JPS649373B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coke charging method in blast furnace operation, and more specifically, the present invention relates to a method for charging coke in blast furnace operation, and in particular, by adjusting the layered state of charging raw materials (coke and ore) in the blast furnace at the coke charging stage. This article relates to a method for ensuring a stable central flow and contributing to stable blast furnace operation.

In recent years, as blast furnaces have become larger, the amount of pig iron produced per blast furnace has increased dramatically, but in order to make the most of the advantages of larger sizes, it is important to keep the operating conditions of the blast furnaces stable. The important point is how to maintain it. Particularly in large blast furnaces, as the furnace conditions deteriorate, the production volume decreases significantly, and the impact on the next process is also significant. Therefore, when operating a blast furnace, various operating conditions must be skillfully controlled, and it is particularly important to appropriately control the distribution of the charging material within the furnace. In other words, the ore charged into the furnace is heated and reduced by the high-temperature reducing gas rising inside the furnace, but in order to efficiently perform this heating and reduction, it is necessary to It is necessary to maintain a uniform distribution of the gas and supply the reducing gas evenly to all ores. However, in actual operations, it is difficult to maintain a uniform distribution state due to various factors such as the characteristics of the raw material charging device and the deposition characteristics of the charged material. In particular, it is difficult to avoid disturbances in the distribution state due to physical or chemical fluctuations occurring during the charging raw material preparation process or deterioration of furnace conditions, etc. with current operating methods. If these things disrupt the circumferential balance of the rising gas,
Localized drift of the reducing gas occurs, and shelving, slipping, flattening, etc. occur frequently. In particular, when shelving occurs, the air blowing pressure temporarily increases, and this wind pressure causes the floating and slugging phenomena in which the charged material is blown up, resulting in extremely poor furnace conditions. Therefore, in order to maintain stable operation even when there are unavoidable changes in furnace conditions as mentioned above, it is necessary to
Rather than simply distributing the furnace gas flow evenly,
It has recently become a general decision to concentrate a portion of the gas flow in a certain area, particularly in the core (hereinafter referred to as the "center flow"), to function as a safety valve against the rise in gas pressure in the reactor. Although this has been confirmed empirically, the technology for continuously obtaining a safe central flow has not yet been fully developed to a satisfactory level. In other words, in a normal charging method such as the bell method, ore and coke flow in and fall from the furnace wall side, but since the angle of repose of ore is smaller than that of coke, it is easy to flow toward the core side and the ore layer and coke layer are separated. The thickness ratio of ore/coke (hereinafter simply referred to as O/C) becomes higher in the reactor core. In particular, in blast furnaces that use pelletized ore, the angle of repose of the pelletized ore is even smaller, so the flow of the ore toward the center of the furnace is significant, and the O/C at the center of the furnace tends to become even higher. There is a particularly strong desire to lower the O/C in the center of the furnace. The most common method proposed to solve the above problem is to drop and charge coke with good ventilation into the reactor core. Figure 1 is a schematic diagram showing the raw material charging method and the distribution of the charged raw materials according to the proposed improvement. , by displacing the armor plate 6 by the cylinder 5, the position at which the charged raw material falls into the furnace is changed. For example, when charging coke 2,
With the armor plate 6 in the state shown by the broken line in Figure 1,
The falling position of coke 2 is set to the core side, while ore 3
When charging the ore, the armor plate 6 is placed in the solid line state shown in FIG. 1 so that the falling position of the ore 3 is concentrated on the furnace wall side. By this method, the O/C in the core is reduced, the coke ratio in the core is increased, and the tendency to form a central flow is strengthened.

However, in the above method, as is clear from Figure 1, the O/C gradually decreases from the furnace wall toward the core, so the gas flow velocity in each part of the blast furnace 1 is as shown in Figure 2. As shown in the graph, a gradual increase pattern was formed in which the temperature gradually increased from the reactor wall side to the reactor core side, and as will be described later, it was found that the gas utilization rate and thermal efficiency could not be sufficiently increased. In other words, it was found that ideally, as shown in Figure 3, it would be desirable to have a high gas flow rate only in a very limited area of the reactor core, and to provide a nearly uniform gas flow rate distribution in other areas. However, in order to obtain the gas flow velocity distribution as shown in Fig. 3, a single layer of coke or a raw material layer with extremely low O/C would be formed in a narrow area of the reactor core, and a layer of raw material with extremely low O/C would be formed in other wide areas. It is necessary to form a raw material layer in which the O/C ratio is as equal as possible. The present invention deals precisely with this field.

