Why should the switching cycle be shortened during the start-up phase of the full low pressure air separation plant with self-oil removal process?
Answer: As we know, in order to ensure self-cleaning of all low-voltage air separation plant, the temperature difference of cold end of switching heat exchanger must be controlled within the allowable range of temperature difference to ensure self-cleaning. The self-clearing temperature difference of the cold end is the temperature difference between the positive air passing through the section of the cold end and the return air passing through this section. In normal operation, the measured temperature difference at the cold end is self-cleaning temperature difference. However, in the start-up stage of the air separation unit, the temperature of the switching heat exchanger decreases continuously with time, and the self-clearing temperature difference of the temperature of the positive return flow through the channel is far greater than the measured temperature difference of the cold end. In addition, with the extension of switching time and the acceleration of temperature drop, the temperature difference of self-clearing at the cold end will be enlarged. Therefore, in the start-up stage of the air separation unit, with the cooling of the switching heat exchanger, in order to ensure self-cleaning, the switching period must be shortened.
The shortening of switching cycle is beneficial to the removal of frozen water and carbon dioxide. But at this time, the loss of air switching is relatively large.
As for the cooling accumulator, because it is a cold accumulator heat exchanger, the shorter the switching time is, the smaller the temperature difference at the cold end will be. Moreover, the amount of water and carbon dioxide frozen will be reduced, and the frozen layer will be thin, it is easier to clear.
In a word, in the start-up of the air separation plant, shortening the switching cycle is an effective measure to ensure the self-cleaning of the switching heat exchanger.
