Air purification method and device and low-temperature air separation method and equipment

Abstract

The system of the present invention is configured for generating compressed pure air. In such a system, feed air (1) is introduced into an air compressor (2) comprising a penultimate stage (2a) and a last stage (2b). The feed air from the penultimate stage is cooled in an intermediate compressor cooler (3). The feed air cooled in the intermediate compressor cooler (3) is further compressed in the last stage (2b) and produces a compressed air stream (4). The compressed air flow (4) is conducted into a final compressor cooler (5) in order to produce a cooled compressed air flow (6, 6a, 6b). Such a cooled compressed air stream (6, 6a, 6b) is introduced into a purification unit (8, 9) comprising an adsorber with an adsorbent for generating a compressed pure air stream (11). In the system, the adsorber inlet temperature (AIT) is controlled by directing at least a portion of the compressed air flow at least temporarily through a bypass line (16) surrounding the final compressor cooler (5) and thereby regulating the portion of the compressed air flow that bypasses the final compressor cooler (5); and / or adjusting the workload of the final compressor cooler (5).

Description

[0001] The invention relates to an air purification method and an apparatus according to the preambles of the independent patent claims, as well as a cryogenic air separation method and an apparatus (ASU=Air Separation Unit) using such a purification method and apparatus.

[0002] Upstream of the cryogenic section of the ASU, components that freeze at cryogenic temperatures, in particular water and carbon dioxide, must be removed (see textbook (Industrial Gases Processing, 2008, p. 24, section "Purification," and Hausen, Linde, Tieftemperaturtechnik, 1985, section 4.4.2 "Adsorber for Wasserdampf und Kohlendioxid," pp. 303-310.) In modern air separation units (ASUs), the corresponding purification step is typically carried out in a pair of reversible vessels containing one or more adsorbents. These vessels alternately perform adsorption and regeneration operations, thereby ensuring stable operation of the ASU. The purification step may also additionally remove other impurities present in the feed air, such as hydrocarbons, nitrogen oxides, carbon monoxide, or hydrogen.

[0003] The object of the present invention is to improve the performance of such systems, in particular with regard to the removal performance and / or the switching time of the adsorber and / or the amount of active material required.

[0004] This problem is solved by the features of claim 1 .

[0005] Normally, the inlet temperature of the adsorber varies with changes in the ambient temperature. However, this has not yet been considered a critical parameter. However, the present invention has discovered the adsorber inlet temperature (AIT) and developed an effective method for controlling AIT. AIT can be measured directly at the adsorber inlet by any known temperature measurement method; alternatively, AIT can be measured indirectly within the framework of the present invention. Normally, all feed air is cooled in all compressor coolers, including the final compressor cooler. This is wise because the air enters the cryogenic device later and the lower its temperature, the better for the cryogenic process and the adsorption step. Contrary to what might be imagined, in the present invention, a portion of the adjustable air bypasses the final compressor cooler in order to control the AIT.

[0006] This measure significantly increases the average AIT, leading to thermodynamic disadvantages. However, the present invention surprisingly reveals significant advantages in purification operation that greatly outweigh the expected disadvantages. The process of the present invention enables the feed inlet temperature of the prepurifier of an air separation plant to be maintained stable, making its operation and removal performance unaffected by changes in ambient temperature.

[0007] Although the feed inlet temperature and the adsorber inlet temperature - AIT - are not exactly the same theoretical terms, there is no practical difference between these two temperatures because the feed air is neither cooled nor heated between the prepurifier inlet (upstream of the switching valves) and the adsorber inlet (downstream of the first set of switching valves).

[0008] The present invention establishes stable and reliable operation. This eliminates the need for:

[0009] - Unnecessary equipment shutdowns due to contaminant penetration,

[0010] - Reduce equipment airflow to eliminate penetration,

[0011] Increased liquid discharge due to contaminant buildup in the main condenser is not an unnecessary waste of refrigeration / power.

[0012] Eliminating each of these points provides economic advantages for operating the equipment.

[0013] Such purification units containing catalyst material are preferably regenerated by hot regeneration gas - TSA (temperature swing adsorption). Alternatively, other types of operation are possible, such as PSA (pressure swing adsorption), a combination of PSA and TSA or other regeneration methods.

[0014] Although useful in all types of adsorption purification, especially in TSA (temperature swing adsorption), it has particular advantages in PSA (pressure swing adsorption).

