JP5962912B2 - Blast furnace operation method - Google Patents

Description

  The present invention suppresses deterioration of the air permeability of the furnace due to the collapse and pulverization of the blast furnace operating method, in particular, the temperature rise and reduction of the charged raw materials such as sintered ore and iron ore charged in the blast furnace. The present invention relates to an effective blast furnace operation method.

A blast furnace is a furnace that produces molten iron by reducing and melting charged raw materials such as iron ore and sintered ore while descending in the furnace. In the operation of this blast furnace, What is important is to maintain a rapid and stable reduction reaction. For this purpose, it is necessary to ensure a certain furnace temperature, that is, to appropriately supply heat and supply a reducing gas such as CO and H ₂ .

  By the way, in recent years, global warming due to an increase in carbon dioxide emission has been a problem. Even at steelworks, the suppression of carbon dioxide emissions is an extremely important issue. Therefore, in recent blast furnaces, low reductant ratio (low RAR) operation is in the spotlight. In addition, RAR is the ratio of the total amount of coke charged from the injected fuel and the top of the furnace when producing 1 ton of pig iron.

  In blast furnace operation, generally, when the reducing material ratio (RAR) decreases, the blowing rate decreases, and as a result, the temperature rise of the charged materials (sintered ore, coke, etc.) is delayed at the top of the shaft, resulting in a smooth reduction. Is known to be inhibited. In addition, when the low temperature region at the upper part of the shaft is expanded, the attachment of a wall of zinc compound or the like is promoted, and there is a concern that the furnace condition deteriorates such as wind pressure fluctuation or unloading abnormality. In addition, when the temperature at the top of the furnace is lowered and falls below 100 ° C., there is a problem that moisture in the exhaust gas is condensed in the pipe.

  Also, in the operation of the blast furnace, in order to promote the reduction of iron oxide contained in the charged sinter or the like, it is important to improve the air permeability in the furnace, and the generation of powder in the blast furnace It is effective to suppress as much as possible. For that purpose, adjustment of the characteristics of the sintered ore itself as the charging raw material, for example, RDI indicating the reduced powdering characteristics or DI indicating the powdering characteristics of coke is an important index.

As described above, in the recent blast furnace operation, as a result of operating with a low RAR as a target, the upper part of the shaft tends to be low temperature. On the other hand, in order to eliminate the adverse effect of the low temperature tendency, in Patent Document 1, conventionally, a preheating gas using combustion gas from which CO ₂ has been removed is blown into the furnace from the upper portion of the shaft. Has proposed a method for preventing the expansion of the low temperature region and the temperature drop of the furnace top gas.

  Further, in Patent Document 2, in order to prevent a malfunction of the furnace due to low RAR blast furnace operation and an insufficient temperature rise of the charge in the upper part of the furnace, the position and speed of the preheating gas are adjusted when the preheating gas is injected. Or, by making selections and adjustments of preheating gas species, we are making proposals aimed at realizing stable low RAR operations.

JP 2009-221547 A Japanese Patent No. 4743332

  By the way, in blast furnace operation, when considering the reduction reaction of iron oxide contained in iron ore and sintered ore, especially in the shaft, how to use heat and reducing gas supplied to the shaft However, it is important to realize stable operation of the blast furnace. Particularly important is ensuring air permeability in the furnace.

  In this respect, due to the depletion of high-quality raw material resources in recent years, inferior raw materials such as pisolite ore containing a large amount of crystal water for iron ore and non-minor cohesive coal must be used. For this reason, blast furnace charging materials in recent years have lower reduced dustability (RDI) and lower coke dustability (DI) compared to the previous ones, and securing of air permeability in the blast furnace is increasing. It has become difficult.

  By the way, the above-mentioned two prior arts (Patent Documents 1 and 2) focus on preheating gas blowing adjustment, and the viewpoint of in-furnace air permeability that needs to be reexamined in accordance with the recent deterioration of raw material circumstances. It does not mention how to improve it.

