A process for using additives in a large smelting furnace

Abstract

This invention provides a process for using additives in large-scale smelting furnaces, relating to the technical field of additives in smelting furnaces. The invention includes the following steps: S1. Pre-treating the additives and then preparing preforms by gradient pressing; S2. Adding the preforms and additives in stages with gradient, while controlling the composite flow field during the process; S3. Performing online composition monitoring and dynamic closed-loop compensation. In step S1, the pre-treated mixed powder is gradient pressed to prepare multi-layered preforms with gradient density and gradient melting rate, where the external density of the preform is lower than the internal density. In step S2, some preforms are pre-laid at the furnace bottom during the initial melting stage; during the middle melting stage, the preforms are added layer by layer between the scrap steel layers; during the clearing stage, the additives are sprayed into the melt in powder or small particle form using a spraying device; and during the refining stage, the additives are added to the melt by wire feeding. This invention improves additive yield, enhances compositional uniformity, and achieves closed-loop intelligent control.

Description

Technical Field

[0001] This invention relates to the field of additive application technology in smelting furnaces, and more specifically to a process for applying additives in large-scale smelting furnaces. Background Technology

[0002] In the metal smelting process, the use of alloying element additives is a crucial step in controlling the composition and performance of the product. Currently, additives are mainly used in three ways: intermediate alloying additives, ordinary alloying element additives, and novel high-concentration alloying element additives. However, these three types of additives still face the following common technical challenges in large-scale smelting applications:

[0003] (1) High burn-off rate and unstable yield. In large smelting furnaces, when trace elements are directly poured into the surface of the melt through the upper feeding bin, the elements float on the surface of the molten steel or form a large amount of splashing and boiling at the upper part of the melt, resulting in a large amount of burn-off of trace elements. The yield fluctuates from 30% to 80%, and even element segregation occurs.

[0004] (2) It is difficult to balance concentration and melting performance. Mainstream alloying element additives usually require the addition of a large amount of flux to ensure melting performance in hot melts. However, excessive flux content will reduce the proportion of alloying elements (concentration), and impurities in the flux will reduce purity and affect alloy performance after entering the alloy. Conversely, increasing the concentration of alloying elements and decreasing the flux content will affect melting performance. It is difficult to simultaneously achieve the desired balance among alloying element concentration, yield, melting time, and melting temperature.

[0005] (3) Insufficient mixing uniformity. Large smelting furnaces have large molten pools and complex melt flow, making it difficult to ensure uniform dispersion of additives in the melt using traditional manual addition methods. Even with electromagnetic or gas stirring, some trace elements still exhibit uneven composition, resulting in substandard material composition.

[0006] (4) Lack of dynamic compensation and closed-loop control. Existing processes mostly adopt a fixed value one-time addition or fixed batch addition method, which lacks the ability to monitor the real-time composition of the melt online and the ability to dynamically compensate. Once the burn-off exceeds the standard or the composition deviates, the adjustment is delayed and it is difficult to achieve accurate composition control. Summary of the Invention

[0007] The purpose of this invention is to develop a comprehensive technical solution to the problems of high burn-off rate of added elements, unstable yield, poor uniformity of melt composition, and lack of dynamic control methods in large-scale smelting furnaces. This invention provides a process for using additives in large-scale smelting furnaces that improves additive yield, enhances composition uniformity, and achieves closed-loop intelligent control.

[0008] This invention is achieved through the following technical solution:

[0009] A process for using additives in a large smelting furnace includes the following steps:

[0010] S1. The additives are pretreated and then gradient pressing is performed to prepare preforms;

[0011] S2. Precast blocks and additives are added in stages and gradients, with composite flow field control during the process;

[0012] S3. Perform online component monitoring and dynamic closed-loop compensation;

[0013] In step S1, the preform is prepared by gradient pressing of the pretreated mixed powder to prepare a multi-layer preform with gradient density and gradient melting rate, wherein the external density of the preform is less than the internal density.

[0014] The steps in step S2 are divided into the initial melting stage, the middle melting stage, the clearing stage, and the refining stage. In the initial melting stage, some precast blocks are laid in advance at the bottom of the furnace. In the middle melting stage, the precast blocks are added to the scrap steel layer by layer. In the clearing stage, the additives are sprayed into the melt in powder or small particle form through the spraying device. In the refining stage, the additives are added to the melt by feeding wire for precise fine-tuning of the composition.

