A method for optimizing slag desulfurization performance of blast furnace under high sulfur load

Abstract

This invention relates to the field of ironmaking process technology, specifically to a method for optimizing slag desulfurization performance in response to high sulfur loads in blast furnaces. This method targets blast furnaces operating under sulfur loads >4 kg / tHM. It optimizes slag desulfurization performance by controlling the physical heat of molten iron at 1480-1520℃, the binary basicity of slag at 1.16-1.22 times the rated value, and adjusting the MgO content in the slag to ≥8.2%, Al2O3 content ≤16%, and the MgO / Al2O3 ratio between 0.52-0.61. This invention significantly improves slag desulfurization capacity under high sulfur load conditions, stabilizes the sulfur content of molten iron, reduces steelmaking desulfurization and raw material procurement costs, minimizes furnace condition fluctuations, and ensures long-term stable and efficient operation of the blast furnace, providing a practical technical solution for high-sulfur-load blast furnaces.

Description

Technical Field

[0001] This invention relates to the field of ironmaking process technology, and in particular to a method for optimizing the desulfurization performance of slag in response to high sulfur loads in blast furnaces. Background Technology

[0002] Sulfur is a typical harmful element in steel products. Excessive sulfur content can cause hot brittleness in steel, making it prone to cracking during subsequent processing such as rolling and forging, severely affecting the mechanical properties and processing quality of the steel. Because the desulfurization process in steelmaking is difficult, energy-intensive, and costly, precise control of the sulfur content in molten iron during the blast furnace smelting stage has become a crucial step in ensuring steel product quality and reducing overall production costs.

[0003] Currently, the steel industry faces the dual pressures of persistently high upstream raw material prices and weak downstream market demand, resulting in persistently high production and operating costs and increasingly fierce industry competition. To alleviate cost pressures, most steel companies have had to use low-quality raw materials with relatively high sulfur content in their ironmaking systems, including high-sulfur iron ore powder, high-sulfur coking coal, and high-sulfur pulverized coal. While these raw materials have a significant price advantage and can reduce raw material procurement costs to some extent, they directly lead to a sharp increase in the sulfur load of blast furnaces. The sulfur load of most blast furnaces has far exceeded the industry standard of 4 kg / tHM, and they have been operating under high sulfur load conditions for a long time.

[0004] High sulfur loads pose numerous severe challenges to blast furnace smelting: On the one hand, existing slag-forming systems are ill-suited to high sulfur inputs, resulting in insufficient slag desulfurization capacity, drastic fluctuations in molten iron sulfur content, and frequent occurrences of high-sulfur molten iron. This not only affects the molten iron quality pass rate but also forces the steelmaking process to increase desulfurizing agent usage and energy consumption, further pushing up production costs. On the other hand, high sulfur loads easily lead to abnormal slag viscosity and melting temperature fluctuations, disrupting stable slag-forming and thermal systems within the blast furnace, causing frequent furnace condition fluctuations and an increase in unplanned shutdowns, severely impacting the stable and efficient operation of the blast furnace. Furthermore, to avoid excessive sulfur content in molten iron, enterprises impose strict restrictions on the sulfur content of raw materials and fuels entering the furnace, greatly limiting the selection space in the raw material and fuel procurement market and making it difficult to fully utilize the price advantage of low-cost, low-quality raw materials and fuels, further exacerbating cost pressures.

[0005] In summary, existing blast furnace smelting technologies suffer from prominent problems such as poor desulfurization effect, poor furnace stability, and weak adaptability to raw materials and fuels when dealing with high sulfur load conditions. There is an urgent need for a systematic method to optimize slag desulfurization performance. By precisely controlling key process parameters, the slag desulfurization capacity can be improved, achieving a dual guarantee of molten iron quality and blast furnace operation stability under high sulfur load conditions, and providing technical support for steel companies to reduce costs and increase efficiency. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for optimizing the desulfurization performance of blast furnace slag in response to high sulfur loads.

