Clean a 100-liter liquid nitrogen storage tank
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Our company’s air separation unit is about to be put into operation, and preparations need to be done in advance. One of these preparations involves reducing the oxygen content in the 100-liter liquid nitrogen tank (~0.8 Mpa) to below 1 PPM. The tank was just delivered by the manufacturer, and it contains nitrogen under pressure; however, its exact purity is unknown. I am responsible for carrying out the process of purging the tank. What preparations are needed? What are the methods and precautions for this process? Also, how much liquid nitrogen is required? (The liquid nitrogen we purchase has an oxygen content of 0.5 PPM.) :handshake
First, conduct dew point and oxygen content analysis; if both are within acceptable limits, pre-cooling with liquid nitrogen can be used directly. If the dew point does not meet the requirements, the dew point is first adjusted; once it meets the standards, liquid nitrogen is introduced, and pre-cooling takes place during this process. With a nitrogen purity of 99.9%, it takes about 1–2 tons of liquid nitrogen to reduce the oxygen content to less than 3 ppm~~
I asked the people at Air Chemicals, and they said that if they were to deliver the liquid and send specialized experts to carry out the cleaning of the storage tanks, the cost would be around 230 yuan per hour; cleaning one day would thus cost a certain amount. Later, our manager suggested that we carry out the cleaning ourselves. I wonder if it would really be that difficult if we did it on our own. I have cleaned tank trucks a few times before – is there a big difference? I’d like to learn more about these things beyond just the technical aspects. Thank you for your advice.
““Clean”? Is the storage tank contaminated? This requires professional analysis and replacement~~
It hasn’t been used yet; it’s a tank that has just arrived from the manufacturer. There is nitrogen under pressure inside the tank, but its purity is unknown. It seems to be a process of purging rather than cleaning – pressure is applied to the tank using a truck-mounted system, and then the pressure is released again. This process is repeated until the purity of the nitrogen in the tank meets the required standards
Sure, it’s best to analyze the dew point first; if it’s too high, it’s recommended to use air at room temperature for purging until the value is within the acceptable range. If the dew point is fine, then direct vaporization replacement with tank truck gas can be used for pre-cooling~~
It’s better to hire a specialized expert; having me go there would cost 230 yuan per hour, which is way too much. I went and got it done for free. I will now inform you of the cleaning and replacement method. 1. First, analyze whether the dew point is within acceptable limits; if it is, have someone bring in the qualified liquid nitrogen right away. 2. Analyze whether the liquid nitrogen supplied meets the standards. 3. Pressurize the liquid nitrogen tank truck and use the gas side to purge and displace the storage tank. Air intake from the top, with large-scale discharge from the storage tank. This gradually cools the temperature of the storage tank while also improving the purity of the cold gas. 4. Perform a displacement analysis over 4 hours, and then analyze the oxygen content in the storage tank. 5. After the analyzed purity is found to be satisfactory, the liquid is slowly poured in.
Importing liquid to replace pure liquid results in excessive waste.
It enters the storage tank after being vaporized in a tank truck; it is basically low-temperature nitrogen~~
There is a difference between nitrogen and liquid nitrogen.
I was a bit busy just now. Thank you; it’s quite detailed, and I basically understand it now.