Method for producing low-silicon molten iron through blast furnace hydrogen spraying

Abstract

The invention discloses a method for producing low-silicon molten iron through hydrogen injection of a blast furnace, which is characterized in that hydrogen spray guns with specific angles (15-45 degrees) and intervals (more than or equal to 200mm) are arranged in a tuyere area, and a gradient injection control strategy is combined to realize stability of a thermal system and accurate regulation and control of silicon content. When the temperature of the molten iron is lower than 1480 DEG C, hydrogen-rich gas which is preheated to 300-450 DEG C and has the concentration of 80%-90% is injected to compensate heat, and the theoretical combustion temperature is maintained to be 1850-1950 DEG C; when the silicon content is larger than 0.4%, pure hydrogen injection is switched, the furnace top pressure is increased to 220 kPa to 260 kPa, the center airflow intensity is increased by 20% to 30%, a soft melting zone is made to move downwards by 1.2 m to 1.8 m, the contact time of liquid slag iron and SiO gas is shortened to 2 seconds to 4 seconds, and the SiO gasification rate is reduced by larger than or equal to 35%. Industrial application shows that the silicon content of molten iron can be stably controlled to be 0.1%-0.2%, the coke ratio per ton of iron is reduced by 13.2%, CO2 emission is reduced by 21%, and the ultralow-silicon smelting target with the stable heat system, low carbon and high efficiency is achieved.

Description

Technical Field

[0001] The present invention relates to the technical fields of ironmaking and hydrogen technology, and particularly provides a method for producing low-silicon hot metal with stable physical heat and low carbon by injecting hydrogen in a blast furnace. Background Art

[0002] High-silicon hot metal has significant effects on blast furnace operation in many aspects. The increase in silicon content will cause changes in the slag basicity, affecting the fluidity and desulfurization ability of the slag, which is not conducive to the stable operation of the blast furnace. Secondly, high-silicon hot metal will increase the internal heat load in the blast furnace. The reduction of silicon is an endothermic process, which will lead to an increase in the fuel ratio and affect the energy efficiency of the blast furnace. A higher silicon content will also accelerate the erosion rate of the blast furnace lining, shorten the service life of the blast furnace, and may lead to unstable product quality and increased production costs.

[0003] When hot metal with a high silicon content enters the converter, it will trigger a more intense oxidation reaction, consume more oxygen, and generate a large amount of molten slag such as calcium silicate. This not only reduces the metal yield but also may erode the converter lining due to the increase in slag volume and shorten its service life. Therefore, in blast furnace operation, controlling the silicon content in hot metal is crucial for ensuring the efficiency, quality, and cost control of the entire steel production.

[0004] In the process of producing hot metal with low silicon in a blast furnace, when the silicon content in hot metal decreases, the heat consumption for direct reduction decreases, the heat required in the high-temperature zone decreases, and the energy consumption per ton of hot metal also decreases accordingly. The coke demand is reduced, thereby reducing the carbon consumption and carbon dioxide emissions.

[0005] However, blindly reducing the silicon content in a traditional blast furnace may lead to instability of the internal heat regime, especially when the furnace condition fluctuates, there will be a risk of freezing. Once the furnace temperature is not controlled properly, it is easy to cause the molten hot metal to solidify in some parts, seriously affecting the normal operation of the blast furnace.

[0006] In order to overcome the above problems, there is an urgent need on site for a new technology that can reduce the silicon content in hot metal and reduce the coke consumption without affecting the heat regime and avoiding the trend of the furnace condition getting cooler. Summary of the Invention

[0007] To achieve the above object, the present invention provides a method for producing low-silicon hot metal with stable physical heat and low carbon by injecting hydrogen in a blast furnace, including the following steps:

[0008] (1) Setting of the hydrogen injection system:

[0009] A hydrogen lance is arranged above the coal powder lance in the tuyere area of the blast furnace hearth. The injection direction of the hydrogen lance forms an angle θ with the pulverized coal injection flow, and 15° ≤ θ ≤ 45° and the distance between them is ≥ 200 mm. The injection medium is a hydrogen-rich gas with a hydrogen volume concentration ≥ 50%.

[0010] (2) Gradient injection control:

[0011] When the molten iron temperature T < 1480 °C is detected, the heat compensation mode is turned on, and hydrogen-rich gas preheated to 300 - 450 °C is injected, with a hydrogen concentration of 80% - 90%, a flow rate of 10 - 15 m / s, and an injection pressure of 1.2 - 1.8 MPa;

[0012] When the silicon content [Si] of the molten iron > 0.4%, the silicon suppression mode is switched, and hydrogen with a normal temperature purity ≥ 99% is injected, with a flow rate of 6 - 8 m / s and an injection pressure of 0.5 - 0.9 MPa.