  However, in order to consider the reduction reaction at the blast furnace shaft, reducing powdering characteristics of the charged raw material, especially by adjusting the lowering of the charged raw material in consideration of this characteristic, in particular, reducing powdering is less likely to occur, and air permeability It is thought that it is necessary to control the lowering of the charged raw material, which is difficult to cause deterioration.

  Accordingly, an object of the present invention is to reduce the reduction powder of the charged raw material in the blast furnace shaft portion and improve the air permeability in the furnace, thereby establishing a method for achieving stable operation of the blast furnace. There is.

  Intensive research on how to overcome the above-mentioned problems in the prior art in order to cause a good reduction reaction in the blast furnace shaft even when the quality of raw materials deteriorates due to recent raw material circumstances Repeated. As a result, the inventors have obtained the knowledge that the following method is effective, and have developed the present invention.

That is, according to the present invention, a preheated gas at 950 ° C. or higher obtained by burning CO ₂ -removed blast furnace gas (BFG) using a de-CO ₂ device into the furnace of the blast furnace from the shaft portion is 100 Nm ³ / t or more. Proposing a blast furnace operation method characterized in that the residence time of the charged raw material that passes through the temperature range of 800 to 1000 ° C. is 60 minutes or longer when the charged raw material is unloaded in the furnace by blowing. To do.

In the blast furnace operating method according to the present invention,
( 1 ) The charging material is sintered ore and / or iron ore,
( 2 ) Blowing pulverized coal and / or a reducing agent from the inlet of the blast furnace,
However, it can be considered as a solution to a more preferable problem.

  According to the blast furnace operating method according to the present invention configured as described above, the residence time below 800 ° C. at the upper part of the blast furnace shaft is shortened, and the residence time at 800 ° C. to 1000 ° C. is lengthened, A stable blast furnace operation can be achieved by forming a cross-linked structure mainly of metallic iron particles in the cracks of the charging materials such as iron ore, and thus preventing the reduced charging and collapse of the charging materials at the shaft. Can be performed.

It is a graph which shows the relationship between the interruption temperature in the temperature rising / reduction experiment which simulated the inside of a blast furnace, and the powdering rate of a sintered ore. It is a cross-sectional photograph of a sintered ore structure when reduction is interrupted at 1000 ° C. It is a cross-sectional photograph of a sintered ore structure when reduction is interrupted at 900 ° C. It is a cross-sectional photograph of the sintered ore structure when the reduction is interrupted at 800 ° C. It is the schematic which shows the presumed mechanism of the process in which metallic iron etc. bridge-form in the crack of a sintered ore. It is a schematic diagram which shows the metal bonding process of a crosslinked structure | tissue. It is the schematic of a blast furnace and peripheral equipment which shows one Embodiment of this invention. It is a graph which shows the average temperature history accompanying the fall of the charging raw material in a blast furnace.

  The inventors first examined by a laboratory experiment a method for suppressing the reduction powdering of charging raw materials such as iron ore and sintered ore in a blast furnace. As a result, the following facts were found regarding the reduction powdering characteristics of the raw material charged in the blast furnace at the top of the blast furnace shaft.

FIG. 1 shows the results of a temperature increase and reduction experiment simulating the inside of a blast furnace by charging sintered ore into a reactor. According to FIG. 1, it was found that the powdering rate of the sintered ore is lowered by 4 to 5% when the reduced powdering temperature is 500 ° C. to 600 ° C. and the temperature is higher than this. In this figure, the interruption temperature is a temperature at which the heating of the furnace is stopped and at the same time the gas supplied to the reactor is switched from a reducing gas containing CO or H ₂ to an inert N ₂ gas. Is the temperature rise and gas conditions assuming general blast furnace operation, and condition B assumes the situation where the proportion of H ₂ gas in the reducing gas has increased due to the increase in the amount of pulverized coal injected into the blast furnace Temperature rise and gas conditions. The sintered ore after the reduction experiment is taken out of the reactor when the sample temperature is lowered to about room temperature, and the inside of the reactor at that time is replaced with N ₂ gas as described above.

