Low-alkalinity high-magnesia sinter bed synergistic regulation method

Abstract

A kind of low basicity high magnesia sinter bed synergistic regulation method, belong to steel metallurgy sintering technical field;The method is first with iron-containing raw material and calcareous flux one-time granulation, outer layer is wrapped with magnesia flux and fuel, form the particle structure of MgO enrichment in outer layer, realize MgO mineralization in advance, stagger with CaO reaction time sequence, then carry out differentiating layering preparation, component-thermal regime coupling layering distribution, form the vertical gradient distribution of upper layer lower basicity low MgO, lower layer higher basicity high MgO in reasonable range of basicity and MgO;The present application solves the technical problems of low basicity high MgO sinter such as low strength, low composition rate and poor reducibility by staggering the reaction time sequence of MgO from microcosmic point of view and causing the difference of composition and temperature of material layer from macroscopic point of view, realizes the double-optimal effect of sufficient generation of high-quality bonding phase and full mineralization of MgO, significantly improves the yield, drum strength and metallurgical properties of sinter, and reduces solid fuel consumption.

Description

Technical Field

[0001] This invention relates to a synergistic control method, specifically a synergistic control method for the bed of low-alkalinity, high-magnesium oxide sinter, which is particularly suitable for improving the quality of sinter under low-alkalinity, high-magnesium oxide conditions; it belongs to the field of metallurgical sintering technology. Background Technology

[0002] During blast furnace smelting, the slag needs to maintain an appropriate amount of MgO to improve fluidity and desulfurization capacity. Simultaneously, MgO is beneficial for increasing the low-temperature reduction pulverization index of sinter. In traditional processes, when the proportion of sinter in the blast furnace burden is too large, MgO is usually supplemented by adding magnesium-containing fluxes such as dolomite and magnesite powder during the sintering process. At the same time, an increase in the proportion of sinter inevitably leads to a decrease in the proportion of acidic pellets. To maintain the overall basicity balance of the blast furnace, the basicity of the sinter needs to be reduced accordingly. Therefore, the demands of blast furnace smelting and actual operating conditions have jointly spurred the development of low-basicity sintering... The production requirements for high-MgO sintered ore are as follows; however, an increase in MgO content in sintered ore has a significant negative impact on its quality. Studies have shown that when the MgO mass fraction in the sinter increases from 2.04% to 3.96%, the amount of liquid phase generated during the sintering process gradually decreases, the hematite mass fraction decreases from 13.57% to 9.99%, the calcium ferrite mass fraction decreases from 38.7% to 30.17%, while the proportions of magnetite, silicates, and porosity gradually increase, and the drum strength decreases from 71.33% to 61.13%. Under low alkalinity conditions... In sintered ore, the binder phase is primarily composed of fritillary olivine and glass, resulting in a significantly lower formation rate of high-quality calcium ferrite compared to high-basicity sintered ore. When low basicity is combined with high MgO, MgO further inhibits calcium ferrite formation, reduces the amount of liquid phase, and increases the liquid phase formation temperature. This synergistic effect exacerbates problems such as low sinter strength, low yield, poor reducibility, and high solids fuel consumption. Furthermore, the uneven heat distribution between the upper and lower parts of the sintering process due to the automatic heat storage effect of the material layer, combined with low basicity and high MgO conditions, further complicates the situation. The temperature difference between the upper and lower material layers and the different reaction temperature ranges further exacerbate the deterioration effect on the quality of sinter. In particular, the lower material layer suffers from the triple negative effects of low basicity, high MgO, and overheating, resulting in a particularly severe quality deterioration. Therefore, how to ensure that the MgO content of sinter reaches more than 2.5% under low basicity conditions to meet the blast furnace slagging requirements, while effectively overcoming the multiple adverse factors such as insufficient binder phase caused by low basicity, inhibition of calcium ferrite formation by high MgO, and uneven thermal regime of the material layer, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for synergistic control of the material layer of low-alkalinity high-magnesium oxide sinter, thereby achieving high strength, high yield and excellent metallurgical properties of low-alkalinity high-magnesium oxide sinter.

