JP7616516B2 - Blast furnace operation method - Google Patents

Description

The present invention relates to a method for operating a blast furnace when operations are stopped, the blast furnace is shut down, and then blasting is restarted.

A blast furnace is a facility that heats, reduces, and melts iron ore using high-temperature reducing gas produced by the reaction between high-temperature air and oxygen blown in through numerous tuyeres arranged in the direction of the air flow and coke charged from the top of the furnace along with the raw materials, and then discharges molten iron and molten slag from a tap hole installed below the tuyeres. During normal operation of a blast furnace, the reaction heat inside the furnace and the heat supply from the tuyeres are balanced, allowing the blast furnace to operate stably.

Here, when the blast furnace is shut down or stopped for a long time, the heat supply to the blast furnace is stopped. On the other hand, because heat radiation continues due to the temperature difference between the inside of the blast furnace and the atmosphere, the inside of the furnace cools down and some of the molten material solidifies. When restarting the blast furnace from this state, the solidified material in the furnace must be melted, and in order to do so, the coke packed bed through which the solidified material passes must be heated. For this reason, when the blast furnace is shut down for a long time or when it is expected to be restarted, the coke ratio in the furnace is increased and the furnace is shut down, and thermal compensation is performed until the injection of pulverized coal can be started after the blast. At the same time, all but one or two tuyere openings above the tap hole are blocked with refractories, etc., to limit the amount of molten iron and slag generated with the blast, and a cycle of smooth discharge of a small amount of molten material is established. After that, the adjacent tuyere openings are opened, and the number of open tuyere openings is gradually increased, and normal operation is restored.

As a method for restoring a blast furnace to normal operation after cessation of blowing, Patent Document 1 discloses that a burner is inserted from the tap hole, oxygen or the like is blown in from the burner to burn the coke between the tap hole and the tuyere, reducing the volume of the solidified material, and then new coke is added from the top of the furnace to the reduced volume area, and blowing air from the tuyere, thereby restoring the blast furnace to normal operation.

Patent No. 6947345

However, in Patent Document 1, new coke is added from the top of the furnace, so the impact of the fall breaks the coke, and the fine coke powder produced by this breakage fills the gaps between the coke, reducing the air permeability of the coke layer. This reduced air permeability could make it impossible to smoothly start up the blast furnace after the cessation of blowing.

The object of the present invention is to propose a blast furnace operation method in which operations are stopped, the blast furnace is tuned off, and then blasted again, in which new coke can be charged into the furnace while suppressing the impact of the fall, allowing the blast furnace to be started up smoothly.

The blast furnace operation method of the present invention was developed to solve the above-mentioned problems, and is a blast furnace operation method in which the height of the surface of the raw material packed bed is reduced below the height of the upper end of the morning glory of the blast furnace, and the furnace is shut down, and then air is blown again. After the blast furnace is shut down, oxygen-containing gas is blown in from a burner inserted into the tap hole, and the coke remaining in the furnace is burned to reduce the volume of the residue in the furnace. Then, new coke is lowered from the top of the furnace into the area where the volume of the residue in the furnace has decreased, and then air is blown from the blast furnace tuyere.

In addition, in the blast furnace operation method of the present invention,
(1) filling a container with the new coke and lowering the container into a furnace to charge the new coke;
(2) filling a container with the new coke, suspending the container in a furnace, and charging the new coke into the container;
(3) charging the new coke into the container so that the new coke is 1.0 m or more higher than the blast furnace tuyere;
(4) The container is a flexible container having a diameter of 1.5 m or less and a height of 1.5 m or less.
(5) The strength of the new coke is 85.6% by mass or more;
(6) The moisture content of the new coke is 2.0% by mass or less;
are each considered to be a preferred embodiment.

According to the blast furnace operation method of the present invention, in blast furnace operation in which the surface of the raw material packed bed directly above the blast furnace tuyere is lowered below the upper end of the blast furnace morning glory section to stop blowing air, and then blowing air again, it is possible to suppress the destruction of the coke charged in the volume reduction section, making it possible to perform a stable and smooth start-up.

