Guidelines for the Initial Use of Cryogenic Storage Tanks

The cryogenic storage tank is an indispensable piece of equipment in modern industry, widely used for storing media such as liquid oxygen, nitrogen, argon, and carbon dioxide. When initially using a cryogenic storage tank, it's crucial to pay attention to a series of key steps to ensure the safe operation of the equipment and the quality of the stored media. Here are the precautions to take when using a low-temperature storage tank for the first time.
 
1. Equipment Inspection and Calibration
 
Prior to the initial filling, conduct a thorough inspection and calibration of the liquid level gauges and pressure gauges. Ensure that all valves are in the correct open or closed position and that the pipelines are unobstructed. Follow the operating procedures of the liquid level gauges to ensure they are in working condition.
 
2. Preparation for Filling
 
Initial filling typically involves a tank container that is at ambient temperature, including tanks that have been unused for a period and are being reactivated. Prior to filling, check the sealing performance of the tank and related equipment to ensure there are no leaks.
 
3. Handling of High-Purity Liquids
 
For the storage of high-purity low-temperature liquids, a purging and replacement process is necessary. This involves using dry, oil-free air or nitrogen at temperatures of 70°C to 80°C to purge the container for a minimum of 8 hours, followed by replacement with product gas. For nitrogen, which is lighter than air, it should be introduced from the vent valve and discharged from the bottom liquid inlet and outlet valves. For oxygen or argon, which are heavier than air, they should be introduced from the bottom liquid inlet and outlet valves and discharged from the vent valve. After several cycles of purging and replacement, when the pressure in the low-temperature tank reaches 0.1-0.2 MPa, the purged gas is released. Conduct purity tests on the discharged gas and only stop the replacement process when the purity requirements are met. Additionally, all valves and pipelines should be purged with product gas and meet purity requirements. Following replacement, the tank should be sealed under positive pressure to prevent the ingress of ambient air.
 
4. Handling of General Liquids
 
For the storage of general low-temperature liquids, the purging and replacement process described above may not be necessary. However, it is still essential to ensure the purity and quality of the liquid being filled, as well as the sealing performance of the equipment.
 
5. Filling Method Selection
 
It is recommended to use atmospheric pressure filling for the initial filling process. This involves opening the container vent valve before filling and closing it after filling is complete. This ensures that the container remains at atmospheric or low pressure, facilitating the process. For the filling of rare or precious low-temperature liquids, the inner cylinder of the low-temperature tank can be cooled with liquid nitrogen, followed by replacement with low-temperature product gas to the required purity level before filling. Pressurized filling may be chosen for this process.
 
In conclusion, the initial use of cryogenic storage tanks requires careful consideration of the specific circumstances and adherence to the recommended procedures to ensure the safe operation of the equipment and the quality of the stored medium. Regular inspections of the equipment and medium status are also necessary to maintain the safe and reliable storage of the medium.