Method for starting an argon separation column of an air separation device by cryogenic distillation and unit for implementing said method

Abstract

An argon production unit by cryogenic distillation, adapted to be connected to a double air separation column consisting of a first and a second column (K1, K2) thermally connected to each other, comprises an argon separation column (K3) surmounted by a top condenser and a deazotation column (K4), means for withdrawing an argon-rich and nitrogen-depleted product (LAR) from the tank of the deazotation column, means for connecting the top of the argon separation column to the deazotation column, means for sending a top gas (13, 15) from the argon separation column to the atmosphere, means for withdrawing a nitrogen-rich fluid from the top of the deazotation column, an analyzer (AIC1,AIC2) for measuring the nitrogen content at the top of the argon separation column and means for opening and closing the means for connecting the top of the argon separation column to the deazotation column as a function of the nitrogen content detected by the analyzer.

Description

[0001] The present invention relates to a method for starting an argon separation column in a cryogenic distillation air separation apparatus and also concerns a unit capable of being started by this method in accordance with the preambles of claims 5 and 1 respectively. Such a method and such a unit are known from document JP-S55 60164A.

[0002] The scope of the present invention is limited to air separation units equipped with a cryogenic argon production, i.e., an impure argon column (which allows the separation of argon and oxygen) and a pure argon column (also called a deazotation column which allows the nitrogen to be removed and thus to obtain pure argon).

[0003] The air separation devices concerned by this invention comprise a double column, including a first column operating at a first pressure and a second column operating at a second pressure, lower than the first pressure. The second column is fed with a nitrogen-enriched liquid and an oxygen-enriched liquid from the first column.

[0004] Due to the differences in relative volatility between argon, nitrogen, and oxygen, practically pure nitrogen is formed at the top of the second column, practically pure oxygen at the bottom, and argon-rich gas in the middle. An argon-enriched gas, often called crude argon, is drawn off from the second column and sent to an argon separation column with an overhead condenser. The crude argon is rectified into an oxygen-rich reflux (which is subsequently sent back to the second column) and a very rich argon stream (often called "argon mixture") that contains virtually no oxygen (the oxygen content in the argon mixture is typically less than 3 ppm). This argon mixture is sent to a deazoling column to remove nitrogen by reboiling. At the bottom of the deazoling column, pure argon is drawn off in liquid form and sent to a liquid argon storage tank.

[0005] The argon separation column (argon "mixture" column) can be in two parts in order to reduce the size of the cold box.

[0006] As described in FR2911392, at startup, the deazotting column is not fed until the oxygen content of the fluid extracted at the top of the argon separation column is correct. During this period, the gas produced at the top of the argon separation column is vented to the air.

[0007] The process described in FR2911392 proposed feeding the deazolation column during startup even if oxygen levels were unsatisfactory and returning the tank liquid from the deazolation column to the argon separation column. EP1482266 shows the case where the gas released to the atmosphere during startup is heated in the main heat exchanger to recover cooling. It does not explain how the gas release is controlled.

[0008] KR101964331 proposes to store the argon produced at the top of the mixing column while the double column is not operating.

[0009] There are also argon mixing columns that are not used to provide an argon-rich product but only to reduce the argon content of an oxygen-rich product from the double column. In this case, the flow withdrawn from the top of the column contains up to 10 mol% oxygen, or even up to 15 mol% oxygen.

[0010] The invention also applies to processes with the production of gaseous or liquid argon.

[0011] The invention aims to optimize and accelerate the start-up phase of an argon mixture column.

[0012] According to one object of the invention, a cryogenic distillation argon production unit is provided according to claim 1.

[0013] The unit may include a double air separation column comprising a first column operating at a first pressure and a second column operating at a second pressure, lower than the first pressure, the head of the first column being thermally connected to the tank of the second column and comprising means for sending air to the first column, means for sending a nitrogen-enriched fluid and an oxygen-enriched fluid from the first column to the second column, optionally another column fed by a gas from an intermediate point of the second column, the argon separation column being connected to receive an argon-enriched gas from an intermediate point of the second column or, as appropriate, an argon-enriched gas from the other column.

