I have some questions regarding low-temperature gas separation
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I have some questions regarding low-temperature gas separation: how long does it take before it is unnecessary to drain the liquid from the cryogenic tank after it has been shut down? If liquid needs to be drained, what should be taken into account during the drainage process? ?
After the cryogenic tank is shut down, the drainage from the tank should be determined based on the freezing point of the gas at a certain pressure. When draining, care must be taken to avoid gas poisoning and frostbite; different gases have different physical properties
The drainage from cryogenic tanks is generally carried out based on actual needs – for example, when drying is required or when the liquid level is high. The liquid is usually discharged into a buffer tank, where it evaporates naturally before being sent to a flare for combustion. When draining, attention must be paid to the speed of drainage; it should not be too fast. Care also needs to be taken to prevent freezing damage. If it is the drainage from an air separation cryogenic tank, there is no need to send the liquid to a flare – usually, a heater is used, and after supplying low-pressure steam, the drainage valve is opened slowly to allow the liquid to be released. It is essential to pay attention to the drainage speed, as too fast a rate can result in the transport of liquid, which poses a risk.
When parking the system, drainage should be arranged in a sequential manner, starting from the lowest temperature points in the system: backwashing of the nitrogen washing tower, backwashing of the flash tank, and backwashing of the tail liquid throttle valve.
During short-term shutdowns with a downtime of no more than 24 hours, the air separation cold box can have its system inlets and outlets closed, thereby severing the connections between various subsystems; this allows for maintenance to be carried out while preserving the cold condition and liquid levels, in preparation for restarting the system. If it exceeds one day, the liquid air in the distillation tower and the liquid oxygen in the main cooler must be drained. When doing so, safety must be taken into account: there should be no oils or flammable materials in the area where drainage takes place ； Be extremely careful to avoid frostbite when discharging; it is strictly prohibited to operate without protective clothing and for unauthorized personnel to approach. On the other hand, when discharging, attention should be paid to the temperature rise rate of the distillation tower to ensure that the tower is not damaged by stress.