A Brief Analysis of the Corrosion Problems of Refractory Materials and Equipment Caused by the Use of Special Raw Materials and Fuels

A Brief Analysis of the Corrosion Problems of Refractory Materials and Equipment Caused by the Use of Special Raw Materials and Fuels

In the context of rapid industrial development, the production of refractory materials and equipment is inseparable from the use of raw materials and fuels. With the increasing variety of special raw materials and fuels, the content of elements such as sulfur, phosphorus, chlorine, and oxygen is also increasing, leading to increasingly serious corrosion problems of refractory materials and equipment. Therefore, to improve the corrosion resistance of refractory materials and equipment, it is necessary to conduct an in-depth analysis of their corrosion mechanisms and characteristics.

Corrosion Elements and Their Cyclic Characteristics in Special Raw Materials and Fuels

1.1 Sources of Corrosion Elements
During the production of refractory materials and equipment, to further enhance their corrosion resistance and prevent corrosion problems, special elements are often added to raw materials and fuels. These elements react chemically with the refractory materials, leading to more severe corrosion problems. This phenomenon is particularly common in steelmaking and ironmaking processes. Adding iron or magnesium to steelmaking, and chromium, titanium, vanadium, etc., to ironmaking increases the content of these special elements in raw materials and fuels, accelerating the corrosion rate of refractory materials and equipment. Under normal circumstances, to improve the performance of refractory equipment and materials and accelerate production rates, existing raw materials and fuels are often used directly. The large number of impurities present in these materials not only significantly reduces the corrosion resistance of refractory materials and equipment, leading to damage, but also causes corrosion, affecting production quality and performance.

Taking iron and steel smelting as an example, in some regions where blast furnace raw material resources are relatively scarce, the fuel source is entirely dependent on external purchases. However, in order to reduce the production cost of iron and steel smelting, some production enterprises usually choose lower-priced ores. These ores are characterized by complex origins, low grade of ore entering the furnace, and high content of harmful elements. Among them, when the content of harmful elements such as sulfur, phosphorus, arsenic, fluorine, chlorine, potassium, sodium, lead, and zinc is high, it will have a corrosive effect on the refractory materials and equipment in iron and steel smelting. If the control of the corrosive element content in the raw materials and fuels of iron and steel smelting is ignored, not only will the quality of the raw materials and fuels for iron and steel smelting be greatly reduced, leading to an increase in slag and flux usage during the smelting process, but the workload outside the steelmaking furnace will also be further increased. If the control and treatment of waste are neglected during the production of refractory materials and equipment, as harmful elements such as sodium, potassium, zinc, and lead accumulate, expand, and permeate in the refractory materials and equipment, when the content of corrosive elements such as chlorine, sulfur, sodium, and potassium in the system exceeds the target value control requirements, it will affect the stability of the production system to a certain extent, reduce the quality of product production, and severely corrode the refractory materials and equipment that come into direct contact with them in the production system, thus affecting their production indicators and service life.

1.2 Characteristics of Raw Materials and Fuels

Clay, slag, fly ash, desulfurization ash, and other substances generated during the production of refractory materials and equipment are all considered raw materials and fuels. The type and quantity used depend on the amount of harmful impurities in the raw materials and the actual output required by the production system. Different qualities of raw materials and fuels should be selected based on the actual demand of the production system. The type of raw material and fuel required should be determined based on the intended use of the product. This is evident from the fact that raw materials and fuels used in the production of metals such as steel cannot be used in the production of refractory materials and equipment, and raw materials and fuels used in cement production cannot be used as raw materials for glass production. If the raw materials and fuels contain harmful impurities such as sulfur and phosphorus, or toxic substances such as sulfur dioxide, their use must be based on the intended use and properties of the product, and the appropriate usage conditions must be accurately assessed. When using raw materials and fuels in high-temperature working environments, their stability under those conditions must be fully considered, and their high-temperature resistance must be scientifically assessed in conjunction with the specific conditions of the high-temperature environment.

1.3 Corrosion Element Characteristics
In modern industrial production, elements such as iron, magnesium, chromium, vanadium, and silicon are typically chosen as the main raw materials and fuels. Imbalances in raw material ratios or the reuse of raw materials and fuels can lead to excessively high levels of chlorine, sulfur, and alkali. When an imbalance in the concentration of corrosive elements occurs during the production of refractory materials and equipment, large amounts of potassium sulfate, sodium chloride, potassium chloride, and other salt compounds accumulate in the thermal production process. These compounds are not discharged from the system along with the production products but gradually accumulate and precipitate on the surface of the refractory lining as production activities continue. Under certain conditions, they can even gradually penetrate into the interior. Based on the volatilization and melting temperatures of chlorine, sulfur, and alkali compounds, it can be observed that their boiling and melting points fall within the ambient temperature range of the refractory material and equipment production environment, thus affecting the refractory materials and equipment in the production system and other components.

