JP2012188742A - Method for operating blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for operating a blast furnace capable of enhancing a combustion temperature, and, as a result, reducing discharged CO.SOLUTION: A lance 4 for injecting fuel from a tuyere 3 is formed into a double tube to inject fine powdery coal from an inner tube 21 of the double-tube lance 4, and to blow oxygen from an outer tube 22 of the double-tube lance 4. A notch 23 is provided in a blowing end of the inner tube 21 of the double-tube lance 4 to set an oxygen concentration of a gas consisting of a carrier gas of the fine powdery coal and the gas blown from the outer tube to 35 vol.% or more. Thereby, the combustion temperature can be raised even in an operation of a high fine powdery coal ratio in which a volatile matter concentration of the fine powdery coal is 25 mass% or less, and a fine powdery coal ratio is 150 kg/t-pig iron or more, and, as a result, discharged COcan be reduced, and oxygen unit consumption can be suppressed by setting the oxygen concentration to less than 70 vol.%. Moreover, the combustion efficiency is further improved by providing a plurality of notches 23 at an even interval in the circumferential direction of the inner tube 21 of the double-tube lance 4.

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. Blast furnace, mainly we use blown pulverized coal coke and tuyere as reducing agent, the difference in carbon dioxide emissions generated by the pre-treatment, the use of pulverized coal than possible coke discharge CO ₂ Leads to suppression. For example, in Patent Document 1 below, pulverized coal with a pulverized coal ratio of 150 kg / t-pig iron or more and volatile content of 25 mass% or less is used, and pulverized coal and oxygen are supplied to a lance for injecting fuel from the tuyere. Combustion efficiency can be improved by setting the oxygen concentration of the gas to 70 vol% or more. In Patent Document 1, when the lance is a single pipe, a mixture of oxygen and pulverized coal is blown from the lance. When the lance is a double pipe, the pulverized coal is injected from the inner pipe of the double pipe lance. It has also been proposed to blow oxygen from the outer tube of the double tube lance. The pulverized coal ratio is the mass of pulverized coal used per 1 ton of pig iron.

Moreover, in the following patent document 2, irregularities are provided on the outer tube of the double tube lance to disperse the pulverized coal so as to promote the reaction between the pulverized coal and oxygen.
In Patent Document 3 below, when pulverized coal is blown from the inner pipe of the double pipe and oxygen is blown from the outer pipe of the double pipe lance, the inner pipe of the double pipe lance is made shorter than the outer pipe. That is, the contact property between the pulverized coal and oxygen is improved by using the pulverized coal blowing tip of the inner tube as the front side in the blowing direction from the oxygen blowing tip of the outer tube.

Japanese Patent No. 4074467 Korean Patent Publication No. 2002-047359 Japanese Patent Application Laid-Open No. 6-10092

Although a large amount of air is blown through the tuyere, the lance may be exposed to high temperatures, and as described in Patent Document 1, a mixture of high-concentration oxygen and pulverized coal is supplied to the single tube lance. This is not practical from a safety standpoint. Further, since further reduction of exhausted CO ₂ is required, for example, it is desired that the pulverized coal ratio be 170 kg / t-pig iron or higher, but the pulverized coal ratio is higher than 170 kg / t-pig iron. In the pulverized coal 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 the outer pipe, the combustion temperature is saturated and combustion efficiency is increased. Does not increase.

  In addition, since the gas flowing in the outer tube of the double tube lance also plays a role of cooling the outer tube, as described in Patent Document 2, the flow of gas is similar to the unevenness provided in the outer tube. If there is something that hinders the heat flow, a heat load is applied to the portion where the flow is weak, and wear such as cracking or melting may occur. If such wear occurs, there is a risk of causing backfire or clogging of the lance. Moreover, when the amount of pulverized coal increases, there is a problem that the occurrence of wear on the convex portions cannot be avoided due to the pulverized coal ejected from the inner pipe.

Further, as described in Patent Document 3, even if the tip of the inner pipe of the double pipe lance is simply made shorter than the outer pipe, the contact between pulverized coal and oxygen is improved, The dispersion of pulverized coal is suppressed, and a sufficient combustibility improvement effect cannot be obtained.
The present invention has been made paying attention to the above-mentioned problems, and an object of the present invention is to provide a blast furnace operating method capable of improving the combustion temperature and, as a result, reducing the exhaust CO _2. It is what.

  In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention provides an inner pipe for preparing pulverized coal having a volatile content of 25 mass% or less and blowing pulverized coal and combustion-supporting gas from the tuyere. A double tube lance having an outer tube is prepared, hot air is blown from the tuyere, and a plurality of notches recessed in the axial direction are provided in the circumferential direction at the blowing tip of the inner tube of the double tube lance The pulverized coal is blown together with the carrier gas at a pulverized coal ratio of 150 kg / t-pig iron or more from the inner pipe, and the combustion-supporting gas is blown from the outer pipe of the double-pipe lance. This is a blast furnace operating method in which the oxygen concentration of the gas composed of the gas is 35 vol% or more.

Moreover, the invention which concerns on Claim 2 among this invention is the blast furnace operating method of Claim 1 with which the said notch is provided at equal intervals in the front-end | tip part circumferential direction of the inner side pipe | tube of the said double pipe lance. is there.
In the invention according to claim 3 of the present invention, the width of the notch exceeds 0 in the ratio of the total width of all the notches to the inner circumference of the inner tube of the double pipe lance. The blast furnace operating method according to claim 2, wherein the blast furnace is 0.5 or less.

