Method for defrosting an air separation device by cryogenic distillation

Abstract

Title of the invention: Method for defrosting an air separation apparatus by cryogenic distillation. During the defrosting of an air separation apparatus by cryogenic distillation, defrosting gas is sent to a heat exchanger (15) and from the heat exchanger to the top of a column (21) via a line (C6) used in normal operation to draw nitrogen, entering the column, defrosting gas is drawn from the tank of the second column via a line and sent to the heat exchanger and then to the air, a flow of defrosting gas is sent to the top of another column via a line (C7) at a temperature above 0°C, defrosting gas is drawn from the other column via the line used in normal operation to send air to the other column, sent to the heat exchanger and sent to the air. Abstract figure: Fig. 2

Description

Title of the invention: Method for defrosting an air separation device by cryogenic distillation

[0001] The present invention relates to a method for defrosting an air separation apparatus by cryogenic distillation. It also relates to a separation apparatus capable of being defrosted by such a method. One object of the invention is to enable the defrosting of a cold box of an efficient air separation apparatus, while minimizing the installation of dedicated piping and equipment. A separation apparatus typically comprises a heat exchanger, a first column operating at a first pressure, and a second column operating at a second pressure. A vessel of the second column is thermally connected to a head of the first column by a vaporizer supplied with a gas from the head of the first column.

[0002] The air to be sent to the apparatus is compressed (unless it is already under pressure), purified in an adsorption purification unit to remove the water and CO2 it contains, cooled in the heat exchanger, and sent at least to the first column. Reflux lines send oxygen-enriched and nitrogen-enriched liquid to the second column, and an oxygen-rich product is drawn off in a tank from the second column. This method of operation constitutes the normal operation.

[0003] The columns and the cold part of the heat exchanger operate at cryogenic temperatures and must be periodically heated to ambient temperature to remove accumulated impurities and / or to perform maintenance or repairs. This operation is called defrosting.

[0004] To ensure the defrosting of the column, the columns are heated by the arrival of a defrosting gas at a temperature above the cryogenic temperature, or even ambient, often above 40°C.

[0005] Dedicated piping with control devices is placed at the outlet of the purification unit at the top on the purified air and routed to defrost inlets at different locations in the cold box.

[0006] Similarly, specific defrosting outlets are available on each piece of equipment (columns, exchangers, turbines, pumps): the defrosting of each piece of equipment is done sequentially.

[0007] The invention makes it possible to use as much as possible of the existing piping of an air separation device for its defrosting and to use the majority of those used in the opposite direction to that used in normal operation.

[0008] This makes it possible to keep a very compact cold box, without providing a link between a dedicated source that generates a dry fluid at room temperature and the cold box.

[0009] All the equipment in the cold box is preferably defrosted at the same time.

[0010] During defrosting, according to the prior art, it is necessary to heat the top of the The first column, located below the vaporizer, is heated to a high temperature (e.g., above 40°C) to ensure thorough defrosting, as it is a dead end. An advantage of the invention is that part of the defrosting process is performed using air below this high temperature. In this embodiment, it is not necessary to use such high-temperature air to defrost the second column and other equipment. Lower-temperature air, such as ambient temperature, is sufficient. This results in cost savings by heating only the defrosting gas for the first column, thus requiring smaller equipment and reducing energy consumption.

[0011] CN220229764 mentions the very general idea of ​​using the same conduct in a direction in normal operation and in the opposite direction during defrosting.

[0012] CN111981760 describes a defrosting process in which air heated in a blower is sent to the top of a second column of a double column, designed to operate at a lower pressure than a first column, and flows down the second column from top to bottom. By adjusting the cooling after the blower, it is possible to generate a hot defrosting gas to be sent directly into the first column below the vaporizer.

[0013] According to various embodiments of the present invention, the defrosting gas can be a gas from an external source containing neither water nor carbon dioxide, for example, a flow of dry nitrogen. In this case, the air compressor of the device and its purification unit do not operate during defrosting.