By the way, the raw material in the blast furnace gradually descends over time, and as it goes downward, it encounters higher-temperature reducing gas. Therefore, the temperature of the raw material layer gradually rises as it descends, and when it eventually reaches the softening temperature unique to the ore, a softening phenomenon begins within the ore layer, and the ores, which were previously granular or lumpy, begin to soften from the surface and fuse together. do. The ore layer that has started softening and fusion falls further and encounters higher-temperature gas, and the reduction reaction progresses as it is further softened to the inside, and eventually falls to the temperature range where melting and dripping starts, which is unique to the ore, and the softened ore begins to melt. It begins as a melt and trickles down between particles in the lower coke layer, further dropping towards the hearth. The ore that exists between the start of softening and the completion of melting is called the softened cohesive layer, and the distribution of this softened cohesive layer in the blast furnace is macroscopically called the softened cohesive zone. The shape of the softened cohesive zone changes in various ways depending on the operating conditions of the blast furnace, but assuming that the above-mentioned central flow is ideally formed, it can be expressed as shown in FIG. 4. That is, in Fig. 4, ore 2 and coke 3
The reducing gas is charged in alternating layers and descends one after another. However, when the aforementioned reducing gas forms a central flow and rises, the temperature becomes higher in the center, so the inside of the blast furnace is shaped like a mountain as shown in the figure. Can draw isotherms. And now if 1200℃ is the softening start temperature line L ₁ , 1450
If ℃ is the melting dripping temperature line L ₂ , the ore existing between them softens and a softened cohesive layer C is formed there, and a chevron-shaped (commonly known as an inverted V-shape) softened cohesive zone D is formed as a whole. It turns out. Furthermore, softened fusion layer C
In this case, the ore has softened and the ventilation resistance has become extremely large, but the coke that exists between each cohesive layer C has a high melting point, so it is difficult to form it at the time of charging (granular or lumpy).
It is called coke slit E because it maintains a low ventilation resistance. Therefore, the high-temperature air blown from the tuyere 8 burns the coke that has fallen directly above it, and the generated reducing gas passes through the coke slit E and onto the softened cohesive zone D as shown by the arrow. It rises while heating ore 2 and coke 3. The shape of the above-mentioned softened cohesive zone D is determined by the operating conditions of the blast furnace, particularly the internal temperature distribution unique to each blast furnace, which depends on the gas flow distribution in the furnace, and is of course also controlled by the control of operating conditions. However, it has been found from dismantling surveys when the blast furnace is shut down that it can be classified into three types: inverted V-type, W-type V-type, and W-type V-type as shown in FIGS. 5A to 5C.

As mentioned above, the shape of the softened cohesive zone D has a strong causal relationship with the operational status of the blast furnace, but it is also well known that the operation of the blast furnace is greatly influenced by this shape. For example, this affects the reducing gas utilization rate and heat exchange efficiency, and may also cause abnormal dropping of the raw material due to slipping or hanging on the shelf. Therefore, controlling the shape of the softened cohesive zone inside the furnace is considered to be an important issue in maintaining proper blast furnace operating conditions and performing stable and efficient blast furnace operation. Many efforts have been made to understand the shape of the softened cohesive zone inside the material and to establish methods for its control.

The present invention was made in view of these circumstances, and it is a method of loading raw materials (especially coke) that can maintain the softened cohesive zone shape in an optimal form by ensuring a central flow. This is the result of research aimed at providing a method for entering the system. That is, the present invention is a coke charging method in which ore and coke are alternately charged into a blast furnace, in which the coke charging in each charge is divided over time into at least two series, and the total charging of the charge is 92 to 98.5 of coke amount
Charge % by weight so as to cover all the ore layer previously charged,
In the last charging series, 8 to 1.5% by weight of the total amount of coke charged in the charge is intensively charged into the furnace center, thereby reducing the O/C in the furnace center to the O/C in the area other than the furnace center. The gist lies in depositing the metal so that it is substantially smaller than /C.

