GAS MIXTURE RECTIFICATION

the present invention relates to an improved method of separating by rectification a mixture composed of at least three components"

More specifically, the present invention relates to a method for increasing yield of a component ' in small proportions in a mixture of at least three [...] which two are made of major proportions, point d * boiling constituent in small proportions being located between the boiling points of the two components in major proportions and being closer to that of the less volatile of these two constituents"

The present invention is particularly applicable to the separation of air by rectification and relates to a method for increasing the rate of extraction of argon*

-The present invention also relates to any installation in conducting the above methods"

It is known that it is possible to separate air into its component parts by means of two successive rectification zones, medium and low-pressure for example " Therefore, air previously purified [...] and traces of water contained therein, is brought, to its dew point for the pressure considered, in a first rectification zone said pressure. average area. Is collected in the bottom of this area a liquid fraction rich in oxygen and a liquid fraction head oxygen-deficient. At least a portion of [...] of these two liquid fractions collected is sent in a second region said low-pressure region. The fraction lean in oxygen is introduced at the head of the second region while the rich fraction is introduced approximately in the middle of the second region"

In the known methods, a portion of the cold required for keeping cold of the installation, can be obtained by expanding a portion of the feed air stream and introducing by blowing into the second rectification zone to an intermediate level of said area₀

The degree of blow is, in general, between 5 and

15 f °f by volume, relative to the supply air volume. A degree of blowing too high, however, causes a significant lowering of the oxygen efficiency of the separating operation and, on the other hand, a substantially completely separating argon"

Different methods for improving the extraction efficiency have been proposed"

It is thus possible to use the refrigeration released by the _AOE296A0AO> vaporization of a portion of the liquid oxygen collected in the bottom of said second zone to condense, in the condenser head of a auxiliary column, a portion of a fraction withdrawn from an intermediate level of said second zone, the condensed portion is fed to said second area at the same intermediate level. This method gives relatively satisfaction, it requires a high energy expenditure "Indeed, to condense a mixture containing essentially of" the argon in the auxiliary condenser, it is necessary that the vapour pressure of! "_AOE296A0AO> oxygen is less than that of the condensed mixture is, which has the drawback of requiring, for example, the presence of a suction fan-with the risks of leakage and air introduction related to the fact that the operation is carried out in [...] enhance substantially all of the pressures in said two zones of the primary stripper"

The present invention is an improvement of the existing methods and installation, which is no to the aforementioned difficulties and considerably reduce cost and energy consumption, the improvement which 1' object of the present invention can enhance the efficiency of extraction of a constituent in small proportions in a mixture; is made possible without requiring a special facility"

A fear object an improved method of separation by rectification for increasing the performance of a component d^{1 extraction} in low [...] in a mixture of at least three components, of which two are in major proportions, the boiling point of the component in small proportions being located between the boiling points of the major components in the proportions and being more [...] that of the less volatile of these two constituents, wherein a gaseous fraction is withdrawn from an intermediate level of a primary stripper and grinded in an auxiliary zone, the liquid fraction obtained in the auxiliary area being of the-: intermediate [...] Lan [...] ith the main-

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-valley embodiment of the present invention, said [...] \ c:i I sense withdrawn is at... eh least condensed portion α Pushes [...] tank zone- auxiliary ' because the [...] & claim ~ a * u. u--hands a portion of the. liquid fraction collected in the bottom of the second main 30ne the grinding.

Soda In another embodiment of the present invention, said gaseous fraction withdrawn is at ' least partially condensed in the bottom of said auxiliary area by the vaporization of at least a portion ae the liquid fraction collected at the head of the first area ae [...] main.

In another embodiment of the present invention, said gas fraction-withdrawn is at least in part condensed into head-the said auxiliary area by the vaporization of at least a portion of the the liquid fraction collected e: vessel V! _AOE280A2AO>: [...] area of said primary stripper"

In another embodiment-of--' T fs between i prevention, said gaseous fraction withdrawn is at least partially condensed to the head of said auxiliary zone by vaporization at least a portion 8 d ae the liquid fraction collected er head of the first area of said main rectification.

In a to^{1 embodiment of the present} invention, the concentration of the gaseous fraction drawn off at said component in small proportions, based on component the least volatile, is the strongest [...], and the concentration of the more volatile constituent is as small as possible.