FIG. 2 is a schematic cross-sectional view showing a part of a cross section of a furnace body of a blast furnace. FIG. 2 is a schematic cross-sectional view of the lower part of a blast furnace showing the state in which a burner is inserted from the tap hole. FIG. 2 is a schematic diagram showing an example of a burner. FIG. 2 is a schematic cross-sectional view showing a state in which the volume of the residue in the furnace is reduced by burning the remaining coke using a burner. FIG. 2 is a schematic cross-sectional view illustrating a method of loading coke into a furnace by suspending a flexible container from the top of the furnace. 1 is a schematic cross-sectional view showing a state in which new coke is charged into a volume reduction region together with a flexible container. FIG. FIG. 1 is a top view of a volume reduction area of the furnace residue before being charged into a flexible container. FIG. 1 is a top view of a volume reduction region of the furnace residue after the flexible container is charged.

The following is a detailed description of the embodiments of the present invention. Note that the following embodiments are merely examples of devices and methods for embodying the technical ideas of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical ideas of the present invention can be modified in various ways within the technical scope described in the claims. In addition, in the following embodiments, an example of a blast furnace operation method that is the subject of the present invention will be described, and then the features of the blast furnace operation method of the present invention will be described.

<One example of a blast furnace operation method to which the present invention is applicable>
FIG. 1 is a schematic cross-sectional view showing a part of the cross section of the furnace body of a blast furnace. In the embodiment shown in FIG. 1, when the blast furnace is shut down for a long period of time, the height of the surface of the raw material packed bed directly above the tuyere of the blast furnace is reduced below the upper end of the morning glory part of the blast furnace to shut down the blast furnace. After that, to blow hot air from the tuyere to return the blast furnace to normal operation, first, a burner is inserted from the tap hole, and oxygen-containing gas or oxygen-containing gas and combustible gas are blown from the burner to burn the coke remaining in the furnace and reduce the volume of the residue in the furnace.

Figure 2 is a schematic cross-sectional view of the lower part of a blast furnace showing the state in which a burner has been inserted from the tap hole. In the embodiment shown in Figure 2, when the blast furnace is shut down, the tap hole is blocked with a material called mud material, so in order to insert the burner into the furnace, the tap hole blocked with mud material is first opened. A known tap hole opening machine can be used to open the tap hole. After the tap hole is opened, a burner is inserted from the tap hole into the lower part of the blast furnace.

3(a) and (b) are schematic diagrams showing an example of a burner. In the embodiment shown in FIG. 3(a) and (b), the burner has a double-tube structure of an inner tube and an outer tube through which gas flows, a cap covering the ends of the inner tube and the outer tube, and a thermocouple for measuring the burner temperature outside the outer tube. When the cap is present as shown in FIG. 3(a), the gas blown in from the gas inlet of the inner tube is discharged from the gas outlet of the outer tube without leaking to the outside. On the other hand, when the cap is not present as shown in FIG. 3(b), the gas blown in from the gas inlet of the inner tube is supplied into the furnace. Therefore, the burner has the function of cooling the burner by flowing gas from the inner tube to the outer tube with the cap present, so that the burner can be stably inserted into the furnace.

To start combustion, the cooling caused by the gas flow from the inner tube to the outer tube is stopped, the cap is dissolved and removed, and, for example, combustible gas is blown into the furnace from the inner tube of the burner, and oxygen-containing gas is blown into the lower part of the furnace from the outer tube as a combustion supporting gas. When the temperature at the tip of the burner exceeds the combustion start temperature of the surrounding coke (approximately 800°C), the gas blown from the burner is switched to only oxygen-containing gas to burn the coke. It is preferable to blow pure oxygen as the oxygen-containing gas, but a gas with an oxygen concentration lower than 100% can be used as long as the coke combustion can be sustained.