In the invention according to claim 4 of the present invention, the width of the notch is 0.05 as a ratio of the total width of all the notches to the inner peripheral length of the inner tube of the double tube lance. The blast furnace operating method according to claim 3, wherein the blast furnace is 0.3 or less.
In the invention according to claim 5 of the present invention, the width of the notch is 0.1 as a ratio of the total width of all the notches with respect to the inner peripheral length of the inner tube of the double tube lance. The blast furnace operating method according to claim 4, wherein the blast furnace is 0.2 or less.

Moreover, the invention which concerns on Claim 6 among this invention is the blast furnace operating method of Claim 2 which makes the depth of the said notch exceed 0 mm and 12 mm or less.
Moreover, the invention which concerns on Claim 7 among this invention is the blast furnace operating method of Claim 6 which makes the depth of the said notch 2 mm or more and 10 mm or less.
Moreover, the invention which concerns on Claim 8 among this invention is a blast furnace operating method of Claim 7 which makes the depth of the said notch 3 mm or more and 7 mm or less.

In the invention according to claim 9 of the present invention, when the integer part when the inner peripheral length of the inner pipe of the double pipe lance is divided by the width of one notch is the maximum notch number, The number of notches is a blast furnace operating method according to claim 2, wherein the ratio of the number of notches to the maximum number of notches exceeds 0 and is 0.8 or less.
Moreover, the invention which concerns on Claim 10 among this invention WHEREIN: The number of the said notches is 0.1 or more and 0.6 or less by ratio of the number of notches with respect to the said maximum number of notches. It is a blast furnace operation method.

Moreover, the invention which concerns on Claim 11 among this invention sets the number of the said notches to 0.2 or more and 0.5 or less by ratio of the number of notches with respect to the said maximum number of notches. It is a blast furnace operation method.
Further, in the invention according to claim 12 of the present invention, the combustion-supporting gas is oxygen, and a part of oxygen enriched in blowing is blown from the outer pipe of the double pipe lance. This is the blast furnace operation method.

Moreover, the invention which concerns on Claim 13 among this invention is a blast furnace operating method of Claim 1 in which the said pulverized coal has a volatile matter of 3 mass% or more and 25 mass% or less.
The invention according to claim 14 of the present invention is the blast furnace operation according to claim 1, wherein the combustion-supporting gas blown from the outer pipe of the double pipe lance has an outlet flow velocity of 20 to 120 m / sec. Is the method.

Moreover, the invention which concerns on Claim 15 among this invention is a blast furnace operating method of Claim 1 whose said pulverized coal ratio is 170 kg / t-pig iron or more.
In the invention according to claim 16 of the present invention, the pulverized coal ratio is 170 kg / t-pig iron or more, and the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 35 vol% or more and less than 70 vol%. It is a blast furnace operating method of Claim 1 which is.

Moreover, the invention which concerns on Claim 17 among this invention is a blast furnace operating method of Claim 16 whose oxygen concentration of the gas which consists of the said carrier gas and combustion support gas is 40 vol% or more and 65 vol% or less.
Moreover, the invention which concerns on Claim 18 among this invention is a blast furnace operating method of Claim 17 whose oxygen concentration of the gas which consists of the said carrier gas and combustion support gas is 45 vol% or more and 60 vol% or less.

Moreover, the invention which concerns on Claim 19 among this invention is a blast furnace operating method of Claim 15 whose said pulverized coal ratio is 170 kg / t-pig iron or more and 300 kg / t-pig iron or less.
Moreover, the invention which concerns on Claim 20 among this invention is a blast furnace operating method of Claim 16 whose said pulverized coal ratio is 170 kg / t-pig iron or more and 300 kg / t-pig iron or less.
Moreover, the invention which concerns on Claim 21 among this invention is a blast furnace operating method of Claim 1 whose oxygen concentration of the gas which consists of the said carrier gas and combustion support gas is 35 vol% or more and less than 70 vol%.

The invention according to claim 22 of the present invention is the blast furnace operating method according to claim 21, wherein the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 40 vol% or more and 65 vol% or less.
Moreover, the invention which concerns on Claim 23 among this invention is a blast furnace operating method of Claim 22 whose oxygen concentration of the gas which consists of the said carrier gas and combustion support gas is 45 vol% or more and 60 vol% or less.

Moreover, the invention which concerns on Claim 24 among this invention is a blast furnace operating method of Claim 1 whose said pulverized coal ratio is 150 kg / t-pig iron or more and 300 kg / t-pig iron or less.
Moreover, the invention which concerns on Claim 25 among this invention is a blast furnace operating method of Claim 1 whose said pulverized coal ratio is 150 kg / t-pig iron or more and less than 170 kg / t-pig iron.
In the invention according to claim 26 of the present invention, the ratio of the pulverized coal is 150 kg / t-pig iron or more and less than 170 kg / t-pig iron, and the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is It is a blast furnace operating method of Claim 1 which is 35 vol or more and less than 70 vol%.

Moreover, the invention which concerns on Claim 27 among this invention is a claim which adds at least 1 out of the group which consists of a waste plastic, waste solid fuel, an organic resource, a waste material, and CDQ dust collection coke to the said pulverized coal. It is a blast furnace operating method as described in any one of 1-26.
Further, the invention according to claim 28 of the present invention uses the waste plastic, waste solid fuel, organic resources, waste material, CDQ dust collecting coke, wherein the ratio of the pulverized coal is 80 mass% or more. The blast furnace operating method described in 1.

