Method and apparatus for gasification of purge liquid from a cryogenic liquid gasifier

Abstract

A method for vaporizing a cleaning fluid from a cryogenic liquid vaporizer (R), the liquid containing at least one impurity, wherein the cleaning fluid (3) is taken from a liquid bath surrounding or generated by the vaporizer, and all the cleaning fluid is vaporized in a heater (H), characterized in that the content of at least one impurity in at least a portion (5,7) or even all of the heated vaporized liquid is analyzed, and the flow rate of at least a portion or even all of the heated vaporized liquid is measured.

Description

[0001] This invention relates to a method and apparatus for vaporizing purge liquid from a cryogenic liquid vaporizer. The cryogenic liquid vaporizer partially vaporizes a liquid containing impurities to form a gas. At low temperatures, some of these impurities tend to deposit in components of air separation units, particularly in the vaporizer-condenser of a distillation column. Therefore, understanding the impurity content is essential for both product quality and plant safety.

[0002] These cryogenic liquids, typically oxygen, nitrogen, or argon, have temperatures below approximately -170°C. They are produced, in particular, using distillation columns that are part of an air separation unit.

[0003] It is known that these cryogenic liquids are sampled for subsequent analysis. This allows for the specific examination of the levels of low-volatility impurities in these liquids, such as nitrous oxide (N₂O), carbon dioxide (CO₂), or hydrocarbons (C₂). n H m .

[0004] The challenge in analyzing low-volatility impurities lies in obtaining a vaporized sample at ambient temperature that is as representative as possible of the liquid being analyzed.

[0005] This is because commonly used analytical methods, such as gas chromatography or infrared spectroscopy, involve heating the collected sample to temperatures close to ambient temperature. For this, the sampled cryogenic liquid must first be vaporized and then heated.

[0006] Under these conditions, in order to obtain analytical results representative of the cryogenic liquid bath, it is recommended to take out a liquid sample representing the average composition of the entire bath and then rapidly and completely vaporize it.

[0007] In the case of air separation units, two cryogenic liquid sampling modes are particularly known.

[0008] The first sampling mode, also known as liquid boost, is based on the thermosiphon effect. To achieve this, the liquid to be analyzed is bypassed, with the bypass flow provided by the vaporization of a portion of the liquid.

[0009] The liquid is lifted and transferred to the cold chamber wall of the air separation unit, within an insulated enclosure, such as rock wool, to limit any heat inflow. A continuous sample of the cryogenic liquid flowing in this lift is then vaporized in a finned atmospheric heat exchanger associated with a mixer, a process commonly referred to as "flash vaporization."

[0010] Another sampling mode, also known as capillary sampling, involves drawing liquid under pressure through a capillary tube, specifically a first tube with a small inner diameter, such as about 0.5 mm. This liquid is then transported to a hot spot in a second tube with a larger cross-section to ensure that all the liquid to be analyzed is vaporized instantaneously.

[0011] These known sampling systems are common and generally guarantee satisfactory results. However, they do have some drawbacks.

[0012] Therefore, they can lead to problems with the representativeness of the samples taken, especially with capillary sampling. This is because the latter, if connected to a liquid bath, does not allow forced flow of the liquid being analyzed.

[0013] In addition, these systems age, especially in liquid lifting systems.

[0014] This is because, in the latter case, moisture gradually seeps into the insulating outer shell, leading to the formation and subsequent accumulation of ice. The inflow of heat then becomes so that the flow of the liquid may be adversely affected.

[0015] Under these conditions, the present invention proposes a method for reliably sampling cryogenic liquids, while using a device that requires very little maintenance.

[0016] FR-A-2839153 describes a method according to the preamble of claim 1, wherein a cryogenic liquid is vaporized by heat exchange with a hot fluid.

[0017] Therefore, one subject of this patent is a method for sampling at least one cryogenic liquid (particularly oxygen or nitrogen), wherein the cryogenic liquid contains impurities such as nitrous oxide, carbon dioxide or hydrocarbons, wherein the liquid vaporizes to form a gas, and the gas is first sent to a flow meter and then to an analyzer.

[0018] According to one aspect of the invention, a method is provided for vaporizing a cleaning fluid from a cryogenic liquid vaporizer, the liquid containing at least one impurity, wherein the cleaning fluid is taken from a liquid bath surrounding or generated by the vaporizer, and all the cleaning fluid is vaporized in a heater, characterized in that the content of at least one impurity in at least a portion or even all of the heated and vaporized liquid is analyzed and the flow rate of at least a portion or even all of the heated and vaporized liquid is measured.

