Gas separation: processes – Solid sorption – And liquid contact
Patent
1998-06-08
2000-05-23
Spitzer, Robert
Gas separation: processes
Solid sorption
And liquid contact
95 99, 95101, 95114, 95143, 95146, B01D 53047
Patent
active
060661925
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to methods of easily and effectively recovering gaseous hydrocarbons from waste gases containing the gaseous hydrocarbons.
The invention pertains also to methods of treating gaseous hydrocarbons contained in waste gases in order that the waste gases can be released after reducing the concentration density of gaseous hydrocarbons, one of substances causing photochemical smog, to 1 vol % or less.
BACKGROUND ART
The density of gaseous hydrocarbons, one of substances causing photochemical smog, that are released into the atmosphere is strictly regulated by law not only in such advanced countries as the United States, European countries and Japan but also in Taiwan, Mexico, China, and so forth.
Although specific levels of regulatory standards vary depending on the situation of each country, the advanced countries, except for Japan, adopt the criterion of 1 vol % or less (38 mg/l or less) set by the United States Environmental Protection Agency (EPA). Among them, the United States and European countries strictly comply with this criterion. A recent trend has been to make the regulatory standards even more stringent.
Waste gases which are released when landing volatile hydrocarbons for storage or when loading or unloading them during transportation is a matter of particular concern as a source of gaseous hydrocarbons. This concern involves tank trucks, railroad freight cars, storage tanks and tankers engaged in domestic trade, for example.
Widely known conventional techniques for treating and recovering such waste gases containing gaseous hydrocarbons include:
(1) Absorption method (normal pressure absorption and reduced pressure recovery method) based on the use of a nonvolatile hydrocarbon solvent;
(2) Membrane gas separation method based on the use of a gas separating membrane;
(3) Low temperature processing method in which waste gas is cooled to an extremely low temperature; and
(4) Adsorption method based on the use of activated carbon or zeolite.
Among the aforementioned methods (1)-(4), an example of the absorption method (1) is disclosed in Japanese Examined Patent Publication No. 54-8632, in which waste gas is passed through, or washed out with, a nonvolatile hydrocarbon solvent, causing volatile hydrocarbons contained in the waste gas to be dissolved, and remaining air which is insoluble in the solvent is released into the atmosphere. The solvent containing the volatile hydrocarbons is then flashed in a vacuum vessel to separate volatile hydrocarbon vapor and the nonvolatile hydrocarbon solvent from each other. In this method, the separated volatile hydrocarbons are recovered by washing them with a hydrocarbon liquid of the same properties while the nonvolatile hydrocarbon solvent also recovered in the separation process is recycled for further use. This method is most widely used in Japan.
The method mostly commonly used in other countries is the aforementioned adsorption method (4) which employs activated carbon. Specific examples of the activated carbon adsorption method are disclosed in Japanese Unexamined Patent Publications Nos. 57-14687 and 57-42319 as well as in Japanese Examined Patent Publications Nos. 59-50715, 59-50716 and 2-46630. Compared to the earlier proposed absorption method (1) mentioned above, the activated carbon adsorption method is almost same as the absorption method in system configuration and is regarded as a technique which differs from the absorption method merely in that a process of absorbing gaseous hydrocarbons by the nonvolatile hydrocarbon solvent is replaced by an adsorption process using activated carbon. Accordingly, the aforementioned absorption method (1) can be regarded as a method in which a liquid adsorbent is used in a fluidized bed.
The aforementioned absorption method (1) has one drawback, however, in that the vacuum vessel must be depressurized to the degree of vacuum of about 3 mmHg to meet the United States EPA regulations, because the concentration of gaseous hydrocarbons remaining in air which is release
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Hiroshi Tahara
Kenithirou Suzuki
Toshinaga Kawai
Cosmo Engineering Co., Ltd.
Idemitsu Engineering Co., Ltd.
Spitzer Robert
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