Thus, according to the blast furnace operating method of the present invention, the lance for injecting fuel from the tuyere is a double pipe, pulverized coal is blown together with the carrier gas from the inner pipe of the double pipe lance, and the double pipe lance Of the gas consisting of the carrier gas and the combustion-supporting gas in the double-pipe lance. When the volatile content of pulverized coal is 25 mass% or less and the pulverized coal ratio is 150 kg / t-pig iron or higher, the combustion temperature can be increased. , Exhaust CO ₂ can be reduced. In addition, when the pulverized coal ratio is 170 kg / t-pig iron or more, the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas in the double-pipe lance is less than 70 vol%, so that The basic unit of the combustion-supporting gas can be suppressed.

In addition, by providing a plurality of notches at equal intervals in the circumferential direction of the tip of the inner pipe of the double pipe lance, diffusion of pulverized coal and combustion-supporting gas can be promoted, and combustion efficiency can be further improved.
In addition, by blowing a part of oxygen enriched in the blast from the outer pipe of the double pipe lance as a combustion-supporting gas, it is possible to avoid excessive supply of oxygen without impairing the gas balance in the blast furnace. it can.

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 only pulverized coal is blown in from the lance of FIG. It is explanatory drawing of the combustion mechanism of the pulverized coal of FIG. It is explanatory drawing of a combustion mechanism when pulverized coal and oxygen are blown. It is explanatory drawing of a combustion experiment apparatus. It is explanatory drawing of concentration of a pulverized coal flow. It is detail drawing of the blowing front-end | tip part of the lance of FIG. It is explanatory drawing of the pulverized coal flow of the lance which consists of a lance and a straight pipe of FIG. It is a graph which shows the relationship between the oxygen concentration in a lance supply gas, and a combustion rate when pulverized coal ratio is 150 kg / t-pig iron or more and less than 170 kg / t-pig iron. It is a graph which shows the relationship between the oxygen concentration in a lance supply gas when a pulverized coal ratio is 170 kg / t- pig iron or more, and a combustion rate. It is explanatory drawing of the shape of a notch when it sees from the radial direction of an inner side pipe | tube. It is explanatory drawing of angle (theta) which the front-end | tip center and notch center of a notch make. It is explanatory drawing of experiment of the contact area of oxygen and pulverized coal, and the dispersion width of pulverized coal. It is explanatory drawing of the contact area of oxygen and pulverized coal when the width | variety of a notch is changed, and the dispersion | distribution width | variety of pulverized coal. It is explanatory drawing of the contact area of oxygen and pulverized coal when the depth of a notch is changed, and the dispersion width of pulverized coal. It is explanatory drawing of the contact area of oxygen and pulverized coal when the number of notches is changed, and the dispersion width of pulverized coal. It is explanatory drawing of the contact area of oxygen and pulverized coal, and the dispersion | distribution width | variety of pulverized coal when the shape of a notch is a square and when it is a triangle, when the width of those notches is changed. It is explanatory drawing which shows the relationship between the exit flow velocity of a lance, and the lance surface temperature.

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 the reducing material is mainly combusted and gasified in this combustion space.

  FIG. 2 shows a combustion state when only pulverized coal 6 is blown from the lance 4 as a solid reducing material. The pulverized coal 6 that has passed through the tuyere 3 from the lance 4 and is blown into the raceway 5 is combusted with coke 7 and its volatile matter and fixed carbon, and the volatile matter is released and is generally called char. The aggregate of carbon and ash is discharged as unburned char 8 from the raceway. The hot air velocity at the tip of the tuyere 3 in the direction of blowing hot air is about 200 m / sec, and the oxygen existing area in the raceway 5 from the tip of the lance 4 is about 0.3 to 0.5 m. In addition, it is necessary to improve the temperature rise of the pulverized coal particles and the contact efficiency (dispersibility) with oxygen at a level of 1/1000 second.

  FIG. 3 shows a combustion mechanism when only pulverized coal (PC: Pulverized Coal in the figure) 6 is blown into the blow pipe 2 from the lance 4. The pulverized coal 6 blown into the raceway 5 from the tuyere 3 is heated by the radiant heat transfer from the flame in the raceway 5, and the temperature of the pulverized coal 6 is rapidly increased by the radiant heat transfer and conduction heat transfer. The thermal decomposition starts when the temperature is raised to 300 ° C. or more, and the volatile matter is ignited to form a flame. The combustion temperature reaches 1400 to 1700 ° C. When the volatile matter is released, the above-described char 8 is obtained. Since the char 8 is mainly fixed carbon, a reaction called a carbon dissolution reaction such as a solution loss reaction and a hydrogen gas shift reaction also occurs along with the combustion reaction.

  FIG. 4 shows a combustion mechanism in the case where oxygen 9 is blown as flammable gas together with pulverized coal 6 from the lance 4 into the blower pipe 2. The method of blowing pulverized coal 6 and oxygen 9 simply shows a case of blowing in parallel. In addition, the dashed-two dotted line in a figure has shown the combustion temperature at the time of injecting only the pulverized coal shown in FIG. 3 with reference. When pulverized coal and oxygen are injected at the same time, mixing of pulverized coal and oxygen is promoted in the vicinity of the lance, and combustion of the pulverized coal is considered to start earlier, thereby burning near the lance. The temperature rises further.

