JPH0726131B2 - Blast furnace operation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention prevents the generation and growth of an inert zone associated with the pulverization of sinter ore in the periphery of the furnace wall of a blast furnace, and constantly stabilizes the operation of the blast furnace. It is about how to do it.

(Prior art) In the blast furnace ironmaking process, iron ore (sintered ore etc.) pretreated in the raw material process and coke are properly blended, charged from the top of the blast furnace, and heated to 1200 ° C in a hot blast stove. This is a process in which high-pressure air before and after is blown from the tuyere at the bottom of the furnace to burn coke to reduce and melt the iron ore, and the generated hot metal is intermittently taken out from the tap at the bottom of the furnace.

The sintered ore charged into the blast furnace is rapidly pulverized due to volume expansion during the process of reducing hematite to magnetite at around 550 ° C. This is generally called reduction powdering. Therefore, if there is a low-temperature charge layer area around 550 ° C in the indirect reduction zone in the blast furnace, sinter ore powder is promoted in this area to increase ventilation resistance and rise from the lower part of the furnace. The distribution of reducing gas is hindered. Since the blast furnace is always supplied with a constant amount of gas in the steady state, the ratio of the heat capacity of the solid to the heat capacity of the gas (heat flow ratio), which is an indicator of the heat exchange status of the solid and gas when the gas flow rate locally decreases Locally rises, resulting in poor heat exchange from gas to solid, resulting in a lower temperature below and a so-called inactive zone. When such an inactive zone is formed on the furnace wall of the blast furnace, the ventilation resistance increases, so that the unloading of the contents inside the furnace stagnates and so-called rack hanging occurs or the unloading failure occurs. It becomes continuous, slipping,
Reactor condition becomes poor. If the furnace condition deteriorates, stable operation of the blast furnace, which is a continuous process, cannot be expected, and the reaction efficiency also decreases, leading to a significant decrease in blast furnace productivity. Therefore, prevention of reduction and pulverization of sinter in the furnace is an important management target in operation.

Usually, the reduction and pulverization of sinter is controlled by the RDI index (reduction and pulverization rate). This is a sinter of 15 to 20 mm heated to 550 ℃, reduced with a mixed gas of CO 30% + N ₂ 70% for 30 minutes, cooled, rotated 900 times with a small tumbler, and then sieved with a 3 mm sieve,
It is expressed as a percentage (% by weight) of 3 mm or less.

In conventional blast furnace operation, the furnace condition of the blast furnace as described above is judged, and sinter having an RDI index set empirically according to the furnace condition is charged to stabilize the operation. There is. Technological development for quantifying the change criterion of this RDI index is also underway, for example, in Japanese Examined Patent Publication No. 63-61365, the pressure loss in the blast furnace is measured, and the measured value is a predetermined standard with respect to the theoretical value. Disclosed is a method of charging a sinter having a low RDI index, that is, a reduced reduction powder depending on the degree of increase above the value. According to this method, it is said that measures will be taken to inactivate the blast furnace wall before it causes a malfunction in the blast furnace, which will stabilize the unloading of the blast furnace and facilitate gas distribution. However,
Since reduction dusting depends not only on the RDI index but also on the temperature distribution in the blast furnace, the weight ratio of the ore and coke in the charge or the cooling conditions of the furnace wall must be established in order to establish comprehensive furnace wall deactivation measures. It is necessary to consider operating factors that affect the temperature inside the furnace such as.

Japanese Unexamined Patent Publication No. 60-33305 discloses a method of measuring the temperature distribution in the peripheral area of a high-rise interior to prevent furnace wall inactivation. That is, when low fuel ratio operation or all coke operation is performed in the blast furnace, the charge temperature cannot be sufficiently obtained in the furnace peripheral part of the blast furnace shaft, so that water condensation occurs in the upper stage of the shaft and zinc oxide deposition in the middle and lower stages of the shaft occurs. Reduction and pulverization of the sinter occurs, which deteriorates air permeability and forms an inert zone. In order to prevent this, according to the method disclosed in Japanese Patent Laid-Open No. 60-33305, when the temperature measurement value becomes lower than the reference value, a high temperature partial combustion gas is blown into the charge in the peripheral portion of the furnace. However, this method does not show the management criteria for the RDI index of sinter and the cooling conditions of the furnace wall.

