CA1136065A - Pressure swing adsorption process and system for gas separation - Google Patents
Pressure swing adsorption process and system for gas separationInfo
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- CA1136065A CA1136065A CA000378988A CA378988A CA1136065A CA 1136065 A CA1136065 A CA 1136065A CA 000378988 A CA000378988 A CA 000378988A CA 378988 A CA378988 A CA 378988A CA 1136065 A CA1136065 A CA 1136065A
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Abstract
PRESSURE SWING ADSORPTION PROCESS
AND SYSTEM FOR GAS SEPARATION
ABSTRACT OF THE DISCLOSURE
A pressure swing adsorption process and system including at least two adsorption beds and a segregated storage adsorp-tion bed which is isolated from direct communication with the feed gas stream. During the process the pressures in the adsorption beds are equalized from the feed ends theroof at the end of adsorption in one of the beds and after pressuriza-tion of the other bed. The segregated storage adsorption bed is pressure equalized with a depressurizing adsorption bed and then after purging of the bed the segregated storage adsorp-tion bed is equalized with that adsorption bed during repressurizing thereof. A pair of flow control valves are connected in a gas flow path connected to the outlet of the adsorption beds, each valve being located adjacent a corres-ponding one of the beds and allowing unrestricted flow away from the corresponding bed and controlled flow toward that bed.
A reservoir connected to the system output conduit stores product gas for use during a system malfunction of for aug-menting system function.
AND SYSTEM FOR GAS SEPARATION
ABSTRACT OF THE DISCLOSURE
A pressure swing adsorption process and system including at least two adsorption beds and a segregated storage adsorp-tion bed which is isolated from direct communication with the feed gas stream. During the process the pressures in the adsorption beds are equalized from the feed ends theroof at the end of adsorption in one of the beds and after pressuriza-tion of the other bed. The segregated storage adsorption bed is pressure equalized with a depressurizing adsorption bed and then after purging of the bed the segregated storage adsorp-tion bed is equalized with that adsorption bed during repressurizing thereof. A pair of flow control valves are connected in a gas flow path connected to the outlet of the adsorption beds, each valve being located adjacent a corres-ponding one of the beds and allowing unrestricted flow away from the corresponding bed and controlled flow toward that bed.
A reservoir connected to the system output conduit stores product gas for use during a system malfunction of for aug-menting system function.
Description
il3~065 . . .
BACKGROUND ~F THE INVENTION
This ;nvention relates to the art of separation of gas mixtures, and more partîcularly to a new and improved process and system for separating gas mixtures by pressure swing adsorption.
One area of use of the present invention is in separating air to provide a product stream of high purity oxygen, although the principles of the present invention can be variously applied.
In basic pressure swing adsorption processes and systems for separating air, adsorption is carried out at a high pressure and desorption is carried out at a low pressure. Compressed air is introduced into a fixed bed of adsorbent material and nitrogen is then preferentially adsorbed to produce oxygen rich gas product.
When the adsorption bed is about saturated, the bed pressure is reduced to desorb nitrogen from the adsorbent material and re-generate the adsorption capacity. To increase the efficiency of regeneration, a purge by some of the product or an intermediate process stream often is used. To facilitate continuous operation, two or more adsorption beds are employed so that while one bed performs adsorption the other bed undergoes regeneration.
In the design and operation of pressure swing adsorption processes and systems, it would be highly desirable to provide >~ ~
.
~ 1~36(~65 maximum utilization of adsorbent material in the adsorption beds,reduction in energy requirements for operation of the system, a substantially constant degree of product purity, and reduction in adsorbent material requirements while maintaining a high degree of product purity, along with improved efficiency and reliability.
SI~MARY OF THE INVENTION
It is, therefore, a primary object of this invention to provide a new and improved process and system for separation and fractionat;on of gas mixtures by pressure swing adsorption.
It is a further object of this invention to provide such a process and system characterized by maximum utilization of adsorbent material in the adsorption beds.
It is a further object of this invention to provide such a process and system having reduced energy requirements for operation.
It is a further object of this invention to provide such a process and system which is balanced and yields a substantially constant de~ree of product purity.
It is a further object of this invention to provide such a process and system which has reduced adsorbant material re~uirements along with a high degree of product purity.
il3~65 It is a further object of this invention to provide such a ~rocess and system which maintains a reserve supply of product for use during a system malfunction or in augmenting system functions.
It is a further object of this invention to provide such a process and system which is reliable, efficient and economical.
In general terms and in one aspect thereof, the present invention provides a pressure swing adsorption process using at least one adsorption bed having a gas inlet and a gas outlet and at least one segregated storage adsorption bed, said process comprising the steps of flowing a feed gas mixture into said inlet of said at least one adsorption bed to adsorb at least one gas of said mixture within said bed while flowing the remainder of said gas mixture out of said bed outlet as product gas until said adsorption bed is about saturated with said one gas; flowing product gas fro~ said bed outlet into said segregated storage adsorption bed by depressurising said at least one adsorption bed into said segregated storage adsorption bed until a mass transfer zone within said adsorption bed moves into said segregated storage adsorption bed, closing the flow path between said adsorption bed and said segregated storage adsorption bed; purging said one bed in a countercurrent direction; and flowing gas from said segregated storage adsorption bed back into said adsorption bed by depressurising said segregated storage adsorption bed and repressurising said purged at least one adsorption bed.
In another aspect of the present invention, a pressure swing adsorption process using at least one adsorption bed having a gas inlet and a gas outlet and at least one segregated storage zone, comprising the steps of 11361~65 flowing a feed gas mixture into said bed inlet to adsorb at least one gas of said mixture within said bed while flowing the remainder of said gas mixture out of said bed outlet as product gas until said ~ed is about saturated with said one gas, flowing gas from said bed outlet into said zone by depressurising said bed into said zone until the mass transfer front within said bed moves into said zone, closing the flow path between said bed and said zone, purging said one bed in a counter-current direction, flowing gas from said zone back into said bed by depxessurising said zone and repressurising said purged one bed, using at least two adsorption beds each having a gas inlet, a gas outlet, and conduit means connecting said gas outlets to product outlet conduit means, said process comprising the additional steps of alternately and sequentially flowing said feed gas mixture into the inlet of one of said beds to adsorb at least one gas in said mixture in said one bed and flowing the remainder of the mixture out of said one bed outlet as said product gas until said one bed is about saturated within said one gas, purginga second bed while performing the producing ste in said one bed, controlling the repetition of said steps to permit their alternate and sequential repetition to stop only at an optimum point in the process, and wherein said optimum point is a point in time immediately after the process has completed at least two complete cycles and the pressures in said at least two beds have been equalized.
The present invention can also be defined, in general terms, as providing in a pressure swing process for fractionating at least one component from a gaseous mixture by selective adsorption in each of at least two adsorption zones, each adsoprtion zone having a gas inlet and a gas outlet, by sequentially passing the gaseous mixture from a feed . -5-~36~5 stream through a first adsorption zone until the zone is about saturated while simultaneously purging and then pressurising a second adsorption zone and then passing the gaseous mixture from the feed stream through the second adsorption zone until the zone is about saturated while simultaneously purging and thenpressurising the first adsorption zone, the improvement comprising: (a) withdrawing low purity gas from one of the adsorption zones in a direction cocurrent with feed flow when the zone is at the end of the adsorption operation therein and prior to purging of the zone;
(b) introducing the withdrawn low purity gas to one end of a segregated storage adsorption zone and closing the flow path between said one of the adsorption zones and the segregated storage adsorption zone; and (c) re-opening the flow path between said one of the adsorption zones and the segregated storage adsorption zone and withdrawing gas from said one end of the segregated storage adsorption zone and passing said withdrawn gas into said one adsorption zone in a direction countercurrent to feed flow after purging of the zone and when the zone is at a relatively low pressure.
The foregoing and additional advantages and characterizing features of the present invention will become clearly apparent from the ensuing detailed description wherein:
BRIEF DESCRIPTION OF THE DRAI~ING FIGURES
, Fig. 1 is a schematic diagram of a pressure swing adsorption system according to the present invention;
Fig. 2 is a cycle sequence chart illustrating the pressure swing adsorption process of the presentinvention;
Fig. 3 is a schematic diagram of a pressure swing adsorption system with parts removed according to another embodiment of the present invention; and Fig. 4 is a schematic block diagram of a control arrangement according to the present invention for a pressure swing adsorption system.
-5a-~L~36~S
DETAILED DE5 ~IPT_ON OF THE ILLUSTR:~TE:D EMBODIMENTS
Referring now to Fig. 1, there is shown a system ac-cording to the present invention for fractionating at least one component from a gaseous mixture by pressure swing adsorption.
The gaseous mixture is supplied to the system by a feed gas stream which flows along an input conduit 10 and is moved there-along by means of a pump or compressor 12. Although the present system and process is specifically described and illustrated in relation to the application of pressure swing adsorption to the fractionation of air to produce an oxygen rich stream, the present invention is broadly applicable to the separation of organic and/or inorganic gas mixtures.
The system includes a first adsorption bed 16, also designated A, having a gas inlet 18 and a gas outlet 20. The system further includes at least one additional adsorption bed 24, also designated B, ha~ing a gas inlet 26 and a gas outlet 28.
Adsorption beds A and B are the type comprising a vessel con-taining adsorbent material and are well known to those skilled in the art. A preferred vessel construction includes an outer pressure cell with an inner annulus, and one skilled in the art can provide suitable pressure vessels, piping or tubing, con-nectors, val~es and auxiliary devices and elements. Likewise, adsorbent materials are well-known in the art, and one skilled in the art may select an adsorbent material(s~ wh;ch is com-mercially recommended for the separation or fractionation of theparticular gaS to be purified. Examples of typical adsorbent materials for use in adsorption beds include natural or synthetic zeolites, silica gel, alumina and the like. Generally, the ad-sorbent beds in a system contain the same adsorbent material, however, each bed may contain a different type of adsorbent material or different mixtures of adsorbent material as desired.
The particular aasorbent material or mixtures used are not critical in the practice of this invention as long as the material separates or fractionates the desired gas Components.
The system of the present invention further comprises a segregated storage adsorption bed 32, also designated c, and in the system shown in Fig. 1 gas is introduced to and withdrawn from the segregated storage adsorption bed C at the same end which is provided with a conduit 34. The segregated storage ad-sorption bed c likewise is a vessel containing adsorbent material, but bed C does not communicate with the feed gas stream from con-duit 10. In the system shown, adsorption bed C is approximatelythe same size as the adsorpt;on beds A and B and may contain the same type of aasorbent material, but the segregated storage ad-sorption bed C can ~e smaller in size, include different adsorb-ent material, and be operated at a different capacity as com-pared to th.e adsorption beds A and B.
The gas inlet 18 of adsorption bed A is connected toconduit lQ containing the feed gas stream by suitable conduit means lncluding an automatic valve 40A and, similarly, the gas inlet 26 of adsorption bed B is connected to the feed gas stream in conduit 10 by suitable conduit means including an automatic valve 40B. The system further.includes a waste gas outlet 44 which can ~e open to the atmosphere or which can ~e in fluid communication with a waste gas stream. The gas inlets 18 and 26 of adsorption beds A and B, respectively, also are connected to the waste gas outlet 44 by suitable corresponding conduit means includi.ng automatic valves 46A and 46B, respect;vely. The auto-matic valves 40 and 46 and those addit~onal automatic valves to be described can be of the solenoid-operated type, but in any eVent are of the type which are operated to ~e either fully open or fully closed.
The system of the present invention further comprises means such as suitable conduits or piping defining a gas flow X
1136~6S
path connected at one end to gas outlet 20 of adsorption bed Aand connected at the opposite end to gas outlet 28 of adsorption bed B. A first flow control valve 50A is in the gas flow path between gas outlet 20 of adsorption bed A and adsorp~ion bed B.
Valve 50A allows unrestricted gas flow in a direction from the outlet 20 of bed A through the valve toward adsorption bed B, and the valve provides controlled flow therethrough in a direction to gas outlet 20 of adsorption bed A. The controlled flow pre-ferably is provided by manual adjustment. A second flow control valve 50B is in the gas flow path between gas outlet 28 of ad-sorption bed B and the adsorption bed A. Valve 50B allows un-restricted gas ~low therethrough in a direction from yas outlet 28 of adsorption bed B toward adsorption bed A, and it provides controlled flow therethrough in a direction to gas outlet 28 of adsorption bed B. The controlled flow preferably is provided by manual adjustment. Valves 50A, 50B preferably are identical and can be of the type known commercially as Parker-Hannifin flow control valves. An isolation valve in the form of an automatic valve 54 is provided in the gas flow path between gas outlets 20 and 28 of the adsorption beds, and in the system shown valve 54 is connected between gas outlet 20 of adsorption bed A and the flow control valve 5OA.
The system of the present invention includes a second gas flow path provided by suitable conduits or piping which joins the gas outlets 20 and 28 of the adsorption beds A and B, re-spectively. A first automatic valve 60A is connected in the pathadjacent outlet 20 of bed A, and a second automatic valve 60B is connected in the path adjacent outlet 28 of adsorption bed B.
The segregated storage adsorption bed C is connected through an automatic valve 62 to a point in the gas flow path between the automatic valves 60A and 60B.
The system of the present invention further comprises a product outlet designated 66 and output conduit means for coupling the gas outlets of the adsorption ~eds to the product outlet 66. In the system shown the output conduit means is con-nected to the first flow path at a point between the flow control valves 50A and 50B and includes a first section 70 including an automatic valve 72 and a second section 74 including the series S combination of a pressure regulator 76, a throttle valve 78 and a flow meter 80. The flow rate of product to the outlet 66 is con-trolled by valve 78 which preferably is a manually adjustable needle-type valve, and the flow rate is indicated visually by the meter 80.
