Selective adsorption gas separation process

© Start of patent period: 1977 02 15 Longest possible duration:

© Issued on: 1977 10 10 © inventor:

© dependence:

© Pamphlets considered to delineate the prior art:

OE 339265 - 2 -

Nr.339265

The invention relates to an adiabatic process for separating gas mixtures, in particular air, at superatmospheric pressure in two to four adsorption beds by selectively adsorbing at least one component in a first adsorption bed, discharging the gas freed from this component (s) as product at different pressures, desorbing the selectively adsorbed component (s) by pressure reduction, Purging gas released from the adsorbed component (s) from another adsorbent bed, partially recharging the gas freed from the component (s), equalizing the pressure between the first adsorbent bed and a second adsorbent bed, and further pressure reloading the first one Bed with the hot superatmospheric pressure held gas mixture.

Adiabatic adsorption adsorption processes have long been known for separating gas mixtures with selectively adsorbable components. Such a system is described in US Pat. No. 3,430,418 wherein the (unadsorbed) product is obtained at substantially the feed pressure. At least four separate adsorber beds are required by this known method; these beds are fed parallel to each other. Each of the beds undergoes four cycle steps: (1) adsorption at constant (feed gas) pressure; (2) recovering the white space gas; (3) removal of the adsorbate; and (4) pressure recharge.

Adsorption at constant feed gas pressure is accomplished by passing feed gas through the adsorbent bed while simultaneously withdrawing unadsorbed product from the bed at substantially the pressure of the feed gas. Recovery of the headspace gas is accomplished by depressurizing the bed from the outlet end and the resulting high purity white space gas is used to pressure recharge a second, flushed bed and to rinse a third, relaxed bed. Removal of the adsorbate is achieved by relaxation from the inlet end and rinsing of the bed at low pressure from the outlet to the inlet end with high purity white space gas. The pressure recharge is carried out with a gas from which the component to be adsorbed was completely or largely removed.

In particular, the required gas is obtained in part from a bed by its expansion from the outlet end, ie by white space gas, and partly from another bed during the adsorption step, ie by product gas. The four individual cycle steps are preferably the same in duration, and as previously stated, at least four adsorbent beds are required to allow for a constant flow of the feed gas and product.

In some cases, this process becomes uneconomical due to the cost and complexity of the four-bed plant, although the product is obtained in very high yield and purity.

Compared to a three-bed system, the fourth bed entails a one-third increase in investment and loading, and the increase in the number of valves and ducts required is of the same order of magnitude. In addition, the fourth bed also increases the total bed volume, increasing the cost of adsorbent.

Attempts to apply the known system to three instead of four beds have seriously disrupted gas flow equilibria. This is because at certain moments during the cycle, a large amount of product is available for removal-far more than the average of production-and far more than can be readily used by the consumer.

As an alternative to using the current excess of product, large ballast tanks and product compressors are required to store the excess product gas until a time has come in the cycle when that gas is brought into one of the beds. On the other hand, at other times in a three bed system according to the known method, the total amount of product gas available from the adsorbent beds is insufficient to satisfy even the plant's purge gas and pressure reload gas requirements. Therefore, ballast tanks are again needed to provide the product deficit, both for the needs within the system and for the needs of the consumer.

As the cycle steps are reorganized to make the product flow more uniform, thus avoiding the unevenness of product flow to the consumer, fluctuations and interruptions in the flow of the compressed feed gas into the system occur.

The aforementioned problems, which occur by adapting the known method for a three-bed system, are especially acute in gas separations where the non-selectively adsorbed components of the feed gas are adsorbed to a significant degree in the beds. For example, while nitrogen is preferentially adsorbed by calcium zeolite A at ambient temperature, the non-preferentially adsorbed oxygen is also adsorbed by the same material simultaneously. Under these circumstances, a very large amount of the non-preferentially adsorbed product fraction is loaded onto the adsorbent when pressure-reloading is performed with such product. During the subsequent adsorption step, this adsorbed product is displaced from the adsorbent by the more strongly adsorbed feed gas component. This means that a large amount of adsorbed product is constantly kept within the system.

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When the cycle passes through the steps of recharging and adsorption, the internal

Flow rate of mitadsorbierten product very high and can easily reach three or four times the average discharge rate of the product from the plant.

The object of the invention is to provide an improved process for the separation of gas mixtures by selective adsorption, which allows the same high yield and purity of the product as in the prior art, but with less than four Adsorberbetten manages.

