WO2024234041A1

WO2024234041A1 - A pressure swing adsorption system

Info

Publication number: WO2024234041A1
Application number: PCT/AU2024/050476
Authority: WO
Inventors: Paritosh Wadekar
Original assignee: Paritosh Wadekar
Priority date: 2023-05-17
Filing date: 2024-05-14
Publication date: 2024-11-21
Also published as: AU2024274103A1

Abstract

A pressure swing adsorption system comprises first and second crossover valves operably connecting first and second sieve beds to a compressor inlet, a vacuum outlet and a separated gas take-off. This dual crossover valve arrangement allows each sieve bed to be simultaneously connected between the compressor inlet and the vacuum outlet during its desorption cycle, which improves the rate of desorption and thereby increasing separated gas output of the system. The system preferably further comprises a pulsing valve connected between the compressor inlet and the second crossover valves configured to pulse gas flow from the compressor inlet through each bed during desorption to further improve the rate of desorption.

Description

A pressure swing adsorption system

Field of the Invention

[0001 ] This invention relates generally to a type of pressure swing adsorption (PSA) system.

Background of the Invention

[0002] Pressure swing adsorption (PSA) is used to separate a gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. For example, PSA may be used to separate oxygen from air.

[0003] Selective adsorbent materials such as zeolites, (e.g. molecular sieves), activated carbon and the like are used as a trapping medium which preferentially adsorbs the unwanted species gas species at high pressure, while allowing the desired species to pass through, whereafter the process then swings to low pressure to desorb the adsorbed gas.

[0004] US 8236095 B1 (Bassine) 7 August 2012 discloses a way to improve operational efficiency by employing a crossover valve interconnected between the sieve beds that opens shortly before each sieve bed is fully pressurised to deliver oxygen to the other sieve bed to help purge filtered nitrogen and other impurities from that bed and further reduce system pressure. However, this approach can waste between 15 and 20% of generated oxygen.

[0005] It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country.

Summary of the Disclosure

[0006] There is provided herein a pressure swing adsorption system that comprises first and second crossover valves operably connecting first and second sieve beds to a compressor inlet, a vacuum outlet and a separated gas take-off.

[0007] This dual crossover valve arrangement allows each sieve bed to be simultaneously connected between the compressor inlet and the vacuum outlet during its desorption cycle, which improves the rate of desorption and thereby increases separated gas output of the system and avoids having to employ wasteful prior art techniques of purging with generated separated gas.

[0008] Preferably, the system further comprises a pulsing valve connected between the compressor inlet and the second crossover valves configured to pulse gas flow from the compressor inlet through each bed during desorption which further improves the rate of desorption and thereby increasing separated gas output of the system . [0009] Other aspects of the invention are also disclosed.

Brief Description of the Drawings

[0010] Notwithstanding any other forms which may fall within the scope of the present invention, preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[0011 ] Figure 1 shows a pressure swing adsorption system in accordance with an embodiment; and

[0012] Figure 2 shows a cycle timing diagram implemented by the system of Figure 1.

Description of Embodiments

[0013] Figure 1 shows a pressure swing adsorption system comprising a first sieve bed 5a and a second sieve bed 5b containing selective adsorbent material, such as zeolites, (e.g. molecular sieves), activated carbon and the like.

[0014] The system separates input gas mixture into a separated gas and expels exhaust gas. In the embodiment shown, the system separates air into oxygen gas and expels nitrogen gas. In this embodiment, the system may be used for generating medical grade oxygen gas having a purity of above approximately 93±2%. In alternative embodiments, the system may generate food grade nitrogen having a purity of above 99.9%. The system may be used for generating helium from natural gas and the like. [0015] The system comprises a first crossover valve 4 and a second crossover valve 9 operably connecting the sieve beds 5 to a compressor inlet 2c, a vacuum outlet 2d and a separated gas take-off, which may feed a product storage tank 14.

[0016] In a preferred embodiment, system comprises a single compressor and vacuum unit 2 having an intake 2a interfacing the compressor input 2c for gaseous mixture and the vacuum outlet 2d interfacing an exhaust 2b. When used for separating oxygen, the system would draw air in via the intake 2a and expel nitrogen gas by the exhaust 2d.

[0017] With reference Figure 2, the crossover valves 4 and 9 are controlled for alternating between a first and second cycles.

[0018] During the first cycle, the first sieve bed 5a is connected between the compressor inlet 2c and the vacuum outlet 2d for desorption and the second sieve bed 5b is connected between the compressor inlet 2c and the separated gas take-off for adsorption.