[0015] Classic prepurifiers in air separation plants are typically designed for the most severe operating conditions. For a given design flow and pressure, the most severe conditions coincide with the highest inlet temperatures, typically during hot summer months. Hot inlet air carries the highest moisture load, and at higher temperatures, the adsorbent in the prepurifier has a lower capacity. The combination of these two effects results in the most challenging conditions for the prepurifier, so the prepurifier bed is designed to successfully operate at the highest temperature it may experience.

[0016] Conversely, during typical cold winter months, the moisture load in the incoming air is lower, and the adsorbent has a higher capacity at these lower temperatures, so the prepurifier is expected to operate on cold days at the same design it was designed for on hot days without any problems.

[0017] However, particularly in the case of pressure swing adsorption (PSA) prepurifiers, where the regeneration gas is not heated, cooler ambient temperatures and cooler feed inlet temperatures to the prepurifier also mean lower regeneration temperatures, which can result in less efficient cleaning of the bed. Therefore, maintaining a relatively high feed inlet temperature to the prepurifier on cold days is crucial to allow the bed to regenerate properly and achieve successful prepurifier performance, as achieved by the present invention.

[0018] The solution of the present invention is to maintain the feed inlet temperature of the pre-purifier within a narrow design range, for example, within the range of 15°C to 40°C, preferably within the range of 30°C to 40°C, while the ambient temperature can vary, for example, from 0°C to 40°C. This is achieved by adjusting the duty in the air compressor aftercooler (final compressor cooler) in such a way that it runs at a higher rate during hot days (for example, 40°C) to achieve maximum cooling of the incoming air, and runs at a reduced rate during cold days (for example, 0°C) so as not to overcool the compressed air so that it does not fall below 30°C. This can be achieved by adjusting the bypass around the compressor aftercooler to control the duty of the aftercooler at a given temperature in the feed inlet.

[0019] Another embodiment of the present invention is to insulate the feed inlet line to the prepurifier to eliminate further cooling of the feed due to the lower ambient temperature. In addition, if necessary, the feed inlet line can even be heated to achieve the desired inlet temperature of the prepurifier.

[0020] The cryogenic air separation process according to the invention comprises the process for producing compressed pure air as described above and further comprises the step of insulating the cold section of the ASU, typically by at least one cold box. The purification process of the invention can be combined with any known or unknown cryogenic ASU section.

[0021] Furthermore, the invention relates to a device for purifying air and a device for cryogenic air separation; both of which can be combined with device features corresponding to the features of the dependent method claims.

[0022] The invention and further details of the invention will now be described with reference to two embodiments shown in the accompanying drawings:

[0023] Figure 1 A first embodiment is shown which comprises a classic PSA unit having only an adsorbent as active material.

[0024] Figure 2 In relation to the second embodiment, the purification unit contains at least one catalyst material.

[0025] exist Figure 1 In the embodiment of the invention, atmospheric air enters the compressor 2 as feed air 1. The compressor comprises n compressor stages and n-1 intercoolers 3. In a specific example, n can be 4, that is, it is a four-stage compressor with three intercoolers. At least a portion of the compressed air 4 is at least temporarily directed to the final cooler (aftercooler) 5 for cooling. The aftercooler 5 can use forced ambient air or cooling water as the cooling medium. The cooled compressed air stream 6 flows into a purification unit 7 comprising two containers 8 and 9, which contain one or more adsorbents and optionally a catalyst in a known manner. (There may be a third or even more containers in parallel.) This or these adsorbents are mainly used to remove water and carbon dioxide, hydrocarbons, nitrogen oxides, carbon monoxide, hydrogen, etc. from the air stream. They can include one or more of the following materials:

[0026] Silicone

[0027] Alumina

[0028] molecular sieves

[0029] Composite adsorbent of molecular sieve and alumina

[0030] catalyst

[0031] exist Figure 1 In the current operating state of the embodiment of FIG, vessel 9 is in adsorption mode and vessel 8 is in regeneration mode by receiving regeneration gas, which is preferably dry exhaust gas from the ASU (to which air is ultimately fed), in particular a nitrogen- or oxygen-rich stream. The regeneration gas has a much lower pressure (PSA) than the feed air.

[0032] Cleaned air 11 is extracted from the cleaning unit 7 after an optional dust filter 10 and is sent via line 12 to the main heat exchanger of the ASU ( Figure 1 Optionally, a portion 15 of the purified air can be admixed to the regeneration gas 13 .

[0033] According to the invention, the system comprises a bypass line 16 around the final cooler 5, such bypass line 16 comprising a temperature controller (Tc) 17 capable of controlling the AIT by regulating the portion of the compressed air flow bypassing the final compressor cooler.