[0004] The problem described in this invention is solved by the following technical solution: A method for synergistic regulation of the bed structure of low-alkalinity, high-magnesia sinter includes the following steps: S1. Preparation of the upper layer material: The mass of MgO in the upper layer material accounts for 2.0% to 2.3% of the total mass of the upper layer material; the binary basicity is 1.72 to 1.82; Based on the percentage of the total mass of the upper layer materials, the mixture contains 80%–86% iron raw materials, 4%–7% calcium flux, 5%–7% magnesium flux, and 3%–6% solid fuel. The iron-containing raw materials and calcium flux in the upper layer material, as well as 40% to 50% of the total solid fuel in the upper layer material, are added to the mixer for pre-mixing. The mixed material is fed into a cylindrical pellet mill for primary pelleting to produce primary pellets with a particle size of 2-8 mm; then the magnesium flux in the upper layer material is premixed with the remaining solid fuel in the upper layer material and fed into a cylindrical pellet mill for secondary pelleting to obtain the upper layer material. S2. Preparation of the lower layer material: The mass of MgO in the lower layer material accounts for 2.8% to 3.1% of the total mass of the lower layer material; the binary basicity is 1.82 to 1.92; Based on the percentage of the total mass of the lower layer material, prepare 72%–78% iron-containing raw materials, 5%–8% calcium flux, 9%–13% magnesium flux, and 3%–6% solid fuel; add the iron-containing raw materials and calcium flux in the lower layer material, as well as 40%–50% of the total solid fuel in the lower layer material, to the mixer for pre-mixing; The mixed material is fed into a cylindrical pellet mill for primary pelleting to produce primary pellets with a particle size of 2-8 mm; then the magnesium flux in the lower layer material is premixed with the remaining solid fuel in the lower layer material and fed into a cylindrical pellet mill for secondary pelleting to obtain the lower layer material. S3. Using a layered material distribution method, the upper layer material obtained in step S1 is placed on the upper part of the sintering trolley, and the lower layer material obtained in step S2 is placed on the lower part of the trolley. The layer thickness ratio of the upper layer material to the lower layer material is (3.5~4.5):(5.5~6.5), and the total thickness of the material layer is within the range of 600mm~750mm. S4. Ignition of the furnace and sintering by exhaust; ignition negative pressure of 5000 Pa to 7000 Pa; sintering negative pressure of 12000 Pa to 16000 Pa; sintering temperature controlled at 1250℃ to 1320℃; overall weighted average basicity of finished sintered ore of 1.75 to 1.87; MgO mass fraction of finished sintered ore of 2.5% to 3.1%; MgO / Al2O3 ratio of finished sintered ore controlled within the range of 1.15 to 1.95.

[0005] In the above-mentioned method for synergistic regulation of the material layer of low-alkalinity high-magnesium oxide sinter, the magnesium flux mentioned in steps S1 and S2 is added during the secondary granulation of the remaining solid fuel, and participates in the secondary granulation together and is enriched in the outer layer of the particles, so that the MgO content in the outer layer of the particles is more than 20% higher than the MgO content in the inner layer of the particles.

[0006] In the above-mentioned method for synergistic control of the material layer of low-alkalinity, high-magnesium oxide sinter, the first granulation time in steps S1 and S2 is 2.0 min to 4.0 min; the drum speed during the first granulation process is 8 rpm to 12 rpm; and the amount of water added during the first granulation is 6.0% to 7.5% of the total mass of the mixture in the granulator. The secondary granulation time is 1.0 min to 3.0 min, the drum speed during the secondary granulation process is 6 rpm to 10 rpm, the amount of water added during the secondary granulation is 1.0% to 2.5% of the total mass of the mixture in the granulator, the water is added in the form of atomized water, and the total time of the two pre-mixing in the mixer is in the range of 0.5 min to 2.0 min.

[0007] In the above-mentioned method for synergistic regulation of the bed of low-alkalinity high-magnesia sinter, the magnesium flux mentioned in steps S1 and S2 is one or more of dolomite powder, light-burned dolomite powder, magnesite powder, and light-burned magnesite powder, and its particle size is ≤1 mm and MgO content is ≥20%.

[0008] The above-mentioned method for synergistic regulation of the bed material of low-alkalinity high-magnesia sintered ore, wherein the light-burned dolomite powder or light-burned magnesite powder is a product of the light-burning pre-decomposition of natural dolomite or magnesite at 700℃~900℃, and its MgO exists in the form of highly active periclase microcrystals with a specific surface area ≥3.0 m² / g, and the reaction initiation temperature of MgO in the light-burned dolomite powder or light-burned magnesite powder is 50~100℃ lower than the reaction initiation temperature of MgO produced by the decomposition of natural dolomite.

[0009] In the above-mentioned method for synergistic regulation of the bed of low-alkalinity high-magnesium oxide sinter, the calcium flux mentioned in steps S1 and S2 is quicklime or a mixture of limestone and quicklime, and quicklime accounts for more than 70% of the total calcium flux.

[0010] The above-mentioned method for synergistic regulation of the bed material of low-alkalinity, high-magnesium oxide sinter, The upper material serves as a strength support layer, which generates needle-like calcium ferrite under conditions of MgO content of 2.0%–2.3% and alkalinity of 1.72–1.82 to provide a strong framework. The lower layer material serves as a functional supply and structural support layer. Under conditions of MgO content of 2.8%–3.1% and basicity of 1.82–1.92, the high basicity offsets the inhibitory effect of high MgO, while the heat storage during sintering allows MgO to be fully mineralized and dissolved.