[0014] Alternatively, the defrosting gas can be formed from at least a portion of the compressed and purified air flow in the purification unit. In this case, means must be provided for regenerating the purification unit.

[0015] An important difference between the CN111981760 process and that of the invention is that in the CN111981760 process, all the defrosting gas outlets are on the cryogenic side of the device (see the abbreviation DO in the diagram, which stands for "Deriming Outlet"), whereas according to the invention, the defrosting gas outlets are mostly or entirely downstream of the heat exchanger, i.e., where the temperature is ambient. It is also possible to use an existing cryogenic vent for normal operation.

[0016] One problem with defrosting is the subtle adjustment required in the various flow rates (particularly to cryogenic and non-cryogenic vents) to prevent the heat exchanger from cooling at the hot end while simultaneously injecting heat into the cold box. This risk is eliminated when the defrost outlets (DO) are located between the column and the cold end of the heat exchanger, as in the CN111981760 process: all the cold air exits through these outlets designed for this purpose. According to the present invention, at least Some defrost gas outlets discharge gases from the heat exchanger directly into the air. By directing some of the defrost gas to the column without passing through the heat exchanger, the heat exchanger can become unbalanced if all the defrost gas passes through the heat exchanger before being discharged into the air.

[0017] Indeed, at the beginning of defrosting, the gas that has passed through the column(s) is cold. To compensate for the gas that does not pass through the heat exchanger, possibly after reheating in the heater, a gas supply (to the air) from at least one column can be provided upstream of the exchanger. In this case, it is recommended to send a portion of the defrosting gas, corresponding at least to that sent through the heater (whether operating or not), to the air via an outlet provided between the column and the cold end of the heat exchanger.

[0018] It is even possible to use the start-up short-circuiting line for the purification unit to send the defrosting gas to the purification unit, if the defrosting gas is not air, and to the device to send the gas to the head of the second column.

[0019] An advantage of the present invention is that the only pipe added specifically for defrosting is a line that leads to the first column, via a heater. Apart from this, no additional circuit is provided for use solely during defrosting.

[0020] Another difference is that all circuits that can introduce pollution (i.e., all circuits except the oxygen supply line) are defrosted in reverse, including the low-pressure and medium-pressure air circuits, which is not the case for CN111981760

[0021] It is desirable to minimize the duration of the defrosting operation. The present invention makes it possible to significantly reduce this duration, which without the invention is typically between 12 and 36 hours, because the defrosting of all parts of the appliance is carried out simultaneously.

[0022] The temperature of the defrosting gas is chosen according to the heat required at the point in the column where it is injected, with at least two gas temperatures being used. This reduces energy consumption and minimizes thermal shock.

[0023] According to one object of the invention, a method is provided for defrosting an air separation device by cryogenic distillation in which a. In normal operation, air is cooled in a heat exchanger and sent from the heat exchanger to a first column operating at a first pressure via a first pipe, a tank of a second column being thermally connected to a head of the first column by a vaporizer supplied with a gas from the head of the first column, possibly Air is sent to an intermediate level of the second column via a second pipe, an oxygen-enriched liquid is sent from the first column to the second column via a third pipe, a nitrogen-enriched liquid is sent from the first column to the second column via a fourth pipe, an oxygen-rich fluid is withdrawn from the second column via a fifth pipe and sent to the heat exchanger, and a nitrogen-rich gas is withdrawn from the top of the second column and sent to the heat exchanger via a sixth pipe. b. During at least part of the appliance defrosting process, defrosting gas, for example air, is sent to the heat exchanger and from the heat exchanger to the top of the second column via the sixth pipe, entering the second column at a first temperature not more than 60°C higher, or even not more than 40°C higher, than the temperature of the second column; defrosting gas is drawn from the tank of the second column via the fifth pipe and sent to the heat exchanger and then to the air; optionally, defrosting gas is drawn from the second column via the third and / or fourth pipe and sent to the first column; a flow of defrosting gas is sent at a second temperature above 0°C, preferably above 20°C, to the top of the first column via a seventh pipe, without passing through the heat exchanger or the second column; defrosting gas is drawn from the first column via the first pipe.sent to the heat exchanger and then to the air.