[0015] Optionally, in step S1, the pretreatment of the additive includes drying, surface modification, and addition of fluxing components.

[0016] Optionally, in step S1, the precast blocks are arranged from the inside out as an inner core, a middle layer, and an outer layer. The precast block mass ratio of the inner core is 50% to 60%, the precast block mass ratio of the middle layer is 20% to 30%, and the precast block mass ratio of the outer layer is 15% to 25%.

[0017] Optionally, the inner core is pressed at a pressure of 8-12 MPa, has a density of 85%-92% of the theoretical density, and a green strength ≥3.5 MPa; the intermediate layer is pressed at a pressure of 3-5 MPa, has a density of 55%-70% of the theoretical density; the outer layer is pressed at a pressure of 0.8-1.5 MPa, has a density of 35%-50% of the theoretical density, and has a porous structure.

[0018] Optionally, the pressing of the precast block includes: mixing the inner core powder ingredients and then pre-pressing the inner core, then trimming and rounding the inner core, roughening the inner core surface, mixing the middle layer powder and coating it around the inner core, then pressing it a second time, then mixing the outer layer powder and coating it around the middle layer for a third pressing, and finally degreasing and drying at low temperature to obtain the finished precast block.

[0019] Optionally, the precast blocks that are laid in the furnace bottom during the initial melting stage in step S2 must be passivated, pre-oxidized or coated with an anti-carburizing coating, and buried in the cold zone at the bottom of the scrap steel.

[0020] Precast blocks are added during the middle stage of melting when the depth of the molten pool reaches 1 / 3 to 1 / 2 of the furnace height;

[0021] Inert gas is used as the carrier gas during the melting and cleaning stage, and the particle size D50 of the blown powder is controlled between 0.5 and 2.0 mm.

[0022] Optionally, in step S2, power frequency electromagnetic stirring is applied in the initial and middle stages of melting to form a vertical convective circulation. In the clearing stage, the stirring is switched to a horizontal strong circulation field mode, the electromagnetic stirring frequency is adjusted to 30-50Hz, and bottom blowing inert gas stirring is turned on to form a horizontal rotating circulation. In the refining stage, the stirring intensity is reduced, the electromagnetic stirring frequency is 15-25Hz, and the bottom blowing gas flow rate is reduced.

[0023] Optionally, in step S3, a laser-induced breakdown spectroscopy online composition analysis device is installed on the side wall or top of the melting furnace. The device performs multi-point scanning on the surface of the melt through an optical fiber probe to analyze the content of easily burnable elements in the melt in real time, with a detection cycle of 30 to 120 seconds.

[0024] Optionally, the laser-induced breakdown spectroscopy online component analysis device is equipped with an inert gas purging optical path protective sleeve, and the detection timing is selected in the naked-eye area formed by electromagnetic stirring, or an immersion probe is used for sampling instead of surface detection.

[0025] Optionally, the real-time detection results from the laser-induced breakdown spectroscopy online component analysis device are input into the process control system. Based on the deviation between the target component setpoint and the actual detection value, the system calculates the required additive mass and addition method using a dynamic compensation strategy based on a compensation algorithm.

[0026] If the element content deviation is ≤±5% during the melting and cleaning stage, no action is taken, the deviation value is recorded, and the wire is fed uniformly for fine-tuning after entering the refining stage.

[0027] If the element content deviation is greater than ±5% during the melting and cleaning stage, supplementary blowing will be started. The blowing volume will be calculated based on the deviation value to correct the deviation to within ±3%.

[0028] If the element content deviation is ≤±5% during the refining stage, a small amount of compensation shall be made according to the normal wire feeding process to adjust it to within ±2% of the target value;

[0029] If the element content deviation is > ±5% during the refining stage, the abnormal response procedure will be activated:

[0030] If time permits, extend the refining time, increase the amount of wire fed, feed it in batches, and strengthen the stirring.