The system of the present invention further comprises a reservoir 84 which functions primarily to store product gas re-ceived through a conduit 86 and serve as a reserve supply of pro-duct for use in the event of a system malfunction. A first reser-voir conduit means is connected at one end of the system output conduit means and at the other end to the reservoir 84 through conduît 86 and includes flow control means in the form of check valve 90 which allows gas flow only in one direction from the system output conduit means to the reservoir 84. Another valve 92 in the form of a throttle valve which preferably is manually adjustable is connected in the conduit and preferably ~etween check valve 90 and reservoir 84. Valve 92 can be used to control the rate of flow of gas product into reservoir 84. A second reservoir conduit means is connected at one end to reservoir 84 through conduit 86 and at the other end to the system output con-duit means and includes valve means 96 for controllin~ the flowof product gas from reservoir 84 to the output conduit means. A
control lO0 is connected by lines 102 and 103 to valves 72 and 96, respectively, and unctions to open the normally closed valve 96 in response to closing of valve 72. A pressure indicator meter 104 can be connected to the output of reservoir 84 for the purpose of indicating the pressure of gas product remaining therein.
_g_ . .
~36~i5 In general, the present invention is illustrated in terms of a process and system utilizing a first adsorption bed, a second adsorption bed and a segregated storage adsorption bed.
However, the process and system can employ more than one first adsorption bed, more than one second adsorption bed and more than one segregated storage adsorption bed. The adsorption beds com-munlcate with the feed gas stream which supplies the gaseous mix-ture, and the segregated storage adsorption bed never directly communicates with or is ~irectly exposed to the feed gas stream.
Although the process and system of the present invention are descr;bed with particular reference to separation or fraction-ation of air to provide a high purity product oxygen by removal of - nitrogen, essentially any gas mixture m~y be separated by the pro-cess and system of the present invention by the proper selection of time for each cycle and step and by the selection of a proper adsorbent material, adsorbent materials or mixtures of adsorbent materials.
As used herein, depressurizing or depressurization refers to the reduction of pressure in the vessel and associated piping of an adsorption bed and the level to which pressure is reduced can be selected by those skilled in the art depending upon operating conditions and the nature of the gas mixture being fractionated. Desorption and purging pressures are selected in a similar manner. Pressurizing or pressurization refers to the increase of pressure in the vessel and associated piping of an adsorption bed. The process and system of the present invention have the capability of product gas delivery in a low pressure range down to about 2 p.s.i.g. and in a high pressure range up to about 40 p.s.i.g. The present invention is not limited to particular pressures of the product gas or any other pressures, and one skilled in the art can manipulate and adjust pressures throughout the system to provide the desired delivery or product gas pressure. For example, when air is fractionated to deliver .
~136~6S
.
high purity oxygen gas product, a delivery pressure of around 3 p.s.i.g. is employed for medical uses and breathing devices whereas ahigher delivery pressure of up to about 40 p.s.i.g. is ideally suited for commercial uses such as in metal cutting or welding equipment.
Fig. 2 illustrates a process timing sequence according to the present invention for use with the system of Fig. 1. In Fig. 2 preferred times in seconds are indicated for each step, and preferred pressures in each adsorption bed for each step are shown parenthetically and given in pounds per square inch gage.
The particular operation carried out in each adsorption bed during each step is shown in Fig. 2, most of which are ab-breviated for convenience in illustration. Thus "FEE" refers to feed end e~ualization and will be explained in further detail presently, "ISOL" refers to isolation of a particular adsorption, "EQ" refers to pressure equalization of two adsorption beds and will be explained in further detail presently, "REP" refers to repressurization or repressurizing to increase the pressure in an adsorption bed, and "P~RGE" refers to introduction of purge gas or purging.
2Q Referring now in detail to Fig. 2, prior to step No. 1 the gaseous mixture i.e. ordinarv air, has been flowing from the feed gas stream in conduit 10 and through valve 40A which is open into and through adsorption bed ~ wherein nitrogen is adsorbed.
~igh purity oxygen gas leaves bed A through outlet 20 and flows through the opened valve 54 and flow control valve 50A and then flows along conduit section 70 through the opened valve 72, along conduit ~ection 74 and through the series combination of pressure regulator 76, needle valve 78 and flow meter 80 to the product outlet 66 ~or use. Just prior to the beginning of step No. 1, adsorption bed A is about saturated and nearing the end of the adsorption operation therein. Also just prior to the beginning of step No. 1, adsorption bed A is at a higher pressure than the >~
~136(~65 adsorption beds B and C.
At the beginning of step No. 1, valve 40B is opened, and valve 40A is kept open as well as valve 72. As indicated in Fig. 2, at the beginning of step No. 1, typical pressures in beds A, B and C are 30, 7 and 7, respectively.
During this step, gas flows from the bottom or feed end of adsorber A in a reverse direction through valve 40A whereupon it mixes with the incoming feed air stream from conduit 10 and flows through valve 40B into the bottom or feed end of adsorber B. Adsorption bed A is very near the end of the adsorption step therein. As a result, during this step, adsorption bed A is de-pressurized countercurrently to feed flow, and adsorption bed A
is pressure equalized with adsorption bed B causing the pressure in bed B to rise. Also in this step, adsorption bed A continues to supply oxygen ga~ product, but this is terminated by the end of the step. Step No. 1 preferably has a duration of about 7 seconds. Throughout this step and all other steps there is con-tinuous air flow into the system and continuous product flow out.
Cocurrent to feed flow is in a direction from the inlet to the outlet of the adsorption bed and countercurrent to feed flow is in a direction from the outlet to the inlet of the adsorption bed.
The process of step No. 1 may be described as continuing to disch~rge product gas from the outlet of the first bed ~hile simultaneously equalizing the pressures of the first and second adsorption beds from the feed ends thereof by withdrawing gas from the feed inlet of the first adsorption bed at the end of the adsorption operation therein in a direction countercurrent to feed flow and introducing the withdrawn gas along with the gaseous mixture from feed gas stream to the feed inlet of the second adsorption bed in a direction cocurrent with feed flow and after pressurization thereof.
1136()65 As shown in Fi~. 2, at the transition between the end of step No. 1 and ~eginning of step No. 2, the pressures in beds A
and B are equalized at 20 p.s.i.g. and the pressure in the seg-regatèd storage adsorption ~ed C has remained at 7 p.S.i.g. At the beginning of step No. 2, valve 40B remains open, valve 40A
closes, and val~e 60A opens. No product gas is obtained from ad-sorption bed A. During this step, feed air continues to flow into the feed inlet 26 of adsorber B, and oxygen rich gas is taken as product from the outlet 28 of adsorber B and flows through flow control valve 50B into ~onduit section 7a and through the remaining system components as previously described to product outlet 66. At the same time, low purity gas flows from the outlet 20 of adsorber A through valve 60A and valve 62 into the segregated storage adsorption ~ed C. As a result, during this step adsorption bed A is pressure equalized with the 1~ segregated storage adsorption bed C. The automatic valve 62 can remain open during all steps or it can be opened and closed when necessary. Step No. 2 preferably has a duration of about 7 seconds.
The process of step No. 2 may be described as simul-taneously terminating the pressure equalization of step 1, ad-80rbing the gaseous mixture from the feed gas stream in the ~econd adsorption bed, releasing product gas from the outlet of the second adsorption bed, and eqalizin~ the pressures of the first adsorption bed and the segregated storage adsorption bed by wit~drawing low purity gas from the outlet of the first ad-sorption bed in a direction cocurrent with feed flow and intro-ducing the low purity gas into the segregated storage adsorption bed.
As is e~ident from steps 1 and 2 on Fig. 2 and from the foregoing descriptions thereof, it can be seen that bed A has undergone a decreasing pressure adsorption process; i.e., it has been producing product gas while simultaneousl~ experiencing a ~136(~65 reduction in pressure. While this is shown in Fig. 2 as oc-curring at the same time as beds A and B are undergoing FEE, it will be clear to those skilled in the art that concurrence with a FEE step is not essential, e.g., a bed cOula be made to per-form a decreasing pressure aasorption step while connected to an 5 SST, or to atmosphere, or otherwise.
As shown in Fig. 2, at the transition between the end of step No. 2 and the ~eginning of step No. 3, the pressures in adsorption beds A and C are equalized at 14 p.s.i.g. ana the pressure in adsorption bed B has risen to 28 p.s.i.g. At the beginning of step No. 3, valve 40B remains open, valve 60A closes and valve 46A opens. During this step feed air continues to enter bed B, and product quality oxygen rich gas continues to be taken as product from the outlet of bed 8 and is available at product outlet 66. Also during this step, adsorption bed A is depressurized to the atmosphere through valve 46A and waste out-let 44 in a direction countercurrent to feed flow. As a result, nitrogen rich waste gas is rejected to the atmosphere, and the pressure in adsor~er A drops from 14 p.s.i.g. to 0 p.s.i.g. Con-currently with the foregoing depressurization, a portion of the oxygen gas product flowing from adsorber B through flow control valve SOB flows throuqh valve 50A and valve 54 into adsorber A.
The product quality oxygen gas flows through bed A and out through valve 46A and waste outlet 44 in a direction opposite to that o~ air separation. This oxygen purge flowing countercurrent to feed flow displaces nitrogen from the adsorbent material in bed A, and nitrogen rich stream leaves the system through valve 46A and outlet 44 to the atmosphere. As a result, product ~uality oxygen gas is taken from the adsorbing bed B to purge the nitrogen loaded bed A in a reverse direction to reject un-wanted impurîty to the atmosphere. Step No. 3 preferably has aduration of about 39 seconds.
The process of step No. 3 may be described as simul-X
.
i~3~U65 taneously terminating the pressure equalization of step 2, con-tinuing adsorption of the gaseous mixture from feed gas stream in the second adsorption bed, releasing product gas from the outlet of the second adsorption bed, and depressurising the first ad-sorption bed in a direction countercurrent to feed flow and purging the first adsorption bed by diverting some product gas from the outlet of the second adsorption bed into the first aa sorption bed in a direction countercurrent to feed flow.
As shown in Tig. 2, at the transition between the end of step No. 3 and the beginning of step No. 4, the pressure in bed A
is at Q p.s.i.g., the pressure in segregated storage adsorption bed C has remained at 14 p.s.i.g., and the pressure in bed B has risen to 30 p.s.i.g. At the beginning of step No. 4, valve 40B
remains open, valve 46A closes, and valve 60A opens. Valve 62 if not already open is opened at the beginning of this step. During this step feed air continues to enter bed B, and product quality oxygen gas continues to be taken as product from the outlet of bed B and is available at product outlet 66. At the same time, gas flows from the segregated storage tank C through valves 62 and 60A into adsorber A through the outlet 20 thereof. This gas withdrawn from adsorption bed C during step 4 is a version of the gas supplied to bed C during step 2 which gas has been in1uenced by travel în bed C.
As a result, during this step the segregated storage adsorption bed C is pressure equalized with the adsorption bed A. At least during the initial portion of step 4, there is some additional flow of gas from bed B through valves 50B, 50A and 54.
Step No. 4 preferably has a duration of about 7 seconds.
The process of step No. 4 may be described as simul-taneously terminating the depressurîzing and purging of the first 3Q adsorption bed, continuing adsorption of the gaseous mixture from the ~eed gas 8tream in the second adsorption bed, releasing pro-duct gas from the outlet of the second adsorption bed and - il36065 equalizin~ the pressures of the se~regated storage adsorption bed and the first adsorption bed by withdrawing gas from the segregated storage adsorption bed and introducing the withdrawn gas into the first adsorption bed in a direction countercurrent to feed flow.
The foregoing process steps are repeated consecutively beginning with pressUre equalization of the adsorption beds from the feed ends t~ereof reversing the functions of the adsorption beds A and B. In particular, as shown in Fig. 2, at the transi-tion between the end of step No. 4 and the beginning of step No.
5, the pressures in beds A and C are equalized a~ 7 p.s.i.g. and the pressure in bed B has remained at 30 p.s.i.g. At the begin-ning of step No. 5, valve 4OB remains open, valve 6OA closes and valve 40A opens. During this step, gas flows from the bottom or feed end of adsorber B, which is near the end of its adsorption operation, in a reverse direction through valve 40B whereupon it mixes with the incoming feed air stream from conduit 10 and the resulting mixture flows through valve 40A into the bottom or feed end of adsorber A. As a result, adsorption bed B is pressure equalized with adsorption bed A, and bed A begins to adsorb the feed gas m;xture. This feed end equalization is similar to that which occurred during step No. 1 but in this step the roles of the beds A and B are interchanged. Also during this step, pro-duct quality oxygen rich gas continues to be taken as product from bed B and is available at product outlet 66. This step be-gins the second half of the process cycle wherein steps 5 - 8 are similar to 1 - ~ with the roles of beds A and B interchanged and with the valve sequence being the same with the A and B
designations interchanged. For example the process of step No.
6 (the same as step 2 with beds reversed) may be described as simultaneously terminating the pressure equalization of step No.
5, repressurizing the first adsorption bed while ~ithdrawing product gas therefrom, and egualizing pressures in the second ~ -16-.
adsorption bed and the segregated storage adsorption zone.
