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Vapor Recovery Around the World |
Gasoline storage tank evaporative emissions occur as gasoline undergoes a change from liquid phase to vapor phase to re-establish an equilibrium vapor concentration in the tank’s head space (ullage). When motorists refuel their automobiles, liquid is withdrawn from the underground storage tanks and the equilibrium concentration is driven below natural levels by the ingestion of lean vapor or pure air. One gallon of liquid gasoline will expand to approximately 520 gallons of vapor at 40 percent hydrocarbon concentration. Thus, storage tank pressure will increase quickly and will cause vapor emissions through open vents, pressure vacuum vents or leaks in the vapor recovery piping. Evaporative emissions of volatile fuels, such as gasoline (from aboveground and underground tanks at service stations and fixed roof tanks at bulk plants and other facilities), are well known in the petroleum industry and are typically referred to as "wet stock losses." The magnitude of these losses ranges from 0.10 percent to 0.50 percent of throughput and are dependent upon gasoline Reid Vapor Pressure (RVP), temperature and ingested air volume. That is, evaporative emissions are much greater in areas with the highest gasoline throughputs or higher gasoline volatility and storage tank temperatures. Positive pressure spikes during tanker deliveries (even with Stage I vapor recovery) will generate additional emissions. Therefore, for vapor recovery systems at service stations to be effective in the overall scheme of things, they must include not only front-end components that capture vapor displaced from vehicles’ tanks during refueling, but also back-end components that reduce evaporative emissions through vents and vapor piping leaks. Today’s technology for such back-end components (usually installed on storage tank vent lines) include a "membrane" system that separates hydrocarbon vapor from air, exhausts the cleaned air into the atmosphere and returns the hydrocarbon vapor to the storage tank. This is the technology employed in ARID Technology’s PERMEATOR, which reduces the evaporative losses by more than 95 percent; and the energy recovered by the system is 30,000 to 100,000 times greater than the energy consumed by operating the system. As with any developing technology, and especially petroleum equipment technology for protecting the environment, prospective users want to know how reliable it is. This means getting credible information on how the technology was developed, where it is being used and the results of such usage. The development of ARID’s membrane technology and its use, both in the US and around the world, are discussed in the remainder of this article. |
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