The adiabatic process of the invention for separating gas mixtures at superatmospheric pressure by selectively adsorbing at least one component in a first adsorption bed at higher pressure, venting the component-removed product gas from that bed at various lower pressures, Desorbing the selectively adsorbed component by depressurizing to a lowest pressure and purging with the component-removed gas from another adsorbent bed; followed by partial pressure reloading of the first bed with this component-released gas and pressure equalization between the first adsorbent bed and a second adsorbent bed and further pressurized recharging of the first bed with the gas mixture held at superatmospheric pressure is characterized by that feed gas mixture held in the inlet end of the first bed at superatmospheric pressure and at the same time into the outlet end of the component (s) liberated gas from the outlet end of the second bed, which is initially also at superatmospheric pressure, so that both End-to-end recharge occurs until the gas pressures in the first and second beds are substantially equal, and thereafter stopping the supply of the gas freed from the component (s) from the second bed to the first bed, further feed gas mixture is introduced into the inlet end of the first bed, thereby further charging to a pressure above the equalizing pressure of the previous step is reached until the distance of the adsorption front of the component (s) to be removed from the inlet end within the adsorption bed has reached a certain desired value, and thereafter removing gas released from the outlet end of the charged first bed from the component (s) and a portion thereof for purging the component (s) from the second adsorbent bed, or another optional adsorption bed, another portion for recharging another Adsorption bed, which has previously been cleaned of the (the) component (s), and another part is taken as a product, whereupon this sequence of steps is repeated cyclically in the existing adsorption beds.

Fig.l shows a schematic flow diagram of an inventive arrangement with three adsorption beds; Fig. 2 indicates a timing program for the various stages of this embodiment of the invention, which may be carried out with the arrangement shown in Fig. 1; Fig. 3 shows another timing program similar to Fig. 2, but using two pressure equalizing steps; Fig. 4 shows a schematic flow diagram of an embodiment with two adsorption beds; Fig. 5 illustrates a timing program for the various process steps suitable for the embodiment of Fig. 4; Fig. 6 is a schematic flow diagram of a four adsorption bed embodiment; and FIG. 7 illustrates a timing program for the method steps of the embodiment of FIG.

From the above summary it can be seen that a substantial portion of the component-removed gas is released from the adsorbent bed during its expansion from the highest, super-atmospheric pressure of the process to a lower, above-purge pressure. The discharge of the component-free gas from the outlet end of the bed is due to two processes:

a) by adsorption of the one component within the adsorption bed from the inlet to the adsorption front, and

b) by displacement of non-preferentially adsorbed component from the non-loaded bed in front of the adsorption front, ie between adsorption front and Bettauslaßende.

The feed gas mixture can flow to the adsorption front in bed as feed gas mixture is fed to the inlet end of the bed and at the same time the deoxygenated gas is removed from the outlet end of the bed. Alternatively, the gas mixture may already be in bed behind the adsorption front and flow to the adsorption front as the gas volume in the bed expands as the depleted of a component gas is removed. The displacement of non-preferentially adsorbed component from the unloaded bed may, on the one hand, be the result of advancing the adsorption front towards the outlet end of the bed while the one component is adsorbed in the bed, or may be the result of the volume expansion of the non-preferentially adsorbed component in the bed which occurs in the removal of the component-removed gas from the bed.

For some gas mixtures, eg, air, in which the non-preferentially adsorbed component is adsorbed to the bed to a considerable extent, the non-preferred component displaced from the unloaded part of the bed can be the predominant part. For other gas mixtures, eg hydrogen or helium-containing feed gases, the non-preferentially adsorbed component is only slightly adsorbed, and the non-preferentially adsorbed component from the unloaded portion of the bed is largely obtained by expansion of the unadsorbed gas.

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The component-removed gas comprises the product gas delivered to the consumer and the gas used in the interior of the system for pressure equalization, pressure reloading and purging. Since the product is formed by the component-released gas, which is at least in part at a pressure below the highest superatmospheric pressure of the process, it is best suited for those cases where the product gas is needed at a pressure lower than the feed gas pressure or such a low pressure of the product gas is annoying. For example, oxygen is increasingly used in place of air for the treatment of wastewater, and the oxygen is introduced into the aeration chamber at a little over-atmospheric pressure. The process according to the invention can advantageously be used for separating air, after which the oxygen product with lower than the feed gas pressure is introduced directly into the aeration chamber of a sewage treatment plant.

