EP-4737892-A1 - METHOD FOR ANALYZING MOLTEN SLAG

Abstract

The present invention provides a molten slag analysis method that can quickly and accurately obtain the basicity and the iron oxide content of molten slag based on a relationship between the impedance between electrodes immersed in the molten slag and the temperature of the molten slag. This method is characterized by including: a first step of measuring a reference slag temperature of reference molten slag, and measuring a reference impedance of the reference molten slag by applying an alternating current between a pair of electrodes immersed in the reference molten slag at the reference slag temperature; a second step of creating a constituent content calibration curve from a content of the constituent included in the reference molten slag and the reference impedance measured in the first step; a third step of measuring a slag temperature of molten-slag-being-measured, and measuring a measured impedance at the slag temperature; and a fourth step of estimating a content of the constituent included in the molten-slag-being-measured based on the measured impedance and the constituent content calibration curve.

Inventors

• KIYOIZUMI, KOTA

Assignees

• JFE Steel Corporation

Dates

Publication Date

20260506

Application Date

20240315

Claims (6)

1. A molten slag analysis method that analyzes a constituent of molten slag, comprising: a first step of measuring a reference slag temperature of reference molten slag, and measuring a reference impedance of the reference molten slag by applying an alternating current between a pair of electrodes immersed in the reference molten slag at the reference slag temperature; a second step of creating a constituent content calibration curve from a content of the constituent included in the reference molten slag and the reference impedance measured in the first step; a third step of measuring a slag temperature of molten-slag-being-measured, and measuring a measured impedance by applying the alternating current between the pair of electrodes immersed in the molten-slag-being-measured at the slag temperature; and a fourth step of estimating a content of the constituent included in the molten-slag-being-measured based on the measured impedance and the constituent content calibration curve.
2. The molten slag analysis method according to claim 1, wherein the constituent is iron oxide, and the constituent content calibration curve is an iron oxide content calibration curve.
3. The molten slag analysis method according to claim 1, wherein: the constituent is a specific constituent needed to calculate a basicity of the reference molten slag; and the constituent content calibration curve is a basicity calibration curve.
4. The molten slag analysis method according to any one of claims 1 to 3, wherein the reference impedance and the measured impedance are measured by applying alternating currents of two selected types of frequencies.
5. The molten slag analysis method according to claim 4, wherein: a voltage that is applied between the pair of electrodes is 10 mV or higher but 1.0 V or lower; and the two types of frequencies are respectively 10 Hz or lower and 10 kHz or higher.
6. The molten slag analysis method according to any one of claims 1 to 3, wherein a difference in immersion potentials in the molten-slag-being-measured between the pair of electrodes is less than 50 mV.

Description

Technical Field The present invention relates to a molten slag analysis method. In particular, the present invention relates to a molten slag analysis method that can obtain the basicity and the iron oxide content of molten slag based on a relationship between an impedance between a pair of electrodes immersed in the molten slag at a predetermined temperature of the molten slag and the content of a constituent included in the molten slag. Background Art In a steel refining process, the main purpose of a molten steel refining step is to remove impurities included in the molten steel, such as phosphorus, silicon, and sulfur, by supplying a refining agent, such as a CaO source, or oxygen to molten iron that is the main raw material of the molten steel. Generally, refining of molten steel is performed by oxidation refining or reduction refining. In steel refining, therefore, the basicity is employed as an index to evaluate the intensity of the basicity of molten slag. This basicity can be represented, for example, by a ratio between the content of CaO (%CaO) and the content of SiO2 (%SiO2) included in the molten slag. Thus, the basicity can be represented by (%CaO)/(%SiO2). In the molten steel refining step, feeding a predetermined amount of refining agent, such as a CaO source, into the molten steel can increase the basicity of the molten slag and thereby promote an oxidation reaction of the molten steel. In the molten steel refining step, a dephosphorization reaction of the molten steel is accompanied by a reduction reaction of iron oxide included in molten slag. Therefore, by manipulating the oxygen feeding speed and the level of a lance through which oxygen is supplied, the content of iron oxide included in the molten steel can be adjusted so as to promote the dephosphorization reaction of the molten steel. Thus, for impurities included in the molten steel, such as phosphorus, silicon, and sulfur, it is necessary to determine the amount to be fed of a refining agent, such as a CaO source, according to the amount to be removed of target impurity components and to feed the predetermined amount of refining agent into the molten steel. In the molten steel refining step, therefore, it is extremely important to analyze the slag composition of the molten slag present inside a furnace. To analyze the slag composition of molten slag, a quantitative analysis using the intensity of a fluorescent X-ray (hereinafter referred to as "fluorescent X-ray analysis method") has been hitherto widely adopted. A slag composition quantitative analysis method for molten slag using this fluorescent X-ray analysis method is as follows: First, part of the molten slag present inside a furnace is sampled, and the sampled slag is transferred to an analysis room to prepare a specimen for analysis. Thereafter, the prepared specimen for analysis is irradiated with a fluorescent X-ray (primary X-ray). Then, the intensity of a fluorescent X-ray (secondary X-ray) that is emitted from the specimen for analysis as the specimen for analysis is irradiated with the fluorescent X-ray (primary X-ray) is measured for each element. Finally, the content of each element is obtained from the measured value of the intensity of the fluorescent X-ray using a calibration curve indicating a relationship between the intensity of the fluorescent X-ray of each element and the content of each element that is created beforehand. In the fluorescent X-ray analysis method, however, determining the amount of each constituent included in molten slag with high accuracy requires preparing a specimen for analysis. In the fluorescent X-ray analysis method, preparing a specimen for analysis needed to determine the amount of each constituent included in molten slag with high accuracy requires a time of at least ten minutes or longer. Meanwhile, the slag composition of molten slag during converter blowing changes incessantly with time according to the degree of progress of the blowing. It is therefore grossly inaccurate to determine the amount to be fed of a refining agent or the blowing pattern based on the analysis result of the slag composition of the molten slag obtained by implementing the fluorescent X-ray analysis method. Under these circumstances, quick analysis technologies for slag compositions have been proposed. For example, Patent Literature 1 proposes a slag constituent analysis method that can quickly and highly accurately measure a slag constituent generated in refining molten iron. Specifically, the slag constituent analysis method described in Patent Literature 1 is an analysis method that irradiates a surface of a slag-being-analyzed with a pulsed laser multiple times to turn part of the slag into a plasma, and derives a target constituent concentration or constituent amount ratio from an emission spectrum that is acquired by spectrally dispersing excitation light obtained from the slag turned into a plasma. Further, Patent Literature 2 proposes an impedance