DD288533A5 - METHOD FOR SEPARATING GAS MIXTURES BY PRESSURE CHANGE ADSORPTION - Google Patents

Abstract

The invention relates to a method for separating gas mixtures by pressure swing adsorption. The invention includes the adsorptive separation of gas mixtures. It is used in particular in the extraction of oxygen from the air. After completion of the adsorption process, a two-stage pressure reduction of the loaded adsorber occurs. In the first stage, a pressure equalization with a second adsorber is carried out via the outlet ends of the two adsorbers. In the second stage of the pressure reduction is a two-sided relaxation of the loaded adsorber simultaneously over its inlet end and outlet end to the ambient pressure. The thereby flowing out of the outlet end of this adsorber gas is guided in a third adsorber on the outlet end and used to flush this adsorber. The gas, which simultaneously escapes from the inlet end of the loaded adsorber, is removed as residual gas. Figure {method, separate; Gas mixture; pressure swing adsorption; extraction; Oxygen; Air, two-stage; Pressure reduction; adsorber; Pressure equalization; Exit end; Entering, relaxing, spilling}

Description

For this 1 page drawing

Field of application of the invention

The invention is used in the adsorptive separation of gas mixtures, in particular in the recovery of oxygen from the air.

Characteristic of the known state of the art For cleaning or decomposing gases, for example, to recover oxygen or nitrogen from the air

often used adsorption because of the economy and their effectiveness. The pressure swing adsorption process, in which the regeneration of the loaded adsorbent passes through, has particularly boasted

Pressure reduction takes place. The released in the pressure reduction of a loaded adsorber gases are usually for Pressure increase in other adsorbers, which are located at a lower pressure level, used by a Pressure equalization is performed. Such a method is known from DE-PS 2739955, in which the regeneration dos loaded adsorber in 3 stages

he follows. In the first stage of the pressure reduction leaves the gas through the inlet opening, ie in countercurrent to

Production direction, the adsorber and is led away by a residual gas line. This outflow of the gas over the Eintriiisöffnung the boladenen adsorber over the entire duration of the pressure reduction. The first stage will be after the Reaching a certain pressure of the second and third stage superimposed, wherein in the second stage, a pressure equalization

with another adsorber in each case via the outlet openings of the two adsorbers and in the third stage also via the

Outlet of the laden adsorber pressure equalization is performed with a buffer tank. This procedure with the use of a buffer container is relatively complicated and complicated. From DE-OS 3132758 is a method for decomposing a gas mixture according to the pressure swing adsorption process

known in which after completion of the adsorption of a first adsorber followed by a first DC stress phase and the resulting flash gas is used for flushing einos located in a desorption phase second adsorber. This is followed by a second DC voltage phase, wherein the resulting flash gas for

Pressing the second adsorber is used. This is followed by a gas flow tension, while a residual gas

is deducted from the inlet end of the first adsorber.

Similarly, from DE-OS 3046268 a pressure swing adsorption process for the recovery of hydrogen from a Gas mixture known in which over the outlet end of the loaded adsorber pressure equalization successively with 3rd Adsorbers and then the flushing of a fourth and fifth adsorber. Subsequently, over the entrance end of

loaded adsorber carried out a residual relaxation.

In both methods, there is a risk due to multiple DC voltage phases that in the loaded Adsorber the adsorption front far enough to the outlet end, that the adsorptive this adsorber by its Exit end leaves. It is also known that the pressure equalization by simultaneously opening the at the inlet end and at the outlet end of the Perform pressure equalization adsorber involved. In this case, the adsorber to be loaded with before reloading Help of a vacuum pump evacuated. Such a method is described in DE-OS 2441447. The use of a vacuum pump, however, involves a higher expenditure on equipment. Object of the invention

Target <* P ^r invention is the development dinas pressure swing adsorption process for separating gas mixtures, in particular for the recovery of oxygen from the air, an increase in product yield can be achieved with the apparatus at low cost.

