The Methodology Development for Improving Energy Utilization and Reducing Fluoride Pollution of the Electroslag Remelting Process: A Review

Abstract

Traditional electroslag remelting (ESR) technology using the slag with a high CaF2 content is faced with a high specific power consumption and fluoride pollution. Under double pressure, it is therefore very important to have a good understanding of the ESR process. The energy utilization, η, of the ESR depends on both the electrical, ηE, and thermal efficiency, ηH. Tailoring slag composition is one of the useful techniques to enhance energy utilization, because slag is very important to generate Joule heat for melting electrodes, control horizontal heat transfer, and maintain uniform distribution of alloy elements from the bottom to top of the remelted ingots in the ESR process. Therefore, herein, the aim is to review the effects of slag composition, especially CaF2 content, and temperature on the electrical conductivity and thermal conductivity, which further influence the heat balance during the ESR process. The volatilization mechanism of the liquid fluoride‐containing slag at an elevated temperature is introduced from the perspective of thermodynamics and kinetics. Meanwhile, some of the recent advances and technology improvements in energy utilization and productivity enhancements for the ESR process are summarized, which provide benefits to achieve sustainable development for the ESR process.

Effect of Different Remelting Parameters on Slag Temperature and Energy Consumption during ESR

“…However, the rising awareness and the regulatory requirements regarding sustainability, environmental protection and emissions control along the entire process chain have recently activated new awareness for this topic. 4,5) Based on data in 4), estimating the total annual ESR production with 2 million tons, and assuming a rather optimistic average energy consumption of 1 000 kWh/t, ESR accounts for at least 2 TWh in annual consumption of electric energy worldwide.…”

“…Furthermore, low-CaF 2 containing, high-resistivity slags contribute to reduced fluorine pollution. 5) Through other factors such as fill ratio and the amount of slag or the melt rate can also have a strong effect. 4) Such factors need to be taken into consideration when evaluating and comparing different results.…”

Investigation of fluoride evaporation from CaF2–CaO–Al2O3–MgO–TiO2–(Li2O) slag for electroslag remelting

“…The estimated diffusion coefficients of LiF and CaF 2 in Ar gas were also calculated using Eq. (11), and the values are listed in Table 5. The diffusion coefficient of LiF in Ar gas is higher than that of CaF 2 at a given temperature within the experimental range 1743-1803 K, which further confirms that the evaporation rate of LiF is higher than that of CaF 2 .…”

“…However, fluoride evaporation from high CaF 2 -content slags is a potential health- and safety hazard. Furthermore, it would alter the chemical composition and cause changes in the metallurgical properties of the slags 8 – 11 . Therefore, it is important to develop low-fluoride slags and study their effect on fluoride evaporation during the ESR process.…”

Fluoride Evaporation and Melting Characteristics of CaF2–CaO–Al2O3–MgO–Li2O–(TiO2) Slag for Electroslag Remelting

“…The main technique for developing lowfluoride slags is to control the CaO/Al 2 O 3 mass ratio and substitute a small amount of MgO or Li 2 O for CaF 2 to improve the physicochemical properties of ESR slags. [11][12][13][14] Adding a small amount of Li 2 O has been observed to significantly reduce slag viscosity, which is beneficial for as-cast ingot molding during ESR refining. [15] Based on this principle, CaF 2 -CaO-Al 2 O 3 -MgO-Li 2 O slag was designed for ESR processing.…”