A method for judging failure of a bottom gun of a converter

Abstract

The application discloses a method for judging failure of a converter bottom lance, comprising the following steps: 1) calculating a bottom lance ring gap permeability index a after converter tapping is finished, if a>0.2, it is considered that the bottom lance state is normal; if a≤0.2, calculating permeability index fluctuation stability S, if S≤0.04 and continuously reaching 3-5 heats, the following step 2) is performed; 2) measuring the thickness of the furnace bottom refractory of several heats, calculating the average erosion rate E and the average erosion depth δh of the refractory; 3) if: the average erosion rate E≥2.0 mm / heat, and the average erosion depth δh≥250 mm, the bottom lance is judged to be failed; if: the average erosion rate E≤1.5 mm / heat, and the average erosion depth δh<120 mm, the bottom lance is judged to be normal; otherwise, the bottom lance is judged to be in an unstable state. The application can accurately judge the failure time of the bottom lance, so that timely plugging measures can be taken to prevent bottom lance back burning and leakage accidents.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking technology in the metallurgical industry, and in particular, it is a method for determining the failure of the converter bottom lance. Background Technology

[0002] Large top-and-bottom blown converters are equipped with bottom lances or permeable bricks at the bottom. Oxygen, nitrogen, argon, and other gases are injected into the furnace through bottom pipes to enhance molten pool agitation and promote the steelmaking reaction. Benefiting from bottom blowing agitation, the blown converter has metallurgical advantages such as good molten pool uniformity, low oxygen content in the final molten steel, and high dephosphorization efficiency.

[0003] For conventional converters, the bottom blowing gas volume is controlled at 0.08 Nm. 3 Approximately / (min·t). Excessive bottom blowing intensity shortens the lifespan of the furnace bottom refractory material. Furthermore, with increasing furnace age, bottom blowing is prone to blockage during production, causing the bottom blowing function to fail. Generally, this is remedied by replacing the permeable bricks, or by continuously eroding the furnace bottom to expose the bottom lance again. Bottom blowing blockage and failure weaken molten pool stirring and worsen metallurgical indicators, but do not cause major accidents or hazards. However, bottom blowing oxygen and bottom powder injection converters use double sleeves at the bottom lance, allowing for the injection of lime powder and oxygen into the furnace bottom, achieving a bottom blowing intensity of 0.85 Nm. 3 / (min·t). The superior bottom-blowing intensity gives the smelting process advantages such as being greener, more efficient, and cleaner. During the smelting process, oxygen is injected through the bottom-blowing central tube; the outer sleeve and the central tube form an annular gap, through which natural gas is injected. The decomposition and heat absorption of natural gas cause the molten steel at the bottom of the lance to cool and solidify, forming a mushroom head that covers the annular gap and protects the bottom lance from high-temperature molten steel corrosion. The failure of bottom-blowing in bottom-blowing oxygen and bottom-injection powder converters differs significantly from that in conventional converters: First, blockage of the bottom lance during smelting causes natural gas to flow back into the central tube through the annular gap tube and mix with oxygen, leading to a combustion and explosion accident in the bottom-blowing pipeline and causing bottom lance failure; usually, it is necessary to clear the blockage according to the situation to prevent combustion and explosion accidents. Second, without the protection of the mushroom head, the bottom lance and the surrounding refractory material burn back, forming erosion pits, leading to bottom lance failure. After the bottom lance fails, the natural gas in its annular gap tube mixes and burns with the oxygen in the central tube below the refractory material, intensifying the erosion of the bottom lance and refractory material, causing bottom lance burn-back accidents, and even causing molten steel to backflow into the bottom lance and causing steel leakage accidents. For the failure of the bottom gun caused by combustion, explosion, or backfire, the failed bottom gun is usually removed and sealed with refractory material.

