Method and apparatus for separating air by means of cryogenic distillation

Abstract

The invention relates to a method for separating air by means of cryogenic distillation, in which method: - during a first step, a liquid is withdrawn from a first store (S1) and vaporises in a first heat exchanger (E, E1) in order to produce a vaporised liquid by indirect heat exchange with gaseous air, which is thus liquefied at a first pressure in the heat exchanger and sent to a second store (S2); and - during a second step, a gaseous oxygen flow (3, 7) from an external source cools and liquefies in the first heat exchanger by exchange of heat with the liquid nitrogen to be vaporised, is expanded and is sent to the overhead condenser of a column in order to vaporise therein, forming part of the vaporised liquid exiting the overhead condenser.

Description

[0001] Description

[0002] Title of the invention: Method and apparatus for air separation by cryogenic distillation

[0003] The present invention relates to a method and apparatus for air separation by cryogenic distillation. It also relates to an integrated method for electrolysis, air separation by cryogenic distillation, and ammonia production.

[0004] It is known to use a simple column to produce nitrogen, the simple column having a condenser at the top and sometimes a reboiler at the bottom. The book "Razdelenia Vozdukha" by Epifanova et al., published by Mashinostroenie, 1964, describes on page 241 an apparatus with a simple column where the cooling is provided by a Claude turbine, a pump pressurizes liquid nitrogen from the top of the column, and the pressurized liquid nitrogen vaporizes against air in a heat exchanger.

[0005] The invention aims to utilize an available oxygen flow at a pressure between 5 and 30 bar absolute, originating, for example, from a water electrolysis unit that produces a hydrogen flow at a pressure between 5 and 30 bar absolute. The oxygen pressure is utilized by using it to vaporize a liquid nitrogen flow drawn from the top of a single column and pressurized by a pump, without mixing the oxygen with the air intended for distillation. Alternatively, it can be utilized, according to a variant, by using it to heat the column's reboiler. The pressurized liquid nitrogen is vaporized in the process heat exchanger where the oxygen and air flow intended to feed the column are cooled for separation.

[0006] One object of the invention is to produce a gas by distillation during the first run of an air separation apparatus by vaporizing a stored liquid that was withdrawn from the separation apparatus during a second run of the apparatus. The first run may correspond to a period when oxygen from an electrolyzer is unavailable, and the second run may correspond to a period when the electrolyzer is available and supplies oxygen to the air separation apparatus.

[0007] It is necessary to treat the oxygen produced by water electrolysis to remove the residual hydrogen it contains, as well as the water and possibly other impurities that could freeze at cryogenic temperatures. The water and possibly other impurities can be removed by adsorption, for example, by temperature or pressure switching.

[0008] Vaporized liquid nitrogen can be heated in the heat exchanger, expanded in a turbine, and then heated again in the heat exchanger, thus providing the necessary cooling for separation. The expanded nitrogen can be used as a product at a pressure lower than that of the pump outlet. Alternatively, cooling for separation can come from other sources, such as expanding air for the column and / or adding liquid nitrogen from an external source at the top of the column.

[0009] In a particular variant, the process is optimized to be part of an integrated process of electrolysis, air separation by cryogenic distillation and ammonia production in which the oxygen from the electrolysis constitutes the pressurized gaseous oxygen which is used to vaporize liquid nitrogen produced by the air separation column, hydrogen from the electrolysis unit being combined with the nitrogen produced by the air separation to constitute an ammonia synthesis gas.

[0010] The aim is to determine the oxygen pressure at the electrolyzer outlet, given that the ratio is 1.5 O2 to 1 N2 when producing 2 NH3, and that electrolysis produces one oxygen atom for every two hydrogen atoms. This follows from the following simple chemical equilibria:

[0011] [Cheml]

[0012] 2H₂O <-> 2Hr + O₂

[0013] And

[0014] [Chem2]

[0015] 2NH3 < > N2+ 3H2

[0016] The nitrogen efficiency of the device that will be described varies between 60 and 100%.

[0017] According to one aspect of the invention, a process for separating air by cryogenic distillation is provided in which

[0018] a) During the first run, a liquid is drawn from a first storage and vaporized in a first heat exchanger to produce a vaporized liquid by indirect heat exchange with gaseous air, compressed by a first compressor and then purified into water and / or CO2 in a first adsorption unit, which is thus liquefied at a first pressure in the first heat exchanger and sent to a second storage and

[0019] b) During a second walk:

[0020] i. Compressed air from the first compressor or a second compressor, purified of water and / or CO2 in the first or a second adsorption unit and cooled in the first or a second heat exchanger to a second pressure lower than the first pressure, preferably by at least 2 bar, is separated by distillation in a single column operating at a pressure of at least 4 bar abs, wherein the air at the second pressure is sent essentially in gaseous form, nitrogen from the top of the column condenses at least partially in a top condenser of the column against column tank liquid that has been expanded and sent to the top condenser

[0021] ii. Condensed nitrogen is returned to the top of the column

[0022] iii. Vaporized liquid exits the column's top condenser and is heated in the heat exchanger where the purified air is cooled.