  Based on such knowledge, a combustion experiment was performed using the combustion experiment apparatus shown in FIG. Simulating the inside of the blast furnace, the experimental furnace 11 is filled with coke, and the inside of the raceway 15 can be observed from the viewing window. A lance 14 is inserted into the blower pipe 12 so that hot air generated in the combustion burner 13 can be blown into the experimental furnace 11 as a hot air to be blown from the hot blast furnace to the blast furnace. Moreover, in this ventilation pipe 12, it is also possible to adjust the oxygen enrichment amount of ventilation. The lance 14 can blow either one or both of pulverized coal and oxygen into the blower pipe 12. The exhaust gas generated in the experimental furnace 11 is separated into exhaust gas and dust by a separator 16 called a cyclone, the exhaust gas is fed to an exhaust gas treatment facility such as an auxiliary combustion furnace, and the dust is collected in a collection box 17.

The specifications of pulverized coal are 71.4% fixed carbon (FC), 19.5% volatile matter (VM), and 9.1% ash (Ash). The air blowing conditions were as follows: air temperature 1200 ° C., flow rate 300 Nm ³ / h, tuyere wind speed 130 m / s, oxygen enrichment 6% (oxygen concentration 27.0%, air oxygen concentration 21%, richness 6.0% ). As a pulverized coal blowing condition, a double pipe lance was used for the lance 14, pulverized coal was blown from the inner pipe of the double pipe lance, and oxygen was blown as a combustion supporting gas from the outer pipe of the double pipe lance. . The pulverized coal was blown together with the carrier gas, and nitrogen was used as the carrier gas for the pulverized coal. The solid-gas ratio between the pulverized coal and the carrier gas that conveys the pulverized coal is 10 to 25 kg / Nm ³ in the solid-gas ratio in the method of transporting the powder, that is, the pulverized coal with a small amount of gas (high concentration conveyance). In the method of transporting with gas (low concentration transport), the solid-gas ratio is 5 to 10 kg / Nm ³ . In addition to nitrogen, air can also be used as the carrier gas. Then, the pulverized coal ratio was variously changed between 100 kg / t-pig iron to 180 kg / t-pig iron, and an experiment was conducted particularly on the change in the pulverized coal flow. In addition, when injecting oxygen as a combustion-supporting gas, a part of oxygen enriched in ventilation was used so that the total amount of oxygen injected into the furnace did not change. Moreover, oxygen-enriched air can also be used as the combustion-supporting gas.

  Through this experiment, the present inventors further obtained the following knowledge. That is, when pulverized coal is blown from the inner pipe of the double pipe lance and combustion supporting gas, that is, oxygen is blown from the outer pipe, even if the volatile content of the pulverized coal is 25 mass% or less, the pulverized coal ratio is 150 kg / If it is a low pulverized coal ratio operation less than t-pig iron, combustion temperature will become high by raising oxygen concentration. However, in high pulverized coal ratio operation where the pulverized coal ratio is 150 kg / t-pig iron or more, the combustion temperature does not increase even if the oxygen concentration is increased. In the region where the pulverized coal ratio is 150 kg / t-pig iron or more, the combustion temperature is saturated at an oxygen concentration of about 35 vol%. This is because, as will be described later, the pulverized coal blown from the inner pipe of the double pipe lance concentrates (also referred to as concentration) in the central portion of the blow flow, and oxygen blown from the outer pipe of the double pipe lance. This is because it becomes difficult to contact or no longer contacts. Therefore, in the present invention, the pulverized coal is blown from the inner pipe of the double pipe lance and the combustion-supporting gas such as oxygen is blown from the outer pipe. A notch is provided to promote the diffusion of pulverized coal and combustion-supporting gas, making them easy to contact and improving the combustion temperature. However, on the other hand, even if a notch is provided at the inner tube blowing tip of the double tube lance, if the pulverized coal ratio is 170 kg / t-pig iron or more, the oxygen concentration of the entire lance becomes 70 vol% or more. After all, the combustion temperature is saturated and does not increase. In other words, even if the oxygen concentration is further increased, the combustion efficiency does not increase only by increasing the oxygen intensity. Note that when notches are provided in the inner pipe of the double-pipe lance, unlike when projecting projections such as baffle plates, troubles such as pulverized coal colliding with the projections and the projections being worn out can occur. Absent.

  FIG. 6a shows the pulverized coal flow in the low pulverized coal ratio operation state where the pulverized coal ratio is less than 150 kg / t-pig iron. In the experiment, since the shape of the lance is a straight pipe having a constant diameter, the dispersion width of the pulverized coal is almost constant. Thus, when the pulverized coal ratio is low, the pulverized coal flow has a substantially uniform concentration within the dispersion width. However, in the high pulverized coal ratio operation state where the pulverized coal ratio is 150 kg / t-pig iron or more, as shown in FIG. 6b, the central portion within the dispersion width is concentrated, and in particular, the pulverized coal ratio is 170 kg / t-pig iron or more. In the high pulverized coal ratio operation state, the central part of the pulverized coal flow is remarkably concentrated. Since oxygen is blown from the outer pipe of the double-pipe lance, the pulverized coal concentrated in the center of the pulverized coal flow does not come into contact with oxygen, but is brought into the furnace unburned to ventilate the blast furnace. make worse. Even if the amount of oxygen injection is increased to promote contact with oxygen, as shown in FIG. 6c, when the amount of oxygen injection exceeds a certain amount, pulverized coal is further increased in the center of the surrounding oxygen flow. Only the flow is concentrated, contact with oxygen is not substantially promoted, and the combustion temperature is saturated as described below.