[0004] However, there is no accurate method for judging the failure of the bottom lance to reheat, and judgment is often made based on the experience of the workers. This poses a significant safety hazard to the bottom-blown converter operation. If the failure of the bottom lance is not identified in a timely and accurate manner, it will cause a bottom lance reheating accident, which may lead to major safety accidents such as steel leakage from the furnace bottom. If the bottom lance is normal but is wrongly judged to be failed, it will be removed and sealed with refractory materials. This not only shortens the service life of the bottom lance and increases operating costs, but also weakens the advantages of bottom-blown metallurgy and worsens metallurgical indicators. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for accurately judging the failure of the converter bottom gun.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes the following steps:

[0007] 1) After the converter tapping is completed, calculate the permeability index a of the bottom lance circumferential seam. If a > 0.2, the bottom lance is considered to be in normal condition. If a ≤ 0.2, calculate the permeability index fluctuation stability S. If S ≤ 0.04 and reaches 3 to 5 heats consecutively, proceed to step 2).

[0008] 2) Measure the thickness of the refractory material at the bottom of several furnaces, and calculate the average erosion rate E and the average erosion depth δh of the refractory material;

[0009] 3) If the average erosion rate E ≥ 2.0 mm / furnace and the average erosion depth δh ≥ 250 mm, then the bottom gun is deemed to have failed.

[0010] If the average erosion rate E ≤ 1.5 mm / furnace and the average erosion depth δh < 120 mm, then the bottom lance is considered normal.

[0011] Otherwise, the bottom gun is determined to be in an unstable state.

[0012] Furthermore, in step 1), the air permeability index α of the bottom gun circumferential seam is calculated using the following formula (1):

[0013] a = P s / F s (1);

[0014] In the formula: F s The flow rate of the gas in the bottom gun annular gap, Nm 3 / min; P s The pressure of the gas in the bottom gun circumferential slit is MPa.

[0015] Furthermore, in step 1), several bottom gun circumferential seam air permeability indices a are calculated, and the maximum air permeability index is found to be MAX(a) and the minimum air permeability index is found to be MIN(a). The air permeability index fluctuation stability S is calculated using the following formula (2):

[0016] S = MAX(a) - MIN(a) (2).

[0017] Furthermore, calculate the air permeability index 'a' for at least 30 bottom gun circumferential seams.

[0018] Furthermore, the calculation process for the average erosion rate E in step 2) is as follows: calculate the average thickness of the refractory material in the base gun area, using h i This represents the average thickness of the refractory material measured in the i-th thickness measurement, relative to h. i A linear fit was performed, and the slope was denoted as the average erosion rate of the refractory material, E, in mm / furnace.

[0019] Furthermore, the base gun area is an annular area with a radius of 25 to 50 mm around the base gun.

[0020] Furthermore, the calculation process for the average erosion depth δh in step 2) is as follows: calculate the average thickness of the refractory material around the base gun, and calculate the average erosion depth δh using the following formula (3):

[0021] δh=(∑(H i -h i )) / n (3)

[0022] In the formula: n is the number of thickness measurements; H i h represents the average thickness of the refractory material measured in the i-th thickness measurement area of ​​the bottom gun region, in mm. i This represents the average thickness of the refractory material in the area surrounding the bottom gun during the i-th thickness measurement, in mm.

[0023] Furthermore, the area surrounding the base gun is an annular region with a radius of 200-300mm around the base gun.

[0024] The beneficial effects of adopting the above technical solution are as follows: This invention can accurately determine the timing of bottom lance failure, thereby enabling timely sealing measures to prevent bottom lance backburning and steel leakage accidents, extending the service life of the bottom lance, reducing operating costs, and ensuring long-term stable operation of bottom blowing. This invention uses standard logical judgment and formulas to quantitatively determine bottom lance failure conditions and can operate online; compared with manual experience-based judgment, it is more accurate, safe, and reliable. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to specific embodiments.

