CA1143301A - Pressure swing adsorption process and system for gas separation - Google Patents
Pressure swing adsorption process and system for gas separationInfo
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- CA1143301A CA1143301A CA000378989A CA378989A CA1143301A CA 1143301 A CA1143301 A CA 1143301A CA 000378989 A CA000378989 A CA 000378989A CA 378989 A CA378989 A CA 378989A CA 1143301 A CA1143301 A CA 1143301A
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Abstract
PRESSURE SWIEG ADSORPTION PROCESS
AND SYSTEM FOR GAS SEPARATION
ABSTRACT OF THE DISCLOSURE
A pressure swing absorption 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 thereof 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 putlets 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 or for aug-menting system function.
AND SYSTEM FOR GAS SEPARATION
ABSTRACT OF THE DISCLOSURE
A pressure swing absorption 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 thereof 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 putlets 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 or for aug-menting system function.
Description
11~33~1 BA~KGROUND OF THE INVENTION
This invention relates to the art of separation of gas mixtures, and more particularly 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 ~he adsorbent material and re-generate the adsorption capacity. To increase the efficiency ofregeneration, a pùrge 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 proce6ses and systems, it would be highly desirable to provide
This invention relates to the art of separation of gas mixtures, and more particularly 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 ~he adsorbent material and re-generate the adsorption capacity. To increase the efficiency ofregeneration, a pùrge 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 proce6ses and systems, it would be highly desirable to provide
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1~433~1 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.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of this invention to provide a new and improved process and system for separation and fractionation 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 degree of product purity.
It is a further object of this invention to provide such a process and system which has reduced adsorbant material requirements along with a high degree of product purity.
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11~33~1 It is a further object of this in~ention to provide such a process and system whic~ ~aintains 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, the present invention provides, 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 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 pressurizing 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 then pressurizing the first adsorption zone, the improvement comprising withdrawing gas from one of said adsoprtion zones 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 the feed stream into the other of said adsorption zones in a direction cocurrent with feed flow to equalize the pressures in said adsorption zones from the feed ends thereof.
In another aspect, the present invention can be generally defined as providing a system for fract-ionating at least one component from a gaseous mixture by pressure swing adsorption, including 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; means for connecting said gas inlets of said adsorption beds to each other and to ~4~
li433~1 a feed gas stream; a product outlet; means for coupling said gas outlets of said adsorption ~eds to said product outlet;
and a system control unit for controlling system operation including sequentially passing the gaseous mixture from a feed stream through said first adsorption bed until said bed i5 substantially saturated while simultaneously purging and then pressurizing said additional adsorption bed and then passing the gaseous mixture from the feed stream through said additional adsorption bed until said bed is substantially saturated while simultaneously purging and then pressurizing said first adsoprtion bed.
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 DRAWING 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 present invention;
Fig. 3 is a schematic diagram of a pressure swing adsoxption system with parts removed according to another embodiment of the present invention; and Fig. 4 is a shematic block diagram of a control arrangement according to the present invention for a pressure swing adsorption system.
11~3301 DETAILED DESCRIPTION OF THE ILLUSTRAT~D EMBODIMENTS
Referring now to ~ig. 1, there is shown a system ac-cording to the present invention for fractionating at least one c~mponent from a gaseous mixture ~y 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 or~anic and/or inorganic gas mixtures.
The system includes a first adsorption bed 16, also desi~nated 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, having 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 6uitable pressure vessels, piping or tubing, con-nectors, valves and auxiliary devices and element~. Likewise, adsorbent materials are well-known in the art, and one skilled in the art may select an adsorbent material(s) which is com-mercially recommended for the separation or fractionation of theparticular gas to be purified. Examples of typical adsorbent materials for use in ad orption beds include natural or synthetic zeolites, silica ~el, alumina and the like. Generally, the ad-~orbent beds in a system contain the same adsorbent material,
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1~433~1 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.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of this invention to provide a new and improved process and system for separation and fractionation 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 degree of product purity.
It is a further object of this invention to provide such a process and system which has reduced adsorbant material requirements along with a high degree of product purity.
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11~33~1 It is a further object of this in~ention to provide such a process and system whic~ ~aintains 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, the present invention provides, 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 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 pressurizing 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 then pressurizing the first adsorption zone, the improvement comprising withdrawing gas from one of said adsoprtion zones 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 the feed stream into the other of said adsorption zones in a direction cocurrent with feed flow to equalize the pressures in said adsorption zones from the feed ends thereof.
In another aspect, the present invention can be generally defined as providing a system for fract-ionating at least one component from a gaseous mixture by pressure swing adsorption, including 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; means for connecting said gas inlets of said adsorption beds to each other and to ~4~
li433~1 a feed gas stream; a product outlet; means for coupling said gas outlets of said adsorption ~eds to said product outlet;
and a system control unit for controlling system operation including sequentially passing the gaseous mixture from a feed stream through said first adsorption bed until said bed i5 substantially saturated while simultaneously purging and then pressurizing said additional adsorption bed and then passing the gaseous mixture from the feed stream through said additional adsorption bed until said bed is substantially saturated while simultaneously purging and then pressurizing said first adsoprtion bed.
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 DRAWING 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 present invention;
Fig. 3 is a schematic diagram of a pressure swing adsoxption system with parts removed according to another embodiment of the present invention; and Fig. 4 is a shematic block diagram of a control arrangement according to the present invention for a pressure swing adsorption system.
