HSG176 – Emergency venting can be handled by a number of different methods:
Pros: One vent to handle both normal & emergency conditions
Ultimate protection from external ignition sources
E-Flow technology reduces connection size for large capacity requirements
Sealed unit with no easy access to tank products
Easy clean, replacement, element
Cons: Tank is essentially free venting to atmosphere
One piece of equipment for both venting scenarios
As the outside temperature rises during the day, the pressure inside a tank increases and vapour-air will be expelled from the tank thus leading to the product losses.
The expelled vapour-air is dependent on the pressure difference between the tank pressure and atmospheric pressure and vapour-air space inside the tank, but independent of the size of a vent pipe or a flame arrester connection size
When the tank pressure approaches the atmospheric pressure, the out-breathing rate is extremely small and no pressure drop due to the flame arrester is appreciated.
The flame arrester is used to provide a venting path only; although the breathing rate for a large size of flame arrester may be greater than that of a small size of flame arrester, the total amount of out-breathing vapour-air is essentially the same.
During tank filling, the vapour in the vapour space over the liquid is displaced from the tank, leading to the product losses.
Working losses depend on the annual amount of liquid pumped in, the vapour pressure of the liquid stored and ambient temperature. The working losses have nothing to do with the flame arrester connection size.
Product losses are essentially the same no matter what size of flame arrester is installed.