Figure 4 is a schematic cross-sectional view showing the state in which the volume of the residue in the furnace is reduced by burning the remaining coke using a burner. In the embodiment shown in Figure 4, when the coke is burned away by combustion, more coke rolls into the space that has been burned away according to the angle of repose, and as the coke is burned away one by one, the volume of the residue in the furnace is reduced.

<Features of the blast furnace operation method according to this embodiment>
The feature of the blast furnace operation method according to this embodiment is that new coke is charged into the volume-reduced region where the volume of the furnace residue has been reduced.

Figure 5 is a schematic cross-sectional view illustrating a method of lowering a flexible container from the top of the furnace to load coke into the furnace. In the embodiment shown in Figure 5, new coke is loaded into the flexible container in advance. The flexible container filled with new coke is suspended by the furnace top crane to above the volume reduction area of the furnace residue. After positioning the flexible container in this manner, the flexible container is dropped into the volume reduction area. As a result, new coke is loaded into the volume reduction area together with the flexible container.

It is preferable to use an autohook for the hook of the furnace top crane. When a flexible container suspended from this autohook lands, the hook rotates and the load wire is automatically released from the hook. In this way, a flexible container filled with new coke is loaded into the furnace. At this time, the container suspended into the furnace is burned and disappears after the start of air blowing, so it does not adversely affect start-up operations.

This operation is repeated, and new coke is charged together with the flexible container into the residue reduction area. Figure 6 is a schematic cross-sectional view showing the state in which new coke is charged together with the flexible container into the volume reduction area. In the embodiment shown in Figure 6, it is preferable to charge the flexible container into the furnace so that the upper surface position of the flexible container is 1.0 m higher than the tuyere height of the blast furnace. An operator can visually determine from the furnace mouth whether the upper surface position of the flexible container is 1.0 m higher than the tuyere height.

As shown in FIG. 6, when a flexible container is charged in a volume reduction region, a gap is created between the flexible containers. After the flexible container is charged at the tip of the tuyere, hot air is blown from the tuyere, and the flexible container burns due to this hot air, spreading the coke inside the container in the furnace. Since the coke penetrates into the gaps between the flexible containers, the charging height of the coke becomes lower than the charging height of the flexible container. Therefore, if the charging height of the flexible container is set to the same as the tuyere height, there is a risk that the charging height of the coke will be lower than the tuyere height. In contrast, by charging the flexible container into the furnace so that the charging height of the flexible container is 1.0 m or more higher than the tuyere height, coke can be charged at the tip of the tuyere even if the charging height of the coke is lowered. Therefore, it is preferable to charge the flexible container into the furnace so that the upper surface position of the flexible container is 1.0 m higher than the tuyere height of the blast furnace.

The dimensions of the flexible container used in this embodiment are, for example, a diameter of 1.2 m and a height of 1.3 m. It is preferable that the dimensions of the flexible container are a diameter of 1.5 m or less and a height of 1.5 m or less. This is because such dimensions allow the flexible container to be suitably loaded into the volume reduction area of the actual furnace residue.

The strength of the new coke used in this embodiment is preferably 85.6 mass% or more in drum strength (DI15/150). This is because using coke with such strength can further suppress the pulverization of the coke due to the impact when it is loaded into the furnace. Drum strength (DI15/150) can be measured according to JIS K 2151:2004.

Furthermore, the moisture content of the new coke used in this embodiment is preferably 2.0 mass% or less. By using coke with such a moisture content, the amount of fine powder that adheres to the coke surface and is brought into the furnace is reduced, which makes it possible to suppress a decrease in the air permeability of the coke layer due to the fine powder.

In the above-described embodiment, as an example of the present invention, a case has been shown in which new coke is filled into a container, the container is lowered into the furnace, and the new coke is charged into the volume reduction area of the furnace residue together with the container. However, the blast furnace operation method of the present invention is not limited to a method using a container, and other methods that do not use a container can also be used, as long as new coke can be lowered into the furnace and charged into the volume reduction area of the furnace residue.