[0034] Alternatively or additionally, the workload of the aftercooler 5 is regulated by the temperature control of the present invention. If the workload of the aftercooler after such control is capable of maintaining the adsorber inlet temperature at the desired level, the bypass line 16 may not be used or even omitted.

[0035] In the temperature control process of the present invention, temperature measurement can be accomplished by directly measuring the temperature to be controlled or indirectly measuring the temperature to be controlled, for example, by a program using one or more other parameters (such as the ambient temperature and / or the temperature of the cooling water of the aftercooler 5).

[0036] In a practical example, the feed inlet temperature to the prepurifier (typically equal to the adsorber inlet temperature AIT) is maintained within a narrow design range, for example, within a range of 30° C. to 40° C., while the ambient temperature can vary, for example, within a range of 0° C. to 40° C. This is achieved by regulating the workload in the air compressor aftercooler (final compressor cooler) by the temperature controller 17 in such a way that it operates at a higher rate during hot days (for example, 40° C.) to achieve maximum cooling of the incoming air, and operates at a reduced rate during cold days (for example, 0° C.) so as not to overcool the compressed air, so that it does not fall below 30° C. This can be achieved, for example, by controlling the workload of the aftercooler according to the temperature in the feed inlet line 6 and / or by regulating a bypass around the compressor aftercooler.

[0037] The air flow rate into the pre-purifier is maintained within a narrow acceptable design range by such a control process using the controller 17 to adjust the aftercooler workload and / or the bypass line 16. For example, the aftercooler workload can be adjusted by running more / less cooling medium flow (such as cooling water or forced ambient air).

[0038] exist Figure 2 , purification unit 7 and upstream steps appear to be Figure 1 Very similar. Figure 2 The steps with three-digit reference numerals may be located in Figure 1 In the process. Figure 1 In addition, it also shows the details of the ASU 14. However, Figure 2 The purification unit 7 and upstream steps in the can be combined with any known or unknown type of ASU for compressing and purifying the ASU feed air.

[0039] Figure 2The compressor in the embodiment comprises only two stages 2a, 2b (n=2) with an intercooler 3. Atmospheric air (AIR) 1 flows through a filter 121 and is then compressed in line 4 to a pressure of about 5 to 8 bar. (Other types of ASUs may have other air pressures, typically in the range of 8 to 13 bar; the compressor then typically has 3 to 4 stages.) At least a portion of the compressed air 4 is directed, at least temporarily, to a final cooler (aftercooler) 5 for cooling. The cooled compressed air stream 6a flows into a water separator 122 for separating liquid water 123 and is further directed via line 6b to a purification unit 7 comprising two containers 8, 9 containing one or more adsorbents, such as Figure 1 As shown, however, there is at least one additional active material in the form of a catalyst. This difference will be described in detail below.

[0040] exist Figure 2 In the current operating state of the embodiment of the present invention, vessel 9 is in adsorption mode, and vessel 8 is in regeneration mode by receiving regeneration gas from the ASU 14 (to which air is ultimately fed), specifically a nitrogen-rich stream. It is operated by the TSA. The regeneration gas is heated to an elevated temperature of 100° C. to 300° C., preferably 150° C. to 220° C., before entering vessel 8 for regeneration.

[0041] Cleaned air 11 is extracted from purification unit 7 and fed to main heat exchanger 21 of ASU 14. Cooled air is extracted slightly before the cold end of main heat exchanger 21 and directed in a gaseous state to distillation column 23. In this embodiment, the main heat exchanger is an integrated heat exchanger that combines the functions of a classic main heat exchanger and a classic subcooler. Distillation column 21 is a single column, and the process is implemented as a Spectra process, including recycling the exhaust gas from the overhead condenser into the column via cold compression.

[0042] Slightly above the introduction of the feed air 22, a middle distillate 24 is withdrawn in liquid form from the column 23. This middle distillate is cooled in the subcooler section of the MHE 21, expanded and evaporated in the first evaporation space of the overhead condenser 26 of the column 23. The evaporated middle distillate 27 serves as a recycle stream 28 which is fed to the inlet of the cold compressor 30. (A portion 29 of the evaporated bottoms fraction 27 can be released into the atmosphere—ATM.)

[0043] The cold compressor 30 is driven by an expansion turbine 31, the combined machine also including a dissipative brake 32 for generating process refrigeration. The recompressed recycle stream 33 is cooled in the MHE 21. The cooled recycle stream 34 is fed back into the column directly above the column base.