[0007] To achieve the above objectives, this invention provides a method for optimizing slag desulfurization performance in response to high sulfur loads in blast furnaces. Specifically, for scenarios where the sulfur load in a blast furnace is >4 kg / tHM, desulfurization performance is optimized by controlling the physical heat of molten iron, the binary basicity of the slag, and the slag composition parameters. The specific control requirements are as follows: The physical heat of molten iron is controlled at 1480-1520℃; The binary basicity of the slag is adjusted to 1.16-1.22 times by adding slag-forming agents; The slag contains ≥8.2% MgO and ≤16% Al2O3, with an MgO / Al2O3 ratio of 0.52-0.61.

[0008] Preferably, the control of the physical heat of the molten iron is based on the fact that the slag desulfurization reaction is an endothermic reaction, and this temperature range can increase the equilibrium constant K of the desulfurization reaction, ensuring the smooth progress of the desulfurization reaction.

[0009] Preferably, the control of the binary basicity of the slag is based on the following: when the basicity is less than 1.16 times, the sulfur capacity of the slag is insufficient and the desulfurization capacity is limited; when the basicity is greater than 1.22 times, the slag will generate high-melting-point substances, increase viscosity, worsen slag-iron mass transfer conditions, and reduce desulfurization efficiency.

[0010] Preferably, the content and ratio of MgO and Al2O3 are controlled based on the following: under the same alkalinity, when the increment of both is within 3%, the positive effect of MgO on slag desulfurization is greater than the negative effect of Al2O3. This ratio range can ensure that the slag fluidity and desulfurization kinetics are optimal.

[0011] Preferably, the binary basicity is the mass ratio of CaO to SiO2 in the slag.

[0012] Preferably, the slag-forming agent is at least one of limestone, dolomite, or fluorite.

[0013] Preferably, the optimization mechanism of the slag desulfurization performance optimization method for dealing with high sulfur loads in blast furnaces according to the present invention is explained as follows: The core essence of slag desulfurization is to promote the reaction between sulfur in molten iron and basic oxides in the slag by regulating the thermodynamic reaction conditions and kinetic mass transfer efficiency of the slag, thereby achieving the goal of desulfurization of molten iron. The desulfurization optimization mechanism of this technical solution revolves around three core influencing factors: temperature, binary basicity, and slag composition (MgO, Al2O3), and constructs the optimal desulfurization reaction environment through systematic regulation.

[0014] From a thermodynamic perspective, temperature is a crucial prerequisite for the successful conduct of the desulfurization reaction. The desulfurization reaction between slag and molten iron is a typical endothermic reaction. According to the principle of chemical equilibrium, the equilibrium constant K of an endothermic reaction increases significantly with increasing temperature. This means that the higher the temperature, the stronger the tendency of the desulfurization reaction to proceed towards the formation of sulfides (such as CaS and MgS), and the more thorough the desulfurization reaction. In the actual blast furnace smelting scenario, the physical heat of molten iron not only directly affects the equilibrium state of the desulfurization reaction but also has a crucial impact on the physical properties of the slag. A suitable temperature ensures that the slag maintains a good molten state, avoiding excessively low temperatures that lead to increased slag viscosity and decreased fluidity, thereby hindering the transfer and reaction of sulfur at the slag-iron interface. In this invention, the physical heat of molten iron is controlled at 1480-1520℃, which combines the dual requirements of thermodynamics and kinetics: this temperature range can raise the equilibrium constant K of the desulfurization reaction to an ideal level, providing sufficient thermodynamic driving force for the desulfurization reaction, and can also ensure that the slag is in a low viscosity and high fluidity state, laying the foundation for the subsequent mass transfer process of sulfur elements; if the temperature is below 1480℃, the insufficient equilibrium constant K will lead to a weakening of the driving force of the desulfurization reaction, and at the same time, the fluidity of the slag will decrease, and the desulfurization efficiency will be significantly reduced; if the temperature is above 1520℃, it will excessively consume blast furnace smelting energy, increase production costs, and may also cause an imbalance in the furnace thermal regime, which is not conducive to the stable operation of the blast furnace.

