Gas separation: processes – Solid sorption – Including reduction of pressure
Patent
1996-10-30
1998-05-26
Spitzer, Robert
Gas separation: processes
Solid sorption
Including reduction of pressure
95102, 95105, 95130, B01D 53047
Patent
active
057558566
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process of recovering oxygen-enriched gas. More specifically, the present invention relates to a process for enriching and recovering oxygen by pressure swing adsorption (hereinafter referred to as "PSA") of a gas mixture which mainly contains nitrogen and oxygen.
BACKGROUND ART
Oxygen obtained by a PSA process is widely used in industrial fields which continuously use oxygen. Specific examples which require use of oxygen obtained by a PSA process include electric steel making, oxygen aeration in water treatment, pulp bleaching, and ozonizers. In recent years, further, oxygen-enriched gas takes the place of air in combustion for realizing a NOx reduction and an efficiency improvement. In addition, oxygen-enriched gas is also utilized in the field of biochemistry such as fermentation.
There are various prior art PSA processes for enriching oxygen, wherein 2-4 adsorbers are used to repetitively perform adsorption, depressurization, desorption and pressurization for obtaining enriched gas at a high recovery yield. In particular, various improvements have been made to lower initial cost, running cost and maintenance cost with respect to PSA utilizing two adsorbers.
For instance, according to the PSA process disclosed in each of Japanese Patent Application Laid-open Nos. 1-236914, 2-119915, 4-222613 and 4-505448, product oxygen from a product gas storage tank is made to flow reversely into each adsorber for pressurization in a pressurization step. This is because if the pressurization is performed solely by feeding of the gas mixture through the inlet end of each adsorber, nitrogen contained in the gas mixture may break through the outlet end of the adsorber. Thus, it was conventionally considered essential, for obtainment of high-concentration oxygen at a high yield, to prevent such a breakthrough by causing product oxygen to flow reversely through the outlet end of the adsorber.
However, reverse flow of product oxygen for pressurization of the adsorber entails a waste of energy. This is because product gas once forced out of the adsorber into the product oxygen gas storage tank by consuming of energy must be made to flow reversely into the adsorber in the pressurization step and then return into the storage tank again.
On the other hand, a PSA process which does not utilize product oxygen for pressurization is known from Japanese Patent Publication No. 6-170. According to this known PSA process, an outlet end of an adsorber having completed adsorption is brought into conduction with an outlet end of another adsorber having completed desorption via a pressure equalization line to introduce remaining oxygen-enriched gas emitted from the depressurizing adsorber into the pressurizing adsorber for pressurization (equalizing pressurization), thereby taking the place of pressurization by reverse flow of product oxygen. Subsequently, the adsorber having undergone equalizing pressurization is subjected to pressurization by feeding the gas mixture, whereas the adsorber having undergone equalizing depressurization is subjected to evacuating desorption (depressurizing desorption) by a vacuum pump.
However, according to the latter PSA process, the vacuum pump is idly operated in the pressurization step by pressure equalization between both adsorbers, so that the energy of the vacuum pump is wasted. Further, the pressure equalization between both adsorbers is not thoroughly performed to the point where there is no pressure difference between both adsorbers, so that the controlled recovery of remaining oxygen-enriched gas determines the degree to which the pressuring adsorber is pressurized. Thus, the remaining oxygen-enriched gas is insufficiently recovered and utilized.
DISCLOSURE OF THE INVENTION
Therefore, an object of the present invention is to provide a process which is capable of effectively utilizing the energy of a vacuum pump while recovering oxygen-enriched gas with a high oxygen concentration at a high yield.
To fulfil the above object, the present inven
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Haruna Kazuo
Miyake Masanori
Sasano Hiroaki
Bednarek Michael D.
Spitzer Robert
Sumitomo Seika Chemicals Co. Ltd.
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