-2- 288 533 Explanation of the nature of the invention

The invention is based on the invention of developing a pressure swing adsorption process for at least three adsorbers,

in which, after completion of the adsorption process, the pressure reduction in the loaded adsorber is carried out so that the non-adsorbed product-rich gas is fed to a subsequent adsorption process and then not yet desorbed gas is subjected to such a further desorption that a gas with the highest possible proportion of

Product gas desorbed and this product-rich gas is used in a subsequent adsorption process, that the Meng & the product gas used as purge gas can be reduced. The object is achieved in that in the first: ι stage of DruckerniedriQung in a first adsorber a Pressure equalization with a regenerated second adsorber takes place via the outlet ends of the two adsorbers. In this stage, production-rich gas from the outlet end (oxygen-enriched gas in oxygen production)

of the first adsorber led from dome Zwischenkornvolumen dos adsorbent in the unloaded second adsorber.

After pressure equalization with the second adsorber in the second stage of the pressure reduction is a two-sided Relaxation of the first adsorber at the same time over its inlet end and outlet end to the ambient pressure

performed. The product-type gas passing from the pore volume and from the micropores of the adsorbent gas (gas enriched with oxygen in the extraction of oxygen) flows via the outlet end of this adsorber and over the latter

Exit end of a third adsorber in the latter and flows through this, wherein primarily oxygen adsorbs

becomes. The desorbed gas exiting simultaneously from the inlet end of the first adsorber contains the separated one

Gas content (in the oxygen production from the air, the nitrogen), which led away in a conventional manner as residual gas By the simultaneous and two-sided relaxation of the first adsorber in the second stage of the pressure reduction are on

whose entrance end and exit end polarize the concentration profiles more strongly than in a successive one

Pressure reduction. As a result, a product-rich (oxygen-rich) gas passes through the outlet end of this adsorber and through

the inlet end of a gas which is rich in the separated gas fraction (nitrogen). In this way, higher ones

Yields of product gas achieved as in processes with consecutive successful pressure reduction. The third absorber, which has previously undergone a desorption process, is thus countercurrent to Adsorptionsrichtung flows through a product-rich gas, so that a rinse takes place with product-rich gas. It

It has been found that this purging is advantageous to produce the product gas in the required purity. It is therefore appropriate that the pressure equalization taking place in the first stage of the pressure reduction with the subsequent adsorber is carried out with smaller amounts of purge gas or without densen previous flushing with product gas.

For the purposes of the invention, the end is seen below the inlet end of an adsorber through which the gas mixture in the Adsorber occurs. In contrast, the exit end is that end of the adsorber, through which the product gas the Adsorber leaves. If, for example, oxygen from the air is to be obtained with the aid of the method according to the invention,

thus, the inlet end is that end of the adsorber through which the air enters the absorber and the outlet end is that adsorber end through which the oxygen exits the adsorber.

Furthermore, for the purposes of the invention that gas is referred to as product gas, which is characterized by the inventive Adsorption should be obtained in almost pure form. If you want, for example, oxygen from the air

win, so the oxygen is the product gas.

Surprisingly, it was found that with the procedure according to the invention even at high Gas mixture (air) loads of the adsorber biw. relatively coarse Zeoiith with a grain size above 2 mm high Yields of product gas (oxygen) can be achieved in comparison to the known methods. This is due to,

that the purging gas quantities consisting of product gas can be greatly reduced and thus, in particular, the product gas quantity ad- and desorbed in the circuit, which is limited for the process design, is lower.

