JP5824811B2 - Blast furnace operation method - Google Patents

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 tube as a lance for injecting fuel from a tuyere, and injects a combustion-supporting gas from the inner tube of the double tube lance. A mixed fuel in which a flammable fuel and a solid fuel are mixed is blown from an outer pipe of a pipe lance.
Further, the ratio of the flammable fuel or the flammable fuel and the combustion-supporting gas to the total amount of gas blown from the double pipe lance is 25 vol% or more.

The combustion-supporting gas blown from the inner pipe of the double pipe lance is oxygen, and a part of oxygen enriched in blowing is blown from the inner pipe of the double pipe lance. It is.
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 is explosively diffused by burning the flammable fuel first together with the combustion-supporting gas blown from the inner pipe of the double pipe lance, At the same time, the temperature of the solid fuel is greatly increased by the combustion heat of the flammable fuel, thereby increasing the heating speed of the solid fuel and greatly improving the combustion temperature, thereby reducing the reducing material basic unit.
Moreover, a high combustion temperature can be ensured by setting the ratio of the flammable fuel or the flammable fuel and the combustion-supporting gas to the total amount of gas blown from the double-pipe lance to 25 vol% or more.
In addition, by blowing a part of oxygen enriched in the blast from the inner 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 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 of the combustion temperature of a combustion experiment result.

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, and 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 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. In this case, a combustion-supporting gas, in this case O ₂ , is blown from the inner pipe of the double-pipe lance and a mixed fuel of LNG and pulverized coal is blown from the outer pipe. The combustion temperature, combustion position, unburned char combustion status, and diffusivity were measured. 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 was based on the combustion temperature, combustion position, unburned char combustion status, and diffusibility (mainly pulverized coal) when only pulverized coal (using N ₂ as a medium) was injected from a single pipe lance. When pulverized coal is blown from the inner pipe of the double pipe lance and LNG is blown from the outer pipe, LNG is blown from the inner pipe of the double pipe lance and pulverized coal is blown from the outer pipe. When a mixed fuel of LNG and pulverized coal is blown from the pipe lance, a combustion-supporting gas, in this case O ₂ , is blown from the inner pipe of the double pipe lance, and a mixed fuel of LNG and pulverized coal is blown from the outer pipe. Each case 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. In addition, when injecting O ₂ as a combustion-supporting gas, a part of oxygen enriched in the ventilation was used so that the total amount of O ₂ injected into the furnace was not changed. The atmosphere can also be used as the combustion-supporting gas.

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 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, as a result of mixing LNG and pulverized coal in advance and injecting the mixed fuel from a single-pipe lance, a significant improvement was seen in three points: combustion temperature, combustion position, and combustion status of unburned char. It was. However, in terms of diffusivity, the method did not reach the method of blowing LNG from the inner pipe of the double pipe lance and blowing pulverized coal from the outer pipe of the double pipe lance. Therefore, in order to promote the explosive diffusion effect associated with the combustion of LNG, diffusibility is improved by injecting O ₂ from the inner pipe of the double pipe lance and injecting mixed fuel of LNG and pulverized coal from the outer pipe. Significant improvements have been made and the combustion temperature, combustion position, and combustion status of unburned char have been maintained.

FIG. 7 shows the relationship between the combustion position and the combustion temperature in all experiments. As is clear from FIG. 6 and FIG. 6, in contrast to the method of blowing only pulverized coal from the single tube lance, the method of blowing pulverized coal from the inner tube of the double tube lance and blowing LNG from the outer tube, double LNG is blown from the inner pipe of the pipe lance, pulverized coal is blown from the outer pipe, mixed fuel of LNG and pulverized coal is blown from the single pipe lance, and O ₂ is blown from the inner pipe of the double pipe lance. The combustion temperature increases in the order of the method of injecting the mixed fuel of LNG and pulverized coal from the outer pipe, and the combustion position in particular is greatly improved by the method of injecting the mixed fuel of LNG and pulverized coal from the single tube lance. However, a significant improvement is seen in the method in which O ₂ is blown from the inner pipe of the double pipe lance and the mixed fuel of LNG and pulverized coal is blown from the outer pipe.

Next, the present inventors variously changed the ratio of the combustion temperature by changing the ratio of LNG or LNG as a flammable fuel and O ₂ as a combustion-supporting gas to the total amount of gas blown from the double pipe lance 4. Was measured. This is because, for example, as described above, LNG burns with O ₂ first, and the effect of rapidly increasing the temperature of the pulverized coal by the combustion heat is confirmed. Therefore, as shown in Table 1 below, the flow rate of N ₂ that is a carrier gas of pulverized coal is kept constant at 15 Nm ³ / h from CASE ¹ to 5, and the flow rates of LNG or LNG and O ₂ are changed variously. A combustion temperature at a distance of 165 mm and a combustion temperature at a distance of 315 mm from the tip of the heavy pipe lance were measured.