[0024] According to other optional aspects: • Defrosting gas is sent simultaneously to the first and second columns • Air is cooled in the heat exchanger and sent from the heat exchanger to an intermediate level of the second column operating at the second pressure via the second line and during defrosting, preferably only during defrosting, defrosting gas is drawn from the intermediate level of the second column via the second line, sent to the heat exchanger and sent to the air. • The seventh pipe and the heater, if present, are not used during normal operation. • the defrosting gas is heated by a heater, possibly electric, other than a booster, to a temperature of at least 20°C, or even at least 40°C. • The defrosting gas is split in two upstream of the heat exchanger, one part being sent to the heater and then to the head of the first column and part being sent to the heat exchanger and then to the top of the second column. During the first part of the defrosting, the defrosting gas is sent to the first column without having been heated by the heater, and during the second part of the defrosting which follows the first part, the defrosting gas is sent to the first column after being heated by the heater, so that the defrosting gas arriving in the first column is hotter during the second part than during the first part. During normal operation, the air is purified in an adsorption purification unit; during appliance start-up, some of the purified air is sent to the purification unit as regeneration gas via a ninth line; and during defrosting, air used as defrost gas is sent partly to the heat exchanger, partly to the seventh line, and partly to the purification unit via the ninth line. During normal operation, part of the air is sent to a turbine inlet to be expanded and sent as expanded air from a turbine outlet to the second column. During defrosting, defrosting gas is drawn from the second column, sent to the turbine outlet, passes through the turbine, exits through the inlet and is sent to the heat exchanger and then to the air. The air sent to the turbine during normal operation passes into the second column through the second pipe, and the de-icing gas, for example air, sent to the turbine during de-icing is sent from the second column to the turbine through the second pipe. During normal operation, the air intended for the turbine is cleaned in a cleaning unit and compressed in a blower upstream of the heat exchanger. The compressed air in the booster is at the first pressure. The booster pump does not operate during defrosting. The heater does not work during defrosting. Defrosting gas is sent simultaneously to the first and second columns The first and second columns are contained in a thermally insulated vacuum chamber containing a powdered thermal insulator. during at least the first part of the defrosting process, defrosting gas from the second column is sent to the air from the second or fifth pipe upstream of the heat exchanger and / or defrosting gas from the first column is sent to the air from the first pipe upstream of the heat exchanger. • The defrosting gas, sent from the heat exchanger to the top of the second column via the sixth pipe, enters the second column at an initial temperature below 40°C • the defrosting gas sent from the heat exchanger to the head of the second column by the sixth pipe, enters the second column at a first temperature below 40°C without having been heated by a blower and / or other heater.

[0025] According to another object of the invention, a cryogenic distillation air separation apparatus is provided comprising a heat exchanger having a first end and a second end, a purification unit, an air supply line connected to the purification unit and to the first end of the heat exchanger, a first column designed to operate at a first pressure, a second column designed to operate at a second pressure lower than the first pressure, a tank of the second column being thermally connected to a head of the first column by a vaporizer supplied by a gas from the head of the first column, a first line for sending cooled air into a heat exchanger from the heat exchanger to the first column, optionally a second line for sending air to an intermediate level of the second column,a third pipe to send an oxygen-enriched liquid from the first column to the second column, a fourth pipe to send a nitrogen-enriched liquid from the first column to the second column, a fifth pipe to draw an oxygen-rich fluid from the second column connected to the heat exchanger, and a sixth pipe to draw a nitrogen-rich gas from the top of the second column connected to the heat exchanger; a defrosting pipe; means for sending defrosting gas free of water and carbon dioxide to the top of the second column via the defrosting pipe but without passing through the heat exchanger.