[0023] iv.lln Liquid nitrogen flow is drawn from the column, part of the flow is pressurized, heated and vaporized in the heat exchanger where the purified air is cooled, and another part of the flow is sent to the first storage

[0024] v.lln liquefied air flow is sent from the second storage to an intermediate level of the column and

[0025] vi.lln flow of gaseous oxygen from an external source is cooled and liquefied in the first heat exchanger, without being mixed with air intended for distillation, by heat exchange with the liquid nitrogen to be vaporized, is expanded and sent to the top condenser of the column to vaporize there, forming part of the vaporized liquid that exits the top condenser

[0026] and in which

[0027] vii) during the first step, the column is not supplied with air and / or

[0028] (viii) during the first run, all the air destined for the first heat exchanger is compressed to the first pressure and / or (ix) during the second run, all the air cooled in the first or second heat exchanger and destined for the column is at a pressure lower than the first pressure and preferably enters the column in a gaseous state and / or

[0029] x) During the second run, all the liquefied air intended for the column comes from the second storage

[0030] Depending on other optional characteristics:

[0031] • During the second run, the air compressed by the first or second compressor, purified of water and / or CO2 in the first or second adsorption unit is cooled in the first heat exchanger, vaporized liquid exits the column head condenser and is heated in the first heat exchanger, a pressurized part of the liquid nitrogen flow is heated and vaporized in the first heat exchanger where the purified air is cooled, the gaseous oxygen flow from an external source is cooled and liquefied in the first heat exchanger.

[0032] • During the first run, the air compressed by the first compressor and purified into water and / or CO2 in the first adsorption unit is boosted by a blower to the first pressure upstream of the first heat exchanger and during the second run, the air compressed by the first compressor and purified into water and / or CO2 in the first adsorption unit is not boosted by a blower to the first pressure upstream of the first heat exchanger and enters the first exchanger at the outlet pressure of the first compressor which is the second pressure.

[0033] • during the first run, air is compressed by a compressor, other than the first compressor, to the first pressure and purified into water and / or CO2 in the first adsorption unit upstream of the first heat exchanger and during the second run, the air is compressed by the first compressor to the second pressure and purified into water and / or CO2 in the first adsorption unit and enters the first exchanger at the outlet pressure of the first compressor which is the second pressure.

[0034] • during the second walk,

[0035] Compressed air from the first or second compressor and purified into water and / or CO2 in the first or second adsorption unit is cooled in the second heat exchanger; vaporized liquid exits the column head condenser and is heated in the second heat exchanger; a pressurized portion of the liquid nitrogen flow is heated and vaporized in the second heat exchanger where the purified air is cooled; the gaseous oxygen flow from an external source is cooled and liquefied in the second heat exchanger.

[0036] • during the second walk,

[0037] The air compressed by the second compressor and purified of water and / or CO2 in the second adsorption unit is cooled in the second heat exchanger and sent entirely to the column

[0038] • During the first run, only the liquid drawn from the first storage tank vaporizes in the first heat exchanger, and only the gaseous air liquefies there. • During the first run, only the liquid drawn from the first storage tank and the gaseous air are sent to the first heat exchanger.

[0039] • No fluid is sent to the second heat exchanger during the first run.

[0040] • Purified air is cooled in the second heat exchanger during the second run.

[0041] • The first step corresponds to a period where the external source does not supply oxygen or supplies oxygen with a flow rate below a threshold, and the second step corresponds to a period where the external source supplies oxygen or supplies oxygen with a flow rate above a threshold.

[0042] • the first step corresponds to a period of electricity load shedding and the second step is outside of a period of electricity load shedding.

[0043] • the first march can take place only during the night and the second march takes place at least partially during the day.

[0044] • during the first run a non-renewable energy source powers an air compressor motor producing air and preferably no renewable energy source powers this motor and during the second run at least a renewable energy source powers an air compressor motor producing air and / or an electrolyzer producing the oxygen flow.

[0045] • The flow of gaseous oxygen comes from a water electrolysis unit.

[0046] • The gaseous oxygen flow is at a pressure of at least 7 bar abs., or even at least 10 bara. • During the second run, a gaseous oxygen flow from an external source is cooled in the heat exchanger and is sent to heat a tank reboiler of the single column in which it condenses, the condensed flow is expanded and sent to the head condenser to vaporize there.