11~3301 DETAILED DESCRIPTION OF THE ILLUSTRAT~D EMBODIMENTS
Referring now to ~ig. 1, there is shown a system ac-cording to the present invention for fractionating at least one c~mponent from a gaseous mixture ~y 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 or~anic and/or inorganic gas mixtures.
The system includes a first adsorption bed 16, also desi~nated 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, having 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 6uitable pressure vessels, piping or tubing, con-nectors, valves and auxiliary devices and element~. Likewise, adsorbent materials are well-known in the art, and one skilled in the art may select an adsorbent material(s) which is com-mercially recommended for the separation or fractionation of theparticular gas to be purified. Examples of typical adsorbent materials for use in ad orption beds include natural or synthetic zeolites, silica ~el, alumina and the like. Generally, the ad-~orbent beds in a system contain the same adsorbent material,
3~ however, each bed may contain a different type of adsorbent material or different mixtures of adsorbent material as desired.
11~3301 The particular adsorbent material or mixtures used are notcritical 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, ad orption bed C is appr~ximatelythe same s~ze as the adsorption beds A and B and may contain the same type of adsorbent material, but the segregated storage ad-sorption bed C can be 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 10 containing the feed gas stream by suitable conduit means including an automatic valve 40A and, similarly, the gas inlet 26 of adsorption bed B i5 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 be open to the atmosphere or which can ~e in fluid communication with a waste ~a~ stream. The gas inlets 18 and 26 of adsorptiGn beds A and B, respectively, also are connected to the waste gas outlet 44 by suitable corresponding conduit means includi.n~ automatic valves 46A and 46B, respectively. The auto-matic valves 40 and 46 and those additional automatic valves to be described can be of the ~olenoid-operated type, but in any event are of the type ~hich are operated to be either fully open 3Q or fully closed.
The system of the present invention further comprises means 5uch as suitable conduits or piping defin~ng a gas flow _7_ ., -.. .
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 adsorption 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 flow therethrough in a direction from gas 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 2B of thr adsorption beds, and in the system shown valve 54 20 i8 connected between gas outlet 20 of adsorption bed A and the flow control valve 5OA.
The system of the present invention includes a second ga6 flow path provided by ~uitable conduits or piping wh~ch ~ins the gas outlets 20 and 28 of the adsorption beds A and B, re-~pectively. A first automatic valve 60A is connected in the pathaajacent outlet 20 of bed A, and a ~econd automatic valve 60B is connected in the path ad~acent outlet 28 of adsorption bed B.
The ~egregated 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 ~ystem of the present invention ~urther comprises a product outlet designated 66 and output conduit means for ~1~3301 coupling the gas outlets of the adsorption beds to the productoutlet 66. In the system shown the output conduit means is con-nected to the first flow path at a point between the fl~w control valves 50A and 50B and includes a first section 70 including an automatic valve 72 and a second section 74 including the series combination of a pressure regulator 76, a throttle valve 78 and a flow meter 80. The flow rate of product to the outlet 66 i~ con-trolled by valve 78 which preferably is a manual~y adjustable needle-type valve, and the flow rate is indicated visually by the meter 80.
The system of the present inven~ion further comprises a reservoîr 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 conduit 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 ~orm of a throttle valve which preferably is manually adju~table is connected in the conduit and preferably between check valve 30 and reservoir 84. Valve 92 can be used to control the rate of ~low of gas product into reservoir 84. A ~econd reservoir conduit means is connected at one end to reservoir 84 through conduit 86 and at the other end to the sy~tem output con-duit means and includes valve means 96 for controlling the flowof product gas from reservoir 84 to the output conduit means. A
control lO0 îs connected by lines 102 and 103 to valveæ 72 and 96, respectiY~ly, and functions 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.
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1~33~
In general, the present invention is illustrated in terms of a process and system utilizing a first ads~rption bed, a second adsorption bed and a segregated storage adsorption bed.
However, the process and system can employ more than one first adsorption bed, mare than one second adsorption bed and more than one segregated storage adsorption bed. The adsorption beds com-municate with the feed gas stream which supplies the gaseous mix-ture, and the segregated storage adsorption bed never directly communicates with or is directly exposed to the feed gas stream.
Altbough the process and system of the present invention are described 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 may 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 ~elected in a ~imilar manner. Pressurizing or pressurization refers to the increase of pressure in the vessel and associated piping of an 2~ 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 4a 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 ;, -10-~ `" ' ' ' 1~33~)1 high purity oxygen gas product, a delivery pressure of around 3 p.s.i.g. is employed for medical uses and breathing de~ices whereas ahigher delivery pressure of up to about 40 p.~.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 ~ystem 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 ~quare inch gage.
lQ The particular operation carried out in each ads~rption bedduring each step is shown in Fig. 2, most of which are ab-breviated for convenience in illustration. Thus "FEE" refers to feed end equalization 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 repsessurizing to increase the pressure in an adsorption bed, and "PURGE" refers to introduction of purge gas or purging.
Referring now in detail to Fig. 2, prior to step No. 1 the gaseous mixture i.e. ordinary air, has been flowing from the feed gas stream in conduit 10 and through valve 40A which is open into and through adsorption bed A wherein nitrogen is adsorbed.
High 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 coduit ~ection 74 and through the series combînation of pressure regulator 76, needle valve 78 and flow meter 80 to the product outlet 66 for use. Ju~t prior to the beginning of step No. 1, 3Q adsorption bed A i8 about saturated and nearing the end of the adsorption operation therein. ~lso ~u~t prior to the beginning of ~tep ~o. 1, adsorption bed A i~ at a higher pressure than the : , ~1~3301 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.