Equalizing the pressures of the adsorption beds A and Bat the feed ends thereof according to the present invention, as illustrated in step No. 1, advantageously reduces energy require-ments and increases oxygen recovery. When an adsorption bed at the end of the adsorption step therein is depressurized counter-currently to feed flow, i.e. as bed A from 30 p.s.i.g. to 20 p.s.i.g. in step No. 1, this gas can be introduced into the feed end of a repressurizing adsorber, i.e. adsorption bed B in step No. 1, without any appreciable loss in system performance com-pared to repressurizing with air from the system compressor 12.Feed and equalization according to the present invention thus greatly reduces the feed air requirement and increases oxygen recovery, i.e. decreases the size of compressor 12 required to produce a given amount of oxygen. Feed end equalization recovers energy, increases system efficiency and can be used for both low and high product delivery pressures. The foregoing advantages of course apply to both of the feed end equalizations which occur during a single cycle as illustrated in step Nos. 1 and 5.
The feed end equalization according to the present in-vention requires less adsorbent material in a given bed as com-pared to product end equalization for the follow~ng reasons. In product or outlet end equalization, the bed at the higher pres-sure depressurizes in a direction cocurrent to feed flow during the pressure equalization step. This causes the mass transfer zone to advance toward the product end of the bed as the pressure decreases. In order to contain the mass transfer zone during this step to maintain product purit~, a larger bed, i.e. more adsorbent material, is required. In feed end equalization ac-cording to the present invention, on the other hand, the bed at the higher pressure depressurizes in a direction countercurrent to feed flow durin~ the equalization step. In this step the mass transfer zone does not advance due to the direction of the 113S~
flow. The countercurrent depressurization also is beneficial for the subsequent purge step because nitrogen starts to flow toward the feed end of the bed during this step. ~he combination of no advancing of the mass transfer zone and countercurrent de-pressurization rèduces the amount of adsorbent material required.
S Bed size factor is a ~uantity used to compare the amount of adsorbent material required from one system or cycle to an-other. At a given bed siæe ~actor, it has been determined that using feed and equalization according to the present invention produces oxygen at a ~igher purity as compared to using product end equalization.
The combination of equalizing pressures of an adsorption bed and the segregated storage adsorption bed when the adsorption bed is at the end of the adsorption operation therein and prior to purging o~ the bed as illustrated in step No. 2 and thereafter equalizing pressures between these same two components after purging of the adsorption bed when it is at a relatively low pressure as illustrated in step No. 4 maximizes the utilization of the adsorption bed while at the same time maximizing purity of the product. In particular, during step No. 2 as the de-pre8sUriZing adsorber A equalizes cocurrently to feed flow intosegregated storage adsorption ~ed C, part of the nitrogen con-tained in the mass transfer zone of bed A will be transferred into the bed C. This allows for maximum and continual utiliza-tion of adsorption bed A, i.e. the mass transfer zone can be moved along bed A from inlet to outlet as far as possible. At the beginning of the flow from bed A to bed C the gas iS rich in oxygen but as flow continues the gas becomes more like air.
In addition, the segregated storage adsorption bed recovers some potential energy from the depressurizing adsorber and this, in turn, reduces system blo~down pressure and increases recovery and efficiency. Providing the segregated storage adsorption bed C in effect provides a mixing volume to smooth out any 1~6(~65 fluctuations in product purity which otherwise might occur whenthe front of the mass transfer zone breaks out of the output end of an adsorption bed. The foregoing advantages result when the system is operating at equilibrium conditions and at flow con-ditions for which the system is optimally designed. For example, when the system is used to supply oxygen for medical use, desi~n conditions occur at a flow rate of about 3.0 liters per minute.
During step No. 4 as the segregated storage adsorption bed C pressure equalizes countercurrently to feed flow into ad-sorber A, the gas returned to adsorber A is distxibuted or dis-persed therethrou~h in a manner which does not adversely affectproduct purity. The gas is not returned to adsorber A in a lump quantity concentrated in the output region of bed A but instead is spaced, equalized or dispersed through and along the bed A.
The fore~oing is believed to result from the fact that gas retu~n to adsorber A occurs when the latter is at a relatively low pressure, i.e. 0 p.s.i.g. after purging of adsorber A, which low pressure allows the gas to disperse through the bed. It is believed that low or zero pressure in bed A allows the incoming gas to move along the bed in a manner such that a large amount of nitrogen is not taken up by the adsorbent material adjacent the outlet end of the bed. At the beginning of gas flow from bed C to bed A, the gas is rich ln nitrogen but as the ~low con-tînues it becomes more rich in oxygen. The foregoing advantages are of course equally associated with the relationship between adsorption bed B and segregated storage adsorption bed C during step Nos. 6 and 8.
Providing the flow control valves 50A and 5QB allo~s the system to be balanced by providing individual control or adjustment of the purge gas flow to each of the adsorption beds 3a A and B. Providing an adjustable flow control valve associated with each bed permits compensating for differences in the beds and pipiny by simple manual ad~ustment of valves 50A, 50B.
3 13G(~S
An unbalanced system is characterized by the front of the mass transfer zone breaking through the output end of one bed sooner than in the other bed. In order to maintain purity, this would limit system operation to that o the bed which is first to ex-perience nitrogen breakthrough thereby causing the other ad-sorber to be underutilized with the result that the entire systemproduces less oxygen at a given purity. System balance and optimization are achieved by the independently adjustable flow control valves 50A, 50B. Advantageously, product gas also travels through these same valves toward the system product out-let 66. Alternatively, flow control valves 50A and 50B could bereplaced by two needle valves for independently controlling purge flow and then the combination of two check valves would be con-verted in parallel with the needle valves and poled to transmit product gas from the bed outlets to the system product outlet 66.
The automatic valve 54 in the path containing valves 50A, 50B is a shut down isolation valve which serves to isolate beds A and B when the system is shut down to maintain the re-spective pressures in the beds and prevent pressure equalization.
When the system is shut down, all the other automatic valves close also. Then when the system is placed in operation, less time is required to reach desired operating conditions by virtue of the beds A and B having been maintained at the respective pressures prior to shut down.
Table I presents data illustrating the effect of the segregated storage tank or segregated storage adsorption bed C
on system performance. The data presented in Table I is for oxygen product at a purity of 90% and the oxygen recovery in percent is presented for both low pressure and high pressure delivery conditions. The abbreviations S.S.T. for segregated 3Q storage tank and F.E.E. for feed end equalization are used.
~36~65 TABLE I
Low High Pressure Pressure Delivery Delivery S~S~To Absent 21% 21%
S . S . T . Present But Empty 25% 23%
S.S.T. Half Full of Adsorbent Material 35% 31%
S . S . T . Full And With F.E.E. 49% 48~6 Fig. 3 shaws a system according to another enibodim~t of the present invention wherein gas product can ~e withdra~ fmm the other end of t~e segregated storage adsorption bed. In the system shown in Fig. 3, o~
ponents identical to those of Fig. 1 are provided with the sane reference ~merals but with a prime designation. In addition, the system of Fig. 3 15 would also include adsorption beds identical to those designated A ar~l B in the ~ystem of Fig. l, along with similar connections of the fee~l gas stream to the gas inlets of the beds, connections of the gas inlets to the waste outlet, and connections of the gas outlets of the beds to the gas flow path ccxntaining the flaw control valves 50A' and 50B' Thus, the arra~2ds at 20 o~osite ends of the path sh~7wn in Fig. 3 containing autcmatic valves 60~', 60B' and the path containing flow control valves 5Q~' and 50B' indicate con-nection to the gas outlets of the corresponding adsorption beds A and B.
Similarly, the output of regulator 76' is cannecte~ through a throttle valve and flow indicator to a product outlet as indicated }~y the ar~ead in the 25 portion 74' of the gas flow path.
The opposite end of the segregated storage adsorption bed C ' is connected by a conduit 108 which contains an automatic valve 110 to the output conduit means, in particular to portion 74 ' thereof and upstream from regulator 76 ' . Upon opening of ~13~ 65 valve 110, product quality gas can be withdrawn from the segre-gated storage adsorption bed C' and introduced to the output con-duit means. Withdrawing product gas from the segregated storage adsorption bed can be advantageous in situations where low pres-sure rather than high pressure product delivery is needed. In addition, when product is delivered from the segregated storage adsorption bed C', the bed serves also as a product surge tank enabling product to be withdrawn from the system at a high flow rate for a short period of time before the mass transfer zone breaks through that end of the bed. On the other hand, recovery from a breakthrough condition can be relatively slow. Another advantage of withdrawing product gas from the segregated storage adsorption bed C' is that it provides a relatively higher rate of recovery of product. This is because withdrawal of product from bed C' reduces the pressure therein so that when the pressure equalizes with either of the adsorption beds that adsorption bed, in time, will be at a lower pressure. The lower pressure, in turn, imposes a lower blowdown requirement for that bed with a result that less gas is released to the atmosphere. This re-duction in the ~aste losses, in time, results in a higher per-2Q centage of product recovery. Another advantage associated withthe segregated storage adsorption bed involves feed end equaliz-tion which lowers the front of the mass transfer zone in each of the other two beds so that when the beds are equalized from the tops with the segregated storage adsorption bed there is less nitrogen to be taken up by the segregated storage adsorption bed.
As shown in Fig. 3, the system can also include a third reservoir conduit designated 114 connected at one end to the reservo;r 84' and coupled at the other end to the adsorption beds. In the present illustration, the other end of conduit 114 is connected to the flow path containing the automatic yalves 60A' and 60B' and is connected between these valves. Conduit 114 contains an automatic valve 116. Upon opening of valve 116, ~( . .
:~136065 product gas from reservoir 84', flows to the adsorption beds andit can be used for operations such as purging and repressuriza-tion.
The primary role of the reservoir in the system of the present invention is a reserve supply of product gas in the event of equipment malfunction or power failure. This is of particular importance when the system of the present invention supplies oxygen for medical use. Under normal operating conditions the reservoir is at a pressure of 28-29 p.s.i.g., and product oxygen flows through valve 72 and regulator 76 to product outlet 66.
If electrical power ;s interrupted, valve 72 closes and this is sensed by control 100 which opens valve 96. Oxygen flow con- !
tinues from the reservoir through valve 96 to the output conduit to outlet 66 until the supply in the reservoir is depleted. An alarm can ~e sounded to indicate the power interruption.
lS The reservoir also can be used to supply part or all of the purge oxygen required for an adsorber during its purge step.
This is accomplished by opening valve 116 at the appropriate time. The reservoir also can be used as another surge tank.
Pressure equalizations to and from the adsorbers can be accom-plished through the correct sequencing of valves 116 and 62.
The primary purpose of the reservoir is a xeserve oxygen supply in the event of a malfunction. The length o~ time the reserve oxygen lasts depends on the pressure in the reser-voir at the time of the malfunction. If the reservoir is used 25 only as a back-up oxygen supply, the reservoir pressure will be at its maximum at all times. If the reservoir is used to supply supplemental purge and or repressurization gas, the pressure in the reservoir will vary as will the reserve supply of oxygen.
The reservoir can comprise an adsorption bed but it also can comprise an ordinary tank of larger size.
Fig. 4 shows an arrangement for controlling the system and process of the present invention. The output conduit means >~
can be connected to a tank or similar storage receptacle orvessel 120 and gas product can be withdrawn therefrom through a conduit or path 122 for use. The sequencing and timing of the system including the control of the automatic valves is performed by a system control designated 124, and control signals or com-mands generated by the control 124 are transmitted by linescollectively designated 126 to the valves and other appropriate components of the system. Persons skilled in the art are readily familiar with such controls so that a detailed description there-of is believed to be unnecessary. Generally, the control 124 is responsive to the pressure of product gas within the storage element 120, and to this end a pressure sensor 130 is operatively connected to the storage element 120 by the connection designated 132. In accordance with the present invention, the output from sensor 130 is connected by a line 134 to an additional control means 136 which, in turn, is connected in controlling relation to the system control 124 by the connection designated 138. In accordance ~ith the present invention, it has been determined that once operation of the process and system has begun there is an optimum time at which to terminate operation, both in terms 2Q of a minimum number of cycles to be completed and a point within a cycle to terminate operation. The additional control functions to cause the System control 124 to maintain operati~n of the system, once begun, for a predetermlned number of cycles. It has been determined that in a system of the present invention for producing oxygen from ~eed air that a ~otal of two complete cycles pro~ides desirable results. One complete cycle includes step Nos. 1-8 described in Fig. 2. Furthermore, it has been determined that there is an optimum point within a cycle at which operation of the system and process should be terminated.
3a This is when the pressures are equal in the two adsorption beds A and B which is at the beginning of step Nos. 2 and 6 described in Fig. 2. Thus, the additional control 136 also functions to X
~136~5 stop the system only after two complete cycles have been com-pleted and only at an optimum point within the next cycle when the pressures are equal in the two adsorption beds A and B. The additional control can be of the cam type or step switch type, for example, and persons skilled in the art are readily familiar S with the construction and operation of these and other types which can be used for additional control 124 so that a detailed description thereof is believed to be unnecessary. Thus, the system control means 124 is responsive to gas pressure in storage means 120 signalled by sensing means 130 for stopping operation of the process and system normally when gas pressure in storage means 120 reaches a predetermined magnitude. The additional control means 136 overrides the system control means to terminate operation of the process and system only at a predetermined time.
lS It is therefore apparent that the present invention ac-complishes its intended objects. While several embodiments of the present invention have been described in detail, this is for the purpose of illustration, not limitation.
BACKGROUND ~F THE INVENTION
This ;nvention relates to the art of separation of gas mixtures, and more partîcularly to a new and improved process and system for separating gas mixtures by pressure swing adsorption.
