Is it necessary to install a vent valve on a 20-cubic-meter methanol tank after sealing it with nitrogen?

Hello, after installing a nitrogen seal on a storage tank, it is necessary to install a vent valve. Its main function is to ensure the safety of the tank and its proper operation in case the nitrogen seal system fails (such as when the nitrogen seal valve or the nitrogen release valve malfunctions). Generally, larger storage tanks are also equipped with emergency pressure relief manholes to ensure emergency pressure release in the event of a fire in the tank or a failure of the breathing valve. 2. Regarding the nitrogen sealing pressure, the following relationships can be used as a guide for setting it according to actual production conditions: Maximum operating pressure of the tank > Exhaling pressure of the breathing valve > Setting pressure of the nitrogen sealing valve for releasing nitrogen > Setting pressure of the nitrogen sealing valve for introducing nitrogen > Atmospheric pressure > Inhaling pressure setting of the breathing valve > Minimum designed operating pressure of the tank

As mentioned above, since their uses are different, they are definitely necessary. You can take a look at the design drawings; it’s written there

For storage tanks at normal or low pressure, in accordance with the requirements of 5.1.3 in SHT3007-2014 \"Design Code for Tank Areas in Petrochemical Storage and Transportation Systems\", breathing valves shall be installed on the vent pipes leading to the atmosphere for the following types of tanks: a) Fixed-roof tanks and above-ground horizontal tanks used for storing Class A and B liquids； b) Tanks equipped with nitrogen sealing or other inert gas sealing protection systems. For atmospheric storage tanks equipped with a nitrogen seal, having a design pressure of 2 kPaG and a design vacuum level of -0.5 kPaG, the opening/closing pressure of the nitrogen seal is typically controlled between 200 and 500 PaG; the opening pressure of the breather valve is 1.35 kPaG, while the suction pressure of the breather valve is -0.3 kPaG