  FIG. 7 shows the details of the blowing tip of the double tube lance 4 of this embodiment, FIG. 7a is a longitudinal sectional view, and FIG. 7b is an AA sectional view of FIG. 7a. Therefore, in the present embodiment, as shown in FIG. 7, a notch 23 is provided at the blowing tip of the inner pipe 21 of the double pipe lance 4, and the pulverized coal 6 and the combustion-supporting gas are provided through the notch 23. Oxygen 9 diffuses with each other, thereby creating a state of efficient contact between the two, thereby increasing the combustion temperature. For example, when the inner tube 21 has an inner diameter of about φ16 mm, the notches 23 have a rectangular cross section of about 5 mm × 5 mm, and four are provided at equal intervals of 90 degrees in the circumferential direction of the inner tube 21. The outer tube 22 was a straight tube. Note that the shape of the notch 23 is not limited to the above, but may be, for example, a triangular shape or a U-shape as described later, and the number of the notches 23 is also limited to the above. is not.

  When the notch 23 is provided at the blowing tip of the inner tube 21 of the double-pipe lance 4 in this way, as shown in FIG. 8a, the pulverized coal 6 and the oxygen 9 as the combustion-supporting gas are passed through the notch 23. Can diffuse and contact each other to increase the combustion temperature. On the other hand, in the conventional double pipe lance 4 in which there is no notch at the blowing tip of the inner pipe 21, as shown in FIG. 8b, the pulverized coal 6 is in the central part of the oxygen 9 which is a combustion-supporting gas. As a result, the amount of contact with oxygen 9 decreases and the combustion temperature is saturated. As described above, when the notch 23 is provided in the inner tube 21 of the double-pipe lance 4, unlike the case where a projection such as a baffle is projected, the pulverized coal collides with the projection and the projection. There is no trouble such as wear.

  FIG. 9 shows a pulverized coal ratio of 150 kg / t-pig iron, a volatile content of pulverized coal of 25 mass% or less, a constant blowing condition, a constant oxygen enrichment rate, and a notch 23 provided in the blowing tip of the inner pipe 21. The combustion temperature in the case of using the heavy pipe lance 4 and the case of using the double pipe lance 4 having no notch at the blowing tip of the inner pipe 21 is represented by a combustion rate. In either case, pulverized coal was blown from the inner pipe of the double pipe lance 4, and oxygen was blown from the outer pipe as a combustion-supporting gas. As is apparent from the figure, when the double pipe lance 4 without notches is used in the inner pipe 21, the oxygen concentration of the gas composed of the carrier gas for conveying the pulverized coal in the lance and the combustion-supporting gas. Is over 35 vol%, the combustion temperature will be saturated. That is, in the case of the double pipe lance 4 in which the inner pipe 21 is not cut, the combustion temperature does not increase even if the oxygen concentration is 35 vol% or more. On the other hand, when the double pipe lance 4 provided with the notch 23 in the inner pipe 21 is used, the combustion temperature becomes high even if the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 35 vol% or more. This means that the pulverized coal flow blown from the double pipe lance 4 is not concentrated in the region where the pulverized coal ratio is 150 kg / t-pig iron or more and less than 170 kg / t-pig iron.

  However, on the other hand, even when the double pipe lance 4 provided with the notch 23 in the inner pipe 21 is used, if the pulverized coal ratio is 170 kg / t-pig iron or more, as shown in FIG. When the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 70 vol% or more, the combustion temperature is saturated, and even if the oxygen concentration is increased further, the combustion temperature does not increase. In other words, in the region where the pulverized coal ratio is 170 kg / t-pig iron or more, the combustion efficiency is good only by increasing the oxygen consumption rate when the oxygen concentration of the carrier gas and the combustion-supporting gas in the lance is 70 vol% or more. Don't be. Therefore, even when using the double pipe lance 4 provided with the notch 23 in the inner pipe 21, the pulverized coal ratio is 150 kg / t-pig iron or more and less than 170 kg / t-pig iron, or the pulverized coal ratio is 170 kg / t. -In the case of pig iron, the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 35 vol% or more and less than 70 vol%, preferably 40 vol% or more and 65 vol% or less, more preferably 45 vol% or more and 60 vol% or less. The upper limit of the pulverized coal ratio is 300 kg / t-pig iron or less, preferably 250 kg / t-pig iron or less.

  The shape of the notch 23 when viewed from the radial direction of the inner tube 21 is a quadrangle as shown in FIG. 11a, a triangle as shown in FIG. 11b, a U-shape as shown in FIG. The size is simply expressed by the width of the opening of the notch 21 and the depth from the opening of the notch 21 to the bottom. Further, the angle θ formed by the center of the notch 23 and the center of the lower end, specifically, the angle θ formed by the line connecting the center of the opening and the center of the bottom of the notch 23 and the string connecting the opening is shown in FIG. As shown, it is preferably 30 to 90 °. Experiments were conducted on the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal when the shape of the notch, particularly the size, was changed in various ways. As shown in FIG. 13, the experiment was conducted by letting smoke flow from the inner and outer pipes of the double-pipe lance, that is, the pulverized coal flow path and the oxygen flow path, respectively. The area where the smoke overlapped was calculated by image analysis as the contact area of oxygen and pulverized coal, and the dispersion width of the pulverized coal was determined from the spread angle of the smoke emitted from the pulverized coal flow path. The experiment was mainly performed on a rectangular cutout when viewed from the radial direction of the inner tube.

