How to purge the unit when it is shut down and connected to the acidic gas line (hydrogen sulfide)
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When the solvent regeneration and acidic water stripping units are shut down for maintenance, should the acidic gas lines be purged with steam or nitrogen? If steam is used for purging, it has completely condensed into water after air cooling – how can purging be carried out in such a case? If nitrogen is used for purging, can hydrogen sulfide be completely removed? Can the equipment meet the conditions required for entry during maintenance? Are the pipelines suitable for welding work? What is the standard for achieving complete purification?
I’m quite worried – why hasn’t there been a response? This is a problem that larger refineries generally encounter; let me explain it first. We at Laozhuang have always used steam purging; it’s an old tradition, as there isn’t enough nitrogen in the entire plant, making it impossible to achieve balance. Since the new unit is equipped with air cooling, it is not practical to purge it with steam; I wonder if nitrogen can be used instead.
Nitrogen can be used. When my facility shuts down, the acidic gas lines are first purged with nitrogen and then cleaned with steam; it’s fine to use air cooling as well – just extending the purging time will ensure thorough cleaning.
Using nitrogen is better than steam; the amount of gas used for displacement must be appropriate. You only need to consider the amount of purging gas and the suitability of the inlet and outlet ports. The standard for achieving thorough purging is determined by gas analysis.
First, purge with steam, then dry with nitrogen, and finally release the nitrogen. Blowing directly with nitrogen requires a large amount of gas; if there is an adequate supply of nitrogen, it can be used for blowing. The combustible material content is less than 0.5%, so work with open flames is permissible ； When entering the tower or tank, the oxygen content must be 20%, and it must be free of toxic substances such as H2S and NH3.
If nitrogen is used for displacement, can H2S, NH3, etc. attached to the pipelines be completely displaced?
First, purge with steam for a longer period of time, and then purge with nitrogen. The cost of steam is much lower than that of nitrogen, and at the same time, the high temperature of steam facilitates the volatilization of hydrogen sulfide gas in the sediments.
Using nitrogen is better; steam can easily cause corrosion of the pipelines due to hydrogen sulfide
Nitrogen purging should be used; since most H2S pipelines are equipped with internal anti-corrosion coatings, nitrogen purging is recommended to protect these coatings.
Our factory generally uses N2 for purging, and then steam, as there is not enough N2 available throughout the factory. As for whether it is qualified, it must pass inspections; the oxygen content, the content of flammable gases, and the H2S level must all meet the standards. Only when it meets these requirements will the safety department issue a permit for operation, and this is very important.
1. First, use nitrogen to purge the torch until proper displacement is achieved; 2. Then switch to steam cooking and vent it to the atmosphere. Reduce the smell of people entering the tower.