Especially in recent years, blast furnaces have become larger and higher in pressure,
A stave system is adopted in which a stave in which a pipe is cast and wrapped with cast iron is inserted between a furnace shell and a brick in the furnace in order to prevent leakage of gas in the furnace and cooling efficiency. However, when the furnace body is deteriorated and the bricks inside the blast furnace are eroded, the stave is exposed inside the furnace and excessively cools the inside of the furnace. Especially when the damaged stave is replaced with a new stave, the cooling state becomes stronger. If the cooling by the stave becomes excessive, the temperature of the furnace wall will drop, and the charge will fall to the lower part of the furnace without being sufficiently heated, which will delay the reduction of the ore and increase the amount of pulverization especially in the sintered ore. Seen. However, conventionally, no measures have been taken against the reduction and pulverization of the sintered ore due to such supercooling of the furnace peripheral part,
RDI index, which is the property of the sinter itself, the operating conditions that affect the temperature around the furnace and the cooling conditions of the furnace wall, are not known to prevent the generation of the inert zone.

(Problems to be Solved by the Invention) An object of the present invention is to predict the influence of the cooling conditions of the furnace wall of the blast furnace on the reduction and pulverization of the sinter, detect the malfunction of the blast furnace quickly, and reduce the sinter and the reduction powder. It is intended to provide a blast furnace operation method capable of preventing liquefaction and unloading of a charge, and quickly recovering a furnace condition in which gas distribution is good.

(Means for Solving the Problem) The gist of the present invention is to calculate a distribution in the furnace height direction of the reduction rate and temperature in the periphery of the furnace from the overall heat transfer coefficient of the furnace wall in the indirect reduction zone of the shaft of the blast furnace. The calculated value is used to calculate the particle size of the sinter in the furnace, and the RDI index of the sinter to be charged is adjusted so that the calculated value is above a certain limit value. And the blast furnace operating method.

The specific method for carrying out the method of the present invention is as follows.

First, a method of calculating the distribution of the reduction rate and the temperature around the furnace wall in the blast furnace will be described.

Multiple temperature detectors were installed on the furnace wall of the blast furnace to control the temperature inside the furnace.
In addition to measuring Ti and the shell temperature Tw, a heat flux is installed on the surface of the shell to set the heat flux q flowing from the furnace toward the shell.
By constantly monitoring, the overall heat transfer coefficient α of the furnace wall is calculated by the following formula.

α = q / (Ti-Tw) Next, the reduction ratio and temperature distribution in the furnace are calculated using the above α. There are various calculation methods, but in the method of the present invention, it is necessary to know the reduction rate and the temperature distribution especially in the peripheral portion of the furnace wall.
As described below, we have created a mathematical model that can simulate not only the height direction in the furnace but also the radial temperature distribution and reaction rate distribution.

That is, the cross section of the blast furnace shaft is divided into 10 equal cross-sectional areas by multiple concentric circles, and the state distribution in the height direction within each division is a well-known countercurrent moving bed one-dimensional mathematical model, for example, "iron and steel" 68 ( 198
2) Calculate based on the mass balance formula and heat balance formula of the following formulas (1) to (4) introduced on P.2369 and P.2377. This model takes into account heat conduction in the radial and height directions, and heat dissipation from the furnace wall in the outermost shell division near the furnace wall.

[Material balance equation]

(gas) (solid) [Heat balance type] Where, Ζ: downward height position (m) relative to the bed top (furnace top) in the furnace, r: radial position in the furnace (m) Vg, ρg: gas flow velocity (m / sec), Density (kg / m ³ ) ρs: Solid bulk density (kg / m ³ ) Xj, Yi: Solid weight ratio (-), mole fraction (-) Tg, Ts: Gas temperature (° C), Solid temperature ( ℃) C: Heat capacity (Kcal / Kmol ・ ℃) m: Molar molecular weight (kg / kmol) hp, ap: Heat transfer coefficient (Kcal / m ²・ sec ・ ℃), Specific surface area (m ² / m ³ ) kz, kr: Effective thermal conductivity of packed bed (Kcal / m · sec · ° C), R, M: Reaction rate (Kmol / m ³ · sec), stoichiometric coefficient ΔH: Reaction heat (Kcal / Kmol) i: CO , CO ₂ , H ₂ , H ₂ O, N ₂ j: Fe ₂ O ₃ , Fe ₃ O ₄ , FeO, Fe, C, gangue l: CO reduction, H ₂ reduction, carbon deposition, shift reaction, etc. α: Heat transfer coefficient of furnace wall (however, only the outermost shell division is considered) (kcal / m ² · sec · ° C) Next, a method of determining the particle size of the sintered ore in the blast furnace will be described.