S 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 r~se. Also in this step, adsorption bed A continues to supply oxygen gas product, but this is terminated by the end of the step. Step No. 1 preferably has a duration of about 7 seconds. Thxoughout this step and all other steps there is con-tinuous air flow into the system and continuous product flow out.
Cocurrent to feed flow îs 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 ~ed.
The process of step No. 1 may be described as continuing to discharge 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 ga~ 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.
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As shown in ~ig. 2, at the txansition between the end o~
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-regated storage adsorption bed C has remained at 7 p.s.i.g. At the beginning of step No. 2, valve 40B remains open, valve 4QA
closes, and valve 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 conduit section 7Q 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 6Q~ and valve 62 into the segregated storage adsorption bed C. As a result, during this step adsorption bed A is pressure equalized with the 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 ~econds.
The process of step NQ. 2 may be described as simul-taneously terminating the pressure equalization of step 1, ad-sorbing the gaseous mixture from the feed gas stream in the ~econd adsorption bed, releasing product gas from the outlet of the second adsorpti~n bed, and eqalizing the pressures of the first adsorption bed and the segregated storage adsorption bed 2~ by withdrawing low purity gas from the outlet of the first ad-soxption bed in a direction cocurrent with feed flow and intro-ducin~ the low purity gas into the segregated storage adsorptîon bed.
As is evident from steps 1 and 2 on Fig. 2 and from the foregoing descriptions thereof~ it can be ~een that bed A has undergone a decreasing pressure adsorption proces~; i.e., it has been producing product gas whlle simultaneously experiencing a ~3301 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 could be made to per-~orm a decreasing pressure adsorption step while connected to an SST, or to atmosphere, or otherwise.
As shown in Fig. 2, at the transition between the end of step No. 2 and the beginnîng of ~tep No. 3, the pressures in adsorption beds A and C are equalized at 14 p.s.i.g. and 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 B 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 adsorber 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 flowin~ from adsorber B through flow control valve 50B flows through ~alve 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 of air separation. This oxygen purge flowing countercurrent to feed ~low 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 ~ in a reverse direction to reject un-wanted impurity to the atmosphere. Step No. 3 preferably has aduration of about 39 seconds.
The process of step No. 3 may be described as simul- -~33(~
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 æecond 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 ad-sorption bed in a direction countercurrent to feed flow.
As shown in ~ig. 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 40~
remains open, valve 46A closes, and valve 60A opens. Valve 62 if not already open is opened at the beginning of this step. During lS this step eed air continues to enter bed B, and product ~uality oxy~en 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 ~rom adsorption bed C during step 4 is a version of the gas supplied to bed C during step 2 which gas has been in~luenced by travel in bed C.
As a result, during this step the ~egregated storage adsorption bed C is pressure equalized with the adsorption bed A. At least durin~ the initial portion of step 4, there i6 some additional flow of gas from bed B through valves 50B, 50A and 54.
Step No. 4 preferably has a duration of about 7 ~econds.
The process of step No. 4 may be descrîbed as simul-taneously terminating the depressurizing and purging of the first 3a adsorption bed, ~ontinuing adsorption of the gaseous mixture from the feed gas stream in the second adsorption bed, releasing pro-duct gas from the outlet of the second adsorption bed and 11~33~
equalizing the pressures of the segregated 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 thereof 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 at 7 p.s.i.g. and the pressure in bed B has remained at 30 p.s.i.g. At the begin-ning of ~tep No. 5, valve 40B remains open, valve 60A closes and valve 4OA opens. During this step, gas flows from the bottom or feed end of ~dsorber 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 - 4 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 ~tep No.
6 tthe same as step 2 with beds reversed~ may be described as ~imultaneously texminating the pressure equalization of step No.
5, repressurizing the first adsorption bed while withdrawing product gas there~rom, and equalizing pressures in the second -~6-.
. . . .
33~1 adsorption bed and the segregated storage adsorp~ion zone.
Equalizing the pressures of the adsorption beds A and Bat the feed ends thereof according to the presen~ 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 egualization 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 eed 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 t~ product end equalization for the following 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 8tep to maintain product purit~, a larger bed, i.e. more adsorbent material, iB required. In feed end equalizatàon ac-cording to the present invention, on the other hand, the bed at the higher pressure depressuxizes in a direction countercurrent to feed flow during the equalization 6tep. In this ~tep the mass transfer zone does not advance due to the d$rection of the 1~4335~1 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. The combination of no advancing of the mass transfer zone and countercurrent de-pressurization reduces the amount of adsorbent material required.
S Bed size factor is a quantity used to compare the amount of adsorbent material required from one system or cycle to an-other. At a given bed size factor, it has been determined that using feed and equalization according to the present in~ention 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 i8 at the end of the adsorption operation therein and prior to purging of the bed as illustrated in step No. 2 and thereafter lS 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-pressurizing adsorber A equalizes cocurrently to feed flow intosegregated storage adsorption bed C, part of the nitrogen con-tained in the mass trans~er zone of bed A will be transferred into the bed C. This allows for maximum and continual util~za-tion Oæ 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 fIow continues the gas becomes more like air.
In addition, the ~egregated storage adsorption bed recovers some potential energy from the depressurizing adsorber and this, in turn, reduces sy~tem blowdown pressure and increases recovery and efficiency. Providing the segregated storage adsorption ~ed C in effect provides a mixing volume to smooth out any .. . . . . .
