Method for quickly reproducing after long-term damping-down reproducing of blast furnace

Abstract

The invention belongs to the technical field of metallurgy, and discloses a method for quickly reproducing after long-term damping-down reproducing of a blast furnace, which comprises the following reproducing steps: step 1, a hearth core active preheating step: before blast reproducing of a main tuyere of the blast furnace or at the initial stage of reproducing, introducing oxygen-containing gas into a hearth central area through at least one iron notch, the central area of the hearth is actively heated; and 2, a drainage channel pre-construction step: opening the other iron notch after the blast of the main tuyere of the blast furnace is recovered and before a large amount of liquid iron slag is formed, and enabling high-temperature coal gas to be sprayed outwards from the iron notch by utilizing the pressure of gas formed in the furnace so as to dredge the hearth, heat the iron notch area and pre-construct the iron slag drainage channel. The cold state problem of the center of the hearth is solved through active preheating, a smooth drainage channel is constructed in advance through high-pressure coal gas flow, an iron notch area is heated, and the fatal risk that a high-temperature liquid phase newly produced in the initial stage of re-production gathers in the front edge area of the tuyere is fundamentally avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and in particular to a method for quickly resuming production of a blast furnace after a long-term shutdown. Background Art

[0002] Blast furnace ironmaking is a fundamental process in the modern steel industry. During long-term production operations, blast furnaces need to be shut down periodically due to planned maintenance, changes in the market environment, or restrictions on external supply conditions. This is known in the industry as a "blowing halt." Resuming production after a blowdown, especially after a long-term blowdown of more than 48 hours or even several days, is a key step in determining whether the blast furnace can quickly and safely resume normal production, thereby ensuring the overall production efficiency and economic benefits of the enterprise. Currently, the industry generally adopts a conventional, passive waiting-based resumption method for resuming production after a long-term blowdown. This method usually involves simple insulation of the furnace body during the blowdown period, and then directly blowing hot air into the furnace through the main tuyere of the blast furnace when resuming production. Relying solely on the heating effect of the hot air, the coke and other furnace materials in the furnace hearth are slowly reheated from the outside to the inside to the melting temperature. During this process, the operators passively wait for a sufficient amount of liquid slag with a certain fluidity to form in the furnace, and hope that the liquid slag can rely on its own gravity and heat to gradually melt and clear the solidification channel from the center of the furnace to the iron mouth, and finally realize iron tapping and resume production.

[0003] However, technicians in this field have found in long-term practice that the above-mentioned conventional resumption method has a series of inherent and interrelated technical defects, especially after the blast furnace has been shut down for a long time, the problems caused by these defects become more serious.

[0004] Due to the long-term air outage, the temperature in the hearth's center has dropped significantly, leaving the coke inside in a "cold, dead, and silent" state. When resuming production relies solely on heating through the main tuyere, heat cannot be quickly and effectively transferred to the hearth's core, resulting in an unusually slow activation process in the hearth's center. More critically, this slow and uneven heating method introduces a fatal contradiction: the small amount of initial liquid slag formed in hotter areas, such as the tuyere front, has extremely poor fluidity due to the overall low furnace temperature. As it moves toward the cooler ironmouth area, it easily solidifies or becomes highly viscous due to the cooling, forming a physical "blockage" at the bottom of the hearth. This results in the subsequent generation of high-temperature liquid phase in the tuyere area having its outward discharge channel artificially blocked.