Sintered ore expands in volume during the reduction of hematite to magnetite, cracks and powders. There is also a method of examining the particle size by sampling from inside the furnace, but it is difficult to actually measure the particle size of the sintered ore in the operating blast furnace because the pulverization further progresses due to the impact during sampling. Also,
Since the temperature and reduction conditions in the blast furnace and the conditions of the reduction pulverization test are different, it is not possible to judge from the RDI index how much the sinter is pulverized in the blast furnace.

In order to solve such a difficulty, in the method of the present invention, the sintered ore particle size is theoretically obtained from the temperature distribution in the blast furnace and the reduction rate distribution, and the sintering is performed so that this value becomes a predetermined value or more. The RDI index of the ore is adjusted to prevent powdering of the sintered ore.

The sinter ore descends in the furnace while being reduced, but the particle size Ds (mm) in this process is the charged particle size. It can be expressed as in the following equations (5) to (11) using the furnace temperature T (° K), the reduction rate fs (%), and the RDI index (%).

here, Ds: Particle size after pulverization (mm) f: Reduction rate (%) T: Temperature (° K) RDI: RDI index (%) γ, n: Constant (= 25, 2.69) Therefore, the overall heat transfer coefficient is Substituting equation (4) into (1)
By solving the mass balance equation and heat balance equation up to (4), the temperature (T) and the reduction rate (fs) are calculated, and the results are substituted into the equations (5) to (11). Particle size of ore (D
s) can be obtained. Like this (1) ~ (11)
The particle size change can be obtained by making simultaneous equations and sequentially calculating from the upper side to the lower side.

In this way, the RDI index of the sinter to be charged is adjusted so that the theoretically obtained particle size becomes equal to or greater than a predetermined value to prevent pulverization in the furnace. That is, if the brick wall wear is significant and the overall heat transfer coefficient is abnormally high, RD
Blast furnace operation can be performed smoothly by charging a sinter having a small I index (excellent reduction pulverization resistance).

(Operation) FIG. 1 shows the reduction powdering rate equation, that is, the equations (5) to (11), from the overall heat transfer coefficient α and the distribution of the temperature in the furnace calculated using the α as described above, and the temperature distribution. 2 is a graph showing the relationship between the particle size of the sinter ore in the peripheral portion of the furnace wall at the bottom of the blast furnace shaft calculated according to the above and the number of slips actually measured.

Here, the slip is a phenomenon in which the charge in the blast furnace discontinuously unloads by 1 m or more, and its occurrence can be actually measured by a measuring rod for measuring the height of the furnace internal charge. The frequent occurrence of slips indicates that the unloading of the contents inside the furnace is unstable and the furnace conditions are poor.

As shown in Fig. 1, the frequency of slip occurrence increases as the particle size of the sinter decreases, and especially the particle size of the sinter increases from 7 to 8 m.
Slip increases sharply when m or less. From this result, the grain size of the sintered ore in the peripheral portion of the furnace wall in the indirect reduction zone of the shaft portion of the blast furnace is not less than a predetermined value, for example, 7 to 8 m in the case of this blast furnace.
If it is more than m, the slip frequency will be drastically reduced and the furnace condition will be stable.

As one of the means for maintaining the grain size of the sintered ore in the furnace at the above-mentioned value of, for example, 7 to 8 mm or more, the cooling conditions from the furnace wall, specifically, the overall heat transfer coefficient of the furnace wall is adjusted. There is a way. However, especially when the bricks of the furnace wall are significantly worn, a method of relaxing the conditions for cooling the furnace wall and lowering the overall heat transfer coefficient cannot be used to protect the iron shell. Therefore, in the method of the present invention, the characteristics of the sinter to be charged, specifically, the RDI index is changed to suppress the reduction pulverization and maintain the above-mentioned particle size.

Examples of the method of the present invention will be described below in comparison with comparative examples.

(Example) Table 1 shows the blast furnace operation results of the example of the method of the present invention and Comparative Examples 1 and 2.

Comparative Example 1 is an example in which the blast furnace is operating smoothly even if the furnace wall brick is sound and the sinter having an RDI index of 37, which has a relatively poor reduction powdering property, is used.

