JPH0726130B2 - Blast furnace operation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention stabilizes the operation of a blast furnace by preventing the generation and growth of an inert zone associated with the pulverization of sinter in the periphery of the furnace wall of the blast furnace. It is about the method.

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

The sintered ore charged into the blast furnace rapidly expands into powder 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 in the furnace is an important management target in blast furnace 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 the blast furnace operation, the furnace condition of the blast furnace as described above is judged, and the sinter having the RDI index set empirically according to the furnace condition is charged to stabilize the operation. This RDI
Technological development to quantify the change criterion of the index has also been advanced, for example, in Japanese Patent Publication No. 63-61365, the pressure loss in the blast furnace is measured, and the measured value is a predetermined reference value 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 to which the sinter becomes higher. 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, reduction pulverization depends not only on the RDI index of the sinter to be charged, but also on the temperature distribution in the blast furnace, so to establish a comprehensive furnace wall deactivation measure, the ore and coke of the charge should be established. It is necessary to consider operating factors that affect the temperature of the inside of the furnace, such as the weight ratio of the furnace or the cooling conditions of the furnace wall.

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.

Particularly in recent blast furnaces, as the size and pressure have been increased, in consideration of gas leakage prevention in the furnace, cooling efficiency, etc., a stave in which the pipe is cast and wrapped with cast iron is placed between the furnace shell and the brick in the furnace. The stave method is used to insert and cool.
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.

(Problems to be Solved by the Invention) An object of the present invention is to prevent reduction powdering of sinter in the furnace of a blast furnace to prevent a malfunction of the blast furnace in advance, or to promptly recover a malfunctioning blast furnace. It is to provide a method for operating a blast furnace capable of recovering the furnace conditions.

(Means for Solving the Problem) The present invention is to install a plurality of furnace wall temperature detecting thermometers and heat flux meters in a furnace wall portion corresponding to an indirect reduction zone of a blast furnace shaft portion, and The blast furnace operating method is characterized in that the calculated overall heat transfer coefficient of the furnace wall is adjusted to 20 kcal / m ² · h · ° C or less ”.

The above-mentioned adjustment of the overall heat transfer coefficient can be performed by switching the cooling system from the forced water cooling system to the evaporative cooling system in the stave cooling type blast furnace. Further, nitrogen gas cooling can be adopted to adjust the overall heat transfer coefficient.

The basic idea of the present invention is to make the cooling conditions of the shaft part of the blast furnace appropriate, to reduce the temperature range (about 550 ° C) where reduction powdering is likely to occur in the indirect reduction zone as much as possible, and to reduce the particle size of the sintered ore in the furnace. The point is to keep it above a certain level.
As a means for this, adjustment of the overall heat transfer coefficient of the furnace wall is selected.

Figure 1 shows the overall heat transfer coefficient α and the particle size of the sintered ore around the furnace wall under the blast furnace shaft calculated from the reduction rate and temperature distribution in the furnace calculated using that α according to the reduction powdering rate equation. And the number of slips actually measured. The method for obtaining the overall heat transfer coefficient and the reduction powdering rate formula will be described in detail later.

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, if the sintered ore grain size around the furnace wall in the indirect reduction zone of the blast furnace shaft is set to a predetermined value or more, specifically 7 to 8 mm or more, the slip frequency is drastically reduced and the furnace condition is stabilized. It will be. Therefore, in the present invention, the grain size of 7 to 8 mm or more of the sintered ore in the furnace is secured by suppressing the overall heat transfer coefficient of the furnace wall portion to the above value or less.

In order to carry out the method of the present invention, it is necessary to install a plurality of furnace body thermometers on the furnace wall portion of the shaft portion (corresponding to the indirect reduction zone) of the blast furnace and measure the furnace temperature Ti and the shell temperature Tw. I won't. Further, a heat flow meter is installed on the surface of the iron shell to constantly monitor the heat flux q flowing from the furnace toward the iron shell. From these detected values, the overall heat transfer coefficient α of the furnace wall is calculated from the following equation.

α = q / (Ti-Tw) FIG. 2 shows the overall heat transfer coefficient α obtained as described above,
This α, the reduction rate in the furnace, the temperature, and the RDI of the sintered ore
It is a figure which shows the relationship with the particle size of the sintered ore in a furnace calculated from the index (here, 32 to 37%) using the reduction pulverization rate formula. As is clear from the figure, the grain size of the sintered ore in the furnace decreases as α increases. A large α means that the heat removal from the furnace wall is large, and therefore the temperature around the furnace wall decreases, and the sinter becomes long at a temperature of 400 ° C to 600 ° C that is likely to cause reduction powdering. The powder will stay for a long time, and the pulverization will proceed significantly.

From Fig. 1 above, if the control target is to suppress slipping to 2 times / day or less, it is necessary to keep the grain size of the sintered ore at about 8 mm or more. From Fig. ² , it can be seen that the overall heat transfer coefficient α of the furnace wall must be set to 20 kcal / m ² · h · ° C or less in order to maintain the grain size of 8 mm or less. RD of commonly used sinter
Since I is 32 to 37, if α is controlled to be 20 kcal / m ² · h · ° C or less, it will be possible to suppress stable reduction of sinter ore in general blast furnace operation. .