[0019] Based on some optional aspects:

[0020] • Analyze the content of at least one impurity in all heated and vaporized liquids and measure the flow rate of all heated and vaporized liquids, with the analysis sampled upstream of the flow rate measurement;

[0021] • The vaporizer is located at the bottom of the distillation column;

[0022] • Divide the heated liquid into two parts, analyze the content of at least one impurity in the first part and measure the flow rate of the second part;

[0023] • The first part constitutes less than 5% of the heated liquid, preferably less than 1%, or even 0.5%;

[0024] • The second part constitutes more than 95% of the heated liquid, preferably more than 99%, or even 99.5%;

[0025] • A cryogenic liquid vaporizer vaporizes cryogenic liquids to produce gaseous products;

[0026] • The second portion of liquid, vaporized in the heater, is sent to mix with the gaseous products;

[0027] A portion of the liquid vaporized in the heater, preferably with its flow rate already measured, is sent to be mixed with the gaseous products.

[0028] • The gaseous product is heated to a temperature above 0°C in a heat exchanger and then mixed with a second liquid component that has been vaporized in a heater.

[0029] According to another aspect of the invention, a method for separating air by cryogenic distillation is provided, the method comprising a tower system in which air is cooled and separated to produce a cryogenic liquid vaporized in a vaporizer, from which a cleaning fluid is vaporized as described above.

[0030] The cryogenic liquid vaporized in the vaporizer can be liquid oxygen.

[0031] The cryogenic liquid vaporized in the vaporizer can be an oxygen-rich liquid containing at least 25 mol% oxygen.

[0032] According to another aspect of the invention, an apparatus is provided for vaporizing a cleaning fluid from a cryogenic liquid vaporizer, the liquid containing at least one impurity, the apparatus comprising a cryogenic liquid vaporizer, a line for drawing the cleaning fluid from a liquid bath surrounding or generated by the vaporizer, a heater for vaporizing the cleaning fluid, a flow meter, and an analyzer for analyzing the content of at least one impurity in the cleaning fluid, characterized in that it includes means for conveying at least a portion of the vaporized cleaning fluid to the analyzer for analyzing the content of at least one impurity, and a line for conveying at least a portion of the vaporized cleaning fluid to the flow meter.

[0033] If all the cleaning fluid is delivered to the flow meter and the analyzer, then the apparatus for delivering at least a portion of the vaporized cleaning fluid to the analyzer to analyze the content of at least one impurity consists of a pipeline for delivering at least a portion of the vaporized cleaning fluid to the flow meter.

[0034] Possibly, the device includes means for delivering a first portion of the vaporized cleaning fluid to an analyzer and / or means for delivering a second portion of the vaporized cleaning fluid to a flow meter.

[0035] In this case, preferably, the device does not include means for delivering a first portion of the vaporized cleaning fluid to the flow meter and / or does not include means for delivering a second portion of the vaporized cleaning fluid to the analyzer.

[0036] According to another aspect of the invention, an apparatus for separating air by cryogenic distillation is provided, the apparatus comprising a tower system for producing cryogenic liquid and the aforementioned apparatus for vaporizing cleaning liquid, the tower system being connected to a cryogenic liquid heater.

[0037] The tower system preferably includes a first tower operating at a first pressure and a second tower operating at a second pressure below the first pressure.

[0038] The device may include:

[0039] • Apparatus for removing cleaning fluid from a second tower connected to a heater;

[0040] • A device for removing the bottom liquid from a first column connected to a heater.

[0041] The liquid flow from the vaporizer purging to the dual-tower cryogenic distillation air separator represents a small flow rate, especially for small-sized equipment that is difficult to measure. However, accurate measurement of this flow rate is important, as it sets the level of impurity concentration in the liquid oxygen bath, especially if the equipment generates gaseous oxygen directly from the low-pressure tower.

[0042] The existing solution is a sampling cleaning system, which involves filling and periodically emptying a known volume over a known duration to ensure an average cleaning flow rate. This requires a tank, several valves, and instruments (level measurement). Instantaneous cleaning flows are large and are often "thrown" into cryogenic cleaning systems. Molecules are not recovered. In some cases, the cleaned liquid may be sent to a storage tank as a backup in case of equipment failure.

[0043] Impurity analysis is performed using a dedicated sampling system on a cryogenic liquid bath in the vaporizer, typically a flash type.

[0044] The present invention also relates to an air separation device, which includes a cryogenic liquid vaporizer and a device for vaporizing a cleaning fluid.

[0045] The present invention aims to upgrade the deconcentration and cleaning stream from the gasifier in the form of gaseous products by combining it with the analysis of secondary impurities.

