CN111847388A - Pressure swing adsorption oxygenerator - Google Patents

Abstract

The invention relates to a pressure swing adsorption oxygen generator, part of oxygen gas flow discharged from the top of an adsorption tank flows back to a raw material gas tank and is mixed with air to form high-oxygen-content raw material gas for air separation oxygen generation, and the nitrogen content in the raw material gas is diluted by the returned oxygen, so that the pressure loss of the gas flow caused by nitrogen adsorption is smaller compared with that of the direct air feeding when the gas flow passes through a bed layer, thereby ensuring that molecular sieve particles at the top of the adsorption tank are in a relatively higher pressure environment, having higher adsorption and separation capacity and improving the nitrogen adsorption capacity of the whole bed layer; the distribution of bed resistance and nitrogen adsorption capacity on the height of a bed layer is improved by using molecular sieve particles with gradient particle sizes, so that the relatively higher atmospheric pressure environment and nitrogen adsorption performance (caused by high specific surface area) of non-atmospheric pressure are locally arranged at the top of a bed layer in a low-atmospheric pressure environment caused by dual reasons of bed resistance and nitrogen adsorption in the traditional filling scheme; in order to overcome the problem of reverse discharge caused by a filling layer with gradient particle size, a plurality of reverse discharge branch pipes are arranged in the adsorption tank to assist in reverse discharge and exhaust, so that reverse discharge and exhaust efficiency is greatly improved.

Description

Pressure swing adsorption oxygenerator

Technical Field

The invention relates to a medical apparatus, in particular to a pressure swing adsorption oxygen generator.

Background

The oxygen generator is a common medical device, and the conventional medical oxygen generator can be divided into two types according to the oxygen generation principle: one is the production of oxygen by electrolysis of water; the other is to separate air by molecular sieve adsorption to prepare oxygen, namely Pressure Swing Adsorption (PSA); the water electrolysis oxygen generation mode has low separation cost, low noise and high oxygen generation concentration, but is easy to generate potential safety hazard. Although the theoretical maximum concentration of molecular sieve oxygen generation is only 96 percent and is lower than that of water electrolysis oxygen generation and deep cooling oxygen generation (mainly used for large-scale industrial oxygen generation), the equipment is simple, the safety is high, and the oxygen generation concentration can meet most of clinical oxygen requirements, so the molecular sieve oxygen generation method is the main mode clinically used for oxygen deficiency prevention and treatment of patients at present.

The core part of PSA oxygen production is the molecular sieve adsorption tank, and at present, the mainstream molecular sieve adsorption tank all adopts the fixed bed filling mode, piles up the filling with granular zeolite molecular sieve in jar internal, during the absorption, makes the air pass the bed according to predetermined flow direction and realizes the absorption to nitrogen gas or oxygen in the air. In this process, to ensure the outlet oxygen concentration, it is necessary to ensure sufficient bed thickness (referring to the path of air passing through the bed) so that the nitrogen in the air flow is gradually and completely adsorbed during the air passing through the bed. The content of nitrogen in the air accounts for 78%; the molecular sieves at the two ends of the bed layer show different adsorption efficiencies (the pressure at the upstream side is high, the adsorption quantity of the molecular sieves is large; the pressure at the downstream side is low, the adsorption quantity of the molecular sieves is small) due to the obvious pressure drop at the two ends of the bed layer, so that when the oxygen content of an outlet is ensured, a larger bed layer thickness is required to be used, and the low utilization rate of the molecular sieves at the downstream side is caused; moreover, because the nitrogen content in the gas flow contacted with the molecular sieve at the upstream side is relatively large, adsorption saturation can be achieved firstly, and the separation function is lost; at this time, the molecular sieve on the upstream side is still in a relatively low-pressure working environment because a large amount of nitrogen in the gas flow is adsorbed, and the relative adsorption amount of the molecular sieve is close to saturation. Therefore, to provide a relatively long adsorption duty cycle to allow the desorption regeneration process of another adsorption tank to be completed, it is necessary to fill the adsorption tank with a sufficient amount of molecular sieve adsorbent to cope with a too early adsorption saturation time of the molecular sieve on the upstream side. But the balance of the molecular sieve adsorbent will result in a greater bed resistance, further broadening the difference in adsorption capacity of the upstream and downstream adsorbents.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides an oxygen generator. The specific scheme is as follows:

