Regarding the vent behind the synthesis tower
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For membrane separation hydrogen production and isobaric absorption, from which point in the synthesis system is the gas taken?
The processes are different, and the locations for venting are also different. In the ammonia separation process after the tower, venting generally occurs before fresh gas is introduced; whereas in the ammonia separation process before the tower, venting takes place sometimes after ammonia cooling in the last stage.
Synthesis off-gas is generally vented after ammonia separation; the ammonia content in the gas vented here is low, which helps to protect the hydrogen extraction membrane
Ammonia is vented after separation; the ammonia content is low while the inert gas content is high
Before fresh make-up air is introduced after the separator, the concentration of liquids such as ammonia is low, while the concentration of inert gases such as methane is high; moreover, it does not result in any waste of compressor power. This should be a common-sense issue
Venting is carried out before the unit downstream of the separator (in the circulation section); this is where the concentration of inert gases such as CH4 is highest
Several of our systems use ammonia after separation; the reason was explained clearly upstairs – the ammonia content is low while the inert gas content is high
We use ammonia cooling and ammonia separation for gas replenishment; therefore, hydrogen is released after the tower for recovery between the cold exchanger and the recycled ammonia cooling system. The processes in different factories are not exactly the same; the locations where air is added vary, so the procedures also differ.