[0046] This invention involves rapidly vaporizing the entire liquid purge stream to obtain a gas at ambient temperature, easily measuring its flow rate, and extracting a gaseous sample for continuous delivery to an impurity analyzer. The remaining gas is not analyzed and is then mixed with the production gas, thereby avoiding molecular loss.

[0047] The advantages are reliable and continuous flow measurement, and the elimination of the expensive, bulky, and difficult-to-install cryogenic sampling system for measuring impurities in a vacuum-insulated cold box.

[0048] The method according to the invention will now be described in more detail with reference to the accompanying drawings: Attached Figure Description

[0049] [ Figure 1 ]and[ Figure 2 [Illustratively representing the method according to the present invention.]

[0050] exist Figure 1 In this system, the air separation equipment via cryogenic distillation consists of a main heat exchanger E and two towers K1 and K2, located in one or more insulated chambers, such as a vacuum insulated cold box, and is capable of operating at low temperatures.

[0051] The twin towers consist of a first tower K1, above which is a second tower K2 that operates at a lower pressure than the first tower.

[0052] Air 1 is cooled in exchanger E and sent to the bottom of the first column K1, where it is separated by distillation. An oxygen-enriched stream is fed from the bottom of the first column K1 to the midpoint of column K2. A nitrogen-enriched stream is fed from the top of the first column K1 to the second column K2.

[0053] Nitrogen gas from the top of the first column is condensed in the vaporizer-condenser R at the bottom of the second column, where it is used to vaporize the bottom liquid of the second column surrounding the vaporizer R. A stream of gaseous oxygen 9, constituting a product of one or even one device, is drawn from the second column and heated in the exchanger E. Gaseous nitrogen 11 from the top of the second column is heated in the exchanger E.

[0054] The vaporizer R referred to here is a conventional bath vaporizer in which the purging stream is drawn from the bath. In contrast, the vaporizer R can be a diaphragm vaporizer in which the liquid “bath” is below the vaporizer, or a so-called bath vaporizer with a built-in tank or recirculation line, without a true bath in the traditional sense.

[0055] Therefore, the cleaning fluid can be removed from the liquid bath surrounding the vaporizer or generated by the vaporizer.

[0056] The cleaning stream 3 from the liquid oxygen bath surrounding the vaporizer R is continuously drawn off at the bottom of the bath. It then relies on the fluid to "suddenly" vaporize (flash evaporate) to ensure a high wall temperature (making the ΔT between the cleaning liquid and the fluid greater than 100°C) to avoid secondary impurities (C). n H m The high local concentrations of CO2 and N2O are hazardous to the safety of heater H. This also ensures that all impurities present in the liquid cleaning process are present in the resulting gas, which allows for reliable analysis of the impurities (therefore, no impurities that would affect the analysis are deposited in heater H). The gas is then heated to ambient temperature in heater H in gaseous form.

[0057] Heat exchange in heater H can occur with ambient air in an atmospheric pressure vaporization hairpin, with water in a shell-and-tube exchanger, or preferably in an exchanger having a shell and a spiral tube or coaxial spiral tube. The exchanger may also include spiral tubes for a cleaning stream and for water, each embedded in an aluminum or copper substrate. The exchanger may also include electric heating.

[0058] The heater H can be located outside any insulated chamber.

[0059] The wall of the heater H, which is intended to contact the cryogenic liquid 3 or each cryogenic liquid 3, is maintained at a temperature at least 15°C, preferably at least 50°C, or even at least 100°C above the temperature of the cleaning liquid, thereby heating the vaporized liquid to at least -50°C, or even at least -20°C, preferably at least 0°C.

[0060] To achieve this, the fluid heating heater H must typically be at least 100°C hotter than the cryogenic liquid.

[0061] The temperature of the heater wall is also preferably higher than the sublimation or vaporization temperature of the least volatile impurities contained in the cryogenic liquid.

[0062] A small sample 7 is taken from the cleaning stream 3, for example, up to 5% of the cleaning stream, preferably less than 1% or 0.5%, and this stream is transported through a pipe several meters long to an impurity analyzer for analysis at ambient temperature, i.e., at least 0°C. The total vaporization of the cleaning stream 3 makes it possible to reliably measure its flow rate (because it is a gaseous flow at ambient temperature). Separation due to sampling is performed upstream of the flow measurement. The small sample stream only slightly and in a safe manner (upper limit) interferes with the measurement of the cleaning stream 3. Alternatively, separation can be performed downstream of the flow measurement.

