Carbamate condensation unit

1. A submerged carbamate condensation unit for synthesis urea production plants, comprising:

a substantially cylindrical shell, closed at the opposed ends thereof by an upper and a lower bottom, respectively, defining an intermediate portion, an upper portion and a lower portion of the condensation unit;

a tube bundle for the condensation of gaseous compounds, fitted into said intermediate portion of the condensation unit, in fluid communication with said upper portion and said lower portion and comprising an upper and a lower tube plate, respectively, and a plurality of tubes supported by said upper and lower tube plates;

a first duct extended in said lower portion below said tube bundle for feeding said gaseous compounds to be condensed and having a free end located inside a gas distribution chamber supported inside said lower portion of the condensation unit;

discharge openings provided in said upper portion for discharging outside the condensation unit uncondensed gaseous compounds and condensed gaseous compounds, respectively;

a second duct, structurally independent from said tube bundle and said discharge openings, in fluid communication with said upper and lower portions for the circulation of part of said condensed gaseous compounds, wherein said second duct is external to said shell; and

a tank associated to said upper bottom and in fluid communication with said upper portion and said second duct external to said shell, said discharge openings being provided in said tank.

2. The carbamate condensation unit according to claim 1 , wherein said second duct is in communication with said lower portion via an opening that is positioned lower than said free end of said first duct supplying said gaseous compounds.