[0005] The direct consequence of this blockage is that large amounts of hot, highly corrosive liquid slag are forced to dangerously accumulate in the front area of ​​the tuyere. This accumulation not only seriously interferes with the working state of the tuyere, but is also likely to burn through the tuyere and cooling equipment in a short period of time, causing serious safety accidents such as leaks in the water cooling system. To avoid this risk, operators are forced to adopt an extremely conservative and slow air supply system, which undoubtedly further prolongs the production resumption period, resulting in huge fuel consumption and wasteful production costs. It is also difficult to ensure product quality in the early stages of production resumption. When faced with adverse operating conditions such as poor furnace conditions before the shutdown or excessively long shutdown periods, the risks and inefficiencies brought about by the above defects become even more difficult and prominent. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention provides a method for quickly resuming production of a blast furnace after a long period of shutdown, which solves the problem of how to overcome the defects of the existing blast furnace resumption method, such as slow resumption process, high safety risks and uncontrollable nature caused by the coldness of the furnace center and blockage of the drainage channel.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for quickly resuming production of a blast furnace after a long-term shutdown, comprising the following resumption steps: Step 1: Active preheating of the hearth core: Before or at the initial stage of resuming blast at the main tuyere of the blast furnace, oxygen-containing gas (with an oxygen concentration greater than 99.5%) is introduced into the center area of ​​the hearth through at least one iron mouth to actively heat the center area of ​​the hearth; Step 2: Pre-construction of the drainage channel: After the blast at the main tuyere of the blast furnace resumes production and before a large amount of liquid slag and iron is formed, open another iron mouth and use the gas pressure already formed in the furnace to spray high-temperature coal gas out of this iron mouth to clear the furnace hearth, heat the iron mouth area and pre-construct the slag and iron drainage channel.

[0008] Preferably, the method further includes a furnace environment pretreatment step before the wind-down step before resuming production, and the step includes: before the planned wind-down, programmatically lowering the binary basicity of the slag from the conventional range of 1.15 to 1.18 to the target range of 1.08 to 1.10.

[0009] Preferably, the furnace environment pretreatment step before the wind stop also includes: activating all spare iron mouths to perform iron tapping operations in turn, and opening all long-dormant air ports to supply air to activate the dead zones of the furnace body.

[0010] Preferably, the first step of actively preheating the furnace core includes a programmed multi-stage oxygen supply control procedure to achieve staged heating of the furnace center.

[0011] Preferably, the programmed multi-stage oxygen supply control procedure includes: Low temperature activation stage: the oxygen flow rate is 5-15% of the maximum design flow rate; Coordinated heating stage: the oxygen flow rate is 20-50% of the maximum design flow rate; Intensified melting stage: the oxygen flow rate is 100% of the maximum design flow rate.

[0012] Preferably, the drainage channel pre-construction step is initiated based on the monitoring that the pressure difference between the gas pressure in the furnace and the blast pressure at the tuyere reaches a preset threshold.

[0013] Preferably, the method further includes a blast furnace charge filling step after the furnace environment pretreatment step before blasting, which step includes: charging blast coke and silica as a slag-forming agent into the furnace, wherein the mass ratio of silica to blast coke is 1:8 to 1:12.

[0014] Preferably, the method further comprises a heat preservation step during the wind-down period, which comprises: controlling the cooling water inlet temperature at 45±1°C, and reducing the total cooling water flow rate in stages to 50-60% of the normal flow rate.

[0015] Preferably, the method is applicable to working conditions where the outage time exceeds 48 hours, wherein the active preheating step of the furnace core is started about 4-8 hours before the resumption of air (determined based on both safety and resumption of production needs).

[0016] Preferably, the method further includes an adaptive production recovery step after step 2, which includes: determining the rhythm of subsequently increasing the ore charging amount and resuming the coal injection amount based on the evaluation results of the slag iron temperature and fluidity of the first iron tapping.

[0017] The present invention provides a method for quickly resuming production of a blast furnace after a long-term shutdown. It has the following beneficial effects: 1. The present invention significantly improves the safety and controllability of the blast furnace resumption process by setting up an "active preheating step for the hearth core" and a "pre-construction step for the drainage channel" and making them work together. Specifically, before a large amount of liquid slag is formed, active preheating is used to solve the "cold" state problem in the center of the hearth, and a smooth drainage channel is pre-constructed using high-pressure coal gas flow, fundamentally avoiding the fatal risk of newly produced high-temperature liquid phases gathering in the front area of ​​the tuyere in the early stage of resumption, thereby effectively preventing the occurrence of serious accidents such as tuyere burning, and transforming the entire resumption process from passive waiting full of uncertainty to safe and controllable active guidance.