One area of use of the present invention is in separating air to provide a product stream of high purity oxygen, although the principles of the present invention can be variously applied.
In basic pressure swing adsorption processes and systems for separating air, adsorption is carried out at a high pressure and desorption is carried out at a low pressure. Compressed air is introduced into a fixed bed of adsorbent material and nitrogen is then preferentially adsorbed to produce oxygen rich gas product.
When the adsorption bed is about saturated, the bed pressure is reduced to desorb nitrogen from the adsorbent material and re-generate the adsorption capacity. To increase the efficiency of regeneration, a purge by some of the product or an intermediate process stream often is used. To facilitate continuous operation, two or more adsorption beds are employed so that while one bed performs adsorption the other bed undergoes regeneration.
In the design and operation of pressure swing adsorption processes and systems, it would be highly desirable to provide >~ ~
.
~ 1~36(~65 maximum utilization of adsorbent material in the adsorption beds,reduction in energy requirements for operation of the system, a substantially constant degree of product purity, and reduction in adsorbent material requirements while maintaining a high degree of product purity, along with improved efficiency and reliability.
SI~MARY OF THE INVENTION
It is, therefore, a primary object of this invention to provide a new and improved process and system for separation and fractionat;on of gas mixtures by pressure swing adsorption.
It is a further object of this invention to provide such a process and system characterized by maximum utilization of adsorbent material in the adsorption beds.
It is a further object of this invention to provide such a process and system having reduced energy requirements for operation.
It is a further object of this invention to provide such a process and system which is balanced and yields a substantially constant de~ree of product purity.
It is a further object of this invention to provide such a process and system which has reduced adsorbant material re~uirements along with a high degree of product purity.
il3~65 It is a further object of this invention to provide such a ~rocess and system which maintains a reserve supply of product for use during a system malfunction or in augmenting system functions.
It is a further object of this invention to provide such a process and system which is reliable, efficient and economical.
In general terms and in one aspect thereof, the present invention provides a pressure swing adsorption process using at least one adsorption bed having a gas inlet and a gas outlet and at least one segregated storage adsorption bed, said process comprising the steps of flowing a feed gas mixture into said inlet of said at least one adsorption bed to adsorb at least one gas of said mixture within said bed while flowing the remainder of said gas mixture out of said bed outlet as product gas until said adsorption bed is about saturated with said one gas; flowing product gas fro~ said bed outlet into said segregated storage adsorption bed by depressurising said at least one adsorption bed into said segregated storage adsorption bed until a mass transfer zone within said adsorption bed moves into said segregated storage adsorption bed, closing the flow path between said adsorption bed and said segregated storage adsorption bed; purging said one bed in a countercurrent direction; and flowing gas from said segregated storage adsorption bed back into said adsorption bed by depressurising said segregated storage adsorption bed and repressurising said purged at least one adsorption bed.
In another aspect of the present invention, a pressure swing adsorption process using at least one adsorption bed having a gas inlet and a gas outlet and at least one segregated storage zone, comprising the steps of 11361~65 flowing a feed gas mixture into said bed inlet to adsorb at least one gas of said mixture within said bed while flowing the remainder of said gas mixture out of said bed outlet as product gas until said ~ed is about saturated with said one gas, flowing gas from said bed outlet into said zone by depressurising said bed into said zone until the mass transfer front within said bed moves into said zone, closing the flow path between said bed and said zone, purging said one bed in a counter-current direction, flowing gas from said zone back into said bed by depxessurising said zone and repressurising said purged one bed, using at least two adsorption beds each having a gas inlet, a gas outlet, and conduit means connecting said gas outlets to product outlet conduit means, said process comprising the additional steps of alternately and sequentially flowing said feed gas mixture into the inlet of one of said beds to adsorb at least one gas in said mixture in said one bed and flowing the remainder of the mixture out of said one bed outlet as said product gas until said one bed is about saturated within said one gas, purginga second bed while performing the producing ste in said one bed, controlling the repetition of said steps to permit their alternate and sequential repetition to stop only at an optimum point in the process, and wherein said optimum point is a point in time immediately after the process has completed at least two complete cycles and the pressures in said at least two beds have been equalized.
The present invention can also be defined, in general terms, as providing in a pressure swing process for fractionating at least one component from a gaseous mixture by selective adsorption in each of at least two adsorption zones, each adsoprtion zone having a gas inlet and a gas outlet, by sequentially passing the gaseous mixture from a feed . -5-~36~5 stream through a first adsorption zone until the zone is about saturated while simultaneously purging and then pressurising a second adsorption zone and then passing the gaseous mixture from the feed stream through the second adsorption zone until the zone is about saturated while simultaneously purging and thenpressurising the first adsorption zone, the improvement comprising: (a) withdrawing low purity gas from one of the adsorption zones in a direction cocurrent with feed flow when the zone is at the end of the adsorption operation therein and prior to purging of the zone;
(b) introducing the withdrawn low purity gas to one end of a segregated storage adsorption zone and closing the flow path between said one of the adsorption zones and the segregated storage adsorption zone; and (c) re-opening the flow path between said one of the adsorption zones and the segregated storage adsorption zone and withdrawing gas from said one end of the segregated storage adsorption zone and passing said withdrawn gas into said one adsorption zone in a direction countercurrent to feed flow after purging of the zone and when the zone is at a relatively low pressure.
The foregoing and additional advantages and characterizing features of the present invention will become clearly apparent from the ensuing detailed description wherein:
BRIEF DESCRIPTION OF THE DRAI~ING FIGURES
, Fig. 1 is a schematic diagram of a pressure swing adsorption system according to the present invention;
Fig. 2 is a cycle sequence chart illustrating the pressure swing adsorption process of the presentinvention;
Fig. 3 is a schematic diagram of a pressure swing adsorption system with parts removed according to another embodiment of the present invention; and Fig. 4 is a schematic block diagram of a control arrangement according to the present invention for a pressure swing adsorption system.
-5a-~L~36~S
DETAILED DE5 ~IPT_ON OF THE ILLUSTR:~TE:D EMBODIMENTS
Referring now to Fig. 1, there is shown a system ac-cording to the present invention for fractionating at least one component from a gaseous mixture by pressure swing adsorption.
The gaseous mixture is supplied to the system by a feed gas stream which flows along an input conduit 10 and is moved there-along by means of a pump or compressor 12. Although the present system and process is specifically described and illustrated in relation to the application of pressure swing adsorption to the fractionation of air to produce an oxygen rich stream, the present invention is broadly applicable to the separation of organic and/or inorganic gas mixtures.
The system includes a first adsorption bed 16, also designated A, having a gas inlet 18 and a gas outlet 20. The system further includes at least one additional adsorption bed 24, also designated B, ha~ing a gas inlet 26 and a gas outlet 28.
Adsorption beds A and B are the type comprising a vessel con-taining adsorbent material and are well known to those skilled in the art. A preferred vessel construction includes an outer pressure cell with an inner annulus, and one skilled in the art can provide suitable pressure vessels, piping or tubing, con-nectors, val~es and auxiliary devices and elements. Likewise, adsorbent materials are well-known in the art, and one skilled in the art may select an adsorbent material(s~ wh;ch is com-mercially recommended for the separation or fractionation of theparticular gaS to be purified. Examples of typical adsorbent materials for use in adsorption beds include natural or synthetic zeolites, silica gel, alumina and the like. Generally, the ad-sorbent beds in a system contain the same adsorbent material, however, each bed may contain a different type of adsorbent material or different mixtures of adsorbent material as desired.
The particular aasorbent material or mixtures used are not critical in the practice of this invention as long as the material separates or fractionates the desired gas Components.
The system of the present invention further comprises a segregated storage adsorption bed 32, also designated c, and in the system shown in Fig. 1 gas is introduced to and withdrawn from the segregated storage adsorption bed C at the same end which is provided with a conduit 34. The segregated storage ad-sorption bed c likewise is a vessel containing adsorbent material, but bed C does not communicate with the feed gas stream from con-duit 10. In the system shown, adsorption bed C is approximatelythe same size as the adsorpt;on beds A and B and may contain the same type of aasorbent material, but the segregated storage ad-sorption bed C can ~e smaller in size, include different adsorb-ent material, and be operated at a different capacity as com-pared to th.e adsorption beds A and B.
The gas inlet 18 of adsorption bed A is connected toconduit lQ containing the feed gas stream by suitable conduit means lncluding an automatic valve 40A and, similarly, the gas inlet 26 of adsorption bed B is connected to the feed gas stream in conduit 10 by suitable conduit means including an automatic valve 40B. The system further.includes a waste gas outlet 44 which can ~e open to the atmosphere or which can ~e in fluid communication with a waste gas stream. The gas inlets 18 and 26 of adsorption beds A and B, respectively, also are connected to the waste gas outlet 44 by suitable corresponding conduit means includi.ng automatic valves 46A and 46B, respect;vely. The auto-matic valves 40 and 46 and those addit~onal automatic valves to be described can be of the solenoid-operated type, but in any eVent are of the type which are operated to ~e either fully open or fully closed.
The system of the present invention further comprises means such as suitable conduits or piping defining a gas flow X
1136~6S
path connected at one end to gas outlet 20 of adsorption bed Aand connected at the opposite end to gas outlet 28 of adsorption bed B. A first flow control valve 50A is in the gas flow path between gas outlet 20 of adsorption bed A and adsorp~ion bed B.
Valve 50A allows unrestricted gas flow in a direction from the outlet 20 of bed A through the valve toward adsorption bed B, and the valve provides controlled flow therethrough in a direction to gas outlet 20 of adsorption bed A. The controlled flow pre-ferably is provided by manual adjustment. A second flow control valve 50B is in the gas flow path between gas outlet 28 of ad-sorption bed B and the adsorption bed A. Valve 50B allows un-restricted gas ~low therethrough in a direction from yas outlet 28 of adsorption bed B toward adsorption bed A, and it provides controlled flow therethrough in a direction to gas outlet 28 of adsorption bed B. The controlled flow preferably is provided by manual adjustment. Valves 50A, 50B preferably are identical and can be of the type known commercially as Parker-Hannifin flow control valves. An isolation valve in the form of an automatic valve 54 is provided in the gas flow path between gas outlets 20 and 28 of the adsorption beds, and in the system shown valve 54 is connected between gas outlet 20 of adsorption bed A and the flow control valve 5OA.
The system of the present invention includes a second gas flow path provided by suitable conduits or piping which joins the gas outlets 20 and 28 of the adsorption beds A and B, re-spectively. A first automatic valve 60A is connected in the pathadjacent outlet 20 of bed A, and a second automatic valve 60B is connected in the path adjacent outlet 28 of adsorption bed B.
The segregated storage adsorption bed C is connected through an automatic valve 62 to a point in the gas flow path between the automatic valves 60A and 60B.
The system of the present invention further comprises a product outlet designated 66 and output conduit means for coupling the gas outlets of the adsorption ~eds to the product outlet 66. In the system shown the output conduit means is con-nected to the first flow path at a point between the flow control valves 50A and 50B and includes a first section 70 including an automatic valve 72 and a second section 74 including the series S combination of a pressure regulator 76, a throttle valve 78 and a flow meter 80. The flow rate of product to the outlet 66 is con-trolled by valve 78 which preferably is a manually adjustable needle-type valve, and the flow rate is indicated visually by the meter 80.
The system of the present invention further comprises a reservoir 84 which functions primarily to store product gas re-ceived through a conduit 86 and serve as a reserve supply of pro-duct for use in the event of a system malfunction. A first reser-voir conduit means is connected at one end of the system output conduit means and at the other end to the reservoir 84 through conduît 86 and includes flow control means in the form of check valve 90 which allows gas flow only in one direction from the system output conduit means to the reservoir 84. Another valve 92 in the form of a throttle valve which preferably is manually adjustable is connected in the conduit and preferably ~etween check valve 90 and reservoir 84. Valve 92 can be used to control the rate of flow of gas product into reservoir 84. A second reservoir conduit means is connected at one end to reservoir 84 through conduit 86 and at the other end to the system output con-duit means and includes valve means 96 for controllin~ the flowof product gas from reservoir 84 to the output conduit means. A
control lO0 is connected by lines 102 and 103 to valves 72 and 96, respectively, and unctions to open the normally closed valve 96 in response to closing of valve 72. A pressure indicator meter 104 can be connected to the output of reservoir 84 for the purpose of indicating the pressure of gas product remaining therein.
_g_ . .
~36~i5 In general, the present invention is illustrated in terms of a process and system utilizing a first adsorption bed, a second adsorption bed and a segregated storage adsorption bed.
However, the process and system can employ more than one first adsorption bed, more than one second adsorption bed and more than one segregated storage adsorption bed. The adsorption beds com-munlcate with the feed gas stream which supplies the gaseous mix-ture, and the segregated storage adsorption bed never directly communicates with or is ~irectly exposed to the feed gas stream.
Although the process and system of the present invention are descr;bed with particular reference to separation or fraction-ation of air to provide a high purity product oxygen by removal of - nitrogen, essentially any gas mixture m~y be separated by the pro-cess and system of the present invention by the proper selection of time for each cycle and step and by the selection of a proper adsorbent material, adsorbent materials or mixtures of adsorbent materials.
