Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
1999-04-07
2001-09-11
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S103000, C095S105000, C095S130000
Reexamination Certificate
active
06287366
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application corresponds to French application 98 04303 filed Apr. 7, 1998, the disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to a process for the production of oxygen from air by adsorption with transatmospheric pressure variation, of the type in which, by means of a unit comprising at least two adsorbers, there is carried out in each adsorber a cycle comprising, successively and cyclically:
a phase (a) of repressurization to the high pressure of the cycle, this phase comprising a step (a1) of first repressurization countercurrent with at least one gas from a first decompression countercurrent in another adsorber, this phase (a) terminating in a step (a4) of production with admission of air countercurrent in which the oxygen produced is removed from the adsorber; and
a phase of regeneration comprising:
a step (b) of first decompression countercurrent in which the gas from the adsorber is sent to another adsorber in the course of step (a1);
a step (c) of countercurrent purge comprising pumping to the low pressure (Pm) of the cycle; and
a step (d) of purge/elution in which production gas is introduced countercurrent into the adsorber, which is subjected simultaneously to countercurrent pumping. cl BACKGROUND OF THE INVENTION
The PSA (pressure swing adsorption) processes are more and more widely used to produce oxygen of limited purity from atmospheric air. Of course, it is a continuous aim to reduce the cost of the oxygen produced.
To do this, there can be used adsorbents that are particularly specific and effective for the O
2
/N
2
separation, such as zeolites exchanged with lithium. However, the cost of these adsorbents is very much higher than that of conventional adsorbents such as molecular sieves
5
A or
13
X, such that their acceptance presupposes that only a small quantity of adsor-bents will be necessary.
To minimize the volumes of adsorbents used, it has been proposed to shorten the cycle, in particular by overlap ping the steps that are conventionally sequential.
The air can thus be introduced into the adsorber as soon as possible after the end of the purge/elution step, even immediately following the latter.
However, all things being equal, this introduction of air at low pressure has a negative influence on the advance of the adsorption fronts, which progress faster as the pressure in the adsorbent is low.
This is true for removing nitrogen but also for removing atmospheric impurities (water, CO
2
, traces of hydrocarbons, . . . ), for which there is used either a specific bed such as a bed of alumina or silica gel, or an adsorbent serving for the separation of O
2
/N
2
. In all these cases, the introduction of air at low pressure requires in effect greater volumes of adsorbents, which is contrary to the stated object.
On the other hand, the growth of the region in which takes place removal of the impurities increases the volume of air uselessly compressed and then pumped, to the detriment of the specific energy.
To limit these drawbacks, there has been proposed (EP-A-449 448) a process of the type mentioned above in which, in a unit with two adsorbers, the step (a1) mentioned is carried out only by introduction countercurrent of gas from the first countercurrent decompression of the other adsorber, and is followed by a second partial repressurization countercurrent step solely with production gas. After this second step, the air is introduced co-current into the adsorber to carry out the production step, in the course of which the production gas (oxygen) is sent to a storage.
SUMMARY OF THE INVENTION
The invention has for its object to permit obtaining, under satisfactory operating conditions, a cycle of further reduced duration.
To this end, the invention has for its object a process of the type mentioned above, characterized in that, in the course of a final step of phase (a), the air is introduced co-current into the adsorber immediately following the step (a1) of first countercurrent repressurization.
The process according to the invention can comprise one or several of the following characteristics, taken alone or in all technically possible combinations:
production gas is also introduced countercurrent into the adsorber during the step (a1) of first countercurrent repressurization;
the two gases introduced counter-current during step (a1) are introduced simultaneously and during all the duration of this step (a1);
during all said final step of phase (a), production gas is withdrawn from the adsorber and is sent to at least one storage;
during an initial portion of said final step of phase (a), the production outlet of the adsorber is closed, whilst this outlet is open following this final step;
in the course of step (b), there is carried out the countercurrent depressurization first by venting the adsorber to the air, to substantially atmospheric pressure, then by countercurrent pumping.
the duration of the cycle does not exceed 120 seconds, typically it does not exceed 80 seconds.
REFERENCES:
patent: 3280536 (1966-10-01), Berlin
patent: 3313091 (1967-04-01), Berlin
patent: 3564816 (1971-02-01), Batta
patent: 3636679 (1972-01-01), Batta
patent: 3717974 (1973-02-01), Batta
patent: 3738087 (1973-06-01), McCombs
patent: 3973931 (1976-08-01), Collins
patent: 4160651 (1979-07-01), Pivard
patent: 4781735 (1988-11-01), Tagawa et al.
patent: 4810265 (1989-03-01), Lagree et al.
patent: 4917710 (1990-04-01), Haruna et al.
patent: 4969935 (1990-11-01), Hay
patent: 4981499 (1991-01-01), Hay et al.
patent: 5122164 (1992-06-01), Hirooka et al.
patent: 5330561 (1994-07-01), Kumar et al.
patent: 5407465 (1995-04-01), Schaub et al.
patent: 5429666 (1995-07-01), Agrawal et al.
patent: 5518526 (1996-05-01), Baksh et al.
patent: 5520720 (1996-05-01), Lemcoff
patent: 5529607 (1996-06-01), Tan
patent: 5536299 (1996-07-01), Girard et al.
patent: 5540758 (1996-07-01), Agrawal et al.
patent: 5565018 (1996-10-01), Baksh et al.
patent: 5702504 (1997-12-01), Schaub et al.
patent: 5733359 (1998-03-01), Doong et al.
patent: 5755856 (1998-05-01), Miyake et al.
patent: 5997612 (1999-12-01), Doong
patent: 0 449 448 (1991-10-01), None
Derive Nathalie
Dubois Anne
Monereau Christian
L'Air Liquide Societe Anonyme pour l'Etude et l'E
Spitzer Robert H.
Young & Thompson
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