DE3345379A1 - Process for the isolation and recovery of gases relatively strongly adsorbable to adsorbents from gas mixtures otherwise containing essentially gases only weakly adsorbable - Google Patents

Abstract

Process for the isolation and recovery of gases (product gas components) relatively strongly adsorbable to adsorbents, in particular methane or carbon dioxide, from gas mixtures otherwise containing essentially gases (exhaust gas components) only weakly adsorbable onto, in particular, carbon-containing adsorbents using the pressure swing adsorption method in adsorbers in which a) in the adsorption phase, the starting gas mixture (crude gas) to be separated is passed through an adsorbent layer with adsorption of the product gas component(s) and flow off of the exhaust gas component(s), b) the adsorber is then flushed (flushing phase) essentially at atmospheric pressure, the product gas components having, at least until the end of the flushing, roughly product gas quality, the gas first flowing off being preferably supplied to the exhaust gas and gas enriched in the product gas component(s) flowing off later being, if required, returned to the pressure swing process, then c) the product gas component(s) is (are) desorbed by pressure reduction and, if necessary, flushing and thus a highly enriched product gas is obtained (product gas recovery), from which a part is returned for flushing to the pressure swing process and the rest is recovered and finally d) the gas pressure in the adsorber is built up again using a gas mixture, in particular from the pressure swing process, for a new adsorption phase, if a product gas of high purity and yield ... Original abstract incomplete.

Description

The invention relates to a method according to the preamble

of claim 1.

One can get carbon dioxide, methane and others, relatively strong on adsorbents Adsorbable gases (product gas components) from gas mixtures containing them separate by the product gas components, in particular carbon-containing, Adsorbent adsorbed. So far, however, it has not been possible to adsorb them Product gas components in pure form, for example with concentrations of over 99.5% by volume, to be recovered in the desorption with a satisfactory product gas yield. In some technical applications, such product gas components fall into place Quantities of about 15 to 50 vol .-%, so that their extraction is quite interesting would be so z. E.g .: - methane from mine gas acetipylene from an acetXylene / hydrogen cycle gas - Carbon monoxide from a reformer gas - Carbon dioxide from converter gas or flue gas.

The difficulty of separating such product gas components from gas mixtures by adsorption is so far that in the desorption of a loaded adsorber also the simultaneously adsorbed, other gas components of the Starting gas mixture are released. In this way they are desorbed Gases (product gas) also the components contained in the starting gas mixture more or contain less than impurities. The applicant already has this problem in the context of an earlier patent application (P 32 22 560.1) within the scope of the preamble of claim 1 solved.

The invention is therefore based on the object of gas mixtures which the product component (s) below 15 % By volume to over 50% by volume contain, selectively to, in particular carbonaceous, adsorbents so to separate that a product gas component (s) in the highest possible purity of z. B. is obtained over 99.5 vol .-% and in even higher yield (are).

This task is carried out with regard to a method by the characterizing Features of claim 1 solved.

The invention is based on the basic idea in which called pressure swing adsorption / desorption process for recovery relatively strong adsorbable product gas components, in which between the adsorption and desorption phases a special flushing phase (adsorption flushing) is inserted, increasing the yield to achieve product gas components that between the end of the adsorption phase and before the start of the production phase (product gas extraction by lowering the pressure) a special pressure reduction phase is inserted while the pressure in the adsorber by flowing off a partial amount of gas in cocurrent to the flow direction of the preceding Work phase is lowered. This displaces product gas components from the outflowing gas in the end area of the adsorber a good part of the still existing there Exhaust gas components on the adsorption sites of the adsorbent and in the space in between the adsorbent layer. This particular depressurization step can be before or after the flushing phase with product gas components.

This flushing phase of the adsorber is preferably carried out in cocurrent to the Adsorption and the adsorption phase is carried out before the breakthrough of the product gas component (s) terminated by the adsorbent layer because these measures in combination with the special pressure reduction step the most favorable increase in yield and bring about the best product gas enrichment. According to the invention it is therefore possible the Adsorption of the raw gas at a pressure well above atmospheric pressure Perform gas pressure, in particular at the pressure at which the raw gas z. B. off a chemical process. This adsorption step at elevated pressure can a pre-adsorption stage at the same pressure as preferred Water vapor is removed from the raw gas (drying stage). After the end of adsorption the pressure is then reduced to approximately atmospheric pressure and the rinsing phase at this point with a gas of approximately product gas quality. This adsorption leads to increased pressure to smaller adsorber volumes and allows the pressure build-up of a Adsorbers at pressures above atmospheric pressure z. T. with the pressure reduction of another adsorber between the adsorption phase and the purging phase perform. The special pressure reduction step can, however, also be done with a take place at about atmospheric pressure operated adsorption phase into a vacuum, the subsequent adsorption rinsing preferably again at approximately atmospheric pressure he follows. Finally, the special pressure reduction step can also take place after the adsorption flushing take place, with either a pressure equalization with an evacuated adsorber or a special vacuum pump can be used, so that the product gas recovery is subsequently carried out takes place at an even lower pressure level due to a further pressure reduction.