[0063] It is then easy to measure, for example, at least 95%, preferably greater than 99%, or even 99.5% of the remaining gas purging flow 5 constituting the purging flow in the flow measurement device FIC, such as by a simple orifice plate or hot-wire mass flow meter. This measurement means that the FIC is located outside the chamber, just like the heater H, because the flow measurement is performed at ambient temperature.

[0064] Then, the heated cleaning stream 5 is remixed with the product of gaseous oxygen 9 at the hot end of the exchanger E, which allows the yield to be increased by several percentage points, typically about 1%.

[0065] Throughout the operation of the equipment, the cleaning flow 3 is delivered to the heater H through the open valve V1. The cleaning flow rate is regulated by valve V1 based on FIC flow measurement.

[0066] This invention makes it possible to minimize the number of components required for continuous and more reliable management of the cleaning flow, and its compactness and simplicity allow for easy integration into vacuum-insulated cold boxes.

[0067] The device may include a turbine ( Figure 1 (Not shown in the image) to keep the equipment cold. In the case of a vacuum cold box, the turbine body can be welded directly to the shell of the cold box, which allows for better compactness and ensures a seal relative to the vacuum. The internal components of the turbine, often referred to as the cylinder, can be removed from the outside without entering the vacuum cold box, for example, to replace the impeller in case of machine failure. Similarly, a filter can be positioned at the turbine's suction end to protect the impeller. Integrating it into the cylinder or turbine body is also advantageous, while still allowing external access for replacement or cleaning.

[0068] In addition, for better compactness, cryogenic valves can have their bodies mounted in a vacuum chamber and their extension channels welded to the chamber wall, optionally via flanges and / or bellows located between the extension channels and the outer shell of the vacuum chamber.

[0069] The turbine and valves can be installed in a portion of the refrigerated container that has a smaller diameter compared to the rest of the container, so that these components can be placed in the "shadow" of the container without being affected by factors such as shipping dimensions.

[0070] Furthermore, during extended equipment downtime, it is necessary to purge all cryogenic liquids, which are typically sent to external storage tanks where they slowly vaporize. These tanks are large and therefore expensive. This functionality can be added to the exchanger H, which vaporizes the continuous purging stream from the vaporizer R, by increasing its size: this makes it possible to have a device that does not discharge any cryogenic liquids, thus eliminating the associated safety concerns.

[0071] [ Figure 2 The diagram above shows an improved version of the equipment, where heater H is used to vaporize the bottom liquid of the first tower K1 in addition to vaporizing the cleaning fluid. Specifically, during equipment shutdown, liquid descends through the tower and accumulates at the bottom. To start the tower when the liquid level is too high, or if it is necessary to fully heat the equipment by de-icing it with gas supplied at ambient temperature, the bottom liquid must be removed. This bottom liquid is typically sent to a dedicated heat exchanger where it is vaporized and then sent to the atmosphere or any other cleaning system, such as an external storage tank, where it is slowly vaporized. Here, during normal operation of the equipment, heat exchanger H is used to vaporize the cleaning fluid 3, with valve V1 open and valve V2 closed.

[0072] After shutdown, before restarting or de-icing, valve V2 is opened to allow the bottom liquid to enter heat exchanger H through pipeline 13.

[0073] The heat source used to vaporize the two liquids at different times can be electricity or a fluid 15 present on site, such as air or water.

[0074] The liquid at the bottom is thus vaporized and released into the air.

[0075] In this diagram, the liquid at the bottom is from the first tower K1, but it could come from another tower, such as K2 or the argon tower.

[0076] In this diagram, the liquid that is vaporized and heated in exchanger H is divided into two parts. Only part 7 is analyzed, and only part 5 passes through flow meter FIC. Therefore, part 5 is not analyzed, and the flow rate of part 7 is not measured.

[0077] Alternatively, the heated liquid can be analyzed and measured without separating the entire flow. In this case, it is preferable to place the analysis sampling point upstream of the flow meter to ensure that the pressure inside the analyzer is sufficiently high.

[0078] To reduce the footprint of the cleaning fluid reaching heat exchanger H and increase the hydrostatic pressure, the heat exchanger is placed below the first tower K1, preferably below the chamber containing towers K1 and K2. Heat exchanger E can be placed between the bottom of tower K1 and heat exchanger H.

[0079] For both graphs, tower K1 operates between 1.2 and 6.5 bar, preferably between 1.2 and 4.5 bar.