[0047] • during the first run, no flow of gaseous oxygen from an external source is cooled in the heat exchanger and sent to heat a reboiler in the single column tank where it condenses.

[0048] • Nitrogen vaporized in the heat exchanger exits the heat exchanger at an intermediate temperature, is expanded in a turbine and is returned to the heat exchanger, possibly to the cold end of the heat exchanger, to be heated.

[0049] • the turbine provides at least 90%, or even substantially 100%, of the cooling required for the cryogenic distillation air separation process.

[0050] • Vaporized nitrogen, possibly expanded, and heated in the heat exchanger is mixed with hydrogen gas to form a synthesis gas of ammonia.

[0051] • the turbine expands vaporized nitrogen to the pressure of the gaseous hydrogen with which it is mixed.

[0052] • During the second run, no liquid is drawn from the first storage tank.

[0053] • During the second run, no liquefied air flow is sent to the second storage

[0054] • During the first run, no liquid nitrogen flow is sent to the first storage

[0055] • during the first run, no liquefied air flow is sent from the second storage to an intermediate level of the column.

[0056] • During the first run, no airflow is sent to the column. • During the first run, all the air cooled in the first or second heat exchanger is sent to the second storage tank.

[0057] • During the second step, the second pressure is lower than the pressure of the gaseous oxygen flow that cools in the first heat exchanger. According to another object of the invention, an integrated process for the production of ammonia synthesis gas is provided, in which:

[0058] i. Water is transformed by electrolysis into a flow of oxygen gas and a flow of hydrogen gas

[0059] ii. The gaseous oxygen flow is sent to a cryogenic distillation air separation process as described above and is condensed, sent to the head condenser and vaporized

[0060] iii. The flow of vaporized and heated liquid nitrogen is mixed with at least a portion of the flow of gaseous hydrogen to form ammonia synthesis gas. According to another aspect of the invention, an air separation apparatus by cryogenic distillation is provided, comprising a first heat exchanger, a single column having an overhead condenser, means for sending all the purified air to be cooled in the first heat exchanger at a single pressure, means for sending the air at the single pressure from the first heat exchanger to the single column for separation by distillation, a conduit for sending nitrogen from the top of the column to condense at least partially in the overhead condenser of the column, means for expanding a column tank liquid, means for sending the expanded tank liquid to the overhead condenser, and a conduit for sending condensed nitrogen from the condenser to the top of the column.a pipe connected to the top condenser to send vaporized liquid from the top condenser of the column to be heated in the first heat exchanger, a pump, a pipe connecting the top of the column with the pump inlet to send a flow of liquid nitrogen drawn from the column, a pipe to send the liquid nitrogen pressurized by the pump to be heated in the first heat exchanger,

[0061] means for sending a flow of gaseous oxygen from an external source to cool and liquefy in the first heat exchanger, without being mixed with air intended for distillation, by heat exchange with liquid nitrogen, means for expanding the gaseous oxygen downstream of the first heat exchanger, means for sending the expanded oxygen at least partially liquefied to the top condenser of the column to vaporize there as part of the vaporized liquid exiting the top condenser, a first storage connected to the top of the column to receive a nitrogen-enriched liquid and to the inlet of the pump and a second storage connected to an intermediate section of the single column to send liquefied air to it and to the first heat exchanger to receive the air at the first pressure.

[0062] Depending on other optional characteristics:

[0063] • The device includes another heat exchanger connected to the first storage to receive nitrogen-enriched liquid to be vaporized and connected to the second storage to send liquefied air to it.

[0064] • The device does not include an oxygen compressor.

[0065] • The device includes at least one air compressor upstream of the heat exchanger.

[0066] • The device includes an air blower and means for bypassing the blower.

[0067] • The apparatus includes a reboiler to allow indirect heat exchange between the single-column tank liquid and an oxygen flow from the external source

[0068] • The means for modifying the single pressure consist of a purified air booster connected to means for short-circuiting the air booster and to the first heat exchanger.

[0069] • The means for modifying the single pressure consist of means connected to a first and a second compressor connected in parallel in order to receive air at the first pressure from the first compressor or air at the second pressure from the second compressor.

[0070] • The apparatus comprising a single column tank reboiler and means for heating the tank reboiler by sending gaseous oxygen to it from the external source.

[0071] • The apparatus includes a line to send condensed oxygen from the tank reboiler to the head condenser of the single column.

[0072] The invention will be described in more detail with reference to the figures where: [FIG.1] illustrates a process for separating air by cryogenic distillation according to the invention,

[0073] [FIG.2] illustrates an integrated process for electrolysis, air separation and ammonia production according to a variant of the invention, [FIG.3] illustrates a heat exchange diagram for the heat exchanger E of [FIG.1] and

[0074] [FIG. 4] shows a McCabe Thiele diagram for the column of [FIG. 1] operating according to a second step.