[0014] According to other optional aspects of the invention: The analyzer is also connected to measure the nitrogen content in the argon-enriched gas sent to the argon separation column. The analyzer is connected to measure, alternatively, the nitrogen content in the argon-enriched gas and the nitrogen content at the top of the argon separation column. According to another aspect of the invention, a method for starting an argon separation column by cryogenic distillation is provided according to claim 5.

[0015] During start-up, if the nitrogen content at the top is above the first threshold, preferably no gas to be separated is sent to the denitrification column or, if applicable, to the pipeline.

[0016] According to other optional aspects: During startup, if the nitrogen content at the top of the argon separation column is below the second threshold, no gas is released from the top of the argon separation column to the atmosphere. The nitrogen content at the top of the argon separation column is measured using an analyzer capable of analyzing nitrogen concentration in a range from 10 ppm to 100% N2 in a mixture of oxygen, nitrogen, and argon.

[0017] According to another aspect of the invention, a method for regulating a separation device is provided, comprising a method for starting the device as described above, in which: During start-up, the nitrogen content at the top of the argon separation column is measured with an analyzer, and outside of start-up, the nitrogen content of a gas feeding the argon separation column is measured with the analyzer; during start-up, the nitrogen content at the top of the argon separation column increases.

[0018] The second threshold can be less than or equal to the first threshold.

[0019] According to another object of the invention, a method for regulating a separation apparatus is provided, comprising a method for starting the apparatus according to any one of claims 5 to 11, in which during the start-up the nitrogen content at the top of the argon separation column is measured with an analyzer and outside of the start-up the nitrogen content of a gas feeding the argon separation column is measured with the analyzer.

[0020] An analyzer that allows the measurement of nitrogen in oxygen and argon would allow regulation of the degassing valve in order to minimize the loss of argon during the start-up phase and thus accelerate it.

[0021] The main feature of the invention is the addition of a control loop to the degassing valve of the argon separation column, also known as the argon mixing column. By measuring the nitrogen concentration at the top of the mixing column with an analyzer, it is possible to vent a flow from the top of the mixing column to the atmosphere when the nitrogen concentration is above a threshold and to direct the flow to a deazoling column as soon as the nitrogen concentration falls below the threshold. This analyzer allows for the analysis of nitrogen concentration in a range from 10 ppm to 100% N2 in a mixture of oxygen and argon.

[0022] The main benefit is to minimize argon losses and speed up unit start-up.

[0023] During the start-up phase, where the O2 concentration is high, the measurement of nitrogen in the gas produced at the top of the argon separation column is distorted by the presence of O2.

[0024] Therefore, the non-condensable gas valve remains open until the N2+O2 measurement falls below a certain threshold. However, nitrogen is quickly expelled from the column, and opening the non-condensable gas valve only serves to lengthen the start-up time.

[0025] In the proposed process, the non-condensable degassing valve is a valve regulated by measuring nitrogen concentration using a dedicated analyzer.

[0026] With this configuration, argon losses during the startup phase are significantly reduced. Furthermore, it allows for automation of this phase for optimal startup.

[0027] Start-up time gains can be up to 25% depending on the type of startup.

[0028] The invention will be described in more detail with reference to the figures. [ Fig. 1 [ shows a unit according to the invention.] Fig. 2 ] shows the variation of the vaporized rich liquid flow rate produced by the argon separation column's top condenser over time with a simulation using manual degassing valve compared to the case with degassing valve regulation according to the invention. Fig. 3 ] shows the variation of the total percentage of nitrogen and oxygen in the overhead gas of the argon separation column over time, comparing a simulation with manual operation of the degassing valve and a case with regulation of the degassing valve according to the invention. Fig. 4 ] shows the opening of the degassing valve over time for the case of a simulation with manual operation of the degassing valve and a case with regulation of the degassing valve according to the invention. Fig. 5 ] shows the percentage of nitrogen in the overhead gas of the argon separation column over time for the case of a simulation with manual operation of the degassing valve and a case with regulation of the degassing valve according to the invention. Fig. 6 ] shows the percentage of oxygen in the middle of the argon separation column over time for a simulation with manual operation of the degassing valve and a case with regulation of the degassing valve according to the invention. Fig. 7 ] shows the percentage of oxygen in the overhead gas of the argon separation column over time for a simulation with manual operation of the degassing valve and a case with regulation of the degassing valve according to the invention. Fig. 8 ] shows the gas flow rate at the top of the argon separation column over time for the case of a simulation with manual use of the degassing valve and a case with regulation of the degassing valve according to the invention.