The structure and effects of the present invention will be clarified below while referring to the background of the research.

First, the inventors thought that it would be necessary to more accurately grasp the shape of the softening cohesive zone online, and tried to estimate the profile of the softening start temperature line L ₁ (1200°C) in Fig. 4 in an actual furnace. I have thought about this and have conducted various studies, so I will explain from this point.

In other words, by focusing on the layered structure of the blast furnace charging material as mentioned above and calculating the heat balance and mass balance in each layer of the coke layer and the ore layer, it is possible to estimate the temperature distribution in the height direction inside the furnace. I thought it could be done.
In other words, each layer that has descended to the charge position i in the furnace is heated in an atmosphere at the gas temperature (Ti) for the charging interval (H time), and then heated to the charge position i+1.
Move to charge position. The heating equations for the coke layer and the ore layer at the i charge position are both expressed by equation (1).

d/dθ (ρbCst) = a hp (Ti-t) + 〓 ^j Rj (-ΔHj) (1) where ρb: Bulk density Cs: Solid specific heat t: Solid temperature a: Heat transfer specific surface area hp: Gas to solid Ti: Gas temperature at i charge position Rj: Reaction rate of component j reacting in the coke layer or ore layer ΔHi: Heat of reaction of component j reacting in the coke layer or ore layer θ: Time θ=0 , t=ti-1, by integrating equation (1) up to the charging interval H time, the temperature ti reached by the solid in each layer at the i charge position can be obtained.

On the other hand, from the overall heat balance of each layer at the i charge position,
i Gas temperature flowing into each layer at the charge position (Ti
+1) is calculated using equation (2).

T _i-1 = Ti + Gi (ti-t _i-1 ) + 〓 ^j Mj (-ΔHj) (2) where Gi = Δk Fs ρb Cs/ΔFg ρg Cg (k=c, o) Δk (k=c, o): Thickness of coke layer and ore layer, Δ=Δc+Δo Fs: Falling amount of charge Fg: Gas flow rate ρb: Gas density Cg: Gas specific heat Mj: Reaction amount of j component related to reaction Also, i-1, i charge The change in gas component [X ^(j) _i ] due to the reaction between

X ^(j) _i = X ^(j) _i-1 −mjMj (3) mj: Stoichiometric coefficient Next, substitute the gas temperature Ti at the furnace top or a certain designated i charge position into equation (1) and integrate it. By doing this, the solid temperature ti can be obtained, and the gas temperature and components of the next charge can be calculated from equations (2) and (3). Then, by substituting the gas temperature obtained in equation (2) again into equation (1) and updating i, by repeating the calculations of equations (1) to (3), The temperature at the charge position, that is, the temperature distribution in the height direction can be calculated.

In addition, the blast furnace is divided into n parts in the radial direction, and each divided area is
By applying equations (1) to (3) and repeating the above calculation procedure, the temperature distribution in the furnace radial direction and height direction can be determined. The height direction position and layer thickness of the coke layer and ore layer for each divided area are calculated by adding the contraction caused by the descent of each layer to the measurement results of the radial layer thickness distribution at the top of the furnace. FIG. 6 shows an example of calculating the temperature distribution in the height direction of each divided area when divided into five areas in the radial direction. As shown in FIG. 6, by connecting the positions in the furnace at an arbitrarily specified temperature (for example, 1200° C.), its isothermal line can be determined.

Since it is necessary to adapt equations (1) to (3) accurately to actual operation, the in-furnace reaction rate [Rj in equation (1)]
Regarding the above, it is determined so that the actual measurement results (Japanese Patent Publication No. 57-48621, etc.) of the temperature distribution in the furnace by simultaneous measurement at multiple points match the calculated results. It is also possible to calculate equations (1) to (3) starting from the top of the furnace, but the top of the furnace is far from the cohesive zone, and the measurement information at the top of the furnace depends on the deposition angle of the charge. It is difficult to accurately estimate the situation in the high-temperature range of 1000℃ or higher and the starting position of ore fusion because it does not necessarily reflect the situation inside the furnace due to the influence of gas drift. be. Therefore, as the starting position for calculating equations (1) to (3), the installation position of the measuring device that is close to the cohesive zone and that can measure both the gas temperature and gas components in the radial direction is adopted.