[0015] Binary basicity, as a core control index for slag desulfurization capacity, focuses on optimizing the thermodynamic basis of the desulfurization reaction by adjusting the proportion of basic oxides in the slag. The binary basicity of slag is defined as the mass ratio of CaO to SiO2, while the core of the desulfurization reaction is the reaction between sulfur (represented by [S]) in the molten iron and O in the slag. 2- Combine to form S 2- Then with Ca 2+ Cations combine to form stable sulfides. Increasing the binary basicity of slag essentially increases the relative content of strongly basic oxides such as CaO in the slag. On the one hand, CaO, as a strongly basic oxide, will ionize into a large amount of O in the molten slag. 2- These O 2- It can react with [S] that diffuses from molten iron to the slag-iron interface to generate S. 2- On the other hand, Ca 2+ An increase in the concentration of sulfur will reduce the amount of sulfur in the slag. 2-The activity coefficient of sulfur, according to the formula for the sulfur distribution ratio (the ratio of sulfur content in slag to sulfur content in molten iron), shows that a decrease in the sulfur activity coefficient directly leads to an increase in the sulfur distribution ratio, meaning that more sulfur will be transferred from molten iron to slag. However, increasing the binary basicity is not always better. When the binary basicity exceeds 1.22 times, excess CaO in the slag will combine with SiO2, Al2O3, and other components to form complex high-melting-point compounds (such as tricalcium silicate and calcium aluminate). These high-melting-point substances will form non-homogeneous phase particles in the slag, destroying the homogeneity of the slag and causing a sharp increase in slag viscosity. The increase in slag viscosity will severely hinder the mass transfer process between the slag and iron phases, making it difficult for [S] in the molten iron to diffuse into the slag, and the S generated in the slag... 2- It also cannot diffuse smoothly into the slag, effectively cutting off the "mass exchange channel" for the desulfurization reaction, thus reducing desulfurization capacity. Therefore, the technical solution controls the binary alkalinity at 1.16-1.22 times, finding a balance between thermodynamic advantages and kinetic feasibility: this range allows sufficient CaO to provide adequate O. 2- This strengthens the thermodynamic driving force of the desulfurization reaction, while avoiding the deterioration of slag viscosity caused by excessive alkalinity, ensuring the kinetic mass transfer efficiency of the desulfurization reaction, and achieving the dual goals of desulfurization effect and furnace condition stability.

[0016] The regulation of the content and ratio of MgO and Al2O3 in slag is key to optimizing desulfurization kinetics. The core mechanism lies in improving the mass transfer environment at the slag-iron interface by adjusting the physical properties of the slag, while simultaneously enhancing the desulfurization effect of binary basicity. As a basic oxide, MgO's optimization effect on slag desulfurization is mainly reflected in two aspects: first, a dilution effect, where the addition of MgO reduces the relative concentration of components such as CaO and SiO2 in the slag, preventing excessively high concentrations of certain components from forming high-melting-point substances, thereby improving slag stability; second, a fluidity improvement effect, where MgO significantly reduces slag viscosity. With increasing MgO content, the slag's melting state becomes more uniform, intermolecular forces weaken, and fluidity is greatly improved, which accelerates the formation of sulfur dioxide (S2O3) in the desulfurization reaction at the slag-iron interface. 2- The MgO diffuses into the slag and promotes the migration of [S] from the molten iron to the interface, greatly optimizing the kinetic mass transfer conditions of the desulfurization reaction. However, there is a critical value for the addition of MgO. When the MgO content is too high, it will combine with Al2O3 in the slag to form insoluble spinel (MgO·Al2O3), and may also precipitate free periclase (MgO). These insoluble substances will disrupt the uniform melting state of the slag, leading to a reverse increase in slag viscosity and poor fluidity, which in turn worsens the desulfurization kinetic conditions. Therefore, the technical solution controls the MgO content to above 8.2%, which ensures its optimization effect on slag fluidity while avoiding the negative effects caused by excessive addition.