[0018] 2. The present invention achieves a substantial improvement in the efficiency of resumption of production and a significant reduction in the time. Before the wind-down period, the "furnace environment pretreatment step" creates a clean initial condition for resumption of production; during the wind-down period, the "refined energy retention step" maximizes the preservation of furnace heat; when resuming production, active preheating and pre-building of channels ensure that slag with good fluidity can be obtained when the iron is first tapped. This series of interlocking designs eliminates the lengthy "suffocating furnace" heating and solidified slag treatment time in traditional methods, allowing the blast furnace to resume normal production in the shortest possible time. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0021] Please see the attached Figure 1 , an embodiment of the present invention provides a method for quickly resuming production of a blast furnace after a long period of shutdown. By setting an "active preheating step for the hearth core" and a "pre-construction step for the drainage channel" and making them work together, the safety and controllability of the blast furnace resumption process are significantly improved. Specifically, before a large amount of liquid slag is formed, active preheating is used to solve the "cold" state problem in the center of the hearth, and a smooth drainage channel is pre-constructed using high-pressure coal gas flow, fundamentally avoiding the fatal risk of newly produced high-temperature liquid phases gathering in the front area of ​​the tuyere in the early stage of resumption, thereby effectively preventing the occurrence of serious accidents such as tuyere burning, and transforming the entire resumption process from passive waiting full of uncertainty to safe and controllable active guidance.

[0022] Please see the attached Figure 1 This method is a method for quickly resuming production of a blast furnace after a long-term shutdown, including the following resumption steps: Step 1: Active preheating of the hearth core: Before or at the initial stage of resuming blast at the main tuyere of the blast furnace, oxygen-containing gas is introduced into the center area of ​​the hearth through at least one tap hole to actively heat the center area of ​​the hearth; Step 2: Pre-construction of the drainage channel: After the blast at the main tuyere of the blast furnace resumes production and before a large amount of liquid slag and iron is formed, open another iron mouth and use the gas pressure already formed in the furnace to spray high-temperature coal gas out of this iron mouth to clear the furnace and pre-construct the slag and iron drainage channel.

[0023] In this embodiment, firstly, a systematic and planned pretreatment step 1 of the furnace environment before the blast furnace is shut down is performed.

[0024] In one possible implementation, the pre-treatment step is started within a specific time window before the planned wind-down, for example, 72 hours. Specifically, the pre-treatment step includes activating the physical state of the furnace and programming the chemical composition of the slag.

[0025] Regarding the activation of the physical state of the furnace and the preliminary optimization of the chemical environment: The present invention conducts a comprehensive "cleaning" of the interior of the blast furnace before shutting down, so as to remove to the greatest extent possible the enriched layers of harmful substances such as alkali metals and zinc and physical adhesives that inevitably accumulate in the furnace wall, the dead corners of the furnace hearth and other areas during the long-term production process.

[0026] Exemplarily, this activation operation involves opening all tuyeres that have been idle for various reasons, such as those blocked due to small sleeve damage or process requirements, and switching to a full-tuyeres air supply mode. Simultaneously, all spare tapholes are activated, switching from a conventional two- or three-taphole operation mode to a multi-taphole rotational tapping mode.

[0027] It should be noted that the technical principle of the above operation is that by physically expanding the air inlet and iron outlet channels of the blast furnace, the fluidity of the working medium (coal gas, slag and iron) in the furnace and the flushing ability of the interior of the furnace can be significantly enhanced.

[0028] To facilitate this physical activation process, in this embodiment, the thermal system is simultaneously adjusted. Preferably, the target temperature (PT) of the molten iron is raised from the conventional minimum of 1460°C to a maximum of 1470°C, and the target silicon content (Si) is adjusted to a relatively high level of 0.3-0.5%. This approach is intended to leverage the enhanced fluidity and heat transfer capabilities of high-temperature, high-Si molten iron. Furthermore, this thermal system creates a more reducing atmosphere within the furnace, increasing the gas temperature and flow rate accordingly. This enhances its ability to carry volatile harmful elements like zinc (Zn), allowing them to be discharged from the furnace along with the gas, achieving chemical "detoxification" of the furnace.

