reduction of sintered ore due to its high reactivity and contains partially reduced iron ore. Therefore, the temperature of the heat storage zone of the blast furnace can be lowered, and the reducing material ratio can be lowered.

  However, on the other hand, the heat storage zone temperature affects not only the reducing material ratio but also the furnace top gas temperature. When the furnace top gas temperature decreases, problems such as the occurrence of condensation at the furnace top and defective dust discharge due to dust adhesion may occur.

  The mechanism by which the furnace top gas temperature decreases will be described with reference to FIGS.

  The temperature distribution in the height direction of the upper part of the blast furnace is described using a heat flow ratio (a heat capacity ratio between a charge and a gas) (for example, see Non-Patent Document 1). A typical example of the temperature distribution in the blast furnace is shown in FIG. FIG. 1 is a schematic diagram of a longitudinal section of a blast furnace 1 and a graph showing a temperature distribution in the section. Generally, the heat flow ratio is less than 1 in the upper part of the furnace, while the endothermic reaction proceeds in the lower part of the furnace. Becomes apparently larger and the heat flow ratio exceeds 1. A region 2 where the heat flow ratio is approximately 1 is formed between the two, and this corresponds to a heat storage zone.

  In the heat exchange between the furnace top charge (solid) and gas, the gas side inlet temperature corresponds to the temperature of the heat storage zone gas, the solid side inlet temperature corresponds to the charge temperature at the time of charging, and the heat flow ratio is the same. The temperature distribution in the height direction and the gas outlet temperature (corresponding to the furnace top gas temperature) vary depending on both values. FIG. 2 shows a calculation example of the solid temperature and the gas temperature when the heat preservation zone temperature and the heat flow ratio are changed. The height of the vertical axis indicates the height position in the blast furnace, and the height at the top of the furnace is assumed to be 0 m, and the height is indicated by the downward length from the top of the furnace. FIG. 2A shows a case where the heat storage zone temperature is 950 ° C. and the heat flow ratio is 0.864, and the furnace top gas temperature is 151 ° C. FIG. 2B shows a case where the heat storage zone temperature is 750 ° C. and the heat flow ratio is 0.864, and the furnace top gas temperature is 124 ° C. FIG. 2C shows a case where the heat storage zone temperature is 750 ° C. and the heat flow ratio is 0.915, and the furnace top gas temperature is 88 ° C. Even if the heat flow ratio is the same, if the heat preservation zone temperature (corresponding to the gas inlet temperature of the furnace top heat exchange) decreases, the furnace top gas temperature decreases, and if the heat flow ratio increases due to the reduction of the reducing material ratio, It can be seen that the furnace top temperature further decreases.

  FIG. 3 shows a case where the heat storage zone temperature is lowered by 100 ° C. from the base condition with a constant shaft efficiency derived from a heat / mass balance model (hereinafter referred to as “list model”) based on the list diagram. It is a graph which shows the prediction result of the change of furnace top gas temperature. In this calculation, the coke ratio decreased by 27 kg / t and the heat flow ratio increased by 0.015 due to a decrease in the temperature of the heat preservation zone, and as a result, the furnace top gas temperature decreased by 58 ° C. Of the furnace gas temperature decrease of 58 ° C, the decrease of 24 ° C is due to the increase in the heat flow ratio (calculated by increasing the heat flow ratio by 0.015 with a constant heat storage zone temperature). This is the effect of a decrease in storage zone temperature.

  FIG. 4 shows changes in the furnace top gas temperature from the base condition when the reduction of the reducing material ratio is aimed at by reducing the temperature of the heat preservation zone, increasing the shaft efficiency, and increasing the blowing temperature calculated by the list model. When aiming at low-reducing-material ratio operation by lowering the temperature of the heat preservation zone, the furnace top temperature is greatly reduced at the same heat flow ratio as compared with means such as increasing shaft efficiency and raising the blowing temperature. This is because the inlet temperature on the gas side in the gas-solid heat exchange in the upper part of the furnace is lowered in addition to the increase in the heat flow ratio as described above.

  On the other hand, when the furnace top gas temperature is lowered, deterioration of air permeability occurs due to a decrease in the amount of discharged dust, and therefore, a lower limit is set for the furnace top gas temperature in operation. In particular, if the furnace top gas temperature continues below 100 ° C, in addition to the reduction in dust emissions, the ash in the dust catcher used as the primary dust remover for the blast furnace exhaust gas is created by the atmosphere at the furnace port becoming a moisture coagulation atmosphere. In addition to the difficulty of taking out, the damage of the furnace refractory becomes a problem (for example, refer nonpatent literature 2).

As mentioned above, when aiming at low-reducing material ratio operation by lowering the temperature of the heat preservation zone, the amount of furnace top temperature decrease for the same heat flow ratio increase is larger than the operation for improving shaft efficiency, etc. It is necessary to pay attention to. Conventionally, the heat flow ratio is regarded as an index that roughly corresponds to the furnace top gas temperature, and operation design using the heat flow ratio as a parameter has been implemented. However, when the heat preservation zone temperature operation is performed, as shown in FIG. 4, the relationship between the two shifts from the normal relationship, so the conventional concept of the heat flow ratio is insufficient.
JP 2006-28594 A Akitoshi Shigemi "Seikan Handbook" Jinjinshokan 1979, p. 190 “Nippon Steel Pipe Technical Report” 95, 1982, p. 425

  In normal blast furnace operation, in order to prevent the occurrence of problems due to a decrease in the furnace top temperature, the operation is performed with the furnace top temperature maintained at 100 ° C. or higher, preferably 120 ° C. or higher. However, as described above, when ferro-coke is used as the blast furnace raw material and the operation is directed to low reducing material ratio operation by lowering the temperature of the heat preservation zone, the gas temperature at the top of the furnace is greatly reduced. There is a fear that the temperature cannot be maintained, which is a problem because it becomes a restriction of operation.

  Therefore, the object of the present invention is to solve such problems of the prior art, and to perform a blast furnace operation that can suppress a decrease in the gas temperature at the top of the furnace when performing blast furnace operation using ferro-coke as a raw material from the top of the furnace. It is to provide a method.

The features of the present invention for solving such problems are as follows.
(1) During blast furnace operation using ferro-coke as part of the charged raw material, the oxygen enrichment rate of the blowing air from the tuyere, the amount of reducing material blown from the tuyere, the nitrogen richness of the blowing air from the tuyere A method for operating a blast furnace, wherein the top gas temperature is controlled by controlling one or more selected from among the conversion amounts.
(2) The blast furnace according to (1), wherein a relationship between the oxygen enrichment rate and the furnace top gas temperature is obtained, and the oxygen enrichment rate is decreased using the relationship to raise the furnace top gas temperature. Operation method.
(3) The relationship between the reducing material blowing amount and the furnace top gas temperature is obtained, and the furnace top gas temperature is increased by increasing the reducing material blowing amount using the relationship (1) or The blast furnace operating method described in (2).
(4) The relationship between the nitrogen enrichment amount and the furnace top gas temperature is obtained, and the furnace top gas temperature is increased by increasing the nitrogen enrichment amount using the relationship (1) to (3 ) A blast furnace operating method described in any of the above.

  According to the present invention, even if ferrocoke is used as a blast furnace raw material and the heat preservation zone temperature is lowered, it is possible to prevent the furnace gas temperature of the blast furnace from being lowered, and an operation with a reduced reducing material ratio is performed. It can be performed stably.

  The present inventor clarified the influence of the heat preservation zone temperature and various operating conditions on the furnace top gas temperature by heat / material balance analysis using a list model, and clarified a method for managing these in conjunction with each other. Was completed.

  The base conditions for blast furnace operation were a reducing material ratio of 490 kg / t (pulverized coal ratio of 100 kg / t), a furnace top gas temperature of 140 ° C., and an oxygen enrichment ratio of 2.4 vol%. As an example of examination, the heat flow ratio and furnace when the oxygen enrichment rate is ± 2.4%, the pulverized coal ratio is changed by ± 50 kg / t, and the heat preservation zone temperature is changed by ± 50 ° C. and ± 100 ° C. The relationship of the top gas temperature was calculated. The results are shown in FIG. It has been clarified that the relationship between the heat flow ratio and the furnace top temperature is greatly different when the oxygen enrichment rate and the amount of pulverized coal injection are changed and when the temperature of the heat preservation zone is changed. Thus, it can be seen that the estimation based on the heat flow ratio is insufficient for predicting the furnace top gas temperature when the temperature of the heat preservation zone changes. Based on the above, Table 1 summarizes the effects of various operating factors on the furnace top temperature.

  The heat storage zone temperature is reduced using ferro-coke by designing the operation in consideration of the oxygen enrichment rate, pulverized coal injection amount, natural gas injection amount, and nitrogen enrichment amount, not the heat flow ratio. In this case, it is possible to set operation conditions for ensuring the target furnace top gas temperature. The above coefficient varies slightly depending on the composition of the blown-in reducing material and on the base condition with respect to the blowing conditions. The above is an example, and the influence may be scrutinized according to the base condition each time.

