Process and device for separating gases by adsorbents.

0001The invention relates to a method according to the preamble of claim 1 and a system for performing the method.

0002Carbon dioxide, methane and other gases (product gas components) which can be adsorbed relatively strongly on adsorbents can be separated from such gas mixtures by adsorbing the product gas components on, in particular carbon-containing, adsorbents. So far, however, it has not been possible to recover these adsorbed product gas components in pure form, for example with concentrations of more than 99.5% by volume, during the desorption. On the other hand, in some technical applications such product gas components occur in proportions of about 15 to 50% by volume, so that their extraction would be quite interesting. B .:<ul id="ul0001" list-style="none"><li>- methane from mine gas</li><li>- Acethylene from an acetylene / hydrogen cycle gas</li><li>- Carbon monoxide from a reformer gas</li><li>- Carbon dioxide from converter gas or flue gas.</li></ul>

0003The difficulty in separating such product gas components from gas mixtures by adsorption has hitherto been that the desorption of a loaded adsorber also releases the other gas components of the starting gas mixture which are adsorbed at the same time. In this way, the components contained in the starting gas mixture are more or less contained as impurities in the desorbed gases (product gas).

0004The invention is therefore based on the object of selectively separating gas mixtures which contain the product gas component (s) from below 15% by volume to over 50% by volume, in particular carbon-containing adsorbents, in such a way that a product gas component (s) in the highest possible purity of z. B. over 99.5 vol .-% and in as high a yield as possible.

0005This object is achieved with respect to a method by the characterizing features of patent claim 1.

0006The pressure swing technology for the separation and extraction of gas components on adsorbents in adsorbers is known to include a cyclic process in which, within a cycle that begins at adsorption pressure, the strongly adsorbable gases in the entrance area of ​​the adsorbent layer are adsorbed in an adsorption phase from the starting gas mixture flowing through the adsorbent layer. Before the loading begins, the gas components, which are easier or hardly adsorbable, flow out at the end of the adsorbent layer, because these components have been displaced by more adsorbable gas components in their original adsorption sites. This is followed by a desorption step in which the adsorbed gas components are desorbed as much as possible and flow off by lowering the pressure or partial pressure in the adsorber. Finally, the pressure builds up to adsorption pressure and the cycle then begins again. All of these phases can run in several stages, and in particular it is known to carry out the desorption as completely as possible by using flushing gas.

0007According to the invention, product gas components are understood to be those gas components of the starting gas mixture which adsorb relatively strongly and therefore in the entrance area of ​​the adsorbent layer and which displace the more easily adsorbable gas components from their adsorption sites as the adsorption front proceeds; The reverse applies accordingly to the more easily adsorbable gas components, which for the sake of simplicity are referred to as exhaust gas components. Accordingly, the product gas contains a higher volume fraction of product gas components than the starting gas mixture, while the exhaust gas is correspondingly strongly depleted in product gas components.

0008The rinsing step according to the invention (item b) is now carried out with a gas mixture from the pressure change process which is enriched in product gas components; the purge gas can gradually or gradually increase in concentration in the product gas component in the course of the purge phase, but in any case it is necessary to purge with a gas of approximately product gas quality at the end of the purge phase. The best result is achieved if the entire purge is carried out with a gas mixture of product gas quality. This rinsing step, which is actually more of a second adsorption step, since it takes place at adsorption pressure, leads to the fact that the adsorption sites not yet occupied by the product gas components are filled with product gas components, displacing the exhaust gas components adsorbed there. In this way, at the end of the rinsing phase, the entire adsorbent is coated with product gas components, so that only slightly insignificantly contaminated product gas flows out in the desorption phase when the pressure is subsequently reduced. For a high yield of the product gas component, it is understood that the actual adsorption is stopped when the product gas component is about to breakthrough or has just broken through, and it is further understood that the "flushing" is operated at most until the breakthrough of initially only a few percent of product gas component is almost complete, ie approximately 100% product gas flows out of the adsorbent layer. The gas mixture flowing out during the "purging" may have a higher product gas concentration than the starting gas mixture after a longer purging period and in this case is preferably fed back to the pressure change process, specifically for the adsorption phase or the purging phase; at least the gas mixture flowing out towards the end of the rinsing phase is, however, best suited for use in the adsorption or Purge phase in a parallel adsorber, because then the product gas concentration quickly rises to product gas quality and thus particularly meets the requirements of the "purge step".