[0075] [FIG.5] illustrates another method of separating air by cryogenic distillation according to the invention.

[0076] [FIG.6] illustrates a variant for the operation according to the first step of a cryogenic distillation air separation process according to the invention.

[0077] In Figure 1, according to a first step, an air flow 1 is compressed by a compressor C and purified of water and CO2 in an adsorption unit A. The flow 1 is cooled in the heat exchanger E to a first pressure P1 of at least 4 bar abs until it reaches a temperature close to its dew point, then expanded to liquefy it and sent to a storage S2. Liquid nitrogen from a storage S1 is pressurized by a pump (which may be pump P or another pump) and then sent to the heat exchanger E where it vaporizes, forming nitrogen gas, which serves as the product. No other fluid is sent to the heat exchanger E to participate in the heat exchange between this gas and the pressurized liquid. Thus, flow rates 3, 5, 7, and 13 are not present. The air pressure P1 is chosen to completely vaporize the pressurized nitrogen, and the nitrogen pressure depends on the desired pressure for the formed gaseous nitrogen.Liquefied air is sent directly from exchanger E to storage S2 via pipe 21. Storage S2 therefore fills with liquefied air during the first run and does not send air to column K1 or elsewhere.

[0078] According to a second step, an air flow 1 compressed by compressor C and purified into water and CO2 in the adsorption unit A is cooled in the heat exchanger E to a temperature close to its dew point and to a second pressure P2, lower than P1, then sent to an intermediate part of a simple column K1 operating at a pressure of at least 4 bar abs having a CO2 head condenser and possibly a tank reboiler.

[0079] The air supplied to the heat exchanger is at a pressure lower than that used during the first run, depending on the desired nitrogen pressure. This air enters the column in essentially gaseous form, with at least one structured packing or tray layer above its entry point into the column and at least one structured packing or tray layer below its entry point into column K1. The term "essentially gaseous" means that the air may contain up to 5% liquefied air.

[0080] Liquefied air is also sent from the second storage S2 to an intermediate level of column K1, above the gaseous air arrival point via pipe 21.

[0081] In order to have air at a first pressure P1 entering the exchanger E during the first run and air at a second pressure P2, lower than the first, entering the exchanger E during the second run, it is recommended to use during the first run a blower B (illustrated in dotted lines downstream of the purification unit A) and to purify the air at the second pressure before blowing it in the blower B up to the first pressure.

[0082] Alternatively, instead of a booster pump after the scrubber, a dedicated compressor other than compressor C could be used. This dedicated compressor would be small and operate at the correct pressure, i.e., the initial pressure P1. The air scrubber would then run at a reduced flow rate and the higher pressure (initial pressure) during the first run. This dedicated compressor would operate only during the first run, while compressor C would produce air at the second pressure, lower than the first pressure, only during the second run.

[0083] Thus during the first step, no part of the air enters the column at the second pressure P2 and during the second step, no part of the air enters the column at the first pressure.

[0084] It follows that during the first step, the column does not work and during the second step the column works on the second press.

[0085] The difference between the first and second pressures is preferably at least two bars.

[0086] The air separates in the column, forming an oxygen-enriched liquid in the tank and a nitrogen-enriched gas at the top. The gas condenses, at least partially, in the CO₂ top condenser of column K1 and is returned to column K1.

[0087] Oxygen under a pressure of at least 7 bar abs, or even at least 10 bar abs, preferably from an electrolysis unit, is purified to remove any impurities that could solidify in the heat exchanger. This purification is carried out in a unit such as a catalyst, and in an adsorption unit, for example, of the TSA or PSA type, to remove water and possibly other impurities. The catalyst for removing residual hydrogen from the oxygen can be palladium, platinum, cerium, or one of their oxides. The purified oxygen is cooled in the heat exchanger and is split in two, preferably upstream of the heat exchanger, forming a flow rate of 5 and a flow rate of 7.The flow 5, under a pressure of at least 7 bar abs, or even at least 10 bar abs, cools almost to the cold end of the heat exchanger E and is sent in a gaseous state close to its dew point to the tank reboiler R of column K1, where it condenses, providing heat for reboiling column K1. The resulting liquid 11 is expanded through valve V2 and feeds the overhead condenser CO. Oxygen-enriched liquid 9 is drawn from the tank of column K1 and expanded through valve V1. Both expanded liquids, 9 and 11, are sent to the overhead condenser C of column K1 to cool the nitrogen at the top of the column.