[0017] In contrast to the positive effects of MgO, Al2O3 exhibits a significant inhibitory effect on slag desulfurization. This mechanism primarily stems from its dual negative impact on the chemical environment and physical properties of the slag. In alkaline slag systems, Al2O3, being an amphoteric oxide, tends to exhibit acidic characteristics and actively absorbs free O2 from the slag used in the desulfurization reaction. 2- and form Al x O y z- The presence of complex anions such as silicon-aluminum-oxygen complex anions directly leads to the free oxygen in the slag. 2- Concentration decreases, while O 2- Al2O3 is a core reactant in the desulfurization reaction, and insufficient concentration of it will directly weaken the driving force of the desulfurization reaction. Simultaneously, Al2O3 can combine with components such as TiO2 and SiO2 in the slag to generate a series of titanium aluminosilicate composite salts, which also consume free oxygen. 2- This further reduces the thermodynamic driving force of the desulfurization reaction. Furthermore, an increase in Al2O3 significantly raises the slag melting temperature, requiring higher temperatures to maintain the molten state. At the same smelting temperature, excessively high Al2O3 content increases slag viscosity and worsens fluidity, hindering mass transfer between slag and iron, and thus inhibiting the desulfurization reaction from a kinetic perspective. Therefore, controlling the Al2O3 content below 16% is to minimize its impact on O2 content. 2- The negative effects of concentration and slag fluidity create favorable conditions for the desulfurization reaction.

[0018] More importantly, the effects of MgO and Al2O3 on desulfurization are not isolated but exhibit a significant synergistic effect. This is the core mechanism behind the technical solution's emphasis on controlling the MgO / Al2O3 ratio between 0.52 and 0.61. Experimental studies show that under the same binary basicity conditions, when the increments of both MgO and Al2O3 are controlled within 3%, the positive effect of MgO on slag desulfurization (reducing viscosity, improving fluidity, and replenishing alkaline sites) outweighs the negative effect of Al2O3 (consuming O2). 2- (Increased viscosity), resulting in improved slag desulfurization performance. The essence of this synergistic effect is the "offsetting and repairing" of the negative impact of MgO on Al2O3: appropriately increasing MgO can neutralize some of the negative effects of Al2O3 when forming complex anions on O2O3. 2-The MgO / Al2O3 ratio is controlled at 0.52-0.61, which is the optimal synergistic range verified by a large number of previous experiments. This ratio can ensure that the positive effect of MgO is fully exerted and effectively counteract the inhibitory effect of Al2O3, while avoiding the imbalance of slag performance caused by excessive MgO or excessive Al2O3. This ensures that the slag has sufficient desulfurization capacity thermodynamically and good mass transfer efficiency kinetically.

[0019] In summary, the desulfurization optimization mechanism of this technical solution is a systematic approach combining thermodynamic driving force, kinetic assurance, and component synergy: temperature provides sufficient thermodynamic impetus for the desulfurization reaction; binary basicity provides the core alkaline environment and reaction carrier; and the content and ratio of MgO and Al2O3 ensure mass transfer efficiency and synergistically enhance desulfurization by optimizing the physical properties of the slag. These three factors work together and mutually constrain each other, ultimately constructing an optimal slag system suitable for high-sulfur load conditions, achieving the dual goals of effective hot metal desulfurization and stable blast furnace operation. The beneficial effects of this invention are: 1. This invention enables the construction of an optimal desulfurization reaction system under high-sulfur conditions (blast furnace sulfur load >4 kg / tHM) by systematically controlling the physical heat of molten iron, the binary basicity of slag, and the content and ratio of MgO and Al2O3. This ensures that the sulfur content in the molten iron is stably controlled within a specified range. Its core lies in enhancing the slag desulfurization capacity through the synergistic effect of thermodynamic driving and kinetic protection, preventing the generation of high-sulfur molten iron from the source, thereby reducing the additional energy consumption for desulfurization in downstream steelmaking processes, lowering auxiliary material consumption and production costs in the steelmaking process, and providing crucial support for cost control throughout the entire steel production process.