[0026] According to other optional aspects, the device comprises: • the air supply line connected to the first or second line, the second end of the heat exchanger being connected to the first column and the second column and venting means connected to the air supply line between the purification unit and the first end of the heat exchanger. • a heater other than a blower, preferably capable of heating the defrosting gas to a temperature above 40°C, the means for send defrosting gas without water and without carbon dioxide to the top of the second column via the defrosting line and the heater.

[0027] The invention will be described in more detail with reference to the figures:

[0028] [Fig. 1] represents an air separation device that can be defrosted according to the method of the invention with fluid circulation in nominal operation

[0029] [Fig.2] represents an air separation device of the [Fig.1] which can be defrosted according to the method of the invention with the circulation of fluids during the defrosting sequence; the bold lines in the figure represent the pipes in which the direction of flow is reversed during defrosting compared to the direction during normal operation.

[0030] [Fig. 3] represents an air separation device that can be defrosted according to the method of the invention with fluid circulation in nominal operation

[0031] [Fig.4] represents an air separation device from [Fig.3] which can be defrosted according to the method of the invention with the circulation of fluids during the defrosting sequence; the bold lines in the figure represent the pipes in which the direction of flow is reversed during defrosting compared to the direction during normal operation.

[0032] In [Fig. 1], a cryogenic distillation separation apparatus comprises an adsorption purification unit 4, a heat exchanger 15, a first column 19 operating at a first pressure and a second column 21 operating at a second pressure, a vessel of the second column being thermally connected to a head of the first column by a vaporizer 20 supplied by a head gas from the first column 19. The first and second columns 19, 21 and optionally the heat exchanger 15 are contained in a thermally insulated enclosure, for example a vacuum enclosure containing a powdered thermal insulator.

[0033] Ambient air is filtered in filter 1, then compressed in compressor 2, then cooled in exchanger 3. It is then purified in purification unit 4.

[0034] A portion is sent directly into the heat exchanger 15, being sent from a first end of the exchanger 3 operating at a first exchange temperature to the second end of the exchanger 15 operating at a second exchange temperature and then to the second column 21 by a second conduit C2.

[0035] Another portion is compressed in the compressor 8, then cooled in the exchanger 9, then in the heat exchanger 15, and then divided in two. One portion is partially cooled in the exchanger 15 and then sent to the turbine 14, if present. The other portion is completely cooled in the heat exchanger 15 and then sent to the first column 19 via a first pipe CL The expanded portion in turbine 14 is sent into the second column 21 at an intermediate level via the second pipe C2.

[0036] The tank-rich liquid from the first column 19 is cooled in the subcooler 22, then expanded in the valve 24 and then sent into an intermediate section of the second column 21 by a third pipe C3.

[0037] The lean liquid at the top of column MP is cooled in the subcooler 22, then expanded in the valve 23 and then sent to the top of column BP 21 by a fourth line C4.

[0038] The reflux of the first column 19 and the reboiling of the second column 21 are ensured by the vaporizer-condenser 20.

[0039] Gaseous oxygen is produced in the tank of the second column 21, exits through the fifth pipe C5 and is heated in the exchanger 15, then is sold as a product.

[0040] Alternatively, liquid oxygen can be produced in the tank of the second column 21, which exits through the fifth pipe C5, is vaporized and then heated in the exchanger 15, and then is sold as a product.

[0041] At the top of the second column 21, residual nitrogen is produced and exits through the sixth pipe C6. It is heated in the exchanger 22, then in the exchanger 15. Part of the heated residual nitrogen is used for regeneration of the purification unit 4, passing through the heater 6. The remainder is released into the atmosphere via the open valve 13. It can also be partially sold.

[0042] A seventh line C7, connecting the head of the first column 19 to the residual nitrogen line exiting the hot end of the exchanger 15, is present, as well as an electric heater 17, but they are not used during normal operation. Line C7 is therefore closed.

[0043] The presence of the turbine 14 is not essential. The apparatus can, for example, be kept cool by an inlet of cryogenic liquid nitrogen (not shown) at the top of the second column 21.

