JP2007231326A - Blast furnace operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blast furnace operation method where, when an operation is performed using highly reactive coke in a blast furnace, a reduction material ratio in the blast furnace can be reduced while deterioration in the gas permeability of the blast furnace is prevented. <P>SOLUTION: In the blast furnace operation method, in blast furnace operation where ore and coke are charged from a furnace top so as to alternatively form an ore layer and a coke layer, the coke layer is composed of coke in which CRI (coke reactivity index) value is ≤32, and the average particle diameter is ≥45 mm, and the ore layer is mixed with coke having a CRI value of ≥31 and the average particle diameter of ≤35 mm by ≥120 kg/t. As the coke mixed into the ore layer, ferrocoke produced by mixing ore and coal and carbonizing the mixture is preferably used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a blast furnace operating method for stably reducing a reducing material ratio.

Reducing the ratio of reducing material in the blast furnace has become an important issue in order to reduce the amount of expensive coke used, and from the viewpoint of contributing to global environmental conservation by suppressing the generation of CO ₂ from the ironmaking process.

In order to reduce the reducing material ratio of the blast furnace, there are methods of improving reduction efficiency (shaft efficiency) and reducing heat loss, and reduction efficiency and heat loss are the most basic operating factors. These two operating factors can be controlled to some extent by performing the blast furnace charge distribution control with high accuracy. By controlling the gas flow in the blast furnace near the raw material by controlling the distribution of charges, the reduction efficiency is improved by improving the utilization rate of the reducing gas (gas utilization rate η _CO = CO ₂ / (CO + CO ₂ )) By optimizing the gas flow in the vicinity of the furnace wall, heat loss from the furnace wall is reduced. However, the range in which reduction efficiency (shaft efficiency) and heat loss can be controlled is the properties of the charge used in the blast furnace (sintered ore strength, reducible RI, reduced dusting RDI, coke strength, reactivity, etc.) ). In other words, since the restrictions on air permeability are relaxed under the use of high-strength raw fuel, it is easy to reduce the reducing material ratio (coke ratio), resulting in improved reduction efficiency (shaft efficiency) and reduced heat loss. easy.

  In addition to the above, two methods for actively controlling the reduction equilibrium are known as measures for reducing the reducing material ratio.

  The first method is a method of charging metallic iron into a blast furnace, and the reduction load can be reduced, so that the ratio of reducing material as a heat source can be reduced. As metallic iron, scrap, direct reduced iron (DRI, HBI, etc.), etc. are used. These iron sources are charged in a lump form from the top of the furnace, or powdered material is blown from the tuyere (for example, see Non-Patent Document 1). However, metallic iron usually has a metallization rate of about 90% or more, is difficult to obtain, and is expensive, so the amount of metallic iron used in a blast furnace has not increased.

The second method is a method for lowering the reduction equilibrium temperature. By reducing the reduction temperature, the gas composition in the FeO-Fe equilibrium is shifted to the high gas utilization rate side, and the utilization efficiency (η _CO ) of the reducing gas (CO gas) is increased, resulting in a reduction in the amount of reducing material used. It is to reduce. As a means for lowering the reduction equilibrium temperature, the use of so-called highly reactive coke is known (for example, see Non-Patent Document 2). Increase of the reducing gas utilization efficiency eta _CO by the use of highly reactive coke, and techniques to reduce the reducing agent ratio has also been disclosed (e.g., Non-Patent Document 3, Non-Patent Document 4 reference.). In Non-Patent Document 3, when coke containing a catalyst component (Ca) that promotes reactivity is blended, both the drum test 150 rotation index DI (15, 150) and the JIS reactivity index RI representing coke reactivity are the base conditions. It is disclosed that high coke can be produced compared to As a result, Non-Patent Document 4 states that reduction of the reducing material ratio of 15 to 20 kg / t was possible.

  However, the highly reactive coke as described above has a problem of resource limitation and cost increase because it is necessary to select a coal type that contains the catalyst component in advance or to add the catalyst component by pretreatment. In addition, since coke that does not depend on such special coal types or production methods generally tends to decrease in strength when reactivity is increased, reduction of the reduction equilibrium temperature can be achieved by using highly reactive coke. However, a large amount of powder is generated in the process of descending the inside of the furnace, and the air permeability in the blast furnace, particularly in the lower part of the furnace (the dripping zone to the raceway part), is markedly deteriorated. As a result, it is not possible to obtain a reducing material ratio reduction effect commensurate with a reduction in the reduction equilibrium temperature.

