Method for reducing coke rate of closed blast furnace

Abstract

The invention relates to the technical field of non-ferrous metal smelting, and discloses a method for reducing the coke rate of a closed blast furnace. The method comprises the following steps: preparing functional complex ore, so that the proportion of small and medium-sized mine mixed ore in raw material ore is less than or equal to 30wt%; introducing oxygen-enriched air to enable the oxygen concentration of the sintering initial reaction zone or the sintering reaction zone to be greater than or equal to 22%, and sintering to obtain a sintered block; putting the sintered blocks and coke into a closed blast furnace, and blowing hot air at the temperature of more than or equal to 850 DEG C; by optimizing the raw material ore structure, strengthening oxygen-enriched sintering, increasing the proportion of zinc elements in the form of zinc oxide in the sintered block and reducing the proportion of zinc elements in the form of zinc silicate, the reduction efficiency of zinc is improved, the coke amount consumed per ton of zinc is reduced, it is guaranteed that the drum rate is larger than or equal to 75%, and the defect that zinc silicate is difficult to reduce is systematically overcome in combination with the blast furnace air temperature control larger than or equal to 850 DEG C; the coke rate is reduced, the consumption cost of zinc coke per ton is reduced, the zinc loss of fuming slag is reduced, and the economic competitiveness of the ISP process is comprehensively improved.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal smelting technology, and in particular to a method for reducing the coke yield of a closed blast furnace. Background Technology

[0002] The Imperial Smelting Process (ISP), also known as the closed blast furnace zinc-lead smelting process, is a smelting method that has been applied to large-scale production and can simultaneously produce metallic lead and zinc. The traditional ISP zinc smelting process includes the following operations: mixed lead-zinc ore or single concentrate, along with lead-zinc rich miscellaneous materials (oxide materials), are sintered and roasted to produce intermediate sintered briquettes. The sintered briquettes and coke are then added into the furnace from the top of the lead-zinc closed blast furnace (ISF), forming a material column of a certain height inside the furnace. High-temperature air at around 1000°C is then introduced into the furnace from the bottom tuyeres, where it undergoes a violent physicochemical reaction with the coke and sintered briquettes, resulting in ISF smelting. ISF smelting is a reduction process using metallurgical coke as a reducing agent. In order to reduce the zinc in the charge as much as possible, while preventing the iron in the charge from being reduced to metallic iron, which would cause iron accumulation in the hearth and difficulties in slag discharge, the reducing atmosphere controlled throughout the smelting process is stronger than that of a lead blast furnace but weaker than that of an iron blast furnace. That is, the iron in the charge can only be reduced to ferrous oxide (FeO) in the end, so that it enters the slag. About 40% of the zinc oxide in the charge is reduced in the solid state and 60% is reduced in the liquid slag. Therefore, the degree of reduction of zinc oxide in the charge ultimately depends on the degree of reduction of zinc oxide in the slag.

[0003] Due to the significant difference in boiling points between lead and zinc (lead 1525℃, zinc 906℃), during the smelting process, lead, in a liquid state, enters the hearth along with liquid slag. The lead and slag are periodically discharged into the electric heating forebed, where they separate due to their different densities, producing crude lead. Zinc, in a gaseous state, enters the top space of the furnace along with the furnace gas. To minimize the re-oxidation of zinc by CO2 before it reaches the condenser, secondary air is blown into the upper space of the furnace to rapidly raise the furnace temperature above the equilibrium temperature for zinc re-oxidation (approximately 920℃), ensuring that the low concentration of zinc vapor in the furnace gas reaches the condenser smoothly. Using lead rain as the condensing medium has a high heat transfer coefficient and a large heat exchange area, effectively enhancing the physical condensation process of zinc while minimizing the chemical re-oxidation process. In the lead rain condenser, the lead rain absorbs zinc and heat from the furnace gas, raising the temperature of the molten lead (500-530℃) and simultaneously increasing the amount of dissolved zinc. Since the solubility of zinc in molten lead varies with temperature, the molten lead containing zinc is pumped from the lead pump pool into the cooling and separation system using a lead pump. The temperature is reduced to 430-445℃, at which point some zinc precipitates out of the molten lead and separates due to the difference in specific gravity. The molten lead returns to the condenser, while the molten zinc overflows into the zinc storage tank and is heated to become crude zinc.

