Hydrogen and nitrogen recovery from ammonia purge gas

A process for recovering nitrogen and hydrogen contained in ammonia synthesis loop purge gas, taken from an ammonia synthesis loop and containing hydrogen and nitrogen, plus some methane and/or argon, wherein:

• ammonia purge gas is extracted from an ammonia synthesis loop at a loop pressure;
• a purge gas feed is treated to remove ammonia and directed as an ammonia-free purge gas at loop pressure to a recovery unit for recovering at least part of its nitrogen and hydrogen content,
• the process comprising the following steps:
• cooling said ammonia-free purge gas feed at loop pressure to a cryogenic temperature, and partial liquefaction of methane and argon is achieved;
• separating at least one gaseous stream containing hydrogen and nitrogen from the cooled purge gas feed in a plurality of phase separators arranged in a cascade of said recovery unit, said plurality comprising at least one first high pressure separator forming a high pressure separation section and at least a second separator operating at a pressure lower than said loop pressure, the second and any subsequent separator receiving a liquid outlet from a previous separator of said cascade;
• the recovery unit being able to export a recovery gaseous stream containing hydrogen and nitrogen at loop pressure, and at least another gaseous stream containing hydrogen and nitrogen at a lower pressure;
• and
• reheating said gaseous stream containing hydrogen and nitrogen at loop pressure obtained at said separating step, and the so obtained reheated gaseous stream is exported from said recovery unit at loop pressure, and returned to the synthesis loop at loop pressure.