providing a pressure swing adsorption oxygen generator, which comprises a left molecular sieve adsorption tank, a right molecular sieve adsorption tank, an air compressor and a raw material air tank; the air compressor is connected with the raw material air tank and supplies air to the raw material air tank; the raw material gas tank is connected with gas inlets at the bottoms of the left tank and the right tank through a left raw material gas pipe and a right raw material gas pipe respectively; the left raw material air pipe and the right raw material air pipe are respectively provided with an air inlet valve; molecular sieve adsorbents are filled in the left tank and the right tank and are used for adsorbing nitrogen in the feed gas; the exhaust ports at the top parts of the left tank and the right tank are respectively connected with a product air pipe through a left exhaust pipe and a right exhaust pipe; the left exhaust pipe and the right exhaust pipe are respectively provided with an exhaust valve; the left and right feed gas pipes are respectively communicated with a reverse release pipe at a certain position between the air inlet valve and the air inlet of the corresponding adsorption tank through a pipeline with a reverse release valve; and a certain position on the left exhaust pipe and the right exhaust pipe, which is positioned between the exhaust valves and the exhaust ports of the adsorption tanks, is communicated through a pressure equalizing pipe with a pressure equalizing valve.

The oxygen generator also comprises an oxygen return pipe and a return oxygen compressor arranged on the oxygen return pipe; the lower end of the oxygen return pipe is connected with a raw material gas tank; and the left exhaust pipe and the right exhaust pipe are respectively connected with the upper end of the oxygen return pipe at a position on the upstream of the exhaust valve through a return branch pipe with a return valve.

When the oxygen generator works, part of oxygen discharged from the top of the adsorption tank is pressurized by the reflux oxygen compressor and then enters the raw material gas tank, and is mixed with air conveyed by the air compressor to form high-oxygen-content raw material gas; the high oxygen-containing feed gas then enters an adsorption tank for air separation oxygen generation. And oxygen continuously flows back in the adsorption process of the corresponding adsorption tank.

In the operation process, oxygen continuously flows back, so that the oxygen content in the feed gas entering the molecular sieve adsorption tank is higher than that in normal air; when the airflow passes through the whole molecular sieve adsorption tank, the pressure loss degree caused by nitrogen adsorption is reduced; for example, when direct air feed is used, the pressure loss due to nitrogen adsorption can reach 78% without considering bed resistance; when 50% high oxygen content raw material gas is adopted for feeding, the pressure loss caused by nitrogen adsorption is only 50%; this allows the molecular sieve at the upper end of the adsorption tank to be also in a higher pressure environment, thus exhibiting a higher adsorption capacity, resulting in a significant increase in the adsorption capacity of the overall bed.

The processes of pressure equalization, reverse discharge, regeneration and the like of the molecular sieve adsorption tank can be carried out according to the traditional process.

Further, in order to improve the bed resistance of the adsorption tank, the filling mode of the adsorption tank is improved.

Specifically, adsorbent particles with gradually reduced particle size are filled in a molecular sieve adsorption tank along the airflow direction; the molecular sieve filling layers with different particle sizes are separated by using a separator, so that particles in different layers are prevented from migrating to each other, and the separator can be a grid plate, a wire mesh or the like. The filling thickness of each filling layer can be the same or gradually reduced along the airflow direction.