[0088] Flow 7, under an absolute pressure of 10 bar, is cooled and then condenses at the cold end of the heat exchanger. It is then expanded through valve V3 to the pressure of the CO₂ overhead condenser. The resulting liquid is sent to the CO₂ overhead condenser of column K1. The liquids are heated and partially vaporized by the CO₂ condenser, forming a gas 13 that is richer in oxygen than liquid 9 and slightly less rich in oxygen than flow 11. Gas 13 is then heated in the heat exchanger E from the cold end to the hot end.

[0089] A flow rate of liquid nitrogen (15) is drawn from the top of column K1 and divided in two. One portion is pressurized by a pump to a pressure of 18 bar abs and sent to vaporize in the heat exchanger (against the flow rate of 7). At least some of the pressurized vaporized nitrogen exits the heat exchanger at an intermediate temperature, is expanded in a turbine T to approximately 0 bar abs to provide cooling for the separation, and is then returned to the cold end of the heat exchanger at a pressure of 10 bar abs. By introducing liquefied air into the column, the size of turbine T can optionally be reduced. The expanded nitrogen (19) heats up as it passes completely through the heat exchanger and exits exchanger E to serve as a product of the air separation apparatus. The T turbine provides at least 90%, or even substantially 100%, of the cooling required for the cryogenic distillation air separation process.The remainder of the flow drawn from the top of column K1 is sent to the first storage S1.

[0090] Thus, during the second step, it is primarily oxygen that provides the heat necessary to vaporize the liquid nitrogen.

[0091] Preferably, during the second run, the second pressure is lower than the pressure of the gaseous oxygen flow that is cooling in the first heat exchanger

[0092] The choice of using the first step and the second step can be made depending on several conditions.

[0093] For example, if the amount of oxygen 10 available is below a threshold, for example if oxygen 10 is not available, the first step will be used and when if the amount of oxygen 10 available is above the threshold, the second step will be used.

[0094] In another context, the first step falls during a period of electricity load shedding and the second step falls outside of a period of electricity load shedding.

[0095] The first phase can occur solely at night, and the second phase at least partially during the day. For example, the first and second phases could each last 12 hours out of a 24-hour period. Nitrogen production during the first phase could be less than 25%, or even less than 15%, of the consumption during the second phase.

[0096] During the first run, a non-renewable energy source can power a motor of the air compressor C producing air and during the second run a renewable energy source (solar panels, wind turbines, hydroelectric dam, etc.) can power a motor of the air compressor C producing air and / or an electrolyzer EL producing oxygen 10. Alternatively, electricity from a renewable source during the second run can be stored in a battery and used during the first run.

[0097] Optionally, during the second stage, a renewable energy source can produce some of the required energy, in cases where renewable energy is available but insufficient to meet all needs. In this case, a non-renewable energy source will provide supplemental energy. Conversely, excess renewable energy during the second stage can be stored (for example, in a battery) for use during the first stage.

[0098] In Figure 2, an electrolysis unit EL is powered by water and preferably by green electricity and produces a flow of hydrogen 21 which exits under pressure, for example 10 bar abs, and mixes with nitrogen 19 to form a synthesis gas 23 containing approximately one mole of nitrogen for every three moles of hydrogen. The gas 23 is compressed by a compressor V and then sent to an ammonia synthesis unit N which produces a flow of ammonia 27. Nitrogen 19 can be produced during the first and / or second run, for example in a smaller quantity during the first run compared to the second run.

[0099] Preferably, the pressures of hydrogen 21 and the expanded nitrogen 19 are chosen to be the same. However, they may differ, and one of the gases can be compressed to the pressure of the other, preferably nitrogen, which is easier to compress. Preferably, the pressure to which the nitrogen 19 has been expanded is chosen to be the pressure at which the hydrogen 21 exits the electrolysis unit EL.

[0100] The pressurized oxygen gas 3 exiting the electrolysis unit EL is sent to the air separation unit (ASU), illustrated in Figure 1, after being dried and having residual hydrogen and other impurities removed, according to the second step and possibly the first step. The air separation unit processes the dried and compressed air 1 and uses the pressurized oxygen 3 to supply nitrogen 19, preferably at the same pressure as the hydrogen flow 21, to form the mixture 23. If the oxygen arrives already pressurized during the second step, this reduces the energy consumption of the air separation unit (ASU), since the energy for vaporizing the liquid nitrogen comes from the pressurized oxygen.

[0101] Liquids 9, 11, and 7 can be subcooled upstream of valves V1, V2, and V3 in a subcooler against gas 13. The subcooler can be integrated into the main heat exchanger. Liquid 11 can be subcooled in heat exchanger E, then in a subcooler before expansion in valve V2.