  Then, in the above experiment simulating the inside of the blast furnace, the cross-sectional structure of the sintered ore collected after reduction and cooling was observed with a metallurgical microscope. FIG. 2 (interrupted at 1000 ° C.), FIG. 4 (interrupted at 800 ° C.), cracks generated at the respective interrupting temperatures (reduction powdering temperatures) remain even at temperatures higher than those interrupting temperatures, but some of the cross-linked structure (○ It was found that destruction, i.e., pulverization, is suppressed because the mark portion) is formed. In particular, it has been found that when the interruption temperature is maintained at 800 ° C. or higher, these suppression effects become more remarkable. An outline of the estimation mechanism is shown in FIG.

  FIG. 5 shows that floating metal iron particles produced by reduction grow by adhering to each other by injecting a reducing gas into cracks generated in the sintered ore, and eventually these metal irons crosslink within the cracks. The mechanism for suppressing powdering is schematically shown. Thus, it can be seen that the crack once generated in the 500 to 600 ° C. region is cross-linked by the generated metallic iron particles and the like by being maintained at a temperature of 800 ° C. or higher.

  FIG. 6 schematically shows a metal bonding process for forming a crosslinked structure. As shown in this figure, when the raw materials such as sintered ore charged in the blast furnace are heated to 500 to 600 ° C. in the shaft portion, the intermolecular bonding force decreases and the iron oxide particles are detached. To do. However, the separated iron oxide particles are also reduced at a temperature of 800 ° C. or more by the reducing gas flowing into the cracks to generate iron oxide (magnetite, wustite) particles and metallic iron particles, and at the same time, the wall surfaces in the cracks. It is thought that it gradually grows and leads to a crosslinked structure to form a strong metal bond structure. From this, it was found that when the charging raw material was kept longer in the temperature range of 800 ° C. or longer, the repair of cracks was more likely to occur due to cross-linking through metallic iron particles and the like.

  In the present invention, as described above, the cracks generated in the charging raw material in the 500 to 600 ° C. region of the shaft portion are held at 800 to 1000 ° C. of the shaft portion for a long time, thereby causing cross-linking by the metal iron particles. Therefore, it is desirable to prevent collapse and pulverization of the charged raw material and improve the air permeability in the furnace. For this purpose, it is effective to maintain the residence time of the charged raw material to be retained in the temperature range of 800 to 1000 ° C. for at least 60 minutes, preferably 65 minutes or more. This is because if the residence time in this temperature range is less than 60 minutes, the above-mentioned effects cannot be obtained sufficiently.

And in order to make it stay for 60 minutes or more in the temperature range of 800-1000 degreeC, in this invention, in blowing in the preheating gas from a blast furnace shaft part, 950 degreeC or more gas is used, and blowing of 100 Nm < ³ > / t or more is carried out. Perform the target operation. The reason is that when the temperature of the preheating gas is less than 950 ° C., the amount of heat required for heating the blast furnace sintered ore and the like is insufficient and does not reach 800 ° C. when the blowing amount is 100 Nm ³ / t. . On the other hand, when the amount is less than 100 Nm ³ / t, when the preheating gas temperature is 950 ° C., the amount of heat required to heat the sintered blast furnace ore and the like is insufficient and does not reach 800 ° C.

  Next, an embodiment of a blast furnace operating method suitable for the present invention will be described with reference to FIG. The embodiment shown in FIG. 7 is an example in which hot air is blown from the blower tuyere 2 of the blast furnace 1 and preheated gas 4 is blown into the furnace from a preheated gas blowing pipe 3 in the shaft portion. In addition, the example which performs blowing of the fuel gas 6 and pulverized coal 7 other than the hot air 5 from the said ventilation tuyere 2 is shown.

In this embodiment, the blowing position of the preheating gas 4 may be any position as long as it is a blast furnace shaft portion. As the preheating gas 4 to be used, a fuel gas such as BFG, COG or reformed COG can be used. In the present invention, blast furnace gas (BFG) is particularly air or oxygen-enriched air (combustible gas 9). ) by that use combustion gas and 950 ° C. or more as is partially combusted in the combustion furnace 10. In order to obtain a preheated gas of 95 0 C or higher, the air ratio at the time of partial combustion is preferably about 0.5 to 0.8. If the air ratio is 0.5 or less, the ignitability is poor and combustion is not stable.