Furthermore, a plurality of reverse-release branch pipes penetrating through a molecular sieve bed layer are longitudinally arranged inside the adsorption tank; the bottoms of the plurality of reverse discharging branch pipes are connected to the collecting pipe through connecting pipes; the collecting pipe penetrates out of the bottom of the adsorption tank and is communicated with the reverse discharging pipe through the reverse discharging auxiliary valve. The head end and the tail end of the reverse release branch pipe are closed, and the side surface of the reverse release branch pipe is provided with air holes which can intercept molecular sieve particles and allow reverse release air to pass through.

Preferably, each inverse placing branch pipe is formed by splicing a plurality of sections, and each section corresponds to different filling layers in the adsorption tank respectively. And the adjacent two sections of the reverse release branch pipes are hermetically connected through a connecting part. A check valve assembly which can only be opened downwards is arranged at the connection position of each section of the reverse release branch pipe so as to allow the passage to be opened in the reverse release process, the reverse release gas to be discharged downwards, and the passage to be closed in the adsorption process, so that gas cross flow is prevented.

Compared with the prior art, the invention can at least obtain the following beneficial effects: in the invention, a part of oxygen gas flow discharged from the top of the adsorption tank flows back to the raw material gas tank and is mixed with air to form high-oxygen-content raw material gas for air separation oxygen generation, and because the nitrogen content in the raw material gas is diluted by the back-flowing oxygen, the pressure loss of the gas flow caused by nitrogen adsorption is smaller compared with that of the direct air feeding when the gas flow passes through a bed layer, thereby ensuring that molecular sieve particles at the top of the adsorption tank are in a relatively higher pressure environment, having higher adsorption and separation capacity and improving the nitrogen adsorption capacity of the whole bed layer; meanwhile, the invention improves the distribution of bed resistance and nitrogen adsorption capacity on the height of the bed by using the molecular sieve particles with gradient particle size, so that the part of the top of the bed in a low-pressure environment caused by dual reasons of bed resistance and nitrogen adsorption in the traditional filling scheme has relatively higher pressure environment and nitrogen adsorption performance (caused by high specific surface area) caused by non-pressure; in addition, in order to overcome the problem of reverse discharge caused by a filling layer with gradient particle size, the invention arranges a plurality of reverse discharge branch pipes in the adsorption tank to assist reverse discharge and exhaust, thereby greatly improving the reverse discharge and exhaust efficiency.

Drawings

FIG. 1 is a schematic view of the pipe connection of a molecular sieve tank;

FIG. 2 is a schematic view of the filling of a molecular sieve tank;

FIG. 3 is a bed resistance schematic of the different packing patterns of FIG. 2;

FIG. 4 is a schematic of a flow equalization grid;

FIG. 5 is a schematic view of the installation of the reverse branch pipe in the molecular sieve tank;

FIG. 6 is a schematic of a reverse branch;

FIG. 7 is a single tube illustration of a retrograde lateral tube;

fig. 8 is an enlarged partial cross-sectional illustration of the circular region of fig. 7.

Detailed Description

In order to better illustrate the technical idea of the present invention, the following further describes the solution of the present invention with reference to the accompanying drawings. It should be noted that the descriptions of "left", "right", "upper" and "lower" used in the present invention are only for the convenience of distinguishing different components from each other in the positional relationship shown in the drawings, and do not represent the left and right positional limitations in actual implementation; and the terms "upstream" and "downstream" are used to refer to a front-to-back relationship that is differentiated along the direction of gas flow.

