Silicomanganese Submerged Arc Furnace 6.3 MVA To 45 MVA For Metallurgical Processes

6.3 MVA to 45 MVA Silicomanganese Submerged Arc Furnace

Silicomanganese is a ferroalloy composed primarily of manganese, silicon, iron, and trace amounts of carbon along with other elements. It is one of the most widely used and high-volume alloys in the ferroalloy industry. In steelmaking, manganese-silicon alloy serves as a compound deoxidizer and is also employed as a reducing agent in the production of medium- and low-carbon ferromanganese, as well as in the manufacture of metallic manganese via the silicothermic process. Based on manganese, silicon, and impurity element content, silicomanganese is classified into eight grades, with chemical compositions conforming to the specifications outlined in the table.

Modern submerged arc furnaces are designed with fully enclosed structures. The primary equipment comprises several integrated systems: the furnace body, low-profile fume hood, exhaust system, short network, electrode assembly, hydraulic mechanism, tapping and slag removal units, bottom cooling system, transformer, high-voltage power supply, low-voltage automatic control system, monitoring instrumentation, raw material mixing and feeding systems, distribution and dosing mechanisms, furnace mouth dust collection, and dry-process gas recovery and dedusting systems.

1. Working Principle

The silico-manganese furnace operates on the submerged arc furnace principle. Electrodes generate arc heat and resistance heat from the charge to reduce the oxides in manganese ore and silica into silico-manganese alloy. The reaction inside the furnace is mainly based on carbothermic reduction. The main deoxidation products are MnSiO₃ and MnSiO₄, with melting points of 1270°C and 1327°C respectively. These products form large particles that easily float up, resulting in a significant deoxidation effect.

2. Process Flow and Operation

Raw material preparation: Manganese ore, manganese-rich slag, silica, and coke are batched according to the formulation requirements. The fixed carbon content of coke must be ≥84%.

Charging and heating: The raw materials enter the semi-closed submerged arc furnace through a hopper. A 35 kV power supply is introduced into the furnace via three-phase electrodes, which are inserted into the charge to create arc heating.

Smelting control: The charge is mixed uniformly, the charge level is maintained, the electrodes are inserted deeply and evenly. The furnace gas is kept at a slight negative pressure, with O₂ < 2%, H₂ < 8%, and the furnace temperature below 600°C.

Tapping of iron and slag: The molten alloy and slag separate naturally. The tap hole can be opened and closed smoothly. Both the hot metal and slag have good fluidity and are easy to separate, finally being cast into ingots.

3. Technical Parameters and Furnace Condition

The slag binary basicity (CaO/SiO₂) is controlled between 0.5 and 0.7, with MnO in the slag <10%.

The working length of the electrodes is 1700–2000 mm, the voltage is about 143 V, the working current is stable, and electrode consumption is uniform.

A normal furnace condition is characterized by good permeability of the charge surface, uniform sinking of the charge, and smooth tapping of iron and slag.

4. Grades and Chemical Composition

Silicomanganese is divided into eight grades based on manganese, silicon, and impurity element content. Its chemical composition shall comply with the provisions of Table 1.

Table 1 – Chemical Composition

Note: Phosphorus content is specified in three grades (I, II, III) according to different maximum limits.

5. Applications and Advantages

The alloy produced by the silico-manganese furnace is widely used in steelmaking, significantly reducing the burning loss rate (the burning loss rate of silico-manganese alloy deoxidation is about 29%, which is lower than using manganese or silicon alone). In addition, silico-manganese alloy can improve the corrosion resistance and rust resistance of steel, making it suitable for outdoor or humid environments. The silico-manganese furnace is similar to the ferrosilicon furnace, but it is dedicated to the production of silico-manganese alloy and cannot be used for high-carbon ferromanganese production unless a small furnace (e.g., 6000 kVA) is used to avoid refractory damage.

In summary, the silico-manganese furnace is an indispensable piece of equipment in steelmaking. By precisely controlling parameters such as charge composition, temperature, electrodes, and slag, it enables efficient and stable production of silico-manganese alloy, ensuring the quality and performance of steel.