JPS6118418A - Improved recovery of product in pressure swing adsorbing process and system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The objects of the present invention are achieved by implementing relatively short co-current pressure reduction, purge step times and relatively long purge step times between processing cycles in each bed. . Product recovery is thereby enhanced by avoiding the relatively high pressure drop requirements associated with relatively short purge steps such as those performed in conventional well-known PSA processing check cycles.

The inventive PSA process and system, as described above, allows each adsorbent bed in the system to perform higher pressure adsorption and parallelization on a circulating basis to an intermediate pressure level that releases void gas from the product end of the bed. Such conventional PSA techniques are subject to flow down, countercurrent down down to a lower desorption pressure that releases the desorbed gas from the raw end of the bed, purge, and repressurization to the higher adsorption pressure.

As disclosed in the above-mentioned patents, a portion of the void gas released from one bed during its cocurrent depressurization is typically
The pressure between the beds is equalized, either directly or through an external storage tank, through the initially lower pressure bed, usually in one or more pressure equalization steps. Another portion of the void gas is used to provide a purge to the bed undergoing the purge step. For this purpose, it is advantageous to pass the discharged void gas directly from the bed undergoing co-current pressure reduction to the bed to be purged. Instead, the prior art does not route the released void gas directly to another bed, but to an external storage tank, which is typically economically disadvantageous compared to a direct pressure equalization system. A system has been adopted in which wastewater is sent from the floor to the floor where it is to be purged.

In the practice of the invention, a portion of the vented void gas to be used for purging is transferred to the adsorbent bed to be purged at that point during the processing cycle of the entire PSA system, as described in the above-mentioned patents. Deploy directly. However, at the same time the remaining portion of the discharged void gas is introduced into the external surge drum. The gas is then passed as a purge gas from the surge drum to the adsorbent bed to be purged. By performing the co-current pressure reduction and purge application processes on each bed in this way, we have adopted an extremely advantageous processing cycle in which the time for the co-current pressure reduction and purge application processes on each bed is significantly shorter than the purge time on that bed. It will be discovered that it can be done. Relatively short purge times/long purge times obtained in each bed increase product recovery in each bed and in the overall adsorption system.

The invention is a multi-bed psA system having at least four adsorbent beds,
Although it may be advantageously practiced in systems having preferably 5 to 10 adsorbent beds, the invention may also be used in yarns having more beds. It will be appreciated that in such multi-bed systems, the feed gas may be passed through more than one bed at any particular stage of the processing cycle. Thus, in the operation of such multi-bed systems, the feedstock is often passed through at least two beds at any given time. As indicated above in connection with conventional practice and practice of the invention, the PSA
In a multi-bed operation, a pressure equalization step is used in a multi-bed operation in which co-current depressurized gas discharged from one bed at a higher pressure is used to partially repressurize another bed initially at a lower pressure. It is desirable to employ two, three or more. Thus, the present invention can be used in a processing cycle, such as a cycle containing five beds of adsorbent, with two beds in adsorption at any one time, and one pressure equalization step, containing six beds of adsorbent. A cycle with 2 beds in adsorption at any time and 2 pressure equalization steps, with 8 beds of adsorbent and 2 beds in adsorption at any time and 3 pressure equalization steps. It can be used in cycles etc. Those skilled in the art will appreciate that a variety of other PSA systems and systems may be adapted to take advantage of the desired advantages of the invention.

The implementation of the invention may be illustrated by the table below for the five-bed fruit-and-garment mode of the invention.