[0102] The presence of the reboiler R is not essential. In this example, a single flow 3 comes from the electrolysis unit and is divided into two flows at the same pressure 5, 7, of which one 7 is used to vaporize the pressurized liquid nitrogen and the other 5 is sent to the tank reboiler R.

[0103] It will be understood that these flow rates 5 and 7 may be at different pressures. Flow rate 5 may originate from one electrolysis unit and flow rate 7 from an external source other than an electrolysis unit, and vice versa. Flow rate 5 may originate from one electrolysis unit and flow rate 7 from another electrolysis unit, and the vaporized nitrogen may be mixed with hydrogen from either electrolysis unit.

[0104] [FIG. 3] illustrates a heat exchange diagram for heat exchanger E in [FIG. 1], with heat H on the y-axis and temperature T on the x-axis, during the second step, showing the nitrogen vaporization and oxygen condensation plateaus from the external source opposite each other. Since both fluids are pure, the condensation and vaporization plateaus are nearly vertical, allowing for good alignment and efficient latent heat exchange.

[0105] [FIG. 4] shows a McCabe Thiele diagram for the column of [FIG. 1] during the second run illustrating on the x-axis the fraction of the most volatile compound in the liquid phase and on the y-axis the fraction y of the most volatile compound in the vapor phase over the height of the column.

[0106] [FIG. 5] illustrates an air separation process in a simple column K1 with an overhead condenser but without a tank reboiler. In the first step, an air flow 1 is purified of water and CO2 in an adsorption unit A. The flow 1 entering the exchanger E is at an initial pressure of at least 4 bar abs and is cooled in the heat exchanger E to a temperature close to its dew point, then expanded to liquefy it and sent to a storage tank S2. Liquid nitrogen from a storage tank S1 is pressurized by a pump and then sent to the heat exchanger E where it vaporizes, forming nitrogen gas, which serves as the product. No other fluid is sent to the heat exchanger E to participate in the heat exchange between this gas and the pressurized liquid. Thus, flow rates 3 and 13 are not present for the first step, and preferably the column is not operating.The initial air pressure is chosen to completely vaporize the pressurized nitrogen, and this nitrogen pressure depends on the desired pressure for the resulting nitrogen gas. Liquefied air is sent directly from the Evers heat exchanger to the second storage tank, S2. Therefore, storage tank S2 fills with liquefied air during the first run and does not supply air to column K1 or elsewhere. In a second run, water-purified air (air 1) is cooled in the heat exchanger E to a second pressure, lower than the first pressure. The cooled gaseous air then enters the tank of column K1 in gaseous form and separates, forming an oxygen-rich liquid within the tank. Liquefied air is also sent from the second storage tank, S2, to an intermediate level in column K1, above the point where the gaseous air enters the tank.

[0107] Purified oxygen gas, containing water and hydrogen, at a pressure between 5 and 30 bar abs, arrives from an electrolyzer or other source, liquefies in the heat exchanger E, is expanded, and is sent to the overhead condenser C of column K1. The condenser is also supplied with expanded tank liquid 9 from column K1 to condense the overhead gas from column K1. A flow rate 15 of liquid nitrogen is drawn from the top of column K1 and divided in two. One portion is pressurized by a pump to a pressure of 18 bar abs and sent to vaporize in the heat exchanger (against the flow rate 7). At least some of the nitrogen vaporized under pressure exits the heat exchanger at an intermediate temperature of the latter, is expanded in a turbine T to about 0 bar abs to provide cold for separation, and then is returned to the cold end of the heat exchanger at a pressure of 10 bar abs.By sending liquefied air into the column, the size of the turbine T can be reduced.

[0108] The relaxed nitrogen 19 heats up as it passes completely through the heat exchanger and exits exchanger E to serve as a product of the air separation device.

[0109] The remainder of the flow drawn from the top of column K1 is sent to the first storage S1.

[0110] This expansion of the turbine T provides at least 90% of the cooling capacity of the process, or even 100%. Otherwise, another method of supplying cooling capacity, such as a nitrogen cycle or feed nitrogen, can be used.

[0111] As in [FIG.1], in order to have air at a first pressure P1 entering the exchanger E during the first run and air at a second pressure P2, lower than the first, entering the exchanger E during the second run, it is recommended to use during the first run a blower B (illustrated in dotted lines downstream of the purification unit A) and to purify the air at the second pressure before blowing it in the blower B up to the first pressure.

[0112] Alternatively, instead of a booster pump after the scrubber, a dedicated compressor other than compressor C could be used. This dedicated compressor would be small and operate at the correct pressure, i.e., the initial pressure P1. The air scrubber would then run at a reduced flow rate and the higher pressure (initial pressure) during the first run. This dedicated compressor would operate only during the first run, while compressor C would produce air at the second pressure, lower than the first pressure, only during the second run.