[0011] This invention employs segmented granulation and MgO targeted distribution technology to stagger the CaO-MgO reaction sequence at the microscale, solving the problem that high MgO levels affect the formation of high-quality calcium ferrite-based binder phases in traditional processes. In traditional processes, CaO and MgO are released into the liquid phase simultaneously during sintering, causing MgO to compete with Fe2O3 and SiO2 for reaction in the same temperature range where CaO forms high-quality calcium ferrite-based binder phases, directly weakening the amount of high-quality calcium ferrite-based binder phases formed. By altering the particle structure to confine MgO to the outer layer of the particles, and utilizing the temperature gradient formed by heat transfer from the particle surface to the interior during sintering, MgO reacts with SiO2 at a lower temperature range of 800~1100℃ to form forsterite or is dissolved into magnetite. When CaO is released in large quantities from the particle interior into the liquid phase at a higher temperature range of 1100~1250℃, MgO mineralizes into an inert mineral phase, no longer interfering with the formation of the high-quality calcium ferrite-based binder phase. After MgO mineralizes into forsterite or magnesium-bearing magnetite, it will not be released again during cooling to interfere with the formation of the high-quality binder phase: forsterite has a melting point as high as 1890℃, making it difficult to participate in the reaction; in magnesium-bearing magnetite, Mg2+ is firmly bound to the spinel lattice, with extremely slow solid-state diffusion efficiency, lacking the kinetic conditions to re-participate in the reaction. In addition, the present invention adopts a differentiated composition strategy of MgO and alkalinity within a reasonable range, which solves the problem caused by the uniform distribution of MgO and CaO in the entire material layer due to the uniform ratio and uniform material distribution in the traditional process. In traditional processes, the MgO in the upper layer inhibits the formation of the high-quality calcium ferrite-based binder phase. At the same time, the proportion of the high-quality calcium ferrite binder phase in the sinter produced under low alkalinity conditions will be further reduced, resulting in low metallurgical performance of the upper layer sinter. Although the lower material can promote the formation of liquid phase through heat storage and promote MgO to enter the liquid phase to complete mineralization to a certain extent, the low basicity of the material layer has a very low ability to form a high-quality binder phase of calcium ferrite, so the proportion of calcium ferrite in the lower sinter is still very low, and the metallurgical performance of the lower sinter is low. This invention proposes a differentiated composition strategy of "high MgO content in the lower layer with high basicity (1.82-1.92) and low MgO content in the upper layer with low basicity (1.72-1.82)" to solve the problems in traditional processes. The technical logic is as follows: the lower MgO content in the upper layer has a weak inhibitory effect on the formation of high-quality calcium ferrite-based binder phase, and the basicity can be appropriately reduced without affecting the formation of high-quality binder phase; the higher MgO content in the lower layer has a strong inhibitory effect on the formation of high-quality calcium ferrite-based binder phase, and the basicity can be increased to increase the CaO supply, thereby thermodynamically promoting the reaction towards the formation of high-quality calcium ferrite-based binder phase. This matching strategy allows the upper and lower layers to complete their respective core reactions under optimal MgO and alkalinity conditions. At the same time, the lower layer utilizes the heat storage advantage of sintering to fully mineralize MgO, while ensuring sufficient liquid phase and the formation of high-quality calcium ferrite-based binder phase through high alkalinity. Through the synergistic effect of two measures, high-quality finished sinter is formed: segmented granulation ensures that the initial mineralization of MgO does not interfere with the formation of the high-quality binder phase of calcium ferrite, allowing MgO to enter the liquid phase and increasing its mineralization content, thus increasing the proportion of the high-quality binder phase; differentiated layered material distribution creates optimal two-dimensional reaction conditions of composition and temperature for the upper and lower parts respectively, providing a suitable environment for MgO mineralization and the formation of the high-quality binder phase. In the finished sinter, the amount of free MgO in the mineral phases where MgO is abundant decreases, while the content of magnesium-bearing magnetite formed by mineralization increases, and the low-temperature reduction pulverization index of the magnesium-bearing magnetite mineral phase is high. The remaining mineral phases have a high proportion of high-quality binder phase calcium ferrite with high reducibility and good strength, achieving high strength, high yield, and excellent metallurgical properties of low-alkalinity, high-MgO sinter; finally, the overall technical solution requires minimal modification to the main equipment of the sintering machine, only requiring the addition of a segmented granulation process and layered material distribution control measures, making the process modification investment controllable and economically viable. Attached Figure Description