[0026] The method for determining the failure of the converter bottom lance includes the following steps:

[0027] 1) Bottom-blown gas permeability index a and its fluctuation stability S: The bottom-blown gas in the circumferential gap is nitrogen, and the flow rate is controlled at 25-30 Nm³. 3 / min; the flow rate F of the gas in the bottom gun annular gap s and pressure P s Calculate the air permeability index 'a' of the bottom gun circumferential seam, where the flow rate F s and pressure P s The results are obtained from the inspection table on the circumferential welded pipe and calculated using the following formula (1):

[0028] a = P s / F s (1);

[0029] In the formula: F s The flow rate of the gas in the bottom gun annular gap, Nm 3 / min; P s ρ is the pressure of the gas in the bottom gun circumferential seam, MPa; a is the air permeability index of the bottom gun circumferential seam.

[0030] If a > 0.2, the bottom gun is considered to be in normal condition, and there is no need to collect the air permeability index again for further judgment in the short term; if a ≤ 0.2, the air permeability index fluctuation stability S is calculated.

[0031] The calculation process for the air permeability index fluctuation stability S is as follows: calculate the bottom gun circumferential seam air permeability index a once per second, and obtain at least 30, preferably 30-40 bottom gun circumferential seam air permeability index results, where the maximum value is MAX(a) and the minimum value is MIN(a); characterize the air permeability index fluctuation stability S by the range, and calculate the air permeability index fluctuation stability S using the following formula (2):

[0032] S = MAX(a) - MIN(a) (2);

[0033] In the formula: MAX(a) is the maximum value of the calculated bottom gun circumferential seam air permeability index; MIN(a) is the minimum value of the calculated bottom gun circumferential seam air permeability index; S is the stability of the air permeability index fluctuation;

[0034] If S≤0.04 and at least 3 heats are achieved consecutively, preferably 3 to 5 heats, then proceed to step 2) below; otherwise, repeat this step.

[0035] 2) Erosion characteristics of the bottom lance and surrounding refractory: The thickness of the bottom lance and surrounding refractory is measured using a thickness gauge. Before measuring the thickness of the converter, the slag splashing operation is not performed. The converter slag is completely poured out and measured after pouring. The thickness of the bottom refractory is measured for several heats. It is preferred to control the measurement to 1 to 3 heats / time, and a total of at least 5 times, preferably 5 to 8 times.

[0036] The average erosion rate E of the refractory is calculated as follows: The average thickness of the refractory in the lance area is calculated; the lance area is a ring-shaped region with a radius of 25–50 mm around the lance; h is used as the erosion rate. iThis represents the average thickness of the refractory material measured in the i-th thickness measurement of the bottom gun region, relative to h. i A linear fit was performed, and the slope was denoted as the average erosion rate of the refractory material, E, in mm / furnace.

[0037] The average erosion depth δh is calculated as follows: Calculate the average thickness of the refractory material around the base gun, where the area around the base gun is a ring-shaped area with a radius of 200-300 mm; calculate the average erosion depth δh using the following formula (3):

[0038] δh=(∑(H i -h i )) / n (3)

[0039] In the formula: n is the number of thickness measurements; H i h represents the average thickness of the refractory material measured in the i-th thickness measurement area of ​​the bottom gun region, in mm. i This represents the average thickness of the refractory material in the area surrounding the bottom gun during the i-th thickness measurement, in mm.

[0040] 3) Determine whether the bottom lance has failed based on erosion characteristics: If the average erosion rate E≥2.0mm / furnace and the average erosion depth δh≥250mm, the bottom lance is determined to have failed; the bottom lance should be removed in time and sealed with refractory material.

[0041] If the average erosion rate E ≤ 1.5 mm / furnace and the average erosion depth δh < 120 mm, the bottom lance is considered normal; there is no need to remove the bottom lance. The proportion of annular gas flow rate during the smelting process should be increased to 15-18 vol% to promote mushroom head formation. The annular gas flow rate proportion is the ratio of the smelting annular gas flow rate to the central tube gas flow rate. Natural gas is injected into the annular gap, and oxygen is injected into the central tube, with the oxygen flow rate controlled at 35-45 Nm³. 3 / min.

[0042] In other cases, the bottom gun is determined to be in an unstable state; there is no need to remove the bottom gun temporarily, and the above steps 1)-3) are taken to monitor the changes in the bottom gun's state.

