In most areas, some type of vapor control system will be required for gasoline and ethanol storage tanks. (I am assuming the location of the tanks are in the US.) As IFR states, you can install Internal Floating Roofs on the tanks to control the vapor emissions(IFRs). However, blanketing will not control the emissions unless the blanket pressure is sufficiently higher than the TVP of the product in the tank. Unfortunately, most gasoline and ethanol storage tank's design pressure is not high enough to blanket at a high enough pressure to reduce the emissions adequately.
Therefore, blanketing is usually not an option. You will likely be required to put some time of vapor control system on the tanks like an IFR. Another alternative is to install a common header that connects all of the vapor spaces of your fixed roof tanks. At the end of this header, a carbon adsorption based VRU can be used or a combustion system that safely burns the generated hydrocarbon vapors. Explosive mixtures can be controlled without blanketing. There are several manufacturers of this type of equipment.
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