As noted above, the present process involves partially pressurized recharging of the purified bed by co-introduction of feed gas mixture into the inlet end and from the deoxygenated product-purity gas into the outlet end of the bed. The use of high purity component-released partial recharge gas has several significant advantages. First, the flow of high purity gas in the opposite direction to the feed gas stream cleans the bed's outlet end and acts as an additional purge gas for that critical zone; secondly, at low pressure during pressure recharge, the front of the adsorbate obtained solely with feed gas would become slightly diffused. The flow of highly pure adsorbate-free gas in the opposite direction facilitates the formation of a sharp front so that no premature adsorbate breakthrough occurs; third, the use of high purity gas facilitates pressure recharge without overcharging the bed with the preferentially adsorbed component of the feed gas. Thus, then the entire supplied feed gas mixture can be separated to obtain a product gas of the desired purity.

In a process where the pressure of the product gas is equal to the pressure of the feed gas, as described in US Pat. No. 3,430,418, the gas migration front first builds up at the inlet end and then gradually travels towards the outlet end. It might be expected that this could be different in the present process because of the significantly different process procedure. However, it has been found that the migration front remains sharp and gradually migrates toward the outlet end, although the adsorbate loading is concurrent with a steady increase in pressure in the bed.

For an adsorbent bed of a given size, the amount of feed gas mixture supplied compared to the amount of component-released gas is such that upon completion of pressure reloading to a predetermined pressure and loading with a component, a defined length of clean, unconsumed bed immediately precedes the outlet end remains. This remaining part of the bed is used in the subsequent expansion steps to separate one component of the gas in the recharged bed. The gas discharged from the bed during these steps contains the non-selectively adsorbed (or non-adsorbable) component (s) of the feed gas mixture. Part of this vented gas forms the previously mentioned component-released gas for the partially pressurized recharge of a previously flushed bed until pressure equalization. Since the component-released gas is not available at the feed gas pressure, only the low-pressure phase of pressure-reloading can be performed with the component-released gas. The further or final phase of pressure reloading can only be done with feed gas.

The process according to the invention is characterized in that at least the predominant part of the feed gas is introduced while increasing the pressure in the adsorption bed. The pressure in the bed increases because the instantaneous rate of gas supply minus the gas removal exceeds the adsorption capacity of the bed. The method thus differs from those in which at least the major part of the feed gas is supplied at a uniform pressure during an adsorption step, ie the total rate of gas feed minus gas removal is equal to the adsorption capacity of the bed.

Reference will now be made to the drawings: Figure 1 shows three adsorption beds, -Α, B and

C--, which are parallel to each other between a branched supply line -11- for feed gas mixture, a branched line -12- for removing the component-freed gas, a branched

Line -13- are arranged for purge gas and a branched line - 14- to the waste.

Automatic valves -15A, 15B and 15C- carry feed gas to the first bed -A-, the second bed -B- and the third bed -C-, respectively. Automatic valves -16A, 16B and 16C- deliver the gas from these beds to branch line -12--. The purge gas line -13- connects the component-released gas line -12- to the outlet end of the three beds, and the automatic valves -17A, 17B, and 17C- supply purge gas to the -Α, B, and C- beds the opposite direction to that of the feed gas. The automatic valves -18A, 18B and 18C- connect the branch line -14- to the waste with the inlet end of the respective beds for removal of flash gas and purge gas from the inlet end. The valves -19A, 19B and 19C- at the outlet end upstream of the

Product valves - 16A, 16B and 16C - are manual throttle valves and restrict the flow of

Pressure equalization gas.

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Fig. 2 illustrates a time sequence suitable for a system according to Fig. 1, using six individual steps, each of which involves the beginning and / or the termination of different gas flows. 2, the flows flowing into or out of the various beds of the system of FIG. 1 are shown and correspond to the flows in branch lines -11 and 12-. The feed gas branch line -11- communicates horizontally with each of the three adsorbent beds, and the latter in turn horizontally communicate with the branch line -12- for discharging component-released gas.

The beds in which the pressure reload and purge steps, which use a portion of the component-removed gas, communicate horizontally with the beds through which the steps through which this component-released gas passes is provided, for example, with the relaxation from the outlet end ago or with the pressure equalization step. In the figure, all running between the beds streams are drawn.