0009It goes without saying that when starting up a system according to the invention, a certain running-in time is required in which the individual flow rates and gas concentrations are still shifting; the state of equilibrium reached after a certain number of cycles is decisive for the invention.

0010Particularly advantageous for a quick and high absorption capacity of the adsorbent for the product gas component (s) during the adsorption phase and for a rapid and as complete as possible desorption of the product gas component (s) during the desorption. This is achieved according to the invention in that the pressure change process is carried out essentially adiabatically.

0011All relatively strongly adsorbable gases, in particular methane and carbon dioxide, containing gas mixtures, for example those with oxygen, nitrogen, carbon monoxide, hydrogen, helium, argon or other gas which is weakly adsorbable on the, preferably carbon-containing, adsorbent, can be added with the method of the invention work up a product gas of high purity and yield. Surprisingly, it is also harmless if traces, e.g. B. less than 1% by volume of gas components which are even more adsorbable than the product gas component (s) - the product gas can also be a gas mixture of particular interest consisting of several gas components which can be adsorbed to approximately the same extent - because these are adsorbed in most cases, in most cases but can not be desorbed by lowering the pressure alone, so that they do not contaminate the desorption gas (product gas), but z. B. can be removed in a rinsing step following the desorption phase; This rinsing step can be dispensed with if the trace impurities are very low and the contamination of the adsorbent caused thereby remains within reasonable limits, or a special prefilter is used for the trace impurities. In any case, the adsorbent - in a manner known per se - must be matched to the product gas component (s) with regard to its adsorption properties.

0012The inventive method can also, for. B. in the production of nitrogen from air on zeolites using pressure swing technology, since the nitrogen is more strongly adsorbed than the oxygen and it is obtained in the desorption step.

0013It was generally known even before the invention to separate gas mixtures using the different adsorption and desorption properties on adsorbents by means of pressure changes or temperature changes. In contrast, the invention is based on a method of working with which it is possible to have practically no gas components other than the product gas component (s) present in the adsorber before the start of the desorption phase.

0014This complete loading of the product gas component is thus achieved in the invention in that after the adsorption phase the adsorber is flushed with part of the product gas, which preferably contains over 99.5% by volume of product gas component, and the product gas component which leaves the adsorber is enriched Gas (return gas), the product gas component concentration of which lies between the starting gas and the product gas, is fed back to the pressure swing process. According to the invention, a portion of the product gas is used for at least the end of the flushing phase. This should be above about 10% by volume and not exceed about 90% by volume of the product gas. The amount of the portion depends on the concentration of the product gas component (s) in the starting gas; the higher the lower the product gas component concentration is here. An advantageous, further feature of the invention is that during the purging of the adsorber with product gas in the first two thirds of the purging phase the gas leaving the adsorber is added to the exhaust gas and only the gas accumulated in the last third and enriched with product gas components (return gas) is used for renewed adsorption or rinsing in a subsequent cycle (claim 3); this reduces the cycle time with a high yield.

0015In special cases, it may prove sufficient not to operate the purge until the product gas component has completely broken through. Then the gas mixture obtained during the desorption of the adsorber is used to purge another adsorber at the beginning of the desorption phase, and only after some time is the product gas obtained in a purity of more than 99.5% by volume being purged and in one portion divided partial stream going into the product gas line.

0016It is also for the desired full load of product gas (s)^ponente (n) important that the pressure build-up in starting gases with z. B. less than about 15 vol .-% carbon dioxide or less than about 10 vol .-% methane with the starting gas itself, on the other hand, for starting gases with a higher concentration of the product gas component (s) is carried out with the exhaust gas of the gas mixture separation. In addition, according to a further, preferred feature of the invention in the adsorption phase after the pressure build-up, the starting gas to be separated is introduced for a limited period of time, but later a gas enriched in the product gas component, from the purging phase of another cycle or a mixture of both. The aim of all of the aforementioned measures is that during the pressure release or evacuation - the adsorption is advantageously carried out at the naturally existing pressure level of the starting gas - in the desorption phase, a product gas with preferably at least 99.5% by volume of product gas component emerges from the adsorber.

0017In the described mode of operation, the adsorber can be flushed in cocurrent for adsorption, on the other hand the desorption of the adsorber in cocurrent or countercurrent for adsorption or, particularly quickly, from both ends of the adsorber can take place simultaneously.