1~433~31 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 desi~ned. For example, when the system is used to supply oxygen for medical use, design conditions occur at a flow rate of about 3.0 liters per minute.
During step No. 4 ~s the segregated storage adsorption bed C pressure e~ualizes countercurrently to feed fl~w into ad-sorber A, the gas returned to adsorber A is distributed or dis-persed therethrough in a manner which does not adversely affe~tproduct 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 foregoing is believed to result from the fact that gas return 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 a~ount of nitrogen is not taken up by the adsorbent material adjacent the outlet end of the bed. At the beginning of gas ~low from bed C to bed A, the gas is rich in nitrogen but as the ~low con-tinues it becomes more rich in oxygen. The foregoing advantageq are of cour~e egually associated with the relationship between adsorption bed B and ~egregated storage adsorption bed C during step Nos. 6 and 8.
Providing the ~low control valves 5QA and 5QB allous the system to be balanced by providing individual control or adjustment of the purge gas flo~ to each of the adsorption beds A and B. Providing an adjustable flow control va~ve associated with each ~ed permit6 compensating for dif~erences in the beds and piping b~ simple manual ad~ustment of valves 5QA, 50B.
' ~433~)1 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 t~ that of 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, 10ss time is required to reach desired operating conditions by virtue of the beds A and ~ having been maintained at the respective pressures prior to shut down.
Table I presents data illustrating the effect of the segregated storage tank or ~egregated storage adsorption bed C
on system performance. ~he 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 abbreviation~ S.S.T. for segregated 3Q storage tank and F.E.E. for feed end equalization are used.
,,~, , ~33~1 TABLE I
Low High Pressure Pressure Delivery Delivery S.S.T. Absent 21% 21%
S.S.T. Present But Empty 25% 23%
S.S.T. ~alf Full of Adsorbent Material 35% 31%
S.S.T. Full And With F.E.E. 49% 48%
~ig. 3 shows a system according to another embodiment of the present invention wherein gas product can be with~rawn from the other end of the segregated storage adsorption bed. In the ~ystem shown in Fig. 3, oomr ponents identical to th~e of Flg. 1 are provided with the same reference numerals but with a prime designation. In addition, the sy6tem of Fig. 3 would also include adsorption beds identical to thnse designated A and B in the system of Fig. 1, along wnth sinilar oonnections of the feed gas stream to the gas inlets of the beds, oonnections of the gas inlets to the waste outlet, and connections of the gas outlets of the beds to the gas flow path containing the flow control valves 5~A' and 50B'. Thus, the arrcwhe~s at opposite ends of the path ~Y~n in Fig. 3 oontaining automatic valves 60A', 60B' and the path conta~ flow oontrol valves 5Q~' and 50B' indicate con-nection bo the gas outlets of the oorre$~ ng ads~rption beds A and B.
Similarly, the output of regulator 76' is con~Y~}~ ~hrough a thrDttle valve and flow ~cator to a p~hct outlet as indicated by the arnx~Yzd in the pDrtion 74' of the gas flow path.
The opposite end of the ~egregated storage adsorption bed C' i8 connected by a conduit 108 which contains an automatic vAlve 110 to the output conduit means, in particular to portion 74' thereof and up6tream from regulator 76'. Upon opening of ' ~33~1 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 pre~-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 80 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 waste losses, in time, results in a higher per-2a centage of product recovery. Another advantage associated withthe segregated storage adsorption bed involves feed end equaliz-tion ~hich lowers the front of the mass transfer zone in each of the other two beds so that when the beds are equalized from the top~ with the segregated storage adsorption bed there is less nitrogen to be taken up ~y the segregated storage adsorption bed.
As ~hown in Fig. 3, the system can also include a third re~ervoir conduit designated 114 connected at one end to the reservo~r 84' and coupled at the otber end to the adsorption beds. In the present illustration, the other end of conduit 114 30 i8 connected to the flow path containing the automatic yalves 60A' and 60B' and i8 connected between these valves. Conduit 114 contains an automatic valve 116. Upon opening of valve 116, ~1~335)1 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 re~ervoir 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 is interrupted, valve 72 closes and this is sensed by control 100 which open valve 96. Oxygen flow con-tinues from the reservoir throu~h valve 96 to the output conduit to outlet 66 until the supply in the reservoir is depleted. An alarm can be sounded to indicate the power interruption.
The reservoir also can be used to supply part or all of the purge oxygen required for an adsorber during its purge step.
~his is accomplished by opening valve 116 at the appropriate time. The reservoir also can be used as another surge tank.
~ressure equalizations to and from the adsorbers can be accom-2Q plished through the correct sequencing of valve~ 116 and 62.
The primary purpose of the reservoir i~ a reserve oxygen supply in the event of a malfunction. The length of time the reserve oxygen lasts depends on the pressure in the reser-voir at the time of the malfunction. If the reservoir is used only a~ 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 nnd or repressurization gas, the pressure in the reservoir will vary a~ will the reserve supply of oxygen.
The reservoir can comprise an adsorption bed but it also can comprise ~n ordinary tank of larger size.
Fig. 4 shows an arrangement for controlling the system and process of the present invention. The output conduit means .
~33~
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 ~ystem 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, ît 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 o~ 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 operation of the system, once begun, for a predetermined number of cycles. It has been determined that in a ~ystem of the present invention for producing oxygen from ~eed air that a total of two complete ~ycleg prov;des desirable results. One complete cycle includes ~tep Nos. 1-8 described in ~ig. 2. Furthermore, it has been determined that there is an optimum point within a cycle at ~hich operation of the system and process should be terminated.