It can be seen from Figure 2 that at each moment one of the adsorption beds releases a component-freed product to the branched gas-free gas passageway: during the first 40 sec bed -C-, in the period between 40 and 50 sec bed -A-, in the period between 50 and 80 sec bed -A- and then between 80 and 120 sec bed -B-. Accordingly, the delivery of product gas to the consumer is continuous.

In this particular cycle, for each individual bed, pressure recharge accounts for 1/3 of the total cycle, product flow and concomitant pressure equalization or relaxation in the direction of product flow accounts for 1/3, and relaxation in the opposite direction to product flow and Flushing make up the remaining third. The gas used for pressure equalization and relaxation in the direction of product flow is indicated in the drawings by horizontal lines. Each pressure equalizing step is connected horizontally with pressure reloading in another bed which has already been rinsed, and each step of relaxing in the direction of product flow is horizontal with a rinsing step in another bed which has been relaxed immediately in the opposite direction to the product flow Connection.

Each step in the cycle of bed -A- is described below and related to the parts of Fig.l which are important in cycle changes. For example, pressures used for a process for separating air by calcium zeolite A are also mentioned.

Time 0 to 15 sec: Bed -A- is pressure-charged, bed -B- is depressurised against the direction of product flow and bed -C- goes through the step of pressure equalization. Valves -15A and 16A- are open and valves -17A and 18A- are closed. Feed air is supplied to the bed -A- through the feed branch line -11- from the inlet end and component-released gas through the branch line -12- simultaneously to the bed from the outlet end. The latter is taken from bed -C- through the throttle valve -19C- and the valve -16C- and fed to the bed -A- through the valve -16A and the throttle valve -19A-. The bed -C- is depressurized in the direction of product flow during this time and the gas flow is continued until the pressure between the bed -A- and the bed -C- is substantially equalized and is about 1.35 atm. During this time, the flow of balance gas is fast, while the flow of feed gas from the compressor -20- is restricted, so that most of the gas for pressure reloading of bed -A- from 0 to 1.33 atü from that of a component liberated gas exists, for example in the case of air separation 72%. During this time another part of the gas coming from bed -C- is supplied as product to branch line -12-.

Time 15 to 40 sec: The valve -16A- is now closed, and only the flow of feed air in bed -A- is continued until a final pressure of 2.8 atm is reached. This completes the pressurized recharging of bed -A-. During recharging, a nitrogen adsorption front forms near the inlet end of bed -A- and travels slowly towards the outlet end. The amount of feed gas compared to the amount of component-relieved gas for pressure recharge is such that upon completion of the recharge, a predetermined length of unloaded bed remains between the adsorption front and the outlet end.

Time 40-55 sec: The pressure equalization step for bed -A- is initiated by closing valve -15A- and opening valves -16A and 16B- so that the bed is depressurized by removing G as from the outlet end. This gas flows through the unloaded part of the bed where the nitrogen component is adsorbed and the nitrogen-freed gas is used in two parts. Oxygen product gas flows through the check valve -21- in the branch line -12- to the consumer line downstream of the valve -21- at a rate suitable to maintain a desired low pressure, eg, 0.21 atm, in the consumer line , The remainder and most of the nitrogen-removed gas flows through valves -16B and 19B- to the outlet end of bed -B- to its partial pressurized recharging. Bed -B- was previously purged to remove the nitrogen adsorbate and is initially at the lowest pressure of the - 6 -

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Systems, ie at about atmospheric pressure. This flow of component-freed gas from bed -A- to bed -B- is continued for about 15 seconds until the two beds are at substantially the same pressure, eg at 1.33 atm.

Time 55-80 sec. Further nitrogen-removed gas is withdrawn from the outlet end of bed -A- to further depressurize this bed, part of which is directed to the outlet end of bed -C- by closing valve 16B- and the automatic valve -17C- is opened in the purge gas line so that the nitrogen adsorbate is flushed out at just over 1 atm. Valves -23 and 24- reduce the pressure of the purge gas to substantially 1 atm and further maintain the purge gas flow rate constant. This, in turn, keeps the total amount of purge gas constant since the purge step is preferably for a fixed period of time. The flow rate is maintained at a constant value by regulating the valve -23-, which maintains the pressure between the two valves -23 and 24- constant. The gas to be discarded from the inlet end of bed -C- flows through the automatic valve -18C- into the line -14- to the waste and is discharged through the automatic valve -25-. This latter valve is more of a flow restricting arrangement than a barrier. In the "closed" state, it restricts the flow in branch line -14-, which reduces the rate of expansion to a level at which no adsorbent particle wear occurs. For purge gas delivery, the valve is open to release the restriction as far as the flow is already restricted by the valve system -23, 24-. Another part of the nitrogen-liberated gas from bed -A- is taken as an oxygen product. During this step, the pressure in bed -A- and branch line -12- continues to decrease until it is about 0.45 atm, which is the case after another 25 sec (80 sec in the cycle or 2/3 of the total cycle) , The lowest pressure for the relaxation proceeding in the direction of product flow, eg 0.45 atm, should be maintained because the pressure is related to the possible breakthrough of the adsorption front at the outlet end of the bed. This completes the production phase for bed -A-.