  Considering the above, the operating conditions for ensuring the target furnace top gas temperature when the heat storage zone temperature decreases are as follows: a) oxygen enrichment rate, b) pulverized coal injection amount, natural gas Three types can be considered: reducing material blowing amount such as blowing amount, and c) nitrogen enrichment amount. Hereinafter, these conditions will be described in detail.

  B) Oxygen enrichment rate: When air is blown from the blast furnace tuyere, oxygen is added to the blown air to enrich it, and if the operation is performed to keep the amount of oxygen blown constant, the amount of gas passing through the furnace can be reduced with constant production. Can be reduced. Therefore, by reducing the oxygen enrichment rate, the heat flow ratio decreases and the furnace top gas temperature rises by increasing the amount of gas passing through the furnace at a constant production rate (solid descending rate). The relationship between the oxygen enrichment rate and the furnace top gas temperature according to the operating conditions can be determined, and the oxygen enrichment rate can be reduced using this relationship to raise the furnace top gas temperature. The oxygen enrichment rate is expressed by volume% of the amount of oxygen mixed in the blown air.

  B) Reducing material injection amount: Operation to reduce the amount of coke used by blowing reducing material such as pulverized coal into the blast furnace together with hot air from the tuyere. By increasing the amount of reducing material blown in, the solid flow rate decreases, the heat flow ratio decreases, and the furnace top gas temperature increases. In addition to pulverized coal, natural gas, waste plastic, etc. can be used as the reducing material. The relationship between the reducing material injection amount and the furnace top gas temperature corresponding to the operating conditions is obtained, and the furnace top gas temperature can be increased by increasing the reducing material injection amount using this relationship. In addition, the reducing material injection amount shall be represented by the injection amount (kg / t) per 1 ton of hot metal.

C) Nitrogen-enriched amount: Nitrogen-enriched operation can be performed on the air blown from the blast furnace tuyere. The amount of blown oxygen decreases due to the enrichment of nitrogen, whereby the amount of gas passing through the furnace can be increased with a constant production volume, and the furnace top gas temperature increases. The relationship between the nitrogen enrichment amount and the furnace top gas temperature according to the operating conditions is obtained, and the furnace top gas temperature can be increased by increasing the nitrogen enrichment amount using this relationship. Note that the nitrogen enrichment amount is represented by the nitrogen gas blowing volume (Nm ³ / t) in a standard state per 1 ton of hot metal.

  The above a), b) and c) are effective even when controlled individually, but by controlling by combining one type or two or more types, it is stable under conditions closer to standard operating conditions. It is possible to operate, but at this time, it is necessary to design the operation in consideration of changes in pulverized coal combustibility and theoretical combustion temperature.

  Ferro-coke used in the present invention is manufactured by heating a molded product produced by molding a raw material mainly composed of coal and iron ore, and dry-distilling the coal in the molded product. The main component of coal and iron ore means that the raw material of ferro-coke is mainly coal and iron ore. Ferro-coke is made of a raw material containing 70 mass% or more of coal and iron ore. Although coke is produced, a raw material containing 80 mass% or more of coal and iron ore is usually used. In addition to coal and iron ore, a binder for molding can be used. Molding is carried out cold or hot, and in the case of cold molding, it is preferable to add a binder to the raw material.

  As a blast furnace operation using ferro-coke as a part of blast furnace charge, ferro-coke is used in addition to or instead of conventional blast furnace charge, and usually iron raw material, coke, ferro Coke is used as a raw material for blast furnace charging. The iron raw material is composed of sintered ore, lump ore, pellets and the like. As a ferro-coke charging method, for example, an “iron raw material + ferro-coke” layer in which ferro-coke is mixed with an iron raw material and a normal coke layer can be alternately charged into a blast furnace. From the top of the blast furnace, first, coke is charged to form a coke layer, and then a mixture of iron ore and ferro-coke is charged to form an “iron raw material + ferro-coke” layer. The blast furnace raw material charging is performed by sequentially repeating the cycle of the layer and the “iron raw material + ferrocoke” layer.

In a blast furnace having an internal volume of 5000 m ³ , iron: coke = 0.4: An operation test (Case 1 to 5) using ferro-coke having a mass ratio of 0.6 was performed.