[0044] The bottom liquid 35 of the column 23 is likewise cooled in the subcooler section of the MHE 21, expanded in the second evaporation space of the overhead condenser 26 of the column 23, and then evaporated. The evaporated bottom fraction 36 is warmed to an intermediate temperature in the MHE 21 and then expanded in the expansion turbine 31. The resulting low-pressure bottom fraction is fully warmed in the MHE 21 and then fed to the purification unit 7 via line 37 to be at least partially used as regeneration gas.

[0045] A first portion 39 of the overhead nitrogen 38 from column 23 is fully warmed in MHE 21. A portion 41 of the warmed gaseous nitrogen 40 can be used as seal gas 41 (seal gas). After compression in product compressor 43 with aftercooler 44, most of the seal gas 42 is recovered as pressurized gaseous nitrogen product (PGAN) 45. The remaining portion 46 of the overhead gas 38 is almost completely condensed in overhead condenser 26. Non-condensable gases are removed from the condenser effluent 47 via purge stream 48, while liquid nitrogen is diverted and either used as reflux liquid 49 in column 23 or withdrawn as a liquid product (PLIN) via lines 50 and 51 after being subcooled in product subcooler 52.

[0046] In this case, refrigeration can be added by LIN injection via line 53.

[0047] According to the invention, the system can include a bypass line 16 around the final cooler 5, such bypass line 16 including a temperature controller 17 (here shown in a simplified manner as a controllable valve) capable of controlling the AIT by regulating the portion of the compressed air flow that bypasses the final compressor cooler. Alternatively or additionally, the workload of the cooler 5 is regulated.

[0048] This can be accomplished by measuring the temperature to be controlled or by indirect measurement as described above.Through such a control process using the controller 17 and the bypass line 16, the air flow rate into the pre-purifier is maintained within a narrow acceptable design range.

[0049] If, as in the embodiment of the accompanying drawings, the container contains Figure 1Such stable temperatures are even more advantageous if at least one layer of catalyst material is present above a known adsorbent layer or any classical purification unit. Such adsorption vessels comprising catalysts are known in the art, for example from EP 799633A1, EP 2662653 A1 or WO 2022039840A1, which disclose specific layering suitable for the present invention. These catalysts are used to remove hydrogen and carbon monoxide to ppb levels in order to produce ultrapure nitrogen in ASU 14. In embodiments of corresponding variants of the present invention, vessels 8, 9 comprise one or more layers, the first layer being a catalyst comprising manganese oxide and copper oxide (sometimes referred to as "hopcalite"), which is configured to remove at least some carbon monoxide and hydrogen from the feed air.

[0050] The efficiency of all these catalyst materials (especially hopcalite) decreases significantly with decreasing temperature. In previously known designs, the AIT is directly related to the cooling water temperature. Cooling water temperature directly affects the power consumption of the ASU. The lower the temperature, the lower the power consumption of the unit. In previous designs, the inlet temperature of the adsorber is directly related to the ambient temperature. In the case of such ASUs operating in the northern hemisphere, the inlet temperature during winter may be too low for an efficient catalyst design.

[0051] By operating the pre-cooling system in accordance with the present invention, the inlet temperature of the purification unit can be adjusted to the value required for efficient operation of the catalyst in the adsorber vessel. A bypass around the final cooler allows the warm gas upstream of the aftercooler to be mixed with the cool gas downstream with the cooling gas to increase the inlet temperature of the purification unit during periods of lower cooling water temperature.

[0052] Operation of such systems (e.g., in Germany) requires cooling water temperatures ranging from 5°C to a maximum of 28°C or even higher. As an alternative to the bypass for increasing the AIT, the cooling water temperature could be increased by 3K in winter. However, this would reduce the power consumption of the compressor by approximately 1%. The present invention avoids this power loss.

Claims

1. A method for producing compressed pure air, comprising the following steps: - introducing feed air (1) into an air compressor (2) comprising the penultimate stage (2a) and the last stage (2b), - cooling the feed air from the penultimate stage in an intermediate compressor cooler (3), - further compressing the feed air cooled in the intermediate compressor cooler (3) in the last stage (2b) and generating a compressed air stream (4), - directing at least a portion of the compressed air flow (4) at least temporarily into a final compressor cooler (5) and generating a cooled compressed air flow (6, 6a, 6b), - introducing the cooled compressed air flow (6, 6a, 6b) into a purification unit (8, 9) comprising an adsorber with an adsorbent for producing a compressed pure air flow (11), in particular by removing water and / or carbon dioxide from the cooled compressed air flow (6, 6a, 6b), It is characterized in that -Control of adsorber inlet temperature (AIT) by: - directing at least a portion of the compressed air flow at least temporarily through a bypass line (16) around the final compressor cooler (5) and thereby regulating the portion of the compressed air flow that bypasses the final compressor cooler (5), and / or - Adjusting the workload of the final compressor cooler (5).