Time 80 to 95 sec: In bed -A- now begins the discharge (desorption) of the adsorbed nitrogen by closing the valves -16A and 17C- and opening the valve -18A-. Additional gas at a pressure of 0.45 atm is removed from the inlet end of bed -A- to relax against the direction of product flow through branch line -14 and outlet valve -25-. This valve -25- is "closed" in this step to allow said restriction and to prevent excessive bed speed. This step takes place at essentially 1 atm in about 15 seconds.

Time 95 to 120 sec: The bed -A - is rinsed of remaining adsorbed nitrogen by opening the valves -17A and 25-. Additional nitrogen-removed gas flows from the outlet end of the bed - B- through branch line -12-, through valves -23 and 24- and purge gas line -13-, then through valve -17A- to the outlet end of bed -A -. The nitrogen-containing purge gas exiting through the inlet end of bed -A- flows through valve -18A- and is vented through valve -25-. Rinsing is continued for 25 seconds, after which the entire cycle is completed. Bed -A- is now ready for the pressure recharging in the manner already described.

Beds -B and C- are successively passed through the steps indicated, with bed

- B - enters the step of simultaneous pressure reloading with feed gas mixture and the gas freed of a component when in step -A- the step of pressure equalization takes place (in the time between 40 and 55 sec). Bed -C- enters the step of simultaneous pressure reloading with feed gas and gas released from a component when in bed -A- the relaxation proceeding counter to the direction of product flow takes place (time interval) of 80 to 95 sec). The necessary changes to the valves can be taken from Figs.l and 2 and the above description of the cycle sequence. A cycle control system is needed to effect and coordinate these valve position changes. For example, the controller may receive a signal from a pressure indicator in the feed gas line -11- behind the compressor -20-.

It should be noted that changes in the time program of Figure 2 are possible. For example, the duration of the purge step need not be exactly the same as that of the concomitant release in the direction of product flow, thereby providing the purge gas. The rinsing step in bed -A- can be terminated somewhat earlier than the product flow relaxation in bed -B-, and bed -A- can be isolated for the short time period before the pressure recharge begins. Accordingly, all of the bed-B- gas produced during depressurization in the direction of product flow is released as product during isolation of bed -A-, and no gas from bed B is internally reused during this time.

3 shows a preferred embodiment of a three-bed system, which can be carried out with the device according to Fig.l. The scheme of Figure 2 is modified to include two pressure equalizing steps during the

Relaxation of each bed instead of just a pressure equalization step. This allows a higher one

Product yield while maintaining the same purity of the product. A stepwise comparison of Figure 3 with

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-7Fig.l (eg for bed -A-) shows that the simultaneous pressure reloading with feed gas mixture and the gas released from a component is of the same duration (0 to 15 sec). Also, the total duration of further pressure reloading with feed gas to the first superatmospheric pressure is the same (15-35 and 35-40 sec). The first stage of pressure equalization of Fig. 3 is similar to the single pressure equalization in Fig. 2 (40 to 55 sec) but is continued to a pressure of 1.61 (vs. 1.33) atm. However, the relaxation in the direction of the product flow according to FIG. 3 is shorter by 5 sec than in FIG. 2, so that the final pressure in bed -A- is about 0.77 atm (compared to 0.45 atm).

During the second stage of the pressure equalization step (75 to 80 sec), more nitrogen-released gas is vented from the outlet end of bed -A- and passed to the outlet end of bed -C-. The valve -18C-- is closed, so that the bed -C- is partially recharged pressure. This flow is continued until the gas pressures in beds -A and C- are substantially equal. This is the case after about 5 seconds and at 0.35 atm.

