JP2011168884A - Method for operating blast furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a blast furnace which attains more improvement of combustion temperature and the decrease of consumption unit of a reducing material. <P>SOLUTION: LNG (Liquefied natural gas) 9 and fine powdery coal 6, are mixed and the mixture fuel is blown from a single-tube lance 4 to a tuyere 3, thereby the fine powdery coal 6 is explosively diffused by precedingly burning with the LNG 9 and at the same time, the temperature of the fine powdery coal 6 is drastically raised with the combustion heat of the LNG 9 and thereby, the combustion temperature is drastically improved by rasing the heating speed of the fine powdery coal 6 and then, the consumption unit of the reducing material can be decreased. Further, by setting the total flowing amount of the gas blown from the single-tube lance 4 to be ≥135 Nm<SP>3</SP>/h and the outlet flowing speed of the blowing gas in the single-tube lance 4 to be ≥20 m/sec, the deformation due to the heat of the single-tube lance 4 can be prevented. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  In the present invention, solid fuel such as pulverized coal and flammable fuel such as LNG (Liquefied Natural Gas) are injected from the blast furnace tuyere and the combustion temperature is increased to improve and reduce productivity. The present invention relates to a method for operating a blast furnace to reduce the basic unit of material.

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. In response to this, in recent blast furnace operations, the ratio of low reducing agent (low RAR: Abbreviation for Reduction Agent Ratio) is the sum of the reducing material injected from the tuyere and the coke charged from the top of the furnace per 1 ton of pig iron. Volume) Operation is being strongly promoted. The blast furnace mainly uses coke and pulverized coal blown from the tuyere as a reducing material, and in order to achieve a low reducing material ratio and, in turn, carbon dioxide emission control, coke etc. is used as waste plastic, LNG, heavy oil, etc. It is effective to replace with a reducing material having a high hydrogen content. In the following Patent Document 1, it is proposed that a lance that blows fuel from the tuyere is a double pipe, LNG is blown from the inner pipe of the double pipe lance, and pulverized coal is blown from the outer pipe of the double pipe lance. ing. Also, in Patent Document 2 below, a lance that blows fuel from the tuyere is a double pipe, pulverized coal is blown from the inner pipe of the double pipe lance, and LNG is blown from the outer pipe of the double pipe lance. Has been proposed.

Japanese Patent No. 3176680 Japanese Patent Publication No. 1-289847

The blast furnace operating method described in Patent Document 1 and the blast furnace operating method described in Patent Document 2 are both improved in combustion temperature and reduced raw material compared to the conventional method of blowing only pulverized coal from the tuyere. Although effective in reducing units, there is room for further improvement.
The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a blast furnace operating method capable of further improving the combustion temperature and reducing the reducing material basic unit. It is.

In order to solve the above problems, the blast furnace operating method of the present invention is characterized in that a flammable fuel and a solid fuel are mixed and the mixed fuel is blown into a tuyere from a single tube lance.
The total flow rate of the gas blown from the single pipe lance is set to 135 Nm ³ / h or more, and the outlet flow velocity of the single pipe lance is set to 20 m / sec or more.
Further, the solid fuel is pulverized coal.
The flammable fuel is LNG.

Thus, according to the blast furnace operating method of the present invention, the solid fuel explosively diffuses by burning the flammable fuel first, and at the same time, the temperature of the solid fuel is greatly increased by the combustion heat of the flammable fuel. As a result, the heating rate of the solid fuel is increased, and the combustion temperature is greatly improved, so that the reducing material basic unit can be reduced.
In addition, the total flow rate of the gas blown from the single pipe lance is set to 135 Nm ³ / h or more, and the outlet flow velocity of the single pipe lance is set to 20 m / sec or more to prevent the deformation of the single pipe lance due to the temperature rise. Can do.

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 LNG are blown. It is explanatory drawing of a combustion experiment apparatus. It is explanatory drawing of a combustion experiment result. It is explanatory drawing of the combustion temperature of a combustion experiment result. It is explanatory drawing which shows the relationship between the flow volume of the gas inject | poured from a lance, and a 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. The pulverized coal 6 that passes through the tuyere 3 from the lance 4 and is blown into the raceway 5, together with the coke 7, combusts its volatile matter and fixed carbon, and remains unburned, generally called char. The aggregate of ash is discharged as unburned char 8 from the raceway. The hot air velocity in the hot air blowing direction ahead of the tuyere 3 is about 200 m / sec, and the existence area of O ₂ in the raceway 5 from the tip of the lance 4 is about 0.3 to 0.5 m. In particular, it is necessary to improve the temperature rise of pulverized coal particles and the contact efficiency (dispersibility) with O ₂ 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 occurs along with a combustion reaction.

