JP6176361B2 - Blast furnace operation method - Google Patents

Description

The present invention relates to a method for operating a blast furnace in which pulverized coal is blown from a blast furnace tuyere and the combustion temperature is raised to improve productivity and reduce exhaust CO ₂ .

In recent years, global warming due to an increase in carbon dioxide emissions has become a problem, and the suppression of emitted CO ₂ is an important issue even in the steel industry. The blast furnace uses coke mainly charged from the top of the furnace and pulverized coal blown from the tuyere as a reducing material, and uses pulverized coal as much as possible from coke due to the difference in carbon dioxide emissions generated by pretreatment. This leads to a reduction in total CO ₂ emissions. The amount of pulverized coal used per 1 ton of pig iron (injected from the tuyere) is referred to as the pulverized coal ratio (kg / t-pig iron or kg / tp). When the combustion efficiency of pulverized coal is reduced when the volatile content of pulverized coal is 25 mass% or less, the pulverized coal and oxygen are injected into the lance that blows the pulverized coal from the tuyere into the furnace. It is said that combustion efficiency can be improved by supplying the oxygen concentration in the lance to 70 vol% or more. Further, in Patent Document 1, when the lance is a single pipe, a mixture of oxygen and pulverized coal is blown from the lance, and when the lance is a double pipe, fine powder is injected from the inner pipe of the double pipe lance. It has also been proposed to blow charcoal and blow oxygen from between the inner and outer tubes of the double tube lance. Moreover, in the following patent document 2, when the combustion efficiency decreases when the pulverized coal ratio is 150 kg / tp or more during the production reduction operation with a yield ratio of 1.8 or less, pulverized coal with a volatile content of 28 mass% or more is used. While being used, the heat flow ratio represented by the ratio between the solid heat capacity and the gas heat capacity is controlled to 0.8 or less to maintain efficient combustion of pulverized coal.

Japanese Patent No. 4074467 JP 2011-127176 A

The role of pulverized coal in the blast furnace is basically a heat source and a reducing material source, and the combustibility is related to the amount of unburned powder (unburned char) generated (the amount of powder charged into the blast furnace). In the blast furnace, a solution loss reaction represented by C + CO ₂ = 2CO occurs, and the reaction amount varies depending on the operation, but is about 80 to 100 kg-C / tp. As the C source consumed in this reaction, lump coke charged in the blast furnace, small lump coke mixed in the ore, and pulverized coal unburned powder can be considered. ) It is said that pulverized coal unburned powder is consumed preferentially from the difference. In other words, when the flammability of pulverized coal decreases, the amount of unburned powder charged into the blast furnace increases, and as a result of being consumed preferentially by the solution loss reaction, the powder coke that would normally be consumed cannot be consumed. In the furnace. It is thought that when the retained powder coke in the furnace is increased, the porosity and the average particle diameter are decreased, and as a result, the air permeability of the blast furnace is deteriorated. On the other hand, the amount of coke in-furnace generated powder is greatly influenced by the cold strength of the coke (drum strength described in the JIS K 2151 coke test method). Therefore, in terms of evaluating the air permeability of the blast furnace, It is considered important to adjust not only the combustibility of pulverized coal but also the properties of coke.

  In the above-mentioned patent document 1, the pulverized coal has a volatile matter content of 25 mass% or less and a pulverized coal ratio of 150 kg / tp or more. It is a technique that can improve combustion efficiency by supplying charcoal and oxygen and setting the oxygen concentration in the lance to 70 vol% or more, thereby improving the air permeability in the furnace. However, regarding the combustion efficiency, even if it is pulverized coal having the same volatile content of 25 mass% or less, depending on the particle size or the blowing temperature, even if the oxygen concentration in the lance is set to 70 vol% or more, the combustion efficiency does not increase or vice versa. In addition, it has been found that the combustion efficiency may be maintained even if the oxygen concentration in the lance is not set to 70 vol% or more. Further, regarding the air permeability in the furnace, it has been found that even if the combustion efficiency of pulverized coal is somewhat reduced, if the strength of the coke is large, the influence on the air permeability in the furnace may be small. Therefore, although Patent Document 1 is an excellent technique, the effect cannot be exhibited depending on the properties of pulverized coal and coke and the blowing conditions, or conversely, the effect is excessive, so high pressure oxygen is prepared in the lance. Considering the cost, it can be assumed that it leads to loss.