Even when highly reactive coke is used, the coke reactivity index and the reducibility index of sintered ore are specified as a technology that can prevent coke deterioration and ensure air permeability in the blast furnace. A method of operating a blast furnace in which the amount of slag is set to a predetermined amount or less is known (see, for example, Patent Document 1).
JP 2005-272968 A K. Kunimoto et al. “JJournal of Japan Institute of Energy” 2005, 84, p. 126-133 Naito Masaaki et al. "Iron and Steel" 2001, 87, p. 357-364 Nomura Seiji et al. “CAMP-ISIJ” 2003, No. 16, p. 1039 Yasuyuki Ninagawa et al. “CAMP-ISIJ” 2003, No. 16, p. 1040

As described above, conventional high-reactivity coke cannot achieve both reactivity and strength, and coke with higher reactivity has lower strength. Therefore, when high-reactive coke is used in a blast furnace, pulverization progresses in the furnace, and the generated powder accumulates in the lower part of the furnace, which deteriorates the lower part air permeability. It is difficult to reduce the coke ratio) if the ratio of the blown reducing material is the same. That is, the conventional method of using highly reactive coke cannot substantially obtain the reducing material ratio reduction effect commensurate with the improvement in gas utilization rate accompanying the improvement in reactivity.
Therefore, when using highly reactive coke, in order to lower the reduction equilibrium temperature and fully enjoy the effect of improving the gas utilization rate, measures to suppress pulverization at the bottom of the furnace and improve air permeability at the same time It is important to take In the method described in Patent Document 1, in order to ensure air permeability, the use of a sintered ore having a high sintered ore reducibility index (RI) is an essential condition. However, in order to produce a sintered ore having a high RI, a high-quality (low slag ratio) material must be used, which is economically disadvantageous. Further, since there is an inverse correlation between RI and the index (RDI) representing reduced powdering in the blast furnace, there is a possibility that the powdering of the sintered ore progresses and rather adversely affects the air permeability.

  Therefore, the object of the present invention is to solve such a problem of the prior art, and to reduce the ratio of reducing material of the blast furnace while preventing the deterioration of the air permeability of the blast furnace when operating using highly reactive coke in the blast furnace. It is to provide a method of operating a blast furnace that can be reduced.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies, and as a result, when charging ore and coke into a blast furnace, a coke layer is formed with coke that has low reactivity and a large particle size, and By mixing and charging 120 kg / t or more of coke with high reactivity and small particle size, the air permeability is remarkably improved compared to the operation of laminating a normal ore layer and a coke layer, The present inventors have found that stable low-reducing material ratio operation that operates at a reducing material ratio of 480 kg / t or less can be realized, and the present invention has been completed. Here, kg / t is a basic unit indicating the amount used per ton of produced hot metal.

  That is, in the present invention, coke having high reactivity is mixed with ore to improve the contact property between these particles to further reduce the reduction equilibrium temperature, and the coke having a small particle size and a size close to the ore particle size. By using this, it is possible to mitigate the decrease in the porosity of the packed bed and suppress the deterioration of air permeability. Even if coke is pulverized, it is considered that gasification disappears quickly due to high reactivity. Further, ferro-coke or the like can be used as highly reactive coke.

  Furthermore, by forming the coke slit with coke having a low reactivity and a large particle size, pulverization due to the gasification reaction is suppressed, so that the air permeability can be ensured more reliably.

The present invention has been made based on such findings, and the features thereof are as follows.
(1) In blast furnace operation in which ore and coke are charged from the furnace top to form ore layers and coke layers alternately, the CRI value of the coke forming the coke layer is 32 or less and the average particle size is A method for operating a blast furnace, comprising coke of 45 mm or more, and coke having a CRI value of 31 or more and an average particle size of 35 mm or less mixed in the ore layer of 120 kg / t or more.
(2) Blast furnace operation according to (1), characterized in that ferro-coke produced by mixing ore and coal and dry distillation is used as coke having a high reactivity and a small particle size to be mixed in the ore layer. Method.

  In addition, the average particle diameter referred to in the present invention is a mass-based length average diameter.

  According to the present invention, the air permeability of the furnace when performing blast furnace operation using highly reactive coke is improved, and the reducing material ratio is reduced. Low-reducing material ratio operation with a reducing material ratio of 480 kg / t or less can also be performed stably.

In order to optimize coke with high reactivity and small particle size, coke with low reactivity and large particle size, and the usage method, the following operation tests 1 to 5 were performed. The reactivity of coke was defined by the CRI value. The CRI value is an index of the reaction rate when a coke sample sized to 20 ± 1 mm is reacted at 1100 ° C. in a CO ₂ atmosphere for 2 hours. A larger CRI indicates a higher reactivity. Table 1 shows the coke used in the test.

