Method for prolonging damping-down time of smelting reduction furnace

Abstract

The invention discloses a method for prolonging damping-down time of a smelting reduction furnace, and belongs to the technical field of damping-down of smelting reduction furnaces. Comprising the following steps: judging whether a fault causing damping down of the smelting reduction furnace affects supply of fuel, flux and oxygen-containing gas of the SRV furnace and operation of a combustible gas treatment system or not, if not, selecting a first damping down mode, and if not, selecting a second damping down mode; and if the supply of the fuel, the flux and the oxygen-containing gas of the SRV furnace and the operation of a combustible gas treatment system are affected, a second damping-down mode is selected, and the technical problem that the damping-down time is short in the technical field of smelting reduction furnaces at present is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of smelting reduction furnace wind-off time, and in particular to a method for extending the wind-off time of a smelting reduction furnace. Background Art

[0002] HIsmelt technology is a non-blast furnace smelting reduction ironmaking process. Its core is the direct use of powdered iron ore and non-coking coal to achieve efficient reduction of iron oxides in an SRV furnace. The SRV furnace is divided into an iron bath zone, a transition zone, and a secondary combustion zone. By regulating the amount of coal injection, the amount of iron-containing material injected, and the oxygen enrichment level (30-40%), the thermodynamic and kinetic balance within the furnace is achieved.

[0003] The smelting reduction furnace as a whole includes SRV furnace, pre-furnace, water-cooling flue and other structures. When a structure in the smelting reduction furnace system fails, such as a water-cooling flue failure, the SRV furnace needs to be shut down to reduce the temperature of the water-cooling flue and make the inside of the water-cooling flue easier to inspect and maintain.

[0004] Unlike the blast furnace, the SRV furnace and the pre-furnace in the molten reduction furnace are connected by a channel. Molten iron in the SRV furnace flows through the channel to the pre-furnace, which then transfers the molten iron. This channel structure limits the duration of the molten reduction furnace's downtime. During downtime, the molten iron's temperature gradually decreases, and during this downtime, it is necessary to prevent the molten iron from dropping below its solidification temperature and causing condensation. In particular, it is important to prevent the molten iron in the channel from solidifying. Once solidified, the channel must be destroyed to remove the iron blocks and rebuild the channel, which is extremely cumbersome. Therefore, the duration of each downtime must be strictly controlled.

[0005] The current outage time of a smelting reduction furnace is about 10 to 12 hours. If the fault handling time exceeds the outage time, the furnace can only be shut down. The shutdown operation is more cumbersome than the outage operation and significantly affects production. Therefore, a method to extend the outage time of a smelting reduction furnace is proposed.

[0006] Chinese patent CN118147382A discloses a method for keeping molten iron warm during a long-term outage of a Hismelt ironmaking furnace. The method extends the outage time by pouring high-temperature molten iron into the front furnace. However, in actual application, as the temperature decreases, the fluidity of the molten iron becomes poor, and the heat of the newly poured high-temperature molten iron in the front furnace is difficult to transfer to the molten iron in the SRV furnace and the channel. Therefore, this method is not significantly effective in extending the outage time.

[0007] In summary, there is currently a technical problem of short wind-down time in the technical field of smelting reduction furnaces. Summary of the Invention

[0008] The main purpose of the present invention is to provide a method for extending the outage time of a smelting reduction furnace, aiming to extend the outage time of the smelting reduction furnace.

[0009] To achieve the above-mentioned object, the present invention proposes a method for extending the shut-down time of a smelting reduction furnace, comprising: S100, determining whether the fault causing the shut-down of the smelting reduction furnace affects the supply of fuel, flux, and oxygen-containing gas to the SRV furnace and the operation of the combustible gas treatment system; If the supply of fuel, flux and oxygen-containing gas to the smelting reduction furnace and the operation of the combustible gas treatment system are not affected, the first air-break mode is selected. The first air-break mode includes: S210, adjusting the furnace condition parameters of the SRV furnace, and after the adjustment is completed, the smelting reduction furnace enters a wind-off state; S220: The molten iron temperature in the pre-furnace is detected at predetermined intervals. If the molten iron temperature in the pre-furnace is lower than 1300° C., combustible gas and oxygen-containing gas are supplied to the SRV furnace for a predetermined period of time. The combustible gas burns and melts the slag crust on the surface of the molten pool. After the slag crust is melted, fuel and flux are supplied to the furnace to increase the molten pool temperature. The pressure in the SRV furnace is controlled to fluctuate periodically to promote heat transfer between the molten irons. This step is repeated until the wind-down period ends. If the supply of fuel, flux and oxygen-containing gas and the operation of the combustible gas treatment system of the SRV furnace are affected, the second air-break mode shall be selected. The second air-break mode includes: S310, adjusting the furnace condition parameters of the SRV furnace, and after the adjustment is completed, the smelting reduction furnace enters a wind-off state; S320. Detect the temperature of the molten iron in the pre-furnace at predetermined intervals. If the temperature of the molten iron in the pre-furnace is lower than the predetermined temperature, use auxiliary tooling to heat the molten iron in the pre-furnace for a predetermined time. Repeat this step until the wind-down period ends.

[0010] Optionally, in one embodiment of the present invention, step S210 further includes measuring the mass fractions of Al2O3 and MgO in the slag before the wind-down period and the binary basicity R2 of the slag. Step S220 also includes: the supply rate of the combustible gas is 3000-3500 MJ / min, and the predetermined time of the supply of the combustible gas is T, T=30+200×(S Al -15.5%)+100×(8%-S Mg )+60×(R2-1.2) Where: T is the supply time of combustible gas, in minutes; S Al is the mass fraction of Al2O3 in the slag before wind stop, unit is %; S Mg is the mass fraction of MgO in the slag before wind shutdown, unit is %; R2 is the binary basicity of the slag before the wind is shut down, and has no unit.

