Method and apparatus with a single rectifying column for air fractionation

Claim 3

The process of claim 1, wherein the liquefaction of gaseous nitrogen coming out from the top of said fractionation column occurs by means of the following working steps: heating in at least a heat exchanger; compressing up to a pressure higher than the outlet pressure from said column; cooling by causing it to flow countercurrently in at least the same heat exchanger in which it flowed before the compression; causing to expand a fraction thereof up to the same pressure and temperature as the one existing at the outlet of gaseous nitrogen; recycling said expanded fraction; letting again as refluxed liquid into the top of the fractionation column nitrogen cooled up to the liquefaction, by causing it to flow through a throttling element; the rest portion being the produced liquid nitrogen.

Claim 4

The method of claim 1, wherein the drawing of liquid oxygen from the bottom of said fractionation column occurs by means of a recycling pump and said oxygen is heated up to a temperature from the room temperature to the one existing at the outlet from said column by causing it to firstly flow through at least one of said heat exchangers countercurrently with the flow of said gaseous nitrogen to be liquefied and then through a throttling element before it enters again the bottom of said fractionation column.

Claim 5

The method of claim 3, wherein a portion of oxygen drawn from the bottom of the fractionation column is not recycled and a fraction thereof heated up to room temperature is used as produced gaseous oxygen, the other fraction which is not heated and caused to flow through a throttling element being used as produced liquid oxygen.

Claim 6

A method according to claim 1, wherein air to be fractionated is caused to expand, after cooling and before forwarding it to said column, in an expansion machine which is working and causes it to cool down to a temperature which is near the one of liquefaction.

Claim 7

The method of claim 2, wherein nitrogen is heated up to room temperature, at which temperature it can be drawn as gaseous nitrogen for use; compressed up to a pressure from 5 to 200 Kg/cm 3 , cooled firstly up to a temperature in the range from -100° to -150° C and then caused partially to cool by expansion to the initial outlet temperature and pressure of gaseous oxygen which are respectively in the range from -180° to -196° C and from 0 to 5 Kg/cm 2 and partially further cooled up to the liquefaction temperature of nitrogen corresponding to said compression pressure.

Claim 8

An apparatus for carrying out the method of claim 16 comprising: (a) a single rectification column having a top portion for withdrawing nitrogen gas, a bottom portion for withdrawing liquid oxygen and an intermediate portion for withdrawing an argon stream; (b) a nitrogen recycling circuit in fluid communication with the top portion of the column, the circuit comprising: (1) heat exchange means including first, second and third heat exchangers for cooling and liquefying a fraction of withdrawn nitrogen gas by countercurrent flow with a fraction of withdrawn liquid oxygen through the first and second heat exchangers, and (2) reflux means for refluxing the liquid oxygen from the third heat exchanger in the top portion of the column; (c) atmospheric air supply means connected to the column at the top portion thereof, the supply means being connected to the first heat exchange to cool the air by a flow countercurrent to the gaseous nitrogen and liquid oxygen; and (d) a circuit for recycling oxygen connected to the bottom of the column and in fluid communication therewith, the circuit comprising: (1) the second heat exchanger to heat a fraction of the liquid oxygen withdrawn from the bottom by countercurrent flow to the returning gaseous nitrogen, to render the oxygen gaseous and (2) means for returning the gaseous oxygen to the bottom of the column, and wherein the circuits and the heat exchange means are located outside the column.

Claim 9

The apparatus of claim 7, wherein said nitrogen recycle circuit comprises two countercurrent flows for each one of a number of heat exchangers respectively at increasing temperatures, at least a compressor and at least an expansion machine.

Claim 10

The apparatus of claim 8, wherein said nitrogen recycle circuit is connected to the top of said column through a pipe and said expansion machine is connected in the backflow branch of said circuit, having the outlet directly connected to said pipe and the inlet paralleling the backflow paths of at least one heat exchanger at lower temperature, disposed mutually in series on a line connected in turn to the top of column through a throttling element and to the utilization place of produced liquid nitrogen.

Claim 11

The apparatus of claim 7, wherein said circuit for oxygen is connected to the bottom of column through a conduit comprising a recycling pump, at least a flowpath of said heat exchangers at a higher temperature and a throttling element through which the circuit come back to the bottom of said column.

Claim 12

The apparatus of claim 10, wherein said recycling pump on said conduit is connected in parallel to another pump for partially drawing liquid oxygen, forwarding through a pipeline to the utilization place the produced gaseous oxygen throughout further flowpaths of said heat exchangers and supplying to the utilization place the produced liquid oxygen through a pipeline and a throttling element.

Claim 13

The apparatus of claim 7, wherein said line for air comprises at least a compressor, drying and purifying elements at least a flowpath in said heat exchangers at a higher temperature and a throttling element having the outlet connected to said column.

Claim 14

The apparatus of claim 12, wherein said throttling element is an expansion machine.

Claim 15

The apparatus of claim 7, further comprising a pipeline for drawing gaseous argon from column.

Claim 16

The apparatus of claim 7, further comprising a pipeline for drawing gaseous 0 2 from column and forwarding it to the utilization place.