[0012] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0013] See Figure 1 The present invention includes the following steps: S1. Preparation of the upper layer material: The mass of MgO in the upper layer material accounts for 2.0% to 2.3% of the total mass of the upper layer material; the binary basicity is 1.72 to 1.82; The binary basicity of sinter is defined as the mass ratio of CaO to SiO2. Based on the percentage of the total mass of the upper layer materials, the mixture contains 80%–86% iron raw materials, 4%–7% calcium flux, 5%–7% magnesium flux, and 3%–6% solid fuel. The iron-containing raw materials and calcium flux in the upper layer material, as well as 40% to 50% of the total solid fuel in the upper layer material, are added to the mixer for pre-mixing. The mixed material is fed into a cylindrical pellet mill for primary pelleting to produce primary pellets with a particle size of 2-8 mm; then the magnesium flux in the upper layer material is premixed with the remaining solid fuel in the upper layer material and fed into a cylindrical pellet mill for secondary pelleting to obtain the upper layer material. Both the upper and lower layers of material are granulated twice, with segmented granulation and MgO targeted distribution layer. Through a special granulation method, MgO is confined to the outer layer of the particles, so that it is released preferentially before CaO during sintering and participates first in the formation of magnesium olivine and magnesium-containing magnetite, thus achieving the separation of the reaction sequence of MgO and CaO at the microscale. S2. Preparation of the lower layer material: The mass of MgO in the lower layer material accounts for 2.8% to 3.1% of the total mass of the lower layer material; the binary basicity is 1.82 to 1.92; Based on the percentage of the total mass of the lower layer material, prepare 72%–78% iron-containing raw materials, 5%–8% calcium flux, 9%–13% magnesium flux, and 3%–6% solid fuel; add the iron-containing raw materials and calcium flux in the lower layer material, as well as 40%–50% of the total solid fuel in the lower layer material, to the mixer for pre-mixing; The mixed material is fed into a cylindrical pellet mill for primary pelleting to produce primary pellets with a particle size of 2-8 mm; then the magnesium flux in the lower layer material is premixed with the remaining solid fuel in the lower layer material and fed into a cylindrical pellet mill for secondary pelleting to obtain the lower layer material. S3. Using a layered feeding method, the material is spread in layers onto the sintering trolley according to a predetermined layer thickness ratio via a round roller feeder and a nine-roller feeder. The upper layer material obtained in step S1 is placed on the upper part of the sintering trolley, and the lower layer material obtained in step S2 is placed on the lower part of the trolley. The layer thickness ratio of the upper layer material to the lower layer material is (3.5~4.5):(5.5~6.5), and the total thickness of the material layer is within the range of 600mm~750mm. By using differentiated layered fabric, MgO is mainly enriched in the lower layer of the material layer, while the upper layer has a low MgO content. This results in a weaker inhibitory effect on the high-quality calcium ferrite binder phase. Under slightly lower alkalinity conditions, the optimal temperature range for calcium ferrite formation can be precisely controlled to generate a sufficient amount of high-quality calcium ferrite binder phase to provide a strong framework. The high MgO content in the lower layer strongly inhibits the formation of high-quality calcium ferrite-based binder phases. By increasing the alkalinity, the high CaO concentration thermodynamically promotes the formation of high-quality calcium ferrite-based binder phases, effectively offsetting the inhibitory effect of high MgO on the formation of liquid phase and the development of high-quality calcium ferrite-based binder phases. At the same time, the sufficient high-temperature residence time in the lower layer allows MgO to be fully mineralized and locked, ensuring the strength of the lower sinter.

[0014] The two levels have their own focus and complement each other: segmented granulation solves the problem of "MgO-CaO reaction sequence", while composition-thermal coupling layered material distribution solves the problem of "precise matching of MgO spatial distribution and temperature field". The two work together.

[0015] S4. Ignition of the furnace and sintering by exhaust; ignition negative pressure of 5000 Pa to 7000 Pa; sintering negative pressure of 12000 Pa to 16000 Pa; sintering temperature controlled at 1250℃ to 1320℃; overall weighted average basicity of finished sintered ore of 1.75 to 1.87; MgO mass fraction of finished sintered ore of 2.5% to 3.1%; MgO / Al2O3 ratio of finished sintered ore controlled within the range of 1.15 to 1.95.

[0016] The magnesium flux mentioned in steps S1 and S2 is added during the secondary granulation of the remaining solid fuel. It participates in the secondary granulation and is enriched in the outer layer of the particles, so that the MgO content in the outer layer of the particles is more than 20% higher than the MgO content in the inner layer of the particles.

[0017] The first pelleting time in steps S1 and S2 is 2.0 min to 4.0 min; the drum speed during the first pelleting process is 8 rpm to 12 rpm; and the amount of water added during the first pelleting is 6.0% to 7.5% of the total mass of the mixture in the pellet mill. The secondary granulation time is 1.0 min to 3.0 min, the drum speed during the secondary granulation process is 6 rpm to 10 rpm, the amount of water added during the secondary granulation is 1.0% to 2.5% of the total mass of the mixture in the granulator, the water is added in the form of atomized water, and the total time of the two pre-mixing in the mixer is in the range of 0.5 min to 2.0 min.

[0018] The magnesium flux mentioned in steps S1 and S2 is one or more of dolomite powder, lightly calcined dolomite powder, magnesite powder, and lightly calcined magnesite powder, and its particle size is ≤1 mm and MgO content is ≥20%.

[0019] The lightly calcined dolomite powder or lightly calcined magnesite powder are products of the light calcination and pre-decomposition of natural dolomite or magnesite at 700℃~900℃. Their MgO exists in the form of highly active periclase microcrystals with a specific surface area ≥3.0 m² / g. Moreover, the reaction initiation temperature of MgO in the lightly calcined dolomite powder or lightly calcined magnesite powder is 50~100℃ lower than the reaction initiation temperature of MgO produced by the decomposition of natural dolomite, which can further advance the MgO mineralization time of the outer layer.