[0031] If the deviation is greater than ±10% or time is tight, assess whether it is necessary to return to the melting and cleaning process or to determine whether the furnace batch should be downgraded or scrapped;

[0032] After the compensation operation, the online component analysis device for laser-induced breakdown spectroscopy is used for verification and testing again. If the requirements are still not met, the compensation operation is repeated to form a closed-loop control.

[0033] The beneficial effects of this invention are:

[0034] This invention significantly improves additive yield and reduces burn-off. Through the synergistic effect of staged release of preformed blocks under gradient pressure, inert gas injection into the melt for internal addition, and composite flow field control, additives are added from the inside of the melt rather than the surface, significantly reducing oxidation burn-off and volatilization loss. The expected alloy element yield can be stabilized at over 92%, which is 10% to 30% higher than that of traditional processes.

[0035] To improve the uniformity of melt composition, the composite flow field dynamic control applies a spiral upward flow field, a horizontal strong circular flow field, and a vertical weak convection field according to the fluid dynamic characteristics of different stages of melting, to ensure that the additives are rapidly and uniformly dispersed in the entire molten pool volume and to eliminate component segregation.

[0036] Achieving closed-loop intelligent control and improving composition control accuracy, the combination of LIBS online composition monitoring and dynamic compensation algorithm transforms the composition control in the smelting process from open-loop to closed-loop and from fixed value to dynamic, significantly improving composition control accuracy and controlling the deviation of key element content within ±5% of the target value.

[0037] Balancing high concentration and high yield, reducing flux usage, the porous core design of the gradient-pressed preform allows high-concentration alloying elements (with an element ratio of up to 90% to 98%) to still melt rapidly, thereby significantly reducing flux usage and minimizing the introduction of impurities into the melt while ensuring high yield.

[0038] Energy saving and consumption reduction, shortening the melting cycle, the phased release mode of gradient density design reduces the temperature drop and reheating requirements caused by concentrated addition at the later stage. Combined with flow field optimization, the melting cycle can be shortened and power consumption reduced.

[0039] With a wide range of applications, the process of this invention is not only applicable to the electric arc furnace and medium frequency induction furnace smelting of steel materials, but can also be extended to the large-scale smelting production of copper alloys, aluminum alloys and high-temperature alloys, and has good process universality. Detailed Implementation

[0040] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the following description is to be considered exemplary in nature and not restrictive.

[0041] The embodiments of the present invention will be described in detail below.

[0042] This invention discloses a process for using additives in large-scale smelting furnaces, comprising the following steps:

[0043] S1. Pretreatment of additives and preparation of gradient pressing preforms;

[0044] S11. Pretreatment of additives: The required alloying element powders (such as manganese powder, silicon powder, chromium powder, titanium powder, vanadium powder, or rare earth element powder, etc.) are pretreated according to the composition requirements of the target alloy, including:

[0045] Drying treatment: Dry the additive powder at 110-200℃ for 30-60 minutes to remove surface adsorbed moisture and volatile matter;

[0046] Surface modification treatment: Add 0.8 to 3.8 parts by weight of surfactant (such as stearic acid, polyvinyl alcohol, etc.) to the dried powder, and ball mill and mix at room temperature for 15 to 30 minutes to make the surfactant uniformly coat the surface of the metal powder particles.

[0047] Addition of fluxing components: Add 1 to 2.6 parts by weight of flux (such as fluoride, chloride, etc.) and 2 to 4.7 parts by weight of chemical fluxing agent as needed, and mix thoroughly.

[0048] S12. Perform gradient density preform pressing: The pretreated mixed powder is subjected to gradient pressing to prepare a multi-layered preform with gradient density and gradient melting rate. Specifically:

[0049] High-density inner core layer (50%–60% of the precast block mass): pressing pressure 8–12 MPa, density 85%–92% of theoretical density, green strength ≥3.5 MPa, slow melting rate, mainly released in the middle and late stages of smelting;

[0050] Intermediate medium-density layer (20%–30% of the precast block mass): pressing pressure 3–5 MPa, density 55%–70% of theoretical density, with a moderate melting rate;

[0051] Outer low-density layer (15%–25% of the precast block mass): pressing pressure 0.8–1.5 MPa, density 35%–50% of theoretical density, porous structure, fast melting rate, mainly used for rapid release in the early stage of smelting;