Developments and particularly preferred embodiments of the object of the invention emerge from the subclaims.

According to the invention, those gas components are used as product gas components of the outlet gas mixture understood, the relatively strongest and therefore in the entrance area adsorb the adsorbent layer and the weaker adsorbable Gas components as the adsorption front advances from their adsorption sites push away; the opposite applies to the more weakly adsorbable gas components, which are referred to as exhaust gas components for the sake of simplicity. Accordingly the product gas contains a higher volume fraction of product gas components than the starting gas mixture, while the exhaust gas is correspondingly high in product gas components is depleted.

The rinsing step (rinsing phase) is now carried out with a gas mixture from the Pressure change process carried out, which is enriched in product gas components; Here, the flushing gas can be concentrated in the product gas component in the course of the flushing phase increase gradually or in stages, but in any case it is at the end of the rinsing phase to purge with a gas of approximately product gas quality. The best result is achieved if the entire purging is carried out with a gas mixture of product gas quality. This Rinsing step, which is actually more of a second adsorption step that occurs in the Usually takes place at atmospheric pressure, so leads to the fact that the not yet of the product gas components occupied adsorption sites, displacing those there adsorbed exhaust gas components are filled with product gas components. To this At the end of the flushing phase, the entire adsorbent with product gas components is wise occupied, so that with the subsequent pressure reduction in the desorption phase only insignificantly contaminated product gas flows off. For a high yield on the product gas component it goes without saying that the actual adsorption then is ended when the product gas component is about to break through or is about to break through has broken through, and it is further understood that the "flushing" at most is operated until the breakthrough of only a few percent at Product gas component is nearly complete, d.

H. approximately 100% product gas flow out of the adsorbent layer. The gas mixture flowing off during "flushing" can after a longer flushing period have and will have a higher product gas concentration than the starting gas mixture in this case preferably fed back to the pressure change process, namely for the adsorption phase or the flushing phase; at least that towards the end of the rinsing phase however, the outflowing gas mixture is best suited for use for the adsorption or flushing phase in a parallel adsorber, because then the gas concentration (concentration in the outflowing gas mixture) quickly increases to product gas quality and so the The requirements of the "rinsing step" are particularly sufficient.

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

A fast and high absorption capacity is particularly advantageous of the adsorbent for the product gas component (s) in the adsorption phase as well as a fast and as complete as possible desorption of the product gas component (s) during desorption. This is achieved according to the invention in that the pressure change process is performed essentially adiabatically.

The method of the invention can all be relatively strongly adsorbable Gas mixtures containing gases, in particular methane and carbon dioxide, for example those with oxygen, nitrogen, carbon monoxide, hydrogen, IIelium, argon or other, on the, preferably carbonaceous, Adsorbent Weakly adsorbable gases, work up to a product gas of high purity and yield. Surprisingly, it is also harmless if there are traces of z. B. less than 1% by volume, of even more strongly adsorbable gas components than the Product gas component (s) - the product gas can also be of particular interest Gas mixture consisting of several gas components that can be adsorbed to the same degree - be present because they are adsorbed in any case, but mostly by lowering the pressure alone cannot be desorbed, so that they do not contain the desorption gas (product gas) contaminate, but z. B. in a subsequent to the desorption phase Rinsing step can be removed but this rinsing step can be omitted, if the trace impurities are only very small and the resulting Contamination of the adsorbent remains within acceptable limits, or is used a special pre-filter for the trace impurities, especially a dryer for water vapor in the feed gas mixture (raw gas). In any case, the adsorbent must - In a manner known per se - in terms of its adsorption properties the product gas component (s) must be matched.

The inventive method can also, for. B. in nitrogen production be carried out from air on zeolites with pressure change technology, since this is the Nitrogen is adsorbed more strongly than oxygen, and it is obtained in the desorption step will.

It was generally known even before the invention, gas mixtures taking advantage of the different adsorption and desorption properties to separate adsorbents by pressure changes or temperature changes. Of the In contrast, the invention is based on a mode of operation with the it is possible that there are practically no other gas constituents before the start of the desorption phase except for the product gas component (s) are present in the adsorber.

This complete loading with the product gas component is at the invention thus achieved on the one hand that after the adsorption phase Adsorber with part of the product gas, which is preferably over 99.5% by volume of product gas component contains, is flushed and the product gas component leaving the adsorber enriched gas (return gas), its product gas component concentration between the starting gas and the product gas is fed back to the pressure swing process will. For at least the end of the rinsing phase, according to the invention, a portion of the Product gas used. This should be above about 10% by volume and about 90% by volume of the product gas. The level of the proportion depends on the concentration the product gas component (s) in the starting gas; the lower it is, the higher it is the product gas component concentration is here. Another advantageous feature the invention consists in that during the purging of the adsorber with product gas in the first two thirds of the purging phase, the gas leaving the adsorber into the Exhaust gas is given and only the product gas components accumulating in the last third enriched gas (return gas) for re-adsorption or purging in a subsequent one Cycle is used (claim 3); this is the high yield Cycle time reduced.

