Process and plant for ammonia-urea production
View Patent ↗A process for ammonia-urea production where: liquid ammonia produced in an ammonia section is fed to a urea section directly at the ammonia synthesis pressure, and where the liquid ammonia is purified at high pressure with the steps of: cooling the liquid ammonia ( 20 ) obtaining a cooled liquid ammonia stream ( 21 ), separating a gaseous fraction ( 22 ) comprising hydrogen and nitrogen from said cooled liquid ammonia, obtaining purified liquid ammonia ( 23 ) at a high pressure, and reheating said purified liquid ammonia ( 23 ) after separation of said gaseous fraction, obtaining a reheated purified ammonia ( 24 ) having a temperature suitable for feeding to the urea synthesis process. The application also deals with an ammonia-urea plant comprising an ammonia cooler, a liquid-gas separator and an ammonia re-heater and with a method for revamping existing ammonia-urea plants.
1. A process for treating liquid ammonia for use in a urea synthesis process, comprising:
a) cooling the liquid ammonia to obtain a cooled liquid ammonia stream, wherein the liquid ammonia is produced by an ammonia synthesis process operated at an ammonia synthesis pressure, wherein the liquid ammonia contains minor amounts of hydrogen, nitrogen, methane and eventually other urea-inert gases,
b) separating a gaseous fraction comprising hydrogen and nitrogen from the cooled liquid ammonia to obtain purified liquid ammonia, and
c) reheating the purified liquid ammonia after separation of the gaseous fraction to obtain reheated purified ammonia having a temperature suitable for feeding to the urea synthesis process, wherein the reheating of the purified liquid ammonia is performed prior to the reheated purified ammonia being fed to the urea synthesis process,
wherein the cooling of the liquid ammonia, the separating of the gaseous fraction from the cooled liquid ammonia, and the reheating of the purified liquid ammonia are performed at substantially the same pressure as the ammonia synthesis pressure.
2. The process according to claim 1 , wherein the liquid ammonia is cooled to a temperature between −35° C. and −15° C.
3. The process according to claim 1 , wherein the re-heating temperature of the purified ammonia is in the range of 10° C. to 120° C.
4. The process according to claim 1 , wherein the reheated purified liquid ammonia is subjected to a dehydrogenation process prior to entering the urea synthesis process to produce a further purified ammonia feed with a low H 2 content for the urea synthesis process.
5. The process according to claim 1 , wherein the urea synthesis process is a CO 2 -stripping process with total condensation, comprising a high-pressure urea synthesis loop with at least a reaction space, a CO 2 stripping section and a total condensation section, the ammonia input of the urea synthesis process being directed fully or in part to the total condensation section.
6. The process according to claim 5 , wherein a major part of the ammonia input is directed to the total condensation section, and the remaining part of the ammonia input is directed to the reaction space.