[0029] In the Figure 1 Compressed air 1 is sent to the first column K1 of a double column comprising a first and second column K1, K2 superimposed and thermally connected by an oxygen / nitrogen exchanger 4 called a vaporizer-condenser. In this exchanger 4, gaseous nitrogen from the first column K1 condenses, vaporizing liquid oxygen from the tank of the second column K2. In the first column K1, operating at a lower pressure, the nitrogen is separated from the air, creating oxygen-rich liquid 3 at the bottom of the column and nitrogen-rich liquid and vapor at the top of the first column. These products are extracted, and the nitrogen-rich liquid and oxygen-rich liquid are sent separately from the first column K1 to the second column K2, which operates at a lower pressure than the first column.Practically pure nitrogen 7 is formed at the top of the second column K2, impure nitrogen 19 is formed at an intermediate level of the second column K2, and practically pure oxygen 5 is formed at the bottom of column K2, with argon-rich gas forming in the middle of column K2. At least some of these fluids are sent to a heat exchanger for heating, where air 1 destined for column K1 is cooled. The impure nitrogen 19 line is adapted for connection to a heat exchanger.

[0030] The central fraction ORG 7, rich in argon and often called raw argon, is drawn from the low-pressure column and fed into an argon separation column K3 operating at substantially the same pressure as the second column K2, with the aim of ultimately producing argon. The first column K3 includes an overhead condenser. The raw argon is rectified into an oxygen-rich reflux ORL 9 (which is subsequently sent to the low-pressure column K2) and into an argon-enriched fluid 13.

[0031] The argon-enriched fluid (¹³¹⁷), containing, for example, less than 3 ppm of oxygen, in liquid or gaseous form, is sent to a K4 deazotation column comprising a tank reboiler and a top condenser to remove nitrogen by reboiling. At the bottom of the K4 deazotation column, pure argon (LAR) is drawn off in liquid form and sent to a liquid argon storage tank (not shown). A nitrogen-enriched flow is drawn off at the top of the K4 deazotation column.

[0032] The K3 argon separation column can be made up of two columns, as illustrated here to reduce the size of the cold box, or it can be made up of a single column as illustrated in the figure 1 .

[0033] To regulate the operation of the deazotation column, if the nitrogen content at the top of the argon separation column is above a first threshold, the gas at the top of the argon separation column is sent to the atmosphere.

[0034] If the nitrogen content at the top of the argon separation column is below a second threshold, less than or equal to the first threshold, the gas at the top of the argon separation column is sent to a deazotation column to separate and an argon-rich fluid is withdrawn from the deazotation column as a product.

[0035] The first and second thresholds can have the same value.

[0036] For example, during the start-up of an argon separation column K3, the nitrogen-rich gas 15 formed at the top of the column is first vented to the atmosphere by opening a venting valve regulated by the nitrogen level measured by the AIC2 analyzer. The AIC2 analyzer is capable of analyzing nitrogen concentrations in a range from 10 ppm to 100% nitrogen in a mixture of oxygen, nitrogen, and argon. The AlC2 analyzer measures the nitrogen content at the top of the K3 column and / or in a fluid 15 drawn from the top of the argon separation column K3. The analyzer does not necessarily analyze the gas to be vented to the atmosphere but can analyze another fluid whose nitrogen content is indicative of that of the flow rate 15.

[0037] As the start-up progresses, gas 15 becomes less and less rich in nitrogen and more and more rich in argon. When the nitrogen concentration drops to 0.5 mol%, the flow of gas 15 to the air is stopped, the degassing valve is closed, and the gas is sent as flow 17 to the deazoling column K4 by opening a valve to the deazoling column K4.