[0004] In recent years, the prices of lead and zinc ores in the market have been rising continuously, leading to a shortage of ore supplies. Coupled with the sustained increase in coke prices, this has resulted in a significant increase in the processing costs of ISP smelting, severely compressing profit margins. Currently, smelters mainly reduce production costs by diversifying the raw materials for ISP smelting processes and increasing the proportion of low-cost mixed ore (small mine mixed ore). However, because the chemical composition of these mixed ores (such as Zn / Pb / Fe / SiO2 content, impurities, etc.) differs from the single zinc concentrate originally designed for use, the physicochemical properties (such as melting point, porosity, strength) and reducibility of the sintered blocks change, resulting in an increase in the coke yield required for ISF smelting. Therefore, reducing the coke yield in closed blast furnaces is of great significance for reducing the processing costs of ISP smelting. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, the object of the present invention is to provide a method for reducing the coke yield of a closed blast furnace.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for reducing the coke yield of a closed blast furnace, comprising the following steps: The raw material is mixed with functional composite ore, so that the proportion of small and medium-sized mixed ore is ≤30wt%; oxygen-enriched air is introduced to make the oxygen concentration in the initial reaction zone or the reaction zone during sintering ≥22%; sintering is then carried out to obtain sintered blocks. The sintered blocks and coke are fed into a closed blast furnace, and hot air at a temperature of ≥850℃ is blown in.

[0007] In some embodiments of the present invention, the proportion of mixed ore from small mines in the raw material ore is 10wt%-30wt%.

[0008] In some embodiments of the present invention, the functional composite ore includes at least one of imported Trafigura mixed ore, high copper mixed ore, high copper zinc ore, Mexican zinc ore, and Russian zinc ore.

[0009] In some embodiments of the present invention, the oxygen concentration in the initial sintering reaction zone or the sintering reaction zone is 22%-24%.

[0010] In some embodiments of the present invention, the air volume of the oxygen-enriched air is 10,000-15,000 m³ / h. 3 / h, oxygen supply is 640-960m³ 3 / h.

[0011] In some preferred embodiments of the present invention, the air volume of the oxygen-enriched air is 12000-13000 m³ / h. 3 / h, oxygen supply is 720-880m³ 3 / h.

[0012] In some embodiments of the present invention, the pressure of the oxygen-enriched air is 13000-28000 Pa.

[0013] In some embodiments of the present invention, the chemical composition of the sintered block meets the following requirements: Pb 15wt%-21wt%; Zn 36wt%-42wt%; S < 1wt%; Cd ≤ 0.2wt%; Sb 0.15wt%-0.25wt%; As < 0.4wt%; SiO2 < 4.5wt%; CaO / SiO2 1.4wt%-1.9wt%; Pb + SiO2 ≤ 26wt%.

[0014] In some embodiments of the present invention, the proportion of zinc element in the sintered block as zinc oxide is ≥12.20 wt%; and the proportion in the form of zinc silicate is ≤14.56 wt%.

[0015] In some embodiments of the present invention, the chemical composition of the coke meets the following requirements: S≤1.0wt%; volatile matter≤1.9wt%; ash content≤15wt%.

[0016] In some embodiments of the present invention, the sintered block has a size of 30-120 mm; the coke has a size of >40 mm.

[0017] In some embodiments of the present invention, the coke has a crush resistance strength M25 ≥ 83% and an abrasion resistance strength M10 ≤ 10.5%.

[0018] In some embodiments of the present invention, the coke has a reactivity (CRI) ≤ 30% and a post-reaction strength (CSR) ≥ 60%.

[0019] In some embodiments of the present invention, the coke is further subjected to dehydration and preheating to 500-750°C before being fed into the closed blast furnace.

[0020] In some embodiments of the present invention, the temperature of the hot air is 850-1100°C.