0018The time for a complete adsorption and desorption step should be divided according to the invention such that the pressure build-up and the loading of the adsorbent with product gas component in the adsorption phase take about half to twice as long as the rinsing phase or the desorption phase. It has been shown that, for example, in a four-adsorber system, the adsorption phase is approximately twice as long as the rinsing or desorption phase. In a three-adsorber system, the same times are generally sufficient for all three phases, but the efficiency is lower than in the four-adsorber system.

0019Further details of the method according to the invention and the installation required for carrying out the method are explained in more detail with reference to the drawing. Show it:<ul id="ul0002" list-style="none"><li>Fig. 1 shows a plant for performing the method with four adsorbers</li><li>FIG. 2 shows a graphical representation of the chronological course of the phases in the four adsorbers of FIG. 1</li><li>Fig. 3 shows a plant for performing the method with three adsorbers</li><li>4 shows a graphical representation of the chronological course of the phases in the three adsorbers of FIG. 3</li><li>Fig. 5 is a diagram of the pressure curve in four adsorbers</li><li>Fig. 6 is a diagram of the pressure curve in three adsorbers</li><li>Fig. 7 shows another system for performing the method with four adsorbers</li><li>8 is a graphical representation of the time sequence in the four adsorbers of FIG. 7</li><li>Fig. 9 is a circuit diagram for the control of the valves of the four adsorbers of Fig. 7 in one cycle</li></ul>

00201, the system consists of four adsorbers 1, 2, 3 and 4 connected in parallel, which via pipeline 6 and valves 18, 11, 21, 31 and 41 with a blower 5 for conveying the exit gas and via valves 14 , 24, 34, and 44 are connected to a pipeline 9 for the exhaust gas. Furthermore, the adsorbers are connected via the valves 16, 26, 36, and 46 via the pipeline 10 to the vacuum pump 17, through which the product gas is discharged via the valve 27. The vacuum pump 17 is also connected via the pipeline 7 and the valves 19, 13, 23, 33 and 43 for transferring part of the product gas as purge gas into the adsorber, while carbon dioxide-enriched gas (return gas) via the pipeline 8 and the Valves 15, 25, 35 45 and 20 as well as 12, 22, 32 and 42 are returned to the respective downstream adsorber for renewed adsorption. The valves 18, 19, 20 and 27 are throttle valves which are open in the unchanged position during operation (except for start-up operation). These valves are not mentioned separately in the description of the mode of operation.

0021The commissioning of a system for the recovery of more than 99.5 vol .-% carbon dioxide can be done in such a way that all the adsorbers simultaneously or successively with starting gas through the valves 11, 21, 31 and 41 and 14, 24, 34 and 44 be loaded up beyond the breakthrough of carbon dioxide. This achieves a loading for adsorber 1, which is to be considered below, which corresponds to that after approx. 18 min in cyclic operation (see FIG. 2). When the valve 27 is closed and the valve 36 is open, adsorber 3 is evacuated and the product gas which accumulates in carbon dioxide during the reduction in pressure is conveyed through adsorber 1 via the vacuum pump 17 and valves 19 and 13. Valve 14 to exhaust pipe 9 is opened. After 6 minutes, valve 14 is closed and the gas mixture leaving the adsorber -1 goes via valves 15, 20 and 22 through adsorber 2 and valve 24 into the exhaust line 9. After 3 minutes, adsorber is evacuated in the same way as in the stationary operating state. This run-in process is carried out in the same way as outlined in FIG. 2 until a mean carbon dioxide concentration is obtained in the exhaust gas which is only slightly less than that in the starting gas. Then valve 27 is opened as far as required in the stationary operating state. Fig. 2nd describes the operation of a system with four adsorbers, with each adsorber going through three phases, some of which can still be divided. Only the state of the first adsorber after a pressure build-up with starting gas for all three phases is described below. The same applies to all three other adsorbers.

0022In the first phase, the pressure builds up with the starting gas over 3 min (the numerical values ​​of the times are exemplary), for which valve 11 is open. The adsorber 1 is then loaded for 12 minutes. When the valves 11 and 14 are open, the starting gas flows through the adsorber 1. Substantially low-carbon gas leaves the adsorber 1 and flows into the exhaust line 9. Subsequently, gas enriched with carbon dioxide (return gas), which leaves the fourth adsorber in the second phase, flows into the first adsorber with the valves 12 and 14 open for 3 minutes. This slightly increases the carbon dioxide concentration within the adsorber 1. At this point, too, no breakthrough of carbon dioxide can be observed in adsorber 1.