  First, FIG. 14 shows the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal when the width of the notch is variously changed. The width of the notch is expressed as the ratio of the total width of all the notches to the inner circumference of the inner pipe.The contact area of oxygen and pulverized coal and the dispersion width of the pulverized coal are the same for the inner pipe without notches. Expressed as a ratio when used. As is apparent from the figure, when the width of the notch is increased, the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal increase, but the dispersion width of pulverized coal tends to decrease from a certain point. This is because, when the width of the notch is increased, the mixing of oxygen and pulverized coal improves, but when the width of the notch is too large, oxygen flows into the radial inner side of the double-pipe lance and suppresses the dispersion of pulverized coal. It is thought that this is because Therefore, the width of the notch is preferably more than 0 and not more than 0.5, more preferably not less than 0.05 and not more than 0.3, as a ratio of the total width of all notches to the outer circumference of the inner tube. More preferably, it is 0.1 or more and 0.2 or less.

  FIG. 15 shows the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal when the depth of the notch is variously changed. The depth of the notch is represented by the dimension of the depth itself, and the contact area between oxygen and pulverized coal and the dispersion width of the pulverized coal are represented by the ratio when an inner pipe without a notch is used. As is clear from the figure, when the depth of the notch is increased, the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal increase, but the dispersion width of pulverized coal tends to decrease from a certain point. This is because if the depth of the notch is increased, the mixing of oxygen and pulverized coal will be improved, but if the depth of the notch is too large, the flow at the tip of the lance will be stabilized, and dispersion of pulverized coal will be suppressed. It is thought that this is because Therefore, the depth of the notch exceeds 0 in dimension and is preferably 12 mm or less, more preferably 2 mm or more and 10 mm or less, and further preferably 3 mm or more and 7 mm or less.

  FIG. 16 shows the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal when the number of notches is variously changed. The number of notches was represented by the ratio of the number of notches to the maximum number of notches, and the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal were represented by the ratio when an inner pipe without notches was used. The maximum number of notches is an integer part obtained by dividing the inner peripheral length of the inner tube by the width of the notch, and specifically, how many notches of a predetermined width can be formed at the maximum in the inner tube. It represents. As is clear from the figure, when the number of notches is increased, the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal increase, but the dispersion width of pulverized coal tends to decrease from a certain point. This is because if the number of notches is increased, the mixing of oxygen and pulverized coal and the dispersibility of pulverized coal will be improved, but if the number of notches is too large, the proportion of oxygen flowing into the inner pipe will increase and the pulverized coal will increase. This is thought to be due to the suppression of dispersion. Therefore, the number of notches is preferably more than 0 and not more than 0.8 in the ratio of the number of notches to the maximum number of notches, more preferably not less than 0.1 and not more than 0.6, still more preferably. It shall be 0.2 or more and 0.5 or less.

  FIG. 17 shows the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal when the notch shape is a square and a triangle, and the widths of the notches are variously changed. FIG. 17 is obtained by overwriting the above-described FIG. 14 with the experimental result of the triangular notch. The width of the notch is expressed as the ratio of the total width of all the notches to the inner circumference of the inner pipe.The contact area of oxygen and pulverized coal and the dispersion width of the pulverized coal are the same for the inner pipe without notches. Expressed as a ratio when used. As is clear from the figure, whether the shape of the notch is square or triangular, increasing the width of the notch increases the contact area between oxygen and pulverized coal and the dispersion width of pulverized coal. The distribution width of charcoal tends to decrease. The reason for this is that even when the shape of the notch is a triangle, if the width of the notch is increased, the mixing of oxygen and pulverized coal is improved, but the width of the notch is too large. This is considered to be because oxygen flows into the radial inner side of the double-pipe lance and dispersion of pulverized coal is suppressed. Therefore, the width of the notch is preferably greater than 0 and less than or equal to 0.5, more preferably 0, as a ratio of the total width of all the notches with respect to the outer periphery of the inner pipe, regardless of the shape of the notch itself. .05 or more and 0.3 or less, more preferably 0.1 or more and 0.2 or less.

  By the way, as the combustion temperature rises as described above, the outer tube of the double tube lance is easily exposed to high temperature. The lance is composed of, for example, a stainless steel pipe. Although there is an example where water cooling called a so-called water jacket is performed outside the lance, the tip of the lance cannot be covered. In particular, it has been found that the tip of the outer tube of the double tube lance that is not subject to water cooling is easily deformed by heat. If the lance is deformed, that is, bent, gas or pulverized coal cannot be blown into a desired part, and there is a problem in replacing the lance that is a consumable item. In addition, the flow of pulverized coal may change and hit the tuyere, and in such a case, the tuyere may be damaged. Also, if the outer pipe of the double pipe lance is bent, the gap with the inner pipe is closed, and if the gas does not flow from the outer pipe, the outer pipe of the double pipe lance is melted, and in some cases, the blower pipe is damaged. There is a possibility. If the lance is deformed or worn out, the combustion temperature as described above cannot be secured, and as a result, the reducing material basic unit cannot be reduced.

  The only way to cool the outer tube of a double-pipe lance that cannot be cooled with water is by cooling with the gas flowing inside. When heat is radiated to the gas flowing inside to cool the outer tube itself of the double tube lance, for example, the gas flow rate is considered to affect the lance temperature. Therefore, the inventors measured the temperature of the lance surface by variously changing the flow rate of the gas blown from the outer pipe of the double pipe lance. The experiment was performed by blowing oxygen from the outer pipe of the double pipe lance and blowing pulverized coal from the inner pipe, and the gas flow rate was adjusted by adjusting the amount of oxygen supplied from the outer pipe. The oxygen may be oxygen-enriched air, and 2% or more, preferably 10% or more of oxygen-enriched air is used. By using oxygen-enriched air, flammability of pulverized coal is improved in addition to cooling. The measurement results are shown in FIG.

