Refractory Materials for Ferrosilicon Smelting Furnaces

Refractory Materials for Ferrosilicon Smelting Furnaces

This article mainly introduces the selection and construction of refractory materials for submerged arc furnaces. A submerged arc furnace is a high-power industrial electric furnace primarily used for reducing and smelting ores, carbon-based reducing agents, and fluxes, producing ferroalloys such as ferrosilicon, ferromanganese, ferrochrome, ferrotungsten, silicomanganese alloy, and carbide, as well as chemical raw materials. The article emphasizes the importance of selecting appropriate refractory materials and proper construction to enhance the service life and smelting efficiency of submerged arc furnaces. It provides a detailed explanation of the operational characteristics of submerged arc furnaces, including the use of carbon or magnesia-based refractory materials for furnace linings, the adoption of self-baking electrodes, and the smelting of metals through submerged arc operation. Additionally, the article outlines the total installed capacity of submerged arc furnaces in China and the company's achievements in the selection and construction of refractory materials for ferrosilicon submerged arc furnaces. Finally, the article underscores the importance of reaching a consensus with manufacturers in the smelting industry, fostering win-win cooperation, and building a shared future.

Ferrosilicon furnace, also known as electric arc furnace or resistance furnace, is an industrial electric furnace that consumes a large amount of electricity.

It mainly consists of the furnace shell, furnace cover, furnace lining, furnace bus bar, water cooling system, smoke exhaust system, dust removal system, electrode shell, electrode pressing and lifting system, loading and unloading system, holder, burn-through device, hydraulic system, a submerged arc furnace transformer, and various electrical equipment.

It is primarily used for the reduction smelting of ores, carbonaceous reducing agents, solvents, and other raw materials. It mainly produces ferroalloys such as ferrosilicon, ferromanganese, ferrochromium, ferrotungsten, and silicomanganese alloys, as well as chemical raw materials. Its operational characteristics include the use of carbonaceous or magnesia refractory materials as furnace linings and self-cultivated electrodes. The electrodes are inserted into the furnace charge for submerged arc operation, utilizing the energy of the electric arc and the current passing through the furnace charge to generate energy due to the resistance of the furnace charge for melting metals. The process involves continuous feeding of materials, intermittent discharge of iron slag, and continuous operation of an industrial electric furnace.

Next, we will introduce refractory materials and their selection for ferrosilicon submerged arc furnaces. Firstly, we need to understand that a submerged arc furnace is a high-temperature thermal equipment, and the furnace is used to sinter and refine minerals at high temperatures. Therefore, we must be aware of the reaction temperature inside it.

Reaction Temperature of Burden in Ferrosillicon Submerged Arc Furnace

(The electricity consumption value varies significantly depending on the composition of raw materials, the composition of finished products, and the capacity of the electric furnace. This is an approximate value.)

Different ferroalloy smelting processes require different reaction temperatures.

1. New material preheating zone: The top layer of the Ferrosillicon Submerged Arc Furnace material is generally about 500mm away, with a temperature of 500℃. The heat at 1000℃ is derived from the ascending high-temperature airflow, heat conduction from the electrodes, combustion of surface furnace materials, and ohmic heating due to the distribution of furnace materials.

2.  Preheating zone: After the evaporation of moisture, the furnace material will gradually move downwards and undergo preliminary changes in the preheating zone, including the transformation of silica crystal structure, volume expansion, and then cracking or bursting. The temperature in this section is around 1300℃. The thickness is about 300mm.

3. Sintering zone: This refers to the crucible shell. The temperature at the lower part of the preheating zone ranges from 1500℃ to 1700℃, where liquid silicon and iron droplets are generated and dripped into the molten pool. In this zone, the sintering of furnace materials occurs, and the permeability is poor. Therefore, it is necessary to break up the lump materials, restore gas ventilation, and increase resistance.

4.  Reduction zone: a zone of intense chemical reactions involving a large amount of material, where the temperature in the crucible zone ranges from 1750℃ to 2000℃. The upper part is the crucible shell, and the lower part is connected to the arc chamber. The main reactions include the decomposition of SiC, the formation of ferrosilicon, and the reaction between liquid Si2O and C, Si, etc.

5. Arc zone: The cavity area at the bottom of the electrode, with a temperature ranging from 2000℃ to 5000℃. This zone is the hottest area of the entire furnace and also the source of the most temperature distribution throughout the furnace body. Therefore, when the electrode is inserted shallowly, the high-temperature zone moves up, the temperature at the furnace bottom is low, and the slag removal is reduced, forming a false furnace bottom. This leads to the upward movement of the tap hole. A certain degree of false furnace bottom is beneficial for furnace maintenance. Generally speaking, the insertion depth of the electrode is largely related to its diameter. The typical insertion depth should be maintained at a distance of 400mm-500mm from the furnace bottom.

After observing the binding reaction of materials in the furnace at high temperatures, we should appropriately select refractory materials based on the metal substances being smelted in the furnace and the temperature distribution zones. In today's submerged arc furnace smelting process, extending the service life of the submerged arc furnace not only requires strengthening scientific management and standardized operation but also more importantly, efforts should be made on the furnace lining. The above (Figure 1) is a schematic diagram of refractory materials designed and installed by our company for Ningxia Puhua Metallurgical Products Co., Ltd. The material quality has high requirements, requiring the selected materials to withstand the pressure of furnace materials, furnace gas, the scouring of molten iron, and the physical and chemical erosion of slag during use. At the same time it must withstand high temperatures. The main materials used in furnace construction include asbestos board, first-grade high-alumina brick, refractory clay, refractory aggregate, phosphate refractory mortar, carbon brick, carbon cold ramming paste, and other materials. We have chosen asbestos board products as the insulation layer for the furnace wall and bottom, which can effectively insulate and prevent the diffusion of a large amount of heat, maintaining a lower temperature inside the furnace and reducing power consumption. Refractory bricks for the furnace bottom and refractory bricks for the furnace wall.

The bellmouth refractory bricks are all made of first-grade high-alumina bricks. The carbon bricks are mainly made from Etaxi coal. The furnace eye bricks are made of through-hole semi-graphitic silicon carbide bricks, and the iron tapping hole bricks are made of high-graphitic carbon bricks. During the design and installation, we increased the thickness of the furnace bottom by laying three layers of ordinary carbon bricks and two layers of seamless precision-machined carbon bricks to prevent the bottom from being too hot and the infiltration of molten iron, which could lead to bottom burnthrough. The temperature of the furnace bottom is an important indicator of the overall furnace temperature. If the temperature of the furnace bottom is too high, it indicates that the temperature inside the furnace is largely shifting towards the bottom, which may pose a risk of bottom burnthrough. If the temperature of the furnace bottom is too low, it may mean that the electrodes inside the furnace are too far from the bottom, resulting in a low reaction temperature of the materials and a high risk of energy consumption. Therefore, the temperature of the furnace bottom is generally maintained at around 400℃ as a normal temperature.