0023In the second phase, the carbon dioxide purging begins, which takes place with the carbon dioxide (product gas) produced, which is obtained during the desorption in adsorber 4. The rinse is divided into two sections. In the first section, with valves 13 and 14 open, a gas mixture leaves the adsorber for 6 minutes, the carbon dioxide concentration of which is below that of the starting gas. If the mass transition zone of the carbon dioxide purging has reached the mass transition zone of the previous starting gas loading, the two mass transition zones break through at the adsorber outlet. Then, with valves 13 and 15 open, a gas mixture leaves the adsorber for 3 minutes, the carbon dioxide concentration of which is between that of the starting gas and that of the product gas. This gas mixture is passed into the adsorber 2 via the open valve 22.

0024If the breakthrough of the carbon dioxide through the adsorber 1 has taken place completely, in the third phase the desorption is started in the third phase by evacuating the adsorber 1 via the open valve 16 with the aid of the vacuum pump 17, which takes about 9 minutes. Part of the product gas obtained with a purity of more than 99.5% by volume is used for purging in the adsorber 2 when the valves 19, 23 and 25 are open. The other part of the product gas is obtained via the valve 27. After the third phase has ended, the cycle described begins again from the beginning with the pressure build-up.

00253, the system consists of three adsorbers 1, 2 and 3 connected in parallel, which via pipeline 6 and valves 18, 11, 21 and 31 with a blower 5 for conveying the starting gas and via valves 14, 24 and 34 are connected to a pipe 9 for the exhaust gas. Furthermore, the adsorbers are connected via the valves 16, 26 and 36 via the pipeline 10 to the vacuum pump 17, through which the product gas is discharged via the valve 27. The vacuum pump 17 is also connected via the pipeline 7 and the valves 19, 13, 23 and 33 for transferring part of the product gas as purge gas into the adsorbers, while carbon dioxide-enriched gas (return gas) via the pipeline 8 and the valves 15 , 25, 35, and 20 is fed back into the starting gas before the blower 5. The valves 18, 19, 20 and 27 are throttle valves which are open in the unchanged position during operation.

0026Fig. 4 describes the operation of a system with three adsorbers, each adsorber going through three phases, some of which can still be divided. The state of the first adsorber for all three phases is described below. The same applies to the other two adsorbers.

0027In the first phase, the pressure builds up with the starting gas over a period of 1 min (the numerical values ​​of the times are exemplary), for which valve 11 is open. Then the adsorber is loaded for 19 minutes with the valves 11 and 14 open.

0028In the second phase, the product is flushed with carbon dioxide product gas. For this purpose, the valves 13 and 14 are open during the first 8 minutes. During this time, the adsorber leaves a gas mixture with carbon dioxide concentrations below that of the starting gas. During a further 2 min of the purging phase, when the valves 13 and 15 are open, carbon dioxide breakthrough occurs, which is why the escaping gas mixture is returned to the starting gas via valve 20.

0029In the third phase, desorption takes place with the vacuum pump 17 when the valves 16 are open. Part of the product gas is used for purging in the adsorber 2 when the valves 23 and 24 or later 23 and 25 are open. The other part is obtained via valve 27. Then a new cycle starts again with the pressure build-up.

0030The following examples show the mass balance during a cycle for six carbon dioxide or methane plants, namely Table 1 for a four-adsorber plant, Table 2 for a three-adsorber plant, Tables 3 to 6 for four-adsorber plants. Investments.

0031In the following examples, a so-called shaped adsorption coke with the following properties was used as the adsorbent:<ul id="ul0003" list-style="none"><li>Specific surface according to Brunauer, Emmet and Teller: 1,100 _{m2 /}G</li><li>Dimensions: diameter 3 mm length 4 mm</li><li>Bulk weight: 470 kg / m³</li><li>Apparent density: 784 kg / m³</li></ul>

0032All examples were once with C0₂ and once with CH₄ carried out as a product gas component - the values ​​and information in brackets apply to CH₄-Try without brackets for the C0₂-Try or for both at the same time.

example 1

0033Each adsorber, dimensions: height 2.5 m, diameter 0.71 m, the four adsorber system has a capacity of 1 m³, which is filled with adsorption coke. After a pressure build-up of 3 min to 1.17 - 1.2 (1.20 - 1.25) bar, the adsorption takes 15 min, followed by rinsing and desorption at a vacuum of⁼ 15 (60) mbar, each lasting 9 minutes.