[0019] During the second cycle, the second sieve bed 5b is connected between the compressor inlet 2c and the vacuum outlet 2d for desorption and the first sieve bed 5b is connected between the compressor inlet 2c and the separated gas take-off for adsorption.

[0020] Applying compressed air to an inlet of a bed 5 simultaneously whilst applying a vacuum at an outlet thereof improves the rate of desorption and thereby increasing separated gas output of the system .

[0021 ] According to the example shown in Figure 2, each cycle may be approximately 60 seconds. However, the cycle duration may be varied depending on various factors, including the types of gases, dimensions of the sieve beds, type of adsorbent material and the like.

[0022] The system may comprise a controller 15 configured for controlling the operation of the crossover valves 4 and 9 and other aspects including those described in further detail below. The controller 15 may comprise a microcontroller having a digital display and various I/O interfaces. [0023] In embodiments, the system comprises a sensor operably interfacing the separated gas take-off and wherein the system is configured for dynamically adjusting a cycle duration according to readings from the sensor. With reference to Figure 1 , a pressure and flow rate sensor 1 1 b may interface the gaseous take-off. Furthermore, a purity sensor 13 may interface the separated gas take-off. The controller 15 may take readings from these sensors 1 1 b and 13 to maximise pressure, flow rate and/or purity by dynamically adjusting the cycle duration. The controller 15 may use a gradient ascent control strategy that updates cycle duration parameters to find the maximum of maximise pressure, flow rate and/or purity.

[0024] In a preferred embodiment, the system further comprises a pulsing valve 8 connected between the compressor inlet 2c and the second crossover valve 9 configured to pulse gas flow from the compressor inlet 2c through each sieve bed 5 during desorption which increases the rate of adsorption of the sieve beds 5.

[0025] As is shown in Figure 2, during desorption of each sieve bed 5, the pulsing valve 8 operates to pulse input gas into the sieve bed 5. In other words, during desorption, each sieve bed 5 is operably connected to the vacuum outlet 2d to suck gas from the sieve bed 5 and also to the pulsing valve 8 to receive pulses of pressurised input gas from the compressor inlet 2c.

[0026] The pulsing valve 8 may be configured to pulse at a frequency of between approximately 0.1 Hz and 5 Hz during desorption. As shown in Figure 2, the pulsing valve 8 may apply six pulses over a duration of 60 seconds.

[0027] The controller 15 may be configured to dynamically adjust the frequency and/or pulse width of the pulsing valve 8 to optimise at least one of pressure, flow rate and/or purity by taking readings from at least one of the aforedescribed sensors 1 1 b and 13 . [0028] The system may comprise a dehumidifier 6 interfacing the compressor 2 and the sieve beds 5 and/or a dehumidifier 1 interfacing the intake 2a. The dehumidifier 1 and 6 may comprise a humidity indicating chemical 6 (such as silica gel) to provide a visual indication for when replacement of a dehumidifier 1 and 6 is required.

[0029] The system may further comprise a humidity sensor 7 interfacing the compressor 2 and the sieve beds 5. The controller 15 may take readings from the humidity sensor 7 and may initiate a humidity safety interlock accordingly. For example, when the controller 15 detects excessive humidity levels using the humidity sensor 7, the controller 15 may generate a warning on a digital display thereof or alternatively cease operation of the system to protect adsorbent material of the sieve beds from humidity. The readings from the humidity sensor 7 may indicate an instantaneous humidity reading and/or a cumulative humidity reading.

[0030] In embodiments, the system may comprise a first sensor 1 1 a interfacing the compressor inlet 2c and the sieve beds 5 and a second sensor 1 1 b and/or 13 interfacing the sieve beds 5 and a separated gas take-off which are configured for measuring at least one of pressure, flow rate and purity and wherein the controller 15 is configured to determine operational efficiency of the sieve beds 5 by comparing readings from the sensors 1 1 a and 1 1 b and/or 13.

[0031 ] For example, the controller 15 may compare the readings to detect efficiency degradation of the absorbent material of the sieve beds 5. For example, the controller 15 may compare a ratio of a volume of separated gas generated from a volume of input gas and detect when the ratio falls beneath a threshold indicative of degradation of the adsorbent material within the sieve beds 5. As such, the controller 15 may accordingly display an indication for the replacement of the absorbent material within the sieve beds 5.

[0032] In embodiments, the controller 15 may take readings from the purity sensor 13 to detect when separated gas purity levels fall beneath a threshold. For example, for oxygen generation, the controller 15 may use an oxygen purity sensor 13 to detect when oxygen purity levels fall beneath an acceptable threshold of 85%. When detecting purity level falling beneath the threshold, the controller 15 may cease operation of the system and/or display an indication of the digital display thereof.

