Blast furnace operation method

Abstract

The present invention resolves the problem that conventional blast-furnace banking techniques have required long-term shutdowns of at least 5.5 months post-shutdown, and proposes a blast-furnace operating method that allows smooth startup of blast furnaces and a short shutdown period. Provided is a blast-furnace operating method in which the height of the surface of the raw-material charge layer directly above the blast-furnace tuyeres is decreased from the height of the upper end of the blast-furnace bosh area, putting the furnace off-wind, and then air is blasted again, wherein: following the blast furnace off-wind, gas containing oxygen is blown in through a taphole, coke remaining between the tuyeres and the taphole is burned to reduce the volume of the residue inside the furnace, and meanwhile, into the region where the volume has been reduced, coke is newly introduced, and thereafter the tuyeres above the taphole are opened to start air blasting.

Description

[Technical Field]

[0001] The present invention proposes a blast furnace operation method for starting up a blast furnace during banking, in which re-venting is performed with the contents remaining in the furnace during a blow-down operation of the blast furnace. [Background technology]

[0002] When blast furnaces are forced to significantly reduce production, the resulting low blast flow rate can lead to poor furnace performance due to inactivation of the furnace core. Therefore, when the productivity falls below 1.5, operations must be continued at coke rates exceeding 400 kg / t. However, since coke is an expensive raw material, this increases the unit cost, making it uneconomical. For example, repeated blast shutdowns can be implemented, but the coke rate must be increased before and after each shutdown, making an increase in the coke rate unavoidable. As described above, it is extremely difficult to economically ensure downward flexibility in blast furnace production. Therefore, a technique called banking is used, in which the blast furnace is shut down for an extended period of time, long enough for the molten iron and slag in the furnace to solidify.

[0003] When banking is implemented, the raw material level is first reduced to the tuyere level, and the remaining coke and slag in the furnace are cooled to room temperature (a period of three months). After that, heavy machinery is brought into the furnace, the remaining coke is removed, and then coke and sleepers are laid in the furnace (a period of two and a half months). This requires a shutdown period of at least five and a half months.

[0004] One of the reasons why it takes 5.5 months to prepare for startup after a blast furnace shutdown is that it is necessary to enter the furnace to scrape out the residual coke, which requires the furnace to be cooled over the course of approximately 90 days as mentioned above, lengthening the time from shutdown to startup. Furthermore, even after cooling, heavy machinery is used to enter the furnace, but safety nets must be installed as a safety condition, and the remaining coke removal work takes approximately 40 days because the coke is removed from the entire periphery. As a result, it may not be possible to keep up with a sudden recovery in demand.

[0005] Furthermore, when updating ancillary equipment for a blast furnace, even in cases where the equipment requires shutting down the blast furnace for around two months, the downtime usually becomes longer than necessary.

[0006] Furthermore, a method for smoothly starting up a blast furnace and resuming operation after a long period of shutdown is disclosed in, for example, the blast furnace operation method of Patent Document 1. In the blast furnace operation method disclosed in Patent Document 1, the height of the surface of the raw material packed bed directly above the blast furnace tuyere is first reduced below the height of the upper end of the blast furnace bosh, and the furnace is shut down. Then, after the blast furnace is shut down, oxygen or oxygen and combustible gas is blown in from a burner inserted into the taphole to burn the coke remaining in the furnace and reduce the volume of the residue in the furnace. After that, new coke is charged into the volume-reduced region, and then air is blown in from the tuyere. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6947345 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the blast furnace operation method described in Patent Document 1 requires the use of a burner with a complex structure and the installation of a combustible gas supply line, which poses the problem of complex preparation of equipment used for blast furnace operation. Furthermore, supplying combustible gas generates hydrogen during coke combustion, which may cause exhaust gas components to fall within the explosive composition range, posing a safety issue.

[0009] Furthermore, if a blast furnace is shut down for an extended period of time, the remaining molten iron and slag solidifies. When the solidified molten iron and slag is heated during the start-up of the blast furnace, the molten iron and slag expands, applying tensile stress to the blast furnace shell. This could cause the shell to crack and break. For this reason, in order to smoothly start up a blast furnace after a long shutdown, it is necessary to keep the tensile stress applied to the blast furnace shell within an allowable range.