0034The starting gas has a concentration of 16.7 (37.3) vol.% Carbon dioxide (methane) and 83.3 (62.7) vol.% Nitrogen. This results in an output gas throughput of 197.27 (77.54) Nm³/ h a net product gas gain of 27.53 (26.60) Nm³/ h carbon dioxide (methane) with a purity of 99.9% by volume. From this, the efficiency of the four adsorber system is calculated to be 0.84 (0.92). The amount of exhaust gas is 169.73 (50.93) Nm³/ h with a carbon dioxide (methane) concentration of 3.18 (4.54) vol .-%.

0035(_Nm³/ h = standard cubic meters per hour)<tables id="tabl0001" num="0001"><img file="EP0103070A2_D0001.tif" /></tables>

Example 2

0036Each adsorber in the three-adsorber system has a capacity of 1 m³, which is filled with adsorption coke. After a pressure build-up of 1 min to 1.17 - 1.2 (1.20 - 1.25) bar, the adsorption takes 9 min, followed by rinsing and desorption at a vacuum of ≦ 30 (60) mbar, each lasting 10 min .

0037The starting gas has a concentration of 16.7 (37.3) vol.% Carbon dioxide (methane) and 83.3 (62.7) vol.% Nitrogen. This results in an output gas throughput of 229.56 (70.02) Nm³/ h a net product gas gain of 27.84 (23.22) Nm³/ h carbon dioxide (methane) with a purity of 99.9% by volume. From this, the efficiency of the three adsorber system is calculated to be 0.73 (0.89). The amount of exhaust gas is 201.72 (46.80) Nm³/ h with a carbon dioxide (methane) concentration of 5.21 (6.14) vol .-%.<tables id="tabl0002" num="0002"><img file="EP0103070A2_D0002.tif" /></tables>

Example 3

0038Each adsorber in the four-adsorber system has a capacity of 1 m³, which is filled with adsorption coke. After a pressure build-up of 3 min to 1.17 - 1.20 (1.05 - 1.10) bar, the adsorption followed for 15 min, followed by flushing and desorption at a vacuum of ≦ 50 (60) mbar from 9 minutes each.

0039The starting gas has a concentration of 45.7 (12.5) vol.% Carbon dioxide (methane) and 54.3 (84.5) vol.% Nitrogen. This results in an output gas throughput of 172.14 (72.67) Nm³/ h net product gas gain of 69.74 (8.27)_'Nm³/ h carbon dioxide (methane) with a purity of 99.9% by volume. From this, the efficiency of the four-adsorber system is calculated to be 0.88 (0.91). The amount of exhaust gas is 102.40 (62.40) Nm³/ h with a carbon dioxide (methane) concentration of 8.7 (1.24) vol .-%.<tables id="tabl0003" num="0003"><img file="EP0103070A2_D0003.tif" /></tables>

Example 4

0040Each adsorber in the four-adsorber system has a capacity of 1 m³, which is filled with adsorption coke. After a pressure build-up of 3 min to 1.17-1.2 (1.10-1.15) bar, the adsorption followed for 15 min, followed by rinsing and desorption at a vacuum of = 40 (60) mbar, each lasting 9 min .

0041The starting gas has a concentration of 33.1 (52.9) vol .-% carbon dioxide (methane) and 66.9 (47.1) vol .-% carbon monoxide (hydrogen). This results in an output gas throughput of 171.61 (68.20) Nm³/ h a net product gas gain of 47.14 (33.67) Nm³/ h carbon dioxide (methane) with a purity of 99.9% by volume. From this, the efficiency of the four adsorber system is calculated to be 0.83 (0.93). The amount of exhaust gas is 124.47 (34.53) Nm³/ h with a carbon dioxide (methane) concentration of 7.8 (7.05) vol .-%.<tables id="tabl0004" num="0004"><img file="EP0103070A2_D0004.tif" /></tables>

Example 5

0042Each adsorber in the four-adsorber system has a capacity of 1 m³, which is filled with adsorption coke. After a pressure build-up of 3 min to 1.30 - 1.35 (1.00 - 1.05) bar, the adsorption takes 15 min, followed by a flushing at 1 (1) bar and desorption at a vacuum of⁼ 15 (60) mbar, each lasting 9 minutes.

