Protection of the catalyst in the synthesis tower
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How is the catalyst in the synthesis tower protected during long-term shutdown? Is it sufficient to fill the system with nitrogen to maintain a slight positive pressure? I’ve seen some information stating that air passivation can be carried out at lower temperatures; I wonder if this method is actually used in practice?
The best way is to use nitrogen protection. Air passivation has an impact on catalyst activity.
Nitrogen-filled micro-positive pressure protection is necessary, but it depends on the specific circumstances. If a long-term shutdown for maintenance requires opening the equipment and pipelines in the synthesis circuit or replacing the catalyst, or if there is no nitrogen available (which is hard to even imagine), it is possible to use air for passivation at very low temperatures. However, two conditions must be met: first, the temperature must be very low; second, the area must be properly purged, with hydrogen and ammonia levels confirmed to be within safe limits before such treatment can be carried out.