JP2011168886A - Blast furnace operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blast furnace operation method which achieves a further elevation in combustion temperature and reduction in unit-consumption of reducing material. <P>SOLUTION: A lance 4 for blowing fuel from a tuyere 3 is formed as a double tube, dust coal 6 is blown from the inside tube of the double tube lance 4, also LNG (liquefied Natural Gas) 9 is blown from the outside tube of the double tube lance 4, and an oxygen excess ratio in the blast into the tuyere 3 is set to be 0.7-1.3, thereby LNG 9 at the inside of the dust coal 6 combusts first, so that the dust coal 6 is explosively diffused and at the same time the temperature of the dust coal 6 is considerably elevated by the combustion heat of the LNG 9, which increases the heating speed of the dust coal, at this time, the oxygen excess ratio of the blast into the tuyere 3 is set to be 0.7-1.3, which sufficiently combusts the fine powdery coal 6, consequently the heating temperature is considerably elevated resulting in reduction in unit-consumption of reducing material. <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 uses a double pipe as a lance for injecting fuel from a tuyere, and injects a flammable fuel from an inner pipe of the double pipe lance. Solid fuel is blown from the outer pipe of the pipe lance, and the oxygen excess rate of the blown air to the tuyere is set to 0.7 to 1.3.
The total flow rate of the gas blown from the outer pipe of the double pipe lance is 85 Nm ³ / h or more, and the outlet flow velocity of the outer pipe is 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 flammable fuel inside the solid fuel burns first, so that the solid fuel explosively diffuses, and at the same time, the solid fuel is burned by the combustion heat of the flammable fuel. The heating speed of the solid fuel is thereby increased, and at this time, the excess oxidation ratio of the air blown to the tuyere is set to 0.7 to 1.3, so that the solid fuel is sufficiently obtained. As a result, the combustion temperature is greatly improved, and the reducing material intensity can be reduced.

Moreover, the total flow rate of the gas blown from the outer pipe of the double pipe lance is set to 85 Nm ³ / h or more, and the outlet flow velocity of the outer pipe is set to 20 m / sec or more. Can be prevented.

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 when changing an oxygen excess rate. It is explanatory drawing which shows the relationship between the flow volume of the gas injected from the outer side pipe | tube of a double pipe | tube lance, and 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 at the same time, LNG, which is a gas gas, is preferentially combusted, and it is considered that the pulverized coal is rapidly heated and raised in temperature by this combustion heat. The temperature rises 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 150 mm and 300 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 combustion experiment described above. 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 studied to further increase the combustion temperature when LNG was blown from the inner pipe of the double pipe lance and pulverized coal was blown from the outer pipe. We focused on oxygen enrichment, that is, oxygen excess. That is, as in the case where the pulverized coal is blown from the inner pipe of the double pipe lance and the LNG is blown from the outer pipe, the O ₂ necessary for the combustion of the pulverized coal is insufficient after the LNG combustion. This is an inference. Therefore, using the above-described combustion experimental device, LNG is blown from the inner pipe of the double pipe lance and pulverized coal is blown from the outer pipe, and the oxygen temperature is changed in various ways to measure the combustion temperature and the combustion position. It was. In this case, the oxygen excess rate is a value obtained by dividing the amount of oxygen being blown by the amount of oxygen necessary for the complete combustion of the pulverized coal.

  The experimental results are shown in FIG. As is clear from the figure, when LNG is blown from the inner pipe of the double pipe lance and pulverized coal is blown from the outer pipe, compared with the case of blowing only pulverized coal by the single pipe lance, oxygen If the excess rate is 0.7 or more, in any case, the combustion temperature at a position close to the lance is increased. In particular, 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 rises at any position from the lance if the oxygen excess rate is 1 or more. For this reason, when LNG is blown from the inner pipe of the double pipe lance and pulverized coal is blown from the outer pipe, the oxygen excess rate is 0.7 or more and the oxygen excess rate is 1.3 or less. If the oxygen excess rate is increased, a further increase in the combustion temperature can be expected, but the upper limit of the oxygen excess rate is set to 1.3 in view of the oxygen production cost.