[0044] In this example, air is sent directly to the second column 21. However, the invention applies to processes in which all the gaseous air, or even all the air, is sent to the first column 19. The second conduit C2 is not necessarily present.

[0045] The device illustrated here corresponds to that of FR3090831A.

[0046] However, the apparatus is not necessarily of this type but can have any possible arrangement with a conventional double column. For example, the apparatus can have a Claude turbine in addition to or instead of the supply turbine 14. Air purification can be carried out not at the second pressure, as illustrated in this figure, but at the first pressure, in a much more conventional manner.

[0047] The invention is described using [Fig.2].

[0048] Before defrosting, all liquids present in the device are drained.

[0049] During defrosting, the ambient air is filtered in filter 1, then compressed in compressor 2, then cooled in exchanger 3. It is then purified in purification unit 4.

[0050] Valve 7 is closed, preventing nominal fluid circulation. Compressor 8 is stopped.

[0051] The bypass valve 5 is used to send a portion of the air purified of water and carbon dioxide in the purification unit 4 to the residual nitrogen circuit via the ninth line C9. A portion of the air thus expanded in the valve 5 is used for the regeneration of the purification unit 4, passing through the heater 6. The remainder is used as defrosting gas for the cold box. Excess air can be vented to the atmosphere via the valve 13.

[0052] The defrosting gas is separated into two at the inlet of the cold box, one part dedicated to the low pressure circuit and another to the medium pressure circuit.

[0053] The portion of the defrosting gas dedicated to the low-pressure circuit flows in reverse through the heat exchanger 15, the subcooler 22, and the second column 21, passing through the sixth line C6. This portion enters the second column 21 at its inlet at an initial temperature that is at most 60°C, or even at most 40°C, higher than the column temperature. Preferably, it is at a temperature below 40°C, having not been heated by a blower 8 and / or a heater 17. As the heat exchanger 15 warms up during defrosting, the initial temperature increases. A portion of the defrosting gas dedicated to the low-pressure circuit exits the tank of the second column 21 via the oxygen circuit C5 in the same direction as in normal operation and passes through the heat exchanger 15 before being vented to the atmosphere.

[0054] Preferably, another part of the defrosting gas exits from an intermediate level of the second column 21 in the opposite direction to the normal operation through the second line C2, then preferably a part is vented upstream of the exchanger 15 via the valve 16 at least during a first part of the defrosting, the other part passes in the opposite direction to the normal operation in the exchanger 15, then is vented via a vent flange 11 downstream of the exchanger 15.

[0055] Valve 16 is used either during start-up (as described in FR 2407306 and FR 2407305) or during shutdown to limit the overpressure in the second column, due to thermal inputs. Thus, valve 16 is used during other process operations and was not added specifically for defrosting.

[0056] At the beginning of defrosting, the columns are still at cryogenic temperature, while the defrosting gas is much hotter, so evacuation through valve 16 is more useful during the first part of defrosting.

[0057] Sending the defrosting gas to the air through valve 16 allows the heat introduced by the air flow sent through pipe C7, which does not pass through the heat exchanger 15, to be evacuated.

[0058] Alternatively or in addition, it is possible to provide another gas outlet, for example connected to the Cl line and / or the C5 line, to send part of the gas from the first column 19 to the air.

[0059] Another portion of the defrosting gas passes through the turbine 14 in the opposite direction to the normal operation. Thus, the defrosting gas enters through the outlet of the turbine 14 and exits through the inlet. Opening the valve 25 limits the flow passing through the turbine 14 to prevent it from rotating. Alternatively, the rotor can be electrically locked in the case of a generator turbine.

[0060] The lean and / or rich liquid circuits C3, C4 may optionally have defrosting gas flow in the reverse direction. However, since defrosting gas is sent to the first and second columns, this is not strictly necessary.