[0052] The gradient density precast block pressing adopts the process route of "core pre-pressing and layer-by-layer coating pressing". After the core powder is mixed, the core is pre-pressed (high pressure). Then the core is trimmed and rounded. The core surface is slightly roughened (sandblasting or leaving demolding marks) to increase the mechanical interlocking between the core and the intermediate layer. The intermediate layer powder is mixed and coated around the core. Then it is pressed a second time (medium pressure). Then the outer layer powder is mixed and coated around the intermediate layer. Then it is pressed a third time (low pressure). Finally, it is degreased and dried at low temperature to obtain the finished precast block.

[0053] Traditional additives are added in a single density and single form. In large melting furnaces, they either float up and burn up quickly or sink too slowly, causing composition lag. This solution uses a gradient density design to release alloying elements in an orderly manner at different positions and time stages in the melt of the same preform. This effectively balances the needs of rapid melting and long-term homogenization. In addition, the total content of flux is controlled at a low level (less than 10 parts by mass), ensuring a high concentration of alloying elements.

[0054] S2. Phased gradient addition and complex flow field control;

[0055] S21. In the initial stage of melting, that is, the stage of molten pool formation, some precast additive blocks (accounting for 10% to 15% of the total additive amount) are pre-laid at the bottom of the furnace so that some alloying elements enter the melt in the early stage of molten pool formation, avoiding violent reactions and splashing caused by concentrated addition in the later stage. The precast blocks pre-laid in this stage must be passivated, pre-oxidized or coated with anti-carburization coating, and must be buried in the cold zone at the bottom of the scrap steel to protect the precast blocks from heating up slowly by using the heat absorption of the scrap steel.

[0056] S22. Mid-melting stage, also known as the molten pool expansion stage, when the depth of the molten pool reaches 1 / 3 to 1 / 2 of the furnace height, precast blocks (accounting for 30% to 40% of the total addition) are added to the scrap steel layer by layer. The heat conduction of the gradually expanding molten pool is used to gradually melt the blocks. The addition method at this stage allows the precast blocks to sink slowly under the protection of the scrap steel layer, reducing direct contact with air and effectively reducing burn-off.

[0057] S23. In the melting and cleaning stage, after the melt is fully formed, the additive (accounting for 40% to 50% of the total additive) is injected into the melt in powder or small particle form through a spraying device. Inert gas (such as argon or nitrogen) is used as the carrier gas for spraying. The spraying pressure is 0.3 to 0.8 MPa, the spraying flow rate is 5 to 20 kg / min, and the spraying position is selected in the lower part of the molten pool (through the side wall spray gun or bottom spraying device) so that the additive can directly enter the interior of the melt rather than the surface, which greatly reduces oxidation loss and volatilization loss. In this stage, the particle size D50 of the blown powder is controlled between 0.5 and 2.0 mm, and the carrier gas flow rate and the depth of the molten pool must be matched to ensure that the momentum of the particles is sufficient to penetrate the surface slag layer and enter the interior of the molten steel.

[0058] S24. In the refining stage, additives (accounting for 5% to 10% of the total amount) are added by feeding thread for precise fine-tuning of the composition;

[0059] In steps S21 and S22, power frequency electromagnetic stirring is applied to form a vertical convective circulation (spiral upward flow field), which promotes the homogenization of the temperature field and composition field in the molten pool, and at the same time makes the gradient preform melt in the melt at the designed speed.

[0060] In step S23, the system switches to a horizontal strong circulation flow mode, the electromagnetic stirring frequency is adjusted to 30-50Hz, and the bottom-blown inert gas stirring (argon or nitrogen, flow rate 0.5-2.0Nm³ / h) is turned on to form a horizontal rotating circulation. In this flow mode, the powdered additives injected into the melt are quickly entrained in the horizontal circulation, achieving rapid and uniform mixing on the transverse cross section of the melt.

[0061] In step S24, switch to vertical weak convection field mode, reduce stirring intensity (electromagnetic stirring frequency 15-25Hz, bottom blowing gas flow rate 0.2-0.8Nm³ / h) to avoid excessive stirring causing melt oxidation and temperature loss, while maintaining uniform suspension of trace elements and preventing segregation.