Thus, the rate of increase of the product gas yield at average zeolite grain sizes of about 1 mm compared to known Procedure about 15%, with grain sizes above 2 mm but up to 25% or at specific air loads of about 0.8m ³ air

per 1 adsorber based on the producing adsorber about 10% and at about 1.2 m ³ air per 1 adsorber based on the producing adsorber up to about 25%.

embodiment

The invention will be explained in more detail using an exemplary embodiment. In the accompanying drawing, the scheme of a pressure swing adsorption plant is shown, in which the inventive method is realized. With the help of this method, oxygen with a concentration of 90% by volume is to be recovered from the air. The core of the pressure swing adsorption plant are the first adsorber 1, the second adsorber 2 and the third adsorber 3. These are filled with the adsorbent Zeoiith type 5A; their volume is in each case 101. In the lower part of these three adsorbers 1,2,3 opens the air supply line 4 through which compressed air enters the adsorber. These ends of the three adsorbers 1,2,3, through which the compressed air enters the adsorber; are referred to as the inlet ends of these adsorbers. In the part of the air supply line 4 leading to each adsorber 1, 2, an air shutoff valve is arranged in each case. Thus, in the leading to the first adsorber 1 part of the air supply line 4, the first Luftabsperrventil 5, in which the second adsorber 2 leading part aas second Luftabsperrventil 6 and in the third adsorber 3 leading part, the third Luftabsperrventil 7 is provided. In the leading to each adsorber 1,2,3 part of the air supply line 4 opens between the adsorber and the Luftabsperrventil the residual gas line 8, in which the first adsorber 1, the first residual gas valve 9, the second adsorber 2 dns second residual gas valve 10 and the third adsorber 3, the third residual gas valve 11 is assigned. In the upper Teii of the three adsorbers 1,2,3 opens the oxygen line 12, through which the recovered oxygen exits the adsorbers. These ends of the three adsorbers 1,2,3, through which the oxygen leaves the adsorbers, have been termed outlet ends. In each leading to the adsorbers 1,2,3 part of the oxygen line 12, an oxygen valve is arranged. In this case, in the part of the oxygen line 12 leading to the first adsorber 1, the first oxygen valve 13 is arranged, in the part leading to the second adsorber 2 the second oxygen valve 14 and in the part leading to the third adsorber 3 the third oxygen valve 15. The three parts of the oxygen line 12 are between the three adsorbers 1,2,3 and

the three oxygen valves 13,14,15 connected by the expansion gas line 16 each with each other. Three expansion valves are provided in the expansion gas line 16, the first expansion valve 17 being associated with the first adsorber 1, the second expansion valve 18 with the second adsorber 2, and the third expansion valve 19 with the third adsorber 3. In this way it is possible that in the two stages of pressure reduction gas can flow through the expansion gas line 16 from the outlet end of an adsorber to the outlet end of another adsorber, wherein the third adsorber remains unaffected by this gas flow. In this process, two expansion valves are opened and one expansion valve is closed.

The three Luftabsperrventile 5,6,7 and the three residual gas valves 9,10,11 are arranged in a common valve block. Likewise, the three oxygen valves 13,14,15 and the three expansion valves 17,18,19 are arranged in a common valve block. Such valve blocks are described in DD-PS 265806. The arrangement of the two valve blocks directly to the three adsorbers 1,2,3 is explained in DD patent application WP Γ301D / 328448-6. For reasons of clarity, the individual gas lines and valves are shown individually in the accompanying drawing. The adsorption process in the adsorber 1 is terminated when the adsorption front in this adsorber begins to reach the exit end. At this time, there is a pressure of 0.46 MPa in this adsorber. The completion of the adsorption process is carried out by closing the first Luftabsperrventiles 5 and by closing the first oxygen valve 13th

The first stage of the pressure reduction of the loaded first adsorber 1 is effected by a pressure equalization with the regenerated second adsorber 2 by opening the first and the second expansion valve 17,18, while all other valves of the pressure swing adsorption are closed at this time. In this pressure equalization oxygen-rich gas flows from the intermediate grain volume of the adsorbent via the outlet end of the first adsorber 1 and the outlet end of the second adsorber 2 in the latter. In the first adsorber 1, the pressure drops from 0.46 MPa to about 0.23 MPa and increases in the second adsorber 2 from 0.1 MPa to 0.23 MPa. The pressure equalization takes about 3 seconds. In another variant of the operation, which is to be considered especially in larger Druckwecheladsorptionsanlagen into consideration, is charged during the pressure equalization of the pressure-releasing adsorber again via its inlet end with compressed air. This air supply is stopped when the pressure equalization is completed.