[0020] 2. This invention, by precisely optimizing the desulfurization performance of slag and fully tapping the desulfurization potential of the slag itself, effectively mitigates the adverse effects of high sulfur load on blast furnace smelting. This advantage eliminates the need for stringent restrictions on sulfur content in raw materials during blast furnace ironmaking, allowing for the flexible selection of more cost-effective high-sulfur, low-quality raw materials, significantly expanding the raw material procurement market and choice. Simultaneously, by rationally utilizing low-cost raw materials, it significantly reduces the procurement costs of raw materials for the ironmaking system, providing a strong guarantee for enterprises to build cost advantages in market competition.

[0021] 3. The slag desulfurization system constructed in this invention can simultaneously maintain a favorable slag-forming and thermal regime within the blast furnace. Reasonable temperature, basicity, and slag composition parameters avoid problems such as abnormal slag viscosity and melting temperature fluctuations caused by high sulfur loads, reducing the factors inducing furnace condition fluctuations. This characteristic ensures the smoothness of the blast furnace smelting process, effectively reduces the probability of unplanned shutdowns and other abnormal situations, and guarantees that the blast furnace operates in a stable and efficient state for a long time, laying a solid foundation for stable smelting intensity and improved production efficiency. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0023] Example: This example uses the No. 4 blast furnace of Lingyuan Iron & Steel Co., Ltd. as the application object. It adopts the slag desulfurization performance optimization method of the present invention to cope with the high sulfur load of the blast furnace. The slag desulfurization performance of the No. 4 blast furnace was optimized from January to September 2021 and from January to September 2022. The data were compared with the data before optimization in the same period of 2020. During the optimization period, the physical heat of molten iron was controlled at 1480-1520℃; the binary basicity of slag was controlled at 1.16-1.22 times; the MgO content in the slag was ≥8.2% and the Al2O3 content was ≤16%, and the MgO / Al2O3 ratio was 0.52-0.61. The relevant data are shown in Table 1.

[0024] Table 1. Relevant data on the slag desulfurization performance optimization method of this patent before and after using the No. 4 blast furnace. Performance Analysis: As can be seen from the data in Table 1, the sulfur load at the No. 4 blast furnace has been maintained at approximately 1.5 times the industry standard for a long period. During the period from January to September 2021, when the optimized method of this invention was adopted, although the average sulfur load was further increased compared to 5.67 kg / tHM in 2020, stable control of the sulfur content in the molten iron was achieved. This result is not a simple balance of indicators, but a direct manifestation of the synergistic system of "thermodynamic driving + kinetic guarantee" in the technical solution. The physical thermal control of molten iron at 1480-1520℃ in this invention provides sufficient thermodynamic driving force for the desulfurization reaction, significantly increasing the equilibrium constant K; the binary basicity range of 1.16-1.22 times ensures sufficient free O₂ in the slag. 2-The concentration enhances sulfur transfer while avoiding slag viscosity deterioration caused by excessive alkalinity. The controlled ratio of MgO ≥ 8.2%, Al2O3 ≤ 16%, and their respective proportions of 0.52-0.61 effectively optimizes slag fluidity and ensures efficient mass transfer between slag and iron. This precise synergy of multiple parameters allows the blast furnace to maintain stable iron sulfur content within the specified range even under high sulfur input conditions, completely resolving the industry pain point of "high sulfur load inevitably leading to excessive sulfur content" in traditional processes. Simultaneously, the significant increase in the first-grade pig iron yield not only signifies stable iron quality compliance but also directly creates high-quality raw material conditions for downstream steelmaking processes. Low-sulfur iron can significantly reduce the consumption of lime and desulfurizing agents during steelmaking, decrease converter slag volume and slag removal difficulty, and shorten the smelting cycle, achieving low-cost operation in the steelmaking process from a whole-industry chain perspective. In addition, the optimization of slag desulfurization performance has fundamentally eliminated the furnace condition fluctuations caused by insufficient desulfurization efficiency under high sulfur load. The stability of blast furnace air pressure, air volume and charging speed has been significantly improved, and the number of unplanned shutdowns has been greatly reduced, which has provided a guarantee for the stable performance of smelting intensity and truly achieved the core goal of "stability, high efficiency, high quality and low consumption" under high sulfur load.