  FIG. 4 shows a combustion mechanism when LNG 9 is blown together with pulverized coal 6 from the lance 4 into the blower pipe 2. The method of blowing pulverized coal 6 and LNG 9 shows a case where the pulverized coal 6 is simply blown 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. In this way, when pulverized coal and LNG are injected simultaneously, the gas gas LNG is preferentially combusted, and it is considered that the pulverized coal is rapidly heated and heated by this combustion heat. Will rise further.

  Based on such knowledge, a combustion experiment was performed using the combustion experiment apparatus shown in FIG. 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 tube 12, and hot air generated in the combustion burner 13 can be blown into the experimental furnace 11 with a predetermined blowing amount. 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 LNG 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.

  In the combustion experiment, two types of lances 14 are used: a single-pipe lance and a double-pipe lance. If only pulverized coal is blown in using a single-pipe lance, a double-pipe lance is used. When pulverized coal is blown from the pipe and LNG is blown from the outer pipe of the double pipe lance, LNG is blown from the inner pipe of the double pipe lance and pulverized coal is blown from the outer pipe of the double pipe lance. For each case, the combustion temperature, combustion position, unburned char combustion status, and diffusivity were measured from a viewing window using a two-color thermometer. As is well known, a two-color thermometer is a radiation thermometer that measures temperature using thermal radiation (electromagnetic wave movement from a high-temperature object to a low-temperature object). Paying attention to the shift, it is one of the wavelength distribution types to obtain the temperature by measuring the temperature change of the wavelength distribution, and in particular to measure the wavelength distribution, the radiant energy at two wavelengths is measured and the ratio The temperature is measured from The combustion state of the unburned char is determined by collecting unburned char with a probe at a position of 100 mm and 150 mm from the tip of the lance 14 in the blast pipe 12 of the experimental furnace 11, filling the resin, polishing, and then analyzing the void in the char by image analysis. The rate was measured and judged.

The specifications of the pulverized coal are 77.8% fixed carbon (FC), 13.6% volatile matter (VM), 8.6% ash (Ash), and the blowing condition is 29.8 kg. / H (equivalent to 100 kg / t in ironmaking base unit). The LNG blowing conditions were 3.6 kg / h (5 Nm ³ / h, equivalent to 10 kg / t in the ironmaking base unit). The blowing conditions are: blowing temperature 1200 ° C., flow rate 300 Nm ³ / h, flow rate 70 m / s, O ₂ enrichment +5.5 (oxygen concentration 26.5%, oxygen concentration 21% in air, richness 5.5% ). The evaluation of the experimental results is based on the combustion temperature, combustion position, unburned char combustion status and diffusibility (mainly pulverized coal) when only pulverized coal is blown from a single pipe, and from the inner pipe of the double pipe lance. When pulverized coal was blown and LNG was blown from the outer pipe, each of the cases where LNG was blown from the inner pipe of the double pipe lance and pulverized coal was blown from the outer pipe was evaluated. The evaluation was represented by Δ when the degree was the same as that of pulverized coal alone, ◯ when it was slightly improved, and ◎ when it was greatly improved.

FIG. 6 shows the result of the above-described combustion experiment (corresponding to the upper three stages). As is clear from the figure, when pulverized coal was blown from the inner pipe of the double pipe lance and LNG was blown from the outer pipe, the combustion position was improved, but other items were changed. Is not seen. This is because the LNG outside the pulverized coal first contacts O ₂ and burns quickly, and although the heating speed of the pulverized coal is increased by the combustion heat, O ₂ is consumed in the combustion of LNG, and the pulverized coal It is considered that O ₂ necessary for the combustion of charcoal has decreased, the combustion temperature has not increased sufficiently, and the combustion state of unburned char has not been improved. On the other hand, when LNG is blown from the inner pipe of the double pipe lance and pulverized coal is blown from the outer pipe, the combustion temperature and the combustion state of unburned char are improved, and the diffusivity is greatly improved. Although it was observed, there was no change in the combustion position. Although it took time to diffuse O ₂ to the inner LNG through the outer pulverized coal region, if the inner flammable LNG burns, explosive diffusion occurs, and the LNG combustion heat It is considered that the pulverized coal is heated and the combustion temperature rises, and the combustion state of the unburned char is improved.

  Based on the results of this experiment, the inventor of the present application paid attention to using a single pipe lance as a lance, mixing LNG and pulverized coal in advance, and blowing this mixed fuel from the single pipe lance. That is, LNG and pulverized coal coexisting with each other is not the cause of the improvement, or if LNG is dispersed, LNG burns first in a wide range, and pulverized coal spreads over a wide range accordingly. It is presumed that the gas is diffused and heated by the combustion heat of LNG, the combustion position approaches the lance, the combustion temperature rises, and the combustion state of the unburned char is also improved. Therefore, using the above-described combustion experiment apparatus, LNG and pulverized coal were mixed in advance, and the mixed fuel was blown from a single pipe lance for experiments.

