Method of producing gaseous oxygen and a cryogenic plant in which said method can be performed

Claim 2

1 . A method for producing gaseous oxygen which method comprises compressing feed air to between 5 and 10 bars absolute, passing said feed air through a molecular sieve adsorber to remove carbon dioxide and water vapour therefrom, fractionating the feed air in a distillation unit comprising a high pressure column operating at between 5-and 9 bars absolute and a low pressure column operating at between 1.3 and 3 bars absolute, withdrawing liquid oxygen from said low pressure column, pressurizing said liquid oxygen, vaporizing said liquid oxygen and warming the vapour, characterized in that at least part of said- feed air from said molecular sieve adsorber is compressed to an elevated pressure in a recycle compressor and is divided into a first sub-stream and a second sub-stream, said first sub-stream is cooled by said liquid oxygen and expanded to produce (on a molar basis) a mainly liquid stream which is introduced into said high pressure column and/or said low pressure column, and said second sub-stream is cooled, expanded in an expander, used to assist in cooling said first sub-stream.and returned, at least in part, to said recycle compressor.

Claim 3

A method according to Claim 1, characterized in that said first sub-stream is compressed to a higher pressure than said second sub-stream.

Claim 4

A method according to Claim 1 or 2, characterized in that said first sub-stream is compressed to between 35 and 65 bars A, and said second sub-stream is compressed to between 34 and 45 bars A.

Claim 5

A cryogenic plant comprising a compressor for compressing feed air, at least one molecular sieve adsorber for adsorbing carbon dioxide and water vapour from said feed air, a distillation unit comprising a high pressure column and a low pressure column for distilling air, a pump for pressurizing, in use, liquid oxygen from said low pressure column, and a first heat exchanger in which pressurized liquid oxygen can be vaporized and warmed, characterized in that said cryogenic plant further comprises a recycle compressor having an inlet arranged to receive air from said molecular sieve adsorber, and first and second outlets, the first of which communicates with said first heat exchanger and an expansion valve downstream of said first heat exchanger whereby, in use, compressed air can be cooled in said first heat exchanger, expanded to produce (on a molar basis) a mainly liquid product, and introduced into said high pressure column and/or said low pressure column, and the second of which outlets is connected to a second heat exchanger and to an expander downstream of said heat exchanger whereby, in use, compressed air can be cooled and expanded in said expander, and a conduit to carry, in use, cold expanded air to the inlet of said recycle compressor via said first heat exchanger wherein it assists in cooling the compressed gas from said first outlet.

Claim 6

A cryogenic plant comprising a compressor for compressing feed air, at least one molecular sieve adsorber for adsorbing carbon dioxide and water vapour from said feed air, a distillation unit comprising a high pressure column and a low pressure column for distilling air, a pump for pressurizing, in use, liquid oxygen from said low pressure column, and a first heat exchanger in which pressurized liquid oxygen can be vaporized and warmed, characterized in that said cryogenic plant further comprises a recycle compressor having an inlet arranged to receive air from said molecular sieve adsorber, and first and second outlets, the first of which communicates with said first heat exchanger and an expansion valve downstream of said first heat exchanger whereby, in use, compressed air can be cooled in said first heat exchanger, expanded to produce (on a molar basis) a mainly liquid product, and introduced into said high pressure column and/or said low pressure column, and the second of which outlets is connected to a second heat exchanger and to an expander downstream of said heat exchanger whereby, in use, compressed air can be cooled and expanded in said expander, and a conduit to carry, in use, cold expanded air to the inlet of said recycle compressor via said first heat exchanger wherein it assists in cooling the compressed gas from said first outlet.

Claim 7

A cryogenic plant according to Claim 4, characterized in that said first and second heat exchangers are incorporated in a single heat exchanger.