As shown in Figure 7A, using the parameter (Rj) determined so that the estimated result of the 1200°C isotherm line and the actual measurement result match, the estimated 1200°C isotherm line and the actually measured one when the operating conditions are significantly different are used. The seventh
A comparison is shown in Figure B, which shows good agreement.

The 1200°C isotherm estimated in this way is regarded as the line at which the fusion of ores begins to coalesce in the furnace, that is, the external shape of the softened cohesive zone, and this is shown in Figure 8.
Divide the blast furnace into upper and lower parts using the 1200℃ isotherm. Let the volume of the deposited layer above this isotherm be _V1 , and let the volume below including the softened cohesive zone be _V2 . Furthermore, the distance between the 1200°C position of the most peripheral part of the blast furnace (shell part) and the position of the central axis of the tuyere is defined as Hw.

Next, the relationship between V ₁ / (V ₁ + V ₂ ) and the gas utilization rate [η _cp ], the relationship between Hw and the position of the slab cooler that receives the maximum heat load on the furnace wall, and the relationship between Hw and the Si concentration in the hot metal are calculated. Since the values were obtained as shown in Figures 9 to 11 (the shaded area indicates the management range), the background thereof will be explained below. These are data when the shape of the softened cohesive zone is an inverted V shape and a W shape, but first, according to Figure 9, the value of V ₁ / (V ₁ + V ₂ ), that is, relatively
It can be seen that the larger the raw material volume (volume of granular or lumpy region) above the 1200°C line, the larger the gas utilization rate. However, there was almost no significant difference in this tendency between the inverted V type and the W type.

On the other hand, FIG. 10 shows a comparison between Hw on the horizontal axis and the maximum position of furnace wall heat load (determined from the distribution of shell temperature or refractory wall temperature) on the vertical axis. Based on the 45° slope line that shows a 1:1 relationship in this figure, it can be seen that in the W type, Hw is generally at the bottom and at a position considerably higher than the maximum heat load position, while in the inverted V type, it is generally at the bottom. It can be seen that Hw is above the reference gradient line and below the maximum heat load position. In other words, in the case of the W-type, the heat load is greater on the furnace wall below the cohesive zone position, and this is because the high temperature gas coming out of the tuyere reaches the cohesive zone as shown in Figure 12A. This is because the gas flow is divided by the downward protruding cape and rises in two directions: towards the reactor core and directly above the tuyere, and the rising gas flow along the reactor wall strongly heats the reactor wall below the cohesive zone. Seem. On the other hand, in the inverted V type, as shown in Figure 12 (b), the high-temperature gas coming out of the tuyeres flows deeply toward the center of the furnace along the slope of the cohesive zone, and passes through the coke slits explained in Figure 4 above to the upper part. This is thought to be because the gas is distributed into a lumpy zone, and at this point the influence of the gas flow appears on the furnace wall. However, in blast furnace operation, it is desirable to maintain a sufficiently high temperature in the center of the furnace in order to prevent a drop in hot metal temperature, and in order to prevent the furnace wall from melting due to damage to the cooling disk, it is desirable to maintain the temperature in the furnace periphery, especially the blade. Since it is said that it is desirable that the temperature directly above the mouth be as low as possible, it can be concluded that the shape of the cohesive zone is preferably an inverted V shape that satisfies the above requirements.

Next, Figure 11 shows the relationship between Hw on the horizontal axis and the Si concentration in hot metal on the vertical axis.
Regardless of type or inverted V type, Hw is required for low Si.
It turns out that it is better to lower the position.
However, if we focus on Hw in the same figure, it tends to be lower in the inverted V type than in the W type, and therefore it seems easier to lower the Si concentration. The conclusion is that a V-type is preferable.

As mentioned above, an inverted V shape is preferred as the cohesive zone shape, but from the viewpoint of gas utilization rate,
It is preferable to increase V ₁ / (V ₁ + V ₂ ), and from the viewpoint of protecting the furnace wall and reducing Si in the hot metal, Hw
It is preferable to make it smaller. That is, it has been found that it is preferable to control the operation so as to form an inverted V-shaped cohesive zone at the lowest possible position within the blast furnace. As a guideline, it was understood that two conditions can be set: V ₁ /V ₁ +V ₂ ≧0.52 (4) from Fig. 9, and Hw≦7.5m (5) from Fig. 11.