  Ferro-coke was produced as follows. 5 mass% of a mixture of asphalt pitch and soft pitch is added as a binder to a mixture of iron ore and coal (mass ratio of 0.4: 0.6), and after stirring and mixing with a mixer, a linear pressure of 5 t / cm, Cold molding was performed at a molding temperature of 25 ° C. to produce a 6 cc briquette molding. A pellet feed having a particle size of 100 microns or less (-100 microns) was used for the iron ore. Coal having a maximum average reflectance of 1.0% was used as the coal. The particle size of the coal used was pulverized to a particle size of 3 mm or less (-3 mm). This briquette was heated in a shaft furnace, which is a dedicated carbonization furnace, and carbon was carbonized to produce ferro-coke. Ferro-coke and iron raw material were mixed, and the mixture and lump coke were alternately charged into the furnace for operation.

  Table 2 shows the base conditions and blast furnace operation results of Cases 1 to 5. The temperature of the heat preservation zone was measured with a vertical sonde charged from the top of the furnace.

  Case 1 is a case where ferro-coke is used by replacing the coke with the blowing condition and the amount of pulverized coal blowing as the base condition. As the furnace top gas temperature dropped to 82 ° C, the dust emission rate, which is the amount of dust discharged, decreased in ventilation, and a large amount of water flowed out during ash extraction from the dust catcher, making it difficult to work. It was difficult to continue operation under the same conditions.

  On the other hand, for the purpose of adjusting the furnace top gas temperature to 110 ° C., the operation that reduced the oxygen enrichment rate simultaneously with the use of ferro-coke (Case 2), the operation that increased the amount of pulverized coal injection simultaneously with the use of ferro-coke ( Simultaneously with the use of Case 3) and ferro-coke, an operation (Case 4) with an increased amount of natural gas (LNG) was carried out. In Cases 2 to 4, although the dust intensity (dust ratio) was slightly lower than the base, the operation was stable and the operation with a reduced coke ratio was possible.

  In addition, in order to raise the furnace top gas temperature further than the base condition, an operation (Case 5) in which oxygen enrichment reduction and nitrogen enrichment were combined was performed. In Case 5, it was possible to continue the operation with a reduced coke ratio.

  The oxygen enrichment rate, nitrogen enrichment amount, pulverized coal and natural gas injection amount were grasped in advance to determine the effect of these single operation amounts on the furnace top gas temperature, and the conditions were changed during actual ferro-coke operation. In the operations of Examples 2 to 5 of the present invention, it was found that the operation at a reduced coke ratio can be stably continued by maintaining the furnace top gas temperature at 100 ° C. or higher.

The schematic which shows the temperature distribution in the schematic of the longitudinal cross-section of a blast furnace, and the cross section. The graph which shows the distribution in a furnace of solid temperature and gas temperature when changing heat preservation zone temperature and heat flow ratio. (A) Heat preservation zone temperature 950 ° C., heat flow ratio 0.864, (b) Heat preservation zone temperature 750 ° C., heat flow ratio 0.864, (c) Heat preservation zone temperature 750 ° C., heat flow ratio 0.915 The graph which shows the prediction result of the change of furnace top gas temperature. The graph which shows the relationship between heat flow ratio variation | change_quantity and furnace top gas temperature variation | change_quantity. The graph which shows the relationship between the heat flow ratio at the time of changing oxygen enrichment rate, pulverized coal ratio, and heat preservation zone temperature, and furnace top gas temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Blast furnace 2 Heat preservation zone 3 Lump zone 4 Fusion zone 5 Dripping zone 6 Raceway

Claims (4)

  During blast furnace operation using ferro-coke as part of the charging material, the oxygen enrichment rate of the air blown from the tuyere, the amount of reducing material blown from the tuyere, and the nitrogen enrichment amount of the air blown from the tuyere A blast furnace operating method characterized by controlling the furnace top gas temperature by controlling one or more selected from among them.   The blast furnace operating method according to claim 1, wherein a relationship between the oxygen enrichment rate and the furnace top gas temperature is obtained, and the oxygen enrichment rate is decreased using the relationship to raise the furnace top gas temperature.   3. The furnace top gas temperature is increased by obtaining a relationship between a reducing material injection amount and a furnace top gas temperature, and increasing the reducing material injection amount using the relationship. The blast furnace operating method described in 1.   4. The furnace top gas temperature is increased by obtaining a relationship between the nitrogen enrichment amount and the furnace top gas temperature, and increasing the nitrogen enrichment amount using the relationship. Blast furnace operation method according to crab.

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