[0061] The portion of the defrosting gas dedicated to the medium-pressure circuit passes through the seventh line C7, which is open for defrosting, via the heater 17. To limit thermal shock, the heater 17 can initially be not activated. At the start of defrosting, the heater is not operating, and the defrosting gas passes through the heater 17 without being heated, so that the defrosting gas reaches the top of the first column 19, without passing through the heat exchanger, at a temperature above 0°C, or even above 20°C. Then the heater 17 is switched on to heat the defrosting gas to a second temperature above 20°C, or to 40°C, for example 55°C, the valve 18 is opened and is sent directly to the top of the first column 19 to defrost the first column 19 and the vaporizer-condenser 20.The portion of the defrosting gas dedicated to the medium pressure circuit exits the tank of the first column 19 through the first pipe Cl, passes through the exchanger 15 in the opposite direction, then is vented to the air via a vent flange 10.

[0062] The heater 17 can be fixed on a foot of the cold box, to gain compactness, as close as possible to the hot end of the exchanger 15.

[0063] The flow rates of defrosting gas sent to columns 19, 21 are substantially at the same pressure.

[0064] It goes without saying that all other purge circuits are open to the atmosphere during the defrosting sequence, as well as all instrument branches, typically analysis ports, level, pressure, flow, and pressure differential measurements. This also applies to secondary circuits not shown in [Fig. 2]. such as a feeding line or a purging device for the vaporizer-condenser 20.

[0065] Valve 13 can be closed. It can be opened if there is an excess of air flow from the pipe. In practice, valve 13 (along with two valves of the purification unit) regulates a target pressure on the residual nitrogen circuit (typically downstream of the heater 6) which allows adjustment of the defrost flow rates, which are not measured. These flow rates are derived from the pressure map of the unit and therefore from the "driving" pressure in the regeneration circuit.

[0066] Figures 3 and 4 illustrate the apparatus which can be defrosted by the process of the invention in the case where the defrosting gas comes from an external source, which may be for example a flow of dry nitrogen without carbon dioxide.

[0067] In [Fig. 3], the air separation process, which is essentially that of [Fig. 1], is shown. The apparatus includes a dry nitrogen gas inlet line 27, free of carbon dioxide, connected to a storage tank. This line is connected to the nitrogen outlet line from the second column, which is connected to the scrubber unit to supply nitrogen as a regeneration gas. However, the dry nitrogen line 27 does not supply nitrogen to the apparatus during normal operation.

[0068] During defrosting, the dry nitrogen line 27 sends dry nitrogen to the sixth and seventh lines C6, C7 via the ninth line C9 as illustrated in [Fig. 4]. Dry nitrogen can be sent to the scrubber unit as a regeneration gas.

[0069] The defrosting gas is separated into two at the inlet of the cold box, one part dedicated to the low pressure circuit and another to the medium pressure circuit.

[0070] Compressor 2, purification unit 4, and blower 9 are not operating.

[0071] The portion of the defrosting nitrogen dedicated to the low-pressure circuit flows in reverse through heat exchanger 15, subcooler 22, and the second column 21, passing through the sixth line C6. This portion enters the column at a first temperature higher than that of the second column by at most 60°C, or even at most 40°C. This portion enters the second column 21 at its top at a first temperature, for example, preferably at ambient temperature, i.e., between 5 and 30°C. A portion of the defrosting nitrogen dedicated to the low-pressure circuit exits the tank of the second column 21 via the oxygen circuit C5 in the same direction as in normal operation and passes through heat exchanger 15 before being vented to the atmosphere.

[0072] Preferably, another part of the defrosting nitrogen exits from an intermediate level of the second column 21 in the opposite direction to the normal operation via the second line C2, then a part is preferably vented upstream of the heat exchanger 15 via the valve 16 at least during the first part of the defrosting, the other part passes in the opposite direction to the normal operation in the heat exchanger 15, then is vented via a vent flange 11 downstream of the exchanger 15. The valve 16 can be used for starting and / or stopping as mentioned above.

[0073] Alternatively or in addition, it is possible to provide another gas outlet, for example connected to the Cl and / or C5 line, to send part of the gas from the first column 19 to the air.

