Process and apparatus for oxygen purification by cryogenic distillation

Abstract

Title of the invention: Process and apparatus for oxygen purification by cryogenic distillation. In a process for oxygen purification by cryogenic distillation, a gas stream (1) containing at least 90 mol% oxygen and nitrogen is cooled in a heat exchanger (E). The gas stream is at least partially condensed in a reboiler (R) of a distillation column (K), the column comprising an upper portion, a lower portion, and an intermediate portion between the upper and lower portions. The at least partially condensed stream is expanded and sent to the intermediate portion of the column for separation. The stream is separated by distillation in the column to form an oxygen-enriched, nitrogen-depleted liquid in the tank and an oxygen-depleted, nitrogen-enriched gas at the top of the column. The oxygen-depleted gas is withdrawn from the top of the column.Oxygen-depleted gas is sent to a top condenser (C) of the column by vaporizing a refrigerant liquid, and oxygen-enriched liquid (3) is drawn off from the column tank. FIG.1,

Description

Title of the invention: Method and apparatus for purifying oxygen by cryogenic distillation

[0001] The present invention relates to a method and apparatus for purifying oxygen by cryogenic distillation.

[0002] The oxygen produced by the electrolysis of water is not pure enough for applications in the field of electronics. While the hydrogen and water contained in the oxygen can be removed by catalysis and drying, it is difficult to remove the argon and nitrogen it contains.

[0003] US3363427 published in 1968 describes a process for purifying oxygen with a 99.7% purity in which oxygen is compressed in a compressor up to 2 bar, used to heat the reboiler in the tank of an operating column, condensed and sent to the top of the column. This is therefore a low-pressure distillation.

[0004] The column has a head condenser which condenses the head gas by indirect heat exchange with liquid nitrogen from an external source or a nitrogen cycle.

[0005] The process of this prior patent uses a hydrocarbon removal system to remove hydrocarbons from the oxygen produced.

[0006] The invention makes it possible to achieve at least one of the following objectives: • elimination of the nitrogen cycle • removal of the oxygen compressor • reduction in the number of valves • simplification of instrumentation • reduction in the number of oxygen tanks • Using the pressure of the oxygen to be purified to provide separation energy • reduction in energy consumption • improved oxygen efficiency • improved process flexibility

[0007] In return, the process column can in some cases be higher.

[0008] According to one aspect of the invention, a cryogenic distillation process for purifying oxygen is provided, in which a gas stream containing at least 90 mol% oxygen, as well as nitrogen and / or argon, is cooled in a heat exchanger; the gas stream is at least partially condensed in a reboiler of a distillation column, the column comprising an upper portion, a lower portion, and an intermediate portion between the upper and lower portions; the at least partially condensed stream is expanded and sent into the intermediate portion of the column to separate, the flow is separated by distillation in the column to form a liquid enriched in oxygen and depleted in nitrogen and / or argon in the tank and a gas depleted in oxygen and enriched in nitrogen and / or argon at the top of the column, an oxygen-depleted gas is drawn off at the top of the column, the oxygen-depleted gas is sent to at least one condenser at the top of the column by vaporizing a refrigerant liquid and the oxygen-enriched liquid is drawn off in the tank of the column.

[0009] According to other optional aspects: • the gas flow is at a pressure of at least 12 bars abs, or even at least 16 bars abs. • the gas flow is produced by electrolysis of water at a pressure of at least 12 bars abs, or even at least 16 bars abs. • The gas flow rate was not compressed • the column operates at a minimum of 9.5 bars abs. • Liquid nitrogen from an external source is vaporized in the heat exchanger and / or in the head condenser. • at least part of the oxygen-enriched liquid withdrawn from the column tank vaporizes in the overhead condenser, forming a gas enriched in oxygen and depleted in argon and / or nitrogen. • at least part of the oxygen-enriched gas is condensed by indirect heat exchange with a refrigerant, for example liquid nitrogen. • according to a first step, all the oxygen-enriched and argon- and / or nitrogen-depleted gas is heated in the heat exchanger, and according to a second step, at least part of the oxygen-enriched gas is condensed by indirect heat exchange with a refrigerant, for example liquid nitrogen. • No airflow is sent to the column. • Oxygen-depleted gas is sent to a first condenser at the top of the column, oxygen-depleted gas is sent to a second condenser at the top of the column, and the condensed gas is sent to the first and second condensers at the column, liquid nitrogen is sent to the first condenser and column tank liquid to the second condenser. • the relaxed flow sent into the intermediate portion of the column is sent at a level between 2 and 5 theoretical plateaus below the head of the column. • Oxygen-depleted gas contains between 40 and 99% oxygen by volume • the gas flow can contain at least 90% mol of oxygen, at least 95% mol of oxygen or even at least 97% mol.

