Performance and Construction Methods of Acid-Resistant Castables for the Petrochemical Industry

Acid-resistant castables are those that can resist corrosion from colloidal media such as nitric acid, hydrochloric acid, sulfuric acid, and acetic acid at temperatures ranging from 80 to 1200℃. Acid-resistant castables are typically made from acid-resistant aggregates, such as silica, cast stone, wax stone, and diabase particles, as well as acid-resistant material powders from waste silica bricks, silica, waste porcelain, and cast stone, using water glass as a binder.

Performance and Applications of Acid-Resistant Castables

The modulus of water glass is between 2.6 and 3.2, and the density is between 1.38 and 1.42 g/m³. The addition amount is typically between 13% and 16%. Sodium fluorosilicate is used as a settling accelerator, added at 10% to 12% of the water glass solution mass. This type of acid-resistant castable is low in cost and has good acid resistance, making it widely used in furnace linings or chimneys in metallurgy and chemical industries. However, it has poor resistance to phosphoric acid, hydrofluoric acid, and high-fatty acid corrosion.

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Technical Performance of Acid-Resistant Castables

Acid-resistant castables possess the following properties:

1. Acid-resistant castables are a new type of anti-corrosion material with strong prestress, composed of multiple components including potassium silicate as a binder, inorganic molecular materials as curing agents, and silicates as acid-resistant fillers.
2. Acid-resistant castables have high mechanical strength and excellent bonding properties. Especially in the construction of granite blocks, acid-resistant ceramic tiles, and ceramic slabs, the adhesion between the castable and cement is greater than that of the base material.
3. The acid-resistant castable exhibits stable performance in various concentrations of organic and inorganic acids. Particularly in dilute acids, industrial water, and neutral aqueous solutions, it does not produce crystalline salts and possesses high impermeability.
4. It has good heat resistance and can be used in titanium dioxide rotary kiln linings at temperatures as high as 950℃-1000℃.
5. The acid-resistant castable uses a non-toxic curing agent, posing no harm to operators and construction personnel. It has been certified by medical and health departments as suitable for corrosion protection in food, pharmaceutical, and other equipment.
6. Compared with organic acid-resistant materials, the acid-resistant castable is inexpensive. In addition to possessing the same acid and corrosion resistance as organic materials, it also has the unique property of resisting corrosion from strong oxidizing media.
7. It cures at room temperature, is simple to construct, convenient to use, easy to transport, and requires moisture-proof storage.

Applications of Acid-Resistant Castables

Acid-resistant castables can be used in various concentrations of sulfuric acid, hydrochloric acid, nitric acid, chromic acid, hypochlorous acid, chlorosulfonic acid, formic acid, oxalic acid, acetic acid, and other acids; various organic solvents; various acidic salts; oxidizing media such as chlorine and hydrogen peroxide; and mixtures of the above media. Rongsheng acid-resistant materials are widely used in corrosion protection projects for reaction vessels, storage tanks, towers, floors, trenches, electrolytic cells, etc., in industries such as petroleum, chemical, metallurgy, power, pesticides, food, fermentation, hydrolysis, and pickling.

Acid-resistant castable refractory construction requirements:

