Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-05-04
2001-11-06
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S641000, C062S908000, C062S909000
Reexamination Certificate
active
06311518
ABSTRACT:
The present invention relates to apparatus for a countercurrent heat exchange, between at least one first fluid available at a temperature near ambient and at least one second fluid available at a cryogenic temperature below −20° C.
The invention is applicable particularly to the cooling of atmospheric air to be distilled, and more generally to liquefaction, separation, purification or cold generation units, in which there is maintained a temperature level substantially below atmospheric temperature, for example below −20° C.
In what follows, reference will be had to the separation of air gases by distillation.
A conventional method to separate air gases consists in compressing atmospheric air, purifying it from water and CO
2
and cooling it, then introducing it into a distillation apparatus in which it is separated into at least one fluid rich in nitrogen and at least one fluid rich in oxygen. At least a portion of these effluents is reheated to ambient temperature, the available cold being used to lower the temperature of the air. The frigorific power necessary is generally supplied by an expansion turbine handling a fraction of the air. Numerous modifications of this process are described in the literature.
Purification and cooling means for air are of three types:
(1) Regenerator-purifiers, which contain a packing, arranged or in bulk, for heat exchange. They can be used pair-wise or group-wise, by rotation. The description which is given below corresponds to pair-wise operation to facilitate explanation.
In a half-period, a given regenerator is cooled by circulation in a first direction of a residual gaseous flow from the distillation apparatus. In the following half-period, the same regenerator is traversed in the other direction by the air to be cooled, from which it traps the water and CO
2
by solidification.
(2) Reversible exchangers, of which each passage is alternately traversed by a cold gaseous flow and by air to be cooled. The reversals permit, as in the preceding case, evacuating by elution the solid impurities which are deposited in the passages traversed by the air.
Reversible exchangers can moreover enclose one or more complementary heat exchange bundles permitting in particular reheating a pure fluid.
(3) Purification at the outset: the compressed air is purified adjacent ambient temperature by selective adsorption of the water and CO
2
, then the purified air is cooled, either in a regenerator, or in a simple heat exchanger.
Regenerator-purifiers and purely thermal regenerators can moreover enclose one or more complementary heat exchange bundles permitting reheating a pure fluid.
In all cases, there is utilized at least one heat exchange apparatus, generally countercurrent, whose external surface has a great area and has a temperature variable between the inlet temperature of the warm fluid, which is air, and a very low temperature, of the order of −180 to −200° C.
So as to limit the parasitic heat exchanges which degrade the performance of the installation, these heat exchange apparatuses are generally insulated from the ambient by a cold box, which is a metallic enclosure provided with an insulation in a nitrogen atmosphere to prevent the entry of moisture.
Despite the presence of this cold box, which represents a substantial investment, the residual heat exchanges, via the insulation, between the warm portions and the cold portion of the heat exchange apparatus and between the cold portions and the environment, remain substantial. Thus, the thermal losses of the heat exchange line to the environment often represent 20 to 25% of all the thermal losses of the installation.
The invention has for its object to reduce the parasitic heat exchanges of countercurrent heat exchange apparatus.
To this end, the invention has for its object a countercurrent heat exchange apparatus, between at least one first fluid at a temperature adjacent ambient and at least one second fluid at a cryogenic temperature below 20° C., characterized in that it comprises means to circulate the first fluid in an overall centripetal manner relative to a general central axis of the apparatus, from an inlet radially outside the apparatus, and means to cause the second fluid to circulate in an overall centrifugal manner relative to said central axis, from an inlet radially inside the apparatus.
The invention also has for its object an installation for the distillation of air, of the type comprising air compression means, means to cool and purify the air, and an air distillation apparatus supplied with cooled and purified air, characterized in that the cooling and purifying means comprise at least one heat exchange apparatus as defined above, whose radially external inlet is for the inlet of air to be distilled and whose radially internal inlet is for the inlet of a fluid from the air distillation apparatus.
The invention also has for its object a process for cryogenic cooling of a first fluid available at about ambient temperature by countercurrent heat exchange with a second fluid available at a cryogenic temperature below −20° C., characterized in that the first fluid is circulated in a heat exchange apparatus in an overall centripetal manner relative to a general central axis of this apparatus, from a first radially external inlet of the apparatus, and the second fluid is circulated in an overall centrifugal manner relative to said central axis, from a radially internal inlet of the apparatus.
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patent: 2724954 (1955-11-01), Maetz
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patent: 2964914 (1960-12-01), Schuftan et al.
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patent: 41 08 744 (1992-08-01), None
patent: 0 438 282 (1991-07-01), None
patent: 1.246.856 (1961-02-01), None
patent: WO 96/23188 (1996-08-01), None
Capossela Ronald
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Young & Thompson
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