What is a Titanium Slag Smelting Electric Furnace?

What is a Titanium Slag Smelting Electric Furnace?

What is a titanium slag smelting electric furnace? The production of titanium slag adopts the electric furnace smelting process (divided into circular and rectangular furnaces according to their shapes), which can be divided into three types based on the different sealing methods of the electric furnace: closed electric furnace smelting, semi closed electric furnace smelting, and open electric furnace smelting.

Titanium slag is a high melting point smelting product. The molten titanium slag has strong corrosiveness, high conductivity, and the characteristic of its viscosity increasing dramatically near the melting point temperature. Moreover, these properties undergo drastic changes with the composition during the smelting process.

Titanium slag is a type of titanium rich material, which is a titanium mineral raw material with high titanium content produced by smelting ilmenite in an electric furnace. The essence of electric furnace smelting of titanium slag is to mix ilmenite with solid reducing agents such as anthracite or petroleum coke and add them to the titanium slag furnace for reduction smelting. The iron oxide in ilmenite is selectively reduced to metallic iron, and the titanium oxide is enriched in the slag. Through slag iron separation, titanium slag and by-product iron are obtained.

The main components of titanium concentrate are TiO2 and FeO, with the rest being SiO2, CaO, MgO, Al2O3, V2O3, etc. Titanium slag smelting is the process of reacting iron oxides with carbon components under high temperature and strong reducing conditions, forming titanium slag and metallic iron in a molten state. Due to differences in specific gravity and melting point, effective separation of titanium slag and metallic iron is achieved. The main chemical reactions that occurred during this period are as follows:

Below:

Fe2O3+C=2FeO+CO                 （1）

FeO+C=Fe+CO                    （2）

Process Flow of Producing Titanium Slag by Furnace Electric Furnace Melting Method

Preparation of Electric Furnace Materials

In production, appropriate chemical composition of ilmenite is selected as raw material based on the purpose of titanium slag and the requirements for impurity content. For example, the production of high-grade titanium slag requires the use of high-quality ilmenite with a high total amount of titanium and iron oxides (i.e. less non iron impurities).

Reducing agents generally require the use of low sulfur and high carbon anthracite or petroleum coke with high activity, low ash content, and low volatile matter.

Dry ilmenite can be directly used to prepare furnace materials for open and semi closed titanium slag furnaces. However, high sulfur primary ilmenite and ore materials used in closed electric furnaces generally require pre oxidation desulfurization treatment, and pre reduction treatment can also be carried out to reduce smelting power consumption. Sealed electric furnaces and semi sealed electric furnaces generally use powdered furnace materials. Titanium iron ore or pre treated titanium iron ore can be melted in the furnace by mixing it evenly with an appropriate amount of reducing agent. Open top electric furnaces generally use pellet materials, which are mixed with an appropriate amount of binder (such as asphalt) to make pellets or mixed and melted in the furnace.

Electric Furnace Smelting

The melting of titanium slag in open and semi closed electric furnaces is an intermittent operation. Each titanium slag furnace operation includes steps such as feeding, melting, discharging, repairing blockages, and pounding the furnace. The smelting process can be roughly divided into three stages: reduction melting, deep reduction, and overheating out of the furnace.

(1) Reduction melting stage. The reduction reaction begins when the furnace charge is preheated to around 11173K; When the temperature rises to 1523-1573K, the furnace charge begins to melt, and melting and reduction occur simultaneously. The melting of the furnace charge gradually expands outward from around the electrodes until all the furnace charge between the electrodes is melted to form a molten pool, marking the end of the reduction melting stage. The energy consumed in this stage accounts for about 2/3 of the total energy in the entire process. A layer of unmelted sintered solid material "bridge" often remains above the melt pool of an open top electric furnace. The "bridge" is prone to partial collapse and collapse into the melt pool under high temperature, causing intense reactions and boiling of slag, resulting in electrode lifting and furnace power fluctuations.

(2) Deep restoration stage. The slag formed after the melting of the furnace charge still contains about 10% FeO. When producing high reducibility titanium slag, it is still necessary to further reduce the residual FeO to iron. The solid material "bridge" above the open electric furnace melt pool has the function of blocking the arc heat radiation, allowing deep reduction to proceed fully.

(3) Overheated furnace stage. After the deep reduction is completed, in order to ensure smooth furnace discharge, it is sometimes necessary to heat the melt to fully separate the slag and iron, and to achieve a certain degree of superheat in the slag.

The closed titanium slag electric furnace adopts continuous feeding and timed slag and iron removal. Under normal melting conditions, the furnace material is melted and reduced immediately after entering the titanium slag furnace, and there is no solid material layer on the surface of the melt pool, and the boiling phenomenon of slag is basically eliminated. If the addition of materials is reduced or stopped for deep reduction, the furnace lining and cover will be directly exposed to arc heat radiation, causing erosion. Therefore, deep reduction is not suitable in a closed furnace, as the reduction degree of titanium slag produced is relatively low.

The electric furnace melting process has a short process flow, and the by-product metal iron can be directly applied without producing solid and liquid waste. The electric furnace gas can be directly utilized, with low costs and small factory footprint. It is an efficient and environmentally friendly method for producing titanium rich materials.

Reduction Melting Electric Furnace

There are generally two types: open type and closed type. Open top electric furnaces can produce high reduction degree titanium slag, but the melting process is unstable, with high heat loss, low metal recovery rate, and poor working conditions. The closed electric furnace melting process has stable furnace conditions, no noise, low heat loss, high metal recovery rate, and the electric furnace gas can be recycled and reused. Figure 2 is a schematic diagram of the structure of a closed electric furnace body. In addition to the electric furnace itself, there are also accessories such as electric furnace transformers, rectangular busbars, electrode holders, electrode lifting mechanisms, measurement and control instruments, and gas purification and recovery systems.

The electric furnace for producing titanium slag is a special furnace type between electric arc furnace and Submerged Arc Furnace (see electric arc smelting and resistance electric arc smelting). Three basic characteristics of titanium slag smelting process should be considered when designing and selecting electric furnace parameters.

(1) The melting temperature of titanium slag is generally 1873-1973K, and the highest melting temperature can reach 2073K. The heat of melting must be concentrated in the central reduction melting zone.

(2) The conductivity of molten ilmenite concentrate at high temperatures is relatively high, and titanium slag has the characteristics of electronic conductors, with a conductivity of up to 15000-20000S/m. The high conductivity of the slag phase determines that the titanium slag melting process has the characteristics of arc melting. The main heat source for melting is the arc heat between the electrode end and the molten pool, and the slag resistance heat is secondary.

(3) Titanium slag melt has high chemical activity, and it is necessary to ensure slag hanging on the furnace lining during the melting process to protect the lining from corrosion.

Overall, the titanium slag smelting electric furnace is the core equipment in titanium slag production, and its performance and operational level directly affect the quality and production efficiency of titanium slag. Therefore, in the process of titanium slag smelting, it is crucial to choose appropriate electric furnace equipment, develop reasonable smelting processes, and strengthen equipment maintenance and management.