1. Acid-resistant castable refractory, 10-20 mm thick, should be applied in sections. The spacing between sections should be 2-3 meters, and the joint width should be 15-20 mm. The joints should be completely filled with a suitable sealant.
2. Acid-resistant castable refractory can also be used to line granite blocks. The bonding layer and joint width are generally 10-15 mm.
3. The construction requirements for acid-resistant castable refractory are the same as those for mortar application.
4. Acid-resistant castable refractory can be used for integral casting linings of reaction vessels, storage tanks, towers, electrolytic cells, trenches, floors, fermentation tanks, etc., in chemical, light industry, metallurgical, pickling, petroleum, pesticide, food, electroplating, and electrolysis industries. With the addition of reinforcing steel, it can serve as a structural corrosion-resistant material.
5. When casting inside carbon steel equipment, the surface of the carbon steel equipment should be sandblasted to remove rust. When casting inside cement concrete equipment, the surface of the equipment should be thoroughly cleaned of oil and dust.
6. The formwork structure used for casting must be tight, dimensionally accurate, and possess sufficient rigidity; a height of 50 cm is recommended.
7. Before construction, the formwork surface should be coated with oil, then a plastic film should be placed on the formwork surface, extending 5-10 cm beyond the joints.
8. Mixing containers and tools must be clean and dry.
9. The temperature at the construction site must be above 15℃. Rain shelters should be erected during the rainy season.
10. Mix the concrete and potassium silicate thoroughly according to the mixing ratio.
11. Pour the mixed material into the formwork and compact it manually or with mechanical vibration.
12. The filling depth should be 30 cm each time.
13. If the ambient temperature is above 35℃, the formwork can be removed after seven days. After demolding, strictly prevent impact and localized high-temperature welding.
14. If casting load-bearing structural equipment, reinforcement should be designed accordingly.

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Precautions for Acid-Resistant Castable Resin Construction

1. Carbon steel equipment should be sandblasted to remove rust before construction. For concrete equipment, surface dust should be cleaned and uneven areas repaired. The moisture content of concrete tanks and pools should be less than 6%.
2. The surfaces of acid-resistant bricks and granite used for lining should be clean and dry.
3. Containers and tools for mixing acid-resistant materials should be clean and dry.
4. The temperature at the construction site should be between 15°C and 35°C, and the ambient air temperature should be below 80°C before construction. If it exceeds 80°C, ventilation and dehumidification facilities should be added.
5. Weigh potassium silicate according to the acid-resistant castable resin mix ratio and add it to the mixer or mixing container. Then add the weighed powder and mix thoroughly. Each batch of mixture should be used within 30 minutes.
6. During construction, it is strictly forbidden to add powder or potassium silicate to the acid-resistant castable resin. If the mortar hardens, it should be discarded.
7. When lining brick slabs, the mortar should be applied fully and compacted with a spatula, squeezing the mortar out of the brick joints. Excess mortar should be scraped away with a knife. The bonding layer and joint should generally be 3- 5 mm.
8. When lining large acid-resistant bricks, they should be supported and secured to prevent movement.
9. After successful lining, the equipment must be cured in an environment above 15 degrees Celsius for at least 14 days. During curing, contact with water and water vapor is strictly prohibited.
10. For open-air construction, a rainproof and sun-protective shed should be erected.

What is the difference between acid-resistant and alkali-resistant castables?

Alkali-resistant castables are castables that resist the corrosion of alkali metal oxides at medium to high temperatures. They can be classified into medium-temperature and high-temperature types according to their service temperature, and into lightweight and heavyweight types according to their bulk density. Medium-temperature alkali-resistant castables typically use aluminosilicate materials as aggregates or fine powders, such as clay clinker, waste porcelain powder, and expanded perlite. Their resistance to alkali corrosion works by reacting with alkali metal oxides to form a high-SiO2, high-viscosity glaze layer on the surface of the refractory castable, thus preventing further penetration of alkali metal oxides into the interior of the refractory castable and improving its corrosion resistance.

Alkali-resistant castables are divided into high-strength alkali-resistant castables and ordinary alkali-resistant castables. They are used extensively in cement rotary kiln preheaters, with SiO2 content around 60% and Al2O3 content between 45% and 75%. High-strength alkali-resistant castables use high-voltage electrical porcelain materials, while ordinary alkali-resistant castables use low-voltage electrical porcelain materials. The higher the operating temperature, the higher the Al₂O₃ content. Depending on the application, calcium aluminate cement, silica powder, etc., can be selected to adjust the process proportions.

For excessively high temperatures, alkali-resistant castables are also made using chromium corundum, zircon, fused spinel, etc., as aggregates or fine powders. These types of alkali-resistant castables are mostly used in hazardous waste incinerators.