[0011] Optionally, in one embodiment of the present invention, step S210 further includes: Maintaining the injection volume of iron-containing materials unchanged, gradually increase the amount of oxygen-containing gas to adjust the slag iron composition and slag iron temperature until the slag temperature is 1420~1450℃, the binary basicity is 1.20~1.30, the magnesium-aluminum ratio is 0.55~0.65, the iron tapping temperature is 1400~1430℃, and the carbon content of the molten iron is 3.8~4.0%. Then the smelting reduction furnace enters the wind-off state.

[0012] Optionally, in one embodiment of the present invention, step S210 further includes: Within 4 to 6 hours before the start of the wind shutdown, increase the frequency of slag discharge to reduce the slag inventory in the furnace to below 200t. Under a furnace pressure of 60 to 65kPa, when the interval between slag discharge at the slag mouth and breathing at the slag mouth is less than 3s, it means that the slag inventory has dropped below 200t.

[0013] Optionally, in one embodiment of the present invention, in step S220, the fuel supply rate is 8000-11000 MJ / min, and the molten pool temperature is increased by 100° C. to 120° C. per hour.

[0014] Optionally, in one embodiment of the present invention, in step S220, the pressure inside the SRV furnace fluctuates periodically within the range of 30~60kPa, and the pressure rise and fall speed is 2~3kPa / min to promote heat transfer between the SRV furnace and the molten iron in the pre-furnace.

[0015] Optionally, in one embodiment of the present invention, step S310 further includes: Before the shutdown, the amount of oxygen-containing gas is maintained, and the injection amount of iron-containing materials is gradually reduced to adjust the slag iron composition and slag iron temperature and furnace conditions, so that the slag temperature before the shutdown is 1450~1500℃, the binary basicity is 1.15~1.20, the magnesium-aluminum ratio is 0.50~0.55, the iron tapping temperature is 1430~1480℃, and the carbon content of the molten iron is 4.1~4.3%.

[0016] Optionally, in one embodiment of the present invention, step S310 further includes: 6~8 hours before the start of the wind-down, slag is discharged twice to reduce the slag inventory in the SRV furnace. The first slag discharge is when the furnace pressure of the SRV furnace is 60~65kPa, and the interval between slag discharge through the slag outlet and gasping at the slag outlet is less than 3s, and the slag inventory in the furnace is reduced to below 200t; The secondary slag discharge is to further reduce the furnace pressure to 40~50kPa, and continue to discharge 80~100t of slag through the residual slag outlet. When the slag level in the furnace is at least 70mm lower than the spray gun tip, the residual slag outlet is blocked.

[0017] Optionally, in one embodiment of the present invention, step S320 further includes: The auxiliary tooling includes a sealing device, a heating spray gun and a carburizing device. A sealing device is provided on the upper part of the pre-furnace mouth to close the pre-furnace. The carburizing device and the heating spray gun extend into the pre-furnace. When the wind-down time exceeds 10 to 12 hours, the temperature of the molten iron in the pre-furnace is detected at predetermined intervals. If the temperature of the molten iron in the pre-furnace is lower than 1340°C, the carburizing agent is supplied to the pre-furnace through the carburizing device, and the combustible gas and oxygen-containing gas are supplied to the pre-furnace through the heating spray gun. The molten iron in the pre-furnace is heated by the combustion of the combustible gas.

[0018] Optionally, in one embodiment of the present invention, step S310 further includes: supplying fuel and flux into the SRV furnace between two slag tapping operations.

[0019] Compared to the prior art, the present invention can achieve at least the following beneficial effects: Before shutting down the furnace, it is first determined whether the cause of the shutting down of the smelting reduction furnace affects the supply of fuel, flux, and oxygen-containing gas to the smelting reduction furnace and the operation of the combustible gas processing system. If not, the shutting down time is extended using the first shutting down method.

[0020] In the first wind-down mode, since the smelting reduction furnace can normally supply fuel, flux and oxygen-containing gas and perform combustible gas treatment during the wind-down process, the wind-down time is extended by heating the furnace in the SRV furnace during the wind-down process.

[0021] Specifically, before the wind-down period begins, the SRV furnace is first adjusted to conditions suitable for the wind-down period. After the wind-down period begins, the molten iron temperature begins to drop from approximately 1430°C. After a period of natural cooling, the molten iron temperature in the pre-furnace is monitored. If the pre-furnace temperature drops below 1300°C, approaching its freezing point (1200°C), the molten iron needs to be heated to extend the wind-down period. As the molten pool in the SRV furnace cools, a slag crust forms on top of the slag. This presence affects subsequent heating of the molten iron, so combustible gas is first injected into the SRV furnace. The combustible gas burns within the SRV furnace, melting the slag crust. Once the slag crust melts, fuel and flux are supplied to the SRV furnace, and the combustion of the fuel raises the temperature of the molten iron. While the temperature is rising, the pressure inside the furnace is controlled to fluctuate periodically. This pressure fluctuation allows the molten iron to flow, promoting heat transfer from the molten iron in the SRV furnace to the molten iron in the channel and the pre-furnace, thereby heating the entire molten iron. Afterwards, the temperature measurement, slag shell melting, molten iron heating, and pressure fluctuation processes are repeated until the wind-down period is complete.

[0022] If the reason for the smelting reduction furnace outage affects the supply of fuel, flux and oxygen-containing gas to the smelting reduction furnace and the operation of the combustible gas treatment system, the outage time will be extended through the second outage mode.

