US 5,806,341 AGranted

Method and apparatus for air separation

AssigneeThe BOC Group, Inc.

InventorThomas Rathbone

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Abstract

Air is compressed in an arrangement of compressors. A first flow of the thus compressed air flows through a main heat exchanger from its warm end to its cold end and is liquefied by passage through a valve. Two second stream of compressed air are taken. One is expanded in one expansion turbine and the other in another expansion turbine. The streams leaving the valve and the one expansion turbine are separated in a double rectification column. Liquid oxygen product is extracted from outlet thereof. Part is taken as liquid product and the rest is vaporized by passage through the heat exchanger from its cold end to its warm end and taken as gaseous oxygen product. The ratio of liquid oxygen product to total oxygen product is capable of being varied. Accordingly a chosen but variable proportion of the two second air streams flows to the double rectification column and a chosen but variable proportion of the two second air streams is returned to the arrangement of compressors to an intermediate compressor.

Claims19

Dependent claims

A method of separating air comprising:

performing a plurality of compression steps to compress and further compress a stream of air;
cooling a first flow of the further compressed air by heat exchange with at least one product of the separation and at least partially liquefying the cooled first flow of the further compressed air;
expanding with the performance of external work at least one second flow of the further compressed air;
rectifying at least part of the liquefied air and at least part of the expanded second flow of air and thereby forming an oxygen fraction and a nitrogen fraction;
taking a liquid oxygen and/or a liquid nitrogen product from the rectification;
causing part of the expanded second air flow to flow in heat exchange passages intermediate the rectification and a location downstream of one of the compression steps and upstream of another of the compression steps;
adjusting the ratio of at least one liquid product to total oxygen product that is taken;
and
adjusting flow direction of a proportion of expanded second flow of air between said location of downstream of said one of the compression steps and upstream of another of the compression steps and said heat exchange passages to inturn adjust recyle of said proportion of expanded second flow of air back to said location and therefore refrigeration and production of said liquid product.

6 more elements

An apparatus for separating air comprising:

a main compressor for forming a stream of compressed air;
a plurality of booster-compressors for further compressing the stream of compressed air;
a main heat exchanger for cooling a first flow of the further compressed air by heat exchange with at least one product of separation of the air;
an expansion device for expanding the cooled first flow of the further compressed air so that the first flow of the further compressed air passes out of the expansion device at least partially in liquid state;
at least one expansion turbine for expanding at least one second flow of the further compressed air;
rectification means including a rectification column communicating with the outlet of said expansion device and the outlet of said expansion turbine for separating the air into an oxygen fraction and a nitrogen fraction;
means for taking at least one liquid product from the rectification means;
the main heat exchanger having passages for part of the second flow of air intermediate an outlet of the main compressor and the rectification means;
means for adjusting the ratio of at least one liquid product to total oxygen product;
and
means for adjusting flow direction of a proportion of the expanded second flow of air by a reverse in the direction of flow through said passages to inturn adjust recyle of said proportion of expanded second flow of air back to said location and therefore refrigeration and production of said liquid product.

8 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/688,750Filed 31 Jul 1996
Priority: GB 95159073 Aug 1995
Granted: 15 Sep 1998
Term ends: Not estimatedThe source records don’t support an estimate.

Classification15 codes

F25J 3/042
Division of the main heat exchange line in consecutive sections having different functions: having an intermediate feed connection
F25J 3/04296
Of feed air, e.g. used as waste or product air or expanded into an auxiliary column: claude expansion, i.e. expanded into the main or high…
F25J 3/04345
Of air: and comprising a gas work expansion loop
F25J 3/04381
Details relating to the work expansion, e.g. process parameter etc.: using work extraction by mechanical coupling of compression and expansion…