Vapor Adsorption System
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Transcript of Vapor Adsorption System
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7/29/2019 Vapor Adsorption System
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Vapor adsorption system
A typical vapor recovery unit is comprised of two adsorption vessels filled with activated carbon, a
vacuum system used to strip hydrocarbon vapor from the carbon bed during the carbon
regeneration process, and a recovery device which turns the regenerated vapors into a liquid
product.
Adsorption-Absorption System
Its most common application is the control of hydrocarbon vapor emissions at terminals handling
petroleum fuel products, e.g. gasoline bulk terminals.
In this configuration, the system is equipped with two identical adsorber vessels filled with activated
carbon. One adsorber vessel is on-stream in the adsorption mode while the other is off-stream in the
regeneration mode. Switching valves are provided to automatically alternate the adsorbers between
adsorption and regeneration so that one adsorber is always on stream to assure uninterrupted vapor
processing capability.
The inlet hydrocarbon vapor-air mixture to be processed flows up through the on-stream adsorber
vessel. In the on-stream adsorber, the activated carbon adsorbs the hydrocarbon vapor and allows
clean air to vent from the bed with only minimal hydrocarbon content. The second adsorber is
offline being regenerated. Carbon bed regeneration is accomplished with a combination of high
vacuum and purge air stripping which removes previously adsorbed hydrocarbon vapor from the
carbon and restores the carbons ability to adsorb vapor during the next cycle.
This design utilizes a liquid ring vacuum pump as the source of vacuum for regeneration. The vacuum
pump extracts concentrated hydrocarbon vapor from the carbon bed and discharges into a three
phase separator which separates the vacuum pump seal fluid, hydrocarbon concentrate, and non-
condensed hydrocarbon/air vapor.
The seal fluid is pumped from the separator through a seal fluid cooler to remove the heat of
compression from the seal fluid, and returned to the liquid ring pump. In some applications, e.g.
chloro-hydrocarbon vapor recovery, a dry type vacuum pump is substituted for the standard liquid
ring pump to avoid incompatibility of the vapor with the seal fluid required by the liquid ring pump.
Non-condensed hydrocarbon vapor plus hydrocarbon condensate flow from the separator to an
absorber column which functions as the recovery device. In the absorber the hydrocarbon vapor
flows up through the absorber packing where it is liquefied and subsequently recovered by
absorption into a liquid hydrocarbon absorbent.
A circulating liquid hydrocarbon absorbent, supplied from storage, serves the dual purposes ofabsorbing the recovered hydrocarbon vapor and providing cooling for the vacuum pump seal fluid.
The absorbent is normally the hydrocarbon liquid which was the original source of the vapor
generation. For example, in gasoline vapor control applications, gasoline product from a storage
tank is used as the absorbent. The recovered product is simply returned along with the circulating
gasoline back to the product storage tank. A lean absorbent supply pump and a rich absorbent
return pump are provided to circulate the required absorbent. A small stream of air and residual
vapor exits the top of the absorber column and is recycled to the on-stream carbon bed where the
residual hydrocarbon vapor is re-absorbed.
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New technology
Legislation is being prepared world-wide or is already in place to limit gaseous hydrocarbon
emissions to atmosphere. A large portion of these emissions are formed by volatile hydrocarbon
compounds derived from the manufacturing, transportation, and application of most liquid
petroleum products.
It is a well-known fact that hydrocarbon vapors emitted to the atmosphere, and in the presence of
ultra violet light from the sun, for low-level atmospheric ozone. Low level ozone has been identified
as a major precursor to the formation of SMOG. These and other hydrocarbon components such as
Benzene, Toluene and Xylene are known as carcinogenic (cancer causing to humans).
In an effort to minimize air pollution and the incidence of cancer, many organizations around the
world have established guidelines for maximum emission levels of various hydrocarbon and chemical
components. These are known globally as the USEPA, the German TA-Luft, and the EC Directive for
petroleum terminals and many similar national regulations.
To help reduce air pollution from the manufacture and handling of chemical and petrochemical
products vapor recovery system was developed.