[0020] The calcium flux mentioned in steps S1 and S2 is quicklime or a mixture of limestone and quicklime, and quicklime accounts for more than 70% of the total calcium flux; that is, the calcium flux can be all quicklime or a mixture of quicklime and limestone. In the case of a mixture of limestone and quicklime, quicklime accounts for more than 70% of the total calcium flux.

[0021] The heat released during digestion increases the temperature of the upper layer material, promoting the formation of a high-quality binder phase based on calcium ferrite.

[0022] The upper material serves as a strength support layer, which generates needle-like calcium ferrite under conditions of MgO content of 2.0%–2.3% and alkalinity of 1.72–1.82 to provide a strong framework. The lower layer material serves as a functional supply and structural support layer. Under conditions of MgO content of 2.8%–3.1% and basicity of 1.82–1.92, the high basicity offsets the inhibitory effect of high MgO, while the heat storage during sintering allows MgO to be fully mineralized and dissolved.

[0023] Example 1: Segmented granulation and targeted distribution of MgO; Iron-containing raw materials mainly include Australian iron ore powder and iron concentrate powder, with Australian iron ore powder accounting for 63% and iron concentrate powder accounting for 19% of iron-containing raw materials; The calcareous flux uses quicklime, and the solid fuel is coke powder; First, iron-containing raw materials, quicklime, and coke powder accounting for 45% of the total fuel are mixed and water is added for primary granulation to produce primary particles with a particle size of 2-8 mm. The magnesium flux is made of dolomite powder with an MgO content of 21% and a particle size of ≤1 mm. It is mixed with the remaining 55% coke powder and coated on the surface of the primary particles for secondary granulation to form particles with MgO enriched in the outer layer structure.

[0024] Preparation of differentiated stratified ingredients; Based on the previous step of segmented granulation, prepare the upper layer material and the lower layer material separately: Upper layer material: Contains 83% iron raw materials, 5.5% quicklime, 5.5% dolomite powder, and 5% coke powder. MgO content is about 2.1%, and alkalinity is about 1.76.

[0025] The lower layer consists of 75% iron raw materials, 7% quicklime, 12% dolomite powder, and 5% coke powder. The MgO content is approximately 2.9%, and the alkalinity is approximately 1.87.

[0026] Return ore is added at 20% of the total mass of the mixture and evenly distributed to the upper and lower layers.

[0027] Layered fabric: The upper layer is approximately 280 mm thick, accounting for 40%, and the lower layer is approximately 420 mm thick, accounting for 60%; the total thickness of the material layers is 700 mm.

[0028] Ignition negative pressure 6000 Pa, sintering negative pressure 14000 Pa, ignition temperature 1100℃, sintering temperature 1250℃~1320℃; The finished sinter has a basicity of 1.81, an MgO content of 2.7%, and an MgO / Al2O3 ratio of 1.50.

[0029] Performance test results: Table 1 Key Indicators of Sintered Ore in Example 1: 80.5 79.2 76.4 86.1 50.2 Comparative Example 1: This comparative example is used to illustrate a comparative test conducted according to a conventional process, in which dolomite powder is directly crushed to ≤3 mm and added to the mixture without segmented granulation. All materials are mixed and granulated at one time without differentiated stratified batching and stratified distribution. The proportions and distribution are uniform, the basicity of both the upper and lower layers is 1.81, the MgO content is 2.7%, and the remaining sintering parameters are the same as in Example 1.

[0030] The yield was 76.5%, the drum strength was 74.3%, the reduction rate (RI) was only 72.3%, and the solid fuel consumption was 55.3 kg / t. All indicators were significantly inferior to those of the embodiments of the present invention.

[0031] Analysis of the causes: In traditional processes, the low alkalinity conditions themselves result in insufficient calcium ferrite formation. MgO and CaO are released simultaneously under homogeneous mixing conditions. MgO directly inhibits the development of the high-quality calcium ferrite-based binder phase within the calcium ferrite formation zone. Homogenized proportions and material distribution lead to uniform MgO distribution throughout the entire material layer. Upper MgO inhibits the formation of the high-quality calcium ferrite-based binder phase, while lower MgO, although possessing heat storage advantages, suffers from a severe deficiency in the lower liquid phase due to the lack of differentiated alkalinity adjustment based on MgO content. This invention achieves pre-mineralization of MgO through segmented granulation to avoid interference, and differentiated stratified batching to achieve a precise match of "high MgO in the lower layer with high alkalinity, and low MgO in the upper layer with low alkalinity." This dual synergy fundamentally reverses the trend of quality deterioration in low-alkalinity, high-MgO sinter.