3Q This is when the pressures are equal in the two adsorption beds and B which is at the ~eginning of step Nos. 2 and 6 described in Fig. 2. Thus, the additional control 136 al50 functions to ,,~ , .. . . . . .
~1~335~
stop the system only àfter 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 exa~lple, and persons skilled in the art are readily familiar 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.
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.
, .
11~3301 The particular adsorbent material or mixtures used are notcritical 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, ad orption bed C is appr~ximatelythe same s~ze as the adsorption beds A and B and may contain the same type of adsorbent material, but the segregated storage ad-sorption bed C can be 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 10 containing the feed gas stream by suitable conduit means including an automatic valve 40A and, similarly, the gas inlet 26 of adsorption bed B i5 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 be open to the atmosphere or which can ~e in fluid communication with a waste ~a~ stream. The gas inlets 18 and 26 of adsorptiGn beds A and B, respectively, also are connected to the waste gas outlet 44 by suitable corresponding conduit means includi.n~ automatic valves 46A and 46B, respectively. The auto-matic valves 40 and 46 and those additional automatic valves to be described can be of the ~olenoid-operated type, but in any event are of the type ~hich are operated to be either fully open 3Q or fully closed.
The system of the present invention further comprises means 5uch as suitable conduits or piping defin~ng a gas flow _7_ ., -.. .
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 adsorption 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 flow therethrough in a direction from gas 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 2B of thr adsorption beds, and in the system shown valve 54 20 i8 connected between gas outlet 20 of adsorption bed A and the flow control valve 5OA.
The system of the present invention includes a second ga6 flow path provided by ~uitable conduits or piping wh~ch ~ins the gas outlets 20 and 28 of the adsorption beds A and B, re-~pectively. A first automatic valve 60A is connected in the pathaajacent outlet 20 of bed A, and a ~econd automatic valve 60B is connected in the path ad~acent outlet 28 of adsorption bed B.
The ~egregated 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 ~ystem of the present invention ~urther comprises a product outlet designated 66 and output conduit means for ~1~3301 coupling the gas outlets of the adsorption beds to the productoutlet 66. In the system shown the output conduit means is con-nected to the first flow path at a point between the fl~w control valves 50A and 50B and includes a first section 70 including an automatic valve 72 and a second section 74 including the series combination of a pressure regulator 76, a throttle valve 78 and a flow meter 80. The flow rate of product to the outlet 66 i~ con-trolled by valve 78 which preferably is a manual~y adjustable needle-type valve, and the flow rate is indicated visually by the meter 80.
The system of the present inven~ion further comprises a reservoîr 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 conduit 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 ~orm of a throttle valve which preferably is manually adju~table is connected in the conduit and preferably between check valve 30 and reservoir 84. Valve 92 can be used to control the rate of ~low of gas product into reservoir 84. A ~econd reservoir conduit means is connected at one end to reservoir 84 through conduit 86 and at the other end to the sy~tem output con-duit means and includes valve means 96 for controlling the flowof product gas from reservoir 84 to the output conduit means. A
control lO0 îs connected by lines 102 and 103 to valveæ 72 and 96, respectiY~ly, and functions 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_ . .
1~33~
In general, the present invention is illustrated in terms of a process and system utilizing a first ads~rption bed, a second adsorption bed and a segregated storage adsorption bed.
However, the process and system can employ more than one first adsorption bed, mare than one second adsorption bed and more than one segregated storage adsorption bed. The adsorption beds com-municate with the feed gas stream which supplies the gaseous mix-ture, and the segregated storage adsorption bed never directly communicates with or is directly exposed to the feed gas stream.
Altbough the process and system of the present invention are described 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 may 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 ~elected in a ~imilar manner. Pressurizing or pressurization refers to the increase of pressure in the vessel and associated piping of an 2~ 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 4a 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 ;, -10-~ `" ' ' ' 1~33~)1 high purity oxygen gas product, a delivery pressure of around 3 p.s.i.g. is employed for medical uses and breathing de~ices whereas ahigher delivery pressure of up to about 40 p.~.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 ~ystem 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 ~quare inch gage.
lQ The particular operation carried out in each ads~rption bedduring each step is shown in Fig. 2, most of which are ab-breviated for convenience in illustration. Thus "FEE" refers to feed end equalization 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 repsessurizing to increase the pressure in an adsorption bed, and "PURGE" refers to introduction of purge gas or purging.
Referring now in detail to Fig. 2, prior to step No. 1 the gaseous mixture i.e. ordinary air, has been flowing from the feed gas stream in conduit 10 and through valve 40A which is open into and through adsorption bed A wherein nitrogen is adsorbed.
High 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 coduit ~ection 74 and through the series combînation of pressure regulator 76, needle valve 78 and flow meter 80 to the product outlet 66 for use. Ju~t prior to the beginning of step No. 1, 3Q adsorption bed A i8 about saturated and nearing the end of the adsorption operation therein. ~lso ~u~t prior to the beginning of ~tep ~o. 1, adsorption bed A i~ at a higher pressure than the : , ~1~3301 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.
S 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 r~se. Also in this step, adsorption bed A continues to supply oxygen gas product, but this is terminated by the end of the step. Step No. 1 preferably has a duration of about 7 seconds. Thxoughout this step and all other steps there is con-tinuous air flow into the system and continuous product flow out.