Further, since further reduction of exhausted CO ₂ is required, for example, it is also desired that the pulverized coal ratio be 170 kg / tp or more, but the high pulverized coal ratio is 170 kg / tp or more. In the charcoal ratio, as described in Patent Document 1, even if pulverized coal is simply blown from the inner pipe of the double pipe lance and oxygen is blown from between the inner pipe and the outer pipe, the combustion temperature is saturated. The combustion efficiency does not increase. In addition, since a large amount of hot air of 1000 to 1200 ° C. is blown into the tuyere, for example, the blowing lance inserted into the tuyere may be exposed to high temperatures, as described in Patent Document 1 described above. In addition, it is impractical to supply a single-pipe lance with a mixture of high-concentration oxygen and pulverized coal in terms of safety.

Moreover, in the said patent document 2, while a combustion efficiency falls as a pulverized coal ratio 150 kg / tp or more at the time of the production reduction operation of the output ratio 1.8 or less, while using pulverized coal whose volatile matter is 28 mass% or more, The heat flow ratio represented by the ratio between the solid heat capacity and the gas heat capacity is controlled to 0.8 or less to maintain efficient combustion of pulverized coal. However, in order to reduce the heat flow ratio, oxygen enrichment is set to 2.0 or less, preferably 1.5%, which lowers the combustion efficiency of pulverized coal. Depending on the charcoal properties (particle size), even if the volatile content is set to 28 mass% or more, there may be a case where the combustion efficiency improvement effect is insufficient.
The present invention has been made paying attention to the above problems, and even if the pulverized coal ratio is an operation condition of 150 kg / tp or more, it is produced by increasing the combustion temperature of the pulverized coal. It is an object of the present invention to provide a blast furnace operating method capable of improving the performance and reducing the exhausted CO ₂ .

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 pulverized coal with an injection amount of 150 kg / tp or more per 1 ton of pig iron is blown by a lance from a blower tuyere. When the strength of the coke to be added is DI ¹⁵⁰ ₁₅ [%] 83 to 85 or less according to the test method described in JISK2151, the weight ratio of the pulverized coal having a particle size of 74 μm or less is 60% or less, and the average volatilization of the pulverized coal When at least two of the three conditions of 25% by mass or less and the blowing temperature of 1100 ° C. or less are satisfied, a flammable gas and a flammable gas are blown from the lance together with pulverized coal, The concentrations of the combustion-supporting gas and the flammable gas injected together with the pulverized coal are 50 to 80 vol% and 10 to 40 vol%, respectively, as the gas concentrations in the lance.

Moreover, the blast furnace operating method of the present invention is a blast furnace operating method in which pulverized coal with a blowing amount of 150 kg / tp or more per 1 ton of pig iron is blown from a blower tuyere with a lance, and the strength of coke charged from the top of the furnace is high. In the test method described in JISK2151, DI ¹⁵⁰ ₁₅ [%] 83 or less, the weight ratio of pulverized coal having a particle size of 74 μm or less is 60% or less, the average volatile content of pulverized coal is 25 mass% or less, the blowing temperature When at least two of the three conditions of 1100 ° C. or lower are satisfied, the combustion support gas and the flammable gas are injected from the lance together with the pulverized coal, and the combustion support is injected together with the pulverized coal. The gas concentration in the lance is 50 to 90% by volume and 10 to 50% by volume, respectively.