Example 1

Referring to fig. 1, a pressure swing adsorption oxygen generator is provided, which comprises two molecular sieve adsorption tanks, respectively marked as a left tank 1 and a right tank 2; the device also comprises an air compressor 3 and a raw material gas tank 4; the outlet of the air compressor 3 is connected with a raw material air tank 4 through an air pipe 5; the raw material gas tank 4 is respectively connected with the gas inlets 17 at the bottoms of the left tank 1 and the right tank 2 through a left raw material gas pipe 61 and a right raw material gas pipe 62; the left raw material gas pipe 61 and the right raw material gas pipe 62 are respectively provided with a left air inlet valve V1 and a right air inlet valve V2; molecular sieve adsorbents are filled in the left tank 1 and the right tank 2 and are used for adsorbing nitrogen in feed gas; the top exhaust ports 18 of the left tank 1 and the right tank 2 are respectively connected with the product air pipe 8 through a left exhaust pipe 71 and a right exhaust pipe 72; the left exhaust pipe 71 and the right exhaust pipe 72 are respectively provided with a left exhaust valve V10 and a right exhaust valve V11; a certain position on the left raw material gas pipe 61 between the downstream of the left air inlet valve V1 and the air inlet 17 of the left tank 1 is communicated with the reverse release pipe 9 through a pipeline with a left reverse release valve V3; a certain position on the right raw material gas pipe 61 between the downstream of the right air inlet valve V2 and the air inlet 17 of the right tank 2 is communicated with the reverse release pipe 9 through a pipeline with a right reverse release valve V4; one position of the left exhaust pipe 71 between the left exhaust valve V10 and the exhaust port 18 of the left tank 1 is communicated with one position of the right exhaust pipe 72 between the right exhaust valve V11 and the exhaust port 18 of the right tank 2 through a pressure equalizing pipe with a pressure equalizing valve V7.

Still referring to fig. 1, an oxygen return line 10 and a return oxygen compressor 11 disposed thereon; the lower end of the oxygen return pipe 10 is connected with a raw material gas tank 4; the left exhaust pipe 71 is connected with the upper end of the oxygen return pipe 10 at a position on the upstream of the left exhaust valve V10 through a return branch pipe with a left return valve V8; the right exhaust pipe 72 is connected to the upper end of the oxygen return pipe 10 at a position upstream of the right exhaust valve V11 through a return branch pipe having a right return valve V9.

The working process of the embodiment is as follows: the air compressor 3 firstly supplies air into the raw material air tank 4 through an air pipe 5; the left air inlet valve V1 and the left return valve V8 are opened, and other valves are closed; air enters the left tank 1 from the air inlet 17 through the left raw material air pipe 61; the molecular sieve adsorbent in the left tank 1 adsorbs nitrogen in the gas flow; the oxygen stream exits the left tank 1 at vent 18; starting a reflux oxygen compressor 11, and enabling oxygen gas flow to enter the raw material gas tank 4 through an oxygen reflux pipe 10 to be mixed with air to form high-oxygen-content raw material gas; after the oxygen content in the raw material gas reaches a preset value (which can be selected according to actual conditions, such as 50 percent and the like), the left exhaust valve V10 is opened, oxygen is supplied to the outside, and meanwhile, the oxygen continuously flows back.

In the operation process, oxygen continuously flows back, so that the oxygen content in the feed gas entering the molecular sieve adsorption tank is higher than that in normal air; when the airflow passes through the whole molecular sieve adsorption tank, the pressure loss degree caused by nitrogen adsorption is reduced; for example, when direct air feed is used, the pressure loss due to nitrogen adsorption can reach 78% without considering bed resistance; when 50% high oxygen content raw material gas is adopted for feeding, the pressure loss caused by nitrogen adsorption is only 50%; this allows the molecular sieve at the upper end of the adsorption tank to be also in a higher pressure environment, thus exhibiting a higher adsorption capacity, resulting in a significant increase in the adsorption capacity of the overall bed.

The processes of pressure equalization, reverse discharge, regeneration and the like of the molecular sieve adsorption tank can be carried out according to the traditional process.

Example 2

In the embodiment 1, the whole adsorption performance of the molecular sieve adsorbent bed layer is greatly improved due to the adoption of the oxygen reflux process. In actual operation, the resistance of the gas flow through the adsorbent bed also results in a large pressure loss (pressure drop); particularly, after the oxygen reflux process is adopted, if the oxygen supply amount is ensured to be unchanged, the flow rate of the air flow in the adsorption tank is obviously increased, which leads to larger bed resistance, and further counteracts the reduction degree of adsorption decompression caused by the oxygen reflux process; that is, the oxygen reflow process may be a reduction in the degree of pressure loss due to the nitrogen adsorption process; but the pressure loss degree caused by bed resistance is increased due to the increase of the flow velocity in the tank caused by the oxygen backflow; thus, there is an upper limit to the amount of oxygen reflux above which the amount of pressure loss increase due to bed resistance will exceed the amount of pressure loss decrease due to nitrogen adsorption.

