Cryogenic separation of tail gases

During ammonia production with the use of nitrogen plants, technological process involves the use of blowdown gas for ammonia reactor blowdown. This gas has significant volume, it is used cyclically and only a part of blowdown gas is discharged during every blowdown cycle, that’s why the volumes of discharged gas is also quite significant and can reach 2000 Nm3/h.

At the same time, the composition of such gas is quite valuable. Blowdown gas contains methane, hydrogen, argon, for example, at one of the CIS nitrogen plant the blowdown gas composition is as follows:

Н2 — 30,0%
СН4 — 17,5%
Ar — 11,5%
N2 — 41,0%

At the output, such plants allow obtaining following gases with the specified purity by using cryogenic separation method, these gases can be completely used both for production on the nitrogen plants and for gas sales, that is:

Synthetic gas (N2 + H2) — 33.78% + 66.22%
Nitrogen — 98.94% + 0.85%
Argon — 99.91% (800 PPm N2 + 50 PPm CH4)
Methane — 99.996% (40 PPm Ar)