The combustion-supporting gas of the present invention is defined as a gas having an oxygen concentration of at least 50 vol% or more.
In addition, the flammable gas used in the present invention is literally a gas that is more flammable than pulverized coal. For example, in addition to hydrogen containing hydrogen as a main component, city gas, LNG, propane gas, in steelworks The generated converter gas, blast furnace gas, coke oven gas, etc. are applicable. Also, shale gas can be used as equivalent to LNG. Shale gas is a natural gas extracted from the shale layer, and is produced from a place other than the conventional gas field, so it is called an unconventional natural gas resource. Combustible gases such as city gas ignite and burn very quickly, and those with a high hydrogen content have high combustion calories, and unlike pulverized coal, flammable gas does not contain ash. It is advantageous for air permeability and heat balance.

The lower limit of the average volatile content of pulverized coal is 5 mass%. If the average volatile content of pulverized coal is less than 5 mass%, the coal is hard and difficult to grind. The lower limit of coke strength is set to 78 in DI ¹⁵⁰ ₁₅ [%]. If the coke strength is less than DI ¹⁵⁰ ₁₅ [%] 78, the coal is not sufficiently shrunk, so the coke becomes undried and damages the coke oven. The lower limit of the weight ratio of pulverized coal having a particle size of 74 μm or less is 30%. When the weight ratio of the pulverized coal having a particle size of 74 μm or less is less than 30%, the temperature rise of the pulverized coal is slow and does not ignite, so that the combustibility is rapidly lowered. Further, the lower limit value of the blowing temperature is set to 900 ° C. Since the bricks of the hot stove are designed to mesh at 900 to 1200 ° C, if the air temperature is less than 900 ° C, the bricks of the hot stove are worn. The upper limit of the amount of pulverized coal injected per 1 ton of pig iron is 300 kg / tp. When the amount of pulverized coal injection per 1 ton of pig iron exceeds 300 kg / tp, the coke replacement rate decreases due to a significant decrease in combustibility, and the tuyere temperature (theoretical combustion temperature) is maintained in terms of operation. Therefore, it is not desirable because it is difficult to adjust the equipment capacity such as greatly increasing the oxygen concentration and the blowing temperature, or drastically reducing the blowing humidity. Preferably it is 250 kg / tp or less.

Thus, according to the blast furnace operating method of the present invention, while considering the various conditions under which the combustion efficiency of pulverized coal decreases together with the coke strength, comprehensively considering the air permeability state of the blast furnace, By improving the combustion efficiency of pulverized coal, it is possible to efficiently improve productivity and reduce exhaust CO ₂ . In other words, the combustion efficiency of the pulverized coal is judged from the amount of pulverized coal blown from the tuyere, the properties of the pulverized coal (particle size, volatile content), and the blowing temperature, and the breathability is determined from the combustion efficiency of the pulverized coal and the coke strength used. By comprehensively judging, the combustion efficiency of pulverized coal can be set efficiently within the optimum range. As a result, it becomes possible to maintain and improve the combustion efficiency of pulverized coal, which in turn stabilizes the air permeability of the blast furnace, and as a result, it is possible to efficiently improve productivity and reduce exhaust CO _2. It is.

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.

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 iron ore is reduced, that is, ironmaking is mainly performed in this combustion space. In the figure, only one lance 4 is inserted into the left blower pipe 2 shown in the figure, but as is well known, either the blower pipe 2 or the tuyere 3 arranged circumferentially along the furnace wall. It is also possible to insert and set the lance 4. Further, the number of lances per tuyere is not limited to one, and two or more lances can be inserted. Moreover, the form of a lance can be applied to a single pipe lance, a double pipe lance, or a bundle of a plurality of lances.

