Storage tank nitrogen seal
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Dear masters! Help! Is nitrogen sealing of storage tanks called nitrogen sealing only when nitrogen is sucked in? One question I have is that when the nitrogen gas source is interrupted, if the pump is still pumping material, the tank will collapse. If the pipe that enters the breathing valve is disconnected, it will not happen, but air will also be sucked in when pumping material. Which one to choose? Is there any master who knows it well?
I am the original poster. Sorry, I forgot to attach the picture.
Look at the picture, if the nitrogen gas source is interrupted, the breathing valve will replenish air.
The breathing valve is the main safety accessory of the storage tank. It must be put into use, otherwise the storage tank cannot be used. Especially when materials enter and leave the storage tank, otherwise once the nitrogen pipeline is cut off, the storage tank will definitely be under pressure (when feeding) or negative pressure (when feeding).
Normally, nitrogen sealing is used with a breathing valve. This mainly depends on what risk you think is the main one in the HAZOP analysis. For example, if your material will explode when exposed to air, then you must not use a breathing valve. At this time, you would rather receive the result that the storage tank is damaged. However, if the contact between the material and air will not cause much harm, then it can be used.
I think there should be a tank pressure interlock pump inlet shut-off valve or pump. Once the pressure is abnormal, the feed valve or pump will be cut off.
A small amount of nitrogen is injected to maintain a slight positive pressure at the top of the storage tank. When the nitrogen supply is stopped, the breathing valve can operate normally and air will be replenished. For safety reasons, in addition to installing a breathing valve on the top of the tank, an explosion-proof and fire-retardant breathing manhole needs to be installed for double insurance.
You should get a nitrogen buffer tank in the installation area or system! Otherwise, it will be dangerous in case of emergency stop.
It must not be removed. If the breathing valve is removed, it will be flammable and explosive if air enters. Generally, even if the nitrogen is stopped, the operator will find it, unless your tank is very small and there is no alarm.
This post was last edited by cjgj008 on 2019-1-21 08:52 Just from your schematic diagram, if the nitrogen gas source is interrupted (closed or malfunctioned), the positive pressure is overpressured, and the breathing valve will exhale.； However, if negative pressure occurs, the breathing valve cannot inhale, and there is indeed a risk of the tank collapsing. I don't understand why the nitrogen source needs to be connected to the breathing valve. Hasn't this process done a HAZOP analysis beforehand? Of course, the tank pressure monitoring equipment will alarm when the pressure is negative, but it does not comply with the design safety principles. You can set up another set of breathing valves for independent breathing and set up an emergency release manhole with positive and negative pressure breathing functions to deal with it. I don't know if it was originally installed on your tank. In addition, the combination of nitrogen sealing and emergency release manhole is standard. Did you not consider this in the original design? (See Petroleum Depot Design Specification GB50074-2014, attached drawings)