A brief introduction to the refining furnace

Research on refining technology began in 1968. At that time, it was found that the reduction refining effect was remarkable by pre-forming the reduction slag in the electric arc furnace, mixing the steel slag, and blowing the ladle with argon, so the development of the ladle refining technology with the arc heating function was carried out for the purpose of omitting the reduction period of the electric arc furnace. In 1971, the first Ladle Refining Furnace (LF) was put into use in Japan's Datong Special Steel Plant. In 1973, Nippon Steel Yawata Steel's converter plant installed LF.

The smelting process of scrap copper generally adopts a refining furnace. The refining furnace includes a combustion furnace arranged in the middle and a reverberatory furnace symmetrically arranged on both sides of the combustion furnace. The combustion furnace has a connecting channel with the two reverberatory furnaces. The refining furnace undertakes three main links: melting, oxidation and reduction. Among them, the melting and oxidation processes are completed in the combustion furnace, and the reduction process is completed in the reverberatory furnace. The practical application shows that the absolute value of the negative pressure in the combustion furnace is greater than the negative pressure in the reverberatory furnace. At the same time, due to the requirements of the process itself, the negative pressures of the combustion furnace and the reverberatory furnace are different, so that the negative pressures in the three furnace chambers are mutually exclusive. Not the same question. At present, most of the negative pressure control of scrap copper smelting has no practical and effective control strategy. Generally, multiple induced draft fans are set and the rotation speed of the induced draft fans is increased to ensure that the furnace body does not "spray fire" for the purpose. As a result, the quality of the anode plates produced cannot be guaranteed on the one hand; on the other hand, the energy consumption in the production process is also increased, and the production cost is increased.

Introduction to Refining Furnace

The process of slag-changing after tapping commonly used in electric furnace process and converter process, namely: electric arc furnace or converter tapping → LF refining (adding aluminum, adding slag material, adding Ca-Si or adding slag-modifying agent) → casting

LF is set in the electric arc furnace steelmaking plant, which reduces the reduction time of the electric arc furnace, and finally cancels the reduction period of the electric arc furnace. The smelting cycle of the electric arc furnace is shortened, the productivity of the electric arc furnace is improved, and at the same time, the continuous casting can be The molten steel with the requirements of temperature, composition and cleanliness ensures the smooth operation of the electric arc furnace + LF refining + continuous casting process, making the electric arc furnace develop into a high-efficiency short-process steelmaking method that can produce ordinary steel grades from ordinary scrap and pig iron , not just equipment for producing high-quality steel grades. The first stage of electric arc furnace development is the traditional electric arc furnace including melting, oxidation and reduction. The second stage is due to the type of electric arc furnace (tapping slot type electric arc furnace), in order to avoid the oxidation slag polluting the molten steel and play the role of deoxidation and desulfurization of the steel slag, the reducing slag must be made in the electric arc furnace. The steel slag is mixed out, and the LF is used to complete the task of further reduction and refining. The third stage is due to the development of slag-free tapping technology, and the reduction period is all completed by LF refining, that is, the form of modern electric arc furnace steelmaking process EAF+LF+CC is formed.

LF is used to produce special steel in the converter process, eliminating the way of distinguishing steel quality by steelmaking methods in the past, and establishing the idea of "primary smelting (electric furnace or converter) + LF refining + continuous casting" to produce multi-variety, high-quality steel . After the successful development of LF technology, it developed in the direction of multi-function. In 1981, the NK-AP method was developed at the Japanese Steel Pipe Fukuyama Steel Works. That is, the wiping-in spray gun replaces the breathable brick for gas stirring method. In 1987, a spray equipment and LF for vacuum equipment.

Due to the simple structure of the LF device. It has a variety of metallurgical functions, flexibility in use, remarkable refining effect, and high economic benefits, and has become an important equipment in the steel production process.

Process analysis

LF furnace refining is one of the main methods of out-of-furnace refining, and its key is to quickly produce white slag. The purpose of LF slag making is to desulfurize, deoxidize, improve alloy yield and remove inclusions. However, in the process of slag making of aluminum-controlled steel, there are certain contradictions in desulfurization, returning to silicon, increasing nitrogen, and removing inclusions, which need to be considered as a whole. Rapid and stable production of reducing white slag with good fluidity and certain emulsification in LF is necessary for LF desulfurization, adsorption of inclusions and guarantee of molten steel quality.

Taking the European standard S235JR aluminum-controlled steel (low silicon steel) as an example, the production process flow: re-blowing converter → argon station → LF → CC. When the converter is tapping, the stirring kinetic energy during tapping is used, and an appropriate amount of lime is added to wash the pre-reduced slag to ensure the basicity and prevent the return of phosphorus and silicon; the whole process of tapping is softly stirred to uniform the composition and temperature; Or aluminum manganese magnesium) to deoxidize the molten steel; according to the amount of slag (generally, the amount of slag is about 5kg/t), add an appropriate amount of modifier in time after tapping; use high-carbon manganese for alloying.

Through the analysis of the slagging process, the slag composition transformation process, and the comprehensive basicity change of the slag, the following technical measures for rapid white slag production are obtained:

(1) The advance modification of the converter tapping slag can provide favorable conditions for the rapid slagging of LF; at the same time, the converter tapping should also be strictly controlled: supplementary blowing, slag blocking, bottom blowing, package condition, and one-time deoxidation.

(2) Rapid slagging in the early stage is the premise of slagging. Control points: rapid heating, submerged arc, stirring, and reasonable addition of slag-forming agent in batches.

(3) Strong stirring desulfurization (4.0~6.0L/(min·t)), the speed should be fast and the time should be short. While ensuring desulfurization, try to control the time of secondary oxidation and molten steel nitrogen absorption. Generally, it is completed within 10 to 20 minutes after the LF starts to be processed. This stage is the main stage of LF refining.

(4) After the desulfurization is completed, the main tasks of LF are temperature control, alloying and removal of inclusions. At this stage, the viscosity of the slag should be ensured and the stirring intensity should be controlled at 0.5-1.0L/(min·t) (with the liquid level fluctuating but not being exposed). The molten steel level is the principle), and the holding time is required to be greater than 8min.