As is well known, the pulverized coal that has passed through the tuyere 3 from the lance 4 and is blown into the raceway 5 is coke and its volatile matter and fixed carbon are burned, and remains unburned. The aggregate of carbon and ash called is discharged from the raceway as unburned char (unburned powder). Since char is mainly fixed carbon, a reaction called a carbon dissolution reaction occurs along with a combustion reaction. Moreover, when the volatile matter of the pulverized coal blown into the blower pipe 2 from the lance 4 is high, the ignition of the pulverized coal is promoted due to the increase in the volatile matter, and the temperature rise of the pulverized coal due to the increase in the combustion amount of the volatile matter. The rate and maximum temperature increase, and the char reaction rate increases due to the dispersibility of pulverized coal and the increase in temperature. At this time, it is considered that the pulverized coal is dispersed with the vaporization expansion of the volatile matter, the volatile matter is combusted, and the pulverized coal is rapidly heated and heated by this combustion heat. Charcoal burns. Regarding the coke strength DI ¹⁵⁰ ₁₅ [%] defined in JISK2151, the larger the coke strength DI ¹⁵⁰ ₁₅ [%], the smaller the proportion of coke powder in the furnace. For example, the amount of coke powder deposited on the furnace core is smaller. It will be smaller.

Next, in a blast furnace with a furnace volume of 5000 m ³ , the above-mentioned coke strength DI ¹⁵⁰ ₁₅ [%], pulverized coal amount, pulverized coal properties (particle size, volatile content), operation temperature to evaluate the air permeability by changing the blowing temperature Went. The amount of air flow was controlled so that the amount of brewing was constant at 10000 t / day (sometimes expressed as d), and the air permeability at that time was compared for each condition. As is well known, the air permeability is obtained from the pressure difference between the pressure at the top of the furnace and the blowing pressure and the blowing amount. During this test operation period, the blast moisture was adjusted so that the tuyere tip temperature was in a certain range, and the hot metal temperature was within a range of 1500 ° C. ± 10 ° C. at each level. As shown in Table 1 below, as a base condition 1, a coke ratio of 340 kg / tp (-p is omitted in the figure), a pulverized coal ratio of 150 kg / tp, an air blowing temperature of 1100 ° C., a coke strength DI ¹⁵⁰ ₁₅ [% ] 87, Operation with pulverized coal volatile matter 25 mass%, particle size of 74 μm or less pulverized coal particle size 60 mass%, the air permeability at that time was set to 1.0, and the air permeability when operating conditions were changed to the following relative comparison did. The larger the numerical value, the worse the air permeability. However, until the air permeability was about 1.05, it was an acceptable range for stable operation. In the base conditions, one single tube lance was used per tuyere.

  As a result of operating the air temperature, the pulverized coal volatile content, and the pulverized coal particle size in the direction of improving the combustion efficiency, the base 2 improved both the coke ratio and the air permeability as expected. The direction in which the combustion efficiency is improved is that the blast temperature is increased, the pulverized coal volatiles are increased, and the pulverized coal particle size is increased (because the weight percent of pulverized coal particles having a particle size of 74 μm or less is the pulverized coal particle size). ) Means. In Base 3, as compared with Base 1, only the pulverized coal ratio was +10 kg / tp. As a result, the air permeability was slightly deteriorated, but it was within the allowable range for stable operation. In the bases 4 to 6, the pulverized coal volatile matter, the pulverized coal particle size, and the air blowing temperature were each operated with respect to the base 3 in the direction in which the combustion efficiency was decreased. The direction in which the combustion efficiency decreases means that the blast temperature is decreased, the pulverized coal volatile content is decreased, and the pulverized coal particle size is decreased. As a result, in Bases 4 to 6, although the air permeability was somewhat deteriorated, it was within the allowable range for stable operation.