In special cases it may prove sufficient to do the rinse not to operate until the product gas component has completely breached. then is the gas mixture obtained during the desorption of the adsorber at the beginning of the desorption phase used to rinse another adsorber, and only after some time will that in a Product gas obtained in purity of more than 99.5% by volume a portion for purging and in a partial flow going into the product gas line divided up.

In addition, it is necessary for the desired full load with the (the) Product gas component (s) important that the pressure build-up in the case of output gases with z. B. less than about 15 volume percent carbon dioxide or less than about 10 volume percent methane Starting gas itself, on the other hand in the case of starting gases with a higher concentration of the product gas component (s) the gas mixture separation is carried out with the exhaust gas. Also, after a Another preferred feature of the invention in the adsorption phase after the pressure build-up the starting gas to be separated only for a limited period of time, later on Gas enriched in the product gas component, from the purging phase of another Cycle or a mixture of both initiated. The aim of all of the above measures it is that when the pressure is released or evacuated - the adsorption becomes advantageous made on 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.

The flushing of the adsorber should be carried out as described take place in cocurrent to the adsorption, on the other hand, the desorption of the adsorber in cocurrent or countercurrent to adsorption or, particularly quickly, of both Ends of the adsorber take place at the same time.

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

A relatively large amount of gas is required to "flush" an adsorber required, which is obtained when evacuating another adsorber. This means, that of the gas obtained during evacuation of an adsorber only a part as product gas can be used, while the other must be used for flushing. Of the The energy required to operate the system is largely determined by the pump energy when evacuating. This depends on the proportions of the product gas and the flushing gas amount (i.e. the less purging gas is required in relation to the product gas, the less is the energy consumption) and the efficiency of the vacuum pump over the entire Pressure area. The invention is therefore based on the further object of the energy consumption and, if necessary, to reduce the specific system size.

It has been found to be particularly advantageous to use two vacuum pumps to be used (Versionl), the first of which is between the flushing pressure and an intermediate pressure and the second operated between the intermediate pressure and the final pressure of the evacuation will. The purging gas is conveyed with the first pump, the product gas with the second. In tests it has been shown to be a particular advantage that both pumps during only have to pass through one pressure range of the respective evacuation process, which is lower than that between the rinsing pressure and the final pressure of the vacuum. It appears namely that during the first evacuation step a relatively large amount of gas with little Differential pressure, relatively little gas during the second evacuation step greater differential pressure occurs. For both requirements there are pumps that come with higher efficiency work than a single pump that covers the entire range is working. It has proven to be a particular unexpected advantage of this approach found that the raw gas throughput can be increased by using two suitable pumps cannot be increased by a pressure change system of a given size, since obviously more time is required for the desorption at negative pressure than the theory (xergl. E. Richter, u.a .; - Chemie-Ingenieur-'Pechnik 50 (1373) S.60ö, / 61l) predicts.

This regards the desorption as a reversal of the adsorption, their Speed is determined solely by the diffusion of the gas in the pores of the adsorbent is. Another advantage of using two vacuum pumps for desorption It has been found that it is not necessary to purge the adsorber a gas is used which has product gas quality. This allows the amount of purging gas can be reduced without the product gas quality being impaired.

This has the major advantage that the performance of the pressure change system less affected by temporary changes in the composition of the raw gas will. Another advantage is that the pumps are less affected by pressure jumps are claimed and that the flow rate of the product gas over the respective Evacuation process iocr fluctuates strongly over time. In addition, you can use The version described has a lower final pressure during, = acuation (since the evacuation time is extended and the product gas generating pump can be specially designed) reach. This allows a higher yield of the component (s) to be obtained can be achieved.

In many cases the raw gas is at a pressure which is substantial is above ambient pressure. Then it is not possible that that during the evacuation Accumulated gas directly for purging the adsorber at the level of the loading pressure to be used, as vacuum pumps can only deliver against a limited overpressure. This would require an additional compressor, in addition to increased investment costs would also require additional operating costs. The loading pressure would have to be lowered a possibility. However, the loading pressure has proven to be particularly advantageous to leave it at the higher pressure level and not to flush the adsorber at the loading pressure but to be carried out at a pressure level that is achieved by the vacuum pump (cl It applies equally to the modifications with one and with two vacuum pumps). it has been found to be advantageous after the loading is complete Adsorbers in (loicìlstrom to relax (see version 4).

