After the production overhaul was completed, the molecular sieve was activated, and the naked cold leak detection showed normal results. Once the bare cooling process was finished, both expanders were shut down, and the entire tower was subjected to a heating cycle. After the heating was completed, all internal and external valves were closed, and the system was pressurized. The maintenance shelf was removed, the foundation of the cold box was cleaned and dried, and then it was filled with perlite sand. Following the sand loading, the air compressor was started to supply air to the air separation unit. The product specifications and all operational parameters met or exceeded the design requirements, and the issue of ice formation outside the main cold box was completely resolved.
From our experience, it is crucial to ensure that the leak detection after installation or major overhauls of the air separation equipment is thorough and leaves no blind spots. Leaks of low-temperature gas or liquid within the cold box are among the leading causes of equipment failure. During installation and pressure testing, every joint and connection must be carefully inspected to guarantee there are no leaks before the cold box is sealed and filled with sand. The layout of the pipelines inside the cold box should be designed reasonably, avoiding placing low-temperature equipment too close to the walls. Since the cold box plates are typically made of ordinary carbon steel, prolonged exposure to low temperatures can cause embrittlement, which is a common cause of cracking in the cold box plates. Additionally, equipment should be maintained and repaired according to the scheduled intervals, and the number of temporary shutdowns should be minimized as much as possible. Thermal expansion and contraction stresses can significantly impact the lifespan of the piping systems.
Every time the air separation equipment is heated, the perlite sand inside the cold box tends to thaw, while other areas remain at low temperature. If the perlite becomes wet or frozen, it can lead to pipe deformation and damage. It’s important to replenish the perlite sand promptly. Over time, the perlite may settle, so regular refilling is necessary. The perlite inside the cold box must also be kept dry. During normal operation, the cold box should be filled with sufficient dry and clean nitrogen. In case of a temporary shutdown, the cold box should be connected to an external source to inflate it and maintain pressure. Proper sealing of the cold box is essential. The inlet and outlet pipes of the cold box should be resealed with high-quality sealant approximately every five years. The manhole seals on the top of the main and auxiliary cold boxes should be checked regularly to prevent rainwater from entering. It is recommended to use waterproof covers for added protection.
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