[0029] The core of this pretreatment process also includes a step for programmatically shaping the slag's chemical composition. The technical concept behind this step is twofold: first, in the final stage before the blast-off, the slag's composition is adjusted to maximize its fluidity, allowing it to carry more harmful impurities and smoothly exit the furnace. Second, and more crucial, a low-melting-point protective slag layer with specific chemical properties is deliberately formed and left at the bottom of the furnace.

[0030] Specifically, this step involves adjusting the ratio of acidic flux (such as silica) to the charge to programmatically lower the slag binary basicity (R2). Slag binary basicity (R2) is a key indicator of slag chemical properties and is calculated as the ratio of the mass fractions of calcium oxide to silicon dioxide in the slag, i.e.: ; For example, in a preferred embodiment, the programmed down-regulation process is carried out in three consecutive stages within 72 hours before the planned wind break: In the first stage (e.g. 72 to 48 hours before the wind down), the slag R2 will be initially lowered from the normal production range of 1.15 to 1.18 to the target range of 1.14 to 1.16.

[0031] In the second stage (e.g. 48 to 24 hours before wind down), the slag R2 will be further lowered to the target range of 1.11 to 1.13.

[0032] In the third stage (e.g. within 24 hours before the wind-down operation), the slag R2 is finally lowered to the target range of 1.08 to 1.10, and this chemical composition is maintained until the wind-down operation.

[0033] It should be noted that the low-basicity slag with R2 in the range of 1.08 to 1.10 thus formed has a relatively low melting point and moderate reactivity. In the overall technical solution of the present invention, the residual slag layer formed in this step is not a useless residue, but a key guarantee for the successful implementation of the subsequent resumption of production steps. When the "active preheating step of the furnace core" is subsequently performed, when the oxygen-containing gas is introduced into the center of the furnace, this pre-constructed protective slag layer can play an important physical buffering and chemical isolation role. It can effectively avoid excessively violent and difficult-to-control oxidation reactions between high-concentration oxygen and the coke at the bottom of the furnace, thereby ensuring the smoothness, safety and controllability of the entire active preheating process.

[0034] In this embodiment, after completing the aforementioned step 1 of pre-treatment of the furnace environment before the wind-down operation, the method then performs the wind-down operation and energy maintenance step 2.

[0035] Understandably, this step is the crucial bridge between "preparation" and "resumption of production." Its core technical concept lies in, on the one hand, solidifying and maintaining the excellent chemical environment within the furnace created in Step 1 by filling it with a specific blast-off charge; and, on the other hand, by finely regulating the external cooling system, maximizing the physical energy (i.e., heat) accumulated by the furnace during long-term production, thus laying a solid foundation for subsequent rapid and low-energy resumption of production.

[0036] Regarding the filling of the blast furnace charge and the sealing of the furnace body: In one possible implementation, this operation is performed within the last few hours, for example, seven hours, before the planned wind down. Specifically, the pulverized coal and oxygen injection into the blast furnace are first stopped, allowing the blast furnace to smoothly transition from combined injection to full coke smelting mode.

[0037] During this stage, the furnace is loaded with special materials for air-retardant combustion in batches. Preferably, this material primarily consists of air-retardant coke and silica, a slagging agent. For example, the total amount of air-retardant coke charged can be 80-85 tons, while the total amount of silica charged can be 12-15 tons.

[0038] It should be noted that the ratio of wind-down coke to silica in the present invention is an important technical feature. In this embodiment, the mass ratio of silica to wind-down coke is controlled in a preferred range, for example, 1:8 to 1:12. The technical principle is that coke, as a skeleton material, provides the necessary physical support for the charge structure during the wind-down period and serves as a basic heat reserve; and the silica added in a specific proportion will react with the CaO-rich low-alkalinity slag remaining in the furnace at the end of step one, further consolidating and stabilizing the low-melting-point protective slag layer with specific chemical properties formed at the bottom of the furnace. This design fully reflects the intrinsic connection and progressive relationship between the various steps of the present invention.

