Production of oxygen by air separation

A process for the separation of oxygen from air, which comprises:

• compressing feed air containing water vapor and CO.sub.2, to relatively low pressure,
• passing the compressed feed air stream through a first passage of a reversing heat exchanger in heat exchange relation with a nitrogen waste stream passing through a second passage of said heat exchanger, whereby water vapor and CO.sub.2 in the feed air are frozen on a surface of said first heat exchange passage,
• reversing the two streams whereby the nitrogen waste stream flows through said first passage and said feed air stream flows through said second passage, causing sublimation or evaporation of said water vapor and said CO.sub.2,
• at the end of this cycle, again reversing the two streams so that the compressed feed air stream passes through said first passage and the nitrogen waste stream passes through said second passage, and repeating the cycle at predetermined intervals,
• withdrawing said cooled feed air stream from the cold end of said exchanger after complete passage therethrough,
• passing a portion of the cooled feed air stream through a Trumpler pass back through the reversing exchanger,
• withdrawing at least a fraction of said portion of feed air stream from said Trumpler pass at an intermediate point in said heat exchanger,
• further cooling said withdrawn fraction of feed air in heat exchange relation within a fractionating device,
• withdrawing the remainder of said cooled feed air stream from the cold end of said heat exchanger after complete passage therethrough,
• mixing said further cooled fraction of feed air and said withdrawn remainder of cooled feed air stream,
• passing said cooled feed air mixture through a first fractionating zone in said fractionating device, whereby oxygen-rich liquid is condensed, and a nitrogen overhead is produced.
• withdrawing said oxygen-rich liquid from said first fractionating zone,
• throttling said withdrawn oxygen-rich liquid to lower pressure,
• passing said throttled liquid downward in a second fractionating zone in said fractionating device, whereby nitrogen vapor is formed and oxygen-rich liquid is produced,
• withdrawing said oxygen-rich liquid as product from said second fractionating zone,
• work expanding nitrogen overhead from said first fractionating zone and discharging cooled work expanded nitrogen at reduced pressure,
• passing said cooled work expanded introgen through a passage in said fractionating device in heat exchange relation with said second fractionating zone and withdrawing heat from said zone,
• withdrawing said nitrogen from said last mentioned passage in said fractionating device and passing said withdrawn waste nitrogen stream into the cold end of said heat exchanger through one of said first and second passages of the reversing heat exchanger as aforesaid,
• said heat exchange in said reversing heat exchanger and the fractionation in said fractionating device being carried out under conditions such that there is only a small temperature difference between the waste nitrogen stream entering the cold end of said heat exchanger and the cold feed air stream withdrawn from the cold end of the heat exchanger.

A process for the separation of oxygen from air which comprises:

• compressing feed air to a pressure of about 3 atmospheres,
• passing the compressed feed air stream through a reversing valve and into a first passage of a reversing heat exchanger,
• passing a nitrogen waste stream through a second passage of said heat exchanger, in heat exchange relation with said feed air stream, whereby water vapor and CO.sub.2 in the feed air stream are frozen on the surface of the first passage of said reversing exchanger,
• reversing the two streams, whereby the nitrogen waste stream flows through said first passage, causing sublimation or evaporation of said water vapor and CO.sub.2,
• at the end of this cycle, again reversing the two streams so that the compressed feed air stream passes through said first passage and the nitrogen waste stream passes through said second passage, and repeating the cycle at predetermined intervals,
• withdrawing a portion of the feed air stream at an intermediate point in the exchanger,
• passing said withdrawn portion of feed air through a gel trap to remove traces of CO.sub.2,
• withdrawing the remainder of said cooled feed air stream from the cold end of said exchanger after complete passage therethrough,
• further cooling said withdrawn portion of feed air by passage thereof in heat exchange relation with the lower end of a low pressure fractionating zone of a fractionating device,
• withdrawing the remainder of said cooled feed air stream from the cold end of said heat exchanger after complete passage therethrough,
• mixing said further cooled portion of feed air and said withdrawn remainder of cooled feed air stream,
• further cooling the resulting feed air mixture by heat exchange with oxygen-rich liquid product, to produce a further cooled feed air mixture,
• passing said further cooled feed air mixture upwardly in a high pressure fractionating zone of said fractionating device, whereby oxygen-rich liquid is condensed, and a nitrogen overhead is produced,
• withdrawing said oxygen-rich liquid from said high pressure fractionating zone,
• throttling said withdrawn oxygen-rich liquid to a lower pressure,
• passing said throttled oxygen-rich liquid downward in said low pressure fractionating zone, whereby nitrogen vapor is formed and oxygen-rich liquid is produced,
• withdrawing said oxygen-rich liquid from said low pressure fractionating zone and evaporating at least a portion of said oxygen-rich liquid by heat exchange relation with said further cooled feed air mixture as aforesaid,
• withdrawing nitrogen as overhead from said high pressure fractionating zone,
• passing said nitrogen overhead downwardly in heat exchange relation with said high pressure fractionating zone,
• withdrawing said overhead nitrogen and work expanding said nitrogen,
• withdrawing nitrogen as overhead from said low pressure fractionating zone,
• mixing said last mentioned nitrogen with said work expanded nitrogen,
• passing said last mentioned mixture downwardly in heat exchange relation with said low pressure fractionating zone,
• said nitrogen passed in heat exchange relation with said high pressure fractionating zone and said low pressure fractionating zone causing a non-adiabatic fractional distillation to take place in said zones,
• withdrawing said nitrogen mixture from heat exchange relation with said low pressure fractionating zone and passing said mixture forming said waste nitrogen stream into the cold end of said heat exchanger through one of the reversing passages thereof,
• passing said evaporated oxygen into a third passage of said reversing exchanger in heat exchange relation with said feed air stream,
• withdrawing gaseous oxygen as product and compressing said product, said work expansion of said nitrogen being used to compress said gaseous oxygen product,
• said heat exchange in said reversing heat exchanger and said fractionation in said fractionating device being carried out under conditions such that there is only a small temperature difference between the waste nitrogen stream and vaporized oxygen entering the cold end of the exchanger, and the cooled feed air stream exiting the cold end of the heat exchanger.

A system for the separation of nitrogen from air, which comprises,

• means for compressing feed air containing water vapor and CO.sub.2 to relatively low pressure,
• a reversing heat exchanger comprising first and second passages,
• valve means for reversing the flow of feed air alternately from the first to the second passage in said heat exchanger, and vice versa, whereby water vapor and CO.sub.2 in the feed air stream are frozen on the surface of one of the heat exchange passages, sublimed and evaporated by reversing the flow of the feed air stream from the first passage to the second passage and the flow of a nitrogen waste stream passing from said second passage, into said first passage, said valve means being operative to repeat the cycle at predetermined intervals,
• means for withdrawing a portion of the feed air stream at an intermediate point in the exchanger,
• a check valve, said withdrawn feed air stream passing through said check valve,
• a fractionating device including a first fractionating column and a second fractionating column,
• means for passing said withdrawn portion of feed air in heat exchange relation with the lower portion of said second fractionating column, for further cooling said withdrawn portion of feed air,
• means for withdrawing the remainder of said cooled feed air stream from the cold end of said heat exchanger after complete passage therethrough,
• means for mixing said further cooled portion of feed air and said withdrawn remainder of cooled feed air stream,
• means for passing said cooled feed air mixture into said first fractionating column, whereby oxygen-rich liquid is condensed, and a nitrogen overhead is produced,
• means for withdrawing said oxygen-rich liquid from said first fractionating zone,
• means for throttling said withdrawn oxygen-rich liquid to lower pressure,
• means for passing said throttled liquid downward in said second fractionating column, whereby nitrogen vapor is formed and oxygen-rich liquid is produced
• means for withdrawing sid oxygen-rich liquid as product from said second fractionating column, p1 a work expander,
• means for passing nitrogen overhead from said first fractionating column to said work expander and discharging cool work expanded nitrogen at reduced pressure,
• passage means in said second fractionating column,
• means for passing said cooled work expanded nitrogen through said last mentioned passage means in heat exchange relation with said second fractionating column,
• means for withdrawing nitrogen from said last mentioned passage and passing said withdrawn nitrogen as nitrogen waste stream into the cooled end of said heat exchanger through one of said first and second passages of the reversing heat exchanger as aforesaid.