Surface Bed Number Cycle (521) E In the table, 1 represents an adsorption step at a high adsorption pressure, and ■ represents a co-current step-down equalization between the bed that has completed the adsorption step and the bed that has been purged at a lower desorption pressure. The co-current depressurization of the invention, where E represents a pressurization step, in which a portion of the void gas released from the bed is sent directly to another bed undergoing a purge step, and at the same time the remaining portion of the gas is introduced into an external surge drum; Represents a purge step, D represents a counter-current depressurization step, P represents a purge step at a lower delayering pressure, and R represents repressurization to a higher adsorption pressure. In the illustrated example process,
It will be seen that two of the five beds are in adsorption stages in overlapping sequences at any given time during the cycle. 1
Since two pressure equalization steps are employed, the whole cycle is referred to as (521) pressure in the heading, 5 represents the number of beds, 2 represents the number of beds during adsorption, and 1 represents one pressure equalization step. where E represents co-current pressure reduction, a novelty of the invention in which the purge gas passes directly from one bed to another and simultaneously to an external surge drum. Thus, the 6 and 8 bed systems specifically mentioned above can be similarly converted to (622)E and (823) respectively.
It is called the E-cycle.

In the processing cycle illustrated in the cycle, bed 1
The co-current depressurization, purging step involves passing the discharge void gas directly from the product end of bed 1 to the product end of bed 5 to provide purge gas for the discharge 5 in the purge step after the step. At the same time, the discharged gas from bed 1 is introduced into the selective storage drum. During the countercurrent step down step in bed 1, void gas is passed from the external surge drum to bed 5 for purging. After the countercurrent depressurization step in bed 1, the void gas is passed from the external surge drum back to bed 1 for purging. In an exemplary embodiment, such an external purge gas is used for the initial portion of the purge of bed 1, followed by further purging of bed 1 using the co-current step-down, purge gas directly from bed 2, and then from the external purge drum. Complete the purge of bed 1 with additional purge gas of . The co-current depressurizing, purge imparting gas from bed 1 is thus used to directly purge bed 5, and
The purge gas from bed 5 is used to directly purge bed 1, the purge gas from bed 4 is used to directly purge bed 3, the purge gas from bed 5 is used to directly purge bed 3, and the purge gas from bed 5 is used to directly purge bed 3. Used for direct purging of bed 4. In each case of carrying out the invention, it is also possible to simultaneously pass the co-current depressurizing, purging gas from each bed to an external surge tank, from which the gas is passed directly from said tank, and the purge gas from said separate bed directly to the drain. Before and after passing, pass back to the bed to be purged.

In the illustrated (521)E embodiment of the invention, rather than a conventional cycle that includes applying purge gas directly from one bed to another within a predetermined allowable or desired total cycle time limit, The small pressure drop for each bed allows for the desirable use of long purge times. On the other hand, in conventional practice, providing such long purge times for each bed typically results in longer adsorption times and longer
The total process processing time is required, reducing the production capacity of the system.

Those skilled in the art will appreciate that by using an external equalization feature that provides a purge, the present invention can be used with some degree of adsorption or impurity front breakthrough from each bed, whereas the purge gas is removed from one bed. It will be appreciated that in conventional practices that only involve feeding directly to another bed, the co-current depressurization, purge application step is typically stopped while the impurity front remains in the bed. This feature allows the use of smaller adsorption beds, but in turn requires the use of larger surge drums. In this regard, 1, the external surge drum through which the discharge void gas passes can be an empty drum, allowing the gas to mix freely and turbulently, or alternatively an exlandied tube, e.g. a U-tube structure. The formation is another storage unit in which the gas originally contained in the container and the discharge void gas are passed through the container gently to avoid turbulent mixing of the gas entering the container. It can be made of what it can. Operating in this so-called plug flow mode, the gas from the external surge vessel or drum is used first to increase the effectiveness of the purge stop, when the gas is later used to purge the adsorbent bed. The impurity profile of the gas can be maintained so that the gas can be withdrawn from the external vessel by introducing a less pure gas into the bed followed by a more pure gas.