[0032] Table 2 Key Indicators of Sintered Ore in Comparative Example 1 76.5 74.3 72.3 79.2 55.3 Comparing Tables 1 and 2, it can be seen that the low-alkalinity high-MgO sinter prepared in this embodiment is significantly better than the traditional process in all indicators; the drum strength is increased by 4 percentage points compared with the comparative example, and the solid fuel consumption is reduced by 5.1 kg / t; mineral phase analysis shows that the calcium ferrite in the sinter of Example 1 has a good interwoven structure of needle-like and plate-column-like structures, with the calcium ferrite content in the upper layer being about 36% and the calcium ferrite content in the lower layer being about 27%, while the calcium ferrite in the comparative example is only about 25% in total and is mainly in an irregular shape; The strength of the lower layer sinter drum was measured at 76.1% independently, indicating that under low alkalinity and high MgO conditions, the lower layer itself maintained good cold strength through composition-thermal regime coupling stratification and auxiliary strengthening. MgO elemental surface scanning showed that MgO in the sinter of Example 1 mainly existed in the form of magnesium-bearing magnetite and forsterite, with extremely low free MgO content. Example

[0033] The difference between this embodiment and Embodiment 1 is that the magnesium flux uses lightly calcined dolomite powder with an MgO content of 35% and a particle size of ≤0.5 mm. The upper layer material composition is 82% iron-containing raw materials, 5% quicklime, 5% lightly calcined dolomite powder, 5% coke powder, with an MgO content of about 2.2% and an alkalinity of about 1.74. The lower layer material composition is 74% iron-containing raw materials, 7.5% quicklime, 11.5% light-burned dolomite powder, and 5% coke powder, with an MgO content of approximately 3.0% and an basicity of approximately 1.90. The sintered ore has a basicity of 1.82 and an MgO content of 2.8%. The sinter drum strength was 80.5%, the reduction RI was 76.3%, the yield was 82.4%, and the lower sinter drum strength was 79.5%. After using lightly calcined dolomite powder, the reaction initiation temperature of the outer MgO was further reduced by about 80℃, and most of the mineralization reaction was completed in the range of 750-950℃, resulting in a more significant time-sequential separation effect. Example

[0034] The difference between this embodiment and Embodiment 1 is that the magnesium flux uses lightly calcined magnesia powder with an MgO content of 38%. The upper layer material composition is 80% iron-containing raw materials, 7% quicklime, 7% lightly calcined dolomite powder, 6% coke powder, with an MgO content of about 2.3% and an alkalinity of about 1.82; The lower layer material composition is 72% iron-containing raw materials, 8% quicklime, 13% lightly calcined dolomite powder, and 6% coke powder, with an MgO content of about 3.1% and an alkalinity of about 1.92; the sinter has an alkalinity of 1.82 and an MgO content of 2.8%.

[0035] The sinter drum strength was 79.8%, the reducibility RI was 76.8%, and the yield was 81.7%. The content of magnesium olivine and magnesium magnetite in the lower layer of sinter increased significantly, but due to the increase in basicity to 1.92, the proportion of calcium ferrite phase remained above 30%. This example is used to prove that the present invention is still effective under the condition of 3.1% MgO. Example

[0036] The upper layer material composition is 83% iron-containing raw materials, 5.5% quicklime, 5.5% lightly calcined dolomite powder, 5% coke powder, with an MgO content of about 2.15% and an alkalinity of about 1.78. The lower layer material composition is 75% iron-containing raw materials, 7% quicklime, 12% lightly calcined dolomite powder, 5% coke powder, with an MgO content of approximately 2.95% and an alkalinity of approximately 1.88; The sinter has a basicity of 1.81 and an MgO content of 2.8%.

[0037] The sintered ore drum strength was 80.9%, the reducibility ratio (RI) was 77.3%, and the yield was 83.5%. SEM-EDS results showed that the MgO concentration in the outer layer of the particles was approximately 2.3 times that in the core layer; a distinct MgO enrichment zone was formed in the outer layer of the particles; after sintering, MgO was mainly found in forsterite and magnesium-bearing magnetite; the free MgO content was less than 0.3%. This example demonstrates that both the mineral phase composition and metallurgical properties are within the optimal range.

[0038] Comparative Example 2 This comparative example is used to demonstrate a comparative test that uses only segmented granulation without differentiated stratified batching and stratified fabrication.

[0039] The same segmented granulation process as in Example 1 was used: iron-containing raw materials, quicklime, and 45% coke powder were mixed and granulated in one step. Primary particles with a particle size of 2-8 mm are formed; dolomite powder with an MgO content of 21% and a particle size of ≤1 mm is mixed with the remaining 55% coke powder and coated onto the surface of the primary particles for secondary granulation, forming particles with MgO enriched in the outer layer.

[0040] However, instead of using differentiated stratified batching and stratified distribution, all sintering materials adopt a uniform ratio and uniform distribution method. The MgO content of the mixture is 2.7%, the basicity is 1.81, the total thickness of the material layer is 700 mm, and the remaining sintering parameters are the same as in Example 1.

[0041] The yield was 79.1%, the drum strength was 77.2%, the reduction rate (RI) was 74.5%, and the solid fuel consumption was 52.0 kg / t. All indicators were better than those of Comparative Example 1, but still lower than those of the present invention.

