Why cannot the argon fraction extraction port be located at the position with the highest argon content?

From the distribution diagram of argon in the upper column, it can be seen that there are two argon-enriched zones in the upper column: one in the distillation section (above the liquid-air feed inlet) and one in the stripping section (below the liquid-air feed inlet). Typically, the vapor argon concentration in the argon-enriched zone of the stripping section is higher than that in the argon-enriched zone of the distillation section. The distribution diagram also shows that the argon-rich region throughout the distillation section contains all three components: oxygen, argon, and nitrogen ； In the argon-rich zone of the stripping section, the upper part contains oxygen, argon, and nitrogen, while the lower part contains only oxygen and argon. It can be seen that when producing argon, it is advantageous to locate the argon fraction extraction port in the argon-rich zone of the stripping section. But why isn’t the sampling point located at the part of the distillation section where the argon fraction is highest? This is because in the crude argon tower, oxygen and argon are separated; most of the oxygen contained in the gaseous argon fraction condenses as it rises, while the low-boiling nitrogen components do not condense and remain entirely in the crude argon. As a result, the nitrogen content in the crude argon is dozens of times higher than that in the argon fraction. Therefore, if the nitrogen content in the argon fraction is too high, it not only reduces the purity of the crude argon but also causes the temperature difference in the crude argon condenser to decrease, or even bring it to zero (resulting in a \"gas plug\"); in such cases, the crude argon column stops operating. Furthermore, excessive nitrogen in the crude argon will make it difficult to produce pure argon; therefore, the sampling point for the argon fraction should be located where the nitrogen content is as low as possible. Generally, the nitrogen content should not exceed 0.06%. As can be seen from the argon distribution diagram in the upper column, the areas with the highest argon content in the argon-enriched zone of the stripping section also contain a relatively large amount of nitrogen. Therefore, it is better to locate the argon fraction extraction port slightly below the position where the argon fraction concentration is highest. The composition of the argon fraction is as follows: 8%–10% argon, 90%–91% oxygen, and less than 0.1% nitrogen.

I wonder what the moderator’s purpose for posting this thread is? Is it just for filling up pages? The questions on the oxygen production worker Q&A forum don’t seem to serve any purpose of genuine discussion.

Haven’t watched “Questions and Answers for Oxygen Technicians”, but I’ve learned it! Thank you!

When reading, one might not notice certain things; only when someone summarizes them do you realize that they were all in the book all along.

\"Oxygen Production Workers\" is an essential reference book for those studying air separation technology; if you haven’t read it, I recommend buying it – many useful informations can be found there!

The argon fraction extraction point requires not only a high argon content but also a low nitrogen content; a high nitrogen level can easily lead to nitrogen clogging. Since the nitrogen content is also high at the areas with the highest argon concentration, extraction should be carried out at a point slightly below those areas.

Because when the argon content is high, the nitrogen content also increases, which can lead to nitrogen blockage in the argon column

It’s simple: place it at the location with the highest argon content. Although the argon level is high, the nitrogen level there is also high, and nitrogen can easily cause a nitrogen plug during the distillation of crude argon. If the argon-rich zone of the stripping section is located as mentioned above, the nitrogen content will be within the normal range, preventing nitrogen plugging in the pressure system; moreover, appropriate discharge from the outlet provided in the pure argon tower will suffice.

When performing simulations using Aspen, the argon content is highest at block 39 in the upper column; however, the nitrogen content is also high. After extracting the argon fraction, nitrogen buildup can occur easily. Therefore, it is advisable to place the argon extraction point around block 46 below, where the argon content is around 9% and the nitrogen content is below 50 ppm, which is ideal.

In simple terms: reducing the nitrogen content in argon facilitates distillation and reduces costs (the boiling points of argon and nitrogen differ by 3 degrees, while that of argon and oxygen differs by 10 degrees)