[0043] Example 1:

[0044] After tapping from the converter, the bottom blowing gas is nitrogen, and the gas flow rate at the bottom lance annular gap is 3.00 Nm³. 3 The pressure at the circumferential seam is 0.60 MPa, and the calculated air permeability index a = 0.2, which meets the requirement of ≤0.2. Air permeability data is calculated and collected every second, totaling 30 values, as shown in Table 1 below. The calculated air permeability index range S = 0.036, and it meets the requirement of S ≤ 0.04, which has been maintained for more than 3 furnace cycles.

[0045] The converter slag was completely poured out. Thickness measurements were taken once per heat using a thickness gauge, for a total of 5 measurements, as shown in Table 2 below. The calculated erosion rate E of the refractory material around the bottom lance was 2.3 mm / heat, and the average erosion depth δh was 311 mm.

[0046] Failure conditions are met: average erosion rate E ≥ 2.0 mm / furnace and δh ≥ 250 mm. The bottom lance is deemed to have failed, and it should be promptly removed and sealed with refractory material.

[0047] Example 2:

[0048] After tapping from the converter, the bottom blowing gas is nitrogen, and the gas flow rate at the bottom lance annular gap is 2.50 Nm³. 3 The pressure at the circumferential seam was 0.48 MPa, and the calculated air permeability index a = 0.19, which meets the requirement of ≤0.2. Air permeability data was calculated and collected every second, totaling 40 values, as shown in Table 1 below. The calculated air permeability index range S = 0.038, and it met the requirement of S ≤ 0.04, which lasted for more than 5 furnace cycles.

[0049] The converter slag was completely poured out. Thickness measurements were taken every 3 heats using a thickness gauge, for a total of 8 measurements, as shown in Table 2 below. The calculated erosion rate E of the refractory material around the bottom lance was 2.8 mm / heat, and the average erosion depth δh was 285 mm.

[0050] Failure conditions are met: average erosion rate E ≥ 2.0 mm / furnace and δh ≥ 250 mm. The bottom lance is deemed to have failed, and it should be promptly removed and sealed with refractory material.

[0051] Example 3:

[0052] After tapping from the converter, the bottom blowing gas is nitrogen, and the gas flow rate at the bottom lance annular gap is 2.80 Nm³. 3 The pressure at the circumferential seam was 0.49 MPa, and the calculated air permeability index a = 0.17, which meets the requirement of ≤0.2. Air permeability data was calculated and collected every second, totaling 30 values, as shown in Table 1 below. The calculated air permeability index range S = 0.028, and it met the requirement of S ≤ 0.04, which lasted for more than 3 furnace cycles.

[0053] The converter slag was completely poured out. Thickness measurements were taken every two heats using a thickness gauge, for a total of six measurements, as shown in Table 2 below. The calculated erosion rate E of the refractory material around the bottom lance was 1.2 mm / heat, and the average erosion depth δh was 108 mm.

[0054] If the bottom gun is deemed not to have failed, it does not need to be removed. The proportion of gas flow in the annular seam during the smelting process is increased to 15-18%, promoting mushroom head formation.

[0055] Example 4:

[0056] After tapping from the converter, the bottom blowing gas is nitrogen, and the gas flow rate at the bottom lance annular gap is 2.80 Nm³.3 The pressure at the circumferential seam is 0.62 MPa, and the calculated air permeability index a = 0.22, which does not meet the requirement of an air permeability index > 0.2. Therefore, the bottom gun is considered to be in normal condition, and no further air permeability index measurement is needed for further judgment.

[0057] Example 5:

[0058] After tapping from the converter, the bottom blowing gas is nitrogen, and the gas flow rate at the bottom lance annular gap is 2.50 Nm³. 3 The pressure at the circumferential seam is 0.48 MPa, and the calculated air permeability index is a = 0.19, which meets the requirement of ≤ 0.2. Air permeability data is calculated and collected every second, totaling 30 values, as shown in Table 1 below. The calculated air permeability index range is S = 0.033, and it meets the requirement of S ≤ 0.04 for more than 3 furnace cycles.