[0039] After all the blast furnace charges are filled, the final slag and iron discharge operation is carried out to drain the liquid phase in the furnace as much as possible. Subsequently, a dedicated mud gun equipment is used to strictly tamp and seal all the tuyere, slag hole and iron hole of the blast furnace to isolate the furnace from the external environment.

[0040] Regarding the maintenance of refined energy during the rest period: The present invention is that traditional wind-stopping and heat-preserving measures are often relatively extensive, while the present invention proposes a set of refined energy preservation solutions.

[0041] As an option, this solution is achieved by dual regulation of the blast furnace cooling system.

[0042] Specifically, one of the controls is the temperature of the cooling medium. During the shutdown period, the cooling system's inlet water temperature is proactively raised from the normal production level of 39±1°C to a preferred higher level, such as 45±1°C. This is understood to be intended to proactively reduce the heat transfer temperature difference between the furnace interior and the cooling medium, thereby directly reducing the rate of heat transfer from the furnace to the cooling medium.

[0043] The second control method is to control the flow rate of the cooling medium. After the shutdown begins, the total flow rate of the circulating water in the main cooling system and the furnace bottom cooling pipes is reduced in stages and steps according to preset time points, such as after 2 hours, 5 hours, and 8 hours of shutdown. Preferably, the total flow rate is ultimately reduced to 50-60% of the flow rate during normal production. The principle is that by reducing the mass of cooling medium flowing through the cooling equipment per unit time, the total amount of heat carried out of the furnace is directly reduced.

[0044] In this embodiment, after completing the energy maintenance during the wind-down period, the method then performs its most core active collaborative production resumption operation steps.

[0045] This step includes the following two core sub-steps that work together: The technical concept of this step is to directly activate the central area of ​​the furnace that has been in a "cold, dead, and silent" state after a long period of wind stoppage by actively heating it from the inside out before or at the initial stage of resuming the main air blast, thereby creating the necessary thermodynamic conditions for restoring its air permeability and liquid permeability.

[0046] Alternatively, at a specific time point, such as eight hours, before the planned re-airing, a preselected iron hole is opened using a large-diameter drill and a special heat-resistant alloy steel oxygen lance is inserted. Subsequently, a programmed multi-stage oxygen supply control procedure is implemented to achieve a staged heating of the furnace core.

[0047] Exemplarily, the multi-stage oxygen supply control procedure includes: Low-temperature activation stage: For example, from 8 hours to 2 hours before re-airing, a small amount of oxygen is introduced, with the flow rate controlled at 5-15% of the maximum design flow rate. The principle is to use a weak oxidation reaction to continuously and gently preheat the cooled and hardened coke in the center of the furnace, breaking its "dead" state without causing a violent reaction.

[0048] Coordinated heating stage: For example, 2 hours before the resumption of air flow to after the resumption of air flow at the main air outlet, the oxygen flow rate is increased to 20~50% of the maximum design flow rate, forming a coordinated internal and external heating trend with the main air outlet air supply that is about to or has already started.

[0049] Enhanced Melting Stage: For example, 30-40 minutes before the taphole is scheduled, the oxygen flow rate is increased to 100% of the maximum design flow rate. This is done to quickly form an initial liquid pool with good fluidity in the core area of ​​the furnace just before tapping, ensuring smooth tapping.

[0050] It should be noted that the low-basicity protective slag layer pre-constructed in step one plays a key role in physical buffering and chemical isolation in this step. It effectively avoids excessively violent reaction between high-concentration oxygen and furnace coke, thereby ensuring the smoothness, safety and controllability of the entire active preheating process.

[0051] This step addresses another core challenge to resuming production: the problem of furnace blockage. The principle is to use the kinetic energy of the high-pressure gas flow to physically clear the coke bed at the bottom of the furnace before any liquid slag and iron are formed, thus establishing a smooth drainage channel from the center of the furnace to the iron mouth.

