Thread Content
Dry urea does not corrode concrete. However, the granulation process often involves trace amounts of ammonia, carbonates, and water vapor, and urea is also hygroscopic. Therefore, the urea solution is alkaline. During the rainy season, urea absorbs moisture more severely. The concrete matrix of the granulation tower has a porous structure, and the urea aqueous solution can undergo a process of infiltration—crystallization (expansion)—deliquescence and re-infiltration—recrystallization (expansion)… When molten or hygroscopic urea or ammonium nitrate infiltrates the micropores of the concrete matrix, it expands due to crystallization, and this expansion force is sufficient to weaken the strength of the concrete matrix, thereby affecting the structural safety of the granulation tower. This crystalline corrosion causes concrete to powder, flake off, and crack. Ammonia also has a strong penetrating power on cement, with quite severe corrosiveness. Urea aqueous solutions containing ammonia and carbonates, along with salts dissolved from cement and dissolved oxygen, cause steel rebar to rust rapidly. The volume expansion that occurs during the formation of rust also leads to cracking in the concrete. Especially on the scraping platform, although there is a 20 mm gap between the lower end of the scraper plate and the surface of the platform, a layer of urea always accumulates on the surface of the platform during production, and the fresh urea particles come into contact only with this surface layer of urea. However, when the granulation nozzle fails and molten urea is unable to form droplets, resulting in a \"thinned\" consistency, the surface of the platform comes into direct contact with the high-temperature, alkaline molten urea, leading to the formation of scabs.