Air separation oxygen production area: [Weekly Topic] Week 10 of 2011 – Discussion on accelerating startup by adding liquid?
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To reduce the startup time, many plants use the method of adding liquid to speed up this process; our plant, for example, uses liquid nitrogen to accelerate startup. However, this approach results in a very slow improvement in both oxygen purity and the performance of the argon column. Please share your thoughts on this matter. Any good suggestions or things to keep in mind would be appreciated; I look forward to your advice
Driving fast isn’t necessarily a good thing; when driving in hot conditions, it’s better to go slowly. What matters to the supervisor is whether you can drive safely, not how fast you go The nitrogen-oxygen side main cooler can be connected to accelerate the cooling of the main cooler
Flushing with liquid nitrogen is done for safety reasons. I have experienced using liquid oxygen for flushing, and it indeed can **reduce the time required for liquid to accumulate. However, it is essential to monitor the hydrocarbon content in the tower, as well as pay attention to the timing of the liquid oxygen flushing process, in order to prevent the tower from becoming overpressured
Reply to 3# yanjie618901: We add liquid nitrogen not for safety reasons, but mainly because we need to get the nitrogen products delivered as quickly as possible; it’s just the only option we have
Reply to 4# gader: Do we need to use liquid nitrogen in order to supply it within a short period of time? Backflushing is intended to shorten the time required for liquid accumulation and to establish a distillation condition as quickly as possible. The supply of liquid nitrogen still depends on the lower column; can backflushing with liquid nitrogen yield nitrogen product earlier than backflushing with liquid oxygen? I haven’t experienced it, so I don’t know how effective this approach is for you guys?
We prevent the back-filling of liquid oxygen; we only inject liquid when there is some liquid present in the main cooling tank. Of course, safety first
Reply to 4# gader: In fact, whether you fill your main cooler with liquid oxygen or liquid nitrogen makes no difference in terms of getting the nitrogen product out as quickly as possible! We all need to establish the liquid level of the main cooler so that there is sufficient reflux liquid in the lower column. Another point you mentioned is that oxygen is released later and it has a significant impact on the argon column; is this compared to using liquid oxygen in the main cooler? Still compare with others!
Agree with what was said above: only when the main cooler is operating can distillation take place in the lower tower
Both liquid nitrogen and liquid oxygen can accelerate driving! The method works; otherwise, it wouldn’t be used! Of course, it is necessary to prevent sudden cooling of the equipment; by controlling the timing of liquid filling and adjusting the heat level properly, the goal can definitely be achieved! Air separation is energy-intensive; it’s absolutely necessary to reduce startup time!
Our factory also filled it with liquid directly on 2 occasions, but it seems that liquid nitrogen was filled in first and then liquid oxygen
Either liquid nitrogen or liquid oxygen will work; the key is to control the pressures in the storage tanks and the tower properly