This relaxation already has the consequence that the (n) to be won Component (s) in the adsorber is (are) enriched relative to the other components. Surprisingly, it has been found in tests that the losses of product gas, which were expected in the expansion, can be avoided if the Loading is canceled at a point in time at which the breakthrough front has not yet been released is advanced to the adsorber outlet and when the expansion in cocurrent in takes place in such a way that when the relaxation is complete there is still no complete breakthrough of the product gas has taken place. Surprisingly, with this approach the amount of purging gas can be reduced.

Unexpectedly it was found that even after a Loading at a pressure that is not significantly above ambient pressure is the amount of purging gas can be reduced when a pressure equalization with an adsorber, its evacuation has just been completed and in which the final pressure of the evacuation still prevails (version 3). It turns out to be a particular advantage that less exhaust gas is used to build up pressure is required. This is especially important when the component (s) to be extracted is already present in relatively high proportions by volume (e.g. over 60% by volume). A decrease the amount of purging gas is the same if the pressure equalization after purging takes place (version 2). This is also observed when loading at increased pressure and then a direct current relaxation takes place.

Further details of the method according to the invention and that for this ~ The system required to carry out the procedure is based on the drawing explained in more detail.

1 shows a system for carrying out the method four adsorbers (version 1); Fig. 2 is a graphic representation of the control flow chart the phases in the four adsorbers of FIG. 1; 3 shows a further installation for implementation the process with four adsorbers (version 2); Fig. 4 is a graphical representation the control flow chart of the phases in the four adsorbers of FIG. 3; Fig. 5 a further system for carrying out the process with four adsorbers (version 3); Fig. 6 is a graphic representation of the control flow diagram of the phases in the four adsorbers of Fig. 5; 7 shows a further system for carrying out the method with four Adsorbers (version 4); 8 is a graphic representation of the control flow chart in the four adsorbers of FIG. 7.

Version 1 In this version two vacuum pumps are used, One vacuum pump draws off a flushing gas and the second vacuum pump that Sucks off product gas. The separation of the functions of both vacuum pumps offers the special Advantage that each of the pumps are designed specifically for the particular function can. This means that the vacuum pump, which is used to generate the purge gas, only needs to draw a lower vacuum than the pump that is used to generate the product gas is used. In addition, the purging pressure and product gas pressure no longer have to be identical but can be within limits that are determined by the design of the respective vacuum pump are set to be adapted to operational requirements. The flow diagram of the The system is shown in FIG. 1, the control flow chart is shown in FIG. 2; in the latter is also the profile of the pressure in adsorber 1 over time during a complete Pressure change cycle entered.

The feed gas is at a pressure that is slightly above ambient pressure is so that the pressure loss in the adsorbers overcome during the flow can be. The product gas is obtained at a pressure that depends on the vacuum pump is more or less above the ambient pressure. The following is how it works the system explained over a complete pressure change cycle. The description limited to one adsorber, since the other adsorbers are staggered in time Step through steps.

The feed (raw) gas flows during the loading step at raw gas pressure Via valve 21 through adsorber 1 and via valves 17 and 26 into the exhaust line. The loading is stopped before the more strongly adsorbed gas in noticeable concentrations leaves the adsorber. The gas flowing out during the adsorption is at the same time to the Part also used to build up pressure in adsorber 2. After the loading is finished Adsorber 1 is flushed with a gas that is more strongly adsorbing with the more strongly Component is enriched as the raw gas. This is done when the Valve 12 gas is sucked out of adsorber 4 with the aid of vacuum pump 27 and via valve 5 pressed by adsorber 1.

During the flushing process, a gas leaves the adsorber 1 via a valve 17, which is largely free of the more strongly adsorbing component. This gas gets into the exhaust pipe. With the rinsing process, the more strongly adsorbing one accumulates Component in adsorber 1 so strongly that during the subsequent evacuation by means of Pump 27 a gas is obtained, the content of which is more strongly adsorbing component is not significantly below the content of this gas in the product gas. The gas will sucked out of adsorber 1 with open valve 9 and with open valves 6 and 18 used to flush adsorber 2. The pressure in adsorber 1 is dependent on the raw gas pressure lowered to a pressure that lies between the raw gas pressure and the ultimate vacuum, which is achieved in the subsequent second evacuation. After finishing this The first evacuation step begins the second evacuation step, which begins with the Obtaining product gas is identical. For this purpose, with the valve 13 open, a vacuum pump is used 28 sucked a gas from the adsorber 1, which has product gas quality. The pressure change cycle is completed by a pressure build-up with exhaust gas after the end of production he follows. For this purpose, the valve 17 on adsorber 1 is open.