This example provides a canister fill scheme to further reduce bed resistance and change the pressure loss profile due to bed resistance, thereby increasing the upper limit of oxygen reflux.

In particular, see fig. 2. FIG. 2A shows a prior art canister fill using substantially uniform sized molecular sieve particles, assuming a particle size of 3. The bed resistance curve along the bed height can be seen in a graph of FIG. 3A;

FIG. 2B is an improved packing scheme using adsorbent particles of progressively smaller size in the molecular sieve adsorbent canister along the gas flow direction; referring to fig. 4, the layers are separated from each other by partitions 13, which prevent particles of different layers from migrating to each other, and the partitions 13 may be, for example, grid plates or wire mesh. The filling thickness of each layer is the same in fig. 2B. In fig. 2B, four molecular sieve filling layers with different particle sizes are arranged from bottom to top. By adopting the filling method shown in fig. 2B, the particle size of the molecular sieve particles in each layer is reasonably selected, for example, the particle size of the molecular sieve particles in each layer from bottom to top is 6, 4, 2, and 1, so that the overall bed resistance can be the same as the filling method shown in fig. 2A, which can be seen in fig. 3B. But due to the change of the bed layer structure, the lower layer adopts adsorbent particles with large particle size, the specific surface area is relatively low, and the nitrogen adsorption quantity is relatively small; and the upper part adopts small-particle-size adsorbent particles, so that the specific surface area is larger and the nitrogen adsorption capacity is larger.

With this modification, the packing scheme in FIG. 2B has a smaller amount of nitrogen adsorbed at the lower part of the bed than the scheme in FIG. 2A, and the bed resistance at this point is also smaller than that in FIG. 2A; thus, the pressure loss is small for the FIG. 2B embodiment when passing through the lower portion of the bed; in the upper part of the bed, the nitrogen adsorption amount in the scheme of FIG. 2B is larger than that in the scheme of FIG. 2A, and the bed resistance is also larger. However, since the pressure loss of the gas flow is smaller in the scheme of fig. 2B before reaching the upper part of the bed, the gas flow still maintains a larger pressure in the region where the nitrogen adsorption mainly occurs and at the upper part of the bed in the filling scheme of fig. 2B; thereby the nitrogen adsorption amount of the whole bed layer is larger than the filling mode of figure 2A.

FIG. 2C is a further modification of the adsorption tank filled with four layers of molecular sieve particles of the same size as in FIG. 2B; the difference is that the filling height of each adsorption layer gradually decreases from bottom to top. This packing pattern can significantly reduce the overall bed resistance of the adsorber tank, see fig. 3C. However, the nitrogen adsorption capacity of the whole bed layer is lower than that of the filling mode in fig. 2B due to the reduction of the filling height of the small-particle-size molecular sieve particles with large specific surface area.

In actual operation, the filling mode shown in fig. 2B or fig. 2C can be selected according to specific situations to meet different requirements of increasing the adsorption amount of the bed layer and/or reducing the pressure drop of the bed layer.

Example 3

In the embodiment 2, the molecular sieve filling layers with different particle sizes are arranged, so that the distribution of the bed resistance and the distribution of the nitrogen adsorption capacity are improved, and the upper part of the adsorption tank is kept with higher airflow pressure; meanwhile, the small-particle-size molecular sieve with larger adsorption capacity (referring to the molecular sieve particles per unit volume) is arranged at the upper part of the tank with relatively low pressure (referring to the bottom of the tank, but not the corresponding position in the figure 2A), so that the overall nitrogen adsorption capacity of the adsorption tank is improved.