[0021] The basic principles of this invention are explained as follows: The main reactions that occur during the ISF smelting process are shown in Equation 1-11: 2C + O2= 2CO + 5024J / kg·C(1); 2CO + O2= 2CO2+ 13071J / kg·C(2); CO2+ C = 2CO - 5862 J / kg·C(3); ZnO(s) + CO = Zn(g) + CO2- 1692J / kg·C(4); PbO(s) + CO = Pb(l) + CO2+ 153J / kg·C(5); 3Fe2O3(s) + CO = 2Fe3O4+ CO2(6); 3Fe2O3(s) + CO = 3FeO(s) + CO2(7); ZnO(l) + CO = Zn(g) + CO2(8); ZnO(l) + C(s)= Zn(g) + CO(9); FeO(l) + C(s)= Fe(l) + CO(10); ZnO(l) + Fe(l) = Zn(g) + FeO(11); Existing technologies primarily utilize mixed ore from small-scale mines (hereinafter referred to as small-scale mixed ore). This type of ore is composed of a mixture of ores supplied by multiple small mines, resulting in dispersed sources and significant differences in lead and zinc grades and large fluctuations in composition among the ores from different small mines. Because its chemical composition differs from that of single zinc concentrate, the physicochemical properties and reducibility of the sintered lumps change, leading to an increase in the coke yield required for ISF smelting. Furthermore, the zinc in small-scale mixed ore exhibits complex occurrence forms, with a high proportion of zinc silicate before sintering and significant zinc silicate residue after sintering. Zinc silicate requires high temperatures or strong reducing conditions to be effectively reduced. Therefore, this invention provides a method for reducing the coke yield in a closed blast furnace: 1) By incorporating imported Trafigura mixed ore, high-copper mixed ore, high-copper-zinc ore, Mexican zinc ore, and Russian zinc ore, among other functional composite ores, Mexican and Russian zinc ores are easily reducible ores. Zinc is mainly found in phases easily reduced by CO, such as zinc oxide and zinc-iron spinel, and has a low zinc silicate content. These are zinc raw materials that can be efficiently reduced in ISP smelting without harsh conditions (high temperature / high coke ratio). Imported Mexican zinc ore also has low silicon properties, which can inhibit the formation of zinc silicate. Imported high-copper-zinc ore has high copper properties, which can catalyze the decomposition of zinc silicate. Imported Trafigura mixed ore contains high levels of free zinc oxide, which can directly provide an easily reducible zinc source. Therefore, by incorporating the above-mentioned functional composite ores into the mixed ore of small mines, the structure of the raw material ore is optimized, and the sintering phase is actively controlled by specific component combinations (low silicon, high copper, high free zinc oxide, etc.), thus overcoming the zinc silicate reduction barrier and reducing the coke ratio of the closed blast furnace. 2) In the initial stage of sintering, oxygen-enriched gas is introduced into the reaction zone. After the addition of oxygen, the diffusion coefficient of oxygen molecules to the reaction interface increases, which enhances the mass transfer at the solid-gas interface and is beneficial to diffusion and adsorption during the reaction. At the same time, the high oxygen environment can accelerate the reaction rate of materials and reduce residual sulfur in materials during sintering, thereby reducing the formation of ZnS (a difficult-to-reducible phase) during the smelting process. In addition, under oxygen-enriched conditions, the ore combustion is more complete, which increases the porosity of the sintering layer and further enhances the airflow penetration ability, making heat transfer and chemical reaction more uniform and avoiding local under-burning or over-burning. At the same time, it is conducive to promoting the crystallization of iron minerals and the uniform distribution of the liquid phase, improving the drum strength and yield of sintered blocks. In other words, by optimizing the sintering and roasting process through oxygen-enriched sintering, the residual sulfur in sintered blocks is reduced. From a physical perspective, the agglomeration rate, permeability, and drum rate of sintered blocks are improved, and the pulverization rate of sintered blocks during furnace entry or smelting is reduced, thereby reducing the throat nodule rate of ISF furnace, extending the ISF production cycle, increasing the utilization rate of coke, and ultimately achieving the goal of reducing coke yield. 3) Increasing the blast temperature can significantly increase the sensible heat brought into the furnace by the blast. This sensible heat can replace the heat of coke combustion, thereby directly reducing coke consumption (coke ratio). For every 100°C increase in the blast temperature of a closed blast furnace, the coke ratio can be reduced by about 2%-3%. Therefore, this invention accelerates the oxidation reaction rate in the furnace, shortens the coke combustion time, improves combustion efficiency, and reduces the amount of unburned coke residue by controlling the blast temperature to ≥850°C.

[0022] Compared with the prior art, the advantages of the present invention are: The method for reducing the coke ratio in a closed blast furnace provided by this invention optimizes the raw material structure by incorporating a functional composite ore with low silicon and high free zinc oxide, and strengthens oxygen-enriched sintering. This ensures that the oxygen concentration in the initial reaction zone or the reaction zone during sintering is ≥22%, increasing the proportion of easily reducible zinc oxide in the sintered block and reducing the proportion of difficult-to-reducible zinc silicate, thereby improving zinc reduction efficiency, reducing the amount of coke consumed per ton of zinc, ensuring a drum rotation rate of ≥75%, and combining this with blast furnace temperature control of ≥850℃. This systematically addresses the difficulty in reducing zinc silicate, resulting in a lower coke ratio, lower coke consumption cost per ton of zinc, and reduced zinc loss in fuming slag, thus comprehensively improving the economic competitiveness of the ISP process. Attached Figure Description

[0023] Figure 1 A flowchart of the lead-zinc production process using a closed blast furnace. Detailed Implementation