[0023] In the second wind-off mode, since fuel cannot be added to the SRV furnace to heat it, the molten iron in the pre-furnace is heated instead. This heat transfer increases the overall temperature of the molten iron, extending the wind-off time. Similarly, in the second wind-off mode, the temperature detection and molten iron heating processes must be repeated until the wind-off is complete.

[0024] Compared with the existing technology, this solution has a more significant effect in extending the outage time, and can greatly extend the outage time of the smelting reduction furnace, providing sufficient time for inspection and maintenance. Among them, the first outage method can continuously extend the original outage time from 10 to 12 hours until the maintenance is completed, solving the current technical problem of the short outage time of the smelting reduction furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0026] Figure 1 This is a flow chart of an embodiment of a method for extending the wind-off time of a smelting reduction furnace according to the present invention; Figure 2 Schematic diagram of the structure of the smelting reduction furnace.

[0027] Description of Figure Numbers: 100, SRV furnace; 200, channel; 300, pre-furnace; 400, auxiliary tooling; 410, sealing device; 420, heating spray gun; 430, carburizing device; 440, pressure regulating device; The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0030] In the present invention, unless otherwise specified or limited, the terms "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can mean fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0031] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the meaning of "and / or" appearing throughout the text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0032] The smelting reduction furnace includes an SRV furnace 100, a channel 200, a pre-furnace 300, a water-cooled flue and other components. Smelting is carried out in the SRV furnace 100. The SRV furnace 100 and the pre-furnace 300 are connected. The molten iron flows into the pre-furnace 300 through the channel 200, and the molten iron is collected through the pre-furnace 300.

[0033] Specifically, the SRV furnace 100 has a top lance and lances obliquely arranged on the side wall. The top lance is a gas lance, and some of the side wall lances are gas lances and some are solid material lances.

[0034] Shutting down or shutting down a molten reduction furnace can both create conditions for troubleshooting and repair. However, due to the difficulty of re-starting the furnace after a shutdown, the extremely tedious preparation for the shutdown, the long restart time, and the high cost of restarting the furnace, shutdown maintenance is usually avoided. For this reason, shutting down the furnace has become the preferred maintenance state after a molten reduction furnace failure. Unlike shutting down the furnace, which requires the furnace to be opened and iron to be discharged, shutting down the furnace does not require the furnace to be opened and iron to be discharged. Therefore, there is molten iron in the SRV furnace, the channel, and the pre-furnace. During the shutting down, it is necessary to ensure that the molten iron in the molten reduction furnace does not condense. Due to structural limitations, the molten iron in the channel cannot be directly heated, so special attention must be paid to prevent condensation in the channel.

[0035] Reference Figure 1~Figure 2 The present invention proposes a method for extending the outage time of a smelting reduction furnace. In this method, two ways of extending the outage time are proposed according to different reasons leading to the outage of the smelting reduction furnace.

[0036] The first method is used during the shutdown period to normally supply fuel, flux and oxygen-containing gas to the SRV furnace 100 and perform combustible gas treatment, such as when the raw material feeding system fails and raw material cannot be supplied, the raw material pretreatment system fails and raw material pretreatment cannot be performed, the raw material blowing system fails and raw material cannot be injected into the furnace, and the molten reduction furnace needs to be shut down.

[0037] Before starting this method, the furnace conditions must be adjusted to meet the wind-off conditions before the wind-off is performed. During the wind-off period, the molten iron temperature will gradually drop. The molten iron temperature in the pre-furnace 300 needs to be measured at regular intervals. If the molten iron temperature in the pre-furnace 300 is found to be below 1300°C, the molten iron is at risk of solidification. Therefore, when the molten iron temperature is detected to be below 1300°C, the SRV furnace 100 needs to be heated to raise the temperature. During the cooling process of the molten iron, the upper layer of slag in the molten pool of the SRV furnace 100 will condense to form a slag shell. Before the molten iron is heated, combustible gas and oxygen-containing gas are first injected into the SRV furnace 100 through the top spray gun. The combustible gas burns above the slag shell to heat and melt the slag shell. After the slag shell is melted, fuel and flux are added to the molten iron in the SRV furnace 100 through the side wall spray gun, and the combustion of the fuel heats the molten iron.

[0038] Since the fluidity of molten iron gradually decreases with the decrease in temperature, when heating the molten iron in the SRV furnace 100, the heat cannot be quickly transferred to the molten iron in the channel 200 and the pre-furnace 300 through the flow of molten iron. For this reason, during the molten iron heating process, the pressure in the SRV furnace 100 is controlled to fluctuate periodically to promote the flow of molten iron, so that the heat in the SRV furnace 100 can be quickly transferred to the channel 200 and the pre-furnace 300 to complete the heating of all the molten iron. Thereafter, the temperature measurement, slag shell melting, fuel supply, and pressure fluctuation steps are repeated until the wind-out period ends. This method can significantly extend the wind-out period, and continuously extend the wind-out period of the SRV furnace 100 from 10 to 12 hours to the end of maintenance, which can not only provide sufficient time for troubleshooting and maintenance, but also quickly resume wind and production.

[0039] The second wind-off mode is that during the wind-off period, the fuel, flux and oxygen-containing gas cannot be supplied and the combustible gas cannot be processed normally in the SRV furnace 100. At this time, the furnace heating method cannot be used to extend the wind-off time.

[0040] In the second wind-off mode, the furnace condition parameters of the SRV furnace 100 are first adjusted so that the wind-off conditions are met and then the wind is shut down.