[0010] Furthermore, a common method for starting up a blast furnace after a long shutdown involves first blocking all tuyere openings except for one or two above the tap hole with refractory materials, limiting the amount of molten iron and slag generated by blasting and establishing a cycle for smooth discharge of a small amount of molten iron. Subsequently, adjacent tuyere openings are gradually increased to restore normal operation. However, this method makes it impossible to determine the level of tensile stress applied to the blast furnace shell during startup. Therefore, opening adjacent tuyere openings too early can increase the rate of expansion of the molten iron and slag, causing the blast furnace shell to fracture and preventing smooth startup.

[0011] The object of the present invention is to solve the above-mentioned problems and to propose a blast furnace operation method that solves the problem that conventional blast furnace banking technology requires a long shutdown of at least 5.5 months after shutdown, and that enables the blast furnace to be started up smoothly with a short shutdown period. [Means for solving the problem]

[0012] The blast furnace operation method of the present invention is a blast furnace operation method in which the height of the surface of the raw material packed bed directly above the blast furnace tuyere is reduced below the height of the upper end of the blast furnace bosh portion to stop airflow, and then airflow is resumed; after the blast furnace is stopped, oxygen-containing gas is blown into the tap hole to combust coke remaining between the tuyere and the tap hole, reducing the volume of residue in the furnace, and after new coke is charged into the volume-reduced region, the tuyere above the tap hole is opened to start airflow.

[0013] In the blast furnace operating method according to the present invention configured as described above, (1) Installing a strain gauge on the hearth shell of a blast furnace and increasing the number of tuyere openings while referring to the measurement values ​​of the strain gauge; This is considered to be a more preferable solution. [Effects of the Invention]

[0014] According to the blast furnace operation method of the present invention, a shutdown period of at least 5.5 months was previously required, but even with simplified equipment, it is possible to shorten this period to about 2 months, and it is also possible to start up the blast furnace safely and smoothly. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram for explaining one embodiment of a blast furnace reduction step in a blast furnace operation method of the present invention. [Figure 2] FIG. 1 is a schematic diagram for explaining one embodiment of an oxygen blowing step in a blast furnace operation method of the present invention. [Figure 3] FIG. 10 is a schematic diagram for explaining another embodiment of the oxygen blowing step in the blast furnace operation method of the present invention. [Figure 4] FIG. 2 is a diagram for explaining one embodiment of a coke charging step in the blast furnace operation method of the present invention. [Figure 5] FIG. 1 is a diagram for explaining an embodiment of the blast start step in the blast furnace operation method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following describes in detail the embodiments of the present invention. Note that the following embodiments are intended to exemplify devices and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to that described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope defined in the claims.

[0017] The blast furnace operation method of the present invention is a blast furnace operation method in which the height of the surface of the raw material packed bed directly above the blast furnace tuyere is reduced below the height of the upper end of the blast furnace morning glory (tuyere level) to stop airflow (blast furnace reduction process), and then airflow is started again (airflow start process).After the blast furnace is stopped, oxygen-containing gas is blown into the tap hole (oxygen blowing process), and coke remaining between the tuyere and the tap hole is burned to reduce the volume of the residue in the furnace (coke volume reduction process), and new coke is charged into the volume reduction area (coke charging process), after which the tuyere above the tap hole is opened to start airflow (airflow start process).

[0018] The blast furnace reduction step (FIG. 1), oxygen injection step (FIGS. 2 and 3), coke charging step (FIG. 4), and blast start step (FIG. 5) in the blast furnace operation method of the present invention will be described in order below. In FIGS. 1 to 5, 1 denotes a blast furnace, 1a denotes the shell of the blast furnace 1, 2 denotes a tuyere, 3 denotes a tap hole, 4 denotes a normal raw material level, 5 denotes a raw material level during reduction, 5a denotes a volume reduction region, 6 denotes molten iron and slag, and 7 denotes new coke.