[Test 1] Using an actually operating blast furnace, charging tests were conducted on sintered ore and coke having various properties. The blast furnace is a blast furnace having a 3 parallel bunker with an internal volume of 5153 m ³ and a bell-less charging device. As a charging raw material, the ore was blended with sintered ore (average particle diameter 18 mm, RI = 65, RDI = 35) 80% by mass and lump ore 20% by mass. The coke used was coke A, coke B1, and coke D3 shown in Table 1.

  In order to investigate the influence of the method of using the raw material on the ratio of reducing material in the blast furnace and the permeability of the lower part of the furnace, the charging methods from Case 1 to Case 4 were examined. The laminated structure in the furnace of Case1-Case4 formed with the coke and ore charged from the furnace top is typically shown in FIG. FIG. 1 is a schematic view of a cross section of a blast furnace 1, and shows a laminated structure at an upper position 2 in the furnace as Cases 1 to 4 on the right side.

  Case 1 is a system in which the coke layer 3 and the ore layer 4 are alternately charged. As the coke layer 3, the entire amount of coke A (average particle diameter 40 mm, CRI = 32) was used. Coke A is a standard coke with an average reactivity and particle size, and Case 1 is a standard operating condition as a base.

  Case 2 is a coke D3 in which a part of the charged coke has a small particle size and a high reactivity, the coke D3 is mixed with the 120 kg / t ore layer 4 to form coke 5 in the ore layer, and the remaining coke is coke A 3 is formed.

  Case 3 is a case where the coke A of Case 1 is changed to coke B1 having low reactivity and a large particle size.

  Case 4 is a condition in which coke D3 having a small particle size and high reactivity is mixed with a 120 kg / t ore layer, and coke layer 6 is changed to coke B1 having a low reactivity and a large particle size, as in Case 2.

At the time of performing operation tests in Case1～4, reducing agent ratio and the furnace bottom ventilation resistance index _{(K l values:. K l = (P blast} 2 -P 2) / V 1.7 However, P _blast: feed air pressure (kg / Cm ² ), P: actual values of furnace wall static pressure (kg / cm ² ), V: Bosch gas amount (Nm ³ / t) at a position of 6.7 m on the tuyere axis are shown in FIG. In Case 1, the pulverized coal injection ratio was 120 kg / t, and the coke ratio was 370 kg / t (reducing material ratio 490 kg / t). According to FIG. 2, compared with Case 1, in Case 2, the reducing material ratio was slightly reduced, but the air permeability was deteriorated. In Case 3, the air permeability was greatly improved, but the ratio of reducing materials was hardly changed. In Case 4, both the reducing material ratio and the air permeability were greatly improved.

From these facts, it is Cases 2 and 4 that are effective in reducing the reducing material ratio. By mixing highly reactive coke in the ore layer, the reduction equilibrium temperature is lowered and the reducing material ratio is lowered. Inferred. However, when standard coke is used in the coke layer like Case 1 like Case 2, the air permeability is rather deteriorated, so that the simple mixing of ore and coke has a large particle size difference. It is surmised that the resulting void ratio of the packed bed is lowered, and there is an adverse effect of increasing the airflow resistance. On the other hand, the air permeability is improved when coke having a large particle size and low reactivity such as Cases 3 and 4 is used as the coke layer. Because such coke has low reactivity with CO _2, is suppressed deterioration of the coke by the gasification reaction _{(C + CO 2 = 2CO)} , which generation amount of flour reduction, hence the porosity of the packed layer is ensured It is guessed. Therefore, in Case 4, since the air permeability improvement effect of the coke layer was greater than the effect of air permeability deterioration due to the mixing of ore and coke, it is estimated that the air permeability was improved as a result.

  [Test 2] In Test 2, in order to clarify the optimum particle size range of the coke forming the coke layer, the coke forming the coke layer of Case 4 of Test 1 has a reactivity index CRI shown in Table 1 of 18 constant. The operation test was conducted after changing the particle size to three types of coke (coke B1 to B3).

  The results of measuring the reducing material ratio and the lower furnace ventilation resistance index are shown in FIG. The reducing material ratio and the airflow resistance index rapidly decreased when the coke particle size was 45 mm or more. This is because, in principle, when the particle size is large, the gas flow resistance becomes small, the reactivity is low and the reaction interface area is also small, so the gasification reaction amount is remarkably reduced and the powdering amount is suppressed, so that the gas flow is further reduced. It is presumed that the reducibility ratio was easily reduced due to the improved air permeability and this ventilation margin. Therefore, the particle size of the coke having low reactivity for forming the coke layer needs to be 45 mm or more, and is preferably 50 mm or more in consideration of the reducing material ratio and the effect of reducing the furnace bottom ventilation resistance.