[0059] The converter slag was completely poured out. Thickness measurements were taken once per heat using a thickness gauge, for a total of 6 measurements, as shown in Table 2 below. The calculated erosion rate E of the refractory material around the bottom lance was 1.8 mm / heat, and the average erosion depth δh was 157 mm. Therefore, the bottom lance was determined to be in an unstable state and did not require immediate removal; further assessment of its condition is needed.

[0060] Table 1: Air permeability data collected in each embodiment

[0061]

[0062] Table 2: Measurement results of refractory thickness around the furnace bottom lance in each embodiment

[0063]

[0064] Statistical Case: This method has been applied in over 2000 heats in bottom-blown oxygen and bottom-injection pulverized iron converters, accurately identifying over 50 bottom lance failures. This has effectively prevented accidents and steel leakage caused by bottom lance failures, ensuring the long-term stability of bottom-blown operation. In the first 5000 heats of this invention, a total of 12 bottom lance failures led to bottom lance backfire, resulting in 6 instances of molten steel backflow and leakage.

Claims

1. A method for determining the failure of a converter bottom lance, characterized in that, Includes the following steps: 1) After the converter tapping is completed, calculate the permeability index 'a' of the bottom lance circumferential seam. If 'a' > 0.2, the bottom lance is considered to be in normal condition. If 'a' ≤ 0.2, calculate the permeability index fluctuation stability 'S'. If 'S' ≤ 0.04 and reaches this level continuously for 3 to 5 heats, proceed to step 2). 2) Measure the thickness of the refractory material at the bottom of several furnaces, and calculate the average erosion rate E and the average erosion depth δh of the refractory material; 3) If the average erosion rate E ≥ 2.0 mm / furnace and the average erosion depth δh ≥ 250 mm, then the bottom gun is deemed to have failed. If the average erosion rate E ≤ 1.5 mm / furnace and the average erosion depth δh < 120 mm, then the bottom lance is considered normal. Otherwise, the bottom gun is determined to be in an unstable state; In step 1), the air permeability index α of the bottom gun circumferential seam is calculated using the following formula (1): a = P s / F s (1); In the formula: F s The flow rate of the gas in the bottom gun annular gap, Nm 3 / min; P s The pressure of the gas in the bottom gun circumferential slit, in MPa; In step 1), several bottom gun circumferential seam air permeability indices a are calculated, and the maximum air permeability index is found to be MAX(a) and the minimum air permeability index is found to be MIN(a). The air permeability index fluctuation stability S is calculated using the following formula (2): S = MAX (a) - MIN (a) (2).

2. The method for determining the failure of a converter bottom lance according to claim 1, characterized in that: Calculate the air permeability index a for at least 30 bottom gun circumferential seams.

3. The method for determining the failure of a converter bottom lance according to claim 1, characterized in that, The calculation process for the average erosion rate E in step 2) is as follows: calculate the average thickness of the refractory material in the bottom gun area, using h i This represents the average thickness of the refractory material measured in the i-th thickness measurement, relative to h. i A linear fit was performed, and the slope was denoted as the average erosion rate of the refractory material, E, in mm / furnace.

4. The method for determining the failure of a converter bottom lance according to claim 3, characterized in that: The base gun area is an annular area with a radius of 25 to 50 mm around the base gun.

5. A method for determining the failure of a converter bottom lance according to any one of claims 1-4, characterized in that, The calculation process for the average erosion depth δh in step 2) is as follows: calculate the average thickness of the refractory material around the base gun, and calculate the average erosion depth δh using the following formula (3): δh=(∑(H i -h i )) / n (3) In the formula: n is the number of thickness measurements; h i H represents the average thickness of the refractory material measured in the i-th thickness measurement area of ​​the bottom gun region, in mm; i This represents the average thickness of the refractory material in the area surrounding the bottom gun during the i-th thickness measurement, in mm.

6. The method for determining the failure of a converter bottom lance according to claim 5, characterized in that: The area surrounding the base gun is a ring-shaped area with a radius of 200-300mm around the base gun.

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