[0019] <About the blast furnace reduction process> 1 is a schematic diagram illustrating one embodiment of the blast furnace reduction process in the blast furnace operation method of the present invention. As shown in FIG. 1, in the blast furnace reduction process, the height of the raw material packed bed surface directly above the tuyere 2 of the blast furnace 1 is reduced from the normal raw material level 4 to the raw material level 5 during reduction. Here, the raw material level 5 during reduction refers to a position lower than the height of the upper end of the blast furnace morning glory, for example, the position of the tuyere 2 (tuyere level).

[0020] To reduce the furnace's operating temperature, first, additional coke is charged and the charging of iron raw materials is stopped. The raw material charging level is lowered while hot air is blown into the furnace from tuyere 2. The hot air blast flow rate from tuyere 2 is reduced according to the degree of lowering of the raw materials. When the charging of iron raw materials is stopped and the hot air blast flow rate is reduced, the reduction proceeds. The rising temperature of the furnace top gas is cooled and reduced by spraying water from the sprinkler pipes installed at the furnace top. The raw material charging level is lowered to the tuyere level, the water spray is stopped, and the hot air blow from tuyere 2 is halted to enter a blast shutdown period.

[0021] <About the oxygen blowing process> Fig. 2 is a schematic diagram illustrating one embodiment of the oxygen blowing step in the blast furnace operation method of the present invention, and Fig. 3 is a schematic diagram illustrating another embodiment of the oxygen blowing step in the blast furnace operation method of the present invention. In the oxygen blowing step, first, as shown in Fig. 2, after the blast furnace is shut down, oxygen-containing gas is blown into the tap hole 3 to combust the coke remaining between the tuyere 2 and the tap hole 3. Then, as shown in Fig. 3, the volume of the residue in the furnace is reduced to form a volume-reduced region 5a.

[0022] In blast furnace operation, if ventilation and liquid permeability between the tuyere and tap hole cannot be ensured, the molten iron and slag produced inside the furnace cannot be discharged from the tap hole, and the molten iron and slag will accumulate inside the furnace. This can result in blow-by problems and tuyere damage due to increased pressure loss inside the furnace, and even furnace cooling problems due to the solidification of molten iron and slag inside the blast furnace.

[0023] When a blast furnace is shut down for an extended period of time, the porosity between the taphole and tuyere may decrease due to solidified molten iron and slag adhering to the gaps in the coke between the taphole and tuyere, and the coke being burned and becoming smaller in size during the cooling process inside the furnace. Therefore, the coke between the taphole and tuyere is burned and consumed by injecting gas containing oxygen.

[0024] In the oxygen injection step of the blast furnace operation method of the present invention, it has been discovered that by injecting oxygen-containing gas directly from the tap hole through a lance pipe, coke can be burned and consumed between the tap hole and the tuyere. Therefore, stable blast furnace refrigeration can be achieved by injecting oxygen-containing gas using a lance pipe with a simple configuration, rather than using a burner with a complex combustion function as in the prior art. Because the lance pipe becomes very hot when burning and consuming coke between the tap hole and the tuyere, it is preferable to use a double-pipe lance pipe, supplying oxygen from the inner pipe and nitrogen to the outer pipe to cool the lance pipe.

[0025] <About the coke charging process> FIG. 4 is a diagram illustrating one embodiment of the coke charging process in the blast furnace operation method of the present invention. As shown in FIG. 4, in the coke charging process, coke without solidified material is charged into the volume reduction zone 5a, which is the hollow space left after the coke is burned and consumed. Coke charging can be performed, for example, as follows: First, new coke 7 is loaded into a flexible container in advance. Next, the flexible container filled with the new coke 7 is suspended by a furnace top crane to above the volume reduction zone 5a of the furnace residue. After positioning the flexible container in this way, the flexible container is dropped into the volume reduction zone 5a. As a result, the new coke 7 is charged into the volume reduction zone 5a together with the flexible container. After the new coke 7 is charged into the volume reduction zone 5a, auxiliary materials added to adjust the composition when the coke ash turns into slag, coke, and iron materials are charged into the furnace through a distribution chute and filled up to the normal material level 4.