[0013] The combustion heat generated by hydrogen injection compensates for the physical heat of the hearth. The theoretical combustion temperature is controlled within 1850 - 1950 °C. By reducing the temperature in the bosh area, the softening-melting zone moves down by 1.2 - 1.8 meters, and the gasification rate of SiO gas decreases by ≥ 35%.

[0014] The hydrogen flow rate is regulated to increase the top pressure of the blast furnace to 220 - 260 kPa, the central gas flow intensity increases by 20% - 30%, the partial pressure of the reducing gas increases to 0.12 - 0.18 MPa, and the contact time between the liquid slag-iron and SiO gas is shortened to 2 - 4 seconds.

[0015] When the molten iron temperature rises back to 1500 °C and [Si] ≤ 0.3%, it switches back to the reference mode, and hydrogen-rich gas at normal temperature with a concentration of 60% is injected.

[0016] The present invention realizes the stable production of low-silicon molten iron by setting hydrogen injection guns at specific angles and spacings in the tuyere area of the blast furnace and combining the gradient injection control strategy: when the molten iron temperature is lower than 1480 °C, high-concentration hydrogen-rich gas preheated to 300 - 450 °C is used to compensate for heat, maintaining the theoretical combustion temperature at 1850 - 1950 °C to avoid freezing of the furnace condition; when the silicon content exceeds 0.4%, pure hydrogen injection is switched. By increasing the central gas flow intensity (+20% - 30%) and shortening the contact time between the liquid slag-iron and SiO gas to 2 - 4 seconds, the gasification rate of SiO decreases by ≥ 35% and the softening-melting zone moves down by 1.2 - 1.8 meters. Finally, the silicon content of the molten iron can be stably controlled at 0.1% - 0.2%. Industrial applications show that the coke ratio per ton of iron is reduced by 13.2% and the CO 2 emission is reduced by 21%, achieving the goal of ultra-low silicon smelting with stable thermal regime, low carbon and high efficiency.

[0017] The following will further illustrate the concept, specific structure and technical effects of the present invention with reference to the accompanying drawings to fully understand the purpose, features and effects of the present invention. Description of the Drawings

[0018] Figure 1 is a schematic diagram of the principle of reducing silicon by injecting hydrogen into the blast furnace of the present invention; Detailed Embodiments

[0019] The following describes several preferred embodiments of the present invention with reference to the accompanying drawings of the specification to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0020] In view of the limited ability of traditional blast furnaces to reduce the silicon content in pig iron while maintaining the thermal state, the present invention proposes an innovative method, that is, by injecting hydrogen into the blast furnace in low-carbon production to supplement the heat at the tuyere, stabilizing the physical heat and the physical heat of the molten iron, and realizing the production of low-silicon molten iron in low-carbon production.

[0021] The technical solution adopted by the present invention is to install a hydrogen lance above the gas lance in the tuyere area of the blast furnace to ensure that it maintains an appropriate distance and angle from the pulverized coal injection flow to avoid direct contact between the two. The hydrogen gas used is not limited to pure hydrogen, but covers a variety of hydrogen-containing fuel gases. These hydrogen-rich fuel gases include, but are not limited to, natural gas, coke oven gas and other types of fuel gases that can provide hydrogen during application.

[0022] The combustion reaction of hydrogen with oxygen in the tuyere area to form water vapor is an exothermic process. As shown in the following chemical formula, it provides a heat source, compensates for the heat required for injecting fuel, and is beneficial to the smooth operation of the furnace condition, stabilizing the physical heat distribution and the physical heat of the molten iron.

[0023]

[0024] The water-gas shift reaction of hydrogen occurs in the tuyere area. As shown in the following chemical formula, it is a slightly exothermic process, supplementing heat for the blast furnace.

[0025] CO(g)+H 2 O(g)=CO 2 (g)+H 2 (g)ΔH=-32196J / molH 2

[0026] When hydrogen is injected at the blast furnace, the hydrogen content in the furnace gradually increases. The indirect reduction of hydrogen in the blast furnace increases, the direct reduction degree decreases, the heat consumption for direct reduction decreases, the heat demand in the region decreases, resulting in a decrease in the theoretical combustion temperature. The decrease in the temperature of the tuyere combustion zone reduces the gasification of SiO and reduces the entry of Si into the molten iron.

[0027] The gasification reaction of SiO is as shown in the following chemical formula. This reaction mainly completes the silicon absorption process in the dripping zone. Injecting hydrogen into the blast furnace makes the high-temperature zone in the furnace move downward, the softening and melting zone of the blast furnace move downward, and the height of the dripping zone decreases. The reduction of Si requires a relatively high temperature, and the downward movement of the positions of the softening and melting zone and the dripping zone reduces the reaction interval for Si reduction.