[0024] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0025] This embodiment explores the effect of raw material ore structure on reducing the coke yield of a closed blast furnace: Starting in March 2024, the main ore source was a blend of small-mine mixed ores with higher economic value. After the sintered blocks made from this material entered the Insulated Blasted Furnace (ISF), the coke ratio remained high, indicating that the ISF was not very adaptable to the small-mine mixed ore. While the mixed material saved on ore source costs, it increased the cost of ISF coke. In order to comprehensively consider the production cost of the ISP process, give full play to the advantages of the ISP's strong adaptability to raw materials, and reduce the ISF coke ratio, starting in August 2024, imported Trafigura mixed ore, high-copper mixed ore, and high-copper-zinc ore were added to optimize the raw material structure of the sintered blocks. In February 2025, Mexican zinc ore and Russian zinc ore were added to further optimize the raw material structure and reduce the proportion of small-mine mixed materials to 15 wt%.

[0026] Table 1. Coke yield of the closed blast furnace in Example 1

[0027] Table 1 shows the coke ratio of the closed blast furnace in Example 1. As can be seen from Table 1, before the large-scale addition of mixed ore from small mines, the coke ratio of the closed blast furnace was 35.38%-35.77%. After the use of mixed ore from small mines as the main ore source began in March 2024, the coke ratio increased. From August 2024 to March 2025, the addition of imported Trafigura mixed ore, high-copper mixed ore, and high-copper-zinc ore stabilized the coke ratio of the closed blast furnace, but did not decrease significantly. This indicates that controlling the sintering phase solely through specific component combinations (high copper, high free zinc oxide, etc.) is not effective. In February 2025, Mexican zinc ore and Russian zinc ore were added. Both are easily reducible ores, with zinc mainly occurring in phases easily reduced by CO such as zinc oxide and zinc-iron spinel. The zinc silicate content is low, which can be efficiently reduced in ISP smelting, further optimizing the raw material ore structure and significantly reducing the coke ratio.

[0028] Example 2 This embodiment investigates the effect of the form in which zinc exists during the smelting process on the coke yield: According to the smelting principle of ISF (Induction Furnace Smelting), approximately 40% of the zinc oxide in the furnace charge is reduced in the solid state, and 60% is reduced in the liquid slag. Therefore, the degree of zinc oxide reduction in the slag determines the degree of zinc oxide reduction in the furnace charge. During production, the zinc content in the slag is mainly controlled by adjusting the coke ratio or increasing the blast temperature. However, even after increasing the coke ratio, the zinc content in the slag still falls short of the normal level for ISF production. Even after further blowing in the fuming furnace, the zinc content in the slag remains difficult to reduce. Therefore, it is necessary to consider whether changes in the ore source will affect the form in which zinc exists in the sintered agglomerates, thereby affecting the coke ratio required for ISF smelting.

[0029] Small-scale mixed ore was used as the main ore source (greater than 30 wt%) for ISP smelting, and the raw ore, sintered ore and slag were subjected to quantitative analysis of elemental occurrence phases.

[0030] Table 2. Quantitative analysis results of various elements in the ISP raw material ore, sintered blocks and slag in Example 2.

[0031] Table 2 shows the quantitative analysis results of the constituent phases of each element in the raw ore, sintered blocks and slag of ISP in Example 2. As can be seen from Table 2, almost all of the zinc in zinc oxide was reduced during ISP smelting, while about 40% of the zinc in zinc silicate was not reduced. In addition, according to thermodynamic software calculations, Zn in zinc silicate begins to be reduced by C above 700℃ and by CO above 810℃. Laboratory test results show that zinc silicate can be reduced in large quantities above 1000℃. That is, the zinc occurrence forms in the mixed ore of small mines are complex, the proportion of zinc silicate is high before sintering, and the zinc silicate residue is significant after sintering. In the ISF production process, zinc in sintered blocks exists in the form of zinc oxide, which results in high zinc reduction efficiency and low coke consumption per ton of zinc. However, when zinc exists in the form of zinc silicate, the reduction process requires more stringent conditions, leading to higher coke consumption per ton of zinc. Therefore, increasing the proportion of zinc in sintered blocks in the form of zinc oxide and decreasing the proportion in the form of zinc silicate is more conducive to reducing coke consumption per ton of zinc, thereby achieving the goal of reducing the coke yield of the closed blast furnace.