2. The method according to claim 1, the purification unit (8, 9) further comprising a catalyst for removing carbon monoxide and / or hydrogen from the cooled compressed air flow, the temperature control increasing the efficiency of such catalyst.

3. The method according to claim 1 or 2, wherein the purification unit (8, 9) is operated by means of a pressure change.

4. The method according to claim 1, wherein at least a portion of the compressed air flow (4) is guided on an insulated pipe on at least a portion of its path to the purification unit (8, 9).

5. Method according to any of the preceding claims, at least part of the compressed air flow (4) being heated on its way to the purification unit (8, 9) by a heating unit.

6. Method according to any of the preceding claims, comprising removing other pollutants besides water and / or carbon dioxide, such as hydrocarbons, nitrogen oxides, carbon monoxide and / or hydrogen, from the cooled compressed air flow in the purification unit (8, 9).

7. A cryogenic air separation process for producing a nitrogen-rich stream and an oxygen-rich stream by cryogenic air separation, - generating compressed pure air (11, 12) by a method according to any of the preceding claims, - cooling the compressed pure air (11, 12) in a main heat exchanger (21) to produce low-temperature air (22), - introducing at least a portion of the low-temperature air (22) into a distillation column system (23), - withdrawing nitrogen-rich and oxygen-rich streams (38, 39, 40; 35, 36, 37) from the distillation system (23), and - raising the temperature of at least a portion of the nitrogen-rich and oxygen-rich streams in the main heat exchanger (21).

8. The method of claim 7, wherein the nitrogen-rich stream (38, 39, 40) is an ultrapure nitrogen stream.

9. The method according to any of the preceding claims, the purification unit (8, 9) comprising, in addition to the adsorbent, a catalyst material for removing hydrogen and / or carbon monoxide.

10. The method of claim 9, wherein the catalyst material comprises manganese oxide and copper oxide.

11. A device for purifying air to produce compressed pure air, the device comprising: - an air compressor (2), said air compressor comprising a penultimate stage (2a) and a final stage (2b), a purification unit (8, 9) which is an adsorber with an adsorbent for producing a compressed pure air flow (11), in particular by removing water and / or carbon dioxide from the cooled compressed air flow (6, 6a, 6b), - a first line (1) for introducing feed air into the air compressor (2), - an intermediate compressor cooler (3) for cooling the feed air from the penultimate stage, a second line for introducing the feed air cooled in the intermediate compressor cooler (3) into the last stage (2b) and a third line for withdrawing a compressed air stream (4) from the last stage (2b), a fourth line for conducting at least a portion of the compressed air flow (4) to a final compressor cooler (5) and a sixth line for withdrawing the cooled compressed air flow (6, 6a, 6b) from the final compressor cooler (5), a seventh line for introducing the cooled compressed air flow (6, 6a, 6b) into the purification unit (8, 9), It is characterized in that The control device can control the adsorber inlet temperature by: - directing at least a portion of the compressed air flow at least temporarily through a bypass line (16) around the final compressor cooler (5) and regulating the portion of the compressed air flow that bypasses the final compressor cooler (5), and / or - Adjusting the workload of the final compressor cooler (5).

12. The device according to claim 11, the purification unit (8, 9) further comprising a catalyst for removing carbon monoxide and / or hydrogen from the cooled compressed air flow, the catalyst in particular comprising manganese oxide and copper oxide.

13. The device according to claim 11 or 12, the purification unit (8, 9) being arranged to be operated by voltage variation.

14. The device according to any one of claims 11 to 13, wherein at one device at least a portion of the seventh pipeline is provided with thermal insulation.

15. A cryogenic air separation unit for producing a nitrogen-rich stream and an oxygen-rich stream by cryogenic air separation, the cryogenic air separation unit comprising: - a device (8, 9) for purifying air to produce compressed pure air according to claims 11 to 14, - a distillation column system (23), - a main heat exchanger (21), - an eighth pipeline for introducing the compressed pure air (11, 12) into the main heat exchanger (21) to cool the compressed pure air to generate low-temperature air (22), a ninth line for introducing at least a portion of the low-temperature air (22) into the distillation system (23), a tenth line for withdrawing a nitrogen-rich stream (38, 39) from the distillation system and for introducing at least a portion of the nitrogen-rich stream into the main heat exchanger (21), and - an eleventh line for withdrawing an oxygen-rich stream (35, 36) from the distillation system (23) and for introducing at least part of the oxygen-rich stream into the main heat exchanger (21).

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