Urea, the world's most widely used nitrogen fertilizer, is not only high in nutrients, but also highly water-soluble, easy to use, and very inexpensive. How is urea produced? Industrial urea production mainly uses the "ammonia-carbon dioxide method," which generally consists of three core stages: raw material processing, synthesis reaction, and product purification.

The first step is raw material processing. The basic raw materials for urea production are liquid ammonia and high-purity carbon dioxide. Liquid ammonia usually comes from ammonia synthesis plants and needs to be purified by distillation to remove impurities; carbon dioxide is mostly recovered as a byproduct of ammonia synthesis, and modern processes have achieved over 90% carbon dioxide recycling. The two raw materials are metered in a 2:1 molar ratio and heated to 160-180℃ in a preheater before entering the reaction system.

The second step is high-pressure synthesis. Inside a urea synthesis tower with a diameter of 3 meters and a height exceeding 20 meters, ammonia and carbon dioxide undergo a two-step reaction under high pressure (14-18 MPa) and temperature (180-190℃). First, ammonium carbamate (NHCOONH) is produced. This intermediate product is further dehydrated under high temperature and pressure to produce urea (NHCONH).

Third, product purification. The synthesized crude urea solution contains unreacted substances, water, and a small amount of byproducts. It requires three stages of evaporation: the first stage removes most of the water at 130℃ and 0.3 MPa; the second stage further concentrates the urea at 140℃ and atmospheric pressure; and finally, the urea is sprayed and cooled in a granulation tower to form particles with a diameter of 2-4 mm. Modern processes employ fluidized bed granulation technology, resulting in uniform particle size and preventing agglomeration.

The entire production process achieves closed-loop utilization of raw materials. Unreacted ammonia and carbon dioxide are recycled and reused in the synthesis, reducing energy consumption by 30% compared to earlier processes. my country currently uses fourth-generation urea production technology, with a single unit capable of producing up to 800,000 tons annually, and the product purity consistently above 98.5%. This efficient and clean production model provides important support for global food security.