[0041] During the wind-out period, the temperature of the molten iron in the pre-furnace 300 is detected at predetermined intervals. When the temperature of the molten iron is lower than the predetermined temperature, the molten iron in the pre-furnace 300 is heated using a heating device. The heating is stopped after the predetermined time, and this step is repeated until the wind-out ends.

[0042] This method proposes two ways to extend the outage time of the smelting reduction furnace according to the different reasons that lead to the outage of the furnace. The outage time can be extended under various conditions to meet the time requirements for complex fault repairs.

[0043] The first wind-break method is described below: Specifically, in the first wind-off mode, the furnace conditions need to be adjusted to the following parameters before wind-off: The slag tapping temperature before wind-down is 1420~1450℃, the binary basicity is 1.20~1.30, the magnesium-aluminum ratio is 0.55~0.65, the iron tapping temperature is 1400~1430℃, and the carbon content of the molten iron is 3.8~4.0%; adjusting the furnace conditions to the above parameters before wind-down can increase the molten pool temperature as much as possible while ensuring that the degree of erosion of the furnace hearth resistant materials is controlled, while reducing the slag melting point, improving the slag fluidity, and enhancing the molten pool stirring and gushing effect, creating conditions for increasing the molten pool temperature before wind-down. In addition, it is beneficial to melt the slag shell as soon as possible after re-blowing, prevent the spray gun from being blocked, and reduce the recovery time of the re-blowing furnace condition.

[0044] Before the wind is shut down, the ferrous oxide content in the iron-containing material is adjusted (the ferrous oxide content is preferably not less than 5%), the injection volume of the iron-containing material is maintained unchanged, and the amount of oxygen-containing gas is gradually increased to adjust the slag iron composition and slag iron temperature.

[0045] Specifically, methods for adjusting the ferrous oxide content include increasing the degree of pretreatment of the iron-containing material and increasing the amount of ferrous oxide-containing material added to the iron-containing material. By increasing the amount of ferrous oxide added, the heat consumption during the reduction of the iron-containing material in the melt pool is reduced, reducing slag production and facilitating a temperature increase and slag control before the furnace shuts down. Preferably, the SiO2 content of the iron-containing material entering the furnace should be controlled to no more than 4%, and the Al2O3 content should be controlled to no more than 2.5%.

[0046] During the process of adjusting the furnace condition, it is necessary to adjust the supply amount of calcium-containing flux and magnesium-containing flux into the furnace at the same time. The supply method of calcium-containing flux is to use a solid material spray gun to blow quicklime powder into the furnace, and the supply method of magnesium-containing flux is to premix magnesium-containing flux and iron-containing material in a certain proportion, preheat or preheat and pre-reduced them, and then use a solid material spray gun to blow them into the furnace.

[0047] By increasing the amount of calcium-containing flux and magnesium-containing flux fed into the furnace, the slag viscosity can be reduced, the formation of the slag shell can be delayed, and the melting temperature of the slag shell can be lowered, thereby shortening the subsequent slag shell melting time.

[0048] Furthermore, before shutting down, it is necessary to reduce the amount of slag in the SRV furnace 100. The slag in the SRV furnace 100 will gradually solidify and form a slag crust after shutting down. If there is excessive slag in the furnace before shutting down, a thick slag crust will form after shutting down, prolonging the time required to melt the slag crust, adversely affecting subsequent fuel supply and combustion, and posing a risk of clogging the spray gun.

[0049] Preferably, the slag in the SRV furnace 100 is reduced to less than 200 tons before shutting down. A method for determining the remaining slag in the SRV furnace 100 is proposed. When the furnace pressure of the SRV furnace 100 is between 60 and 65 kPa, if the interval between slag tapping and slag outlet gasping is less than 3 seconds, the remaining slag in the SRV furnace 100 is determined to be less than 200 tons.

[0050] As the slag residue in the SRV furnace 100 decreases, the thickness of the slag layer gradually decreases. The drop in the slag liquid level will cause the slag liquid level fluctuation at the slag mouth to intensify. The phenomenon of intermittent slag flow is called "slag mouth gasping". When the interval between slag discharge from the slag mouth and slag mouth gasping is less than 3s, it indicates that the slag liquid surface is close to the bottom of the slag mouth, and the remaining slag is difficult to maintain a continuous flow state.

[0051] In addition to reducing the slag residue in the furnace, it is also necessary to increase the molten iron inventory in the furnace before the wind is shut down. Specifically, when the furnace pressure is 60~65kPa, when the distance between the molten iron level in the pre-furnace 300 and the overflow port of the pre-furnace 300 is less than 5cm, it is determined that the molten iron inventory in the SRV furnace 100 is sufficient.

[0052] After the above operations are completed, the SRV furnace 100 is switched to a wind-off state.

[0053] When the SRV furnace 100 is switched to the wind-off state for 4 to 6 hours, the temperature of the molten iron in the pre-furnace 300 is checked every hour. If it is detected that the temperature of the molten iron in the pre-furnace 300 drops to 1300°C, combustible gas and oxygen-containing gas are supplied to the SRV furnace 100. After the slag shell is melted by combustion of the combustible gas, fuel and flux are supplied to the furnace. During the fuel combustion process, the furnace pressure in the SRV furnace 100 is controlled to fluctuate periodically.

[0054] During the cooling process of the molten iron in the SRV furnace 100, a slag shell will form on its surface. The slag shell is composed of high-melting-point components such as Al2O3 and SiO2, and its thermal conductivity is only 20% to 33% of that of the molten iron. It covers the molten iron. If fuel is added for combustion without melting the slag shell, the CO, H2 and other gases generated by the fuel combustion will be difficult to discharge, forming high pressure under the slag shell, creating a safety hazard and the risk of clogging the spray gun. Therefore, the fuel needs to be supplied after the slag shell is melted.

