When the leakage occurs in the air separation unit, the cooling capacity is insufficient and the main cooling liquid level drops continuously. If there is a large amount of gas leakage, the pressure rise in the cold box can be observed. If the cold box is not tight, a lot of cold air will come out of the gap. However, when the cryogenic liquid leaks, there is no obvious pressure rise and gas escape, and the base temperature often drops significantly.
Many units have accumulated some experience in the production practice, in order to have a preliminary judgment on the leakage position and leakage before shutdown maintenance, so as to shorten the shutdown time. (1) Test the purity of the gas escaping from the cold box. When nitrogen or liquid nitrogen leaks, the volume fraction of nitrogen in cold air can reach more than 80%; when oxygen or liquid oxygen leaks, the volume fraction of oxygen can be significantly increased. (2) Observe the "sweating" or "frosting" parts on the wall of the cold box. At this time, attention should be paid to the leakage of low-temperature liquid, and the "frosting" part is below the leakage point. (3) Observe the regularity of escaping gas. It is mainly used to judge the leakage of the switching channel of the switching heat exchanger. For the alternately used containers, the leakage position can be further determined by switching use. The above judgment methods are often combined.
In order to be familiar with the actual location and operation of the cold box, we need to accumulate experience.
