Questions about storage tanks
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Section 6.2.19 of fire code 50160 states that fixed-roof tanks storing Class A B and Class B liquids shall be equipped with flame arresters and vent valves； For storage tanks containing Class A and Class B liquids that are purged with nitrogen or other gases, emergency pressure relief devices shall also be installed. ”In its explanatory notes, it states that “for fixed-roof tanks storing Type A and B liquids that are purged with nitrogen or other gases, accident relief devices such as pressure relief manholes and vent manholes should be installed to ensure the safety of the tanks.” ”. I’m very confused. Can’t splitting the control process, using low-pressure nitrogen supplementation and high-pressure venting to the flare, along with the installation of one or more safety valves leading to the flare, solve this problem? Why are devices such as flame arresters, vent valves, pressure relief manholes, and breathing manholes installed?
No one is paying attention to this post; I’ll bump it up myself.
It’s impossible to install a safety valve with a flare stack on atmospheric pressure storage tanks
Yes, what was said on the 3rd floor is correct; the operating condition for safety valves is above 0.1 MPa, while the pressure in normal-pressure storage tanks is below 6.9 KPa. Different
Normally, these safety accessories may seem useless, but they prove to be very helpful in case of abnormal situations. Take pressure relief manholes for example: in cases of flash boiling, the pipeline leading to the flare system might not be able to handle the instantaneous flow rate, thereby potentially causing the storage tank to overpressurize.
Things like explosion-proof doors, or pressure relief manholes, I can understand. When things are about to explode and nothing else can be done, when the safety valve system isn’t able to handle the pressure, it’s necessary to relieve that pressure quickly. But why use a breather valve? Why? These items are all considered flammable and explosive substances that, in principle, should not be exposed to air. Then why are breathing valves used? Even assuming that the polymerization inhibitor requires oxygen, what’s the point of releasing it into the atmosphere through the breather valve?
Therefore, the vent valves or single-vent valves on atmospheric-pressure storage tanks for flammable and explosive materials must have flame-arresting functions, or flame arresters must be used in series. Emergency pressure relief manholes do not require flame arresters.
This post was last edited by cust008 on 2022-8-31 at 16:18. It seems to follow certain guidelines; for example, the discussions in this topic are all based on considerations related to direct interaction with the atmosphere. And these days, it’s basically not allowed to expose anything to the atmosphere at all; safety inspections simply won’t allow it. If flammable materials are exposed to the atmosphere, safety inspections will never approve such practice. When the pressure is low, you can choose to add nitrogen or another gas depending on the situation (as per the design); introducing air directly generally won’t work ； When the pressure is high, you need to discharge it into a closed system; releasing it directly into the atmosphere won’t work either. So, it seems that, within the scope of this discussion, the idea of installing fire arrestors or vent valves is rather strange.
It also needs to be addressed on a case-by-case basis. As you mentioned with the breathing valve issue, the inhalation of combustible substances into the air can lead to explosions. But for a large container, if the pressure has dropped to the point where air needs to be added, it means that the safety measures in place have failed. At this point, if pressure isn’t replenished in time, the atmospheric pressure could crush the equipment, leading to a massive leak of materials and potentially even a larger accident. In such a situation, a little bit of air doesn’t matter; after all, the explosive limits also depend on the amount of air present. When faced with two evils, one must choose the lesser one