[0055] Specifically, when supplying combustible gas and oxygen-containing gas, the combustible gas and oxygen-containing gas can be supplied separately through the combustible gas spray gun on the side wall of the SRV furnace 100 and the oxygen-containing gas spray gun on the top of the SRV furnace 100, or they can be supplied through a multi-channel combustible gas and oxygen-containing gas composite spray gun on the side wall of the SRV furnace 100.

[0056] Combustible gases include but are not limited to natural gas, coal gas, hydrogen, etc., and oxygen-containing gases include air, oxygen-enriched gas and oxygen.

[0057] In this solution, the slag shell is melted by supplying combustible gas and oxygen-containing gas. The combustible gas and oxygen-rich gas generate less heat and have a high supply cost. During the slag shell melting process, the molten iron in channel 200 is in a state of slow cooling. In order to avoid solidification of the molten iron and reduce the feeding cost, it is necessary to strictly control the supply time of the combustible gas and oxygen-rich gas. If the time is too short, the fuel is directly sprayed when the slag shell has not yet melted, which may cause a risk of gun blockage and easily lead to safety hazards. If the time is too long, the molten iron in channel 200 may be at risk of solidification, the re-airing time may be prolonged, and the re-airing cost may increase.

[0058] Before the wind is shut down, the mass fractions of Al2O3 and MgO in the slag and the binary basicity R2 of the slag are measured. The supply rate of combustible gas is 3000~3500MJ / min. The supply time of combustible gas is calculated according to the following formula: T=30+200×(S Al -15.5%)+100×(8%-S Mg )+60×(R2-1.2) Where: T is the supply time of combustible gas, in minutes; S Al is the mass fraction of Al2O3 in the slag before wind stop, unit is %; S Mg is the mass fraction of MgO in the slag before wind shutdown, unit is %; R2 is the binary basicity of the slag before the wind is shut down, and has no unit.

[0059] The slag characteristics corresponding to the slag composition of Al2O3: 15.5%, MgO: 8%, and binary basicity R2: 1.2 in normal smelting state are selected as the measurement benchmark points.

[0060] In general, the mass fraction of Al2O3 and MgO in the slag and the binary basicity R2 of the slag range respectively: Al2O3: 14~19%, MgO: 7~10%, R2: 1.15~1.30. Al When the value of is 14%, S Al Lower, the slag shell is easy to melt, at this time (S Al -15.5%) is a negative value. If it is substituted into the formula normally for calculation, the time for melting the slag shell will be shortened.

[0061] Since the degree of slag shell melting in the SRV furnace 100 is difficult to observe, the slag shell melting time is estimated by the mass fraction of Al2O3 and MgO in the slag and the slag binary basicity R2, which can accurately control the molten iron heating work immediately after the slag shell melts.

[0062] To illustrate this formula, if the mass fraction of Al2O3 in the slag before wind-down is 17%, the mass fraction of MgO is 8.5%, and R2 is 1.25, then the combustible gas supply time for melting the slag shell is T=30+200×(18.2%-15.5%)+100×(8%-8.3%)+60×(1.25-1.20)=38.1 minutes.

[0063] By strictly controlling the supply time of combustible gas, fuel can be added immediately after the slag shell melts, quickly heating the molten iron, avoiding molten iron coagulation while controlling cost investment.

[0064] After the slag shell is melted, fuel and flux are added to the SRV furnace 100 to increase the molten iron temperature through fuel combustion. Specifically, the fuel can be selected from one or more of anthracite, bituminous coal, and biomass carbon, and the flux includes calcium-containing flux and magnesium-containing flux. The fuel is supplied at a rate of 8,000 to 11,000 MJ / min. At this rate, the molten iron temperature can rise by 100 to 120°C per hour. It is understood that the fuel supply rate can be determined based on the molten iron temperature during testing. For example, when the molten iron temperature is 1240°C during testing, the fuel supply rate is selected to be 11,000 MJ / min. When the molten iron temperature is 1300°C during testing, the fuel supply rate is selected to be 8,000 MJ / min.

[0065] To speed up heat transfer, the furnace pressure in the SRV furnace 100 is controlled to fluctuate periodically during fuel combustion. Specifically, the furnace pressure fluctuates within a range of 30 to 60 kPa, and the pressure rise and fall rate is controlled at 2 to 3 kPa / min.

[0066] During the pressure fluctuation process, when the pressure in the SRV furnace 100 rises, the molten iron in the SRV furnace 100 flows through the channel 200 to the pre-furnace 300, transferring the heat generated by the fuel combustion to the channel 200 and the pre-furnace 300. When the pressure in the SRV furnace 100 drops, the molten iron in the pre-furnace 300 flows through the channel 200 to the pre-furnace 300, flowing from the low-temperature zone generated by the fuel combustion to the high-temperature zone, accelerating heat exchange, and ensuring that the molten iron in the SRV furnace 100, the channel 200 and the pre-furnace 300 are all heated up.

[0067] Subsequently, according to the time requirements for troubleshooting and repair, repeat the molten iron temperature measurement - slag shell melting - feeding combustion and pressure fluctuation operations until the wind shutdown is completed.

[0068] Furthermore, the first air-off mode further includes step S230, re-airing. During re-airing, combustible gas and oxygen-containing gas are supplied to the SRV furnace 100. After the slag skull on the surface of the molten pool is melted, fuel and flux are supplied to the furnace. After maintaining this state for 1-2 hours, the iron-containing material is injected. The injection rates of the fuel, flux, and oxygen-containing gas are gradually increased until the iron-containing material injection rate reaches the normal production level.