[0113] The difference between the first and second pressures is preferably at least two bars.

[0114] [FIG.6] illustrates the use of a dedicated E1 exchanger for the first step.

[0115] The air separation device therefore includes a device according to [FIG.1] or [FIG.5] and at least one exchanger E1 according to [FIG.6]. The storage units S1, S2 are common to the figure chosen between [FIG.1] and [FIG.5] and the figure illustrating the first step, [FIG.6]. According to this mode of operation, the exchanger E1 ([FIG.6]) operates only for the first step and the exchanger E ([FIG.1] and [FIG.5]) operates only during the second step.

[0116] Thus, during the first step, purified air at the first pressure is used to vaporize liquid nitrogen 17 taken from storage S1, without passing through column K1. This liquid nitrogen is pressurized by a pump P' which is not used in the second step. Alternatively, pump P, shown in Figures [FIG.1] or [FIG.5], can be used along with a dedicated line carrying the liquid nitrogen from pump P to heat exchanger E1. The liquid nitrogen vaporized in heat exchanger E1 serves as the product, and the liquefied air is sent to storage S2. The air can come from a dedicated compressor C1 and / or a dedicated adsorption unit A1. Alternatively, the air at the first pressure can be the flow 1A shown in dotted lines in [FIG.1] and [FIG.5], which is air compressed by a compressor that also serves to compress the air 1 to be separated during the second run and / or purified by an adsorption unit that also serves during the second run to purify the air 1 intended for distillation.The apparatus may include means connecting an air compressor motor C1 to a non-renewable energy source to power the air compressor motor C1 producing air during the first run.

[0117] During the second step, the heat exchanger E1 is not used; no fluid is sent to it. However, the heat exchangers in [FIG.1] and [FIG.5] operate as described in the description of the second step in their respective figures, with all the air at the second pressure being sent to be separated in column K1, preferably in gaseous form.

[0118] Preferably, during the second run, the second pressure is lower than the pressure of the gaseous oxygen flow that is cooling in the first heat exchanger

Claims

Demands 1. A process for separating air by cryogenic distillation in which: a) During a first run, a liquid is drawn from a first storage (S1) and vaporized in a first heat exchanger (E, E1) to produce a vaporized liquid by indirect heat exchange with gaseous air, compressed by a first compressor (C, C1) and then purified into water and / or CO2 in a first adsorption unit (A, A1), which is thus liquefied to a first pressure in the first heat exchanger and sent to a second storage (S2) and b) During a second walk i. Air compressed by the first compressor (C, C1) or a second compressor (C), purified of water and / or CO2 in the first or a second adsorption unit and cooled in the first or a second heat exchanger (E, E1) to a second pressure lower than the first pressure, preferably by at least 2 bar, is separated by distillation in a single column (K1) operating at a pressure of at least 4 bar abs, wherein the air at the second pressure is sent to the column essentially in gaseous form, nitrogen from the top of the column condenses at least partially in a top condenser (CO) of the column against tank liquid (9) of the column which has been depressurized (V1) and sent to the top condenser ii. Condensed nitrogen is returned to the top of the column iii. Vaporized liquid (13) exits the column's top condenser and is heated in the heat exchanger where the purified air is cooled iv.lln flow of liquid nitrogen (15) is drawn from the column, part of the flow is pressurized, heated and vaporized in the heat exchanger where the purified air is cooled and another part of the flow is sent to the first storage v.lln liquefied air flow is sent from the second storage to an intermediate level of the column and vi.lln flow of gaseous oxygen (3.7) from an external source is cooled and liquefied in the first heat exchanger, without being mixed with air intended for distillation, by heat exchange with the liquid nitrogen to be vaporized, is expanded and sent to the top condenser of the column to vaporize there, forming part of the vaporized liquid that exits the top condenser and wherein (vii) during the first run, the column is not supplied with air and / or (viii) during the first run, all the air intended for the first heat exchanger is compressed to the first pressure and / or ix) during the second run, all the air cooled in the first or second heat exchanger and destined for the column is at a pressure lower than the first pressure and preferably enters the column in a gaseous state and / or x) During the second run, all the liquefied air intended for the column comes from the second storage 2. A method according to claim 1 wherein during the second run, the air compressed by the first or second compressor (C, C1), purified of water and / or CO2 in the first or second adsorption unit is cooled in the first heat exchanger (E), vaporized liquid (13) exits the top condenser of the column and is heated in the first heat exchanger, a pressurized part of the liquid nitrogen flow is heated and vaporized in the first heat exchanger where the purified air is cooled, the gaseous oxygen flow (3,7) from an external source is cooled and liquefied in the first heat exchanger.