By closing the second expansion valve 18, the pressure equalization and thus the first stage of the pressure reduction is completed. It now follows the second stage of the pressure reduction in the first adsorber 1, which is made by the additional opening of the third expansion valve 19 and the third residual gas valve 11, wherein the first expansion valve 17 remains open. As a result, oxygen-rich gas, which is also desorbed by the pressure reduction in accordance with the equilibrium and kinetic conditions, flows through the outlet end of the first adsorber 1 and the outlet end of the third adsorber 3 into the latter adsorber and flushes it, whereby a portion of the oxygen is adsorbed , This rinsing process takes place in countercurrent to the adsorption direction. The purging of the third adsorber 3 is thus carried out not only with the product gas oxygen, but also with an oxygen-rich gas, which comes from the pore volume and from the micropores of the adsorbent. In this way, the oxygen recovery according to the invention requires less or no oxygen produced for purging an adsorber. After the exit of the purge gas from the third adsorber 3, this leaves the pressure swing adsorption through the residual gas line. 8

Simultaneously with the opening of the third expansion valve 19 also opens the first residual gas valve 9, whereby nitrogen-enriched residual gas from the first adsorber 1 occurs and leaves the Druckwechseladsorptionsanlage through the residual gas line 8. This residual gas flows in countercurrent to Adsorpttonsrichtung from the first adsorber 1. In the second stage of the pressure reduction thus takes place in the first adsorber 1 relaxation simultaneously both on the inlet end and on the outlet end of the adsorber, Da in the residual gas line 8 and in the Relaxation gas line 16 each throttles are provided, this pressure reduction is targeted vonstatten. After about 2-4 seconds (starting with the opening of the third expansion valve 13 and the first residual gas valve 9), the pressure in the first adsorber 1 has dropped to the ambient pressure of the system.

By simultaneously relaxing both sides of the adsorber 1 relatively high oxygen concentrations are achieved at the outlet end. The concentration profiles at the inlet end, here comes out a nitrogen-rich gas, and at the outlet end of the first adsorber 1, at this point exits an oxygen-rich gas, are polarized by the simultaneous and bilateral relaxation stronger than a successive pressure reduction. In this way, a higher yield of oxygen is achieved than in processes with successive pressure reduction. Furthermore, simultaneously with the opening of the third expansion valve 19 and the first residual gas valve 9, the second Luftabsperrventil 6 and the second oxygen valve 14 opens, whereby in the second adsorber 2, a new adsorption process begins. This adsorption process in the second adsorber 2 runs in this way at the same time as the second stage of the pressure reduction in the first adsorber 1. It takes about 35 to 40 seconds. After completion of this adsorption process is carried out in the manner described a new two-stage pressure reduction.

The proposed use of an oxygen-rich gas for Adsorberspülung as a partial or complete replacement of the recovered oxygen brings about an increase in oxygen accumulation by about 15% with it. The recovered oxygen has a concentration of 90% by volume.

Claims (2)

1. A method for separating gas mixtures by pressure swing adsorption using a group of at least three adsorbers, wherein in a first adsorber after completion of the adsorption process, a two-stage pressure reduction is performed, characterized in that in the first stage of the pressure reduction, a pressure equalization with a second adsorber takes place only over the outlet ends of the two adsorber, in the second stage of the pressure reduction, a two-sided expansion of the first adsorber is carried out simultaneously over the inlet end to the ambient pressure, which is guided from the outlet end of this adsorber gas flowing in a third adsorber through the outlet end and flows through this adsorber and the simultaneously flowing out of the inlet end of the first adsorber gas is carried away in a conventional manner as residual gas. 2. The method according to claim 1, characterized in that the pressure equalization is carried out with a subsequent adsorber without its previous flushing with product gas.