[0069] In addition to the first wind-off mode, the present invention also proposes a second wind-off mode.

[0070] When the fuel injection system fails, the combustible gas treatment system requires maintenance, or the top lance of the SRV furnace 100 malfunctions, requiring the SRV furnace 100 to shut down for maintenance, the aforementioned method of heating inside the furnace becomes inapplicable. To extend the shut-down period when a fault affects the supply of fuel, flux, and oxygen-containing gas to the smelting reduction furnace and combustible gas treatment, an external heating method is proposed. It should be noted that external heating refers to heating performed outside the SRV furnace 100.

[0071] When the second wind-off mode is selected, it is also necessary to adjust the furnace condition of the SRV furnace 100 before wind-off so that it enters the wind-off state after reaching the predetermined parameters.

[0072] Specifically, in this method, the furnace conditions before the wind is shut down need to be adjusted to the following parameters: Before the blast-off, the ferrous oxide and elemental iron contents in the incoming iron-containing materials were adjusted, the oxygen-containing gas dosage was maintained, and the injection rate of the iron-containing materials was gradually reduced to adjust the slag and iron composition, slag and iron temperature, and furnace conditions. The slag tapping temperature before the blast-off was 1450-1500°C, the binary basicity was 1.15-1.20, the magnesium-aluminum ratio was 0.50-0.55, the iron tapping temperature was 1430-1480°C, and the carbon content of the molten iron was 4.1-4.3%. Specifically, the method for adjusting the ferrous oxide content in the iron-containing material includes one or more methods such as increasing the pre-reduction degree in the pretreatment step of the iron-containing material, increasing the amount of ferrous oxide-containing material added to the iron-containing material, etc.

[0073] The method for adjusting the elemental iron content in the iron-containing material includes one or more methods such as increasing the degree of pre-reduction of the iron-containing material during pretreatment and reduction, and increasing the amount of granular iron in the recycled slag added to the iron-containing material.

[0074] It should be noted that the content of ferrous oxide in iron-containing materials should not be less than 10%, and the content of elemental iron should not be less than 5%.

[0075] When adjusting the slag composition, it is necessary to control the SiO2 content in the iron-containing material entering the furnace to no more than 3.5%, the Al2O3 content to no more than 2.0%, and adjust the supply amount of calcium-containing flux and magnesium-containing flux entering the furnace.

[0076] Furthermore, the furnace condition adjustment step also includes reducing the slag residue in the SRV furnace 100. Compared to the first air shut-off mode, the second air shut-off mode requires further reduction of the slag residue. Specifically, in this mode, the slag level needs to be lowered to 70-100 mm below the sidewall spray gun tips.

[0077] Compared with the in-furnace heating method, in the current method, since the molten iron in the SRV furnace 100 is indirectly heated, the temperature of the molten iron in the SRV furnace 100 is more difficult to increase. The spray gun on the side wall of the SRV furnace 100 usually has its own water cooling circulation system and continuously sprays nitrogen to prevent the spray gun from being blocked. In order to avoid the nitrogen and water cooling circulation system from quickly taking away the temperature in the SRV furnace 100 when the wind is stopped, the slag liquid level is lowered to 70~100mm below the gun head of the side wall spray gun. There is no risk of spray gun blockage, so the nitrogen spraying can be stopped to reduce the heat taken away by the nitrogen and the side wall spray gun water cooling system circulation.

[0078] Specifically, the residual slag in the SRV furnace 100 is reduced by increasing the frequency of slag tapping. This frequency is increased 6-8 hours before the wind-down period. In the second wind-down period, there are two slag tapping steps. The first slag tapping process is identical to the first wind-down period. When the furnace pressure of the SRV furnace 100 is 60-65 kPa, and the interval between slag tapping through the slag outlet and slag outlet breathing is less than 3 seconds, the residual slag in the SRV furnace 100 is determined to be less than 200 tons.

[0079] During the secondary slag discharge, the furnace pressure in the SRV furnace 100 is further reduced, and 80-100 tons of slag is continuously discharged through the residual slag outlet until the slag level in the SRV furnace 100 is 70-100 mm below the tip of the sidewall spray gun. This blocks the residual slag outlet and stops the slag discharge. This further slag discharge reduces the heat removed by the nitrogen injection from the spray guns and the water cooling system for the sidewall spray guns during subsequent air shut-offs.

[0080] Preferably, between the primary and secondary slag discharges, fuel and flux are supplied to the SRV furnace 100. Specifically, the fuel may be one or more of anthracite, bituminous coal, and biomass carbon, and the flux may be a calcium-containing flux or a magnesium-containing flux.

[0081] After the first slag discharge, the sensible heat of the slag in the SRV furnace 100 decreases significantly as the amount of slag decreases. At this point, fuel is added, and the combustion of the fuel releases heat, maintaining the furnace temperature after the slag discharge. Furthermore, the viscosity of the slag is related to the temperature in the SRV furnace 100; as the temperature decreases, the viscosity of the slag increases. By adding fuel and burning the fuel, the continuity of the slag discharge during the second slag discharge is ensured, shortening preparation time and preventing slag from clogging the slag outlet.

[0082] The calcium-containing flux added during feeding, such as lime powder, can decompose to produce CaO, which reacts with SiO2 in the slag to produce low-melting-point calcium silicate, reducing the slag viscosity and improving fluidity.

[0083] Magnesium-containing fluxes, such as dolomite, can generate MgO after decomposition. MgO and CaO synergistically regulate the basicity of the slag, inhibit the formation of high-FeO slag, and avoid abnormal increase in slag phase viscosity.