[0010] According to one object of the invention, an oxygen purification apparatus by cryogenic distillation is provided, comprising a heat exchanger, means for sending a gaseous flow containing at least 90 mol% oxygen as well as nitrogen and / or argon to be cooled in the heat exchanger, a distillation column having a reboiler in the tank, means for sending the gaseous flow from the exchanger to the reboiler to condense the gaseous flow at least partially in the reboiler in the tank of a distillation column, the column comprising an upper portion, a lower portion and an intermediate portion between the upper and lower portions, a pressure-reducing valve for reducing the at least partially condensed flow from the reboiler, a conduit for sending the reduced flow from the valve to the intermediate portion of the column to separate there,means for heat and mass exchange within the column to separate the flow by distillation within the column to form an oxygen-enriched and nitrogen and / or argon-depleted liquid in the tank and an oxygen-depleted and nitrogen and / or argon-enriched gas at the top of the column; means for drawing off an oxygen-depleted gas at the top of the column; at least one condenser at the top of the column; means for sending oxygen-depleted gas to at least one condenser at the top of the column by vaporizing a refrigerant; and means for drawing off oxygen-enriched liquid from the tank of the column.

[0011] The invention uses the pressure of oxygen, for example generated by electrolysis, to simplify the apparatus. Preferably, the oxygen to be purified is at least 16 bar, this pressure being able to correspond to the outlet pressure of a water electrolyzer. In this way, the energy consumption of the apparatus is greatly reduced.

[0012] The invention will be described in more detail with reference to the figures in which:

[0013] [Fig-1] illustrates a method according to the invention.

[0014] [Fig.2] illustrates another method according to the invention.

[0015] [Fig.3] illustrates another method according to the invention.

[0016] [Fig.4] illustrates another method according to the invention.

[0017] In [Fig. 1], an oxygen flow 1 containing at least 90 mol% oxygen, or even at least 95 mol% oxygen, or even at least 99 mol% oxygen, as well as nitrogen and / or argon, hydrogen, and water, is produced directly at a pressure of at least 12 bar abs by water electrolysis. This flow 1 has been purified to remove the water and hydrogen it contains and does not contain hydrocarbons.

[0018] The flow 1 is cooled in a heat exchanger E and is sent in gaseous form to the reboiler tank R of a distillation column K also having a The head condenser C has an upper section, a lower section, and an intermediate section between the upper and lower sections. Flow rate 1 is preferably at a pressure of at least 16 bar abs, and column K operates at at least 9.5 bar abs, for example 11.3 bar abs, having 54 theoretical trays.

[0019] The flow 1 condenses in the reboiler R by heating the tank of column K and is expanded in a valve VI until the pressure of column K. The condensed flow 1 arrives in the intermediate section of column K at a level between 2 and 5 theoretical trays below the head of the column.

[0020] It is separated, forming an oxygen-enriched, nitrogen- and / or argon-depleted liquid in the tank and an oxygen-depleted, nitrogen- and / or argon-enriched gas at the top of the column. The oxygen-depleted gas is sent to the top condenser C of column K at 10.1 bar abs, vaporizing a refrigerant liquid which, in this example, is all the oxygen-enriched liquid 3 drawn from the tank of column K after expansion in valve V2. The liquid vaporizes in the condenser, forming a gas containing more oxygen and less nitrogen and / or argon than flow rate 1. This very pure UPO gas can then be used in electronic applications after being heated in the heat exchanger E to 10 bar abs.

[0021] An oxygen-depleted gas GOX containing the impurities present in oxygen 1 is drawn off at the top of the column and heated in the heat exchanger E. It contains between 40 and 99 mol% oxygen (for example, if flow 1 has at least 90 mol% oxygen, the GOX gas will have an O2 content of 47 mol%, if flow 1 is at 95 mol%, the GOX gas will have an O2 content of 65 mol%, and if flow 1 is at 99.7 mol%, the GOX gas will have an O2 content of 97 mol%).

[0022] A flow of liquid nitrogen LIN from an external source vaporizes in the heat exchanger E to provide the necessary cold for the process forming a gas GAN.

[0023] In the example of [Fig. 2], the product of the process is liquid oxygen 3 withdrawn from the column tank. In this case, a flow of liquid nitrogen from an external source is vaporized in the head condenser C to provide the cooling required for the process.

[0024] In the example of [Fig. 3], oxygen-depleted gas is sent to a first overhead condenser C1 of column K, oxygen-depleted gas is sent to a second overhead condenser C2 of column K, and the condensed gas is sent to the first and second condensers of the column. Liquid nitrogen is sent to the first condenser C1 and tank liquid 3 of the column to the second condenser C2. The liquid vaporizes in the second condenser, forming a gas containing more oxygen and less nitrogen and / or argon than flow rate 1. This very pure UPO gas can then be used in electronic applications after being heated in the heat exchanger E. The liquid nitrogen vaporized in the first condenser is heated in the heat exchanger E.

[0025] Another part 3' of the tank liquid serves as liquid product.

[0026] The liquid nitrogen-cooled condenser is much colder than the tank reboiler. This can lead to control problems unless a high nitrogen pressure is used to achieve closer temperature differences.