[0032] Example 3 This example investigates the effect of oxygen-enriched sintering on coke yield: Small-scale mixed ore (greater than 30 wt%) was used as the main ore source for ISP smelting. The sintering process was carried out in a sintering machine with 7 blowers. Blower #0 corresponds to branch pipe #0, blower #1 corresponds to branch pipe #1, blower #2 corresponds to branches #2-3, blower #3 corresponds to branches #4-6, blower #4 corresponds to branches #7-11, and blower #5 corresponds to branches #12-15. The 16 branches correspond to 16 air boxes. Blowers #2 and #3 are the initial reaction zone and the reaction zone during sintering. In this embodiment, oxygen enrichment was added to blower #2 for oxygen-enriched sintering (pressure 13000Pa-28000Pa). ICP detection of the main elements in the sintered blocks was performed. The oxygen concentration distribution of oxygen-enriched sintering is shown in Table 3, and the ICP detection results of the main elements in the sintered blocks are shown in Table 4.

[0033] Table 3. Oxygen concentration distribution in oxygen-enriched sintering in Example 3

[0034] Table 4. ICP detection results of major elements in the sintered block of Example 3

[0035] Through production practice, it was found that adding oxygen-enriched air to blowers #2 or #3 can increase the bed temperature of the sintering machine (from 600-700℃ to 700-750℃), optimize the sintering and roasting process, increase the roasting intensity, increase the agglomeration rate during the sintering process, increase the sintering machine's ability to handle complex materials, reduce the sulfur content of the sintered blocks, and improve the drum rotation rate and melting properties of the sintered blocks.

[0036] In summary, by incorporating functional composite ores into the raw ore, reducing the proportion of mixed ores from small mines in the raw ore, optimizing the raw ore structure, controlling the sinter phase, and introducing oxygen-enriched air into the reaction zone during the initial sintering stage or during the sintering process, the coke yield of the closed blast furnace can be effectively reduced. Furthermore, blast furnace ironmaking has verified that increasing the blast furnace temperature can reduce coke combustion demand by replacing sensible heat with coke combustion heat and optimizing reaction kinetics. Therefore, this invention combines optimizing the raw ore structure, oxygen-enriched sintering, and increasing the blast furnace temperature to reduce the coke yield of the closed blast furnace and lower the processing cost of ISP smelting.

Claims

1. A method for reducing the coke yield of a closed blast furnace, characterized in that, Includes the following steps: The raw material is mixed with functional composite ore, so that the proportion of small and medium-sized mixed ore is ≤30wt%; oxygen-enriched air is introduced to make the oxygen concentration in the initial reaction zone or the reaction zone during sintering ≥22%; sintering is then carried out to obtain sintered blocks. The sintered blocks and coke are fed into a closed blast furnace, and hot air at a temperature of ≥850℃ is blown in.

2. The method for reducing the coke yield of a closed blast furnace according to claim 1, characterized in that, The proportion of mixed ore from small mines in the raw materials is 10wt%-30wt%.

3. The method for reducing the coke yield of a closed blast furnace according to claim 1, characterized in that, The functional composite ore includes at least one of the following: imported Trafigura mixed ore, high copper mixed ore, high copper zinc ore, Mexican zinc ore, and Russian zinc ore.

4. The method for reducing the coke yield of a closed blast furnace according to claim 1, characterized in that, The oxygen concentration in the initial reaction zone of sintering or the reaction zone during sintering is 22%-24%.

5. The method for reducing the coke yield of a closed blast furnace according to claim 1, characterized in that, The volume of the oxygen-enriched air is 10,000-15,000 m³ / h. 3 / h, oxygen supply is 640-960m³ 3 / h.

6. The method for reducing the coke yield of a closed blast furnace according to claim 1, characterized in that, The chemical composition of the sintered block meets the following requirements: Pb 15wt%-21wt%; Zn 36wt%-42wt%; S < 1wt%; Cd ≤ 0.2wt%; Sb 0.15wt%-0.25wt%. As<0.4wt%; SiO2<4.5wt%; CaO / SiO21.4wt%-1.9wt%; Pb+ SiO2≤26wt%.

7. The method for reducing the coke yield of a closed blast furnace according to claim 6, characterized in that, In the sintered block, the proportion of zinc element existing in the form of zinc oxide is ≥12.20wt%, and the proportion existing in the form of zinc silicate is ≤14.56wt%.

8. The method for reducing the coke yield of a closed blast furnace according to claim 1, characterized in that, The chemical composition of the coke meets the following requirements: S≤1.0wt%; volatile matter≤1.9wt%; ash content≤15wt%.

9. The method for reducing the coke yield of a closed blast furnace according to claim 1, characterized in that, The sintered blocks have a size of 30-120 mm; the coke has a size >40 mm.

10. The method for reducing the coke yield of a closed blast furnace according to claim 1, characterized in that, The temperature of the hot air is 850-1100℃.

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