Experimental data: Adsorbent: carbon molecular sieve with a BET surface area of 1100 m² / g Loading pressure: 1.05 bar Feed gas: 16.7% by volume CO2 83.3% by volume N2 adsorber volume: 1 m3 Procedure: Version 1 gas volumes under normal conditions C02 (m3) N2 (m) total gas (m3) 1st pressure build-up 0.25 1.32 1.57 (feed gas) 2. Adsorption 3.25 16.94 20.19 (feed gas) 3. Purge 9.57 0.57 10.14 (product gas 1) 4th desorption 3.19 --- 3.19 (product gas 2) exhaust gas: 0; 31 18.26 18.57 (1.67% by volume CO2) Yield = (amount of product gas): (amount of feed gas) = 0.91 version 2 A vacuum pump is used in this version. Loading takes place at a pressure that is close to ambient pressure and a differential pressure above that Exhaust pressure is, which corresponds to the pressure loss in the system during loading. A pressure equalization takes place (after the adsorption flushing has taken place) in the negative pressure area into it, whereby in a particularly advantageous manner the more strongly adsorbent component is enriched in the adsorber and the vacuum pump less strongly due to pressure jumps is claimed when switching from one adsorber to the next. Likewise the accumulation of the product gas is thereby evened out over time.

The flow diagram of the plant is shown in FIG. 3. The tax schedule FIG. 4 also shows the profile of the pressure in adsorber 101 during a complete Pressure change cycle is shown.

The following shows how the system works when it passes through the various steps during a pressure swing cycle of adsorber 101 described. The other adsorbers with their corresponding valves pass through staggered in time the same steps as adsorber 101. This can be seen directly from FIG.

The raw gas (feed gas) flows over during the loading process the raw gas line 105 and the valve 111 in the adsorber 101. That largely of the more strongly adsorbing component freed exhaust gas flows through valve 115 into the Exhaust pipe 110. The loading is interrupted at a predetermined time, at which the more strongly adsorbing gas has not yet reached the exhaust gas line. Adsorber 101 is then purged with a gas, which is generated with the aid of the vacuum pump 160 is sucked from adsorber 104. During this process, the valves 143, 112 and 115 open. The gas is practically product gas quality when it is in adsorber 101 enters. This leaves a gas, the content of which is stronger adsorbent component is below that of the raw gas. After the flush is complete After a specified time, the pressure in the adsorber is reduced in two stages. In the first stage, the pressure is equalized with the evacuated adsorber 104 via the opened valves 116 and 147. A gas flows from here via line 109 Adsorber 101 in adsorber 104, its content of the more strongly adsorbing component is on average above the content in the raw gas. This pressure equalization is after a given time canceled. Then an approximately identical one has been found in both adsorbers Pressure set between the raw gas pressure and that reached during evacuation Final pressure. In the following step, adsorber 101 is activated by opening valve 113 connected to the vacuum pump 160 via line 106. The pressure decreases with the Time down to a final pressure. A gas is sucked out of the adsorber, the product gas quality having. Some of this gas comes from vacuum pump 160 into the product gas line 106, on the other hand it is used to flush adsorber 102, in which it is over the throttle valve 150, line 107 and valve 122 arrives. After the evacuation is finished of adsorber 101 is at a predetermined time with the increase in pressure in this adsorber started on loading pressure.

This pressure increase takes place in two stages. In the first stage takes place a pressure equalization with adsorber 102 with open valves 117 and 126 via line 109. In the second, raw gas flows into the adsorber when valve 111 is open. at In the latter step, the pressure increases from the intermediate pressure already mentioned back to raw gas pressure. Then again with the loading in the already above described way started.

Experimental data: Adsorbent: carbon molecular sieve with a BET surface area of 1100 m2 / g loading pressure: 1.05 bar feed gas: 16.7% by volume CO2 83.3 vol .-% N2 adsorber volume 1 1 m3 Procedure: Version 2 gas volumes under normal conditions CO2 (m3) N2 (m3) total gas (m3) 1st pressure build-up 0.29 1.45 1.74 (feed gas) 2. Adsorption 3.79 18.90 22.69 (feed gas) 3. Purging 10.67 ---- 10.67 (product gas) 4.Desorption 14.20 --- 14.20 (product gas) Net product gas 3.53 --- 3.53 (99.9% by volume CO2) Flue gas: 0.55 20.35 20.90 (2.63% by volume CO2) Yield = (amount of product gas) :( amount of feed gas) = 0.87 Version 3 With this version only one vacuum pump is required. It is used in a particularly advantageous manner that after the flushing process has ended the concentration of the more strongly adsorbing component in the adsorber even further can be increased so that less purge gas is required or a gas with a higher purity can be obtained. Furthermore, the vacuum pump is less powerful Pressure jumps loaded, as there is already pressure at the beginning of the evacuation, which is under the raw gas pressure. This also makes it possible to manage the evacuation process to equalize the resulting product gas flow.

The flow diagram of the corresponding plant is shown in Fig. 5, the control flow chart in FIG. 6. In the latter, the course of the pressure is also shown in Adsorber 201 shown over a complete pressure swing cycle.

The feed gas is at a pressure that is slightly above ambient pressure is so that, taking into account the pressure loss in the system, the exhaust gas with Ambient pressure can flow off. However, this setting of the pressure is not mandatory for the procedure. The product gas is obtained at a pressure which, depending on the vacuum pump, is more or less above the ambient pressure. Below the functionality of the system is explained using a complete pressure change cycle. The description is limited to Adsorber 201, since the other AdsQrber 202-204 go through the same steps at different times.