In the bases 7 to 9, the combustion efficiency is lowered by combining two items of the pulverized coal volatile matter, the pulverized coal particle size, and the blowing temperature with respect to the base 3 under the condition of the coke strength DI ¹⁵⁰ ₁₅ [%] 88. Operated. As a result, in the bases 7 to 9, the air permeability was slightly deteriorated, but was within the allowable range for stable operation. This is considered to be an effect of improving the coke strength DI ¹⁵⁰ ₁₅ [%]. That is, since the coke strength DI ¹⁵⁰ ₁₅ [%] was improved, the accumulation of the powder coke in the furnace was suppressed, and it is considered that the air permeability was not significantly impaired. The bases 10 to 12 have a coke strength DI ¹⁵⁰ ₁₅ [%] of 8% lower than that of the base 3 and further combined with two items of pulverized coal volatile matter, pulverized coal particle size, and blowing temperature to increase the combustion efficiency. Was operated in the direction of decreasing. As a result, the air permeability was greatly deteriorated and the coke ratio was increased, but stable operation was difficult. As described above, this is considered to be because the coke strength DI ¹⁵⁰ ₁₅ [%] was reduced and the in-furnace deposition of the fine coke deteriorated.

  In the following case conditions, a triple pipe lance was used, and city gas was blown from the inner pipe of the triple pipe lance as a flammable gas, and oxygen was blown from the inner pipe and the intermediate pipe as a flammable gas. Pulverized coal was blown from between the intermediate pipe and the outer pipe. At that time, the pulverized coal is conveyed from between the intermediate pipe and the outer pipe of the triple pipe lance together with a carrier gas such as nitrogen. As will be described later, when adjusting the amount of city gas or oxygen blown, the total amount of gas blown from the triple pipe lance is not changed. Specifically, when the amount of city gas or oxygen is increased, the amount of pulverized coal carrier gas is decreased so that the total amount of gas is equivalent. Instead of the triple pipe lance, a lance in which single pipes are bundled may be used. In that case, for example, pulverized coal is blown from one of the three single pipes, and flammable gas is blown from one of them. And oxygen may be blown from either of them. Alternatively, a flammable gas and pulverized coal may be mixed in advance and blown from one lance or between the tubes constituting the lance. In either case, it is desirable to blow oxygen in the immediate vicinity of the pulverized coal being blown. The lance oxygen concentration and lance city gas concentration in the table are all vol%.

  Case 1 is a case where the blast furnace operating method of this embodiment in which oxygen and city gas are blown together with pulverized coal from the lance to the conditions of the base 10 is applied. That is, city gas was blown from the inner pipe of the triple pipe lance, oxygen was blown from between the inner pipe and the intermediate pipe, and pulverized coal was blown together with the carrier gas from between the intermediate pipe and the outer pipe. However, the lance oxygen concentration in the gas transferred from the triple pipe lance, that is, the lance blowing oxygen, city gas and pulverized coal is 47 vol%, and the lance city gas concentration in the gas transferred from the triple pipe lance is 4. The air permeability improvement effect was insufficient only with 4 vol%. In cases 2 to 4, the lance oxygen concentration in the gas conveyed from the triple pipe lance is 55 vol% and the lance city gas concentration in the gas conveyed from the triple pipe lance is 11. It was 8 vol%, and the air permeability improvement effect was confirmed, and stable operation became possible. In cases 5 to 7, the lance oxygen concentration in the gas conveyed from the triple pipe lance is 66 vol%, and the lance city gas concentration in the gas conveyed from the triple pipe lance is set to the bases 10 to 12, respectively. Compared with cases 2 to 4, a further air permeability improvement effect was confirmed, and even when compared with the base 1 conditions, the air permeability was improved. Further, Case 8 is the one in which the blast furnace operating method of the present embodiment in which oxygen and city gas are blown together with pulverized coal from the lance under the same conditions as Cases 2 to 4 with respect to the base 1 condition. As is apparent from the table, the pulverized coal ratio can be increased by the effect of improving the combustion efficiency of the pulverized coal, and the coke ratio can be significantly reduced under good air permeability conditions.