However, the bed resistance of the small-particle-size molecular sieve filling layer is larger, and the small-particle-size molecular sieve filling layer is positioned at the top of the bed, so that the difficulty of the reverse discharge process is increased. The following solution is provided for this embodiment.

Referring to fig. 5-6, a plurality of reverse-discharging branch pipes 14 penetrating through a molecular sieve bed layer are longitudinally arranged inside an adsorption tank; the bottoms of the plurality of reverse discharging branch pipes 14 are connected to a collecting pipe 16 through connecting pipes 15; the collecting pipe 16 penetrates out of the bottom of the adsorption tank. Referring to fig. 1, wherein the manifold 16 of the left tank 1 communicates with the dump line 9 through a left dump assist valve V5; the collecting pipe 16 of the right tank 2 communicates with the reverse release pipe 9 through a right reverse release auxiliary valve V6.

Referring to fig. 7, each of the retrograde branch tubes 14 is composed of several segments, such as a first segment 141, a second segment 142, a third segment 143 and a fourth segment 144 from top to bottom. Wherein, each section respectively corresponds to different filling layers in the adsorption tank.

Referring to fig. 8, two adjacent sections, such as the second section 142 and the third section 143, of the retrograde flow leg 14 are hermetically connected by a connecting portion 145; on the side wall of each section, except for the connecting wall 149 corresponding to the connecting part 145, air holes 148 are arranged; the vent 148 allows reverse gas during reverse venting to pass through but prohibits molecular sieve particles of the corresponding packed bed from passing through.

Because the reverse branch 14 is not filled with molecular sieve particles, in order to prevent the gas flow from channeling from the reverse branch 14 during the adsorption process (meaning that the gas flow bypasses the bed layer and flows directly upwards from the reverse branch), a one-way valve assembly which can only be opened downwards is arranged at the joint of each section of the reverse branch 14 to allow the passage to be opened during the reverse discharge process and the reverse gas to be discharged downwards, and the passage is closed during the adsorption process to prevent the gas from channeling. The check valve assembly includes a check ring 146 fixed inside the reverse branch pipe 14 and a valve plate 147 located below the check ring.

In the embodiment, the reverse release branch pipe 14 is longitudinally arranged in the bed layer, the reverse release passage can be quickly opened when the reverse release process is started, the reverse release gas does not need to overcome the resistance of the bed layer to penetrate through the whole bed layer, so the reverse release speed is higher, the reverse release valve and the reverse release auxiliary valve can be simultaneously opened in the reverse release process, and the reverse release gas in the bed layer is mainly discharged through the reverse release auxiliary valve; the residual gas can be discharged through the reverse bleeding valve, so that a rapid and sufficient reverse bleeding process can be realized, and the requirement for purging the regeneration gas can be remarkably reduced by the sufficient reverse bleeding process.

Example 4

An oxygen generation method based on the oxygen generator is provided, and comprises the following steps:

(1) the air compressor 3 supplies air into the raw material air tank 4 through an air pipe 5; the left air inlet valve V1 and the left return valve V8 are opened, and other valves are closed; air enters the left tank 1 from the air inlet 17 through the left raw material air pipe 61; the molecular sieve adsorbent in the left tank 1 adsorbs nitrogen in the gas flow; the oxygen stream exits the left tank 1 at vent 18; starting a reflux oxygen compressor 11, and enabling oxygen gas flow to enter the raw material gas tank 4 through an oxygen reflux pipe 10 to be mixed with air to form high-oxygen-content raw material gas; after the oxygen content in the feed gas reaches a preset value, opening a left exhaust valve V10 to supply oxygen outwards, and simultaneously continuously refluxing the oxygen;

(2) After the left tank 1 is saturated in adsorption, the opening mode of the valve is switched, and the left return valve V8 is closed; a right air inlet valve V2 and a pressure equalizing valve V7 are opened, and the high-pressure high-oxygen-content residual gas in the left tank 1 is equalized to the pressure in the right tank 2;