The raw gas (feed gas) flows through line 251 when the valve is open 211 in the adsorber 201, in which the raw gas pressure is present. The more adsorbent Component is largely adsorbed during this loading process, so that over Valve 215 is almost completely freed from the adsor1> i # r ### d # n component Gas flows into the exhaust pipe 258.

The loading is stopped before the concentration of the more strongly adsorbent Component in the exhaust gas increases noticeably. The adsorber is then flushed with a Gas recovered from adsorber 204 during evacuation. This is an adsorber 204 the valve 242 opened. The gas is via the vacuum pump 260, the throttle valve 259 pressed by adsorber 201 with valve 213 open. About the open valve 215 a gas enters the exhaust pipe 258, the content of which is the stronger adsorbent component is less than in the raw gas. After completing this During the flushing process, which takes place at raw gas pressure, pressure is equalized between the adsorber 201 and the evacuated adsorber 203. For this purpose, the valves 216 and 234 are open. During the pressure equalization process, a gas from adsorber 201 becomes adsorber 203 sucked, the concentration of which in the more strongly adsorbing component is still significant is below the raw gas concentration. In the next step, the adsorber 201 is evacuated from a pressure between the raw gas pressure and the final pressure of the subsequent Evacuation lies. Valve 212 is open during evacuation. The gas arrives via line 252 through the vacuum pump 260 into the product gas line 261. One part of the gas can be used for the entire duration of the evacuation or for part of it the evacuation time can be used for purging adsorber 202, including valve 223 and 225 on adsorber 202 are open. During evacuation, the pressure in the falls Adsorber 201 from the already mentioned intermediate pressure to a final pressure which can be between 10 and 600 mbar depending on the application and design of the pump 260. After the end of the evacuation, which is identical to the production, takes place after a dead time, the pressure build-up in adsorber 201 in two steps. In the first step a pressure equalization of the adsorber 201 with adsorber 203 is carried out, including the Valves 214 and 236 are open. From the resulting intermediate pressure the second part of the pressure build-up takes place with raw gas. This flows through a line 251 with the valve 211 open in adsorber 201. The pressure change from new.

Experimental data: Adsorbent: carbon molecular sieve with a BET surface area of 1100 m² / g Loading pressure: 1.05 bar Feed gas: 16.7% by volume CO2 83.3% by volume N2 3 Adsorber volume: 1 m Procedure: Version 3 gas volumes under normal conditions CO2 (m3) N2 (m3) total gas (m3) 1st pressure build-up 0.32 1.60 1.92 (feed gas) 2. Adsorption 3.99 19.90 23.89 (feed gas) 3. Purge 8.07 ---- 8.07 (product gas) 4.Desorption 12.18 --- 12.18 (product gas) Net product gas 4.11 --- 4.11 (99.9% by volume CO2) Flue gas: 0.20 21.50 21.70 (0.90% by volume CO2) Yield = (amount of product gas) :( amount of feed gas) = 0.95 Version 4 This version uses a vacuum pump. The loading takes place at increased pressure, with the raw gas already at increased pressure can exist or to compress at this pressure by means of an upstream compressor is. The adsorption at elevated pressure has the particular advantage that the size of the adsorber can be reduced because there is more gas per unit volume Adsorbent can be adsorbed. Furthermore, enables the one described below Relaxation step in cocurrent to adsorption, a further targeted enrichment the more strongly adsorbent component in the adsorber, so a flushing step like him was required for versions 1 to 3, may be omitted here.

The flow diagram of the plant is shown in Fig. 7, the control flow chart FIG. 8 shows the pressure curve in adsorber 301 during a complete Pressure change cycle is shown.

The feed gas is at a pressure that is above ambient pressure lies. The pressure will preferably be above 2 bar. The product gas is at a Pressure gained which, depending on the vacuum pump, is more or less above the ambient pressure lies. The functionality of the system based on the circuits for Adsorber 301 explained about a complete pressure swing cycle. The other adsorbers go through the same steps at different times.

The raw gas flows through the raw gas line during the loading process 351 and the valve 311 in the adsorber 301 and leaves it via valve 315. The Gas largely freed from the strongly adsorbing component flows over Valve 315 in the exhaust line 359 in which the throttle valve 360 is installed. The latter has the function of reducing the pressure in the adsorbers during the loading steps keep constant.