Cocurrent to feed flow îs 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 ~ed.
The process of step No. 1 may be described as continuing to discharge 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 ga~ 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.
',' ~ ' ' 1~433~
As shown in ~ig. 2, at the txansition between the end o~
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-regated storage adsorption bed C has remained at 7 p.s.i.g. At the beginning of step No. 2, valve 40B remains open, valve 4QA
closes, and valve 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 conduit section 7Q 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 6Q~ and valve 62 into the segregated storage adsorption bed C. As a result, during this step adsorption bed A is pressure equalized with the 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 ~econds.
The process of step NQ. 2 may be described as simul-taneously terminating the pressure equalization of step 1, ad-sorbing the gaseous mixture from the feed gas stream in the ~econd adsorption bed, releasing product gas from the outlet of the second adsorpti~n bed, and eqalizing the pressures of the first adsorption bed and the segregated storage adsorption bed 2~ by withdrawing low purity gas from the outlet of the first ad-soxption bed in a direction cocurrent with feed flow and intro-ducin~ the low purity gas into the segregated storage adsorptîon bed.
As is evident from steps 1 and 2 on Fig. 2 and from the foregoing descriptions thereof~ it can be ~een that bed A has undergone a decreasing pressure adsorption proces~; i.e., it has been producing product gas whlle simultaneously experiencing a ~3301 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 could be made to per-~orm a decreasing pressure adsorption step while connected to an SST, or to atmosphere, or otherwise.
As shown in Fig. 2, at the transition between the end of step No. 2 and the beginnîng of ~tep No. 3, the pressures in adsorption beds A and C are equalized at 14 p.s.i.g. and 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 B 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 adsorber 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 flowin~ from adsorber B through flow control valve 50B flows through ~alve 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 of air separation. This oxygen purge flowing countercurrent to feed ~low 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 ~ in a reverse direction to reject un-wanted impurity to the atmosphere. Step No. 3 preferably has aduration of about 39 seconds.
The process of step No. 3 may be described as simul- -~33(~
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 æecond 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 ad-sorption bed in a direction countercurrent to feed flow.
As shown in ~ig. 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 40~
remains open, valve 46A closes, and valve 60A opens. Valve 62 if not already open is opened at the beginning of this step. During lS this step eed air continues to enter bed B, and product ~uality oxy~en 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 ~rom adsorption bed C during step 4 is a version of the gas supplied to bed C during step 2 which gas has been in~luenced by travel in bed C.
As a result, during this step the ~egregated storage adsorption bed C is pressure equalized with the adsorption bed A. At least durin~ the initial portion of step 4, there i6 some additional flow of gas from bed B through valves 50B, 50A and 54.
Step No. 4 preferably has a duration of about 7 ~econds.
The process of step No. 4 may be descrîbed as simul-taneously terminating the depressurizing and purging of the first 3a adsorption bed, ~ontinuing adsorption of the gaseous mixture from the feed gas stream in the second adsorption bed, releasing pro-duct gas from the outlet of the second adsorption bed and 11~33~
equalizing the pressures of the segregated 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 thereof 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 at 7 p.s.i.g. and the pressure in bed B has remained at 30 p.s.i.g. At the begin-ning of ~tep No. 5, valve 40B remains open, valve 60A closes and valve 4OA opens. During this step, gas flows from the bottom or feed end of ~dsorber 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 - 4 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 ~tep No.
6 tthe same as step 2 with beds reversed~ may be described as ~imultaneously texminating the pressure equalization of step No.
5, repressurizing the first adsorption bed while withdrawing product gas there~rom, and equalizing pressures in the second -~6-.
. . . .
33~1 adsorption bed and the segregated storage adsorp~ion zone.
Equalizing the pressures of the adsorption beds A and Bat the feed ends thereof according to the presen~ 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 egualization 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 eed 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 t~ product end equalization for the following 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 8tep to maintain product purit~, a larger bed, i.e. more adsorbent material, iB required. In feed end equalizatàon ac-cording to the present invention, on the other hand, the bed at the higher pressure depressuxizes in a direction countercurrent to feed flow during the equalization 6tep. In this ~tep the mass transfer zone does not advance due to the d$rection of the 1~4335~1 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. The combination of no advancing of the mass transfer zone and countercurrent de-pressurization reduces the amount of adsorbent material required.
S Bed size factor is a quantity used to compare the amount of adsorbent material required from one system or cycle to an-other. At a given bed size factor, it has been determined that using feed and equalization according to the present in~ention 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 i8 at the end of the adsorption operation therein and prior to purging of the bed as illustrated in step No. 2 and thereafter lS 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-pressurizing adsorber A equalizes cocurrently to feed flow intosegregated storage adsorption bed C, part of the nitrogen con-tained in the mass trans~er zone of bed A will be transferred into the bed C. This allows for maximum and continual util~za-tion Oæ 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 fIow continues the gas becomes more like air.
In addition, the ~egregated storage adsorption bed recovers some potential energy from the depressurizing adsorber and this, in turn, reduces sy~tem blowdown pressure and increases recovery and efficiency. Providing the segregated storage adsorption ~ed C in effect provides a mixing volume to smooth out any .. . . . . .
1~433~31 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 desi~ned. For example, when the system is used to supply oxygen for medical use, design conditions occur at a flow rate of about 3.0 liters per minute.