In iron and steel smelting, the blast furnace, as a crucial refractory material and equipment in the production system, is heavily reliant on sulfides in raw materials such as pulverized coal, coke, and ore impurities. These sulfides are a key source of sulfur corrosion in the production system. Generally, most sulfur in the iron and steel smelting system originates from pulverized coal and coke. As the sulfur content of these raw materials increases, the sulfur content in the molten iron also increases, leading to a high susceptibility to hot brittleness in the finished product and a significant decrease in its strength. The ash content of pellets, sinter, pulverized coal, and coke is a major source of sodium, potassium, and other alkali metals that corrode refractory materials and equipment in the iron and steel smelting system. Alkali metals have a significant detrimental effect on blast furnaces and can also catalyze the dissolution reaction of coke, thus degrading it. The presence of alkali metals in the iron and steel production system can further lower the ore softening temperature, exacerbating the reduction pulverization of sinter and the abnormal expansion and pulverization of pellets. When metallic elements such as sodium and potassium circulate and accumulate inside refractory equipment, the oxides generated from their reaction with oxygen can chemically react with the silica and alumina in the refractory lining, producing low-melting-point silicates. This causes the refractory material to expand in volume, impacting the production efficiency of the system. Simultaneously, sodium and potassium oxides can act as catalysts for carburization reactions, resulting in more severe corrosion of the refractory materials and equipment, accelerating their corrosion rate.

Corrosion Mechanisms of Refractory Materials and Equipment under Special Raw Materials and Fuels

2.1 Types of Refractory Materials
Refractory materials can be classified into different types according to their composition. Due to the special chemical properties of some refractory materials, they readily react with oxygen in the air, causing changes in their composition and weakening their corrosive effect on refractory materials and equipment to a certain extent. Therefore, oxides of elements such as magnesium, aluminum, silicon, chromium, and calcium can serve as good refractory materials and raw materials for equipment in steel production systems. Based on their elemental composition, they are classified into three types: magnesia-chromium refractories with magnesium oxide and chromium oxide as the main components; magnesia-alumina refractories with magnesium oxide and aluminum oxide as the main components; and silicon-alumina refractories with silicon oxide and aluminum oxide as the main components. During use in production systems, large quantities of directly usable and refractory magnesia-chromium bricks can be produced. These refractory bricks typically exhibit strong high-temperature resistance in practical applications, effectively resisting the erosion and redox effects of silica. However, the residual materials and waste from such refractory materials cause serious pollution to the natural environment. In many countries with relatively developed industrial industries, the production and use of magnesia-chrome refractories have been discontinued.

Magnesia-alumina refractories, represented by magnesia-alumina spinel bricks, possess strong refractoriness and a certain resistance to erosion from clinker liquid and sulfur and alkali molten materials. They also have advantages in resistance to refractory deformation, thermal shock, mechanical stress, and thermal load. Compared to magnesia-chrome bricks, magnesia-alumina spinel bricks have superior performance in practical applications. They not only have high application value in certain production stages as refractory materials in the main refractory equipment of steel production systems, but are also an important product of modern alkaline brick industry production technology. In silica-alumina refractories, to ensure strong resistance to alkali erosion, the mass fraction of alumina in alkali-resistant bricks is usually strictly controlled. When the mass fraction of alumina in the alkali-resistant brick is maintained at 30%, and the load softening temperature is around 1300℃, it is used in areas of refractory equipment where erosion is relatively severe. Through the development of a series of special high-alumina bricks such as anti-sparging alumina bricks, phosphate-bonded high-alumina wear-resistant bricks, and phosphate-bonded high-alumina bricks, as well as the emergence of new silicon carbide-permeable high-alumina bricks, the needs of different working conditions and parts in the production system for refractory, alkali-resistant, and wear-resistant properties are met.

2.2 Corrosion Mechanism of Corrosion Elements

The corrosion of refractory materials and equipment can be broadly classified into three types: chemical corrosion, mechanical stress, and thermal stress. The corrosion impact of raw materials and fuels is usually dominated by chemical corrosion. Due to the high-temperature environment of the production process, active metal elements and various impurities in raw materials and fuels react chemically with refractory materials and equipment, leading to corrosion. This chemical corrosion occurs throughout the production process and the complete service life of the refractory materials and equipment. Taking the iron and steel smelting process as an example, iron, as the main component in this industrial activity and one of the most widely used raw materials in current smelting processes, has low solubility in molten steel but high solubility in air. Based on its solubility differences under different environments, when molten steel enters the slag, flow occurs, and iron elements in the slag are carried into the molten steel, producing some iron. Because the surface of molten iron has strong oxidizing properties, when refractory materials and equipment come into contact with molten iron, a rapid chemical reaction occurs, generating iron oxide. While iron oxide doesn’t directly corrode refractory materials and equipment due to their strong corrosion resistance, the presence of oxides on their surface affects their corrosion resistance, making them highly susceptible to corrosion during subsequent production processes, significantly reducing their strength and service life.