By the way, when controlling the shape and position of the cohesive zone, the first priority should be to control the shape to an inverted V shape.
The study focused on controlling the gas flow so that the temperature distribution inside the blast furnace becomes mountain-shaped as shown in Figure 4.

As can be understood from the above explanations, the factors governing the gas flow distribution are the distributions of the ore layer and the coke layer, and in order to meet the above objectives, it is absolutely necessary to ensure a central flow. To achieve this, it is necessary to devise a method to reduce the ventilation resistance of the deposited layer in the furnace at the center of the furnace, and it is necessary to achieve this using a method superior to the armor plate method described above (Figure 1). become. Therefore, the present inventors devised a drastic countermeasure and studied it using a model vessel, and found that the coke charging operation was divided into at least two series, and in the initial charging operation series, the total amount of coke input for the charge was If most of the coke is charged so as to cover the entire ore layer of the pre-charging operation, and the remainder of the total amount of coke charged in the charge is intensively charged to the center of the furnace in the last charging operation series, It was confirmed that a laminated state as shown in FIG. 13 could be obtained. That is, in Fig. 13, coke is charged over time in two series, A and B, but ore 3 and coke A are charged by the normal Bell charging method, and the angle of repose of ore 3 is different from that of coke A. Because it is smaller than the angle of repose, if there were no coke B, the thickness of ore 3 in the furnace center would be greater than the thickness of coke A (O/C
), the ventilation resistance at the center of the furnace becomes large, and a central flow cannot be obtained. However, in the charging method of the present invention, after the charging of coke A is completed, coke A
Fill the center recess of the coke B and stack it further.
Since Ore 3 is charged in a concentrated manner, the center of the furnace is already occupied by coke B, so the amount that enters the center of the furnace is extremely small and the amount of O in the center of the furnace is reduced. /C becomes very small and can greatly contribute to securing the central flow. In other words, this charging method actively utilizes the relatively large angle of repose of coke, and additionally charges coke B onto the depression in the center of the furnace created by charging coke A. Even if the coke B is charged, the small mountain of coke B will not flatten, so the coke B/A distribution ratio in the charge does not need to be so large, and the effect of charging coke B will be extremely stable. The effects of the present invention can be maximized by performing split charging as described above each time coke is charged, but if the furnace conditions have stabilized due to the above control or other conditions If the furnace conditions change due to furnace operation conditions, a charging method that deviates from the numerical conditions of the present invention or a normal coke charging method may be combined to some extent.

The method of charging coke B intensively into the center of the furnace to form a mound on coke A is not particularly limited in the present invention, but a typical method is as shown in FIG. 14. Coke B in Bell 4
As shown in Fig. 15, the coke B passes through the upper part of the blast furnace shell.
An example is a method in which the supply pipe 10 is inserted and its tip faces the center of the furnace.

Next, the reason why it is determined that the charging amount of coke B is preferably 2 to 8% by weight based on the total amount (A+B) will be explained. Figure 16 shows the charging ratio of coke B from 8.3 to
(1) O/C distribution (ventilation resistance distribution) in the radial direction of the furnace body, (2) exhaust gas temperature distribution at the top of the furnace, and (3) shape of softened cohesive zone when appropriately varied between 1.4% by weight. ,(Four)
This shows the V ₁ /(V ₁ + V ₂ ) ratio and (5) Hw. Coke (10 to 20 mmφ) and olefin resin (substitute for ore, 6.5 mmφ) were placed in a 0.6 m ³ test furnace using the method of the present invention. The experiment was carried out by charging air at 170°C from below. The fusion start temperature of the olefin resin was 90°C, and the volume ratio of coke/olefin resin was 3.14 in accordance with the actual furnace. Note that (1) above
Among the items in (5), Hw in (5) is the actual furnace equivalent value. A detailed study of FIG. 16 reveals that when coke B is 8.3%, the cohesive zone has an inverted V shape, but V ₁ /(V ₁ +V ₂ ) is 0.515, and the above formula (4) The conditions shown in Figure 2 are not satisfied, and the temperature distribution at the top of the furnace is a gentle curve similar to that shown in Figure 2. Furthermore, the center of the furnace has a relatively wide area with ventilation resistance. It was predicted that the gas utilization rate would be low from each point of view, as there was a risk of gas leakage occurring in the center. On the other hand, Coke B is 1.4%
In this case, only the item V ₁ / (V ₁ + V ₂ ) satisfies each of the above conditions, and the ventilation resistance at the center of the furnace is quite high, and the temperature at the top of the furnace is not high at the center. For various reasons, such as the cohesive zone having a perfect W-shape and the actual furnace equivalent value of Hw not satisfying the condition of equation (5) above, a central flow cannot be obtained and the fusion The shape of the belt deteriorates, the heat load part of the furnace wall goes downward, and no reduction in hot metal Si is expected.