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Preferably, said mixture of at least three components is air is to extract argon (therein in small proportions) the boiling point of which is between that of nitrogen and that of oxygen and is closer to that of oxygen, the least volatile.

As will be understood, however, that the present invention is applicable to any mixture, that it is gaseous or liquid to the ambient conditions of temperature and pressure.

The present invention also relates to any installation for conducting the process according to the present invention.

The invention be included at the reading of the following description and of the accompanying drawings which have by way of non-limiting example, applied to the case of producing argon, various embodiments of the present invention.

Figures 1,2 and 3 represent different embodiments made-

. station of the present invention. The similar portions thereof carry, in ua.. >ut. jie. simplification, , the kids, references * Figure 1 represents one embodiment wherein 1'

. oxygen low, . pressure-is at-& least-in-part _AOE280A2AO> vaporized [...] of ~ the auxiliary column and the rich liquid. oxygen, of. the. medium-pressure column is optionally partially vaporized at the head of the auxiliary column.

Figure 2 represents one embodiment wherein 1' medium pressure liquid nitrogen is at least partially vaporized in the bottom of the auxiliary column..

Figure 3 represents another embodiment wherein the average nitrogen pressure is supplied to the top condenser of the auxiliary column.

These embodiments are obtained with the aid of a double rectification column with two zones, an area 1 medium pressure and a low pressure region 2 and a auxiliary rectification column 4. The air, previously cleaned traces CC > 2 and water that it contains, is brought to the vicinity of its dew point for the mean pressure viewed in the medium-pressure column 1-by the conduit 5. The oxygen-rich liquid fraction obtained by vessel leaves the column 1 through the pipe 12, the nitrogen-rich liquid fraction obtained at the head of the column 1 [...] original

te the column by the conduit 13" [...] or part of the liquid fractions removed from the column 1 are then introduced into the low-pressure column 2.

The auxiliary rectification column 4 has a condenser in head 6 and optionally a condenser tank 7.

Is removed from the double rectification column liquid oxygen through the pipe 14 and nitrogen gas by the pipe 10. Is drawn to an intermediate level of the column a gaseous fraction 2 by the line 8 ; this fraction is supplied to the auxiliary rectification column 4 in which oxygen contained therein is condensed and the condensed fraction is returned by the conduit 9 to the low-pressure region.

The level at which the discharge takes place is a function of the operating conditions: pressure, [...] nature of the mixture, andc.

In the case of rectification low air pressure, , the tapping occurs at [...] the argon concentration is greatest possible and the nitrogen concentration as low as possible. In a conventional installation having about 60 trays, the bleed is generally performed at the^{e tray} 15.

Next, the pipe 11 a much larger proportion of the argon of the air which in the case of known methods. Instead of collecting 70 i > argon present in the air, as is generally the case in the known methods, is determined, for example for the case of Figure 1, which is collected more than 78 fo of 1' argon present in the air. Is also obtained a much better separation between oxygen and nitrogen.

Figure 1, the fraction oxygen-rich liquid leaving the column 1 through the pipe 12 is introduced by the line 112 in the condenser 6 wherein at least a portion of the oxygen-rich fraction is vaporized, and the oxygen-rich fraction is supplied by the conduit 212 [...] in the LP column. Another portion of the supply of cold required for the rectification is obtained in the condenser 7 by vaporizing a portion of the liquid oxygen fraction collected in the column 2.

Figure 2, the oxygen-rich fraction leaving the column 1 through the pipe 12 is fed directly to the column 2, another portion being delivered by the line 112 to the condenser 6 wherein it is at least partially vaporized, and then conducting 212 to the column 2.

A portion of the nitrogen-rich fraction obtained in the column 1 is conducted by a conduit 113 in the condenser 7 * that it leaves at least partially vaporized by the line 213-

Figure 3, the reflux in the auxiliary rectification column 4 is obtained by spraying a part of the nitrogen-rich fraction supplied by the conduit 313 and from the column 1 O

Of course, the invention is not limited to the embodiment shown, it is capable of many variations, accessible to those skilled in the art, according to the intended applications without away from the spirit of the invention"