We selected the Snamprogetti ammonia stripping process for the manufacture of urea. In this process ammonia & CO2 are compressed & fed to the reactor. The unconverted carbamate is stripped and recovered from the urea synthesis reactor effluent solution at reactor pressure, condensed to an aqueous solution in a steam producing high pressure condenser & recycled back to the reactor by gravity. Part of the liquid NH3 reactor feed, vapourized in a steam heated exchanger, is used as inert gas to decompose & strip ammonium carbamate in the steam heated high pressure stripper.
Energy balance & material balance of the plant is done. The selected capacity of the plant is 4,50,000 tons/year of urea producing 62,500 kg/hr of urea with 98 % purity. Urea reactor & vacuum evaporator are designed. The volume of reactor is calculated & found to be 195 m3. The length & diameter of the reactor are 40 m & 2.5 m respectively. The evaporator used is of climbing-film long- tube type.
Snamprogetti ammonia-stripping urea process is selected because it involves a high NH3 to CO2 ratio in the reactor, ensuring the high conversion of carbamate to urea . The highly efficient ammonia stripping operation drastically reduces the recycling of carbamate and the size of equipment in the carbamate decomposition. Snamprogetti technology differs from competitors in being based on the use of excess ammonia to avoid corrosion as well as promote the decomposition of unconverted carbamate into urea.