Claims

1. A method for vaporizing a cleaning fluid from a cryogenic liquid vaporizer (R), the cleaning fluid containing at least one impurity, wherein the cleaning fluid (3) is taken from a liquid bath surrounding or generated by the vaporizer, and all the cleaning fluid is vaporized in a heater (H), characterized in that... Analyze the content of at least one impurity in at least a portion (5, 7) or even all of the heated and vaporized cleaning fluid, and measure the flow rate of at least a portion or even all of the heated and vaporized cleaning fluid. Divide the cleaning fluid heated to at least -50°C into two portions (5, 7), analyze the content of at least one impurity in the first portion, and measure the flow rate of the second portion.

2. The method according to claim 1, wherein the content of at least one impurity in all heated and vaporized cleaning fluids is analyzed and the flow rate of all heated and vaporized cleaning fluids is measured, with the analysis sample taken upstream of the flow rate measurement.

3. The method according to claim 1, wherein the first portion (7) constitutes up to 5% of the vaporized cleaning fluid.

4. The method according to claim 2, wherein the first portion (7) constitutes up to 5% of the vaporized cleaning fluid.

5. The method according to claim 3, wherein the first portion (7) constitutes less than 1% of the vaporized cleaning fluid.

6. The method according to claim 3, wherein the first portion (7) constitutes 0.5% of the vaporized cleaning fluid.

7. The method according to any one of the preceding claims, wherein the cryogenic liquid vaporizer (R) vaporizes the cryogenic liquid to produce a gaseous product (9), and at least a portion of the cleaning liquid vaporized in the heater (H) is sent to mix with the gaseous product.

8. The method according to claim 7, wherein the cryogenic liquid vaporizer (R) vaporizes the cryogenic liquid to produce a gaseous product (9), and a second portion (5) of the cleaning liquid vaporized in the heater (H) is sent to mix with the gaseous product.

9. The method of claim 7 in combination with any one of claims 1 and 3, wherein the gaseous product (9) is heated to a temperature above 0°C in a heat exchanger (E) and then mixed with a second portion of the cleaning fluid vaporized in a heater (H).

10. A method for separating air by cryogenic distillation, the cryogenic distillation comprising a column system (K1, K2) wherein air (1) is cooled and separated in the column system to produce a cryogenic liquid vaporized in a vaporizer (R), vaporizing a cleaning liquid (3) from the vaporizer (R) according to any one of the preceding claims.

11. The method of claim 10, wherein the cryogenic liquid vaporized in the vaporizer (R) is liquid oxygen or an oxygen-enriched liquid containing at least 25 mol% oxygen.

12. An apparatus for vaporizing a cleaning fluid (3) from a cryogenic liquid vaporizer (R), wherein the cleaning fluid contains at least one impurity, the apparatus comprising a cryogenic liquid vaporizer, a line for removing the cleaning fluid from a liquid bath surrounding or generated by the vaporizer, a heater (H) for vaporizing the cleaning fluid, a flow meter (FIC), and an analyzer (AI) for analyzing the content of at least one impurity in the cleaning fluid, characterized in that... The vaporized cleaning fluid heated to at least -50°C is divided into two portions (5, 7). The apparatus includes means for delivering the first portion of the vaporized cleaning fluid to an analyzer to analyze the content of at least one impurity, and a line for delivering the second portion of the vaporized cleaning fluid to a flow meter.

13. The apparatus of claim 12, comprising means for delivering a first portion (7) of the vaporized cleaning fluid to an analyzer (AI) and / or means for delivering a second portion (5) of the vaporized cleaning fluid to a flow meter (FIC).

14. The apparatus according to claim 12 or 13, excluding means for conveying a first portion of the vaporized cleaning fluid to a flow meter (FIC).

15. The apparatus according to claim 12 or 13, excluding means for conveying a second portion of the vaporized cleaning fluid to the analyzer.

16. The apparatus of claim 14, excluding means for conveying a second portion of the vaporized cleaning fluid to the analyzer.

17. An apparatus for separating air by cryogenic distillation, comprising a tower system (K1, K2) for producing cryogenic liquid including a first tower (K1) and a second tower (K2) thereon, and an apparatus according to claim 12, 13, 14 or 15 for vaporizing a cleaning liquid (3) from a cryogenic liquid vaporizer (R), the tower system being connected to a cryogenic liquid heater (H) to deliver bottom liquid (13) from the tower (K1) of the tower system to the cryogenic liquid heater (H), the apparatus comprising means for removing the cleaning liquid (3) from the second tower and removing the bottom liquid from the first tower.

18. The apparatus of claim 17, wherein the tower system comprises a first tower (K1) operating at a first pressure and a second tower (K2) operating at a second pressure below the first pressure.

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