Hot metal composition sensor and its application p

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Molten steel composition sensor and its application progress

I. Introduction

optimizing industrial process with computer control algorithm requires real-time process parameters. The degree to which a process is optimized depends on the quantity and quality of process information, so the development of advanced sensors can improve the control level of the process. The most important parameter in the iron and steel smelting process is the chemical composition of the metal melt. The content of oxygen, nitrogen, hydrogen and other elements in molten steel will increase when it is exposed to the atmosphere; Sometimes some elements will reduce their content in steel by interacting with refractory or atmosphere, which will affect the quality of steel. If we know the real-time information of the chemical composition of molten steel, we can actively control the steelmaking process. Therefore, people have developed various sensors for the determination of the chemical composition of molten steel

the dissolved gases oxygen, nitrogen and hydrogen in steel are important factors affecting the quality of steel. In recent years, the combined control of oxygen, nitrogen and hydrogen in steel has become more and more important. Hydrogen induced cracking of pinholes and bubbles is not entirely caused by a gas. The most effective method is to detect the concentration of these gases in the steel during the process. Silicon and sulfur are the "three removal" elements in hot metal pretreatment. With the increase of the proportion of hot metal pretreatment in China, it is more and more urgent to control the hot metal pretreatment process. This paper introduces the latest progress in the detection technology of these five elements

II. Various component sensors

1 Oxygen sensor

the oxygen sensor based on solid electrolyte, represented by the determination of oxygen in molten steel, has some unique advantages. The conductivity of solid electrolyte increases with the increase of temperature, so the high temperature of steelmaking is more suitable for solid electrolyte oxygen sensor; The output signal of the sensor is determined by the thermodynamic properties of the molten metal and the reference electrode, and calibration is not required; The output signal is DC voltage, so the external electronic device is relatively simple; In addition, ZrO2 Solid electrolyte is a stable compound, which can generally withstand the chemical attack of molten steel

oxygen content of converter blowing end point and molten steel after refining deoxidization can be measured by oxygen sensor. Oxygen sensor based on stabilized zirconia as solid electrolyte is the most successful component sensor in steelmaking industry. The reference electrode usually uses cr/cr2o3 mixture, and the balance between CR and Cr2O3 establishes a reference oxygen partial pressure, which forms a concentration cell with dissolved oxygen in molten steel. Although the oxygen sensor has been used for more than 40 years, there are still some areas that need to be improved

the first is to improve the service life. Current oxygen sensors are disposable and discarded. Extending the service life can not only improve the data quality (such as continuous measurement), but also reduce the cost. A method to prolong its service life is shown in Figure 1 (b) [2], which aims to improve the sealing of the reference electrode. Another method, as shown in Figure 1 (c), is to place the reference electrode above the molten steel, which is called a non isothermal sensor, but this introduces additional thermoelectric potential and needs to be compensated. Another way to prolong the service life of the sensor is to apply a reverse voltage to push the pointer to prevent the degradation of the reference electrode [6]. On the other hand, what needs to be improved is to expand the oxygen partial pressure of the oxygen sensor. If the damage is severe, the measuring range of the tension spring should be changed, especially the extremely low oxygen range. Molten steel with extremely low oxygen content will cause significant electronic conductivity of ZrO2 Solid electrolyte and make the sensor produce wrong output signal. The improved method uses other solid electrolytes to replace ZrO2, such as stable perovskite [5] or ThO2 solid electrolyte; Or the double-layer tube structure can not only prevent electronic conductivity, but also obtain better thermal vibration resistance [7]

Figure 1 several forms of zirconia solid electrolyte oxygen sensor

the problem faced by domestic oxygen sensors is the stability of the quality of oxygen probe, including the purity of solid electrolyte, the density of electrolyte tube after sintering, the purity and treatment process of reference electrode material, battery packaging quality, etc. As there are many processes from raw materials to finished products, there are also many factors that affect the final quality of the probe. In order to reach the advanced level, it is necessary to strengthen research and development. The electronic conductivity characteristic oxygen partial pressure of solid electrolyte must be accurately measured in order to correct the measurement results of molten steel with low oxygen content

2. Hydrogen sensor

although there is an oxide solid electrolyte that can conduct protons under certain conditions, it is technically impossible to use proton conducting solid electrolyte as a hydrogen sensor in steel because its hydrogen ion (proton) migration number is small at the high temperature of steel-making and it is not a pure proton conductor. However, the hydrogen sensor based on proton conducting solid electrolyte has been successfully used for the determination of hydrogen in liquid aluminum [8]

at present, the commonly used hydrogen sensor in molten steel is a device called hydrogen (hydrogen direct reading immersion system). [9] As shown in Figure 2, the carrier gas (nitrogen) is pumped into the molten steel through a conduit made of refractory materials. The bubbles of the carrier gas absorb the dissolved hydrogen in the steel. The porous refractory cover inserted in the molten steel collects these dissolved hydrogen gases. The carrier gas is continuously circulated in the hydris system until the hydrogen reaches the dissolution equilibrium. After filtration, it is introduced into the thermal conductivity cell for analysis. Compared with the usual sampling quenching hydrogen determination instrument, the determination time of hydras is shortened by 4~9min, and the accuracy is improved from s= 0.23 to 0.12. The system has been used in North American steel industry since 1987 and can measure

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