HYDROGEN AND NITROGEN RECOVERY FROM AMMONIA PURGE GAS

摘要

An ammonia plant is disclosed, where ammonia purge gas (20), is sent to a cryogenic recovery unit, said recovery unit comprising means of cooling (102, 202, 302, 402, 502) and a high-pressure phase separator (103, 203, 303, 403, 503) operating at loop pressure; inside said unit the purge gas (20) is cooled to a cryogenic temperature, and a partial liquefaction of methane and argon is achieved; the high-pressure phase separator separates the cooled stream into a gaseous stream and a bottom liquid; the gaseous stream is reheated in a passage of a heat exchanger; the unit is then capable to export a gaseous stream (123, 223, 323, 423, 523) containing nitrogen and hydrogen at loop pressure, that can be reintroduced at the suction side of the circulator (4) of the loop.

主权项

1. 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 directed to a recovery unit for recovering at least part of its nitrogen and hydrogen content, the process comprising the following steps: cooling said purge gas feed 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 is reheated 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.