As used herein, depressurizing or depressurization refers to the reduction of pressure in the vessel and associated piping of an adsorption bed and the level to which pressure is reduced can be selected by those skilled in the art depending upon operating conditions and the nature of the gas mixture being fractionated. Desorption and purging pressures are selected in a similar manner. Pressurizing or pressurization refers to the increase of pressure in the vessel and associated piping of an adsorption bed. The process and system of the present invention have the capability of product gas delivery in a low pressure range down to about 2 p.s.i.g. and in a high pressure range up to about 40 p.s.i.g. The present invention is not limited to particular pressures of the product gas or any other pressures, and one skilled in the art can manipulate and adjust pressures throughout the system to provide the desired delivery or product gas pressure. For example, when air is fractionated to deliver .
~136~6S
.
high purity oxygen gas product, a delivery pressure of around 3 p.s.i.g. is employed for medical uses and breathing devices whereas ahigher delivery pressure of up to about 40 p.s.i.g. is ideally suited for commercial uses such as in metal cutting or welding equipment.
Fig. 2 illustrates a process timing sequence according to the present invention for use with the system of Fig. 1. In Fig. 2 preferred times in seconds are indicated for each step, and preferred pressures in each adsorption bed for each step are shown parenthetically and given in pounds per square inch gage.
The particular operation carried out in each adsorption bed during each step is shown in Fig. 2, most of which are ab-breviated for convenience in illustration. Thus "FEE" refers to feed end e~ualization and will be explained in further detail presently, "ISOL" refers to isolation of a particular adsorption, "EQ" refers to pressure equalization of two adsorption beds and will be explained in further detail presently, "REP" refers to repressurization or repressurizing to increase the pressure in an adsorption bed, and "P~RGE" refers to introduction of purge gas or purging.
2Q Referring now in detail to Fig. 2, prior to step No. 1 the gaseous mixture i.e. ordinarv air, has been flowing from the feed gas stream in conduit 10 and through valve 40A which is open into and through adsorption bed ~ wherein nitrogen is adsorbed.
~igh purity oxygen gas leaves bed A through outlet 20 and flows through the opened valve 54 and flow control valve 50A and then flows along conduit section 70 through the opened valve 72, along conduit ~ection 74 and through the series combination of pressure regulator 76, needle valve 78 and flow meter 80 to the product outlet 66 ~or use. Just prior to the beginning of step No. 1, adsorption bed A is about saturated and nearing the end of the adsorption operation therein. Also just prior to the beginning of step No. 1, adsorption bed A is at a higher pressure than the >~
~136(~65 adsorption beds B and C.
At the beginning of step No. 1, valve 40B is opened, and valve 40A is kept open as well as valve 72. As indicated in Fig. 2, at the beginning of step No. 1, typical pressures in beds A, B and C are 30, 7 and 7, respectively.
During this step, gas flows from the bottom or feed end of adsorber A in a reverse direction through valve 40A whereupon it mixes with the incoming feed air stream from conduit 10 and flows through valve 40B into the bottom or feed end of adsorber B. Adsorption bed A is very near the end of the adsorption step therein. As a result, during this step, adsorption bed A is de-pressurized countercurrently to feed flow, and adsorption bed A
is pressure equalized with adsorption bed B causing the pressure in bed B to rise. Also in this step, adsorption bed A continues to supply oxygen ga~ product, but this is terminated by the end of the step. Step No. 1 preferably has a duration of about 7 seconds. Throughout this step and all other steps there is con-tinuous air flow into the system and continuous product flow out.
Cocurrent to feed flow is in a direction from the inlet to the outlet of the adsorption bed and countercurrent to feed flow is in a direction from the outlet to the inlet of the adsorption bed.
The process of step No. 1 may be described as continuing to disch~rge product gas from the outlet of the first bed ~hile simultaneously equalizing the pressures of the first and second adsorption beds from the feed ends thereof by withdrawing gas from the feed inlet of the first adsorption bed at the end of the adsorption operation therein in a direction countercurrent to feed flow and introducing the withdrawn gas along with the gaseous mixture from feed gas stream to the feed inlet of the second adsorption bed in a direction cocurrent with feed flow and after pressurization thereof.
1136()65 As shown in Fi~. 2, at the transition between the end of step No. 1 and ~eginning of step No. 2, the pressures in beds A
and B are equalized at 20 p.s.i.g. and the pressure in the seg-regatèd storage adsorption ~ed C has remained at 7 p.S.i.g. At the beginning of step No. 2, valve 40B remains open, valve 40A
closes, and val~e 60A opens. No product gas is obtained from ad-sorption bed A. During this step, feed air continues to flow into the feed inlet 26 of adsorber B, and oxygen rich gas is taken as product from the outlet 28 of adsorber B and flows through flow control valve 50B into ~onduit section 7a and through the remaining system components as previously described to product outlet 66. At the same time, low purity gas flows from the outlet 20 of adsorber A through valve 60A and valve 62 into the segregated storage adsorption ~ed C. As a result, during this step adsorption bed A is pressure equalized with the 1~ segregated storage adsorption bed C. The automatic valve 62 can remain open during all steps or it can be opened and closed when necessary. Step No. 2 preferably has a duration of about 7 seconds.
The process of step No. 2 may be described as simul-taneously terminating the pressure equalization of step 1, ad-80rbing the gaseous mixture from the feed gas stream in the ~econd adsorption bed, releasing product gas from the outlet of the second adsorption bed, and eqalizin~ the pressures of the first adsorption bed and the segregated storage adsorption bed by wit~drawing low purity gas from the outlet of the first ad-sorption bed in a direction cocurrent with feed flow and intro-ducing the low purity gas into the segregated storage adsorption bed.
As is e~ident from steps 1 and 2 on Fig. 2 and from the foregoing descriptions thereof, it can be seen that bed A has undergone a decreasing pressure adsorption process; i.e., it has been producing product gas while simultaneousl~ experiencing a ~136(~65 reduction in pressure. While this is shown in Fig. 2 as oc-curring at the same time as beds A and B are undergoing FEE, it will be clear to those skilled in the art that concurrence with a FEE step is not essential, e.g., a bed cOula be made to per-form a decreasing pressure aasorption step while connected to an 5 SST, or to atmosphere, or otherwise.
As shown in Fig. 2, at the transition between the end of step No. 2 and the ~eginning of step No. 3, the pressures in adsorption beds A and C are equalized at 14 p.s.i.g. ana the pressure in adsorption bed B has risen to 28 p.s.i.g. At the beginning of step No. 3, valve 40B remains open, valve 60A closes and valve 46A opens. During this step feed air continues to enter bed B, and product quality oxygen rich gas continues to be taken as product from the outlet of bed 8 and is available at product outlet 66. Also during this step, adsorption bed A is depressurized to the atmosphere through valve 46A and waste out-let 44 in a direction countercurrent to feed flow. As a result, nitrogen rich waste gas is rejected to the atmosphere, and the pressure in adsor~er A drops from 14 p.s.i.g. to 0 p.s.i.g. Con-currently with the foregoing depressurization, a portion of the oxygen gas product flowing from adsorber B through flow control valve SOB flows throuqh valve 50A and valve 54 into adsorber A.
The product quality oxygen gas flows through bed A and out through valve 46A and waste outlet 44 in a direction opposite to that o~ air separation. This oxygen purge flowing countercurrent to feed flow displaces nitrogen from the adsorbent material in bed A, and nitrogen rich stream leaves the system through valve 46A and outlet 44 to the atmosphere. As a result, product ~uality oxygen gas is taken from the adsorbing bed B to purge the nitrogen loaded bed A in a reverse direction to reject un-wanted impurîty to the atmosphere. Step No. 3 preferably has aduration of about 39 seconds.
The process of step No. 3 may be described as simul-X
.
i~3~U65 taneously terminating the pressure equalization of step 2, con-tinuing adsorption of the gaseous mixture from feed gas stream in the second adsorption bed, releasing product gas from the outlet of the second adsorption bed, and depressurising the first ad-sorption bed in a direction countercurrent to feed flow and purging the first adsorption bed by diverting some product gas from the outlet of the second adsorption bed into the first aa sorption bed in a direction countercurrent to feed flow.
As shown in Tig. 2, at the transition between the end of step No. 3 and the beginning of step No. 4, the pressure in bed A
is at Q p.s.i.g., the pressure in segregated storage adsorption bed C has remained at 14 p.s.i.g., and the pressure in bed B has risen to 30 p.s.i.g. At the beginning of step No. 4, valve 40B
remains open, valve 46A closes, and valve 60A opens. Valve 62 if not already open is opened at the beginning of this step. During this step feed air continues to enter bed B, and product quality oxygen gas continues to be taken as product from the outlet of bed B and is available at product outlet 66. At the same time, gas flows from the segregated storage tank C through valves 62 and 60A into adsorber A through the outlet 20 thereof. This gas withdrawn from adsorption bed C during step 4 is a version of the gas supplied to bed C during step 2 which gas has been in1uenced by travel în bed C.
As a result, during this step the segregated storage adsorption bed C is pressure equalized with the adsorption bed A. At least during the initial portion of step 4, there is some additional flow of gas from bed B through valves 50B, 50A and 54.
Step No. 4 preferably has a duration of about 7 seconds.
The process of step No. 4 may be described as simul-taneously terminating the depressurîzing and purging of the first 3Q adsorption bed, continuing adsorption of the gaseous mixture from the ~eed gas 8tream in the second adsorption bed, releasing pro-duct gas from the outlet of the second adsorption bed and - il36065 equalizin~ the pressures of the se~regated storage adsorption bed and the first adsorption bed by withdrawing gas from the segregated storage adsorption bed and introducing the withdrawn gas into the first adsorption bed in a direction countercurrent to feed flow.
The foregoing process steps are repeated consecutively beginning with pressUre equalization of the adsorption beds from the feed ends t~ereof reversing the functions of the adsorption beds A and B. In particular, as shown in Fig. 2, at the transi-tion between the end of step No. 4 and the beginning of step No.
5, the pressures in beds A and C are equalized a~ 7 p.s.i.g. and the pressure in bed B has remained at 30 p.s.i.g. At the begin-ning of step No. 5, valve 4OB remains open, valve 6OA closes and valve 40A opens. During this step, gas flows from the bottom or feed end of adsorber B, which is near the end of its adsorption operation, in a reverse direction through valve 40B whereupon it mixes with the incoming feed air stream from conduit 10 and the resulting mixture flows through valve 40A into the bottom or feed end of adsorber A. As a result, adsorption bed B is pressure equalized with adsorption bed A, and bed A begins to adsorb the feed gas m;xture. This feed end equalization is similar to that which occurred during step No. 1 but in this step the roles of the beds A and B are interchanged. Also during this step, pro-duct quality oxygen rich gas continues to be taken as product from bed B and is available at product outlet 66. This step be-gins the second half of the process cycle wherein steps 5 - 8 are similar to 1 - ~ with the roles of beds A and B interchanged and with the valve sequence being the same with the A and B
designations interchanged. For example the process of step No.
6 (the same as step 2 with beds reversed) may be described as simultaneously terminating the pressure equalization of step No.
5, repressurizing the first adsorption bed while ~ithdrawing product gas therefrom, and egualizing pressures in the second ~ -16-.
adsorption bed and the segregated storage adsorption zone.
Equalizing the pressures of the adsorption beds A and Bat the feed ends thereof according to the present invention, as illustrated in step No. 1, advantageously reduces energy require-ments and increases oxygen recovery. When an adsorption bed at the end of the adsorption step therein is depressurized counter-currently to feed flow, i.e. as bed A from 30 p.s.i.g. to 20 p.s.i.g. in step No. 1, this gas can be introduced into the feed end of a repressurizing adsorber, i.e. adsorption bed B in step No. 1, without any appreciable loss in system performance com-pared to repressurizing with air from the system compressor 12.Feed and equalization according to the present invention thus greatly reduces the feed air requirement and increases oxygen recovery, i.e. decreases the size of compressor 12 required to produce a given amount of oxygen. Feed end equalization recovers energy, increases system efficiency and can be used for both low and high product delivery pressures. The foregoing advantages of course apply to both of the feed end equalizations which occur during a single cycle as illustrated in step Nos. 1 and 5.
The feed end equalization according to the present in-vention requires less adsorbent material in a given bed as com-pared to product end equalization for the follow~ng reasons. In product or outlet end equalization, the bed at the higher pres-sure depressurizes in a direction cocurrent to feed flow during the pressure equalization step. This causes the mass transfer zone to advance toward the product end of the bed as the pressure decreases. In order to contain the mass transfer zone during this step to maintain product purit~, a larger bed, i.e. more adsorbent material, is required. In feed end equalization ac-cording to the present invention, on the other hand, the bed at the higher pressure depressurizes in a direction countercurrent to feed flow durin~ the equalization step. In this step the mass transfer zone does not advance due to the direction of the 113S~
flow. The countercurrent depressurization also is beneficial for the subsequent purge step because nitrogen starts to flow toward the feed end of the bed during this step. ~he combination of no advancing of the mass transfer zone and countercurrent de-pressurization rèduces the amount of adsorbent material required.
S Bed size factor is a ~uantity used to compare the amount of adsorbent material required from one system or cycle to an-other. At a given bed siæe ~actor, it has been determined that using feed and equalization according to the present invention produces oxygen at a ~igher purity as compared to using product end equalization.
