To produce urea from ammonia and carbon dioxide using an ammonia-stripping process.
Ammonia (NH3) and carbon dioxide (CO2) react at 150 bar to yield urea and ammonia carbamate. The conversion in the reactor is very high due to a favorable NH3/CO2 ratio of 3.3~ 3.5:1 and operating temperature of 185°C to 190°C. These conditions prevent corrosion problems.
Carbamate is decomposed in three stages at different pressures: in the stripper at the same pressure as the reactor, in the medium-pressure decomposer at 18 bar and in the low-pressure decomposer at 4.5 bar. Reactants not transformed into urea are recycled to the reactor by an ejector. Main equipment is installed at ground level. This layout is essential for large plants. Heat recoveries are particularly developed to have low-energy usage.
Any finishing can be coupled with the synthesis: prilling and granulation, both direct or via crystallization. Different product quality (biuret, moisture, hardness and size) are obtained according to client requests. The plant is completely free from pollution problems. All vents are efficiently treated or flared so that they are discharged to atmosphere practically free of ammonia and/or urea. Process wastewater is hydrolyzed within the plant to achieve boiler feedwater specification and to recover ammonia and carbon dioxide.
Snamprogetti granulation technology has been applied in a 1,650-tpd plant operating since 1990.