Pressure Swing Adsorption (PSA) Activated Carbon Technology
Pressure swing adsorption vacuum regeneration is the most commonly used pressure swing regeneration systems currently in service. The vacuum regeneration is typically followed by an inert gas (usually air) purge that provides the working capacity necessary for the carbon to meet the required emission regulations.
In the pressure swing system, at least two (2) carbon vessels are provided to insure uninterrupted service. Vapors enter one of the carbon vessels and are dispersed through the bed of activated carbon, most of the hydrocarbons are adsorbed onto the carbon, allowing the cleaned air to exit to the atmosphere through the vessel vent. As hydrocarbons are being adsorbed in the on-line carbon vessel, the second vessel is being regenerated. Hydrocarbons are removed or desorbed from the activated carbon by pulling a mild vacuum on the bed with a mechanical vacuum pumping device and are sent to the next step in the process.
Hydrocarbon vapors and condensed hydrocarbon liquids from the regeneration process are discharged from the vacuum system into a separator vessel. Typically, a liquid ring vacuum pump or a liquid ring pump combined with a positive displacement pump is used to provide the necessary vacuum level for regeneration. The separator vessel is necessary to separate the seal fluid from the recovered hydrocarbon vapor and condenses hydrocarbon liquid. The seal fluid is cooled and returned to the vacuum system. The non-condensed hydrocarbon vapors, mixed with a small amount of air, flow from the separator vessel to the portion of the process where the actual recovery occurs. The actual recovery can be accomplished in a packed absorber column, a direct contact condenser or a refrigerated condenser depending upon the vapors being recovered and the process conditions. Hydrocarbon liquid is collected in the separator and in the recovery device and is pumped to liquid storage. The uncondensed hydrocarbon can be recycled back to the on-line carbon vessel or to a vapor holder.
Applications for these types of systems include gasoline vapors, sweet crude oil vapors, certain chemicals including light alkanes including propane and heavier, light alkenes including butene and heavier and light aromatics including benzene. Other chemicals include additives for motor fuels. The hydrocarbon concentrations in most of these applications will be greater that 1% by volume.
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Manufacturers of the most commonly used PSAC units are: