Nitrogen sealing issue in storage tanks
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Flammable liquid storage tanks are equipped with nitrogen blanketing. Can a breather valve equipped with a flame arrester be used directly, allowing exhaust gases to enter the exhaust system through the breather valve? There is no separate nitrogen release valve on the storage tank. The image was found online
Are there any standards requiring the installation of a nitrogen release valve?
It’s possible, but it requires a larger amount of nitrogen. The control valve leads to the storage tank, while the single exhaust valve is used for exhaust gas treatment.
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For storage tanks of flammable liquids, the liquid inside is volatile, and the gas released by the pressure relief valve may contain flammable substances. Safety regulations may not impose restrictions in this regard, but environmental protection rules do; the gas from the pressure relief valve must be captured and recycled in a sealed manner. Under normal conditions, the tank should be maintained at a slight positive pressure so that the breathing valve does not need to function.
According to current environmental regulations, exhaust gases containing a small amount of organic compounds should not be released directly into the atmosphere. Exhaust gases with a low level of organic compounds cannot be sent to flares either; they must be routed into the exhaust gas treatment system. However, here the pressure design of the breather valve and the nitrogen seal valve must have a certain pressure difference; otherwise, too much nitrogen will be used, resulting in high costs.
This is possible, but the exhaust gases released must be treated in a sealed manner in a safe and environmentally friendly way； Additionally, the tank must be maintained at a slight positive pressure, and the breather valve should be calibrated at least once a year.
Article 6.2.19 of the \"Code for Fire Protection Design of Petrochemical Enterprises (2018 Edition)\” (GB 50160-2008) explicitly requires that fixed-roof tanks storing Class A B and Class B liquids shall be equipped with flame arresters and vent valves； Storage tanks for Class A B and Class C liquids that use nitrogen or other gases as a gas seal should also be equipped with emergency pressure relief devices.
A pressure relief manhole with a nitrogen seal must be provided, as the discharge rate of the vent valve alone is not sufficient to meet accident requirements