The relaxation running counter to the direction of the product flow is of the same duration (80 to 95 sec) according to FIGS. 2 and 3, but the purging step according to FIG. 3 is shorter by 5 sec (95 to 115 sec instead of 95 to 120 sec). In the last 5 seconds of the process, the purged bed is partially pressurized by feeding the nitrogen-freed gas from the outlet end of bed E to the outlet end of bed A until the two beds are at the same pressure of about 0.35 atm , which represents the second stage of the pressure equalization step of bed -B-.

The advantages of the invention are illustrated below by a series of experiments carried out using a three-bed embodiment according to FIG. 1 with a time program according to FIGS. 2 and 3.

Experiment A: Each of three adsorbent beds having an inner diameter of 66 cm and a length of 254 cm was loaded with 5.88 kg of 0.758 cm calcium zeolite Α particles. Air was compressed to 3.85 atm and fed at an average rate of 172,000 1 / hr to the system, which was at atmospheric pressure and 20 ° C, the gas not previously treated, ie without drying and without removal of CO₂, Each bed was pressure charged by simultaneous introduction of compressed air and nitrogen-free gas (oxygen) to a balance pressure of about 2.38 atm (2.45 atm in the dispensing bed and 2.31 atm in the receiving bed). The final recharging with compressed air continued to the final pressure of 3.85 atm. In the next step, the fully charged bed was equilibrated with simultaneous delivery of product to about 2.38 atm. Thereafter, the bed was further relaxed in the direction of product flow to a pressure of about 1.5 atm, while at the same time delivering purge gas to another bed and product to the consumer. The bed was then relaxed against the direction of product flow to about 1.12 atm and purged at that pressure against the direction of product flow.

The oxygen product was supplied at a rate of 21050 1 / h at a pressure of 1.4 atm and with a purity of 90.0%. The yield was 53% over the amount of oxygen in the feed gas. This yield is much higher than using a prior art four-bed system, and investment in adsorbent bed and piping equipment is reduced by about a quarter.

Experiment B: The same system was used as in Experiment A, but the pressure equalization was made in two stages as shown in FIG. The compressed air with a pressure of 38.5 atm was fed to the system at an average rate of 182500 1 / h without pretreatment. Each bed was first pressurized with a second bed to a pressure of about 1.4 atm, then pressure equalized with the third bed and concurrent introduction of feed gas to a higher pressure of about 2.66 atm, and finally pressure alone to pressurize charged by 3.85 atm. The pressure was then first balanced with a second bed at about 2.66 atm while simultaneously delivering oxygen product. Thereafter, the bed was expanded in the direction of product flow to provide third bed sweep and further product with a final pressure of 1.78 atm. After the subsequent second pressure equalization step with the third bed and simultaneous delivery of product oxygen, the final pressure was 1.4 atm. The bed was then depressurized, counter to the direction of product flow, to a scavenging pressure of 1.09 atm and purged with nitrogen-free gas (oxygen) from the second bed. Oxygen product was supplied at a rate of 21100 l / h at 1.4 atm and with a purity of 90% of the oxygen. The oxygen yield was 55.5% of the amount present in the feed gas. This yield is comparable to that obtained using a four-bed pressure equalization system in two steps according to U.S. Patent No. 3,564,816.

The invention may also be used to advantage for a system with only two beds, and gives substantially higher product purity and yield than known two-bed systems, although the results in terms of product yield are less compared to the triple-bed systems of this invention. However, if the required space and weight are the major issues, a two bed design may be preferred.

4 shows two adsorption beds -A and B-, which are arranged parallel to each other, with lines - 8 -

No. 3,392,665 and valves numbered according to the parts of the same function in Fig.l. Fig. 5 illustrates a timing for the arrangement of Fig. 4, using the same six individual process steps as in the embodiment with three beds, but with individual modifications, which will be described in detail below. Each step in the bed -B- cycle will be discussed below and related to those components of Fig. 4 that come into play during the cycle changes. The pressures used to separate air using calcium zeolite A as the adsorbent are exemplified.

Time 0 to 15 sec: Bed -B - is recharged by pressure and bed -A- goes through one

Pressure equalization with the valves - 15B, 16A and 16B - open and valves -17B and 18B- closed. The flow is continued until the pressure in both beds is about the same and at 1.33 atm, during which time another portion of the gas discharged from bed -A- is added as product to branch line 12-. This step is identical to the corresponding step of FIG.