[0042] Analysis of causes: The particle structure formed by segmented granulation makes MgO mainly enriched in the outer layer of the particles. During the sintering heating process, it can preferentially participate in the mineralization reaction. Some MgO is fixed in advance in the form of magnesium olivine and magnesium-containing magnetite, thereby weakening the inhibitory effect of MgO on the formation of high-quality binder phase of calcium ferrite. Therefore, the strength of sintered ore and yield are improved compared with traditional process. However, due to the lack of differentiated stratified batching and stratified distribution, MgO and basicity are still uniformly distributed throughout the entire material layer. In the upper material layer, MgO still inhibits the formation of high-quality calcium ferrite binder phases. Although the lower material layer has the advantage of heat storage, the higher MgO area is not compensated by a correspondingly higher basicity, resulting in insufficient liquid phase and calcium ferrite formation. Therefore, relying solely on segmented granulation is insufficient to fully realize the performance potential of high MgO sinter.

[0043] Comparative Example 3 This comparative example is used to demonstrate a comparative test that uses only differentiated stratified batching and stratified distribution without segmented granulation.

[0044] The dolomite powder is directly crushed to ≤3 mm and then mixed and granulated together with iron-containing raw materials, quicklime and coke powder in one go. All raw materials are mixed at one time, without using the granulation method of enriching MgO in the outer layer.

[0045] The same differentiated layered batching scheme as in Example 1 was adopted: the upper layer had an MgO content of 2.1% and a basicity of 1.76; the lower layer had an MgO content of 2.9% and a basicity of 1.87; the upper layer accounted for 40% of the total material layer thickness, the lower layer accounted for 60% of the total material layer thickness, and the total material layer thickness was 700 mm. The remaining sintering parameters were the same as in Example 1.

[0046] The yield was 78.4%, the drum strength was 76.6%, the reduction rate (RI) was 74.2%, and the solid fuel consumption was 52.8 kg / t. All indicators were better than those of Comparative Example 1, but lower than those of Example 1 and Example 2.

[0047] Analysis of the causes: Differentiated stratified batching allows the upper low-MgO zone to generate more high-quality calcium ferrite-based binder phases under lower alkalinity conditions, while the lower high-MgO zone increases CaO supply by raising alkalinity, effectively mitigating the inhibitory effect of high MgO on liquid phase formation and calcium ferrite development. Simultaneously, the lower layer utilizes automatic heat storage to promote MgO mineralization, thus improving the overall sinter quality compared to traditional processes. However, since segmented granulation was not used, MgO and CaO remained uniformly mixed within the particles and participated in the reaction simultaneously during the sintering heating process. Within the temperature range for the formation of the calcium ferrite-based high-quality binder phase, MgO continued to compete with CaO for reaction resources, inhibiting the formation of the calcium ferrite-based high-quality binder phase. This resulted in both the degree of MgO mineralization and the amount of calcium ferrite-based high-quality binder phase formed being lower than in the embodiments of this invention. Therefore, relying solely on differentiated stratified batching cannot completely solve the problem of insufficient high-quality binder phase in low-basicity, high-MgO sinter.

[0048] Example 1 79.2 76.4 80.5 Example 4 (Best) 80.9 77.3 83.5 Comparative Example 1 74.3 72.3 76.5 Comparative Example 2 77.2 74.5 79.1 Comparative Example 3 76.6 74.2 78.4 Comparing Examples 1, 4, 1, 2, and 3, we can analyze that: Comparative Example 1 uses traditional sintering without segmented granulation and differentiated layered feeding, resulting in the lowest drum strength, RI, and yield; Comparative Examples 3 and 2 show improved metallurgical properties compared to Comparative Example 1, indicating that segmented granulation and differentiated layered feeding alone can optimize low-basicity, high-MgO sinter to a certain extent; Comparative Example 2 shows better metallurgical properties than Comparative Example 3, indicating that segmented granulation improves the performance of Comparative Example 2 better than differentiated layered feeding in Comparative Example 3; Compared to Comparative Examples 1, 2, and 3, Example 1 combines segmented granulation and differentiated layered feeding, resulting in a significant improvement in metallurgical properties; Example 4, based on Example 1, adjusts the parameters to the optimal level to produce sinter with the best metallurgical properties.