[0074] Another portion of the de-icing gas passes through the turbine 14, if present, in the opposite direction to the normal operation. Thus, the de-icing nitrogen enters through the outlet of the turbine 14 and exits through the inlet. Opening the valve 25 limits the flow passing through the turbine 14 to prevent it from rotating. Alternatively, the rotor can be electrically locked in the case of a generator turbine.

[0075] The lean liquid and / or rich liquid circuits C3, C4 may optionally have defrosting gas flow in the reverse direction. However, since defrosting gas is sent directly to the first and second columns, this is not strictly necessary.

[0076] The portion of the defrosting nitrogen dedicated to the medium-pressure circuit passes through the seventh line C7, which is open for defrosting, via the heater 17, which may be operating to heat the defrosting gas to a second temperature above 40°C, for example 55°C, with the valve 18 open, and is sent directly to the top of the first column 19 at a temperature above 0°C to defrost the first column and the vaporizer-condenser 20. To limit thermal shock, the heater 17 may initially not be switched on, so that the defrosting gas arrives in the first column at a temperature above 0°C. Otherwise, we can completely do without the heater 17. The part of the defrosting gas dedicated to the medium pressure circuit exits the tank of the first column 19 through the first pipe Cl, passes through the exchanger 15 in the opposite direction, then is vented to the air via a vent flange 10.

[0077] The heater 17 can be fixed on a foot of the cold box, to gain compactness, as close as possible to the hot end of the exchanger 15.

[0078] The heater 17 can be electric or can be heated by means of a hot fluid, for example water.

[0079] The de-icing nitrogen flow rates sent to columns 19, 21 are substantially at the same pressure.

[0080] It goes without saying that all other purge circuits are open to the atmosphere during the defrosting sequence, as well as all instrument branches, typically analysis ports, level, pressure, flow, and pressure differential measurements. This also applies to secondary circuits not shown in [Fig. 2], such as the feed line or the vaporizer-condenser purge device 20.

[0081] Valve 13 is closed.

Claims

1. Demands Method for defrosting an air separation apparatus by cryogenic distillation in which a. In normal operation, air is cooled in a heat exchanger (15) and sent from the heat exchanger to a first column (19) operating at a first pressure via a first line (C1), a tank of a second column (21) being thermally connected to a head of the first column by a vaporizer (20) supplied by a gas from the head of the first column, optionally air is sent to an intermediate level of the second column via a second line (C2), an oxygen-enriched liquid is sent from the first column to the second column via a third line (C3), a nitrogen-enriched liquid is sent from the first column to the second column via a fourth line (C4),An oxygen-rich fluid is drawn from the second column through a fifth pipe (C5) and sent to the heat exchanger, and a nitrogen-rich gas is drawn from the top of the second column and sent to the heat exchanger through a sixth pipe (C6), and b. During at least part of the appliance defrosting process, defrosting gas, for example air, is sent to the heat exchanger and from the heat exchanger to the top of the second column via the sixth line, entering the second column at a first temperature not more than 60°C higher, preferably not more than 40°C higher, than the temperature of the second column. Defrosting gas is drawn from the tank of the second column via the fifth line and sent to the heat exchanger and then to the air. Optionally, defrosting gas is drawn from the second column via the third and / or fourth line and sent to the first column. A flow of defrosting gas is sent at a second temperature above 0°C, preferably above 20°C, to the top of the first column via a seventh line (C7), without passing through the heat exchanger or In the second column, defrosting gas is drawn from the first column through the first pipe, sent to the heat exchanger and sent to the air.

2. A method according to claim 1 wherein air is cooled in the heat exchanger (15) and sent from the heat exchanger to an intermediate level of the second column (21) operating at the second pressure by the second line (C2) and during defrosting, preferably only during defrosting, defrosting gas is drawn from the intermediate level of the second column by the second line, sent to the heat exchanger (15) and sent to the air.

3. Method according to claim 1 or 2 wherein the seventh conduit (C7) and a heater if present are not used during normal operation.