Time 15 to 30 sec: The valve -16B- is now closed, and only the supply of feed air to bed -B- is continued for further 15 seconds for further pressurized recharging until a pressure of about 2.1 atm is reached. During this time, bed -A- is relaxed in the direction of product flow by passing vented gas from the outlet end through valves -16A and 19A- to product line -12-. This is continued until the nitrogen adsorption front has migrated close to the outlet end and threatens breakthrough, the final pressure in bed -A- being about 0.45 atm.

Time 30 to 35 sec: Since the bed -A- has been relieved to its minimum production pressure in the direction of product flow, it can no longer deliver product to the consumer and the valve

--16A - closes. In order not to interrupt the product flow, during the remainder of the step, pressure-reloading of bed -B- to the highest pressure of the feed mixture in line -11- of, for example, 2.8 atm. Of product from bed -B- must be withdrawn. Accordingly, that opens

Valve -16B - again, and product gas flows to branch line -12- for product. At the same time, the valve -18A-- opens, and the valve -25- to the waste closes for the counter to the direction of the

Product flow extending relaxation of bed -A-.

The described simultaneous supply of feed gas for pressure reloading and removal of product gas is the subject of a non-prior art proposal. However, these steps can be considered as a single step in the process of the invention.

Time 5 to 60 sec: The pressurized recharging of bed -B- with compressed feed air is continued until a final pressure of 2.8 atm is reached. During this 25 sec, however, only a portion of the gas taken from the outlet end of bed -B- is delivered to the consumer. Another part is directed to the bed -A-, which is relaxed against the direction of product flow, for flushing against the direction of product flow by opening valves -17A and 25-. Product quality gas then flows through valves -23, 24 and 17A- to the outlet end of bed -A- for purging. While

Bed -A- is purged, the influx of feed gas to bed -B - is much larger than that

Speed ​​at which product gas is withdrawn from the outlet end. The pressure in bed -B- gradually increases until the final pressure of 2.8 atm is reached.

Time 60 to 75 sec: The pressure equalization step for bed -B- and the pressure reload of

Bed -A- are started while bed - B- is still giving product. This is done by opening the

Valve -16A-- and closing the valve -15B - achieved. This step is analogous to the second step from bed -A- to FIG. 2, which runs between 40 and sec. The beds -A and B- go through a pressure equalization at about 1.33 atm.

Time 75-90 sec: Bed B - is next expanded in the direction of product flow until a pressure of about 0.45 atm is reached, with all the gas discharged as product, and the pressure

Recharging the bed - A - is maintained only by feeding feed gas into the inlet end.

This requires closing valve -16A-.

Time 90-95 sec: Bed -B- is depressurized towards the direction of product flow to about 1 atm by closing valves -16B and 25- and opening valve -18B-. The valve

- 16A- is used for the flow of the component-free gas as product from the outlet end of

Bed - A- to branch line - 12- open.

Time 95-120 sec: Bed -B- is purged with bed-a- solvent-freed gas, contrary to the direction of product flow, and bed -A- is simultaneously recharged by feed gas to a final pressure of 2.8 atm. This is achieved by opening valves -17B and 25-.

At the end of this step, the valves -17B and 18B- are closed, and the bed -B- is ready for the beginning of the described sequence of steps.

It has already been pointed out that a significant advance of the invention is that it eliminates the need for at least one adsorption bed and associated valves and conduits while achieving high product purity and yield, and while the product is uniform and uninterrupted. However, the method according to the invention can also be applied to four - 9 -

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Adsorption beds are applied, in which case the still achievable out of the reduced equipment costs benefits can be realized. The process obviates the usual adsorption step of feeding all of the feed gas at the maximum pressure by feeding this gas during the pressure reloading of each individual bed. The compressor for the feed gas releases the gas over a pressure range ranging from the pressure of the purge gas to the maximum pressure, so that the average feed pressure is substantially below the maximum pressure and power is saved. Another advantage of the four-bed embodiment is that the product is delivered to the consumer at a higher pressure than a two- or three-bed system. While eg In the three bed air separation test described, the oxygen product is delivered at a pressure of 0.35 atm, the optimum pressure for a four bed system of Figures 6 and 7 is about 1.05 atm.