The loading becomes some time before the concentration of the stronger adsorbent component in the exhaust gas increases noticeably, canceled. The loading closes A relaxation of the adsorber 301 occurs, including valve 311 when the valve is closed 316 remains open. During the relaxation phase, which according to a predetermined Time or when a specified pressure is reached, which is above ambient pressure is aborted, a gas flows that is largely free of the more strongly adsorbing Component is, in the exhaust pipe 359. In the next step, a pressure equalization takes place between adsorber 301 and 303, for which purpose the valves 317 and 334 are open. Included the pressure in the adsorber 301 drops to a value which, as a rule, falls below the ambient pressure. The adsorber 301 can then be purged with a gas that accumulates during the evacuation of adsorber 304. The pressure during the flushing can be set at ambient pressure or also slightly below or above will. During the rinsing phase, this is passed through the vacuum pump via valve 342 357 sucked gas after flowing through the throttle valve 356 via line 353 and Valve 313 in the adsorber 301. From this flows a gas whose content of the stronger adsorbing component is above the content in the raw gas, above the opened Valve 315 and line 358 back before compressor 350. After flushing is complete the pressure in adsorber 301 is lowered.

For this purpose, with the valve 312 open, gas is supplied via line 352 with the aid the vacuum pump 357 sucked off. From this gas, which has product gas quality, arrives during part of the evacuation period or during the entire period Evacuation time a fixed proportion of the gas via valve 356, line 353 and valve 323 for flushing in adsorber 302. After the end of the evacuation phase, which is identical to production, the pressure build-up takes place on loading pressure in two stages. In the first stage there is a pressure equalization with adsorber 303, which is in the state after the DC relaxation. The valves 314 are for this purpose and 337 open. The pressure equalization is canceled after a specified time. Then a pressure has set in both adsorbers that is usually below Ambient pressure.

The subsequent pressure build-up takes place with the valve 311 open Raw gas. Then a new cycle begins in the manner described with a new one Loading of the adsorber.

Experimental data: Adsorbent: carbon molecular sieve with a 2 BET surface area of 1100 m loading pressure: 3.0 bar feed gas: 16.7% by volume of CO2 83.3 vol .-% N2 adsorber volume: 1 m3 Procedure: Version 4 gas volumes im Standard condition CO2 (m³) N2 (m³) Total gas (m³) 1st pressure build-up 1.15 5.76 6.91 (feed gas) 2. Adsorption 5.93 29.58 35.51 (feed gas) 3. Purging 6.68 ---- 6.68 (product gas) 4. Desorption 13.48 --- 13.48 (product gas) Net product gas 6.80 --- 6.80 (99.9 vol-3 CO2) Flue gas: 0.28 35.34 35.62 (0.8% by volume CO2) Yield = (amount of product gas) :( amount of feed gas) = 0.96 Test data: Adsorbent: silica gel loading pressure : 3.0 bar Feed gas: 16.7% by volume CO2 83.3% by volume N2 Adsorber volume: 1 procedure : Version 4 gas volumes in the standard state CO2 (m3) N2 (m3) total gas (m3) 1. Pressure build-up 0.80 3.98 4.78 (feed gas) 2nd adsorption 5.23 26.09 31.32 (feed gas) 3rd purge 7.14 ---- 7.14 (product gas) 4. Desorption 12.51 --- 12.51 (product gas) Net product gas 5.37 --- 5.37 (99.9% by volume CO2) exhaust gas: 0.66 30.07 30.73 (2.2% by volume CO2) yield = (Amount of product gas): (amount of feed gas) = 0.89 Comparative example (According to DE patent application P 32 22 560.1 Example 1) Adsorbent: carbon molecular sieve with a 2 BET surface area of 1100 m, loading pressure: 1.2 bar, feed gas: 16.7 Vol .-% CO2 83.3 Vol .-% N2 Adsorber volume: 1 m³ gas volume in standard condition CO2 (m³) N2 (m³) total gas (m³) 1. Pressure build-up 0.85 4.25 5.10 (feed gas) 2. Adsorption 4.09 20.40 24.49 (feed gas) 3. Purge 18.37 ---- 18.37 (product gas) 4. Desorption 22.50 --- 22.50 (product gas) Net product gas 4> 13 --- 4.13 (99.9% by volume CO2) Exhaust gas: 0.81 24.65 25.46 (2.2 vol .-% CO2) Yield = (product gas amount) :( feed gas amount) = 0.84 - blank page -

Claims (18)

