Separation of argon from a gas mixture

Claim 2

A process for the separation of argon from a gaseous mixture comprising argon, nitrogen and oxygen by fractional distillation, which includes the step of mixing fluids and recovering some of the work of mixing, comprising introducing a first fluid stream comprising at least one relatively volatile component and a second fluid stream comprising at least one less volatile component into different regions of a liquid-vapour contact and mixing zone, establishing through the zone a flow of liquid that becomes in the direction of its flow progressively richer in the relatively volatile component through mass exchange with an opposed flow of vapour that becomes in the direction of vapour flow progressively richer in the less volatile component, withdrawing a mixed waste stream containing both said components from the zone, and employing fluid in or from the zone to perform heating or cooling duty (or both) for the distillation of the said gaseous mixture, whereby some of the work of mixing is recovered, wherein said first and second fluid streams pass to said liquid-vapour contact zone from the same or different distillation zones, said at least one relatively volatile component being nitrogen and said at least one less volatile component being oxygen, wherein a product stream comprising argon is recovered from said at least one of the distillation zones, and wherein (a) a third fluid stream comprising vaporous oxygen passes from the warmer end region of the said mixing zone to at least one of the distillation zones, and/or (b) vaporous oxygen is condensed in a condenser associated with said warmer end region and condensate is returned to the mixing zone.

Claim 3

A process as claimed in Claim 1, in which the first fluid stream is introduced into the mixing zone in the vapour state and the second fluid stream is introduced into the mixing zone in the liquid state.

Claim 4

A process as claimed in Claim 1 or Claim 2, in which the mixed waste stream is withdrawn from an intermediate level of the mixing zone.

Claim 5

A process as claimed in any one of the preceding claims, in which the first fluid stream consists of substantially pure gaseous or vaporous nitrogen and the second fluid stream consists of relatively impure liquid oxygen.

Claim 6

A process as claimed in any one of the preceding claims, additionally including the steps of reboiling liquid at the colder end of the mixing zone and returning resultant vapour to the mixing zone.

Claim 7

A process as claimed in any one of the preceding claims in which condensation of the said vaporous oxygen is employed to provide reboil for at least one of the distillation zones.

Claim 8

A process as claimed in any one of the preceding claims, in which the gaseous mixture of oxygen, nitrogen and argon is admitted to a single or double distillation column which produces oxygen at its bottom and nitrogen at its top, and from an intermediate level of which is withdrawn a stream comprising argon and oxygen, whose argon content is greater than that of the incoming gaseous mixture, and in which the argon-rich stream is fractionated in a separate distillation column to produce a pure argon product.

Claim 9

A process as claimed in any one of the preceding claims, in which the ratio of nitrogen to oxygen in the mixed waste stream is substantially the same as the ratio of nitrogen to oxygen in the said gaseous mixture.

Claim 10

A process as claimed in any one of Claims 1 to 7, in which the ratio of oxygen to nitrogen in the mixed waste stream is greater than the ratio of oxygen to nitrogen in the said gaseous mixture.

Claim 11

A process as claimed in any one of the preceding claims, in which the mixing zone operates at an average pressure in the range of from atmospheric pressure to 12 atmospheres.

Claim 12

A process as claimed in any one of the preceding claims, in which the purity of the condensed oxygen is less than that of the second fluid stream.

Claim 13

A process as claimed in any one of the preceding claims, in which the first fluid stream passes directly from the top of a distillation zone to the cold end of the mixing zone and a liquid nitrogen stream flows directly from the mixing zone to the said top of the distillation zone.

Claim 14

Apparatus for performing the process claimed in Claim 1, including means defining a liquid-vapour contact and mixing zone having a first inlet for a first fluid stream comprising said at least one relatively volatile component spaced from a second inlet for a second fluid stream comprising said at least one less volatile component, an outlet for the withdrawal of a mixed waste stream containing both said components, liquid-vapour contact means in said zone which enable there to be established through the zone a flow of fluid that becomes in the direction of liquid flow progressively richer in the said relatively volatile component through mass exchange with an opposed flow of vapour that becomes in the direction of vapour flow progressively richer in the said less volatile component, means defining a plurality of distillation zones, an inlet to at least one of said distillation zones for a gaseous mixture comprising oxygen, nitrogen and argon, an outlet for argon product from said at least one of said distillation zones, means for employing fluid in or from said liquid-vapour contact zone to perform heating or cooling duty (or both) for the distillation of the said gaseous mixture, whereby some of the work of mixing that takes place in said mixing zone in operation of the apparatus is recovered, said first and second inlets to the liquid-vapour contact zone communicating with the said one or more of the distillation zones, whereby in operation said first and second fluid streams are able to pass to said mixing zone from one or more of the distillation zones, and means for passing a third fluid stream comprising vaporous oxygen from the warmer end region of the said mixing zone to one of the distillation zones and/or, in association with the warmer end of said liquid-vapour contact zone a condenser, for condensing vaporous oxygen and for returning condensate to the mixing zone.

Claim 15

Apparatus as claimed in Claim 13, in which the outlet for the withdrawal of the mixed waste stream communicates with a region of the mixing zone intermediate its ends.

Claim 16

Apparatus as claimed in Claim 13 or Claim 14, in which the condenser associated with the warmer end of the mixing zone has a passage therethrough for the flow of heat exchange fluid in a heat pumping circuit which in operation provides reboil for at least one of the distillation zones.

Claim 17

Apparatus as claimed in any one of Claims 13 to 15, in which the distillation zones comprise a single or double distillation column which in operation produce oxygen and nitrogen and from which a stream comprising oxygen and argon is able to be withdrawn, whose argon content is greater than that of the incoming gaseous mixture, and a separate distillation zone able to separate said stream comprising oxygen and argon to produce a pure argon product.