[0062] Dynamic flow field control solves the limitations of traditional electromagnetic stirring with fixed parameters that cannot adapt to the needs of multiple smelting stages, and precisely matches the additive dispersion uniformity with the physicochemical requirements of the smelting process stages.

[0063] S3. Online component monitoring and dynamic closed-loop compensation;

[0064] A laser-induced breakdown spectroscopy (LIBS) online composition analysis device is installed on the side wall or top of the smelting furnace. This device scans the surface of the melt at multiple points through an optical fiber probe to analyze the content of easily burnable elements (such as Mn, Si, Ti, V, rare earth elements, etc.) in the melt in real time. The detection cycle is 30 to 120 seconds. The LIBS monitoring is equipped with an inert gas purging optical path protection sleeve. The detection time is selected in the naked eye area formed by electromagnetic stirring (the slag-free area of ​​the vortex in the center of the flow field), or an immersion probe is used for sampling instead of surface detection.

[0065] The real-time LIBS detection results are input into the process control system. Based on the deviation between the target component setpoint and the actual detection value, the system calculates the amount of additive to be compensated and the method of addition using a dynamic compensation strategy based on a compensation algorithm.

[0066] If the element content deviation is ≤±5% during the melting and cleaning stage, no action is taken, the deviation value is recorded, and the wire is fed uniformly for fine-tuning after entering the refining stage.

[0067] If the element content deviation is greater than ±5% during the melting and cleaning stage, supplementary blowing will be started. The blowing volume will be automatically calculated based on the deviation value to quickly correct the deviation to within ±3%.

[0068] If the element content deviation is ≤±5% during the refining stage, a small amount of compensation shall be made according to the normal wire feeding process to adjust it to within ±2% of the target value;

[0069] If the element content deviation is > ±5% during the refining stage, the abnormal response procedure will be activated:

[0070] If time permits, extend the refining time, increase the amount of wire fed, feed it in batches, and strengthen the stirring.

[0071] If the deviation is extremely large (>±10%) or time is tight, assess whether it is necessary to return to the melting and cleaning process, i.e., reheat, start strong stirring, supplement the blowing, or determine whether the furnace batch should be downgraded or scrapped.

[0072] After the compensation operation, the LIBS is used to verify and test again. If the requirements are still not met, the compensation operation is repeated to form a closed-loop control.

[0073] Throughout the smelting process, the surface of the melt is covered with carbonized rice husks or a special covering agent to reduce the contact area between the melt and air, thereby further reducing the oxidation and burn-off of additives.

[0074] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the technical solutions of the present invention. Any technical solution that can be implemented based on the above embodiments without creative effort should be considered to fall within the scope of protection of the patent of the present invention.

Claims

1. A process for using additives in a large smelting furnace, characterized in that, Includes the following steps: S1. The additives are pretreated and then gradient pressing is performed to prepare preforms; S2. Precast blocks and additives are added in stages and gradients, with composite flow field control during the process; S3. Perform online component monitoring and dynamic closed-loop compensation; In step S1, the preform is prepared by gradient pressing of the pretreated mixed powder to prepare a multi-layer preform with gradient density and gradient melting rate, wherein the external density of the preform is less than the internal density. The steps in step S2 are divided into the initial melting stage, the middle melting stage, the clearing stage, and the refining stage. In the initial melting stage, some precast blocks are laid in advance at the bottom of the furnace. In the middle melting stage, the precast blocks are added to the scrap steel layer by layer. In the clearing stage, the additives are sprayed into the melt in powder or small particle form through the spraying device. In the refining stage, the additives are added to the melt by feeding wire for precise fine-tuning of the composition.

2. The process for using additives in large-scale smelting furnaces according to claim 1, characterized in that, In step S1, the pretreatment of the additives includes drying, surface modification, and addition of fluxing components.

3. The process for using additives in large-scale smelting furnaces according to claim 1, characterized in that, In step S1, the precast blocks are arranged from the inside out as an inner core, a middle layer, and an outer layer. The precast block mass ratio of the inner core is 50% to 60%, the precast block mass ratio of the middle layer is 20% to 30%, and the precast block mass ratio of the outer layer is 15% to 25%.