[0038] As long as the AIC2 analyzer measures a nitrogen concentration at the top of the argon separation column K3 above a threshold, for example 0.5 mol%, flow 15 is vented to air through the open vent valve. As soon as the nitrogen concentration falls below the threshold, venting is stopped and flow 17 is sent to an intermediate level of the deazotting column K4 to produce pure argon in the column tank K4.

[0039] To simplify the device and reduce instrumentation costs, an AIC1 analyzer can be used to measure nitrogen in a fluid, such as the overhead gas, of the K3 argon separation column during startup and to measure nitrogen in the feed gas to the K3 argon separation column during normal operation of the K3 argon separation column. The AIC1 analyzer is capable of analyzing nitrogen concentration in a range from 10 ppm up to 100% N2 in a mixture of oxygen, nitrogen, and argon.

[0040] It is also possible for the AIC1 analyzer to alternately analyze the flow rate 7 and a fluid, for example the head gas 15, from column K3 to measure their nitrogen content. It can therefore analyze the flow rate 7 and the head gas 15 during startup and / or analyze the flow rate 7 and the head gas 15 during normal operation.

[0041] It will be understood that the device according to the invention can constitute a separate module from the double column, which will be built and assembled and then sent to the site to be connected to the double column. Columns K3 and K4 can be isolated by a cold box independent of that of the double column.

[0042] It will be understood that column K3 can be in two sections, one constituting the lower part of column K3 and the other the upper part with condenser 6.

[0043] In some cases, for each variant of the [ Fig. 1 It may be sufficient to have either means to open and close the means to connect the head of the argon separation column to the deazotation column as a function of the nitrogen content detected by the analyzer or means to open and close the means to send a head gas from the argon separation column to the atmosphere as a function of the nitrogen content detected by the analyzer.

[0044] The argon separation column K3 can be connected to receive a gas 7 from an intermediate point in the second column or a gas from a column fed by the gas from an intermediate point in the second column

[0045] [ Fig. 2 ] shows the case of a simulation with manual use of the degassing valve sending gas 15 to the air and a case with regulation of the degassing valve according to the invention. Fig. 2 ] shows the variation of the vaporized rich liquid flow rate produced by the argon separation column's top condenser over time in a simulation with manual operation of the degassing valve compared to the case with degassing valve regulation according to the invention. For all figures from the Fig. 2 The solid line indicates actual data from a device, the dashes the simulation according to the invention and the dotted lines the simulation according to the prior art.

[0046] We can see for the Fig.2 that the flow rate increases in both cases.

[0047] [ Fig. 3 [ ] shows the variation of the total percentage of nitrogen and oxygen in the overhead gas of the argon separation column over time, comparing a simulation with manual operation of the degassing valve and a simulation with regulation of the degassing valve according to the invention. Here we see that the invention allows for a much faster reduction of the nitrogen and oxygen concentration.

[0048] [ Fig. 4 ] shows the opening of the degassing valve over time for the case of a simulation with manual use of the degassing valve and a case with regulation of the degassing valve according to the invention.

[0049] [ Fig. 5 ] shows the percentage of nitrogen in the head gas of the argon separation column over time for the case of a simulation with manual use of the degassing valve and a case with regulation of the degassing valve according to the invention.

[0050] [ Fig. 6 [ ] shows the percentage of oxygen in the middle of the argon separation column over time in the case of a simulation with manual operation of the degassing valve and a case with regulation of the degassing valve according to the invention. It can be seen that the invention allows for a more rapid reduction of oxygen.

[0051] [ Fig. 7 [ ] shows the percentage of oxygen in the overhead gas of the argon separation column over time for a simulation with manual operation of the degassing valve and a simulation with regulation of the degassing valve according to the invention. It can be seen that the invention allows for a more rapid reduction of oxygen.

[0052] [ Fig. 8 ] shows the gas flow rate at the top of the argon separation column over time for the case of a simulation with manual use of the degassing valve and a case with regulation of the degassing valve according to the invention.