Process for the separation and recovery of relatively high levels of adsorbents adsorbable gases from otherwise essentially only more weakly adsorbable gases Gas mixtures containing Patent claims 1. Process for separation and recovery of gases that are relatively strongly adsorbable on adsorbents (product gas components), in particular methane or carbon dioxide, from otherwise essentially only weaker Gas mixtures containing adsorbable gases (exhaust gas components), in particular carbonaceous adsorbents using pressure swing adsorption technology in Adsorbers in which a) the starting gas mixture to be separated in the adsorption phase with adsorption of the product gas component (s) and outflow of the exhaust gas component (s) is passed through an adsorbent layer, b) then the # adsorber essentially at atmospheric pressure with at least about product gas quality at the end of the purging having product gas components is flushed (flushing phase), preferably the first outflowing gas into the exhaust gas and later outflowing on the product gas component (s) enriched gas is possibly fed back to the pressure change process again, then c) the product gas component (s) are desorbed by lowering the pressure and, if necessary, flushing will (become) and thus a highly enriched product gas is obtained (product gas recovery), of which a part is fed back to the pressure change process for flushing and the rest is obtained, and finally d) the gas pressure in the adsorber with a gas mixture, in particular from the pressure change process, for a new adsorption phase again is built up, characterized in that e) temporally between the end of the adsorption phase and before the pressure reduction for the purpose of producing gas Gas pressure in the adsorber due to the outflow of a partial amount of gas in cocurrent to the direction of flow the previous work phase is lowered and f) this partial gas quantity in the pressure change process is reused. 2. The method according to claim 1, characterized in that a proportion 10 - 90% by volume of the product gas is used for purging. 3. The method according to claim 1 or 2, characterized in that the especially in the last third of the early phase, flowing off the product gas component (s) enriched gas at the end of the adsorption phase or at the beginning of the purging phase passed the adsorbent layer of another adsorber connected in parallel will. 4. The method according to any one of claims 1 to 3, characterized in that that the pressure build-up in the adsorber with starting gas mixtures of 15 (10) or less Voi.- ohlendioxid (methane) is carried out with the starting gas mixture. 5. The method according to any one of claims 1 to 4, characterized in that that the adsorption phase before the start of the breakthrough of the product gas component (s) is terminated by the adsorbent layer. 6. The method according to any one of claims 1 to 5, characterized in that that the flush. of the adsorber takes place in cocurrent to the adsorption. 7. The method according to any one of claims 1 to 6, characterized in that that the desorption of the adsorber takes place at the same time from both ends of the adsorber. 8. The method according to any one of claims 1 to 7, characterized in that - # ate the pressure build-up and the loading of the adsorber in the adsorption phase taken together about half as long to twice as long as the rinsing phase or the desorption phase (Product gas extraction) last. 9. The method according to any one of claims 1 to 8, characterized in that that the desorption of the adsorber is carried out in two steps, in the first Step a first vacuum pump at a pressure that changes from the purge gas pressure to an intermediate pressure falls, a gas is sucked out of the adsorber, which is used to flush another adsorber is used, and in a second, directly following step, a second vacuum pump at a pressure which drops from the intermediate pressure to the final pressure of the evacuation, the product gas is sucked out of the adsorber. 10. The method according to claim 9, characterized in that the intermediate pressure by a proportion between 0.1 and 0.95, preferably between 0.4 and 0.8, of the difference from the purging gas pressure and the final pressure of the evacuation is above the final pressure, and that the final pressure is between 0.01 and 0.6, preferably between 0.03 and 0.2 bar. 11. The method according to any one of claims 1 to 10, characterized in, that the purging of the adsorber (purging phase) takes place at a pressure which is lower than the pressure during loading (adsorption phase). 12. The method according to claim 11, characterized in that according to loading at a pressure above ambient pressure, preferably above 3 bar the gas flowing off during the pressure reduction (to the purge gas pressure) is discarded becomes (exhaust gas) as long as the more strongly adsorbing (to be recovered) component (s) is (are) present in volume fractions that are below those in the raw gas. 13. The method according to claim 11, characterized in that according to a Loading at a pressure that is above ambient pressure, preferably above 3 bar, the gas flowing off during the pressure reduction (to the purge gas pressure) to build up pressure is used in another adsorber. 14. The method according to claim 11 to 13, characterized in that after loading at a pressure above ambient pressure, preferably above 3 bar, the gas flowing off during the pressure reduction is upstream of a compressor of the raw gas is returned as soon as the strongly adsorbent (s) (to be recovered) Component (s) is (are) present in proportions by volume that are greater than those in the raw gas lie. 15. The method according to any one of claims 11 to 14, characterized in that that the purge gas pressure is reached when the volume fraction of (the) to be obtained Component (s) in the outflowing gas exceeds a predetermined value between the mean volume fraction in the product gas and the volume fraction in the raw gas. 16. The method according to one of claims 1 to 15, characterized in that that each adsorber after the loading with an adsorber, its evacuation (Product gas recovery) is completed, is connected in such a way that gas out the former flows into the evacuated adsorber in cocurrent to the loading direction, until approximately pressure equalization between the two adsorbers has taken place. 17. The method according to any one of claims 1 to 16, characterized in that that each adsorber after flushing with an adsorber, its evacuation (Product gas recovery) is completed, is connected in such a way that gas out the former flows into the evacuated adsorber in cocurrent to the loading direction, until approximately pressure equalization between the two adsorbers has taken place. 18. The method according to any one of claims 1 to 17, characterized in, that each adsorber with a different adsorber, whose evacuation (product gas recovery) is completed, is connected in such a way that gas from the former in cocurrent flows to the direction of loading into the evacuated adsorber until approximately pressure equalization has taken place between the two adsorbers and a direct current voltage step before this pressure equalization is made.