The combination of equalizing pressures of an adsorption bed and the segregated storage adsorption bed when the adsorption bed is at the end of the adsorption operation therein and prior to purging o~ the bed as illustrated in step No. 2 and thereafter equalizing pressures between these same two components after purging of the adsorption bed when it is at a relatively low pressure as illustrated in step No. 4 maximizes the utilization of the adsorption bed while at the same time maximizing purity of the product. In particular, during step No. 2 as the de-pre8sUriZing adsorber A equalizes cocurrently to feed flow intosegregated storage adsorption ~ed C, part of the nitrogen con-tained in the mass transfer zone of bed A will be transferred into the bed C. This allows for maximum and continual utiliza-tion of adsorption bed A, i.e. the mass transfer zone can be moved along bed A from inlet to outlet as far as possible. At the beginning of the flow from bed A to bed C the gas iS rich in oxygen but as flow continues the gas becomes more like air.
In addition, the segregated storage adsorption bed recovers some potential energy from the depressurizing adsorber and this, in turn, reduces system blo~down pressure and increases recovery and efficiency. Providing the segregated storage adsorption bed C in effect provides a mixing volume to smooth out any 1~6(~65 fluctuations in product purity which otherwise might occur whenthe front of the mass transfer zone breaks out of the output end of an adsorption bed. The foregoing advantages result when the system is operating at equilibrium conditions and at flow con-ditions for which the system is optimally designed. For example, when the system is used to supply oxygen for medical use, desi~n conditions occur at a flow rate of about 3.0 liters per minute.
During step No. 4 as the segregated storage adsorption bed C pressure equalizes countercurrently to feed flow into ad-sorber A, the gas returned to adsorber A is distxibuted or dis-persed therethrou~h in a manner which does not adversely affectproduct purity. The gas is not returned to adsorber A in a lump quantity concentrated in the output region of bed A but instead is spaced, equalized or dispersed through and along the bed A.
The fore~oing is believed to result from the fact that gas retu~n to adsorber A occurs when the latter is at a relatively low pressure, i.e. 0 p.s.i.g. after purging of adsorber A, which low pressure allows the gas to disperse through the bed. It is believed that low or zero pressure in bed A allows the incoming gas to move along the bed in a manner such that a large amount of nitrogen is not taken up by the adsorbent material adjacent the outlet end of the bed. At the beginning of gas flow from bed C to bed A, the gas is rich ln nitrogen but as the ~low con-tînues it becomes more rich in oxygen. The foregoing advantages are of course equally associated with the relationship between adsorption bed B and segregated storage adsorption bed C during step Nos. 6 and 8.
Providing the flow control valves 50A and 5QB allo~s the system to be balanced by providing individual control or adjustment of the purge gas flow to each of the adsorption beds 3a A and B. Providing an adjustable flow control valve associated with each bed permits compensating for differences in the beds and pipiny by simple manual ad~ustment of valves 50A, 50B.
3 13G(~S
An unbalanced system is characterized by the front of the mass transfer zone breaking through the output end of one bed sooner than in the other bed. In order to maintain purity, this would limit system operation to that o the bed which is first to ex-perience nitrogen breakthrough thereby causing the other ad-sorber to be underutilized with the result that the entire systemproduces less oxygen at a given purity. System balance and optimization are achieved by the independently adjustable flow control valves 50A, 50B. Advantageously, product gas also travels through these same valves toward the system product out-let 66. Alternatively, flow control valves 50A and 50B could bereplaced by two needle valves for independently controlling purge flow and then the combination of two check valves would be con-verted in parallel with the needle valves and poled to transmit product gas from the bed outlets to the system product outlet 66.
The automatic valve 54 in the path containing valves 50A, 50B is a shut down isolation valve which serves to isolate beds A and B when the system is shut down to maintain the re-spective pressures in the beds and prevent pressure equalization.
When the system is shut down, all the other automatic valves close also. Then when the system is placed in operation, less time is required to reach desired operating conditions by virtue of the beds A and B having been maintained at the respective pressures prior to shut down.
Table I presents data illustrating the effect of the segregated storage tank or segregated storage adsorption bed C
on system performance. The data presented in Table I is for oxygen product at a purity of 90% and the oxygen recovery in percent is presented for both low pressure and high pressure delivery conditions. The abbreviations S.S.T. for segregated 3Q storage tank and F.E.E. for feed end equalization are used.
~36~65 TABLE I
Low High Pressure Pressure Delivery Delivery S~S~To Absent 21% 21%
S . S . T . Present But Empty 25% 23%
S.S.T. Half Full of Adsorbent Material 35% 31%
S . S . T . Full And With F.E.E. 49% 48~6 Fig. 3 shaws a system according to another enibodim~t of the present invention wherein gas product can ~e withdra~ fmm the other end of t~e segregated storage adsorption bed. In the system shown in Fig. 3, o~
ponents identical to those of Fig. 1 are provided with the sane reference ~merals but with a prime designation. In addition, the system of Fig. 3 15 would also include adsorption beds identical to those designated A ar~l B in the ~ystem of Fig. l, along with similar connections of the fee~l gas stream to the gas inlets of the beds, connections of the gas inlets to the waste outlet, and connections of the gas outlets of the beds to the gas flow path ccxntaining the flaw control valves 50A' and 50B' Thus, the arra~2ds at 20 o~osite ends of the path sh~7wn in Fig. 3 containing autcmatic valves 60~', 60B' and the path containing flow control valves 5Q~' and 50B' indicate con-nection to the gas outlets of the corresponding adsorption beds A and B.
Similarly, the output of regulator 76' is cannecte~ through a throttle valve and flow indicator to a product outlet as indicated }~y the ar~ead in the 25 portion 74' of the gas flow path.
The opposite end of the segregated storage adsorption bed C ' is connected by a conduit 108 which contains an automatic valve 110 to the output conduit means, in particular to portion 74 ' thereof and upstream from regulator 76 ' . Upon opening of ~13~ 65 valve 110, product quality gas can be withdrawn from the segre-gated storage adsorption bed C' and introduced to the output con-duit means. Withdrawing product gas from the segregated storage adsorption bed can be advantageous in situations where low pres-sure rather than high pressure product delivery is needed. In addition, when product is delivered from the segregated storage adsorption bed C', the bed serves also as a product surge tank enabling product to be withdrawn from the system at a high flow rate for a short period of time before the mass transfer zone breaks through that end of the bed. On the other hand, recovery from a breakthrough condition can be relatively slow. Another advantage of withdrawing product gas from the segregated storage adsorption bed C' is that it provides a relatively higher rate of recovery of product. This is because withdrawal of product from bed C' reduces the pressure therein so that when the pressure equalizes with either of the adsorption beds that adsorption bed, in time, will be at a lower pressure. The lower pressure, in turn, imposes a lower blowdown requirement for that bed with a result that less gas is released to the atmosphere. This re-duction in the ~aste losses, in time, results in a higher per-2Q centage of product recovery. Another advantage associated withthe segregated storage adsorption bed involves feed end equaliz-tion which lowers the front of the mass transfer zone in each of the other two beds so that when the beds are equalized from the tops with the segregated storage adsorption bed there is less nitrogen to be taken up by the segregated storage adsorption bed.
As shown in Fig. 3, the system can also include a third reservoir conduit designated 114 connected at one end to the reservo;r 84' and coupled at the other end to the adsorption beds. In the present illustration, the other end of conduit 114 is connected to the flow path containing the automatic yalves 60A' and 60B' and is connected between these valves. Conduit 114 contains an automatic valve 116. Upon opening of valve 116, ~( . .
:~136065 product gas from reservoir 84', flows to the adsorption beds andit can be used for operations such as purging and repressuriza-tion.
The primary role of the reservoir in the system of the present invention is a reserve supply of product gas in the event of equipment malfunction or power failure. This is of particular importance when the system of the present invention supplies oxygen for medical use. Under normal operating conditions the reservoir is at a pressure of 28-29 p.s.i.g., and product oxygen flows through valve 72 and regulator 76 to product outlet 66.
If electrical power ;s interrupted, valve 72 closes and this is sensed by control 100 which opens valve 96. Oxygen flow con- !
tinues from the reservoir through valve 96 to the output conduit to outlet 66 until the supply in the reservoir is depleted. An alarm can ~e sounded to indicate the power interruption.
lS The reservoir also can be used to supply part or all of the purge oxygen required for an adsorber during its purge step.
This is accomplished by opening valve 116 at the appropriate time. The reservoir also can be used as another surge tank.
Pressure equalizations to and from the adsorbers can be accom-plished through the correct sequencing of valves 116 and 62.
The primary purpose of the reservoir is a xeserve oxygen supply in the event of a malfunction. The length o~ time the reserve oxygen lasts depends on the pressure in the reser-voir at the time of the malfunction. If the reservoir is used 25 only as a back-up oxygen supply, the reservoir pressure will be at its maximum at all times. If the reservoir is used to supply supplemental purge and or repressurization gas, the pressure in the reservoir will vary as will the reserve supply of oxygen.
The reservoir can comprise an adsorption bed but it also can comprise an ordinary tank of larger size.
Fig. 4 shows an arrangement for controlling the system and process of the present invention. The output conduit means >~
can be connected to a tank or similar storage receptacle orvessel 120 and gas product can be withdrawn therefrom through a conduit or path 122 for use. The sequencing and timing of the system including the control of the automatic valves is performed by a system control designated 124, and control signals or com-mands generated by the control 124 are transmitted by linescollectively designated 126 to the valves and other appropriate components of the system. Persons skilled in the art are readily familiar with such controls so that a detailed description there-of is believed to be unnecessary. Generally, the control 124 is responsive to the pressure of product gas within the storage element 120, and to this end a pressure sensor 130 is operatively connected to the storage element 120 by the connection designated 132. In accordance with the present invention, the output from sensor 130 is connected by a line 134 to an additional control means 136 which, in turn, is connected in controlling relation to the system control 124 by the connection designated 138. In accordance ~ith the present invention, it has been determined that once operation of the process and system has begun there is an optimum time at which to terminate operation, both in terms 2Q of a minimum number of cycles to be completed and a point within a cycle to terminate operation. The additional control functions to cause the System control 124 to maintain operati~n of the system, once begun, for a predetermlned number of cycles. It has been determined that in a system of the present invention for producing oxygen from ~eed air that a ~otal of two complete cycles pro~ides desirable results. One complete cycle includes step Nos. 1-8 described in Fig. 2. Furthermore, it has been determined that there is an optimum point within a cycle at which operation of the system and process should be terminated.
3a This is when the pressures are equal in the two adsorption beds A and B which is at the beginning of step Nos. 2 and 6 described in Fig. 2. Thus, the additional control 136 also functions to X
~136~5 stop the system only after two complete cycles have been com-pleted and only at an optimum point within the next cycle when the pressures are equal in the two adsorption beds A and B. The additional control can be of the cam type or step switch type, for example, and persons skilled in the art are readily familiar S with the construction and operation of these and other types which can be used for additional control 124 so that a detailed description thereof is believed to be unnecessary. Thus, the system control means 124 is responsive to gas pressure in storage means 120 signalled by sensing means 130 for stopping operation of the process and system normally when gas pressure in storage means 120 reaches a predetermined magnitude. The additional control means 136 overrides the system control means to terminate operation of the process and system only at a predetermined time.
lS It is therefore apparent that the present invention ac-complishes its intended objects. While several embodiments of the present invention have been described in detail, this is for the purpose of illustration, not limitation.
Claims (26)
1. A pressure swing adsorption process using at least one adsorption bed having a gas inlet and a gas outlet and at least one segregated storage adsorption bed, said process comprising the steps of flowing a feed gas mixture into said inlet of said at least one adsorption bed to adsorb at least one gas of said mixture within said bed while flowing the remainder of said gas mixture out of said bed outlet as product gas until said adsorption bed is about saturated with said one gas; flowing product gas from said bed outlet into said segregated storage adsorption bed by depressurising said at least one adsorption bed into said segregated storage adsorption bed until a mass transfer zone within said adsorption bed moves into said segregated storage adsorption bed, closing the flow path between said adsorption bed and said segregated storage adsorption bed; purging said one bed in a countercurrent direction; and flowing gas from said segregated storage adsorption bed back into said adsorption bed by depressurising said segregated storage adsorption bed and repressurising said purged at least one adsorption bed.
2. A process according to claim 1, wherein the segregated storage adsorption bed is segregated from the gas inlet of said at least one adsorption bed and is able to be communicated with the gas outlet of said at least one adsorption bed, and wherein the product gas flown from said bed outlet is of reduced purity due to the adsorption bed being about saturated with said one gas.
3. A process according to claim 2, wherein the withdrawn reduced purity product gas is introduced to only one end of said segregated storage adsorption bed as the sole gas introduced into said segregated storage adsorption bed; and gas is withdrawn from said one end of said segregated storage adsorption bed and passed into said at least one adsorption bed in a direction countercurrent to feed flow after desorption of the said at least one adsorption bed, the feed end of said at least one adsorption bed being closed during such passage, whereby said gas aids in repressurising said at least one adsorption bed.
4. A process according to claim 3, wherein, after withdrawal of gas from the outlet of said at least one adsorption bed into said segregated storage adsorption bed, the flow path between said at least one adsorption bed and said segregated storage adsorption bed is closed and said at least one adsorption bed is purged by flow therethrough of a purging gas in a direction which is countercurrent to the feed direction, before gas from said segregated storage adsorption bed is flowed back into said at least one adsorption bed to repressurise said at least one adsorption bed after purging.
5. A process according to claim 3 or claim 4, wherein the return of gas from said segregated storage adsorption bed into said at least one adsorption bed after purging takes place when the said at least one adsorption bed is at a relatively low pressure and the feed end of the said at least one adsorption bed is closed, whereby said returning gas repressurises that adsorption bed.