  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 double pipe lance is made of, for example, a stainless steel pipe. Of course, the outer tube of the double tube lance is water-cooled called a so-called water jacket, but cannot cover the tip of the lance. 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 deformed by heat. If the outer pipe of the double pipe lance is deformed, that is, bent, pulverized coal or LNG cannot be blown into a desired part, and there is a problem in the replacement work of the lance which 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. 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 may melt and possibly damage the blower pipe. There is also.

The only way to cool the outer tube of a double-pipe lance that cannot be cooled with water is to dissipate heat with the gas supplied to the inside. When heat is released to the gas flowing inside to cool the outer tube of the double tube lance itself, it is considered that the gas flow rate affects 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. In the gas flow rate adjustment, N ₂ which is a carrier gas for transporting pulverized coal in this embodiment was adjusted. The measurement results are shown in FIG.

Two types of steel pipe called 20A schedule 5S and steel pipe called 25A schedule 5S were used for the outer pipe of the double pipe lance. Further, as the inner pipe of the double pipe lance, one kind of steel pipe called 15A schedule 90 was used, and the flow rate of N ₂ which is a carrier gas of pulverized coal was variously changed to measure the temperature of the lance surface. Incidentally, “15A”, “20A”, and “25A” are nominal dimensions of the outer diameter of the steel pipe specified in JIS G 3459, 15A is the outer diameter 21.7 mm, 20A is the outer diameter 27.2 mm, and 25A is the outer diameter 34. 0.0 mm. The “schedule” is a nominal dimension of the thickness of the steel pipe specified in JIS G 3459, the schedule 5S is 1.65 mm, and the 15A schedule 90 is 3.70 mm. When a steel pipe is used as the outer pipe of the double pipe lance, it is practical to use a steel pipe having the above-described two types of outer diameters. It is also possible to use a 20A schedule 90 (wall thickness: 3.9 mm) and a 25A schedule 90 (wall thickness: 4.5 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 the 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 outer pipe of the double pipe lance for each steel pipe of 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 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 or 25A 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 total flow rate of the blown gas from the outer pipe is 85 Nm. ³ / h or more, and when these steel pipes are used, the outlet flow velocity of the outer pipe of the double pipe lance is 20 m / sec or more. When the total flow rate of the blown gas in the outer pipe of the double pipe lance is 85 Nm ³ / h or more and the outlet flow velocity of the outer pipe of the double pipe lance is 20 m / sec or more, the double pipe lance is transformed into a double pipe lance. No bending occurs.

  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, and LNG (flammable fuel) 9 is infused from the inner pipe of the double pipe lance 4. At the same time, pulverized coal (solid fuel) 6 is blown from the outer pipe of the double-pipe lance 4 and the excess oxygen ratio of the blown air to the three tuyere is set to 0.7 to 1.3, whereby pulverized coal (solid The LNG (flammable fuel) 9 inside the fuel) 6 burns first, so that the pulverized coal (solid fuel) 6 explosively diffuses, and at the same time, the pulverized coal by the combustion heat of the LNG (flammable fuel) 9 The temperature of the (solid fuel) 6 is significantly increased, thereby increasing the heating rate of the pulverized coal (solid fuel) 6. At this time, the excess oxidation ratio of the air blown to the tuyere 3 is set to 0.7 to 1. .3, pulverized coal (solid fuel) 6 is sufficiently combusted, and as a result, the combustion temperature is greatly improved. It is possible to reduce the MotozaiHara unit.

Further, the total flow rate of the gas blown from the outer pipe of the double pipe lance 4 is set to 85 Nm ³ / h or more, and the outlet flow velocity of the outer pipe of the double pipe lance 4 is set to 20 m / sec or more. The deformation of the double pipe lance 4 due to can be prevented.

  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)

  The lance for injecting fuel from the tuyere is a double pipe, flammable fuel is blown from the inner pipe of the double pipe lance, solid fuel is blown from the outer pipe of the double pipe lance, and to the tuyere A method of operating a blast furnace, characterized in that the oxygen excess rate of the air blowing is 0.7 to 1.3. 2. The blast furnace operation according to claim 1, wherein the total flow rate of the gas blown from the outer pipe of the double pipe lance is 85 Nm ³ / h or more and the outlet flow velocity of the outer pipe is 20 m / sec or more. Method.   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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