Refrigeration – Cryogenic treatment of gas or gas mixture – Liquefaction
Patent
1995-12-11
1997-09-30
Kilner, Christopher
Refrigeration
Cryogenic treatment of gas or gas mixture
Liquefaction
62632, 62636, 62926, 62908, F25J 308
Patent
active
056716125
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to a process and apparatus for recovering volatile liquids from air-volatile liquid vapor mixtures and, more particularly, to an improved process and apparatus for recovering vaporized hydrocarbons in the form of gasoline from an air-gasoline vapor mixture as is expelled from tank cars, trucks, ships, and the like during loading with gasoline.
BACKGROUND OF THE INVENTION
When handling volatile liquids such as hydrocarbons including gasoline and kerosene, air-volatile liquid vapor mixtures are readily produced. The venting of such air-vapor mixtures directly into the atmosphere results in significant pollution of the environment and a fire or explosion hazard. Accordingly, existing environmental regulations require the control of such emissions.
As a consequence, a number of processes and apparatus have been developed and utilized to recover volatile liquids from air-volatile liquid vapor mixtures. Generally, the removed volatile liquids are liquified and recombined with the volatile liquid from which they were vaporized thereby making the recovery process more economical.
The initial vapor recovery systems utilized in the United States in the late 1920's and early 1930's incorporated a process combining compression and condensation. Such systems were originally only utilized on gasoline storage tanks. It wasn't until the 1950's that local air pollution regulations began to be adopted forcing the installation of vapor recovery systems at truck loading terminals. Shortly thereafter, the "clean air" legislation activity of the 1960's, which culminated in the Clean Air Act of 1968, further focused nationwide attention on the gasoline vapor recovery problem. As a result a lean oil/absorption system was developed. This system dominated the marketplace for a short time.
Subsequently, in the late 1960's and early 1970's cryogenic refrigeration systems began gaining market acceptance (note, for example, U.S. Pat. No. 3,266,262 to Moragne). While reliable, cryogenic systems suffer from a number of shortcomings including high horsepower requirements. Further, such systems require relatively rigorous and expensive maintenance to function properly. Mechanical refrigeration systems also have practical limits with respect to the amount of cold that may be delivered, accordingly, the efficiency and capacity of such systems is limited. In contrast, liquid nitrogen cooling systems provide more cooling than is required and are prohibitively expensive to operate for this type of application.
As a result of these shortcomings of cryogenic refrigeration systems, alternative technology was sought and adsorption/absorption vapor recovery systems were more recently developed. One such system is disclosed in, for example, U.S. Pat. No. 4,066,423 to McGill et al. Such systems utilize a bed of solid adsorbent selected, for example, from silica gel, certain forms of porous mineral such as alumina and magnesia, and most preferably activated charcoal. These adsorbents have an affinity for volatile hydrocarbon liquids. Thus, as the air-hydrocarbon vapor mixture is passed through the bed, a major portion of the hydrocarbons contained in the mixture are adsorbed on the bed. The resulting residue gas stream comprising substantially hydrocarbon-free air is well within regulated allowable emission levels and is exhausted into the environment.
It should be appreciated, however, that the adsorbent is only capable of adsorbing a certain amount of hydrocarbons before reaching capacity and becoming ineffective. Accordingly, the bed must be periodically regenerated to restore the carbon to a level where it will effectively adsorb hydrocarbons again. This regeneration of the adsorbent is a two step process.
The first step requires a reduction in the total pressure by pulling a vacuum on the bed that removes the largest amount of hydrocarbons. The second step is the addition of a purge air stream that passes through the bed. The purge air polishes the bed so as to remove substantially all of
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Service Bulletin 11, Excessive Carbon Bed Temperatures, H. Dinsmore; John Zink Company, Jul. 6, 1993.
Jordan Holding Company
Kilner Christopher
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