0043The starting gas has a concentration of 9.8 (22.1) vol.% Carbon dioxide (methane) and 90.2 (77.9) vol.% Helium (hydrogen). This results in an output gas throughput of 181.60 (65.14) Nm³/ h a net product gas gain of 15.93 (12.8) Nm³/ h carbon dioxide (methane) with a purity of 99.9% by volume. This results in an efficiency of the four adsorber system of 0.90 (0.89). The amount of exhaust gas is 165.67 (52.33) Nm³/ h with a carbon dioxide (methane) concentration of 1.12 (3.06) vol .-%.<tables id="tabl0005" num="0005"><img file="EP0103070A2_D0005.tif" /></tables>

Example 6

0044Each adsorber in the four-adsorber system has a capacity of 1 m³, which is filled with Adsorptionskos. After a pressure build-up of 3 min to 1.25 - 1.30 (1.10 - 1.15) bar, the adsorption takes 15 min, followed by rinsing and desorption at a vacuum of ≦ 60 mbar, each lasting 9 min.

0045The starting gas has a concentration of 79.3 (88.3) vol.% Carbon dioxide (methane) and 20.7 (11.7) vol.% Hydrogen (argon). This results in an output gas throughput of 186.61 (77.0) Nm³/ h a net product gas gain of 134.74 (64.94) Nm³/ h carbon dioxide (methane) with a purity of 99.9% by volume. From this, the efficiency of the four adsorber system is calculated to be 0.91 (0.96). The amount of exhaust gas is 51.87 (12.07) Nm³/ h with a carbon dioxide (methane) concentration of 26.2 (25.35) vol .-%.<tables id="tabl0006" num="0006"><img file="EP0103070A2_D0006.tif" /></tables>

00467, another system consists of four adsorbers interconnected in two groups, adsorber 101 working with adsorber 102 and adsorber 103 working with adsorber 104. The adsorbers 101, 103, 102 and 104 are connected via the valves 115, 116, 117 and 118 to a loading pump 120 for conveying the starting gas, as well as via the valves 105 and 106 to the vacuum pump 121 and via the valves 107 and 108 to the vacuum nozzle 122. The vacuum pump 121 is also connected to convert a part of the product gas as purge gas (return gas) via the valves 111 to the adsorber 102 and via the valve 112 to the adsorber 104, while the vacuum pump 122 is connected to the adsorber 101 via valve 109 and via valve 110 to adsorber 103 is connected. The product gas is obtained via the valves 113 and 114, while the exhaust gas leaves the adsorbers via the check valves 123, 124, 125 and 126 and the system via valve 119.

0047The commissioning of a system for the recovery of more than 99.5 vol .-% carbon dioxide can be carried out by first opening the valves 115, 116, 117 and 118 simultaneously or in succession and the adsorbers 101, 102, 103 and 104 with starting gas be loaded until they are loaded with carbon dioxide to equilibrium. The cyclic operation of the system then begins in the manner shown in FIGS. 2 and 3.

00488 describes the mode of operation of a system with four adsorbers, each adsorber passing through four sections taking into account the two desorption phases for obtaining purge gas or product gas. FIG. 2 also makes it clear in which section the individual adsorbers are located at the same cycle time. Only the state of the first adsorber, for example for all four sections, is described below. The same applies to all three other adsorbers.

0049In the first phase, the pressure builds up with the starting gas over a period of 75 s (the numerical values ​​of the times are exemplary), for which valve 15 is open. The adsorber 101 is then charged for 75 s. In the process, starting gas flows through the opened valve 115 through the adsorber 101. In essence, carbon dioxide-free gas leaves the adsorber 101 through the check valve 123 and flows through the opened valve 119 into the exhaust gas.

0050In the second phase, adsorber 101 is then flushed with desorption gas from the first desorption phase of adsorber 104 with an average concentration below 99.5% by volume of carbon dioxide when valves 108 and 109 are open by means of vacuum pump 122 for 75 s. This increases the carbon dioxide concentration in adsorber 101. At the end of this phase, the breakthrough of carbon dioxide in adsorber 101 can be observed.

0051In the third phase, the first desorption phase, the evacuation of the adsorber 101 is started with the valves 105 and 111 open, the adsorber 102 being flushed for 75 s. Finally, the product gas is extracted in the second desorption phase with the aid of the vacuum pump 121 with the valve 113 open for a further 75 s. This product gas is obtained in a purity of more than 99.5% by volume of carbon dioxide after a running-in period of about 90 minutes after commissioning the system. After the end of the evacuation, the cycle described begins again with the build-up of pressure.