Surprisingly, the present invention employs a combination of direct and indirect purging steps to improve
It has been discovered that cost and performance advantages can be achieved over those obtained with the highly desirable processes and systems of the patents such as R.R. Thus, the (823)E embodiment of the invention referred to above employs an 8-bed system with cost and performance characteristics essentially equivalent to those obtained with a 10-bed, 7-Deller, etc. system. Similar to the (521)E embodiment, the (622)E embodiment includes the use of a cocurrent step-down, purge step to provide purge gas to an external surge drum while simultaneously directing the purge gas directly to bed 1. Pass from the end to the end 6, from the end 2 to the floor 1, from the end 3 to the floor 2, etc. It will be appreciated that specific processing changes may be incorporated into any embodiment of the invention. A particularly desirable (622)E embodiment includes, for example, a delay period between the first and second co-current pressure-down, purge application steps in each bed treatment cycle. The (622)E embodiment of the present invention has been desirably found to be less expensive and more recoverable than the conventional (522) system.

In practicing the present invention, the (832)E embodiment of the invention not only employs the unique purging features of the present invention, but also employs 8 beds, 3 beds in adsorption at any time, and 2 co-current step-downs.
50 than the corresponding (832) system using a pressure equalization step.
% longer purge time. Here, (8
52) The process and system can be employed with a 90 second co-current pressure reduction, purge application time and a 90 second purge time in each bed. Invented the process and yarn (
By modifying the embodiment of 852)E, the co-current depressurization application time can be reduced to 45 seconds and the purge time can be increased to 135 seconds with essentially unchanged overall cycle time. This example of a cycle with a 50% longer purge time than comparable conventional cycles illustrates the practical and extremely important advantages obtained through the use of the invention. The external surge drum required for the (832)E embodiment of the invention is relatively small, only 30% of the volume of one adsorbent bed. The (852)E embodiment is one of the most effective PSA cycles with a well-balanced time distribution and a more uniform flow rate within the external surge drum.
Give the file.

Those skilled in the art will appreciate that various other changes and modifications may be made in the details of the PSA process and system without departing from the scope of the claimed invention. Although the invention has been specifically described with respect to a 5.6.8 bed system, other systems with more than 7 or 8 bed systems may be employed, and the features of various 28-person processes are discussed herein. It will be understood that any particular cycle or thread may be incorporated to incorporate the particular purging invention disclosed and claimed herein. As with the various embodiments listed above, the void gas that is passed through the external drum can be passed back into the same drum from which it was released, but the void gas that is released from the external drum or container can be passed through the void gas. It will be appreciated that it is within the scope of the present invention to pass the gas through a different bed than the one from which it was released. Also, provide purge gas to one bed through the void gas from the external drum,
On the other hand, it is also within the scope of the invention to continue passing void gas from another bed through the external drum at the same time.

Although not required for purposes of obtaining benefits from the present invention, co-current pressure reduction for each bed, purge application times for urinating, as described in the illustrated example with respect to the (825)E embodiment of the invention. Less than about half the time is usually preferred.

In general applications of the invention, it is easy to ensure that the PSA yarn incorporates various conduits, pulps, and other control features to effect the necessary switching of adsorbent beds from one processing step to the next in an appropriate sequence. be understood.

The present invention employs conventional conduit and control features well known in the art as shown in connection with the patents cited above. For purposes of the present invention, an external surge drum is configured to deliver a portion of the void gas released during the co-current step-down, purge process to the external surge drum while simultaneously directing the remaining portion of the released void gas to a conventional conduit. It will be appreciated that the method may be used in conjunction with direct introduction to the bed to be purged through the means, i.e. conduit and appropriate conventional controls. Similarly, the voids may be used to pass purge gas from the external drum and, if desired, to simultaneously continue passing void gas through the drum, and to perform other desired aspects of specific embodiments falling within the scope of this invention. A means is provided for passing the gas from the drum to the bed to be purged, and a means for passing the feed gas to two or more adsorbent beds at all stages of the processing cycle.