During step No. 4 ~s the segregated storage adsorption bed C pressure e~ualizes countercurrently to feed fl~w into ad-sorber A, the gas returned to adsorber A is distributed or dis-persed therethrough in a manner which does not adversely affe~tproduct 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 foregoing is believed to result from the fact that gas return 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 a~ount of nitrogen is not taken up by the adsorbent material adjacent the outlet end of the bed. At the beginning of gas ~low from bed C to bed A, the gas is rich in nitrogen but as the ~low con-tinues it becomes more rich in oxygen. The foregoing advantageq are of cour~e egually associated with the relationship between adsorption bed B and ~egregated storage adsorption bed C during step Nos. 6 and 8.
Providing the ~low control valves 5QA and 5QB allous the system to be balanced by providing individual control or adjustment of the purge gas flo~ to each of the adsorption beds A and B. Providing an adjustable flow control va~ve associated with each ~ed permit6 compensating for dif~erences in the beds and piping b~ simple manual ad~ustment of valves 5QA, 50B.
' ~433~)1 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 t~ that of 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, 10ss time is required to reach desired operating conditions by virtue of the beds A and ~ having been maintained at the respective pressures prior to shut down.
Table I presents data illustrating the effect of the segregated storage tank or ~egregated storage adsorption bed C
on system performance. ~he 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 abbreviation~ S.S.T. for segregated 3Q storage tank and F.E.E. for feed end equalization are used.
,,~, , ~33~1 TABLE I
Low High Pressure Pressure Delivery Delivery S.S.T. Absent 21% 21%
S.S.T. Present But Empty 25% 23%
S.S.T. ~alf Full of Adsorbent Material 35% 31%
S.S.T. Full And With F.E.E. 49% 48%
~ig. 3 shows a system according to another embodiment of the present invention wherein gas product can be with~rawn from the other end of the segregated storage adsorption bed. In the ~ystem shown in Fig. 3, oomr ponents identical to th~e of Flg. 1 are provided with the same reference numerals but with a prime designation. In addition, the sy6tem of Fig. 3 would also include adsorption beds identical to thnse designated A and B in the system of Fig. 1, along wnth sinilar oonnections of the feed gas stream to the gas inlets of the beds, oonnections of the gas inlets to the waste outlet, and connections of the gas outlets of the beds to the gas flow path containing the flow control valves 5~A' and 50B'. Thus, the arrcwhe~s at opposite ends of the path ~Y~n in Fig. 3 oontaining automatic valves 60A', 60B' and the path conta~ flow oontrol valves 5Q~' and 50B' indicate con-nection bo the gas outlets of the oorre$~ ng ads~rption beds A and B.
Similarly, the output of regulator 76' is con~Y~}~ ~hrough a thrDttle valve and flow ~cator to a p~hct outlet as indicated by the arnx~Yzd in the pDrtion 74' of the gas flow path.
The opposite end of the ~egregated storage adsorption bed C' i8 connected by a conduit 108 which contains an automatic vAlve 110 to the output conduit means, in particular to portion 74' thereof and up6tream from regulator 76'. Upon opening of ' ~33~1 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 pre~-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 80 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 waste losses, in time, results in a higher per-2a centage of product recovery. Another advantage associated withthe segregated storage adsorption bed involves feed end equaliz-tion ~hich lowers the front of the mass transfer zone in each of the other two beds so that when the beds are equalized from the top~ with the segregated storage adsorption bed there is less nitrogen to be taken up ~y the segregated storage adsorption bed.
As ~hown in Fig. 3, the system can also include a third re~ervoir conduit designated 114 connected at one end to the reservo~r 84' and coupled at the otber end to the adsorption beds. In the present illustration, the other end of conduit 114 30 i8 connected to the flow path containing the automatic yalves 60A' and 60B' and i8 connected between these valves. Conduit 114 contains an automatic valve 116. Upon opening of valve 116, ~1~335)1 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 re~ervoir 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 is interrupted, valve 72 closes and this is sensed by control 100 which open valve 96. Oxygen flow con-tinues from the reservoir throu~h valve 96 to the output conduit to outlet 66 until the supply in the reservoir is depleted. An alarm can be sounded to indicate the power interruption.
The reservoir also can be used to supply part or all of the purge oxygen required for an adsorber during its purge step.
~his is accomplished by opening valve 116 at the appropriate time. The reservoir also can be used as another surge tank.
~ressure equalizations to and from the adsorbers can be accom-2Q plished through the correct sequencing of valve~ 116 and 62.
The primary purpose of the reservoir i~ a reserve oxygen supply in the event of a malfunction. The length of time the reserve oxygen lasts depends on the pressure in the reser-voir at the time of the malfunction. If the reservoir is used only a~ 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 nnd or repressurization gas, the pressure in the reservoir will vary a~ will the reserve supply of oxygen.
The reservoir can comprise an adsorption bed but it also can comprise ~n ordinary tank of larger size.
Fig. 4 shows an arrangement for controlling the system and process of the present invention. The output conduit means .
~33~
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 ~ystem 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, ît 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 o~ 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 operation of the system, once begun, for a predetermined number of cycles. It has been determined that in a ~ystem of the present invention for producing oxygen from ~eed air that a total of two complete ~ycleg prov;des desirable results. One complete cycle includes ~tep Nos. 1-8 described in ~ig. 2. Furthermore, it has been determined that there is an optimum point within a cycle at ~hich operation of the system and process should be terminated.