In order to set the temperature of the preheating gas to 950 ° C. or higher, it is effective to increase the oxygen concentration of the combustion-supporting gas. On the other hand, from the _{P CO / (P CO + P} CO2)) ratio of the combustion gases in the air ratio is 0.8 or more, a _{P CO / (P CO + P} CO2) ratio of the blast furnace shaft portion 0.3-0.7 Since the iron ore and sintered ore are reoxidized, a strong metal bond structure cannot be obtained. The air ratio at the time of partial combustion is the air ratio at which the composition of the preheated gas at the time of being blown into the blast furnace is obtained. For example, the fuel gas is mixed with the combustion gas burned at the air ratio of 1.2, and the air The ratio may be adjusted to a gas composition corresponding to 0.5 to 0.8.

The combustion-supporting gas 9 may be heated to be supplied to the combustion furnace 10, and the reducing gas containing CO and H ₂ is indirectly heated to raise the temperature to a predetermined temperature. 10 can also be supplied.

  As the preheating gas 4, instead of the combustion furnace 10, a combustion burner may be directly installed on the side surface of the shaft portion of the blast furnace, and the combustion gas may be blown into the furnace.

When the preheating gas 4 is blown into the furnace from the shaft portion of the blast furnace 1, a part of the BFG 8, which is the top gas discharged from the blast furnace 1, is branched as the preheating gas 4, and this is burned using the combustion supporting gas 9. It may be partially burned in the furnace 10 and blown into the blast furnace shaft portion as a combustion gas of 950 ° C. or higher. Also, when using BFG8, with de-CO ₂ apparatus 11 for removing CO _2, the gas to remove CO ₂ is burned in the combustion furnace 10, write no blown into the blast furnace shaft portion as a combustion gas. This is because the amount of oxygen or air necessary for combustion of the preheated gas can be reduced by removing CO ₂ . More preferably, CO ₂ and N ₂ that do not contribute to the reduction are removed. As a method for removing CO ₂ from the preheating gas, a chemical absorption method using an alkylamine or the like may be used, and a physical adsorption method, a physical absorption method, or a membrane separation method may be used. As a method for removing N ₂ , a physical adsorption method, a physical absorption method, a membrane separation method, or the like can be used.

  When a preheating gas such as combustion exhaust gas is used, the blowing position may be any position as long as it is a blast furnace shaft portion. Since these preheated gases are blown into the furnace from the shaft, the preheated gas may be blown at a gas velocity below the fluidization condition of iron ore and coke so as not to hinder the charge drop in the furnace. preferable. The preheating gas is preferably blown evenly in the circumferential direction, and the preheating gas blowing pipe may be arranged in one stage or a plurality of stages.

As a main condition for blowing the preheating gas in the blast furnace, for example, application of a method as disclosed in Patent Document 1 can be considered. That is, the radius of the blast furnace outlet is R0.
When the position where the depth from the stock line is R0 is p1, and the position where the height from the lower end of the shaft part is 1/3 of the total height of the shaft part is p2, the position p1 and the position p2 in the furnace height direction A preheating gas blowing section was provided between them, and the oxygen enrichment rate was 20 vol. % Of hot air is blown into the blast furnace from the blower tuyere, and preheated gas is blown from the preheated gas blowing section. In blowing the preheating gas, it is preferable that the linear velocity is 15 to 72 m / s from the preheating gas blowing portion provided at equal intervals in the furnace circumferential direction at 4 or more and 16 or less.

  The preheating gas blowing section is preferably provided between a position where the depth from the stock line is 7 m and a position where the height from the lower end of the shaft section is 1/3 of the total height of the shaft section.

  In addition, it is preferable to inject the preheating gas (shaft gas) into the shaft portion of the blast furnace horizontally or downward from the shaft gas blowing tube. For example, the air can be blown at an angle of 0 ° to 45 °. In this case, it is more preferable that the preheating gas be blown downward by 15 to 45 degrees from the horizontal direction from the viewpoint of stable operation of the blast furnace, that is, clogging of piping and prevention of backflow of the preheating gas.