(3) the pressure equalizing valve V7 is closed, and the right return valve V9 and the right exhaust valve V11 are opened; the right tank 2 starts to produce oxygen by using the high oxygen-containing raw material gas;

(4) the left reverse release valve V3 and the left reverse release auxiliary valve V5 are opened, and nitrogen adsorbed in the left tank 1 is rapidly discharged through the air inlet 17 and the reverse release branch pipe 14;

(5) after the left tank 1 is completely reversely placed, no gas is discharged through the reverse placing pipe 9, and the left reverse placing auxiliary valve V5 is closed; and opening the pressure equalizing valve V7, purging and regenerating the adsorbent bed in the left tank 1 by using oxygen airflow generated at the top of the right tank 2, closing the pressure equalizing valve V7 after the regenerated gas discharged from the reverse release pipe 9 is detected to be qualified, and finishing the regeneration of the left tank 1.

(6) Repeating the steps of adsorption, pressure equalization, reverse discharge and regeneration to continuously produce oxygen.

The above is only an example of the best mode contemplated by the present invention, which should not be construed as a limitation to all possible embodiments of the present invention, and those skilled in the art can easily substitute conventional means without inventive work, and other appropriate technical solutions also belong to the feasible scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (10)

1. A pressure swing adsorption oxygenerator comprises two adsorption tanks filled with molecular sieve adsorbents, namely a left tank (1) and a right tank (2); the molecular sieve adsorbent can adsorb nitrogen in air; the device also comprises an air compressor (3) and a raw material gas tank (4); the outlet of the air compressor (3) is connected with a raw material air tank (4) through an air pipe (5); the method is characterized in that: the raw material gas tank (4) is respectively connected with the gas inlets (17) at the bottoms of the left tank (1) and the right tank (2) through a left raw material gas pipe (61) and a right raw material gas pipe (62); an air inlet left valve (V1) and an air inlet right valve (V2) are respectively arranged on the left raw material air pipe (61) and the right raw material air pipe (62); the exhaust ports (18) at the tops of the left tank (1) and the right tank (2) are respectively connected with a product air pipe (8) through a left exhaust pipe (71) and a right exhaust pipe (72); the left exhaust pipe (71) and the right exhaust pipe (72) are respectively provided with a left exhaust valve (V10) and a right exhaust valve (V11); a certain position on the left raw material air pipe (61) between the downstream of the left air inlet valve (V1) and the air inlet (17) of the left tank (1) is communicated with a reverse release pipe (9) through a pipeline with a left reverse release valve (V3); a certain position on the right raw material gas pipe (61) between the downstream of the right air inlet valve (V2) and the air inlet (17) of the right tank (2) is communicated with a reverse release pipe (9) through a pipeline with a right reverse release valve (V4); a pressure equalizing pipe with a pressure equalizing valve (V7) is communicated between a certain position of the left exhaust pipe (71) between the left exhaust valve (V10) and the exhaust port (18) of the left tank (1) and a certain position of the right exhaust pipe (72) between the right exhaust valve (V11) and the exhaust port (18) of the right tank (2); also comprises an oxygen return pipe (10) and a return oxygen compressor (11) arranged on the oxygen return pipe.

2. The pressure swing adsorption oxygen plant of claim 1, wherein: the lower end of the oxygen return pipe (10) is connected with a raw material gas tank (4); the left exhaust pipe (71) is positioned at the upstream of the left exhaust valve (V10) and is connected with the upper end of the oxygen return pipe (10) through a return branch pipe with a left return valve (V8); the right exhaust pipe (72) is connected with the upper end of the oxygen return pipe (10) at a position which is positioned at the upstream of the right exhaust valve (V11) through a return branch pipe with a right return valve (V9).

3. The pressure swing adsorption oxygen plant of claim 2, wherein: adsorbent particles of progressively smaller particle size are packed in the molecular sieve adsorption tank in the direction of gas flow, adjacent packed layers of adsorbents of different particle size being separated by a partition (13), said partition (13) allowing gas flow therethrough but inhibiting cross-layer migration of adsorbents of different particle size.