Claims

1. A method for synergistic regulation of the bed structure of low-alkalinity, high-magnesia sinter, characterized in that: Includes the following steps: S1. Preparation of the upper layer material: The mass of MgO in the upper layer material accounts for 2.0% to 2.3% of the total mass of the upper layer material; the binary basicity is 1.72 to 1.82; Based on the percentage of the total mass of the upper layer materials, the mixture contains 80%–86% iron raw materials, 4%–7% calcium flux, 5%–7% magnesium flux, and 3%–6% solid fuel. The iron-containing raw materials and calcium flux in the upper layer material, as well as 40% to 50% of the total solid fuel in the upper layer material, are added to the mixer for pre-mixing. The mixed material is fed into a cylindrical pellet mill for primary pelleting to produce primary pellets with a particle size of 2-8 mm; then the magnesium flux in the upper layer material is premixed with the remaining solid fuel in the upper layer material and fed into a cylindrical pellet mill for secondary pelleting to obtain the upper layer material. S2. Preparation of the lower layer material: The mass of MgO in the lower layer material accounts for 2.8% to 3.1% of the total mass of the lower layer material; the binary basicity is 1.82 to 1.92; Based on the percentage of the total mass of the lower layer material, prepare 72%–78% iron-containing raw materials, 5%–8% calcium flux, 9%–13% magnesium flux, and 3%–6% solid fuel; add the iron-containing raw materials and calcium flux in the lower layer material, as well as 40%–50% of the total solid fuel in the lower layer material, to the mixer for pre-mixing; The mixed material is fed into a cylindrical pellet mill for primary pelleting to produce primary pellets with a particle size of 2-8 mm; then the magnesium flux in the lower layer material is premixed with the remaining solid fuel in the lower layer material and fed into a cylindrical pellet mill for secondary pelleting to obtain the lower layer material. S3. Using a layered material distribution method, the upper layer material obtained in step S1 is placed on the upper part of the sintering trolley, and the lower layer material obtained in step S2 is placed on the lower part of the trolley. The layer thickness ratio of the upper layer material to the lower layer material is (3.5~4.5):(5.5~6.5), and the total thickness of the material layer is within the range of 600mm~750mm. S4. Ignition of the furnace and sintering by exhaust; ignition negative pressure of 5000 Pa to 7000 Pa; sintering negative pressure of 12000 Pa to 16000 Pa; sintering temperature controlled at 1250℃ to 1320℃; overall weighted average basicity of finished sintered ore of 1.75 to 1.87; MgO mass fraction of finished sintered ore of 2.5% to 3.1%; MgO / Al2O3 ratio of finished sintered ore controlled within the range of 1.15 to 1.

95.

2. The method for synergistic regulation of the bed material of low-alkalinity, high-magnesia sinter according to claim 1, characterized in that: The magnesium flux mentioned in steps S1 and S2 is added during the secondary granulation of the remaining solid fuel. It participates in the secondary granulation and is enriched in the outer layer of the particles, so that the MgO content in the outer layer of the particles is more than 20% higher than the MgO content in the inner layer of the particles.

3. The method for synergistic regulation of the bed material of low-alkalinity, high-magnesia sinter according to claim 1, characterized in that: The first pelleting time in steps S1 and S2 is 2.0 min to 4.0 min; the drum speed during the first pelleting process is 8 rpm to 12 rpm; and the amount of water added during the first pelleting is 6.0% to 7.5% of the total mass of the mixture in the pellet mill. The secondary granulation time is 1.0 min to 3.0 min, the drum speed during the secondary granulation process is 6 rpm to 10 rpm, the amount of water added during the secondary granulation is 1.0% to 2.5% of the total mass of the mixture in the granulator, the water is added in the form of atomized water, and the total time of the two pre-mixing in the mixer is in the range of 0.5 min to 2.0 min.

4. The method for synergistic regulation of the bed material of low-alkalinity, high-magnesia sinter according to claim 1, characterized in that: The magnesium flux mentioned in steps S1 and S2 is one or more of dolomite powder, lightly calcined dolomite powder, magnesite powder, and lightly calcined magnesite powder, and its particle size is ≤1 mm and MgO content is ≥20%.

5. The method for synergistic regulation of the bed material of low-alkalinity, high-magnesia sinter according to claim 4, characterized in that: The lightly calcined dolomite powder or lightly calcined magnesite powder are products of the light calcination and pre-decomposition of natural dolomite or magnesite at 700℃~900℃. Their MgO exists in the form of highly active periclase microcrystals with a specific surface area ≥3.0 m² / g. Moreover, the reaction initiation temperature of MgO in the lightly calcined dolomite powder or lightly calcined magnesite powder is 50~100℃ lower than the reaction initiation temperature of MgO produced by the decomposition of natural dolomite.

6. The method for synergistic regulation of the bed material of low-alkalinity, high-magnesia sinter according to claim 1, characterized in that: The calcium flux mentioned in steps S1 and S2 is quicklime or a mixture of limestone and quicklime, and quicklime accounts for more than 70% of the total calcium flux.

7. The method for synergistic regulation of the bed material of low-alkalinity, high-magnesia sinter according to claim 1, characterized in that: The upper material serves as a strength support layer, which generates needle-like calcium ferrite under conditions of MgO content of 2.0%–2.3% and alkalinity of 1.72–1.82 to provide a strong framework. The lower layer material serves as a functional supply and structural support layer. Under conditions of MgO content of 2.8%–3.1% and basicity of 1.82–1.92, the high basicity offsets the inhibitory effect of high MgO, while the heat storage during sintering allows MgO to be fully mineralized and dissolved.

Images