In accordance with the above-described embodiment, a blast furnace having an internal volume of 5,000 ^m3 was actually used to carry out a blast furnace operation method in which the height of the surface of the raw material packed bed was reduced below the height of the upper end of the morning glory of the blast furnace, air was stopped, and then air was blown again. In this operation, new coke was filled into a container, the container was lowered into the furnace, and the new coke was charged into the volumetric reduction area of the furnace residue together with the container, and an example of a suitable container dimension was determined.

Figure 7 is a top view of the volume reduction area of the residue in the furnace before the flexible container is charged. Also, Figure 8 is a top view of the volume reduction area of the residue in the furnace after the flexible container is charged. Since the dimension of the white arrow of the volume reduction area shown in Figure 7 is approximately 3 m, it can be seen that by using a flexible container with a diameter of 1.5 m or less and a height of 1.5 m or less, new coke filled in a flexible container can be charged into the volume reduction area of the residue, as shown in Figure 8.

After the flexible container filled with new coke is placed in front of the tuyere, a predetermined amount of raw ore and coke are charged in alternating layers from a rotating chute at the top of the furnace. Hot air is then blown through the tuyere of the blast furnace, and operation of the blast furnace is resumed.

In this embodiment, a container box with an open bottom may be used instead of the flexible container. In this case, the container box is filled with new coke, and the container box is hoisted into the blast furnace by a crane and charged, and after being positioned above the volume reduction area, the bottom is opened and the new coke is charged into the volume reduction area. After the coke is charged, the empty container box is hoisted up and removed from the top of the furnace, and the container box is filled with new coke again. Furthermore, a plastic container may be used instead of the flexible container. In this case, the plastic container may be filled with new coke, and the container may be hoisted down into the furnace and the new coke together with the container may be charged into the furnace.

When loading coke into the furnace by hanging, it is not necessary to hang it all the way down to the bottom of the furnace; it is also possible to hang it partway down and then drop the flexible container to load it. By hanging it at least a little from the top of the furnace to load it into the furnace, the impact of the drop is mitigated compared to when the flexible container is dropped from the top of the furnace, which helps prevent the coke from breaking and pulverizing.

As explained above, in the blast furnace operation method according to this embodiment, new coke is lowered into the furnace from the top and charged into the volume-reduced area of the furnace residue. This allows coke to be charged into the volume-reduced area without people having to enter the furnace, and also mitigates the impact of the fall, suppressing pulverization due to breakage, allowing a highly permeable coke packed layer to form in front of the tuyere of the blast furnace. As a result, the blast furnace can be started up smoothly even after a long period of refueling.

The blast furnace operation method of the present invention allows for smooth startup of the blast furnace even after a long period of shutdown.

Claims (7)

A blast furnace operation method in which the height of the raw material packed bed surface is reduced below the height of the upper end of the morning glory of the blast furnace , and then air is stopped and then air is blown again,
A method of operating a blast furnace, comprising blowing in oxygen-containing gas from a burner inserted into the tap hole after shutting down the blast furnace, burning the coke remaining in the furnace and reducing the volume of the residue in the furnace, hanging new coke from the top of the furnace into the area where the volume of the residue in the furnace has decreased, and then blowing air from the blast furnace tuyere. The blast furnace operating method according to claim 1, further comprising filling a container with the new coke, lowering the container into the furnace, and charging the new coke. The blast furnace operating method according to claim 1, further comprising: filling a container with the new coke, lowering the container into the furnace, and charging the new coke into the container. The blast furnace operating method according to claim 3, wherein the new coke is charged into the container so that it is at least 1.0 m higher than the blast furnace tuyere. The blast furnace operation method according to claim 3 or 4, wherein the container is a flexible container having a diameter of 1.5 m or less and a height of 1.5 m or less. The blast furnace operation method according to any one of claims 1 to 4, wherein the drum strength (DI15/150) of the new coke measured in accordance with JIS K 2151:2004 is 85.6% by mass or more. The blast furnace operation method according to any one of claims 1 to 4, wherein the moisture content of the new coke is 2.0% by mass or less.

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