  [Test 3] In test 3, in order to clarify the optimum range of the reactivity of coke forming the coke layer, the coke forming the coke layer of Case 4 of test 1 is classified into three types of cokes C1 to C3 shown in Table 1. The operation test was conducted after changing to coke.

  The results are shown in FIG. Both the reducing material ratio and the airflow resistance index rapidly decreased when the reactivity of the coke forming the coke layer was 32 or less. This is probably because the use of coke with low reactivity suppressed the gasification reaction and secured the air permeability of the bed. According to FIG. 4, the reactivity of the coke forming the coke layer needs to be 32 or less by CRI, and is preferably 25 or less by CRI in consideration of the reducing material ratio and the effect of reducing the furnace bottom ventilation resistance. .

  [Test 4] In test 4, in order to clarify the optimum range of reactivity of coke mixed with the ore layer, coke in the ore layer of Case 4 of test 1 (coke in the ore / coke mixed layer) is shown in Table 1. The same operation test was conducted by changing the coke index (Coke D1 to D3) to three kinds of cokes having a constant average particle diameter of 23 mm and changing the reactivity index CRI.

  The results are shown in FIG. The reducing material ratio decreased linearly with the coke reactivity in the ore layer, but the aeration resistance index decreased rapidly when the coke reactivity index CRI was 31 or more. The reduction in the reducing material ratio indicates that the thermal preservation zone temperature is linearly changing with the reactivity. The change in the airflow resistance index suggests that the powdering is suddenly suppressed when the predetermined reactivity is exceeded. Therefore, from the viewpoint of reducing agent ratio and air permeability control, the reactivity of coke mixed with the ore layer needs to be 31 or more, preferably 35 or more in terms of CRI value.

  [Test 5] In test 5, in order to clarify the optimum range of the particle size of the coke mixed with the ore layer, three types of coke shown in Table 1 with a constant reactivity index CRI of 39 and varying the particle size are shown. Using (Coke E1 to E3), an operation test similar to Case 4 of Test 1 was performed.

  The results are shown in FIG. The reducing material ratio and the airflow resistance index rapidly decreased when the coke particle size was 35 mm or less. This is because the contact interfacial area with the sintered ore increased due to the introduction of coke with a particle size of less than the predetermined particle size, the decrease in the temperature of the thermal preservation zone was promoted, and the particle size between the coke and the sintered ore approached. Therefore, it is assumed that the porosity was ensured. Therefore, the particle size of the coke mixed with the ore layer needs to be 35 mm or less, preferably 30 mm or less.

  From the above tests, coke that forms a packed bed by itself (coke with low reactivity and large particle size) and coke that is mixed with ore (coke with high reactivity and small particle size) are used. To summarize the conditions to be provided, the CRI value of “coke that forms a packed bed alone” is 32 or less and the average particle diameter is 45 mm or more, and the CRI value of “coke mixed in the ore layer” Is a coke having 31 or more and an average particle diameter of 35 mm or less.

  The method for producing coke having a CRI value of 32 or less and an average particle diameter of 45 mm or more is not particularly limited. Coke having a predetermined property is obtained by selecting a coal type, controlling a carbonization time in a coke oven, or sieving conditions of coke after carbonization. Or you may perform the modification process of the coke taken out from the coke oven. For example, a thermal treatment may be performed while flowing a hydrocarbon gas in the chamber, and a process for suppressing the reactivity may be performed by coating a carbon component on the coke surface.

  As a method of mixing the ore and coke, they are simultaneously cut out on a belt conveyor and loaded into a bunker installed at the top of the blast furnace furnace as a mixture of raw materials. In the case of a bell-less blast furnace having a plurality of raw fuel cut-out bunker at the top of the blast furnace furnace, coke or sintered ore may be put into separate bunker, and two or more of them may be cut out simultaneously.

  A method for producing coke mixed with ore having a CRI value of 31 or more and an average particle diameter of 35 mm or less is not particularly limited. Depending on the choice of coal type, addition of a catalyst such as CaO in the coal for reactivity control within the cost range, control of the carbonization time in the coke oven, or the sieving conditions of the coke after carbonization Get coke. Alternatively, so-called molded coke obtained by dry distillation after coal is previously molded with a binder may be used. After mixing coal and ore, so-called ferro-coke containing ore partially reduced by molding and dry distillation may be used. Ferro-coke contains metallic iron, so that high reactivity can be realized by its catalytic action. Therefore, it can be particularly suitably used as coke having a CRI value of 31 or more and an average particle size of 35 mm or less. The molded coke or ferro-coke may be used as a part of the coke mixed with the ore layer, or may be used as a whole amount.

