Several issues with nitrogen-sealed storage tanks
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Container: Storage tank. Medium: Methanol. Volume: 5 m³. 1. Must a liquid storage tank equipped with a nitrogen purge system also be fitted with a vent valve? According to HG-20559-93, storage tanks equipped with a nitrogen seal as shown in Figure 1 must also be fitted with vent valves. Since the current process uses nitrogen as the gas source for staged control to achieve nitrogen sealing of the storage tanks, is it still necessary to install vent valves as well? 2. For methanol storage tanks, what is the common design for the nitrogen sealing system? Are there any specific design requirements for methanol storage tanks?
Here, we use two control valves for step control
If there is stage control, then a breathing valve isn’t necessary, right?~~~
But it doesn’t meet this standard
So did you add an additional breathing valve?
Of course not; segmented control is essentially the same as a breathing valve
Can it be understood that when a nitrogen sealing system is installed, a vent valve must also be installed? However, staged control functions as a built-in vent valve, so no additional vent valve is needed. But for storage tanks containing special types of materials with a flash point below 60°C, a vent valve must be installed regardless of the type of nitrogen sealing system used; in addition, a flame arrester should be placed in front of the vent valve, or an explosion-proof vent valve should be utilized. Is this the correct way to understand it?
A breather valve is still necessary; in the event of an emergency, if the nitrogen seal control valve is unable to supply enough nitrogen or fails to function, air needs to be introduced through the breather valve.
The specifications make it clear that when installing a nitrogen seal, it is necessary to consider scenarios in which the nitrogen seal fails; likewise, if the pressure relief valve fails, gas must be released through the breather valve. The main purpose of this is to protect the storage tank.
So, if a proportional control system is used to control the nitrogen seal, is it still necessary to install a vent valve as well?