6. A process according to any one of claims 2, 3 or 4, using each of at least two said adsorption beds by sequentially passing the gaseous mixture from a feed stream through a first of said adsorption beds until the first bed is about saturated while simultaneously purging and then pressurising a second of said adsorption beds, and then passing the gaseous mixture from the feed stream through the second adsorption bed until the second bed is about saturated while simultaneously purging and then pressurising the first adsorption bed, withdrawing low purity gas from said first adsorption bed in a direction cocurrent with feed flow when said first adsorption bed is at the end of the adsorption operation therein and prior to purging of said first adsorption bed; introducing the withdrawn low purity gas to only one end of said segregated storage zone as the sole gas introduced into said segregated storage adsorption zone to move the mass transfer zone from said first adsorption bed into said segregated storage zone;
withdrawing gas from said one end of the segregated storage zone and passing said withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow after purging of said first adsorption bed and when said first adsorption bed is at a relatively low pressure, the feed end of said first adsorption bed being closed during such passage, whereby said gas starts repressurising said first adsorption bed; and then at the end of an adsorption phase in the second adsorption bed withdrawing gas from the outlet end thereof cocurrent with feed flow and into said segregated storage adsorption zone to move the mass transfer zone from said second adsorption bed into said segregated storage adsorption zone and later returning gas from said segregated storage adsorption zone into said second adsorption bed to repressurise said second adsorption bed.
withdrawing gas from said one end of the segregated storage zone and passing said withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow after purging of said first adsorption bed and when said first adsorption bed is at a relatively low pressure, the feed end of said first adsorption bed being closed during such passage, whereby said gas starts repressurising said first adsorption bed; and then at the end of an adsorption phase in the second adsorption bed withdrawing gas from the outlet end thereof cocurrent with feed flow and into said segregated storage adsorption zone to move the mass transfer zone from said second adsorption bed into said segregated storage adsorption zone and later returning gas from said segregated storage adsorption zone into said second adsorption bed to repressurise said second adsorption bed.
7. A process according to any one of claims 2, 3 or 4, wherein after purging of said one adsorption bed and partial repressurisation thereof with said withdrawn gas returned to said one adsorption bed, product gas is with-drawn from the outlet end of said segregated storage adsorption bed and recovered directly without further treatment.
8. A process according to claim 2, wherein the product gas is passed along a conduit system from said bed outlet to a product delivery conduit communicating with a product gas reservoir, said process further comprising the steps of noramlly preventing flow of product gas out of said reservoir, and flowing product gas from said reservoir to said delivery conduit when normal gas flow in said conduit system from said bed to said delivery conduit ceases, whereby product gas continues to be delivered to said delivery conduit even after failure of normal product gas flow until such time as said reservoir is exhausted.
9. A process according to claim 8, wherein normal flow of product gas to said product delivery conduit is by way of a control valve which closes automatically in response to failure of an associated main power supply, and where-in flow of product gas from said reservoir to said product delivery conduit is initiated automatically in response to closure of said control valve.
10. A process according to claim 8 or 9, wherein there are two said adsorption beds with their outlets connected to a product outlet conduit by a conduit system.
11. A process according to claim 8 or 9, wherein there are two said adsorption beds with their outlets connected to a product outlet conduit by a conduit system, and wherein said process comprises the steps of alternately and sequentially flowing a feed gas mixture into the inlet of one of said beds to adsorb at least one gas in said mixture in said one bed and flowing the remainder of the mixture out of the outlet of said one bed as product gas until said one bed is about saturated with said one gas, purging a second of said adsorption beds while performing the adsorption step in said one bed, and controlling the repetition to continue until an instant in the repetition, optimum for shut-down.
12. A process according to claim 8 or 9, wherein there are two said adsorption beds with their outlets connected to a product outlet conduit by a conduit system, and wherein said process comprises the steps of alternately and sequentially flowing a feed gas mixture into the inlet of one of said beds to adsorb at least one gas in said mixture in said one bed and flowing the remainder of the mixture out of the outlet of said one bed as product gas until said one bed is about saturated with said one gas, purging a second of said adsorption beds while performing the adsorption step in said one bed, and controlling the repetition to continue until an instant in the repetition, optimum for shut-down, said optimum point being decided on the basis of both an optimum point during the cycle and the completion of a minimum number of complete cycles from start-up.
13. A process according to claim 8 or 9, wherein there are two said adsorption beds with their outlets connected to a product outlet conduit by a conduit system, and wherein said process comprises the steps of alternately and sequentially flowing a feed gas mixture into the inlet of one of said beds to adsorb at least one gas in said mixture in said one bed and flowing the remainder of the mixture out of the outlet of said one bed as product gas until said one bed is about saturated with said one gas, purging a second of said adsorption beds while performing the adsorption step in said one bed, and controlling the repetition to continue until an instant in the repetition, optimum for shut-down, said optimum point being decided on the basis of both an optimum point during the cycle and the completion of a minimum number of complete cycles from start-up, said minimum number of cycles being 2.
14. A process according to claim 8 or 9, wherein there are two said adsorption beds with their outlets connected to a product outlet conduit by a conduit system, and wherein said process comprises the steps of alternately and sequentially flowing a feed gas mixture into the inlet of one of said beds to adsorb at least one gas in said mixture in said one bed and flowing the remainder of the mixture out of the outlet of said one bed as product gas until said one bed is about saturated with said one gas, purging a second of said adsorption beds while performing the adsorption step in said one bed, and controlling the repetition to continue until an instant in the repetition, optimum for shut-down, said continuation of the repetition terminating at an optimum point in the process, and said optimum point being at an instant when the pressures in the said at least two adsorption beds are equalised.
15. A process according to any one of claims 2, 3 or 4, using each of at least two said adsorption beds by sequentially passing the gaseous mixture from a feed stream through a first of said adsorption beds until the first bed is about saturated while simultaneously purging and then pressurising a second of said adsorption beds, and then passing the gaseous mixture from the feed stream through the second adsorption bed until the second bed is about saturated while simultaneously purging and then pressurising the first adsorption bed, withdrawing low purity gas from said first adsorption bed in a direction cocurrent with feed flow when said first adsorption bed is at the end of the adsorption operation therein and prior to purging of said first adsorption bed; introducing the withdrawn low purity gas to only one end of said segregated storage zone as the sole gas introduced into said segregated storage adsorption zone to move the mass transfer zone from said first adsorption bed into said segregated storage zone;
withdrawing gas from said one end of the segregated storage zone and passing said withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow after purging of said first adsorption bed and when said first adsorption bed is at a relatively low pressure, the feed end of said first adsorption bed being closed during such passage, whereby said gas starts repressurising said first adsorption bed; and then at the end of an adsorption phase in the second adsorption bed withdrawing gas from the outlet end thereof cocurrent with feed flow and into said segregated storage adsorption zone to move the mass transfer zone from said second adsorption bed into said segregated storage adsorption zone and later returning gas from said segregated storage adsorption zone into said second adsorption bed to repressurise said second adsorption bed, during adsorption on each of said first and second adsorption beds the feed gas mixture being flowed into the inlet end of one of the respective beds and product gas being flowed out of the outlet of said respective bed along an outlet conduit system in an unrestricted manner in a flow direction away from the bed and towards a main product outlet conduit whereas during purging of said respective bed using product gas from the other of said first and second adsorption beds the flow of purging gas into the said respective bed passing along said outlet conduit system in a direction from the main product outlet conduit towards the respective bed is restricted.
withdrawing gas from said one end of the segregated storage zone and passing said withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow after purging of said first adsorption bed and when said first adsorption bed is at a relatively low pressure, the feed end of said first adsorption bed being closed during such passage, whereby said gas starts repressurising said first adsorption bed; and then at the end of an adsorption phase in the second adsorption bed withdrawing gas from the outlet end thereof cocurrent with feed flow and into said segregated storage adsorption zone to move the mass transfer zone from said second adsorption bed into said segregated storage adsorption zone and later returning gas from said segregated storage adsorption zone into said second adsorption bed to repressurise said second adsorption bed, during adsorption on each of said first and second adsorption beds the feed gas mixture being flowed into the inlet end of one of the respective beds and product gas being flowed out of the outlet of said respective bed along an outlet conduit system in an unrestricted manner in a flow direction away from the bed and towards a main product outlet conduit whereas during purging of said respective bed using product gas from the other of said first and second adsorption beds the flow of purging gas into the said respective bed passing along said outlet conduit system in a direction from the main product outlet conduit towards the respective bed is restricted.
16. A process according to any one of claims 2, 3 or 4, using each of at least two said adsorption beds by sequentially passing the gaseous mixture from a feed stream through a first of said adsorption beds until the first bed is about saturated while simultaneously purging and then pressurising a second of said adsorption beds, and then passing the gaseous mixture from the feed stream through the second adsorption bed until the second bed is about saturated while simultaneously purging and then pressurising the first adsorption bed, withdrawing low purity gas from said first adsorption bed in a direction cocurrent with feed flow when said first adsorption bed is at the end of the adsorption operation therein and prior to purging of said first adsorption bed; introducing the withdrawn low purity gas to only one end of said segregated storage zone as the sole gas introduced into said segregated storage adsorption zone to move the mass transfer zone from said first adsorption bed into said segregated storage zone;
withdrawing gas from said one end of the segregated storage zone and passing said withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow after purging of said first adsorption bed and when said first adsorption bed is at a relatively low pressure, the feed end of said first adsorption bed being closed during such passage, whereby said gas starts repressurising said first adsorption bed; and then at the end of an adsorption phase in the second adsorption bed withdrawing gas from the outlet end thereof cocurrent with feed flow and into said segregated storage adsorption zone to move the mass transfer zone from said second adsorption bed into said segregated storage adsorption zone and later returning gas from said segregated storage adsorption zone into said second adsorption bed to repressurise said second adsorption bed, during adsorption on each of said first and second adsorption beds the feed gas mixture being flowed into the inlet end of one of the respective beds and product gas being flowed out of the outlet of said respective bed along an outlet conduit system in an unrestricted manner in a flow direction away from the bed and towards a main product outlet conduit whereas during purging of said respective bed using product gas from the other of said first and second adsorption beds the flow of purging gas into the said respective bed passing along said outlet conduit system in a direction from the main product outlet conduit towards the respective bed is restricted, said purging gas flow being restricted using means for simultaneously and automatically restricting flow towards said respective bed but allowing unrestricted flow in a direction away from said bed and towards said main product outlet conduit.
withdrawing gas from said one end of the segregated storage zone and passing said withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow after purging of said first adsorption bed and when said first adsorption bed is at a relatively low pressure, the feed end of said first adsorption bed being closed during such passage, whereby said gas starts repressurising said first adsorption bed; and then at the end of an adsorption phase in the second adsorption bed withdrawing gas from the outlet end thereof cocurrent with feed flow and into said segregated storage adsorption zone to move the mass transfer zone from said second adsorption bed into said segregated storage adsorption zone and later returning gas from said segregated storage adsorption zone into said second adsorption bed to repressurise said second adsorption bed, during adsorption on each of said first and second adsorption beds the feed gas mixture being flowed into the inlet end of one of the respective beds and product gas being flowed out of the outlet of said respective bed along an outlet conduit system in an unrestricted manner in a flow direction away from the bed and towards a main product outlet conduit whereas during purging of said respective bed using product gas from the other of said first and second adsorption beds the flow of purging gas into the said respective bed passing along said outlet conduit system in a direction from the main product outlet conduit towards the respective bed is restricted, said purging gas flow being restricted using means for simultaneously and automatically restricting flow towards said respective bed but allowing unrestricted flow in a direction away from said bed and towards said main product outlet conduit.
