Vapor equilibrium tube for flammable liquids
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Currently, some experts say that vapor equilibrium pipes are also necessary for flammable liquids; this involves connecting a pipe in front of the vent valve on the tank to the tank truck, so that material can be drawn from the tank truck into the storage tank, and the gases inside the tank can return to the tank truck. Has anyone done this before? I think it’s possible, but some people say that pressure buildup can be a risk with atmospheric-pressure storage tanks and tank trucks. The breathing pressure of the tanks ranges from -300 to 1600 millimeters of water column, and they are sealed with nitrogen; I believe the tanks won’t collapse, but I’m not sure about tank trucks. I hope the master can give some guidance!
The balance pressure is there to prevent overpressure, right?
It has always been the case – balancing pressure and reducing exhaust gases
There is a certain safety risk here; how can you be sure that the tank truck contains nitrogen and not air? The gas in the tank truck can be fed into a separate recovery unit
The oxygen content of the gas in the tank truck needs to be analyzed; this is acceptable for fixed-roof tanks that do not have a nitrogen seal, as air is also introduced into such tanks through their breather valves. It is not suitable for floating-roof tanks that are equipped with a nitrogen seal
Without a balance tube, air enters through the breathing valve when the tank truck is unloaded!
The design pressure of atmospheric-pressure tanks is low; it’s uncertain whether the resistance encountered by gas entering through the breather valve as it moves toward the tank truck will be greater than the design pressure specified for the storage tank or the tank truck
The use of a vapor equilibrium tube is based on the principle of a communicating vessel; the system generally maintains its original pressure (without considering the risk of damage to the nitrogen seal), with only a risk of high liquid levels； If gas phase pipes are not used, both the handling of combustible gases inside the tank and the issue of air entering the tank car need to be taken into account, which is more troublesome ； If these factors are not taken into account, there will be safety and environmental issues
The abnormal operating conditions that can occur when the gas-phase equilibrium tube is blocked should be taken into consideration; high pressure in the tank truck may arise during loading, while low pressure may occur during unloading. Appropriate interlock protection must be implemented, or mechanical breather valves should be installed on the tank trucks.