At room temperature, magnesium typically exists as an inert element and doesn’t directly participate in chemical reactions. However, in steelmaking, some manufacturers use magnesium as a flux and deoxidizer to improve production efficiency. When temperature conditions change, magnesium reacts with water vapor and oxygen at high temperatures to produce magnesium oxide, which exists in steel as both bound and free magnesium oxide. This magnesium oxide continues to react with water vapor and oxygen at high temperatures, corroding refractory materials and equipment. Simultaneously, the presence of magnesium oxide forms a dense oxide film on the steel surface, lowering its surface temperature and making the steel billet prone to cracking during heating. Vanadium, titanium, and chromium, among other elements, are relatively corrosive and readily react with refractory materials and equipment during smelting, accelerating the rate of corrosion. Based on a comprehensive understanding of the mechanisms and processes by which raw materials and fuels cause corrosion of refractory materials and equipment, the corrosive effects of various corrosive elements in raw materials and fuels can be reduced by strictly controlling their content. This ensures that the content is below industrial production standards and within specified limits, fundamentally preventing impurities from entering refractory equipment and materials, thus effectively controlling the corrosion problem at its source. During the smelting and production processes, scientifically processing raw materials and fuels with high iron content and strengthening the management of refractory materials and equipment will improve their quality and extend their service life.

Corrosion Problems of Refractory Materials and Equipment under Special Raw Materials and Fuels

3.1 Generation and Treatment of Sulfur Dioxide
In modern industrial production, the production of refractory materials and equipment often generates large amounts of sulfur dioxide gas due to environmental conditions. When the internal temperature of the production system is high, sulfur dioxide reacts with refractory materials and equipment under high-temperature conditions, producing acidic substances such as sulfur trioxide. This acidic substance, while maintaining a constant production system temperature, promotes corrosion of refractory materials and equipment, leading to severe corrosion problems. Taking the smelting production process as an example, when high-sulfur coal gangue is used as a raw material, its relatively high sulfate content causes it to react chemically with coke during production, generating large amounts of sulfur dioxide gas. This results in severe corrosion of refractory materials and equipment caused by the high sulfur content of the coal gangue during production.

3.2 The Impact of Sulfur Dioxide in Aluminum Smelting

Since coal gangue is typically used as the primary raw material in aluminum smelting, and this coal gangue itself contains a large amount of sulfur dioxide, the high-temperature conditions during production cause aluminum to react chemically with the sulfur dioxide in the coal gangue, producing hydrogen and sulfur trioxide. Under the same high-temperature environment, the chemical reaction does not stop there. The hydrogen produced by aluminum and sulfur dioxide further reacts with sulfur oxides at high temperatures to form aluminum sulfate, which then reacts with alkaline substances such as sodium hydroxide in the slag to neutralize the sulfate, continuously increasing the sodium oxide content in the filter residue. The sodium oxide content further shortens the service life of the smelting furnace. To address the indirect corrosive effect of sulfur dioxide on refractory equipment like smelting furnaces during aluminum smelting, technicians must scientifically control the sulfur dioxide content during production, minimizing the content of sulfur oxides and reducing the corrosive impact of raw materials and fuels on refractory materials and equipment.

3.3 Corrosion Problems of High-Sulfur Coal Gangue
In industrial production, high-sulfur coal gangue is often used as a primary raw material. Due to its high sulfur content, a large amount of sulfur dioxide gas is generated during the smelting process. Before being discharged from the production system, this sulfur dioxide reacts with calcium oxide in the coal gangue under high-temperature conditions to form calcium sulfate. This chemical product then reacts with alumina and silica in refractory materials and equipment to produce aluminum sulfate hydroxide. The strong corrosiveness of this alkaline substance severely corrodes refractory materials and equipment. In the blast furnace ironmaking process of a steel plant, high-sulfur coal gangue was selected as a raw material. An investigation into the relationship between its sulfur content and the severity of corrosion problems in refractory materials and equipment revealed that the higher the sulfur content of the coal gangue, the more severe the corrosion problems on refractory materials and equipment during the production process. When the sulfur content of coal gangue is controlled below 0.8%, it will not have a corrosive effect on refractory materials and equipment; when the sulfur content of coal gangue does not exceed 1.5%, it will cause a certain degree of corrosion to refractory materials and equipment, but it will not be particularly serious; when the sulfur content of coal gangue exceeds 1.5%, it will severely corrode refractory materials and equipment.

In conclusion, as society develops rapidly, the types of raw materials and fuels used in production activities are constantly increasing. To reduce the corrosion problems caused by certain special raw materials and fuels to refractory materials and equipment, it is necessary to integrate production theory and technical practice, correctly understand the influence of factors such as pressure, temperature, and humidity, explore the corrosion laws of different raw materials and fuels on refractory materials and equipment, and scientifically select the types of raw materials and fuels to solve corrosion problems.