[0027] To remedy this problem, it is proposed to replace the liquid nitrogen-cooled condenser C with a tank liquid-cooled condenser, as in [Fig. 1], and a dedicated heat exchanger E2. Regardless of the operating mode, tank oxygen 3, taken at 14.8 bar abs, for example, is sent to condenser C. The pure gaseous oxygen produced is then either sent to the main heat exchanger at 10.1 bar abs as a flow rate 7 to be reheated and produced in gaseous form, or sent to a dedicated heat exchanger E1 as a flow rate 5 to be liquefied with LIN to produce ultrapure liquid oxygen. It is also possible to have a combination of the two operating modes and send flow rates 5 and 7 simultaneously to the respective heat exchangers E and E1 to produce a gaseous product and a liquid product. This solution is illustrated in [Fig. 4].

[0028] In this case, oxygen 1 is at 14.8 bars abs, column K operates at 12.8 bars abs and the single condenser C at 10.1 bars abs.

[0029] For example, according to a first step, all the oxygen-enriched and argon- and / or nitrogen-depleted gas is heated in the heat exchanger E, and according to a second step, at least part of the oxygen-enriched gas is condensed by indirect heat exchange with a refrigerant, for example, liquid nitrogen.

[0030] For a cold box processing 1,000 Nm3 / h of gaseous oxygen (GOX)

[0031] [TAB.l] Illljlll^ lllllllllll^^^^^ Differences ijiii liiiiiii » Addition of theoretical trays at the top of the column » Condenser cooling with liquid oxygen from the tank (optional) « Gas production from the condenser (optional) • Liquid production by vaporization of liquid nitrogen condenser vapor center (optional) € injection of oxygen from an external source 482 bW / h 53 Nm% 482 22% Oxygen efficiency 86% 52% 89% i 89% Efficiency i Efficiency improved by; improved by: i « Tray addition * Addition of theoretical trays; * Condenser of theoretical oxygen in liquid instead of liquid nitrogen at the top of the column: Flexibility. Gas production. Difficulty. A lot of liquid nitrogen required for the condenser. If production is gaseous, there is a large disparity between the cooling required for the condenser and the overall heat balance. Flexibility is needed for gas and / or liquid production.

Claims

Demands

1. A cryogenic distillation oxygen purification process in which a gas stream (1) containing at least 90 mol% oxygen and nitrogen and / or argon is cooled in a heat exchanger (E), the gas stream is at least partially condensed in a reboiler (R) of a distillation column (K), the column comprising an upper portion, a lower portion and an intermediate portion between the upper and lower portions, the at least partially condensed stream is expanded (VI) and sent to the intermediate portion of the column for separation, the stream is separated by distillation in the column to form an oxygen-enriched and nitrogen and / or argon-depleted liquid in the tank and an oxygen-depleted and nitrogen and / or argon-enriched gas at the top of the column, an oxygen-depleted gas is withdrawn from the top of the column, and the oxygen-depleted gas is sent to at least one condenser head (C, Cl,C2) From the column, by vaporizing a refrigerant liquid (3, LIN), oxygen-enriched liquid (3) is drawn off from the column tank.

2. Method according to claim 1 wherein the gas flow (1) is at a pressure of at least 12 bars abs, or even at least 16 bars abs.

3. A method according to claim 2 in which the gas flow (1) is produced by electrolysis of water at a pressure of at least 12 bars abs, or even at least 16 bars abs.

4. A method according to any one of the preceding claims wherein the column (K) operates at least 9.5 bars abs.

5. A method according to any one of the preceding claims wherein liquid nitrogen (LIN) from an external source is vaporized in the heat exchanger (E) and / or in the head condenser (C, Cl).

6. A method according to any one of the preceding claims wherein at least a portion of the oxygen-enriched liquid withdrawn from the column (K) tank vaporizes in the head condenser (C, C2) forming a gas (5,7) enriched in oxygen and depleted in argon and / or nitrogen.

7. A method according to claim 6 in which at least a part (5) of the oxygen-enriched gas is condensed by indirect heat exchange (El) with a refrigerant, for example liquid nitrogen.

8. A method according to any one of the preceding claims 6 and 7 wherein in a first step all the oxygen-enriched and argon- and / or nitrogen-depleted gas (7) is heated in the heat exchanger and in a second step at least a part (5) of the oxygen-enriched gas is condensed by indirect heat exchange with a refrigerant (3, LIN), for example liquid nitrogen.

9. A method according to any one of the preceding claims wherein oxygen-depleted gas is sent into a first head condenser (Cl) of the column (K), oxygen-depleted gas is sent into a second head condenser (C2) of the column and the condensed gas is sent into the first and second condensers of the column, liquid nitrogen (LIN) is sent to the first condenser and tank liquid (3) of the column to the second condenser.

10. A method according to any one of the preceding claims wherein the relaxed flow (1) sent into the intermediate portion of the column (K) is sent to a level between 2 and 5 theoretical trays below the head of the column.

Images