00523 shows which valves are open during the four phases in the adsorbers 101, 102, 103 and 104 in order to achieve cyclical operation of the system.

0053Both desorption steps take place in countercurrent to adsorption or rinsing. In this case, adsorbers 101 and 103 are always mutually evacuated by the vacuum pump 21 and the desorption gas is pressed as a purge gas by adsorbers 102 and 104, while product gas is obtained via valve 113. Likewise, adsorbers 102 and 104 are evacuated from the vacuum pump 22 and adsorbers 101 and 103 are purged, while the product gas is obtained via valve 114.

0054The duration of each cycle can be between about 4 times 50 s to 4 times 2,000 s. Here, the amount of purge gas obtained during the first desorption phase for the subsequent loading of the respective downstream adsorber is approximately 10 to 15 times an adsorber volume.

0055The following examples show the results of gas separation in the case of starting gases with different carbon dioxide contents in a four-adsorber system of the type described above (FIGS. 7 to 9), each adsorber having the following dimensions: height 2.5 m, diameter 0.71 m.

0056The shaped adsorption coke used can be characterized as follows:<ul id="ul0004" list-style="none"><li>Specific surface: BET 1,100 m³/G</li><li>Dimensions: diameter 3 mm length 4 _- 5 mm</li><li>Bulk weight: 470 kg / m³</li><li>Apparent density: 785 kg / m³</li></ul>

Example 7

0057Each of the four adsorbers has a capacity of 1 m³, which is filled with adsorption coke. The adsorption time is 150 s. Due to the selected flow rate of the output gas, 15 s are required to build up the pressure. This is followed by rinsing for 150 s and a two-stage desorption of 150 s each to a vacuum of 60 mbar. The cycle lasts 4 x 150 s.

0058The starting gas has a concentration of 16 vol.% Carbon dioxide and 84 vol.% Nitrogen. This results in an output gas throughput of 1,005 Nm³/ h, a net product gas gain of 65 Nm³/ h carbon dioxide with a purity of 99.5 vol .-%.

0059The exhaust gas amounts to 940 Nm³/ h with a carbon dioxide concentration of 10.2 vol .-%. The efficiency of the system is ∿ (CO 2) =^0,40.

Example 8

0060A starting gas with a concentration of 45% by volume of carbon dioxide and 55% by volume of nitrogen is processed in the same system as in Example 7.

0061The adsorption time is 75 s. Due to the selected flow rate of the output gas, 35 s are required for the pressure build-up. This is followed by rinsing for 75 s and a two-stage desorption of 75 s each to a vacuum of 60 mbar. This results in an output gas throughput of 537 Nm³/ h a net product gas gain of 156 Nm³/ h carbon dioxide with a purity of 99.8 vol .-%.

0062The amount of exhaust gas is 381 Nm³/ h with a carbon dioxide concentration of 22.9% by volume. The efficiency of the system is η (C0₂) = ^0,64.

Example 9

0063A starting gas with a concentration of 45% by volume of carbon dioxide, 20% by volume of hydrogen and 35% by volume of carbon monoxide is processed in the same system as in Example 1.

0064The adsorption time is 60 s. 15 s of this is due to pressure build-up. This is followed by a rinsing of 60 s and a two-stage desorption of 60 s each to a vacuum of 70 mbar. This results in an output gas throughput of 972 Nm³/ h a net product gas gain of 209 Nm³/ h carbon dioxide with a purity of -99.8 vol .-%.

0065The amount of exhaust gas is 763 Nm³/ h with a carbon dioxide concentration of 30 vol .-%. The efficiency of the system is η (C02) -^0,48.

Example 10

0066A starting gas with a concentration of 66.4% by volume nitrogen, 17.6% by volume oxygen and 16% by volume carbon dioxide is processed in the same plant as in Example 1.

0067The adsorption time is 300 s. Of this, 90 s is used to build up pressure. This is followed by a rinsing of 300 s and a two-stage desorption of 300 s each to a vacuum of approx. 50 mbar. This results in an output gas throughput of 197 Nm³/ h a net product gas gain of 24 Nm³/ h carbon dioxide with a purity of ≧ 99.5 vol .-%.

0068The amount of exhaust gas is 173 Nm³/ h with a carbon dioxide concentration of 5% by volume. The efficiency of the system is η (CO 2) = 0.74.