[0026] <About the air blowing start process> FIG. 5 is a diagram illustrating one embodiment of the blast furnace operation method of the present invention. In the circumferential direction of the blast furnace where there is no tap hole 3, the residual coke between the tap hole and the tuyere is not burned and consumed, and is not replaced with new coke 7 without solidified deposits. Therefore, as shown in FIG. 5, in the blast furnace blast start step, the tuyere 2 above the tap hole 3 through which the oxygen-containing gas was blown is opened, and blasting is started from the tuyere 2. Here, the position of the tuyere 2 does not necessarily have to be located directly above the tap hole 3 through which the oxygen-containing gas was blown, as long as it is located above the tap hole 3 through which the oxygen-containing gas was blown. Furthermore, it is not necessary to open only one tuyere; multiple adjacent tuyere openings above the tap hole 3 may be opened. Therefore, during start-up operation after a long shutdown, the open tuyere range is preferably within 30-50° (40° in this case) of the tap hole 3 through which the oxygen-containing gas was blown, as shown in FIG. 5.

[0027] Then, after opening the tuyere 2 above the taphole 3 and starting up the furnace, the tuyere opening range is gradually expanded while checking that the molten material can be discharged without any problems, and then all the tuyere openings are opened and air blowing is resumed.

[0028] In a preferred embodiment of the blast furnace operating method of the present invention, strain gauges may be installed in the shell 1a at the hearth of the blast furnace 1, and the number of tuyere openings may be increased while referring to the measured values ​​of the strain gauges. According to this preferred embodiment, for example, the tensile stress applied to the shell 1a at the hearth of the blast furnace 1 can be monitored based on the measured values ​​of the strain gauges. This makes it possible to prevent breakage of the shell 1a of the blast furnace 1 due to the expansion of molten metal and slag caused by heating. As a result, it is possible to smoothly start up the blast furnace. [Example]

[0029] Internal volume 5000m 3 In the blast furnace, the height of the surface of the raw material packed bed directly above the blast furnace tuyere was reduced to the tuyere level, and after the blasting was stopped, oxygen was supplied from the tap hole at a rate of 400 Nm 3 / hr more than 900Nm 3 / hr or less, with an average flow rate of 600Nm 3 At the same time, nitrogen for cooling the lance pipe was supplied from the tap hole at a rate of 400 Nm 3 / hr more than 1300Nm 3 / hr or less, with an average flow rate of 1000Nm 3 / hr, and residual coke between the tuyere and tap hole was burned.

[0030] After the coke combustion and consumption process, coke was charged into the resulting cavity (volume reduction area). The tuyere above the tap hole, which ensured communication between the tap hole and the tuyere, was opened, and the remaining tuyere was closed when blasting began. Strain gauges were attached to the hearth shell of the blast furnace, and the number of open tuyere tubes was increased until the strain gauge readings were within the acceptable range. Table 1 below compares the number of days required for blasting shutdown and subsequent restoration to normal operation between the conventional and new technologies. The conventional technology involves reducing the raw material line to the tuyere level, cooling the remaining coke and slag in the furnace to room temperature, and then bringing heavy machinery into the furnace to remove the remaining coke and lay coke and sleepers.

[0031] [Table 1]

[0032] The results in Table 1 show that with this technology, it takes 20 days from the start of re-blowing to restore normal operation with all tuyere opening compared to the conventional technology, but the total recovery time can be shortened by about 100 days. In addition, there was no fracture of the blast furnace shell, making it possible to start up the blast furnace smoothly. [Explanation of symbols]

[0033] 1 blast furnace 1a iron skin 2 Tuyere 3 Taphole 4. Normal raw material level 5 Raw material level when reducing length 5a Volume reduction area 6 Hot metal slag 7 New Coke

Claims

[Claim 1] In a blast furnace operation method in which the height of the surface of the raw material packed bed directly above the tuyere of the blast furnace is reduced below the height of the upper end of the morning glory of the blast furnace to stop blowing air, and then blowing air again, A method of operating a blast furnace, comprising: after shutting down the blast furnace, injecting a gas containing oxygen through the tap hole, burning coke remaining between the tuyere and the tap hole, thereby reducing the volume of residue in the furnace; and after newly charging coke into the area of ​​reduced volume, opening the tuyere above the tap hole to start blowing air, by installing a strain gauge in the blast furnace hearth shell and increasing the number of tuyere openings while referring to the measured values ​​of the strain gauge.

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