Operation process of AOD steelmaking furnace
1、 Process flow:
Main tasks of AOD furnace: oxygen blowing decarburization, desulfurization, alloying, adjusting chemical composition, and controlling tapping temperature. (Process drawing is omitted)
2、 AOD furnace type and process parameters
Table 1: AOD Furnace Type Parameters
3、 Raw material standard of AOD furnace
AOD's requirements for crude steel are inspected by sampling and analysis in the ladle after the converter is discharged, and the requirements are as follows:
2. The requirements for auxiliary materials are as follows:
3. Requirements for gas: gas header pressure ≥ 1.6Mpa
4、 Preparation before converting
1. Before steel mixing, check whether AOD furnace air, water, electricity and gas are normal. Whether the air circuit instrument is sensitive and reliable, whether the tilting equipment can operate normally, and whether the process interlocking is normal.
2. Before iron mixing, confirm whether the chemical composition of semi steel meets the requirements of AOD furnace.
3. Check that various feeding systems, weighing systems and water cooling systems operate normally.
5、 Precautions for replacing furnace body for installing nozzle oxygen lance
Install the nozzle oxygen lance
The installation of nozzle oxygen lance with an included angle of 60 ° is a key operation directly related to AOD furnace order. The following points must be noted during installation:
1. Before installation, first check whether the red copper core pipe is matched with the stainless steel pipe, whether the core pipe is unblocked, and whether the connection part is damaged. The unqualified core pipe shall be stopped or can only be used after it is confirmed to be reliable by processing.
2. When installing the nozzle of the oxygen lance, the gasket shall be filled with even and appropriate size, and each pipe joint shall be wrapped with raw material belt to make it tight and sealed without air leakage.
3. After the installation, the nozzle shall be fixed on the furnace body, and the spot welding nozzle shall be fixed without all welding.
6、 Operation during oxidation period
1. The operation of the decarburization phase is the key to the whole refining process of AOD. Only by strictly abiding by the gas supply system can the goal of removing C and maintaining Cr be achieved.
Process flow of converting gas supply for AOD furnace in each phase
(Process drawing is omitted)
Input it into the intelligent system according to the number, temperature, molten steel weight, initial value and target value of corresponding molten steel composition, and then select the smelting stage. The system will automatically select the mixed gas of different proportions of emotional gas and oxygen for blowing at the same time from the tuyere and top gun according to different smelting stages. The operator can use the computer to prompt the addition of alloy and slag. When the end carbon is reached, the system will calculate the amount of reductant added and conduct reduction refining.
7、 Oxygen supply system:
1. The top lance oxygen supply operation and lance position control are the same as the converter oxygen lance operation. When C is high in the early stage, the top gun can be used for decarburization. The gun position shall be controlled at 1.6m ± 100mm. When the carbon is reduced to 0.30%, stop the top gun oxygen supply. The oxygen supply is 60% of the total oxygen supply.
2. In principle, the oxygen supply intensity of the gas supply system is 1.0m3/t.min ～ 1.5m3/t.min, the smelting cycle is 60 minutes, and the oxygen flow is controlled at 5100m3/h ～ 7650m3/h.
3. The oxygen distribution of seven oxygen lances is 728-1029m3/h; Argon distribution is 182~257m3/h.
4. In the whole refining process, with the decrease of carbon content and the increase of molten steel temperature, the ratio of oxygen to inert gas continuously changes from 4:1 to 1:4. On the premise of ensuring the nitrogen content of finished products, N2 can be used to replace Ar to the maximum extent.
5. At the end of the oxidation period, observe the flame, control the terminal carbon, and take the oxidation sample to analyze the chemical composition at the end of the oxidation period.
8、 Slagging system:
As AOD has strong stirring effect, low iron oxide content in the slag and difficult lime melting, it is required to add as little lime as possible on the premise of meeting process requirements. If slagging is difficult, appropriate slagging agent can be added to promote slagging.
Alkalinity requirements: alkalinity 1.8~2.0 in oxidation period and 2.0~2.2 in reduction period
The first batch of materials shall be added at the same time of blowing. According to the temperature of semi steel molten steel, 20%~30% of the total amount of lime shall be added; The remaining slag materials are added in 5-7 batches, about 10%~15% each time.
The addition amount of light burned dolomite shall ensure that the MgO content in the slag is about 10%, which shall be added in batches.
Fluorite is added in the reduction period, and the appropriate amount is 10% of lime.
9、 Desulfurization operation
With the development of desulfurization process, AOD has achieved satisfactory results in actual production by using AI+FeSi to replace FeSi for desulfurization. The sulfur content can be controlled below 0.004%, and the reduction refining time can be shortened by 10 minutes.
Table 4 Comparison of desulfurization effect of AOD refining with A1+FeSi and FeSi
10、 Pre original operation:
Add Fe Si according to C content and blow Ar for more than 3 minutes
Precautions: When C ＜ 0.03%, add Fe Si 30kg/T: 0.03% - 0.06%, add Fe Si 25kg/T
＞ 0.08%, add Fe Si 20kg/T
Pour out 80%~85% of pre reduced slag in the furnace
11、 Restore Period Operation
Operation instruction: add 10 kg CaO and fluorite (3:1) to each ton of molten steel, and add Si powder or Si Ca powder to adjust the slag.
After the end point carbon is confirmed to be suitable, MnSi alloy, FeSi, ferrochrome, etc. shall be added according to the requirements of steel type for reduction, and a certain amount of fluorite shall be added according to the slag alkalinity to produce foam slag with good fluidity. After the alloy is fully dissolved, the furnace shall be switched over, temperature measured, and sampling shall be conducted. Adjust the composition to the control target, and the argon blowing time is ≥ 4 minutes.
matters needing attention:
(1) The slag has good fluidity and high alkalinity foam slag;
(2) The tapping temperature is about 1640 ℃, and the temperature of molten steel in the ladle is 1590 ± 10 ℃.
12、 Tapping conditions:
1. The chemical composition enters the control target.
2. Slag requirements: foam slag with high alkalinity and good fluidity.
3. Tapping temperature requirement: 1640 ± 10 ℃
Xi'an Qindong Metallurgical Equipment Manufacturing Co., Ltd. was established on January 23, 2009. The company is located in Xi'an, Shaanxi Province, China. Its leading businesses are metallurgical equipment design and manufacturing, environmental protection and dust removal technology design, smelting raw material treatment and advanced smelting process technology development. The company's vision is to become a service-oriented leading enterprise that can provide users with advanced and applicable complete smelting technology solutions, The company is determined to build "Qindong Metallurgy" into an excellent brand in the electric furnace industry. The company is committed to the design, manufacturing, sales, installation and service of EAF steelmaking electric arc furnace, LF ladle refining furnace, DC DC electric arc furnace, VOD, AOD refining furnace, ferroalloy electric arc refining furnace. Tel.: 13389219118/13630250959.