[0028] SiO(g) + [C] = [Si] + CO(g)

[0029] Inject hydrogen in the blast furnace area, control the hydrogen injection rate and pressure to ensure that hydrogen can directly enter or promote the gas flow in the central area of the blast furnace. The main gas volume in the central burden is increased, the central gas flow is developed, the position of the softening-melting zone is lowered, reducing the reaction interval for Si reduction.

[0030] A hydrogen injection device in a blast furnace, as shown in Figure 1 , introduce a hydrogen lance at the blast furnace, design and install a hydrogen injection system to ensure that it maintains an appropriate distance and angle from the pulverized coal injection stream, avoiding unnecessary chemical reactions or affecting the combustion efficiency caused by their direct interaction.

[0031] In a traditional blast furnace using pulverized coal injection, the theoretical combustion temperature generally remains between 2050°C and 2200°C. After injecting hydrogen into the blast furnace, according to theoretical calculations, the theoretical combustion temperature decreases and can even drop to about 1900°C. To ensure the stability and smoothness of blast furnace operation, the minimum limit of the theoretical combustion temperature of the hydrogen-rich gas usually needs to be set above 1900°C. The decrease in the theoretical combustion temperature helps to stabilize the thermal regime inside, reduce operational instability caused by temperature fluctuations, and lower the overall energy consumption and carbon emissions.

[0032] Research on low-silicon smelting found that the silicon content in the hot metal is the highest at the tuyere level. In the area above the tuyere line, the main process is the reduction of Si, during which the [Si] content in the hot metal gradually increases (i.e., the silicon-increasing process), so this area is called the silicon reduction zone or the silicon-increasing zone of hot metal; in the area below the tuyere horizontal line, an oxidation reaction occurs, resulting in a continuous decrease in the [Si] content in the hot metal (i.e., the desiliconization process), so this area is called the silicon oxidation zone or the desiliconization zone of hot metal.

[0033] SiO2 mainly comes from the ash of coke and pulverized coal and SiO2 in the slag. The reduction of SiO2 in the blast furnace occurs in the dripping zone, corresponding mainly to the hearth, and the reaction occurring at the lower interface of slag and iron is the re-oxidation of silicon in iron. Under high-temperature conditions, the silicon reduction in the dripping zone occurs in two steps. First, SiO2 undergoes a gasification reaction with C in the coke.

[0034] SiO 2 (s) + C(s) = SiO(g) + CO(g)

[0035] The SiO vapor rising with the gas is absorbed by the iron droplets or adsorbed on the coke lumps, and is reduced to Si by [C] in the iron and C in the coke.

[0036] SiO(g) + [C] = [Si] + CO(g)

[0037] When the iron droplet passes through the slag layer, SiO gas is oxidized by the oxides in the slag.

[0038] [Si] + 2(FeO) = (SiO 2 ) + 2[Fe]

[0039] In a traditional blast furnace, when the [Si] content of the hot metal reaches 0.30% - 0.55%, it is considered low silicon. When the [Si] content of the hot metal is less than 0.30%, it is identified as ultra-low silicon. After introducing the hydrogen injection technology, in most cases, the [Si] content of the industrially produced hot metal is between 0.1% and 0.2%, achieving the goal of producing ultra-low silicon hot metal.

[0040] After introducing hydrogen injection into the blast furnace, it can bring many positive effects. On the premise of keeping other operating parameters of the blast furnace unchanged, by accurately calculating and optimizing the hydrogen injection volume, it can not only ensure the stability of the internal heat cycle area of the blast furnace, but also reduce the theoretical combustion temperature within a reasonable range, producing ultra-low silicon hot metal with low carbon.

[0041] In the method for producing low-silicon hot metal by hydrogen injection according to the present invention, hydrogen injection includes: a reference mode, a peak heat supplement mode, and a silicon stabilization and carbon reduction mode. In the reference mode, normal-temperature hydrogen-rich gas with a concentration of 60% is used for injection. When the hot metal temperature is lower than 1480 °C, it enters the peak heat supplement mode, and hydrogen-rich gas with a concentration greater than 80% preheated to 400 °C is used for injection. When the [Si] content of the hot metal is greater than 0.4%, it enters the silicon stabilization and carbon reduction mode, and normal-temperature hydrogen with a concentration greater than 99% is used for injection until the hot metal temperature rises back to 1500 °C and [Si] ≤ 0.3%, and then it switches back to the reference mode.

