Problem with liquid discharge from the distillation tower after air separation unit shutdown
Thread Content
This post was last edited by you*n*nyou on 2012-12-14 at 13:13. Since the plant began operating, during each maintenance period, after the air separation unit is shut down, liquid oxygen is never released (in order to save time during startup, oxygen is produced in advance). What effects does prolonged use have on the equipment and manufacturing processes? What changes occur especially in the hydrocarbons within the main cooler?
Hydrocarbons tend to accumulate, which can lead to main cooling system explosions; it is therefore important to conduct regular inspections to ensure that levels do not exceed the allowed limits
It is recommended to release liquid oxygen if the vehicle is parked for more than 48 hours; otherwise, as the liquid oxygen evaporates naturally, the hydrocarbon concentration will increase (hydrocarbons do not evaporate), and an explosion could occur in the event of a static electricity discharge or heating incident.
If the parking time is long and heat preservation is required, it is recommended to inject some liquid nitrogen into the tower, empty all the liquid from the bottom of the tower, and monitor the concentration of the liquid in the main cooler.
In recent years, it seems there have been many accidents due to the lack of emission control for liquid oxygen during shutdowns. Most importantly, hydrocarbons in the liquid oxygen must be continuously analyzed after shutdown to prevent their accumulation and potential hazards. Generally, if the vehicle is parked for more than 48 hours, all the liquid must be drained, or the purity of liquid oxygen in that liquid must be reduced to a very low level.
Monitoring is sufficient if it is done within a week of parking. Be careful not to let fluid drain out when starting the vehicle; if it’s parked for a long time, it’s advisable to drain the fluid. After all, safety comes first – it’s not worth taking risks to save a little time while driving. Of course, it depends on your leader’s management philosophy
As long as the liquid level is maintained, there should be no problem. However, it is necessary to analyze the content of harmful elements in the liquid of the main cooler/lower column on time as required, to ensure that it does not exceed the specified limits. Generally, the less liquid there is, the higher the concentration of harmful elements becomes.
There is definitely a risk; this has also happened in our factory – if the liquid level drops, it’s possible to inject liquid into the tower
The same is true here; as long as the parking time isn’t too long, the overall impact isn’t significant. After parking, all valves of the distillation tower are closed, and the level of the main cooling liquid remains at its full level from the start. The loss of cooling capacity in the distillation tower is slow, so the concentration of CH compounds doesn’t increase significantly. Of course, if the level of CH compounds is already high when the distillation tower is shut down, attention must be paid. Our methanol air separation unit is located in a location where it’s affected by the emissions from coke ovens; the smell of those emissions can often be detected in the air, and as a result the level of CH compounds can be high. Nevertheless, tests for the concentration of CH compounds are conducted before shutting down the unit, to ensure that these compounds, especially acetylene, do not exceed acceptable levels
During a short stop, it is not necessary to drain the liquid, but drainage is required during a long-term stop; otherwise, it violates the operating procedures and can lead to serious accidents
Drainage for more than 72 hours; for safety reasons