Here, a method of calculating the particle size of the sintered ore in the furnace using the reduction pulverization rate formula will be described. Various blast furnace models are known as this calculation method, and any of them may be used. Described below is one method proposed by the present inventors.

First, the reduction rate and temperature distribution in the furnace are calculated using α in the above equation. Although there are various calculation methods, in the method of the present invention, since it is necessary to know the reduction rate and the temperature distribution in the peripheral portion of the furnace wall in particular, the temperature distribution in the radial direction as well as the height direction in the furnace as described below, We have created a mathematical model that can also simulate the 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. The sinter descends in the furnace while being reduced,
The particle size Ds (mm) in this process is calculated by using the charged particle size Ds (mm), the reduction temperature T (° K), the reduction rate fs (%), and the RDI index (%) below (5) to (11). It can be expressed as an expression.

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 in equation (4), (1)
~ The particle size change can be obtained by making simultaneous equations (11) and calculating sequentially from the top of the furnace downward. When the furnace wall cooling of the blast furnace is a stave cooling type, α is 30 to 50 kcal / m ^{2 in} the case of the forced water cooling method, as shown in the examples described later.
h ・ ° C, 10 to 15 kcal / m ²・ h ・ ° C in case of evaporative cooling
Is. Therefore, in such a case, by switching the stave cooling method from forced water cooling to evaporative cooling, α
It can be 20 kcal / m ² · h · ° C or less.

(Example) Hereinafter, an example of the present invention in a 2700 m ³ blast furnace of a stave cooling system will be described.

Fig. 3 shows the operation frequency for 6 months under the basic conditions shown in Table 1, and shows the frequency of slip occurrence per day in units of one month. That is, when the stave cooling is performed by the forced water cooling method for the first 3 months, the average number of slips per day is 5 to 5.
After seven times, the furnace conditions were unstable. The overall heat transfer coefficient at this time calculated from the detected values of the furnace body thermometer and heat flow meter is 30 to 50.
It was kcal / m ² · h · ° C.

Next, the operation for 4 to 6 months was carried out by changing the stave cooling to the evaporative cooling. As shown in FIG. 3, the number of slips after the 4th month was 2 times or less per day, and the furnace conditions were extremely stable. The overall heat transfer coefficient at this time was 10 to 15 kcal / m ² · h · ° C.

Fig. 4 shows the furnace peripheral part obtained from the reduced powder variable velocity equation (Equation (2)) using the RDI index and overall heat transfer coefficient (average value for one month) of the sintered ore shown in Table 1. The transition of sintered ore grain size at (relative radius 0.85) is shown. In the first 3 months with many slips shown in Fig. 3, the particle size of the sintered ore is small as seen in Fig. 4, and the furnace condition becomes unstable due to reduction pulverization. Understand well. Looking at the particle size after April, change the cooling method of the furnace wall to lower the overall heat transfer coefficient to suppress reduction powdering in the peripheral area of the furnace and maintain a large sintered ore particle size. It is also clear that the reactor conditions can be stabilized.

(Effects of the Invention) According to the method of the present invention, reduction powderization of the sintered ore in the furnace is achieved only by optimizing the cooling conditions of the furnace wall without changing the properties (RDI index) of the sintered ore. It is possible to operate by maintaining the stable furnace condition of the blast furnace. Of course, it is also possible to carry out the method of the present invention in combination with other measures such as changing to a sinter having a small RDI index (hard to be reduced into powder).

INDUSTRIAL APPLICABILITY The present invention brings about a great economic effect of preventing a decrease in productivity and an increase in pig iron production cost due to a poor blast furnace condition.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a sintered ore grain size and a slip occurrence frequency in a peripheral portion of a furnace wall below a blast furnace shaft. FIG. 2 is a diagram showing the relationship between the sintered ore grain size and the overall furnace wall heat transfer coefficient in the periphery of the furnace wall below the shaft of the blast furnace. FIGS. 3 and 4 are diagrams showing the occurrence of slip and the change in the grain size of the in-furnace sintered ore in the blast furnace operation for 6 months, and the latter 4 to 6 months are the cases where the method of the present invention is applied.

Claims (2)

[Claims] 1. A furnace wall temperature detection thermometer and a plurality of heat flux meters are installed in a furnace wall portion corresponding to an indirect reduction zone of a blast furnace shaft portion, and an overall transmission of the furnace wall portion calculated from the measured values is provided. A blast furnace operation method characterized by adjusting the thermal coefficient to 20 kcal / m ² · h · ° C or less. 2. A blast furnace operating method according to claim 1, wherein in the stave cooling type blast furnace, the overall heat transfer coefficient is adjusted by switching the cooling method from the forced water cooling method to the evaporative cooling method.