[0042] Example: Application in a 3800m 3 blast furnace

[0043] Operating conditions background:

[0044] Raw material conditions: The proportion of sintered ore is 78%, the coke load is 4.8, and the baseline value of [Si] in the hot metal is 0.45%

[0045] Goal: Hot metal temperature ≥ 1480 °C, [Si] ≤ 0.25%, CO emissions per ton of iron 2 < 1.35t

[0046] Implementation process:

[0047] Stage 1: Peak heat supplement

[0048] It is monitored that the hot metal temperature drops suddenly to 1465 °C (due to the excessive moisture content of the coke), triggering the injection of 80% hydrogen-rich gas (flow rate 8500m 3 / h). Operating parameters: Injection pressure: 1.2 MPa; Gas composition: 80% H2 + 15% CH4 + 5% N2 (explosion-proof dilution); Preheating temperature: 400 ± 15 °C

[0049] After 30 minutes, the temperature rises back to 1502 °C, and the silicon content briefly rises to 0.48%.

[0050] Stage 2: Stabilize silicon and reduce carbon

[0051] Switch to pure hydrogen injection (pressure 0.75 MPa, flow rate 6200 m 3 / h), and after continuous operation for 12 hours, [Si] drops to 0.22%.

[0052] Operating parameters: Injection pressure: 0.7 MPa; Hydrogen source: Electrolytic hydrogen production (dew point ≤ -60 °C, oxygen content < 10 ppm)

[0053] Flow control: Linearly adjust according to the excess amplitude of [Si] (increase the hydrogen injection volume by 8% for every 0.1% [Si]); Synchronously reduce the pulverized coal injection volume (from 160 kg / t hot metal to 132 kg / t hot metal).

[0054] Table 1 Comparison of energy efficiency data

[0055] Index Before transformation Gradient injection mode Change range Hot metal [Si] 0.43％ 0.21％ ↓51％ Coke ratio per ton of hot metal 325 kg 282 kg ↓13.2％ Theoretical combustion temperature 2140℃ 1925℃ ↓215℃ <![CDATA[CO 2 Emission intensity]]> 1.62 t / t hot metal 1.28 t / t hot metal ↓21.0％ <![CDATA[Top gas H 2 content]]> 3.8％ 9.2％ ↑142％

[0056] In the drawings, components with the same structure are denoted by the same reference numerals, and components with similar structures or functions everywhere are denoted by similar reference numerals. The dimensions and thicknesses of each component shown in the drawings are arbitrarily shown, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustration clearer, the thicknesses of some components in the drawings are appropriately exaggerated.

[0057] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A method for producing low-silicon molten iron by hydrogen injection in a blast furnace, characterized in that: The following steps are involved: (1) Hydrogen injection system settings: A hydrogen spray gun is arranged above the coal gas spray gun in the tuyere area of ​​the blast furnace, the spray direction of the hydrogen spray gun forms an angle θ with the coal powder spray flow, and 15°≤θ≤45° and the distance between the two is ≥200mm, and the spray medium is hydrogen-rich gas with a hydrogen volume concentration of ≥50%; (2) Gradient injection control: When the molten iron temperature T is detected to be less than 1480°C, the heat compensation mode is turned on to spray hydrogen-rich gas preheated to 300-450°C, with a hydrogen concentration of 80%-90%, a flow rate of 10-15m / s, and a spraying pressure of 1.2-1.8MPa; When the silicon content [Si] of molten iron is greater than 0.4%, the silicon suppression mode is switched to spray hydrogen with a purity of ≥99% at room temperature, with a flow rate of 6-8m / s and a spray pressure of 0.5-0.9MPa.

2. The method for producing low-silicon molten iron by hydrogen injection in a blast furnace according to claim 1, wherein: The combustion heat generated by hydrogen injection compensates for the physical heat of the furnace. The theoretical combustion temperature is controlled within 1850-1950°C. By lowering the temperature in the furnace belly area, the soft melting zone moves down 1.2-1.8 meters, and the gasification rate of SiO gas is reduced by ≥35%.

3. The method for producing low-silicon molten iron by hydrogen injection in a blast furnace according to claim 1, wherein: By regulating the hydrogen flow rate, the furnace top pressure is increased to 220-260 kPa, the central airflow intensity is increased by 20%-30%, the reducing gas partial pressure is increased to 0.12-0.18 MPa, and the contact time between liquid slag and SiO gas is shortened to 2-4 seconds.

4. The method for producing low-silicon molten iron by hydrogen injection in a blast furnace according to claim 1, wherein: When the molten iron temperature rises back to 1500°C and [Si]≤0.3%, it switches back to the reference mode and uses room temperature hydrogen-rich gas with a concentration of 60%.

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