[0033] The controller 15 may further take readings from the pressure and flow sensor 1 1 b at the separated gas outlet to determine the total volume of separated gas generated. The controller 15 may further calculate when the adsorbent material requires replacement according to the total volume of separated gas generated and display an indication on a digital display thereof accordingly. [0034] The system may have a pressure regulator 10 interfacing the sieve beds 5 and the pressure and flow rate sensor 1 1 b. The system may further comprise a non-return valve 12 interfacing the pressure and flow rate sensor 1 1 b and the purity sensor 13. The non-return valve 12 prevents purified product (such as oxygen) from flowing back into the crossover valve 9.

[0035] The controller 15 may implement a variety of safety interlocks including a compressor 2 temperature safety interlock which detects an excessive temperature of the compressor 2 to shut down the compressor until the temperature reduces.

[0036] The controller 15 may further implement a pressure and/or flow safety interlock wherein the controller 15 continually monitors pressure and/or flow rate using the pressure and flow rate sensors 1 1 to detect when the pressure and/or flow rate falls beneath an acceptable threshold. When detecting the pressure and/or flow rate falling beneath the acceptable threshold, the controller 15 may cease operation of the system and/or display an indication on the digital display thereof.

[0037] The controller 15 may further comprise an energy monitoring controller configured to measure the energy consumption of the system.

[0038] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that specific details are not required in order to practise the invention. Thus, the foregoing descriptions of specific embodiments of the invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed as obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the invention.

Claims

1 . A pressure swing adsorption system comprising: first and second crossover valves operably connecting first and second sieve beds to a compressor inlet, a vacuum outlet and a separated gas take-off, wherein the crossover valves are controlled to alternate between: a first cycle wherein: the first sieve bed is connected between the compressor inlet and the vacuum outlet for desorption; and the second sieve bed is connected between the compressor inlet and the separated gas take-off for adsorption; and a second cycle wherein: the second sieve bed is connected between the compressor inlet and the vacuum outlet for desorption; and the first sieve bed is connected between the compressor inlet and the separated gas take-off for adsorption.

2. The system as claimed in claim 1 , further comprising a sensor interfacing the separated gas take-off configured for sensing at least one of separated gas pressure, flow rate and purity and wherein the system dynamically adjusts a cycle duration according to a reading from the separated gas purity sensor.

3. The system as claimed in claim 1 , further comprising a pulsing valve connected between the compressor inlet and the second crossover valve configured to pulse gas flow from the compressor inlet through each bed during desorption .

4. The system as claimed in claim 3, wherein the pulsing valve operates at a frequency of between approximately 0.1 Hz and 5 Hz.

5. The system as claimed in claim 3, further comprising a sensor interfacing the separated gas take-off configured for sensing at least one of separated gas pressure, flow rate and purity and wherein the system is configured to dynamically adjust at least one of operational frequency and pulse width of the pulsing valve according to a reading from the sensor.

6. The system as claimed in claim 1 , further comprising a dehumidifier interfacing at least one of the compressor input and the sieve beds and a compressor intake.

7. The system as claimed in claim 6, wherein the dehumidifier comprises a humidity indicating chemical.

8. The system as claimed in claim 1 , further comprising humidity sensor interfacing the compressor inlet and the second crossover valve.

9. The system as claimed in claim 8, wherein the system is configured implement a humidity safety interlock according to readings of the humidity sensor.

10. The system as claimed in claim 9, wherein the humidity safety interlock comprises ceasing operation.

1 1 . The system as claimed in claim 8, wherein the readings indicate an instantaneous humidity reading.

12. The system as claimed in claim 8, wherein the readings indicate a cumulative humidity reading.

13. The system as claimed in claim 1 , further comprising: a first sensor interfacing the compressor inlet and the sieve beds; and a second sensor interfacing the sieve beds and the separated gas take-off, the sensors configured for measuring at least one of pressure and flow rate; and wherein the system is configured to determine operational efficiency of the sieve beds by comparing readings from the sensors.

14. The system as claimed in claim 1 , further comprising a sensor interfacing the separated gas take-off configured for sensing at least one of pressure, flow rate and purity wherein the system is configured to determine operational efficiency of the sieve beds according to readings from the sensor.

15. The system as claimed in claim 1 , further comprising a sensor interfacing the separated gas take-off configured for sensing at least one of separated gas flow rate and pressure wherein the system is configured to determine a total amount of separated gas according to readings from the sensor.

16. The system as claimed in claim 1 , wherein the system is programmed to determine replacement of the sieve beds according to the total amount.