Claims

1. A unit for producing argon by cryogenic distillation, adapted to be connected to a double air separation column consisting of a first and a second column (K1, K2) thermally connected to each other, comprising an argon separation column (K3) surmounted by a head condenser, means for sending a head gas (13, 15) from the argon separation column to the atmosphere, an analyzer (AIC1, AIC2) for measuring the nitrogen content at the top of the argon separation column and / or in a fluid withdrawn from the top of the argon separation column, means, capable of being controlled during the start-up of the unit, for opening and closing the means for sending the head gas of the argon separation column to the atmosphere according to the nitrogen content detected by the analyzer, characterized in that it comprises a de-nitrogenation column (K4), means for connecting the top of the argon separation column to the de-nitrogenation column, means for withdrawing a product rich in argon and depleted in nitrogen (LAR) from the bottom of the de-nitrogenation column, means for withdrawing a fluid rich in nitrogen from the top of the de-nitrogenation column, and means, capable of being controlled during the start-up of the unit, for opening and closing the means for connecting the top of the argon separation column to the de-nitrogenation column according to the nitrogen content detected by the analyzer.

2. The unit according to claim 1, comprising a double air separation column comprising a first column (K1) operating at a first pressure and a second column (K2) operating at a second pressure lower than the first pressure, the top of the first column being thermally connected to the bottom of the second column, optionally another column supplied with an argon-enriched gas coming from an intermediate point of the second column, and comprising means for sending air (1) to the first column, means for sending a nitrogen-enriched fluid and an oxygen-enriched fluid (3) from the first column to the second column, the argon separation column (K3) being connected to receive a gas (7) coming from an intermediate point of the second column or, as the case may be, an argon-enriched gas coming from the other column3. The unit according to claim 2, wherein the analyzer (AIC1) is also connected to measure the nitrogen content in the argon-enriched gas (7) sent to the argon separation column (K3).

4. The unit according to claim 3, wherein the analyzer (AIC1) is connected to alternatively measure the nitrogen content in the argon-enriched gas (7) and the nitrogen content at the top of the argon separation column (K3).

5. A start-up method for an argon separation column by cryogenic distillation, wherein an argon-enriched fluid coming directly or indirectly from a double air separation column comprising a first column (K1) and a second column (K2) thermally connected to each other is sent to an argon separation column (K3), wherein during the start-up of the argon separation column: i. if the nitrogen content at the top of the argon separation column is above a first threshold, the head gas (13, 15) from the argon separation column is sent to the atmosphere, and characterized in that ii. if the nitrogen content at the top of the argon separation column is below a second threshold, lower than or equal to the first threshold, the head gas (13, 17) from the argon separation column is sent to a de-nitrogenation column (K4) to be separated therein and an argon-rich fluid is withdrawn from the de-nitrogenation column as product.

6. The method according to claim 5, wherein during the start-up of the argon separation column if the nitrogen content at the top is above the first threshold, no gas to be separated is sent to the de-nitrogenation column (K4)7. The method according to claim 5 or 6, wherein during the start-up of the argon separation column if the nitrogen content at the top of the argon separation column (K3) is below the second threshold, no gas from the top of the argon separation column is sent to the atmosphere.

8. The method according to one of claims 5 to 7, wherein the nitrogen content at the top of the argon separation column (K3) is measured by means of an analyzer (AIC1, AIC2) capable of analyzing the nitrogen concentration in a range from 10 ppm up to 100% N2 in a mixture of oxygen, nitrogen, and argon.

9. The method according to one of claims 5 to 8, wherein the second threshold is lower than the first threshold.

10. The method according to one of claims 5 to 8, wherein the second threshold is equal to the first threshold.

11. The method according to one of claims 5 to 10, wherein during the start-up of the argon separation column the nitrogen content at the top of the argon separation column (K3) increases.

12. A method for regulating a separation apparatus comprising a start-up method for the apparatus according to one of claims 5 to 11, wherein during the start-up of the argon separation column the nitrogen content at the top of the argon separation column (K3) is measured with an analyzer (AIC1) and outside the start-up of the argon separation column the nitrogen content of a gas (7) feeding the argon separation column is measured with the analyzer.

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