  A steel pipe called 20A schedule 5S was used for the outer pipe of the double pipe lance. In addition, a steel pipe called 15A schedule 90 was used as the inner pipe of the double pipe lance, and the total flow rate of oxygen and nitrogen blown from the outer pipe was variously changed to measure the temperature of the lance surface. Incidentally, “15A” and “20A” are nominal dimensions of the steel pipe outer diameter defined in JIS G 3459, 15A has an outer diameter of 21.7 mm, and 20A has an outer diameter of 27.2 mm. The “schedule” is a nominal dimension of the thickness of the steel pipe specified in JIS G 3459. The 20A schedule 5S is 1.65 mm, and the 15A schedule 90 is 3.70 mm. In addition to stainless steel pipes, plain steel can also be used. In this case, the outer diameter of the steel pipe is specified in JIS G 3453, and the wall thickness is specified in JIS G 3454.

  As indicated by a two-dot chain line in the figure, the temperature of the lance surface decreases inversely with the increase in the flow velocity of the gas blown from the outer pipe of the double pipe lance. When using a steel pipe for a double pipe lance, when the surface temperature of a double pipe lance exceeds 880 degreeC, creep deformation will occur and a double pipe lance will bend. Therefore, when the steel pipe of 20A schedule 5S is used for the outer pipe of the double pipe lance and the surface temperature of the double pipe lance is 880 ° C. or less, the outlet flow velocity of the outer pipe of the double pipe lance is 20 m / sec or more. . And when the exit flow velocity of the outer pipe of the double pipe lance is 20 m / sec or more, the double pipe lance is not deformed or bent. On the other hand, if the outlet flow velocity of the outer pipe of the double pipe lance exceeds 120 m / sec, it is not practical in terms of the operating cost of the equipment, so the upper limit of the outlet flow velocity of the outer pipe of the double pipe lance is 120 m / sec. did. Incidentally, since the single tube lance has a smaller thermal load than the double tube lance, the outlet flow velocity may be set to 20 m / sec or more as necessary.

  In the said embodiment, although the average particle diameter of pulverized coal is used with 10-100 micrometers, when ensuring combustibility and considering the supply property to a lance and supply to a lance, when it is preferably 20-50 micrometers Good. If the average particle size of the pulverized coal is less than 20 μm, the combustibility is excellent, but the lance is easily clogged during pulverized coal transportation (gas transportation), and if it exceeds 50 μm, the pulverized coal combustibility may be deteriorated.

In addition to coal having a volatile content of 25 mass% or less, anthracite coal may be used as the solid reducing material that can be used as pulverized coal blown from the inner tube of the double tube lance. Anthracite has a volatile content of 3-5 mass%. Therefore, in this invention, the pulverized coal to be used is expressed as pulverized coal having an volatile content of 3 mass% or more and 25 mass% or less including anthracite coal.
Further, as the solid reducing material to be blown in, pulverized coal is mainly used, and waste plastic, waste solid fuel (RDF), organic resources (biomass), waste material, and CDQ dust collecting coke may be used therein. CDQ dust collection coke is coke powder collected by a dry fire extinguisher (CDQ). In use, the ratio of pulverized coal to the all-solid reducing material is preferably 80 mass% or more. In other words, pulverized coal and waste plastics, waste solid fuel (RDF), organic resources (biomass), waste materials, CDQ dust collection coke, etc. have different amounts of heat due to the reaction. It tends to occur and the operation becomes unstable. Compared with pulverized coal, waste plastics, solid waste fuel (RDF), organic resources (biomass), waste materials, etc. have a lower calorific value due to the combustion reaction. Since the substitution efficiency for the solid reducing material is reduced, and the CDQ dust collection coke has a high calorific value, it is difficult to ignite because there is no volatile matter, and the substitution efficiency is reduced, so the proportion of pulverized coal is 80 mass% or more It is preferable that

Waste plastics, solid waste fuel (RDF), organic resources (biomass), and waste materials can be used with pulverized coal as fine particles of 6 mm or less, preferably 3 mm or less. The CDQ dust collecting coke can be used as it is. The ratio with pulverized coal can be mixed by merging with pulverized coal fed by carrier gas. You may mix and use beforehand with pulverized coal.
Thus, in the blast furnace operating method of the present embodiment, the lance 4 for injecting fuel from the tuyere 3 is a double pipe, pulverized coal is injected from the inner pipe 21 of the double pipe lance 4, and the double pipe lance is used. 4, oxygen (flammable gas) is blown from the outer pipe 22, a notch 23 is provided at the blowing tip of the inner pipe 21 of the double pipe lance 4, and a carrier gas and a flammable gas for conveying pulverized coal. By setting the oxygen concentration of the gas consisting of 35 vol% or more to a high pulverized coal ratio operation in which the volatile content of pulverized coal is 25 mass% or less and the pulverized coal ratio is 150 kg / t-pig iron or more As a result, emission CO ₂ can be reduced. In addition, when the pulverized coal ratio is 170 kg / t-pig iron or more, the oxygen concentration is suppressed by setting the oxygen concentration of the gas composed of the carrier gas for conveying the pulverized coal and the combustion-supporting gas to less than 70 vol%. can do.

