Talking about leak detection in synthesis towers again
Thread Content
After the urea synthesis tower was switched from using steam for leak detection to air or nitrogen, some users mentioned that the air or nitrogen used for leak detection needs to be heated. Why is heating necessary? To what temperature should it be heated? What other precautions are there? I would appreciate it if everyone with expertise could offer their guidance.
I’ve never used air or nitrogen for leak detection, but I think the reason for heating is to prevent stress damage caused by large temperature differences on either side of the lining.
The air or nitrogen used for leak detection needs to be heated in order to prevent corrosion caused by moisture; if possible, instrument air or cryogenic nitrogen should be used instead. If your air or nitrogen can ensure it is free of water, heating is not necessary.
It’s a matter of removing water, in order to minimize the entry of corrosive substances; it seems to have little to do with temperature differences. Gas that enters the leak detection channel is preheated by the temperature of the tower
The urea used in our new Shanghai-produced vehicles is heated using nitrogen from air separation, with online monitoring in place. This post was last edited by lxq700918 on 2009-3-14 at 16:13.]
Is your nitrogen supplied by an air separation unit? What type of air separation process do you use? What is its scale? Could you provide more details?
Personally, I find it more convincing that heating can eliminate or reduce thermal stress due to temperature differences, for three reasons. 1. In the past, many of our devices used steam as the leak detection medium. Can you say that it was all dry steam? Condensation can occur even in longer leak detection tubes. 2. The instrument air, nitrogen, and plant air we use are usually supplied after being dried externally, so the likelihood of them containing water is low. 3. The reason we do not recommend using steam at the moment is still that steam may carry chloride ions, leading to stress corrosion. It’s not because of the water, right! At the 15th National Annual Conference on Large-Scale Urea Plant Technology held in Chongqing last year, I asked a foreign expert, and he replied that using air is the best option.
Can air be used for leak testing urine towers? Is it harmful to safety? Our factory uses nitrogen – could any member of the community tell us the advantages and disadvantages of that?
For leak testing urine towers, air or nitrogen can be used; as long as there is no water present, it poses no risk to safety.
1) Does nitrogen leak detection require heating? It’s been over 10 years since urea production started, and this is the first time I’ve heard about it ； 2) Nitrogen is delivered from the air separation unit to the pipeline network and then to the users – how could there be water in it? If that were the case, large nitrogen users such as those in ammonia production would have voiced their concerns long ago ； 3) The nitrogen used for leak detection is at positive pressure, so there is no possibility of water vapor entering the leak detection channel ； 4) When constructing the nitrogen pipeline network, work proceeds to the next stage only after the displacement analysis (including dew point) shows satisfactory results; urea is located downstream, so how could it be affected first?
When using nitrogen for leak detection in the synthesis tower, heating is indeed necessary. The temperature inside the synthesis tower is 183 degrees Celsius, while that of nitrogen is only 30 degrees Celsius; the temperature difference between the two is quite large. As mentioned on the second floor, the purpose of heating is to prevent stress damage caused by excessive temperature differences on either side of the lining. Generally, the nitrogen supplied from upstream does not contain water; if any is present, it is water that has accumulated in the pipes by the time it reaches the urea production stage.
Is it online leak detection? If it’s online, it’s best to preheat; the stress caused by temperature differences cannot be ignored. Many synthesis towers do not have external online leak detection; usually, the condition is determined by examining the appearance of the leak detection tubes, and during major repairs, instrument air or nitrogen is used to check for blockages. At this time, gas pressure must be strictly controlled during leak detection, otherwise the lining will be blown off. This post was last edited by Jinchanzi on 2009-3-16 21:55]