In this embodiment, the effect of the present invention is verified by performing a reduction experiment simulating the temperature transition when the preheating gas is blown into the shaft portion by simulation calculation.
In this blast furnace simulation calculation, in an operation in which pulverized coal is blown into a blast furnace having an internal volume of 5000 m ³ , the output ratio: 2.3 t / m ³ / d, tuyere temperature: 2200 ° C., pulverized coal injection amount: 160 kg / t An experiment was carried out in which the temperature of the preheating gas blown into the upper part of the shaft was appropriately changed. As the preheating gas used, BFG partial combustion gas was used, and the diameter of the shaft gas blowing tube was 20 cm. Table 1 shows blast furnace operation patterns 1 to 4 at this time.

  The operation pattern 1 is a conventional general operation condition, in which no preheating gas is blown, and in the pattern 2, the preheating gas is blown from the shaft portion, but the temperature is set to 700 ° C., pattern 3, pattern 4 Corresponds to a conforming example of the present invention, in which preheated gases of 950 ° C. and 1100 ° C. are blown into the shaft portion, respectively.

  As a result, the average temperature history associated with the drop in the charged raw materials including the sintered ore in the blast furnace was as shown in FIG. This temperature history is an intermediate position between the center of the blast furnace and the furnace wall, and takes into account the unloading associated with the operation. The residence time of 800 to 1000 ° C. in each of the patterns 1 to 4 is as shown in Table 2.

Therefore, a reduction test was performed on the temperature history shown in Table 2 to verify the effect of preheating gas blowing for each pattern. The test apparatus is a type in which a reaction vessel having an inner diameter of 75 mmφ through which a reducing gas can flow from below is heated in an electric furnace, and the reducing gas composition is CO / CO ₂ / H ₂ / N, simulating the blast furnace reduction. ₂ = 30/30/5/35 (vol.%). The flow rate of the reducing gas was 15 (lit./min.). As a sample, 500 g of the reaction vessel was filled using a sintered ore having a size of 10 to 15 mmφ. The test was stopped by stopping the heating when the temperature of the sample packed bed reached 1000 ° C. and switching the gas to N 2. The sintered ore after the test was subjected to strength evaluation by a rotating drum according to JIS M8720, and a weight ratio (pulverization rate) of 2.8 mmφ or less was calculated.

  Table 3 shows the powdering rate for each of the temperature control patterns 1 to 4. Compared to Comparative Example 1, which is a temperature control pattern simulating a normal blast furnace operation pattern, no improvement in the powdering rate was observed in Comparative Example 2 (Pattern 2) at a temperature of 700 ° C. On the other hand, in Invention Example 1 (Pattern 3: 900 ° C.), which is a conforming example of the present invention, a reduction in the powdering rate is recognized, and in Invention Example 2 (Pattern 4: 1600 ° C.), it can be confirmed that the improvement is further improved. It was.

  The blast furnace operating method according to the present invention can be applied not only to the residence time control of the charged raw material when the preheating gas is blown into the shaft portion, but also to the operation of blowing fuel or the like without blowing the preheating gas.

DESCRIPTION OF SYMBOLS 1 Blast furnace 2 Fan tuyere 3 Preheating gas blowing piping 4 Preheating gas 5 Blowing 6 Fuel gas 7 Pulverized coal 8 BFG
9 Combustion gas 10 Combustion furnace 11 De-CO ₂ equipment

Claims (3)

By injecting a preheated gas of 950 ° C. or higher obtained by burning CO ₂ -removed blast furnace gas (BFG) using a de-CO ₂ device into the furnace of the shaft from the shaft portion at a rate of 100 Nm ³ / t or more. A blast furnace operating method, wherein a residence time of the charged raw material passing through a temperature range of 800 to 1000 ° C when the raw material is unloaded in the furnace is 60 minutes or more .   The blast furnace operating method according to claim 1, wherein the charging raw material is sintered ore and / or iron ore. The blast furnace operating method according to claim 1 or 2 , wherein pulverized coal and / or a reducing agent is blown from a charging tuyere of the blast furnace.