Comparative Example 2 is an example in which the overall heat transfer coefficient of the furnace wall became abnormally high one week after the furnace wall brick fell off.

The example is an example in which the sinter having an RDI index of 37 was changed from a sinter having an RDI index of 37 to a sinter having a RDI index of 32 according to the method of the present invention after the blast furnace failed in Comparative Example 2.

2 and 3 show Comparative Examples 1 and 2, that is, the temperature distribution in the height direction and the reduction rate distribution in the peripheral portion of the blast furnace wall when the furnace wall is healthy and when it is not.
As can be seen in these figures, in Comparative Example 1 in which the blast furnace is operating smoothly, 600 m
The temperature is higher than ℃, and the reduction is progressing sufficiently. On the other hand, in Comparative Example 2 in which the furnace wall bricks fell off, the cooling of the furnace wall was strengthened, so that the temperature was 600 ° C or less even at 8 m or less from the stock line, and the reduction rate was 10% or less and up to magnetite. It's just a return. As shown in Table 1, the operation result of the blast furnace was that in Comparative Example 1, the fuel ratio was appropriate at 475 kg / t, the ventilation resistance index was small, and slip was good. On the other hand, in Comparative Example 2, the furnace top temperature decreased to 103 ° C., slip increased, the ventilation resistance index and gas utilization ratio deteriorated, and the fuel ratio increased. Also, two days after this, the temperature of the furnace wall at the bottom of the furnace dropped and fell into a disorder.

FIG. 4 shows the temperature and reduction rate distributions of FIGS. 2 and 3.
It is the result of calculating the particle size of the sintered ore in the peripheral part of the furnace based on the RDI index of the charged ore (37 in Comparative Examples 1 and 2, 32 in Example). As is clear from this figure, in Comparative Example 1 in which the operation is favorable, there is little pulverization and the particle size of the sinter is about 7 mm, whereas in Comparative Example 2 after the falling of the bricks of the furnace wall (sintered charged) The RDI of the ore decreased to around 3 mm in 37), indicating that the poor condition of the furnace was due to deterioration of air permeability due to pulverization. On the other hand, after falling into a poor reactor condition as in Comparative Example 2, RD
In the case of the example in which the sinter ore having the I index of 32 was switched to, the distribution of the particle size of the sinter ore in the furnace has almost the same pattern as that of Comparative Example 1 in which the furnace is healthy. In other words, the particle size has recovered to a level close to that of Comparative Example 1 in which the operation is favorable. As a result, the slip was reduced, the air permeability was improved, and the fuel ratio was 485 kg / t, which was an almost appropriate value, as shown in the column of Example in Table 1.

(Effect of the Invention) According to the present invention, the state of reduction and pulverization of the sintered ore in the furnace is grasped by using the temperature of the furnace body and the heat flux of the wall of the furnace, and the sintered ore charged according to the situation is grasped. The operation of the blast furnace can be stabilized by a relatively simple method of adjusting the RDI index of. In particular, it is possible to quickly and surely normalize the furnace condition in which the furnace wall brick falls off, the furnace wall temperature decreases, and slips due to abnormal ventilation occur frequently. Further, in terms of operation, the fuel ratio can be restored to an appropriate value, and the productivity can be maintained at the same level as during normal operation.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the slip occurrence frequency in the blast furnace and the particle size of the sintered ore in the furnace. FIG. 2 is a diagram showing the temperature distribution in the furnace height direction in the peripheral part of the furnace in comparison with the normal operation (Comparative Example 1) and the furnace condition after the falling of the brick wall (Comparative Example 2). is there. FIG. 3 is a diagram showing the reduction rate distribution in the furnace height direction in the peripheral portion of the furnace in the case of Comparative Example 1 and Comparative Example 2 described above. FIG. 4 is a diagram showing the sintered ore particle size distribution in the furnace height direction in the peripheral portion in the furnace in Comparative Examples 1 and 2 and the Example of the present invention charged with the sintered ore having a small RDI index. is there.

Claims (1)

[Claims] 1. A distribution in the furnace height direction of the reduction rate and temperature in the periphery of the furnace is calculated from the overall heat transfer coefficient in the furnace wall of the indirect reduction zone of the shaft of the blast furnace, and the calculated values are used to calculate the inside of the furnace. A method for operating a blast furnace, characterized in that the grain size of sinter ore is calculated, and the RDI index of the sinter to be charged is adjusted so that the calculated value is above a certain limit value.