[0025] In 2022, the No. 4 blast furnace continued to utilize the technical solution of this invention, and data performance further validated the long-term effectiveness and optimization potential of the technology. The sulfur load at the furnace charge remained high at 6.03 kg / tHM that year, but the average sulfur content of the molten iron further decreased to 0.029%, fully meeting the production requirements for high-quality, low-sulfur molten iron. Building on the significant increase in pig iron grade 1 rate in 2021, it continued to rise to 87.91% in 2022, providing crucial support for the company to expand its high-value-added steel products. This achievement represents a dual breakthrough in "long-term stable operation" and "continuous cost reduction and efficiency improvement," fully demonstrating that the technical solution of this invention can not only address the short-term challenges of high sulfur loads but also support the long-term, stable, and economical production operation of the blast furnace, providing a replicable and scalable practical example for similar high-sulfur load blast furnaces.

[0026] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for optimizing slag desulphurization performance in response to high sulphur load in a blast furnace, characterized in that, For the scenario of blast furnace sulfur load > 4 Kg / tHM, the desulfurization performance is optimized by controlling the physical heat of molten iron, the binary basicity of slag and the slag composition parameters, and the specific control requirements are as follows: The physical heat of molten iron is controlled at 1480-1520℃; The binary basicity of slag is controlled at 1.16-1.22 times by adding slagging agent; The MgO content in the slag is ≥8.2%, the Al2O3 content is ≤16%, and the MgO / Al2O3 ratio is 0.52-0.

61.

2. The method for optimizing the slag desulphurization performance in coping with high sulphur burden of blast furnace as claimed in claim 1 wherein, The control basis of the physical heat of molten iron is that the desulfurization reaction of slag is an endothermic reaction, and this temperature range can increase the desulfurization reaction equilibrium constant K to ensure the smooth progress of the desulfurization reaction.

3. The method for optimizing the slag desulphurization performance of a blast furnace in response to high sulphur burden according to claim 1, characterized in that, The control basis of the binary basicity of slag is that when the basicity is lower than 1.16 times, the sulfur capacity of the slag is insufficient, and the desulfurization capacity is limited; when the basicity is higher than 1.22 times, high melting point substances will be generated in the slag, the viscosity will be increased, the mass transfer conditions of slag-iron will be deteriorated, and the desulfurization efficiency will be reduced.

4. The method for optimizing the slag desulphurization performance of a blast furnace in response to high sulphur burden as claimed in claim 1 wherein, The control basis of the content and ratio of MgO and Al2O3 is that under the same basicity, when the increment of both is within 3%, the positive influence of MgO on the desulfurization of slag is greater than the negative influence of Al2O3, and this ratio range can ensure the optimal flowability of the slag and the desulfurization kinetic conditions.

5. The method for optimizing the slag desulphurization performance of a blast furnace in response to high sulphur burden as claimed in claim 1 wherein, The binary basicity is the mass ratio of CaO and SiO2 in the slag.

6. The method for optimizing the slag desulphurization performance of a blast furnace in response to high sulphur burden as claimed in claim 1 wherein, The slagging agent is at least one of limestone, dolomite or fluorite.

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