In cases 9 to 11, the coke strength DI ¹⁵⁰ ₁₅ [%] was reduced from 85.5 to 84.5 as compared to cases 2 to 4. In cases 9 to 11, as in cases 2 to 4, the lance oxygen concentration in the gas conveyed from the triple pipe lance is 55 vol%, and the lance city gas concentration in the gas conveyed from the triple pipe lance is 11.8 vol. %, The air permeability deteriorated. On the other hand, in cases 12 to 14, the lance oxygen concentration in the gas conveyed from the triple pipe lance is 62.6 vol% and the lance city gas in the gas conveyed from the triple pipe lance is compared to cases 9 to 11. By setting the concentration to 15.1 vol%, the air permeability was improved. That is, even under the condition where the coke strength DI ¹⁵⁰ ₁₅ [%] was reduced to 84.5, the pulverized coal combustibility was improved by increasing the lance oxygen concentration and the lance city gas concentration, and stable operation was possible. . Further, in the cases 15 to 17, the coke strength DI ¹⁵⁰ ₁₅ [%] was significantly reduced from 84.5 to 82.5 compared to the cases 12 to 14. In Cases 15 to 17, as in Cases 12 to 14, the lance oxygen concentration in the gas conveyed from the triple pipe lance is 62.6 vol%, and the lance city gas concentration in the gas conveyed from the triple pipe lance is 15. Since it was 1 vol%, the air permeability was greatly deteriorated. On the other hand, in cases 18-20, the lance oxygen concentration in the gas conveyed from the triple pipe lance is 70.8 vol%, and the lance city gas in the gas conveyed from the triple pipe lance is compared to cases 15-17. The air permeability was improved by setting the concentration to 20.4 vol%. In this way, even under the condition where the coke strength DI ¹⁵⁰ ₁₅ [%] is reduced to 82.5, the pulverized coal combustibility is improved by increasing the lance oxygen concentration and lance city gas concentration, and stable operation is possible. there were.

As described above, in the blast furnace operating method of the present embodiment, the combustion efficiency of the pulverized coal is efficiently improved even under the operating conditions in which the combustion efficiency of the pulverized coal decreases when the coke strength DI ¹⁵⁰ ₁₅ [%] is reduced. Therefore, it is possible to achieve blast furnace operation capable of stabilizing and improving production and reducing CO ₂ emission. It was also confirmed that if the operating conditions were constant, the operating specifications could be greatly improved by the blast furnace operating method of the present embodiment.

  1 is a blast furnace, 2 is an air duct, 3 is a tuyere, 4 is a lance, 5 is a raceway

Claims (2)

In the blast furnace operation method in which pulverized coal with an injection amount of 150 kg / tp or more per 1 ton of pig iron is blown from the blower tuyere with a lance, the strength of the coke charged from the top of the furnace is DI ¹⁵⁰ _{15 according to} the test method described in JISK2151. [%] Three conditions of 83 to 85 or less, wherein the weight ratio of pulverized coal having a particle size of 74 μm or less is 60% or less, the average volatile content of pulverized coal is 25 mass% or less, and the blowing temperature is 1100 ° C. or less. When at least two or more of the above are satisfied, flammable gas and flammable gas are blown from the lance together with pulverized coal, and the flammable gas and flammable gas blown together with the pulverized coal are injected. The blast furnace operating method, wherein the gas concentration in the lance is 62.6 to 80 vol% and 15.1 to 40 vol%, respectively. In the blast furnace operation method in which pulverized coal with an injection amount of 150 kg / tp or more per 1 ton of pig iron is blown from the blower tuyere with a lance, the strength of the coke charged from the top of the furnace is DI ¹⁵⁰ _{15 according to} the test method described in JISK2151. [%] Three conditions of 78 to 83, in which the weight ratio of pulverized coal having a particle size of 74 μm or less is 60% or less, the average volatile content of pulverized coal is 25 mass% or less, and the blowing temperature is 1100 ° C. or less. When at least two or more of the above are satisfied, flammable gas and flammable gas are blown from the lance together with pulverized coal, and the flammable gas and flammable gas blown together with the pulverized coal are injected. The blast furnace operating method, wherein the gas concentration in the lance is 70.8 to 90 vol% and 20.4 to 50 vol%, respectively.

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