Equipment Corrosion During Urea Production
In industrial production, urea is synthesized by liquid ammonia and carbon dioxide, following the below reaction formula under a pressure level of 14-25MPa and temperature of 180~210℃.
Pre-reaction raw materials like carbon dioxide and ammonia have weak corrosion, so do post-reaction products urea and water. However, reaction intermediate products like ammonium carbamates can exert strong corrosive effects under high temperatures. Meanwhile, urea produced during synthesis reaction can generate cyanic acid and ammonium cyanate. In water, CNO- ionized from cyanic acid and ammonium cyanate have strong reducibility like chloride ions, damaging the oxidation film on the stainless steel surface. Due to the strong depassivation effect, even stainless steel containing Molybdenum can hardly resist its corrosion. Hence, it is not until the addition of corrosion inhibitor to the corrosive medium does stainless steel have wide application in urea production.