4. The pressure swing adsorption oxygen plant of claim 3, wherein: the filling thickness of each filling layer is the same.

5. The pressure swing adsorption oxygen plant of claim 3, wherein: the filling degree of each filling layer is gradually reduced from bottom to top.

6. The pressure swing adsorption oxygen plant of claim 4 or 5, wherein: a plurality of reverse-discharging branch pipes (14) penetrating through the molecular sieve bed layer are longitudinally arranged inside the adsorption tank; the bottoms of the plurality of reverse discharging branch pipes (14) are connected to the collecting pipe (16) through connecting pipes (15); the collecting pipe (16) penetrates out of the bottom of the adsorption tank and is communicated with the reverse release pipe (9) through a corresponding reverse release auxiliary valve.

7. The pressure swing adsorption oxygen plant of claim 6, wherein: each reverse-placing branch pipe (14) is formed by splicing a plurality of sections, and each section corresponds to different filling layers in the adsorption tank respectively.

8. The pressure swing adsorption oxygen plant of claim 7, wherein: the adjacent two sections of the reverse discharging branch pipe (14) are hermetically connected through a connecting part (145); the side walls of all the sections are provided with air holes (148) except the connecting wall (149) corresponding to the connecting part (145); the vent holes (148) allow reverse gas to pass through but prohibit molecular sieve particles of the corresponding packed layer from passing through.

9. The pressure swing adsorption oxygen plant of claim 8, wherein: a check valve assembly which can only be opened downwards is arranged at the joint of each section of the reverse branch pipe (14), and the check valve assembly comprises a retaining ring (146) fixed inside the reverse branch pipe (14) and a valve plate (147) positioned below the retaining ring.

10. The method for producing oxygen from a pressure swing adsorption oxygen plant of claim 9, further comprising the steps of:

(1) the air compressor (3) supplies air to the raw material air tank (4) through an air pipe (5); the left air inlet valve (V1) and the left return valve (V8) are opened, and other valves are closed; air enters the left tank (1) from the air inlet (17) through the left raw material air pipe (61); a molecular sieve adsorbent in the left tank (1) adsorbs nitrogen in the gas flow; the oxygen gas flow is discharged from the air outlet (18) of the left tank (1); starting a reflux oxygen compressor (11), and enabling oxygen gas flow to enter a raw material gas tank (4) through an oxygen reflux pipe (10) to be mixed with air to form high-oxygen-content raw material gas; after the oxygen content in the raw material gas reaches a preset value, opening a left exhaust valve (V10) to supply oxygen outwards, and simultaneously continuously refluxing the oxygen;

(2) After the left tank (1) is saturated in adsorption, the opening mode of the valve is switched, and the left return valve (V8) is closed; a right air inlet valve (V2) and a pressure equalizing valve (V7) are opened, and the high-pressure high-oxygen-content residual gas in the left tank (1) is equalized to the pressure in the right tank (2);

(3) after the pressure equalization is finished, closing the pressure equalization valve (V7), and opening the right return valve (V9) and the right exhaust valve (V11); the right tank (2) starts to produce oxygen by using the high oxygen-containing raw material gas;

(4) a left reverse discharge valve (V3) and a left reverse discharge auxiliary valve (V5) are opened, and nitrogen absorbed in the left tank (1) is rapidly discharged through an air inlet (17) and a reverse discharge branch pipe (14);

(5) after the reverse discharge of the left tank (1) is completed, closing a left reverse discharge auxiliary valve (V5); opening the pressure equalizing valve (V7), blowing and regenerating the adsorbent bed in the left tank (1) by using the oxygen airflow generated at the top of the right tank (2), closing the pressure equalizing valve (V7) after the regenerated gas discharged from the reverse release pipe (9) is detected to be qualified, and finishing the regeneration of the left tank (1).

(6) Repeating the steps of adsorption, pressure equalization, reverse discharge and regeneration to continuously produce oxygen.

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