[0084] To ensure that the furnace walls of the SRV furnace 100 are not damaged by overheating during normal operation, water-cooled walls are installed within the furnace to protect the walls. In this system, the temperature within the SRV furnace 100 is a key control area. To reduce the amount of heat removed by the water-cooled walls, the water-cooled wall system must be regulated after slag removal is completed.

[0085] Specifically, step S310 also includes stopping the supply of protective gas from the side wall spray gun of the SRV furnace 100, and gradually reducing the circulating water flow of the water-cooled wall. Preferably, the flow is reduced to 3 / 1~2 / 1 of the normal production state. At the same time, the inlet water temperature of the water-cooled wall is increased to maintain its inlet water temperature at 40~50℃.

[0086] Since the design function of the pre-furnace 300 is to accommodate molten iron, it does not have the function of heating the molten iron. A heating device is used to heat the molten iron in the pre-furnace 300.

[0087] Specifically, since the pre-furnace 300 is a non-enclosed structure, an auxiliary tooling 400 is provided to heat the molten iron in the pre-furnace 300 . The auxiliary tooling 400 includes a sealing device 410 , a heating lance 420 and a carbon addition device 430 .

[0088] The sealing device 410 may be a sealing cover, which is connected to the pre-furnace 300 via a flange to form a closed structure. The heating lance 420 and the carburizing device 430 extend through the sealing cover into the pre-furnace 300.

[0089] After the furnace conditions are adjusted and the heating device is set up, the SRV furnace 100 is placed into a wind-off state. After 10-12 hours in the wind-off state, the temperature of the molten iron in the pre-furnace 300 is checked every hour. If the temperature of the molten iron in the pre-furnace 300 is detected to be below 1340°C, the recarburizing device 430 continuously supplies recarburizer into the pre-furnace 300, and the oxy-fuel lance supplies combustible gas and oxygen-containing gas into the pre-furnace 300. The combustible gas burns to heat the molten iron in the pre-furnace 300, extending the wind-off period.

[0090] Due to the different structures and different molten iron contents, the cooling rate of the molten iron in the SRV furnace 100 is slower than that in the pre-furnace 300. The efficiency of heating the molten iron through the pre-furnace 300 is lower than heating the molten iron directly in the SRV furnace 100. Therefore, in the second wind-down process, the starting temperature of heating is higher than that in the first wind-down method.

[0091] During the heating process of the molten iron in the pre-furnace 300, the high-temperature oxidizing gases react with the carbon in the molten iron, causing it to decarburize. Supplying a recarburizer during the heating process can offset this decarburization loss, ensuring that the carbon content in the molten iron meets smelting requirements. Furthermore, the heat released by the combustion of recarburizers (such as anthracite or coke powder) can also assist in heating.

[0092] Specifically, the supply rate of the recarburizer is 0.2~0.5t / h, and the supply rate of the combustible gas is 200~300MJ / min.

[0093] Furthermore, the auxiliary tooling 400 also includes a pressure regulating device 440. Similar to the heating method in the furnace, the pressure regulating device 440 is used to make the pressure of the molten reduction furnace fluctuate periodically within the range of 5~40kPa, and the pressure rise and fall speed is controlled at 3~5kPa / min, so as to accelerate the heat transfer of the molten iron in the pre-furnace 300 to the channel 200 and the SRV furnace 100, thereby achieving the heating of all the molten iron in the molten reduction furnace.

[0094] Subsequently, the steps of molten iron temperature measurement - molten iron heating and pressure fluctuation in the pre-furnace 300 are repeated to extend the wind-out time until the wind-out is completed.

[0095] The second wind-break mode can extend the wind-break time from the original 10~12 hours to 35~40 hours.

[0096] Furthermore, the external furnace heating method also includes step S330, re-airing. Specifically, combustible gas and oxygen-containing gas are supplied to the furnace. After the slag shell on the surface of the molten pool is melted, solid fuel and flux are supplied to the furnace. After maintaining this for 1-2 hours, the iron-containing material and granulated slag are injected. The injection rates of the iron-containing material, granulated slag, fuel, flux, and oxygen-containing gas are gradually increased until the iron-containing material injection rate reaches normal production conditions.

[0097] Specifically, in the re-airing step, the proportion of granulated slag added to the iron-containing material is 10-15%.

[0098] In the external furnace heating method, more slag is discharged before the wind is shut down compared to the internal furnace heating method, and the slag inventory needs to be restored as soon as possible when the wind is resumed. If the slag inventory is small, a stronger reverse reaction will occur, causing the gun to burn.

[0099] Granulated slag melts faster and consumes less heat. Compared with slag produced in normal production, the method of adding granulated slag can restore the slag inventory in the SRV furnace 100 more quickly and achieve rapid re-airing.

[0100] Since the first wind-off mode is easier to operate and has a better effect in heating molten iron, the first wind-off mode is preferred to extend the wind-off time when conditions permit.

