What is the purpose of an emergency shut-off valve on the liquid outlet of an LNG storage tank?
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The specifications require that an emergency shut-off valve be installed on the liquid outlet pipe of the LNG storage tank, and it should be interlocked with the liquid level. It makes sense to have an emergency shut-off valve that can be used in case of an accident, but what’s the use of it in conjunction with a level control system? An alarm is triggered when the liquid level is too low, but then the shut-off valve will cut off the supply – what’s the difference between this and automatic supply cutoff when the level is too low? Especially when there is only one tank in the gasification station, this low liquid level interlock is completely useless.
Once a leak is detected, the emergency shut-off valve can be closed immediately to prevent large-scale leakage of LNG.
It is mainly to prevent the manual shut-off valve from failing to shut off in a timely manner in case of a leakage accident at the rear end of the emergency shut-off valve (1. It is not possible for people to approach the manual valve； 2. In the event of a failure of the manual valve), all the low liquid level alarms you mentioned do exist; the low-temperature liquid tank is not allowed to drop below the set minimum liquid level during operation
I would like to ask why the liquid level in a cryogenic liquid tank is not allowed to drop below a set minimum level during operation. What effects does operating at a low liquid level have on the tank or other equipment?
At normal operating angles, a low liquid level alarm can alert operators to switch tanks or increase the feed rate appropriately, taking measures to ensure continuous and normal transportation
The landlord needs to understand that the chain setup is the ultimate safeguard. You said there is an alarm when the liquid level is low, and someone is monitoring it. But what if human negligence leads to it not being detected when the liquid level is very low? ?
If it cannot be shut off in time during operation at low liquid levels, the storage tank may be drawn to a negative pressure, causing damage to the tank.
Civil defense, physical defense, and technical defense – technical defense is meant to reduce human negligence
An excessively low liquid level results in a supply interruption of the material; this is the same outcome as that caused by a chain shutdown.
Well, LNG storage tanks generally allow the liquid to flow out by gravity, so there is no need to create a negative pressure. I have encountered situations where negative pressure was generated when the breather valve of a fixed-roof storage tank was faulty
The liquid level is too low, or the tank has been emptied; as a result, it goes from a cold state to a normal state. Pre-cooling is necessary before adding liquid again. Additionally, a large amount of BOG may be generated. Such frequent temperature changes can also cause damage to the inner cylinder of the tank. Personal opinion