Nitrogen fertilizers represent a major industry worldwide accounting for nearly 100 million tons of various products per year. Nitrogen fertilizers include many types of liquid and solid products, among which the most common ones are ammonia, ammonium nitrate, and urea.
Ammonia is produced by reacting nitrogen from the air with hydrogen from natural gas at high pressure and temperature using the Haber process (200-300 bars and around 450°C). Anhydrous ammonia is stored as a liquid under pressure or refrigerated. For ease of handling, it is often converted to other types of fertilizers (see the following flow chart).
As a first step, nitric acid is produced by mixing ammonia and air in a tank followed by the absorption of the nitric oxide gas in water. Concentrated nitric acid (50 to 70 %) and ammonia gas are then mixed together in a tank and a neutralization reaction occurs at 100-180 °C, producing ammonium nitrate.
Another important nitrogen-based fertilizer is the urea, which is produced by a reaction of ammonia with carbon dioxide at high pressure. Both ammonium nitrate and urea can be further concentrated and converted into a solid form (prills or granules). Another process step can combine urea with ammonium nitrate solution to make liquid urea ammonium nitrate or UAN.
Equipment failure because of nitric acid corrosion can be avoided by the use of austenitic stainless steel.
Posted in: FAQ - Stickstoffdünger