4. A method according to claim 1 or 2 or 3 wherein the defrosting gas is heated by a heater (17), possibly electric, other than a blower, to a temperature of at least 20°C, or even at least 40°C.

5. A method according to claim 4 wherein the defrosting gas is split in two upstream of the heat exchanger (15), one part being optionally sent to the heater (17) and to the head of the first column (19) and one part being sent to the heat exchanger and then to the head of the second column (21).

6. A method according to any one of claims 4 and 5 wherein during a first part of the defrosting, the defrosting gas is sent to the first column (19) without having been heated by the heater (17) and during a second part of the defrosting which follows the first part, the defrosting gas is sent to the first column after heating by the heater, so that the defrosting gas arriving in the first column is hotter during the second part than during the first part.

7. A method according to any one of the preceding claims, wherein during normal operation, air is purified in an adsorption purification unit (4), during the start-up of the apparatus, a portion (5) of the purified air is sent to the purification unit (4) as a regeneration gas via a ninth line (C9), and during defrosting, air serving as a defrosting gas is sent partly to the heat exchanger (15), partly to the seventh pipe (C7) and partly to the purification unit via the ninth pipe.

8. A method according to any one of the preceding claims wherein during normal operation a portion of the air is sent to an inlet of a turbine (14) to be expanded there and sent as expanded air from an outlet of the turbine to the second column (21) and during defrosting, defrosting gas is drawn from the second column, sent to the outlet of the turbine, passes through the turbine, exits through the inlet and is sent to the heat exchanger (15) and then to the air.

9. Method according to claim 8 wherein the air sent to the turbine (14) during normal operation passes into the second column (21) through the second conduit (C2) and the de-icing gas, for example air, sent to the turbine during de-icing is sent from the second column to the turbine through the second conduit.

10. A method according to claim 8 or 9 wherein during normal operation, the air intended for the turbine (14) is cleaned in a cleaning unit (4) and compressed in a blower (8) upstream of the heat exchanger (15).

11. Method according to claim 10 wherein the compressed air in the blower (8) is at first pressure.

12. A method according to any one of the preceding claims wherein during at least a first part of the defrosting, defrosting gas from the second column (21) is sent to the air from the second line (C2) or the fifth line (C5) upstream of the heat exchanger and / or defrosting gas from the first column (19) is sent to the air from the first line (Cl) upstream of the heat exchanger (15).

13. Cryogenic distillation air separation apparatus comprising a heat exchanger (15) having a first end and a second end, a purification unit (4), an air supply line connected to the purification unit and to the first end of the heat exchanger, a first column (19) designed to operate at a first pressure, a second column (21) designed to operate at a second pressure lower than the first pressure, a vessel of the second column being thermally connected to a head of the first column by a vaporizer (20) supplied by a head gas from the first column, a first line (C1) to send cooled air into the heat exchanger from the heat exchanger to the first column, optionally a second line (C2) to send air to an intermediate level of the second column, a third line (C3) to send an oxygen-enriched liquid from the first column to the second column, a fourth line (C4) to send a nitrogen-enriched liquid from the first column to the second column, a fifth line (C5) to draw off an oxygen-rich fluid from the second column connected to the heat exchanger and a sixth line (C6) to draw off a nitrogen-rich gas from the head of the second column connected to the heat exchanger, a defrosting line (C7),methods for sending defrosting gas without water and without carbon dioxide to the top of the second column via the defrosting line but without passing through the heat exchanger.

14. Apparatus according to claim 13 in which the air supply line is connected to the first or second line (Cl, C2), the second end of the heat exchanger (15) being connected to the first column and the second column and venting means (13) being connected to the air supply line between the purification unit and the first end of the heat exchanger.

15. Apparatus according to claim 13 or 14 comprising a heater (17) other than a blower, preferably capable of heating the defrosting gas to a temperature above 40°C, means for sending defrosting gas without water and without carbon dioxide to the top of the second column (21) passing through the defrosting line (C7) and the heater.

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