17. A process according to any one of claims 2, 3 or 4, using each of at least two said adsorption beds by sequentially passing the gaseous mixture from a feed stream through a first of said adsorption beds until the first bed is about saturated while simultaneously purging and then pressurising a second of said adsorption beds, and then passing the gaseous mixture from the feed stream through the second adsorption bed until the second bed is about saturated while simultaneously purging and then pressurising the first adsorption bed, withdrawing low purity gas from said first adsorption bed in a direction cocurrent with feed flow when said first adsorption bed is at the end of the adsorption operation therein and prior to purging of said first adsorption bed; introducing the withdrawn low purity gas to only one end of said segregated storage zone as the sole gas introduced into said segregated storage adsorption zone to move the mass transfer zone from said first adsorption bed into said segregated storage zone;
withdrawing gas from said one end of the segregated storage zone and passing said withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow after purging of said first adsorption bed and when said first adsorption bed is at a relatively low pressure, the feed end of said first adsorption bed being closed during such passage, whereby said gas starts repressurising said first adsorption bed; and then at the end of an adsorption phase in the second adsorption bed withdrawing gas from the outlet end thereof cocurrent with feed flow and into said segregated storage adsorption zone to move the mass transfer zone from said second adsorption bed into said segregated storage adsorption zone and later returning gas from said segregated storage adsorption zone into said second adsorption bed to repressurise said second adsorption bed , during adsorption on each of said first and second adsorption beds the feed gas mixture being flowed into the inlet end of one of the respective beds and product gas being flowed out of the outlet of said respective bed along an outlet conduit system in an unrestricted manner in a flow direction away from the bed and towards a main product outlet conduit whereas during purging of said respective bed using product gas from the other of said first and second adsorption beds the flow of purging gas into the said respective bed passing along said outlet conduit system in a direction from the main product outlet conduit towards the respective bed is restricted, said purging gas flow being restricted using means for simultaneously and automatically restricting flow towards said respective bed but allowing unrestricted flow in a direction away from said bed and towards said main product outlet conduit said means for simultaneously and automatically restricting flow comprising (a) a first polarised flow control valve, between the product gas outlet of said first adsorption bed and said second adsorption bed, designed to allow unrestricted gas flow in a direction from said outlet of said first bed toward said second adsorption bed but controlled flow in a direction towards said gas outlet of said first adsorption bed; and (b) a second polarised flow control valve, between the product gas outlet of said second adsorption bed and said first adsorption bed, allowing unrestricted gas flow in a direction from said outlet of said second bed toward said gas outlet of said first adsorption bed but controlled flow in a direction toward said gas outlet of said second bed, the main product outlet conduit being connected to a location in the flow path of gas between said first and second polarised flow control valves.
control valves.
withdrawing gas from said one end of the segregated storage zone and passing said withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow after purging of said first adsorption bed and when said first adsorption bed is at a relatively low pressure, the feed end of said first adsorption bed being closed during such passage, whereby said gas starts repressurising said first adsorption bed; and then at the end of an adsorption phase in the second adsorption bed withdrawing gas from the outlet end thereof cocurrent with feed flow and into said segregated storage adsorption zone to move the mass transfer zone from said second adsorption bed into said segregated storage adsorption zone and later returning gas from said segregated storage adsorption zone into said second adsorption bed to repressurise said second adsorption bed , during adsorption on each of said first and second adsorption beds the feed gas mixture being flowed into the inlet end of one of the respective beds and product gas being flowed out of the outlet of said respective bed along an outlet conduit system in an unrestricted manner in a flow direction away from the bed and towards a main product outlet conduit whereas during purging of said respective bed using product gas from the other of said first and second adsorption beds the flow of purging gas into the said respective bed passing along said outlet conduit system in a direction from the main product outlet conduit towards the respective bed is restricted, said purging gas flow being restricted using means for simultaneously and automatically restricting flow towards said respective bed but allowing unrestricted flow in a direction away from said bed and towards said main product outlet conduit said means for simultaneously and automatically restricting flow comprising (a) a first polarised flow control valve, between the product gas outlet of said first adsorption bed and said second adsorption bed, designed to allow unrestricted gas flow in a direction from said outlet of said first bed toward said second adsorption bed but controlled flow in a direction towards said gas outlet of said first adsorption bed; and (b) a second polarised flow control valve, between the product gas outlet of said second adsorption bed and said first adsorption bed, allowing unrestricted gas flow in a direction from said outlet of said second bed toward said gas outlet of said first adsorption bed but controlled flow in a direction toward said gas outlet of said second bed, the main product outlet conduit being connected to a location in the flow path of gas between said first and second polarised flow control valves.
control valves.
18. A pressure swing adsorption process using at least one adsorption bed having a gas inlet and a gas outlet and at least one segregated storage zone, comprising the steps of flowing a feed gas mixture into said bed inlet to adsorb at least one gas of said mixture within said bed while flowing the remainder of said gas mixture out of said bed outlet as product gas until said bed is about saturated with said one gas, flowing gas from said bed outlet into said zone by depressurising said bed into said zone until the mass transfer front within said bed moves into said zone, closing the flow path between said bed and said zone, purging said one bed in a counter-current direction, flowing gas from said zone back into said bed by depressur-ising said zone and repressurising said purged one bed, wherein said process uses at least two adsorption beds each having a gas inlet and a gas outlet, and the step of flowing gas out of the inlet end of one bed and into the inlet end of the other bed to pressure equalise said two beds from their inlet ends while simultaneously flowing product gas out of the product end of said one bed.
19. A pressure swing adsorption process using at least one adsorption bed having a gas inlet and a gas outlet and at least one segregated storage zone, comprising the steps of flowing a feed gas mixture into said bed inlet to adsorb at least one gas of said mixture within said bed while flowing the remainder of said gas mixture out of said bed outlet as product gas until said bed is about saturated with said one gas, flowing gas from said bed outlet into said zone by depressurising said bed into said zone until the mass transfer front within said bed moves into said zone, closing the flow path between said bed and said zone, purging said one bed in a counter-current direction, flowing gas from said zone back into said bed by depressurising said zone and repressurising said purged one bed, using at least two adsorption beds each having a gas inlet, a gas outlet, and conduit means con-necting said gas outlets to product outlet conduit means, said process comprising the additional steps of alter-nately and sequentially flowing said feed gas mixture into the inlet of one of said beds to adsorb at least one gas in said mixture in said one bed and flowing the remainder of the mixture out of said one bed outlet as said product gas until said one bed is about saturated with said one gas, purging a second bed while perform-ing the producing step in said one bed, controlling the repetition of said steps to permit their alternate and sequential repetition to stop only at an optimum point in the process, and wherein said optimim point is a point in time immediately after the process has completed at least two complete cycles and the pressures in said at least two beds have been equalized.
20. A pressure swing adsorption process using at least one adsorption bed having a gas inlet and a gas outlet and at least one segregated storage zone, comprising the steps of flowing a feed gas mixture into said bed inlet to adsorb at least one gas of said mixture within said bed while flowing the remainder of said gas mixture out of said bed outlet as product gas until said bed is about saturated with said one gas, flowing gas from said bed outlet into said zone by depressurising said bed into said zone until the mass transfer front within said bed moves into said zone, closing the flow path between said bed and said zone, purging said one bed in a counter-current direction, flowing gas from said zone back into said bed by depressurising said zone and repressurising said purged one bed, using conduit means for flowing said product gas from said bed outlet to product delivery means and into a product gas reservoir, normally pre-venting flow of product gas out of said reservoir, sens-ing the normal product gas flow in said conduit means from said bed to said delivery means, and flowing prod-uct gas from said reservoir to said delivery means upon sensing failure of said normal gas flow, whereby product gas continues to be delivered even after failure of normal product gas flow until said reservoir is exhausted.
21. In a pressure swing process for fractionating at least one component from a gaseous mixture by selective adsorption in each of at least two adsorption zones, each adsorption zone having a gas inlet and a gas outlet, by sequentially passing the gaseous mixture from a feed stream through a first adsorption zone until the zone is about saturated while simultaneously purging and then pressurising a second adsorption zone and then passing the gaseous mixture from the feed stream through the second adsorption zone until the zone is about saturated while simultaneously purging and the pressurising the first adsorption zone, the improvement comprising:
a) withdrawing low purity gas from one of the adsorption zones in a direction cocurrent with feed flow when the zone is at the end of the adsorption operation therein and prior to purging of the zone;
b) introducing the withdrawn low purity gas to one end of a segregated storage adsorption zone and closing the flow path between said one of the adsorption zones and the segregated storage adsorption zone; and c) re-opening the flow path between said one of the adsorption zones and the segregated storage adsorption zone and withdrawing gas from said one end of the segregated storage adsorption zone and passing said withdrawn gas into said one adsorption zone in a direction countercurrent to feed flow after purging of the zone and when the zone is at a relatively low pressure.
a) withdrawing low purity gas from one of the adsorption zones in a direction cocurrent with feed flow when the zone is at the end of the adsorption operation therein and prior to purging of the zone;
b) introducing the withdrawn low purity gas to one end of a segregated storage adsorption zone and closing the flow path between said one of the adsorption zones and the segregated storage adsorption zone; and c) re-opening the flow path between said one of the adsorption zones and the segregated storage adsorption zone and withdrawing gas from said one end of the segregated storage adsorption zone and passing said withdrawn gas into said one adsorption zone in a direction countercurrent to feed flow after purging of the zone and when the zone is at a relatively low pressure.
22. The improved process according to claim 21 further including withdrawing product gas from the other end of said segregated storage adsorption zone.
23. A pressure swing process for fractionating at least one component from a gaseous mixture by selective adsorption in each of at least two adsorption zones comprising the steps of:
a) providing a first adsorption bed having a gas inlet and a gas outlet, at least one additional adsorption bed having a gas inlet and a gas outlet, the gas inlets of said first and additional adsorption beds being selectively connected to a feed gas stream, and a segregated storage adsorption bed isolated from direct communication with the feed gas stream;
b) withdrawing gas from said first adsorption bed at the end of the adsorption operation therein in a dir-ection countercurrent to feed flow and introducing the withdrawn gas along with the gaseous mixture from the feed gas stream into said additional adsorption bed in a dir-ection cocurrent with the feed flow and after pressurisation thereof to equalize the pressures in said adsorption beds from the feed ends thereof;
c) terminating said pressure equalization of said beds from the feed ends thereof and simultaneously ad-sorbing the gaseous mixture from the feed gas stream in said additional adsorption bed, releasing product gas from the outlet of said additional adsorption bed and equalizing the pressures of said first adsorption bed and said segregated storage adsorption bed by withdrawing low purity gas from said first adsorption bed in a direction cocurrent with feed flow and introducing said low purity gas into one end of said segregated storage adsorption bed;
d) terminating said pressure equalization of said first and segregated storage adsorption beds by closing the flow path between the first adsorption bed and the segregated storage adsorption bed and simultaneously adsorbing the gaseous mixture from the feed gas stream in said additional adsorption bed, and depressurising said first adsorption bed in a direction countercurrent to feed flow and purging said first adsorption bed by diverting product gas from the outlet of said additional adsorption bed into said first adsorption bed in a direction countercurrent to feed flow;
e) terminating said depressurising and purging of said first adsorption bed and simultaneously adsorbing the gaseous mixture from the feed gas stream in said additional adsorption bed, releasing product gas from the outlet of said additional adsorption bed and equalizing the pressures of said segregated storage adsorption bed and said first adsorption bed by withdrawing gas from said one end of said segregated storage adsorption bed and introducing the withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow; and f) thereafter consecutively repeating said steps beginning with pressure equalization of said beds from the feed ends thereof reversing the functions of said first adsorption bed and said additional adsorption bed.
a) providing a first adsorption bed having a gas inlet and a gas outlet, at least one additional adsorption bed having a gas inlet and a gas outlet, the gas inlets of said first and additional adsorption beds being selectively connected to a feed gas stream, and a segregated storage adsorption bed isolated from direct communication with the feed gas stream;
b) withdrawing gas from said first adsorption bed at the end of the adsorption operation therein in a dir-ection countercurrent to feed flow and introducing the withdrawn gas along with the gaseous mixture from the feed gas stream into said additional adsorption bed in a dir-ection cocurrent with the feed flow and after pressurisation thereof to equalize the pressures in said adsorption beds from the feed ends thereof;
c) terminating said pressure equalization of said beds from the feed ends thereof and simultaneously ad-sorbing the gaseous mixture from the feed gas stream in said additional adsorption bed, releasing product gas from the outlet of said additional adsorption bed and equalizing the pressures of said first adsorption bed and said segregated storage adsorption bed by withdrawing low purity gas from said first adsorption bed in a direction cocurrent with feed flow and introducing said low purity gas into one end of said segregated storage adsorption bed;
d) terminating said pressure equalization of said first and segregated storage adsorption beds by closing the flow path between the first adsorption bed and the segregated storage adsorption bed and simultaneously adsorbing the gaseous mixture from the feed gas stream in said additional adsorption bed, and depressurising said first adsorption bed in a direction countercurrent to feed flow and purging said first adsorption bed by diverting product gas from the outlet of said additional adsorption bed into said first adsorption bed in a direction countercurrent to feed flow;
e) terminating said depressurising and purging of said first adsorption bed and simultaneously adsorbing the gaseous mixture from the feed gas stream in said additional adsorption bed, releasing product gas from the outlet of said additional adsorption bed and equalizing the pressures of said segregated storage adsorption bed and said first adsorption bed by withdrawing gas from said one end of said segregated storage adsorption bed and introducing the withdrawn gas into said first adsorption bed in a direction countercurrent to feed flow; and f) thereafter consecutively repeating said steps beginning with pressure equalization of said beds from the feed ends thereof reversing the functions of said first adsorption bed and said additional adsorption bed.
24. The process according to claim 23, wherein the gaseous mixture is air and the product gas is high purity oxygen.
25. The process according to claim 23, further including controlling said process steps in a manner such that said process is continued for a predetermined number of cycles.
26. The process according to claim 23, further including controlling said process steps in a manner such that said process is terminated only at an optimum point therein.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000378988A CA1136065A (en) | 1976-11-26 | 1981-06-03 | Pressure swing adsorption process and system for gas separation |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US74528576A | 1976-11-26 | 1976-11-26 | |
| US745,285 | 1976-11-26 | ||
| CA291,552A CA1132918A (en) | 1976-11-26 | 1977-11-23 | Pressure swing adsorption process and system for gas separation |
| CA000378988A CA1136065A (en) | 1976-11-26 | 1981-06-03 | Pressure swing adsorption process and system for gas separation |
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| Publication Number | Publication Date |
|---|---|
| CA1136065A true CA1136065A (en) | 1982-11-23 |
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| Application Number | Title | Priority Date | Filing Date |
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| CA000378988A Expired CA1136065A (en) | 1976-11-26 | 1981-06-03 | Pressure swing adsorption process and system for gas separation |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114413169A (en) * | 2021-12-25 | 2022-04-29 | 安徽明天氢能科技股份有限公司 | Nitrogen control pipeline system for hydrogenation station |
-
1981
- 1981-06-03 CA CA000378988A patent/CA1136065A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114413169A (en) * | 2021-12-25 | 2022-04-29 | 安徽明天氢能科技股份有限公司 | Nitrogen control pipeline system for hydrogenation station |
| CN114413169B (en) * | 2021-12-25 | 2023-12-22 | 安徽明天氢能科技股份有限公司 | Nitrogen control pipeline system for hydrogenation station |
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