  The experimental results are shown in the lowermost part of FIG. Moreover, the relationship between the combustion position and combustion temperature of all the experiments is shown in FIG. As is clear from these figures, when LNG and pulverized coal are mixed in advance and the mixed fuel is blown from a single pipe lance, the combustion temperature, the combustion position, and the combustion status of the unburned char are three points. Significant improvement was seen. In terms of diffusivity, LNG was blown from the inner pipe of the double pipe lance, and the method of blowing pulverized coal from the outer pipe of the double pipe lance was greatly improved, so the mixed fuel injection was slightly improved. Although the evaluation was limited to this, a substantial diffusion effect was seen, and the overall evaluation was greatly improved.

  By the way, as the combustion temperature rises as described above, the single tube lance is easily exposed to high temperatures. The single pipe lance is made of, for example, a stainless steel pipe. Of course, the single-tube lance is water-cooled called a so-called water jacket, but the tip of the lance cannot be covered. In particular, it has been found that the tip of the single tube lance that is not subject to water cooling is deformed by heat. If the single-pipe lance is deformed, that is, bent, pulverized coal or LNG cannot be blown into a desired portion, and there is a problem in replacement work of 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.

The only way to cool a single-pipe lance that cannot be cooled with water is to dissipate heat with the gas supplied inside. When the single pipe lance itself is cooled by releasing heat to the gas flowing inside, it is considered that the gas flow rate affects the lance temperature. Therefore, the inventors measured the temperature of the lance surface by changing the flow rate of the gas blown from the single tube lance in various ways. The measurement results are shown in FIG.
The single pipe lance uses a steel pipe called 15A schedule 90 and a steel pipe called 20A schedule 90, and the total flow rate of carrier gas (N ₂ ) and LNG for conveying pulverized coal is variously changed. The temperature of the lance surface was measured. 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. “Schedule” is a nominal dimension of the thickness of the steel pipe defined in JIS G 3459. The 15A schedule 90 has a thickness of 3.70 mm, and the 20A schedule 90 has a thickness of 3.90 mm. When a steel pipe is used for a single pipe lance, it is realistic to use a steel pipe having the above-described two types of outer diameters. It is also possible to use a 25A schedule 90 (outer diameter: 34 mm, wall thickness: 4.50 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 in inverse proportion to the increase in the total flow rate of the gas blown from the single pipe lance for each steel pipe having a different size. This is because if the steel pipe size is different, the gas flow rate is different even at the same total gas flow rate. When using a steel pipe for a single pipe lance, if the surface temperature of the single pipe lance exceeds 880 ° C., creep deformation occurs and the single pipe lance is bent. Therefore, when a 15A schedule 90 or 20A schedule 90 steel pipe is used for the single pipe lance, and the surface temperature of the single pipe lance is 880 ° C. or less, the total flow rate of the blown gas is 135 Nm ³ / h or more. When the steel pipe is used, the outlet flow velocity of the single pipe lance is 20 m / sec or more. When the total flow rate of the single tube lance blowing gas is set to 135 Nm ³ / h or more and the outlet flow velocity of the single tube lance is 20 m / sec or more, the single tube lance is not deformed or bent.

  Thus, in the blast furnace operating method of this embodiment, LNG (flammable fuel) 9 and pulverized coal (solid fuel) 6 are mixed and the mixed fuel is blown into the tuyere 3 from the single tube lance 4. Thus, the pulverized coal (solid fuel) 6 is explosively diffused by burning the LNG (flammable fuel) 9 first, and at the same time, the pulverized coal (solid fuel) is heated by the combustion heat of the LNG (flammable fuel) 9. As a result, the heating speed of the pulverized coal (solid fuel) 6 is increased, the combustion temperature is significantly improved, and the reducing material basic unit can be reduced.

Moreover, the total flow rate of the gas blown from the single pipe lance 4 is set to 135 Nm ³ / h or more, and the outlet flow velocity of the single pipe lance 4 is set to 20 m / sec or more to prevent deformation of the single pipe lance due to temperature rise. can do.

  1 is a blast furnace, 2 is a blow pipe, 3 is a tuyere, 4 is a lance, 5 is a raceway, 6 is pulverized coal (solid fuel), 7 is coke, 8 is char, 9 is LNG (flammable fuel)

Claims (4)

  A method of operating a blast furnace, characterized in that a flammable fuel and a solid fuel are mixed and the mixed fuel is blown into a tuyere from a single tube lance. 2. The blast furnace operating method according to claim 1, wherein a total flow rate of the gas blown from the single pipe lance is set to 135 Nm ³ / h or more, and an outlet flow velocity of the single pipe lance is set to 20 m / sec or more.   The blast furnace operating method according to claim 1, wherein the solid fuel is pulverized coal.   The blast furnace operating method according to claim 1, wherein the flammable fuel is LNG.

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