The samples show shows the LNG or LNG and O ₂ flow rate (O ₂ + LNG) and the ratio of O ₂ with respect to LNG (O ₂ / LNG). That is, CASE 1 does not inject O ₂ or LNG. CASE2 injects 5Nm ³ / h only for LNG. CASE 3 injects LNG 5 Nm ³ / h and O ₂ 10 Nm ³ / h. CASE 4 injects LNG at 5 Nm ³ / h and O ₂ at 20 Nm ³ / h. CASE5 is the LNG 10Nm ³ / h, the O ₂ 20Nm ³ / h is blown. The ratio of LNG or LNG and O ₂ to the total amount of gas blown from the double pipe lance is 0 vol% for CASE1, 25 vol% for CASE2, 50 vol% for CASE3, 62.5 vol% for CASE4, and 66.65 for CASE5. 7 vol%.

The specifications of pulverized coal are fixed carbon FC: 77.2%, volatile content VM: 12.2%, ash content Ash: 10.6%, and the blowing conditions are 50 kg / h (142 kg / t in the ironmaking base unit). Equivalent) (using nitrogen as blowing medium). The blowing conditions were a blowing temperature of 1200 ° C., a flow rate of 350 Nm ³ / h, O ₂ enrichment + 3.5 (oxygen concentration 24.5%). In addition, when injecting O ₂ as a combustion-supporting gas, a part of oxygen enriched in the ventilation was used so that the total amount of O ₂ injected into the furnace was not changed. The atmosphere can also be used as the combustion-supporting gas. Further, pulverized coal, LNG, blowing seen how O ₂ is the O ₂ from the inner tube of the double tube lance blowing, blowing a mixed fuel of LNG and pulverized coal from the outer tube. The measurement results are shown in FIG.

As apparent from the figure, in the region of less than 25 vol% ratio of LNG or LNG and O ₂ are relative to the total amount of gas blown from the double tube lance, the proportion of LNG or LNG and O ₂ is increased to the total gas amount As the combustion temperature increases greatly with this, it is difficult to ensure a high combustion temperature in this region. On the other hand, in the region where the ratio of LNG or LNG and O ₂ to the total amount of gas blown from the double pipe lance is 25 vol% or more, the combustion temperature is increased even if the ratio of LNG or LNG and O _{2 to} the total amount of gas increases. Since it tends to saturate, a high combustion temperature can be secured in this region. Therefore, in the blast furnace operating method of the present embodiment, the ratio of LNG or LNG and O ₂ to the total amount of gas blown from the double pipe lance is set to 25 vol% or more, preferably 50 vol% or more.

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 O ₂ (flammable gas) is injected from the inner pipe of the double pipe lance 4. At the same time, by injecting a mixed fuel in which LNG (flammable fuel) 9 and pulverized coal (solid fuel) 6 are mixed from the outer pipe of the double pipe lance, O is blown from the inner pipe of the double pipe lance. _{2 When} LNG (flammable fuel) 9 is burned together with (flammable gas), pulverized coal (solid fuel) 6 is explosively diffused, and at the same time, the combustion heat of LNG (flammable fuel) 9 The temperature of the pulverized coal (solid fuel) 6 is significantly increased, whereby the heating rate of the pulverized coal (solid fuel) 6 is increased and the combustion temperature is greatly improved, thereby reducing the reducing material basic unit. .

Also, the ratio of LNG (flammable fuel) 9 or LNG (flammable fuel) 9 and O ₂ (flammable gas) to the total amount of gas blown from the double pipe lance 4 should be 25 vol% or more. Thus, a high combustion temperature can be ensured.
In addition, by blowing a part of O ₂ enriched in ventilation (as a combustion-supporting gas) from the inner pipe of the double pipe lance, the excess gas supply in the blast furnace is not impaired, and O ₂ is excessively supplied. This can be avoided, and the basic unit of O ₂ used can be reduced.

  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, and inflammable gas is injected from the inner pipe of the double pipe lance, and flammable fuel and solid fuel are mixed from the outer pipe of the double pipe lance. A method of operating a blast furnace, wherein the ratio of the flammable fuel and the combustion-supporting gas to the total gas amount injected from the double pipe lance is 50 vol% or more .   The combustion-supporting gas blown from the inner pipe of the double pipe lance is oxygen, and a part of oxygen enriched in blowing is blown from the inner pipe of the double pipe lance. The blast furnace operating method described in 1.   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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