Further, by providing a plurality of notches 23 at equal intervals in the circumferential direction of the distal end of the inner pipe 21 of the double pipe lance 4, the diffusion of pulverized coal and combustion-supporting gas is promoted, and the combustion efficiency is further improved. Can do.
In addition, by blowing a part of oxygen enriched in blowing air (as a combustion-supporting gas) from the outer tube 22 of the double tube lance 4, the oxygen balance can be excessively supplied without impairing the gas balance in the blast furnace. This can be avoided and the basic unit of oxygen used can be reduced.

1 is a blast furnace 2 is a blower tube 3 is a tuyere 4 is a lance 5 is a raceway 6 is pulverized coal 7 is coke 8 is char 9 is oxygen 21 is an inner tube 22 is an outer tube 23 is notched

Claims (28)

Prepare pulverized coal with a volatile content of 25 mass% or less,
Preparing a double pipe lance with an inner pipe and an outer pipe for injecting pulverized coal and supporting gas from the tuyere,
Hot air is blown from the tuyere,
A plurality of notches recessed in the axial direction are provided in the circumferential direction in the blowing tip of the inner tube of the double tube lance,
Blowing the pulverized coal with a carrier gas at a pulverized coal ratio of 150 kg / t-pig iron or more from the inner pipe,
Blowing inflammable gas from the outer pipe of the double pipe lance,
The oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 35 vol% or more,
Blast furnace operation method.   The blast furnace operating method according to claim 1, wherein the notches are provided at equal intervals in the circumferential direction of the tip of the inner tube of the double tube lance.   The blast furnace according to claim 2, wherein the width of the notch is greater than 0 and less than or equal to 0.5 in the ratio of the total width of all the notches to the inner circumference of the inner tube of the double pipe lance. Operation method.   The width of the notch is 0.05 or more and 0.3 or less as a ratio of the total width of all the notches to the inner peripheral length of the inner pipe of the double pipe lance. Blast furnace operation method.   The width of the notch is 0.1 or more and 0.2 or less as a ratio of the total width of all the notches to the inner circumference of the inner pipe of the double pipe lance. Blast furnace operation method.   The blast furnace operating method according to claim 2, wherein the depth of the notch is greater than 0 mm and not greater than 12 mm.   The blast furnace operating method according to claim 6, wherein a depth of the notch is 2 mm or more and 10 mm or less.   The blast furnace operating method according to claim 7, wherein a depth of the notch is 3 mm or more and 7 mm or less.   When the integral part when the inner peripheral length of the inner tube of the double pipe lance is divided by the width of one notch is the maximum number of notches, the number of notches is the number of notches with respect to the maximum number of notches. The blast furnace operating method according to claim 2, wherein the ratio is more than 0 and 0.8 or less.   The blast furnace operating method according to claim 9, wherein the number of notches is 0.1 to 0.6 in terms of a ratio of the number of notches to the maximum number of notches.   The blast furnace operating method according to claim 10, wherein the number of notches is 0.2 to 0.5 in terms of the ratio of the number of notches to the maximum number of notches.   The blast furnace operating method according to claim 1, wherein the combustion-supporting gas is oxygen, and a part of oxygen enriched in blowing is blown from an outer pipe of the double pipe lance.   The blast furnace operating method according to claim 1, wherein the pulverized coal has a volatile content of 3 mass% or more and 25 mass% or less.   The blast furnace operating method according to claim 1, wherein the combustion-supporting gas blown from the outer pipe of the double pipe lance has an outlet flow velocity of 20 to 120 m / sec.   The blast furnace operating method according to claim 1, wherein the pulverized coal ratio is 170 kg / t-pig iron or more. The pulverized coal ratio is 170 kg / t-pig iron or more,
The oxygen concentration of the gas consisting of the carrier gas and the combustion-supporting gas is 35 vol% or more and less than 70 vol%,
The blast furnace operating method according to claim 1.   The blast furnace operating method according to claim 16, wherein the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 40 vol% or more and 65 vol% or less.   The blast furnace operating method according to claim 17, wherein the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 45 vol% or more and 60 vol% or less.   The blast furnace operating method according to claim 15, wherein the pulverized coal ratio is 170 kg / t-pig iron or more and 300 kg / t-pig iron or less.   The blast furnace operating method according to claim 16, wherein the pulverized coal ratio is 170 kg / t-pig iron or more and 300 kg / t-pig iron or less.   The blast furnace operating method according to claim 1, wherein the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is not less than 35 vol% and less than 70 vol%.   The method for operating a blast furnace according to claim 21, wherein the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 40 vol% or more and 65 vol% or less.   The blast furnace operating method according to claim 22, wherein the oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 45 vol% or more and 60 vol% or less.   The blast furnace operating method according to claim 1, wherein the pulverized coal ratio is 150 kg / t-pig iron or more and 300 kg / t-pig iron or less.   The blast furnace operating method according to claim 1, wherein the pulverized coal ratio is 150 kg / t-pig iron or more and less than 170 kg / t-pig iron. The pulverized coal ratio is 150 kg / t-pig iron or more and less than 170 kg / t-pig iron,
The oxygen concentration of the gas composed of the carrier gas and the combustion-supporting gas is 35 vol. Or more and less than 70 vol.%.
The blast furnace operating method according to claim 1.   The blast furnace operating method according to any one of claims 1 to 26, wherein at least one of a group consisting of waste plastic, solid waste fuel, organic resources, waste material, and CDQ dust collection coke is added to the pulverized coal. .   The blast furnace operating method according to claim 27, wherein the ratio of the pulverized coal is 80 mass% or more, and the waste plastic, waste solid fuel, organic resource, waste material, and CDQ dust collection coke are used.

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