The blast furnace used in the test is a blast furnace having a 3 parallel bunker with an internal volume of 5153 m ³ and a bell-less charging device, using ore and coke as charging materials, and sintered ore (average particle diameter of 18 mm, RI = 65, RDI = 35) 78% by mass and lump ore 22% by mass were used. The coke properties are an average particle size of 40 mm and CRI = 32. Each of these raw materials was divided into two batches, and ore and coke were alternately charged from the top of the furnace. Standard operating conditions were a pulverized coal blowing ratio of 120 kg / t, a coke ratio of 370 kg / t, and a furnace lower portion ventilation resistance index of 1.21.

  In order to confirm the effects of the present invention, the following operation changes were made following the standard operation. That is, a low-reactivity coke having a CRI value of 22 was produced in a coke oven, a coke having a large average particle size of 52 mm was produced by adjusting the sieve mesh, and transported to a storage hopper. On the other hand, standard coke having an average particle diameter of 40 mm and CRI = 32 was transported to another hopper. Both cokes were cut out from the hopper at the same time so that the former coke was 60% by mass in the mass ratio, mixed on a belt conveyor, and transferred to the first bunker at the top of the blast furnace furnace. The coke was charged into the blast furnace in a predetermined charging mode. As a result, the coke layer was charged with coke having an average particle diameter of 47 mm and CRI = 26 as a whole.

  On the other hand, during the charging of coke, the second bunker is charged with the usual ore raw material (78% by mass of sintered ore + 22% by mass of ore), and at the same time the ferrocoke (ore) is supplied to the third bunker. And coal was briquetted in advance and carbonized using a shaft furnace). The average particle size of ferrocoke was 12 mm (average value of major and minor axes), and the reactivity index CRI was 52. The ferro-coke contained 25% of the reduced iron ore in a mass ratio, and the reduction rate of the ore was 73% as a result of chemical analysis. After charging the coke into the blast furnace, ferro-coke and iron ore are simultaneously cut out from the bunker so that the ferro-coke charging amount is 125 kg / t, and is deposited in the furnace in a predetermined charging mode. It was.

  As a result of alternately repeating the above-mentioned coke single charge and mixed charge of ore and ferro-coke, the coke ratio gradually decreased under a constant pulverized coal injection ratio of 120 kg / t. Later, it reached 350 kg / t. Therefore, it was confirmed that the reducing material ratio can be reduced by 20 kg / t from 490 kg / t to 470 kg / t. Also, the furnace bottom ventilation resistance index gradually decreased, and decreased to 1.12 after 1 day.

As described above, the furnace bottom air permeability can be improved, the amount of expensive coke used can be reduced, and the use of the above charging method can lead to a reduction in hot metal costs and a reduction in CO ₂ generation. Proven.

The figure which shows typically the laminated structure in a blast furnace. The graph (Case 1-4) which shows a reducing material ratio and a furnace lower part ventilation resistance index. The graph which shows the change of the reducing material ratio with respect to the particle size of the coke which forms a coke layer, and a furnace lower part ventilation resistance index. The graph which shows the change of the reducing material ratio with respect to the reactivity of the coke which forms a coke layer, and a furnace lower part ventilation resistance index. The graph which shows the change of the reducing material ratio with respect to the reactivity of the coke in an ore layer, and the ventilation resistance index of a furnace lower part. The graph which shows the change of the reducing material ratio with respect to the particle size of the coke in an ore layer, and the ventilation resistance index of a furnace lower part.

Explanation of symbols

1 Blast Furnace 2 Upper Position in Furnace 3 Coke Layer (Coke A)
4 Ore layer 5 Coke in the ore layer 6 Coke layer (Coke B1)

Claims (2)

  In blast furnace operation in which ore and coke are charged from the top of the furnace and ore layers and coke layers are alternately formed, the CRI value of the coke forming the coke layer is 32 or less and the average particle diameter is 45 mm or more. A method of operating a blast furnace, comprising coke, wherein the ore layer is mixed with 120 kg / t or more of coke having a CRI value of 31 or more and an average particle diameter of 35 mm or less.   The blast furnace operating method according to claim 1, wherein ferro-coke produced by mixing ore and coal and dry distillation is used as coke mixed in the ore layer.

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