The pressurized gas ink adsorption systems and systems disclosed and claimed herein are advantageously used to selectively adsorb at least one component in a feed gas mixture, thereby controlling the desired product flow. Outflow gas can be separated and purified. For example, carbon dioxide as a selectively adsorptive component in addition to hydrogen, and one or more additional minor components which are normally to be removed as undesired impurities, such as nitrogen, argon, carbon oxides, light saturated and unsaturated hydrocarbons, The present invention can be advantageously used when separating and refining hydrogen present as a main component of a raw material gas mixture containing aromatics, light sulfur compounds, etc. Those skilled in the art will also appreciate that the invention may also be advantageously employed in other desired separations in which at least one component in a feed gas mixture is selectively adsorbed in an adsorption system of the type described herein. will be understood. Separation and purification of oxygen from air, purification of methane from mixtures of carbon dioxide, ammonia, hydrogen sulfide, etc. on methane, or other heavier hydrocarbon gases are examples of other applications of the invention. Any suitable adsorbent material having selectivity of one component of the feed gas mixture over another, e.g. selectivity of impurities over the desired product, generally PEA.
It should be noted that the process, in particular, may be used to implement the present invention. Suitable adsorbents include zeolite molecular sheets, activated carbon, silica gel, activated alumina, and the like.

Zeolite molecular sheep adsorbents are usually desirable for separating and purifying hydrogen contained in mixtures of hydrogen, carbon dioxide, nitrogen, and the like. Further information regarding suitable adsorbents containing the zeophyto molecular sheep can be found in Kyonaga US Pat. No. 3,174,444 and various other patents, such as those listed above.

As indicated above, various changes and modifications may be made in the PSA process and system to which the present invention is directed without departing from the scope of the invention as disclosed herein and as claimed. I can do it. Thus, the method by which the pressure equalization step is carried out, either directly or indirectly, i.e. through an external equalization vessel, the number of such equalizations, the higher the adsorption pressure, i.e. by the feed gas or from the system. The method of repressurizing with a portion of the product effluent stream is not critical to the invention or to obtaining advantages therefrom. In this regard, and although the purge step has been described herein as being performed at a lower desorption pressure, those skilled in the art will appreciate that the purge step is performed after countercurrent pressure reduction to the lower desorption pressure. It will be appreciated that higher pressures than such lower desorption pressures may be used, although this is more common.

The relatively short purge times/long purge times achieved by practicing the present invention increases product recovery and overall efficiency in multi-bed processes and systems.

There are several reasons why product recovery is enhanced; namely, (1) shorter purge application times and longer purge times result in lower pressure drop during the purge step, thereby increasing the (2) Some impurity breakthrough from each bed is allowed by mixing in the external surge drum, increasing recovery as discussed;
(3) Shorter purge application times increase gas velocity during the process, which in turn increases the gas phase. It increases the rate of mass diffusion from to the same phase, making the mass transfer front sharper and thus resulting in higher recovery. In addition, an external surge drum can also allow for additional, or indirect, pressure equalization within a given cycle time, which can lead to higher recovery rates at a given cost or at a given recovery rate. It can be even cheaper. The system can be operated with shorter adsorption times, which reduces the size of the adsorption bed, thereby reducing overall system cost in the practice of the present invention. Also, in an advantageous implementation of the invention, the purging step is no longer coupled to the purging step as in conventional implementations.

In this manner, there is no need to line up purging steps in one bed with beds being purged at the same time intervals during the entire processing cycle.

This introduces the desired flexibility in the control and operation of the PSA system. Also, as part of the overall flexibility of the invention, it is possible to pass the gas released from the bed during the purging process to more than one other bed in the system, while simultaneously passing the gases released from the bed to more than one other bed in the system. It should be noted that it can be passed through. Similarly, gas withdrawn from an external surge drum can be passed through one or more beds to be purged, and a combination of such features can be used to pass void gas directly and indirectly to one or more adsorbent beds at any given time. can be passed through. By making the cost and performance characteristics of the process and system more advantageous compared to those previously obtained in the highly desirable implementation of the process of the Seven Deller et al. patent with fewer adsorbent beds, The invention provides highly desirable processing flexibility and significantly contributes to the advancement of PSA technology in meeting the generation requirements of industrial gas separation and purification operations.