[0101] The above descriptions are merely optional embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present description and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for extending the wind-down time of a smelting reduction furnace, wherein the smelting reduction furnace comprises an SRV furnace, a channel and a pre-furnace, wherein the SRV furnace is connected to the pre-furnace through the channel, and the SRV furnace has multiple lances, characterized in that the method include: S100: Determine whether the fault that causes the smelting reduction furnace to shut down affects the supply of fuel, flux, and oxygen-containing gas to the SRV furnace and the operation of the combustible gas processing system. If the supply of fuel, flux and oxygen-containing gas to the smelting reduction furnace and the operation of the combustible gas treatment system are not affected, the first air-break mode is selected. The first air-break mode includes: S210, adjusting the furnace condition parameters of the SRV furnace, and after the adjustment is completed, the smelting reduction furnace enters a wind-off state; S220: The molten iron temperature in the pre-furnace is detected at predetermined intervals. If the molten iron temperature in the pre-furnace is lower than 1300° C., combustible gas and oxygen-containing gas are supplied to the SRV furnace for a predetermined period of time. The combustible gas burns and melts the slag crust on the surface of the molten pool. After the slag crust is melted, fuel and flux are supplied to the furnace to increase the molten pool temperature. The pressure in the SRV furnace is controlled to fluctuate periodically to promote heat transfer between the molten irons. This step is repeated until the wind-down period ends. If the supply of fuel, flux and oxygen-containing gas and the operation of the combustible gas treatment system of the SRV furnace are affected, the second air-break mode shall be selected. The second air-break mode includes: S310, adjusting the furnace condition parameters of the SRV furnace, and after the adjustment is completed, the smelting reduction furnace enters a wind-off state; S320. Detect the temperature of the molten iron in the pre-furnace at predetermined intervals. If the temperature of the molten iron in the pre-furnace is lower than the predetermined temperature, use auxiliary tooling to heat the molten iron in the pre-furnace for a predetermined time. Repeat this step until the wind-down period ends.

2. The method for extending the wind-down time of a smelting reduction furnace according to claim 1, wherein: Step S210 also includes determining the mass fractions of Al2O3 and MgO in the slag before the blast-off and the binary basicity R2 of the slag. Step S220 also includes: the supply rate of the combustible gas is 3000-3500 MJ / min, and the predetermined time of the supply of the combustible gas is T, T=30+200×(S Al -15.5%)+100×(8%-S Mg )+60×(R2-1.2) Where: T is the supply time of combustible gas, in minutes; S Al is the mass fraction of Al2O3 in the slag before wind stop, unit is %; S Mg is the mass fraction of MgO in the slag before wind shutdown, unit is %; R2 is the binary basicity of the slag before the wind is shut down, and has no unit.

3. The method for extending the wind-down time of a smelting reduction furnace according to claim 1, wherein: Step S210 further includes: Maintaining the injection volume of iron-containing materials unchanged, gradually increase the amount of oxygen-containing gas to adjust the slag iron composition and slag iron temperature until the slag temperature is 1420~1450℃, the binary basicity is 1.20~1.30, the magnesium-aluminum ratio is 0.55~0.65, the iron tapping temperature is 1400~1430℃, and the carbon content of the molten iron is 3.8~4.0%. Then the smelting reduction furnace enters the wind-off state.

4. The method for extending the wind-down time of a smelting reduction furnace according to claim 1, wherein: Step S210 further includes: Within 4 to 6 hours before the start of the wind shutdown, increase the frequency of slag discharge to reduce the slag inventory in the furnace to below 200t. Under a furnace pressure of 60 to 65kPa, when the interval between slag discharge at the slag mouth and breathing at the slag mouth is less than 3s, it means that the slag inventory has dropped below 200t.

5. The method for extending the wind-down time of a smelting reduction furnace according to claim 1, wherein: In step S220, the fuel supply rate is 8000~11000MJ / min, and the molten pool temperature is increased by 100℃~120℃ per hour.

6. The method for extending the wind-down time of a smelting reduction furnace according to claim 1, wherein: In step S220, the pressure in the SRV furnace fluctuates periodically within the range of 30-60 kPa at a pressure rise and fall rate of 2-3 kPa / min to promote heat transfer between the SRV furnace and the molten iron in the front furnace.

7. The method for extending the wind-down time of a smelting reduction furnace according to claim 1, wherein: Step S310 further includes: Before the shutdown, the amount of oxygen-containing gas is maintained, and the injection amount of iron-containing materials is gradually reduced to adjust the slag iron composition and slag iron temperature and furnace conditions, so that the slag temperature before the shutdown is 1450~1500℃, the binary basicity is 1.15~1.20, the magnesium-aluminum ratio is 0.50~0.55, the iron tapping temperature is 1430~1480℃, and the carbon content of the molten iron is 4.1~4.3%.

8. The method for extending the wind-down time of a smelting reduction furnace according to claim 1, wherein: Step S310 also includes, 6~8 hours before the start of the wind-down, slag is discharged twice to reduce the slag inventory in the SRV furnace. The first slag discharge is when the furnace pressure of the SRV furnace is 60~65kPa, and the interval between slag discharge through the slag outlet and gasping at the slag outlet is less than 3s, and the slag inventory in the furnace is reduced to below 200t; The secondary slag discharge is to further reduce the furnace pressure to 40~50kPa, and continue to discharge 80~100t of slag through the residual slag outlet. When the slag level in the furnace is at least 70mm lower than the spray gun tip, the residual slag outlet is blocked.

9. The method for extending the wind-down time of a smelting reduction furnace according to claim 1, wherein: Step S320 also includes, The auxiliary tooling includes a sealing device, a heating spray gun and a carburizing device. A sealing device is provided on the upper part of the pre-furnace mouth to close the pre-furnace. The carburizing device and the heating spray gun extend into the pre-furnace. When the wind-down time exceeds 10 to 12 hours, the temperature of the molten iron in the pre-furnace is detected at predetermined intervals. If the temperature of the molten iron in the pre-furnace is lower than 1340°C, the carburizing agent is supplied to the pre-furnace through the carburizing device, and the combustible gas and oxygen-containing gas are supplied to the pre-furnace through the heating spray gun. The molten iron in the pre-furnace is heated by the combustion of the combustible gas.

10. The method for extending the wind-down time of a smelting reduction furnace according to claim 8, wherein: Step S310 further includes: Fuel and flux are supplied to the SRV furnace between two slag tappings.

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