4. The process for using additives in large-scale smelting furnaces according to claim 3, characterized in that, The inner core is pressed at a pressure of 8–12 MPa, with a density of 85%–92% of the theoretical density and a green strength ≥3.5 MPa. The intermediate layer is pressed at a pressure of 3–5 MPa, with a density of 55%–70% of the theoretical density. The outer layer is pressed at a pressure of 0.8–1.5 MPa, with a density of 35%–50% of the theoretical density. The outer layer has a porous structure.

5. The process for using additives in large-scale smelting furnaces according to claim 4, characterized in that, The pressing of the precast block includes: mixing the inner core powder ingredients and then pre-pressing the inner core, then trimming and rounding the inner core, roughening the inner core surface, mixing the middle layer powder and coating it around the inner core, then pressing it a second time, then mixing the outer layer powder and coating it around the middle layer for a third pressing, and finally degreasing and drying at low temperature to obtain the finished precast block.

6. The process for using additives in large smelting furnaces according to claim 1, characterized in that, In step S2, the precast blocks that are laid in the furnace bottom during the initial melting stage must be passivated, pre-oxidized or coated with an anti-carburization coating, and buried in the cold zone at the bottom of the scrap steel. Precast blocks are added during the middle stage of melting when the depth of the molten pool reaches 1 / 3 to 1 / 2 of the furnace height; Inert gas is used as the carrier gas during the melting and cleaning stage, and the particle size D50 of the blown powder is controlled between 0.5 and 2.0 mm.

7. The process for using additives in large-scale smelting furnaces according to claim 1, characterized in that, In step S2, power frequency electromagnetic stirring is applied in the initial and middle stages of melting to form a vertical convective circulation. In the clearing stage, the stirring is switched to a horizontal strong circulation field mode, and the electromagnetic stirring frequency is adjusted to 30-50Hz. At the same time, bottom blowing inert gas stirring is turned on to form a horizontal rotating circulation. In the refining stage, the stirring intensity is reduced, the electromagnetic stirring frequency is 15-25Hz, and the bottom blowing gas flow rate is reduced.

8. The process for using additives in large-scale smelting furnaces according to claim 1, characterized in that, In step S3, a laser-induced breakdown spectroscopy online composition analysis device is installed on the side wall or top of the melting furnace. The surface of the melt is scanned at multiple points through an optical fiber probe to analyze the content of easily burnable elements in the melt in real time. The detection cycle is 30 to 120 seconds.

9. The process for using additives in large-scale smelting furnaces according to claim 8, characterized in that, The laser-induced breakdown spectroscopy online component analysis device is equipped with an inert gas-purged optical path protective sleeve. The detection timing is selected in the naked-eye area formed by electromagnetic stirring, or an immersion probe is used for sampling instead of surface detection.

10. The process for using additives in large-scale smelting furnaces according to claim 8, characterized in that, The real-time detection results from the laser-induced breakdown spectroscopy online component analysis device are input into the process control system. Based on the deviation between the target component set value and the actual detection value, the system calculates the amount of additive to be compensated and the method of addition using a dynamic compensation strategy based on a compensation algorithm. If the element content deviation is ≤±5% during the melting and cleaning stage, it will not be processed temporarily. The deviation value will be recorded and then fed into the refining stage for fine-tuning. If the element content deviation is greater than ±5% during the melting and cleaning stage, supplementary blowing will be started. The blowing volume will be calculated based on the deviation value to correct the deviation to within ±3%. If the element content deviation is ≤±5% during the refining stage, a small amount of compensation shall be made according to the normal wire feeding process to adjust it to within ±2% of the target value; If the element content deviation is > ±5% during the refining stage, the abnormal response procedure will be activated: If time permits, extend the refining time, increase the amount of wire fed, feed it in batches, and strengthen the stirring. If the deviation is greater than ±10% or time is tight, assess whether it is necessary to return to the melting and cleaning process or to determine whether the furnace batch should be downgraded or scrapped; After the compensation operation, the online component analysis device for laser-induced breakdown spectroscopy is used for verification and testing again. If the requirements are still not met, the compensation operation is repeated to form a closed-loop control.