Claims (1)

Claims: 1. Having at least four beds of adsorbent, each bed having, on a circulating basis, adsorption at a higher pressure and co-current depressurization to an intermediate pressure which releases void gas from the bed. , subjected to countercurrent depressurization to a lower desorption pressure, purging, and repressurization to the higher pressure, and passing a portion of the void gases released from one bed first through the lower pressure bed to remove them. In a pressure swing adsorption process for selectively adsorbing at least one component of a feed gas mixture in an adsorption system that provides a gas for purging the bed undergoing the purge step and using another portion of the gas to equalize the pressure between the (a) introduce a portion of the vented void gas used to provide the purge directly into the bed being purged; (b) simultaneously introduce the remaining portion of the vented void gas used to provide the purge into an external surge drum. (c) passing the void gas from said external drum through the beds being purged, thereby reducing the co-current pressure reduction in each bed, the time of the purge application step being significantly shorter than the purge step in each of said beds, and comparing A method as described above, characterized in that a significantly short purge time/long purge time increases the product recovery in each bed and in the entire adsorption system. 2. The method of claim 1, wherein the product gas withdrawn from the system consists of hydrogen and the selectively adsorbed component consists of carbon dioxide. 3. A process according to claim 1, in which the feed gas mixture is passed through 5 to 10 adsorbent beds on a circulating basis. 4. The method of claim 1, wherein the void gas passed from the external drum is passed through the same bed from which it was released in order to purge the bed at a lower desorption pressure. 5. The method of claim 1, wherein the void gas discharged from the external drum is passed through a bed different from the bed from which the void gas was discharged. 6. Passing void gas from the external drum to a bed;
2. The method of claim 1, wherein purge gas is provided while void gas from another bed continues to be passed through the external drum. 7. The method of claim 4, wherein the co-current pressure-down, purge application time for each bed is less than about half the purge time for that bed. 8. The method of claim 7, wherein the feed gas mixture is passed through 5 to 10 adsorbent beds on a circulating basis. 9. The method of claim 8, wherein the product gas withdrawn from the system comprises hydrogen and the selectively adsorbed component comprises carbon dioxide. 10. The method of claim 1, wherein the feed gas is passed through at least two adsorbent beds during all stages of the processing cycle. 11. The method of claim 1, wherein a portion of the discharged void gas used to provide the purge gas is passed directly to more than one bed for direct purging. 12. The method of claim 1 or 11, wherein the void gas passing from the external surge drum is passed through more than one adsorbent bed for indirect purging. 13. having at least four beds of adsorbent for selectively adsorbing at least one gaseous component from the feed gas mixture, the void gas released from each bed being passed on a recirculating basis to the lower pressure bed first; In a pressurized gas ink adsorption system having conduit means for equalizing the pressure therebetween and providing purge gas to the bed receiving the purge at a lower desorption pressure: (a) an external surge drum; (c) means for passing a portion of the discharged void gas through the external surge drum while simultaneously introducing the remaining portion of the discharged void gas directly into the bed being purged; (c) passing the void gas from the external drum into the bed being purged; said system, characterized in that a relatively short purge time/long purge time occurs in each bed of the adsorption system, thereby increasing product recovery. 14. The system of claim 13, wherein the adsorption system consists of 5 to 10 adsorbent beds. 15. Said means for passing void gas from the drum to the bed to be purged is adapted to pass said gas through the same bed from which said gas was released, said bed in order to purge the gas at a lower desorption pressure. 14. The system according to claim 13. 16. The system of claim 13, wherein the means for passing void gas from the drum to the bed to be purged is adapted to pass the gas through a system different from the system from which the gas was released. 17. The system of claim 13 including means for providing one bed purge gas through void gas from said external drum while simultaneously continuing to pass void gas from another bed to said external drum. 18. The system of claim 14 adapted to operate on a recirculating basis so that the co-current pressure reduction in each bed, the purge application time follows less than about half the purge time for that bed. . 19. The system of claim 13 including means for passing the feed gas through two or more adsorbent beds during all stages of the processing cycle in the system. 20. The system of claim 19, wherein the adsorption system consists of 5 to 10 adsorbent beds.