3. Method according to claim 2 wherein during the first run, the air compressed by the first compressor (C, C1) and purified in water and / or CO2 in the first adsorption unit is boosted by a blower (B) to the first pressure upstream of the first heat exchanger and during the second run, the air compressed by the first compressor (C, C1) and purified in water and / or CO2 in the first adsorption unit is not boosted by a blower to the first pressure upstream of the first heat exchanger and enters the first exchanger at the outlet pressure of the first compressor which is the second pressure.

4. A method according to claim 2 wherein during the first run, air is compressed by a compressor, other than the first compressor (C, C1), to the first pressure and purified into water and / or CO2 in the first adsorption unit and during the second run, the air is compressed by the first compressor (C, C1) to the second pressure and purified into water and / or CO2 in the first adsorption unit and enters the first exchanger at the outlet pressure of the first compressor which is the second pressure. 5.A method according to claim 1 in which during the second run, the air compressed by the first or second compressor (C, C1) and purified into water and / or CO2 in the first or a second adsorption unit is cooled in the second heat exchanger (E), vaporized liquid (13) exits the top condenser of the column and is heated in the second heat exchanger, a pressurized portion of the liquid nitrogen flow is heated and vaporized in the second heat exchanger where the purified air is cooled, the gaseous oxygen flow (3,7) from an external source is cooled and liquefied in the second heat exchanger.

6. Method according to claim 5 wherein during the second run, the air compressed by the second compressor (C) and purified into water and / or CO2 in the second adsorption unit (A) is cooled in the second heat exchanger (E) and sent entirely to the column (K1).

7. A method according to any one of the preceding claims in which during the first run, only the liquid withdrawn from the first storage (S1) vaporizes in the first heat exchanger (E) and only the gaseous air liquefies there.

8. Method according to claim 6 wherein no fluid is sent to the second heat exchanger (E1) during the first run.

9. Method according to claim 7 wherein purified air is cooled in the second heat exchanger (E1) during the second run.

10. A method according to any one of the preceding claims wherein the first step corresponds to a period where the external source does not supply oxygen or supplies oxygen with a flow rate below a threshold and the second step corresponds to a period where the external source supplies oxygen or supplies oxygen with a flow rate above a threshold.

11. A method according to any one of the preceding claims wherein during the first run a non-renewable energy source powers an air compressor motor (C, C1) producing air and preferably no renewable energy source powers this motor and during the second run at least a renewable energy source powers an air compressor motor producing air and / or an electrolyzer producing the oxygen flow.

12. Cryogenic distillation air separation apparatus comprising a first heat exchanger (E, E1), a single column (K1) having a top condenser (CO), means for sending all the purified air to be cooled in the first heat exchanger at a single pressure, means for sending the air at the single pressure from the heat exchanger to the single column for separation by distillation, means for changing the single pressure between a first pressure and a second pressure, a conduit for sending nitrogen from the top of the column to condense at least partially in the top condenser of the column, means (V1) for expanding a tank liquid (9) from the column, means for sending the expanded tank liquid to the top condenser, a conduit for sending condensed nitrogen from the condenser to the top of the column,a line connected to the overhead condenser for sending vaporized liquid (13) from the overhead condenser of the column to be heated in the heat exchanger, a pump (P), a line connecting the top of the column with the pump inlet for sending a flow of liquid nitrogen (15) drawn from the column, a line for sending the liquid nitrogen pressurized by the pump to be heated in the first heat exchanger, means for sending a flow of gaseous oxygen (3,5) from an external source to be cooled and liquefied in the first heat exchanger, without being mixed with air intended for distillation, by heat exchange with the liquid nitrogen, means (V3) for expanding the gaseous oxygen downstream of the first heat exchanger, means for sending the expanded oxygen, at least partially liquefied, to the overhead condenser (C) of the column to be vaporized there as part of the vaporized liquid exiting the overhead condenser,a first storage unit (S1) connected to the top of the column to receive a nitrogen-enriched liquid and to the pump inlet, and a second storage unit (S2) connected to an intermediate section of the single column to send liquefied air and to the first heat exchanger to receive the air at the first pressure.

13. Apparatus according to claim 12 in which the means for modifying the single pressure are constituted by a purified air blower connected to means for short-circuiting the air blower and to the first heat exchanger.

14. Apparatus according to claim 12 wherein the means for modifying the single pressure consist of means connected to a first and a second compressor connected in parallel in order to receive air at the first pressure from the first compressor (C1) or air at the second pressure from the second compressor (C).

15. Apparatus according to any one of claims 12 to 14 comprising a single-column tank reboiler (R) and means for heating the tank reboiler by sending gaseous oxygen to it from the external source.

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