A comparison of Figures 6 and 7 with the corresponding representations for two and three bed system shows that also the four-bed system goes through the said general steps. Gas mixture is simultaneously introduced through the feed end and deoxygenated gas through the outlet end of each partial pressure recharge bed until the bed is at the same pressure as in the product gas dispensing bed, after which the partially recharged bed is further charged with feed gas mixture alone. The said product gas releasing bed also simultaneously delivers product gas to the consumer. The fully recharged bed is then depressurized from its outlet end to provide component-released gas which is used as: 1) purge gas, 2) recharge gas, and 3) product gas.

A significant difference between the four-bed embodiment and the two- and three-bed systems described is that the relaxation in the direction of the product stream is interrupted for a short time until the relaxation of another bed, contrary to the direction of product flow, is completed, in the embodiment with two beds, the "other" bed is at the same time the so-called "second" bed. When this step has elapsed, the remaining gas used for the product flow relaxation is used to purge the bed, which is relaxed against the direction of product flow.

Each step in the cycle of bed -A- of Fig. 7 will be explained below and related to the device parts shown in Fig. 6, which are involved in a cycle change, in addition also exemplified in the separation of air by calcium -Zeolith A used as an adsorbent pressures.

Time 0 to 15 sec: Bed -A- is partially relieved of pressure by pressure equalization with bed -B- at about 1.33 atm and concurrently with feed gas mixture. Valves -17A and 18A- are closed, valves -15A and 16A- are open.

Time 15-60 sec: Bed -A- is further charged to the highest feed gas pressure by closing valve -16A- and introducing only feed gas from the inlet end until the bed reaches a pressure of 2.8 atm after 60 sec of total cycle time reached.

Time 60-75 sec: bed -A- and bed -C- are subjected to pressure equalization and at the same time product gas is withdrawn from bed -A- until a pressure of about 1.33 atm is reached in both beds. This is achieved by closing valve -15A- and opening valves -16A and 16C-.

Time 75-120 sec. In the first step of the product flow, all of the gas is removed from bed -A- as product by closing valve -16C- so that the pressure in the bed is about 1.19 atm sec cycle time has fallen.

Time 120 to 135 sec: The bed is isolated by closing valve -16A- for 15 sec.

Time 135 to 180 sec: In the second step of the product -Album flattening of bed -A- the valves -17A and 17B- are opened and the component-freed gas flows to the outlet end of bed -B- for purging against the direction of product flow. When a present pressure of about 0.45 atm in bed -A- is measured by pressure switch -30A-, valve -17A- is closed to complete the purge step after about 180 sec of total cycle time.

Time 180 to 195 sec: Bed -A- is depressurized at a pressure of about 1 atm counter to the direction of product flow by opening valve -18A-- and closing valve -25-.

Time 195 to 240 sec. The component-released gas from bed -C- is removed during its second (lower) relaxation step in the direction of the product flow to bed-A-, counter to the direction of product flow in bed -A-. Valves -17A, 17C and 25- are open, and the adsorbent purge gas withdrawn from the inlet end of bed -A- flows into the atmosphere through valve -18A and valve -25-. The purge continues until the pressure switch -30C- detects a drop in pressure to 0.45 atm. Finally, valves -17A and 18A- close and valves -15A and 16A- open to restart the pressurized recharging of bed -A-.

Although individual embodiments have been described in detail herein, variations are possible which are also within the scope of the invention.

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For example, although calcium zeolite -A- was specifically named as an adsorbent, the

Choice of a suitable adsorbent of factors such as the composition of the feed gas and is not

Subject of the invention. Other well-known selective adsorbents include activated carbon and silica gel.

Further, the component-released gas has been described as a product gas, but in some cases it may be described as a product gas

Be desirable to isolate the adsorbate as a product.

The invention has been described in detail for the separation of air. It is also possible to use other gas mixtures which contain, for example, hydrogen as not preferentially adsorbed gas and various impurities as selectively adsorbable components. These include, for example, light hydrocarbons, CO, CO₂, NH₃, H₂S, argon and water. Hydrogen-rich feed gases containing at least one of these adsorbable components include: exhaust gas from catalytic reforming, recycled purge gas from methanol synthesis, dissociated ammonia and overhead of demethanizing, steam reformed hydrocarbons, purge gas recirculated in the ammonia synthesis, hydrogen electrolytically obtained, and Hydrogen from mercury cells. The invention is also useful for the separation of any or all of the abovementioned adsorbable compounds from gas mixtures in which nitrogen or helium forms the main component.