In contrast, coke B was 7.5%, 6.7%, and 5%.
% and 2.5%, the above-mentioned conditions were satisfied, and a good cohesive zone shape (inverted V-shape) and its position, as well as a central flow were secured, and the gas utilization rate and furnace wall Both positions are in satisfactory condition.

The present invention is configured as described above, and the O/C at the center of the furnace is
As a result, the cohesive zone in the blast furnace can exhibit an optimal profile in terms of its shape and height position, and it can also exhibit a stable central flow without any disadvantages in terms of gas utilization. In addition, it is possible to reduce the Si content of hot metal, reduce the heat load on the furnace wall, etc.
Stable blast furnace operation, improved quality of hot metal, protection of the furnace body, etc.
Satisfactory results were obtained in all aspects.

[Brief explanation of drawings]

Figure 1 is a schematic explanatory diagram showing the conventional method of charging raw materials into a blast furnace, Figure 2 is a graph showing the top gas flow velocity distribution at that time, and Figure 3 is a graph showing the ideal furnace top gas flow velocity distribution. , Fig. 4 is an explanatory diagram conceptually showing the inner surface of the blast furnace, Fig. 5 A, B, and C are schematic diagrams of the cohesive zone shape, and Fig. 6 shows each divided area when the blast furnace is divided into five in the radial direction. Figure 7 is a cross-sectional diagram of the right half of a blast furnace showing a comparison between the estimated results of the 1200°C isotherm and actual measurements. The parameters (Rj) were determined so that they matched, and Figure 7 (b) shows a comparison between the estimated results using the determined Rj and the actual measurements. Also, Fig. 8 is an explanatory diagram showing the definition of the volumes of the upper V 1 and lower V ₂ of the cohesive zone and the position Hw of the peripheral cohesive zone based on the 1200°C isotherm, and Fig. ₉ is an explanatory diagram showing the definition of the volume of the upper V ₁ and lower V 2 of the cohesive zone and the position Hw of the peripheral cohesive zone.
(V ₁ + V ₂ ) and gas utilization rate. Figure 10 is a graph showing the relationship between Hw and the maximum heat negative position of the stave cooler. Figure 11 is a graph showing the relationship between Hw and the maximum heat negative position of the stave cooler.
A graph showing the relationship between Si concentration, Figures 12A and 12B are explanatory cross-sectional views of the right half of the blast furnace showing the shape of the cohesive zone and the ascending path of gas, and Figure 13 is the partial coke charging and O/C according to the present invention. Explanatory diagram showing the relationship, No. 14, 1
FIG. 5 is an explanatory diagram of an experimental example showing a method of dividing coke injection, and FIG. 16 is an explanatory diagram showing the results of a model experiment. 1... Blast furnace, 2, A, B... Coke, 3...
Ore, D...Softened cohesive zone, E...Coke slit.

Claims (1)

[Claims] 1. A coke charging method when ore and coke are charged alternately to a blast furnace, in which the coke charging in each charge is divided over time into at least two series, and the total amount of coke charged in the charge is 92 to 98.5% by weight of coke is charged so as to cover the entire ore layer of the pre-charging, and in the last charging series, 8 to 1.5% by weight of the total amount of coke charged in the charge is intensively charged to the center of the furnace. The center of the furnace
The ore/coke ratio in the area other than the center of the furnace
A method for charging coke into a blast furnace, characterized by depositing coke so that the coke ratio is substantially smaller than the coke ratio.