Patent GB-1103041-A (GB)
Title: Method for decomposing ammonium carbamate
IPC: B01J19/24
Filed: 1965-02-17
Abstract: Ammonium carbamate, contained in a liquid, mixture of the carbamate, urea, ammonia and water, is decomposed, and ammonia and carbon dioxide separated therefrom, by carrying out the decomposition in two discrete temperature zones each maintained at 220-320 DEG  F. and at atmospheric pressure to 400 p.s.i.g.  As shown in the drawing the liquid mixture is passed through a primary decomposition zone 15, preferably at 220-285 DEG  F., whereby carbamate decomposes to form gaseous ammonia and carbon dioxide. The liquid and formed vapours pass concurrently through this zone, preferably 75-95% of the <PICT:1103041/C1/1> carbamate being decomposed, to a liquid-vapour separation zone 37. The liquid then falls under gravity through the second heated decomposition zone 41 the flow being as a film of liquid of about 0.25 inch maximum thickness.  The ammonia and carbon dioxide formed in this second zone 41 pass upwards to the separation zone 37.  The second zone 41 can be at 295-320 DEG  F.  In the example the liquid mixture at 6000 p.s.i.g. and 420 DEG  F. is fed to the apparatus and passes through a pressure reducing valve 13 and thence to a distrubuter nozzle 17 at the top of the primary decomposition zone 19.  The zone 15 is in the form of a cylindrical heat-exchanger having a tube bundle 21 20 feet long with saturated steam passing through the jacket at 50 p.s.i.g. The liquid and vapours pass down the column at 80 feet/sec. Suitable residence times in the zone are between 0.2 and 0.5 sec. The tubes are 0.75 inch in diameter.  The head of the zone enclosing the nozzle may be insulated.  The liquid issues from the bottom at 275 DEG  C. and is collected by a tube 35 and delivered to the separating zone tangentially. The separator 37 is cylindrical and insulated and has an outlet for withdrawing vapours.  The second decomposition zone 41 is in the form of a heat exchanger as above with tubes 4 feet long the upper ends of which are notched at 55 and project into the separator so that the liquid collects as a layer not exceeding 1.0 inch in depth.  The tubes are 0.75 inch in diameter and are heated by steam at 200 p.s.i.g. passing through the jacket.  The liquid flows down the inside of the tubes at 4 to 6 feet/sec. with a residence time not exceeding 1.5 sec. preferably 1.0 to 1.2 sec.  The liquid emerges at 300 DEG  F. The residence time in the separator does not exceed 20 sec., preferably 5-10 sec.  The urea feed may be at 2500-10,000 p.s.i.g. and 160-250 DEG  F. and is made from carbon dioxide and ammonia in amounts from stoichiometric to a 200% excess of ammonia, the liquid melt containing 10-60% carbamate and 40-90% urea. The decomposition and separation zones may be in separate vessels and not a unitary apparatus as described.ALSO:Ammonium carbamate, contained in a liquid mixture of the carbamate, urea, ammonia and water, is decomposed, and ammonia and carbon dioxide separated therefrom, by carrying out the decomposition in two discrete temperature zones each maintained at 220-320 DEG  F. and at atmospheric pressure to 400 p.s.i.g.  As shown in the drawing the liquid mixture is passed through a primary decomposition zone 15, preferably at 220-285 DEG  F., whereby carbamate decomposes to form gaseous ammonia and carbon dioxide. The liquid and formed vapours pass <PICT:1103041/C2/1> concurrently through this zone, preferably 75-95% of the carbonate being decomposed, to a liquid-vapour separation zone 37. The liquid the falls under gravity through the second heated decomposition zone 41 the flow being as a film of liquid of about 0.25 inch maximum thickness.  The ammonia and carbon dioxide formed in this second zone 41 pass upwards to the separation zone 37.  The second zone 41 can be at 295-320 DEG  F.  In the example the liquid mixture at 6000 p.s.i.g. and 420 DEG  F. is fed to the apparatus and passes through a pressure reducing valve 13 and thence to a distributer nozzle 17 at the top of the primary decomposition zone 19.  The zone 15 is in the form of a cylindrical heat exchanger having a tube bundle 21, 20 feet long, with saturated steam passing through the jacket at 50 p.s.i.g. The liquid and vapours pass down the column at 80 feet/second. Suitable residence times in the zone are between 0.2 and 0.5 second.  The tubes are 0.75 inch in diameter. The head of the zone enclosing the nozzle may be insulated.  The liquid issues from the bottom at 275 DEG  C. and is collected by a tube 35 and delivered to the separating zone tangentially. The separator 37 is cylindrical and insulated and has an outlet for withdrawing vapours. The second decomposition zone 41 is in the form of a heat exchanger as above with tubes 4 feet long the upper ends of which are notched at 55 and project into the separator so that the liquid collects as a layer not exceeding 1.0 inch in depth.  The tubes are 0.75 inch in diameter and are heated by steam at 200 p.s.i.g. passing through the jacket.  The liquid flows down the inside of the tubes at 4 to 6 feet/second with a residence time not exceeding 1.5 second, preferably 1.0 to 1.2 seconds.  The liquid emerges at 300 DEG  F.  The residence time in the separator does not exceed 20 seconds, preferably 5-10 seconds.  The urea feed may be at 2500-10,000 p.s.i.g. and 160-250 DEG  F. and is made from carbon dioxide and ammonia in amounts from stoichiometric to a 200% excess of ammonia, the liquid melt containing 10-60% carbamate and 40-90% urea.  The decomposition and separation zones may be in separate vessels and not a unitary apparatus as described.