Gasoline Vapor/Air Separation
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Problem In 2000, the California Air Resources Board (CARB), adopted new regulations restricting the emissions of gasoline vapors during retail gasoline dispensing at gas stations. The purpose for these regulations is to combat the formation of ground-level ozone due to hydrocarbon emissions. In addition to reducing air pollution, fuel savings will be realized if the recovered vapors are returned to the underground storage tanks. Solution Two classes of solutions are competing for the gasoline vapor processing market created by the new regulations: incineration and membrane separations. Incinerators are burners, which use fuel and a flame to oxidize vent vapors. Burners consume supplemental fuel to maintain combustion as inlet vapor concentrations vary widely. In addition, there may be concerns about emissions from the burners. Catalytic oxidation is also theoretically an option, but no company is known to be developing such a vapor processor for gasoline stations. Benefits In contrast to burners, membrane gas separation systems recover and recycle gasoline vapors back to the underground storage tanks. While the equipment must be installed for regulatory purposes, a savings in recycled fuel will also result. Examples Competitive silicone membrane based vapor processors pass the hydrocarbon portion of the vapor, and the retained gas (largely air) is vented. Should the system fail, safeguards must be built into the vapor processors to prevent uncontrolled release of gasoline vapors into the atmosphere. Such systems generally require a complex mechanical system to operate properly, including a fan, pump, condenser, valving, and the membrane cartridge. CMS fluoropolymer membranes operate by permeating and venting relatively clean air to the atmosphere, while retaining and recycling gasoline vapors to the tank. Essentially no emissions would then occur should there be power or system failures. No condenser is required for CMS membrane systems, resulting in less complex, more reliable mechanical systems. Performance CMS membrane cartridges for controlling gasoline vapor emissions from underground storage tanks are designed to operate in vapor processors. Vapor processors using CMS membrane cartridges have been certifired by CARB to comply with the 2000 CARB Phase II Enhanced Vapor Recovery regulations. Pre-certification system performance measurements showed total fugitive gasoline vapor to be 27 % of the maximum allowable emissions of 0.38 pounds of gasoline vapor per 1000 gallons of liquid gasoline dispensed. The vapor processor typically converts the saturated gasoline vapor in the storage tank to 98% air to be vented. Related Publications Koch, W. H., ‘Developing Technology for Enhanced Vapor Recovery: Part 1 – Vent Processors’, Petroleum Equipment & Technology, Feb/Mar 2001, pp. 16-22. Contact us If you have a process where you wish to control and recycle hydrocarbons, solvents or other organic vapors, contact CMS today for an evaluation of CMS gas separation membranes in your specific application. |
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