[0052] Specifically, after air has been supplied to the main tuyere of the blast furnace and a certain pressure has been established in the furnace, another iron mouth without an oxygen lance is selected and fully opened to allow high-temperature coal gas to be strongly ejected outward from this iron mouth.

[0053] This step isn't initiated at a fixed time, but rather based on real-time assessment of furnace state parameters. In one possible implementation, this step is initiated only when the pressure difference between the furnace gas pressure (e.g., bosh gas pressure) and the tuyere blast pressure reaches a preset threshold. This threshold ensures that the high-temperature gas flow ejected from the taphole has sufficient kinetic energy to effectively dissipate and loosen the compacted coke layer.

[0054] Working principle: While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for quickly resuming production of a blast furnace after a long-term shutdown, characterized in that: The method comprises the following steps of reproducing: Step 1: Active preheating of the hearth core: Before or at the initial stage of resuming blast at the main tuyere of the blast furnace, oxygen-containing gas is introduced into the center area of ​​the hearth through at least one tap hole to actively heat the center area of ​​the hearth; Step 2: Pre-construction of the drainage channel: After the blast at the main tuyere of the blast furnace resumes production and before a large amount of liquid slag and iron is formed, open another iron mouth and use the gas pressure already formed in the furnace to spray high-temperature coal gas out of this iron mouth to clear the furnace hearth, heat the iron mouth area and pre-construct the slag and iron drainage channel.

2. The method for quickly resuming production after a blast furnace has been shut down for a long time according to claim 1, characterized in that: The method further includes a furnace environment pretreatment step before the wind-down step, which includes: before the planned wind-down, programmatically lowering the slag binary basicity from the conventional range of 1.15 to 1.18 to the target range of 1.08 to 1.

10.

3. The method for quickly resuming production after a blast furnace has been out of service for a long time according to claim 2, characterized in that: The furnace environment pretreatment step before the wind stop also includes: activating all spare tapholes for rotating tapping operations, and opening all long-dormant tuyere for air supply to activate the dead zones of the furnace body.

4. The method for quickly resuming production after a blast furnace has been out of service for a long time according to claim 1, characterized in that: The active preheating step of the furnace core also includes a programmed multi-stage oxygen supply control procedure.

5. The method for quickly resuming production after a blast furnace has been out of service for a long time according to claim 4, characterized in that: The programmed multi-stage oxygen supply control procedure also includes: Low temperature activation stage: the oxygen flow rate is 5-15% of the maximum design flow rate; Coordinated heating stage: the oxygen flow rate is 20-50% of the maximum design flow rate; Intensified melting stage: the oxygen flow rate is 100% of the maximum design flow rate.

6. The method for quickly resuming production after a blast furnace has been out of service for a long time according to claim 1, characterized in that: The initiation of the discharge channel pre-construction step is triggered when it is detected that the pressure difference between the gas pressure in the furnace and the blast pressure at the tuyere reaches a preset threshold.

7. The method for quickly resuming production after a blast furnace has been out of service for a long time according to claim 1, characterized in that: The method further comprises a step of filling blast furnace materials after the step of pre-treating the furnace environment before blasting, which step comprises: charging blast coke and silica as a slag-forming agent into the furnace, wherein the mass ratio of silica to blast coke is 1:8 to 1:

12.

8. The method for quickly resuming production after a blast furnace has been out of service for a long time according to claim 1, characterized in that: During the wind-off period, the method further includes a heat maintenance step, which includes: controlling the cooling water inlet temperature at 45±1°C and reducing the total cooling water flow rate to 50-60% of the normal flow rate in stages.

9. The method for quickly resuming production after a blast furnace has been out of service for a long time according to claim 1, characterized in that: The method is applicable to working conditions where the wind-out period exceeds 48 hours, wherein the furnace core active preheating step is started within 4-8 hours before the wind is resumed.

10. The method for quickly resuming production after a blast furnace has been out of service for a long time according to claim 1, characterized in that: After step 2, the method further includes an adaptive production recovery step, which includes: determining the rhythm of subsequently increasing the ore charging amount and resuming the coal injection amount based on the evaluation results of the slag iron temperature and fluidity of the first iron tapping.

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