Process for the production of melamine

A plant for the production of melamine, comprising:

• a condensation section (OGC), carried out at a pressure ranging from 70 to 220 bar, suitable for condensing:
• i. a gaseous stream of anhydrous off-gas comprising NH3 and CO2, coming via a first line from an off-gas scrubbing section (OGQ) with urea, a stream comprising NH3, CO2 and melamine vapours, produced as a gaseous effluent from the urea pyrolysis reaction and coming via a second line from the reaction section (R) and from the post-reaction and ammonia stripping section (PR),
• ii. a liquid stream comprising NH3, CO2 and H2O, coming via a third line from an ammonia recovery section (AR);
• iii. a gaseous stream comprising NH3, CO2 and H2O coming via a fourth line from a process water treatment section (PWT) and
• iv. a gaseous stream of off-gas comprising NH3, CO2 and H2O, coming via a fifth line from a high-pressure off-gas decomposition section (HPD);
• said condensation section (OGC) being connected via said first, third, fourth and fifth supply lines to the scrubbing (OGQ), ammonia recovery (AR), process-water treatment (PWT) and high-pressure decomposition (HPD) sections, from which it receives streams i.-iv.) at the same pressure present in the condensation section (OGC);
• said condensation section (OGC) being connected via a sixth line to a conversion section (OGR) to which it feeds a liquid stream comprising NH3, CO2 and H2O;
• the conversion section (OGR) to which said liquid stream comprising NH3, CO2 and H2O coming from the condensation section (OGC) is fed via the sixth line, is connected to a high-pressure decomposition section (HPD) to which it feeds via a seventh line a first stream comprising urea, ammonia, carbamate and H2O;
• the high-pressure decomposition section (HPD) to which the first stream comprising urea, ammonia, carbamate and H2O is fed via the seventh line, is connected via the fifth line to the condensation section (OGC) and via an eighth line to a medium-pressure decomposition section (MPD) to which it feeds, via the eighth line, a second stream comprising urea, carbamate and H2O;
• the medium-pressure decomposition section (MPD) to which the second stream comprising urea, carbamate and H2O is fed via the eighth line, is connected via a ninth line to the ammonia recovery section (AR) to which it feeds an off-gas stream comprising NH3, CO2 and H2O, and via a tenth line to a low-pressure decomposition section (LPD) to which it feeds a third stream comprising urea, carbamate and H2O;
• the low-pressure decomposition section (LPD) to which the third stream comprising urea, carbamate and H2O from the medium-pressure decomposition section (MPD) is fed, via the tenth line, is connected via an eleventh line to the process-water treatment section (PWT) to which an off-gas stream comprising NH3, CO2 and H2O is fed, and via a twelfth line to the urea concentration section (CON) to which a fourth stream comprising urea and H2O is fed;
• the urea concentration section (CON) to which the fourth stream comprising urea and H2O is fed, via the twelfth line, from the low-pressure decomposition section (LPD), is connected via a thirteenth line to the off-gas scrubbing section (OGQ) to which it feeds a stream of concentrated urea and via a fourteenth line to the process-water treatment section (PWT) to which it feeds a stream of H2O.