It generally takes 12 to 24 hours to start the cryogenic air separation unit. The core is due to its low-temperature distillation process characteristics and stringent equipment operation requirements. It is unable to start and stop quickly, which is a necessary process to ensure the safe and stable gas production of the unit.
First, multi-level preprocessing takes a long time. At the initial stage of plant startup, it is necessary to complete the unit calibration, system pressure test and leakage detection, instrument commissioning and other preparations in turn, and then start the air compressor and precooling system to cool down. At the same time, the impurities such as moisture and carbon dioxide in the air are completely removed through the purifier to avoid ice blockage in the low temperature environment. This series of pretreatment processes must be steadily promoted and take several hours.
Secondly, it is strictly prohibited to speed up the process of low temperature cooling. The unit needs to be gradually reduced from normal temperature to cryogenic working condition of about -196 ℃. If the cooling rate is too fast, the tower, pipeline and heat exchanger will generate thermal stress due to excessive internal and external temperature difference, which will cause hidden dangers such as deformation and cracking. Therefore, it is necessary to accurately control the temperature and slowly complete the whole process of precooling, cryogenic cooling and air liquefaction.
Finally, the establishment period of distillation condition is long. After air liquefaction, it is necessary to gradually accumulate liquid in the distillation column, rely on the difference of boiling points of oxygen and nitrogen, repeatedly complete mass and heat transfer, gradually establish stable distillation conditions, and finally produce oxygen and nitrogen products with qualified purity. The process of fine-tuning and parameter stability takes the longest time, which is also a key constraint to the start-up time. The whole process is gradual and indispensable to ensure the long-term safe and efficient operation of the plant.