3Q This is when the pressures are equal in the two adsorption beds and B which is at the ~eginning of step Nos. 2 and 6 described in Fig. 2. Thus, the additional control 136 al50 functions to ,,~ , .. . . . . .
~1~335~
stop the system only àfter 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 exa~lple, and persons skilled in the art are readily familiar 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.
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 (42)
1. In a pressure swing process for fractionating at least one component from a gaseous mixture by selective ad-sorption in each of at least two adsorption zones by sequen-tially passing the gaseous mixture from a feed stream through a first adsorption zone until the zone is about saturated while simultaneously purging and then pressurizing 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 then pressurizing the first adsorption zone, the improvement comprising withdrawing gas from one of said adsorption zones 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 the feed stream into the other of said adsorption zones in a direction cocurrent with feed flow and after pressurization thereof to equalize the pressures in said adsorption zones from the feed ends thereof.
2. 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 by sequentially passing the gaseous mixture from a feed stream through a first adsorption zone until the first zone is about saturated while simultaneously purging and then pressurizing a second adsorption zone and then passing the gaseous mixture from the feed stream through the second adsorption zone until the second zone is about saturated while simultaneously purging and then pressurizing the first adsorption zone, the improvement comprising withdrawing gas from one of said adsorption zones at the end of the adsorption operation therein in a direction countercurrent to feed flow and directly introducing the withdrawn gas along with the gaseous mixture from the feed stream into the other of said adsorption zones in a direction cocurrent with feed flow and after pressurization thereof to equalize the pressures in said adsorption zones from the feed ends thereof.
3. The process according to claim 2 in which, simulta-neously as gas is withdrawn from one of said adsorption zones in a direction countercurrent to feed flow, product gas is withdrawn from the other one of said adsorption zones in a direction cocurrent to feed flow.
4. The process according to claim 2, wherein the gaseous mixture is air and the process produces high purity oxygen.
5. The process according to claim 2, further including controlling said process steps in a manner such that said process is continued for at least two complete cycles and is terminated when the pressures in said first and second adsorption zones are substantially equal.
6. 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; said segregated storage adsorption bed having but one opening for the introduction and withdrawal of gas;
b) withdrawing gas from said 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 the feed gas stream into said additional adsorption bed in a direction cocurrent with feed flow and after pressurization 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 adsorb-ing 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 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 and simul-taneously adsorbing the gaseous mixture from the feed gas stream in said additional adsorption bed, and depressurizing 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 counter-current to feed flow;
e) terminating said depressurizing 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 of 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 be-ginning 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; said segregated storage adsorption bed having but one opening for the introduction and withdrawal of gas;
b) withdrawing gas from said 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 the feed gas stream into said additional adsorption bed in a direction cocurrent with feed flow and after pressurization 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 adsorb-ing 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 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 and simul-taneously adsorbing the gaseous mixture from the feed gas stream in said additional adsorption bed, and depressurizing 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 counter-current to feed flow;
e) terminating said depressurizing 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 of 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 be-ginning with pressure equalization of said beds from the feed ends thereof reversing the functions of said first adsorption bed and said additional adsorption bed.
7. The process according to claim 6, wherein the gaseous mixture is air and the product gas is high purity oxygen.
8. The process according to claim 6, further including controlling said process steps in a manner such that said process is continued for at least two complete cycles and is terminated when the pressures in said first and additional adsorption beds are substantially equal.
9. A pressure swing adsorption process for use with 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 steps of alternately and sequentially flowing, in a producing step, a feed gas mixture into the inlet of one of said beds to adsorb at least one gas of said mixture in said one bed and flowing the remainder of the mixture out of said one bed outlet as product gas until said one bed is about saturated with said one gas, purging a second bed while performing the producing step in said one bed, permitting flow in each of said bed outlet conduit means away from the respective bed towards said product outlet conduit means in an unrestricted manner while simultaneously and continually restricting flow in each of said bed outlet conduit means from said conduit means towards each respective bed, withdrawing gas from one bed at the end of adsorption operation thereof in a direction countercurrent to feed flow and flowing the withdrawn gas out of the inlet end of said one bed into the inlet end of the other bed in a direction cocurrent with feed flow after pressurization thereof to pressure equalize said two beds from their inlet ends while simultaneously flowing product gas out of the product end of said one bed.
10. A pressure swing adsorption process for use with at least two adsorption beds each having a gas inlet and a gas outlet, and conduit means interconnecting said gas outlets to product outlet conduit means; said process com-prising 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 said one bed outlet as product gas until said one bed is about saturated with said one gas, purging a second bed while performing adsorption in said one bed, controlling the repetition to stop only at an optimum point in the process, and withdrawing gas from one bed at the end adsorption operation thereof in a direction countercurrent to feed flow and flowing the withdrawn gas out of the inlet end of said one bed and into the inlet end of the other bed in a direction cocurrent with feed flow after pressurization thereof to pressure equalize said two beds from their inlet ends while simultaneously flowing product gas out of the product end of said one bed.
11. A pressure swing process for fractionating at least one component from a gaseous mixture by selective adsorption in each of at least two adsorption beds comprising a first and a second adsorption bed, each having an inlet and an outlet, by sequentially passing the gaseous mixture from a feed stream through the first adsorption bed until the first adsorption bed is about saturated while simultaneously purging and then pressurizing the second adsorption bed, and then passing the gaseous mixture from the feed stream through the second adsorption bed until the second adsorption bed is about saturated while simultaneously purging and then pressurizing the first adsorption bed, part of the pressurizing gas for each of the adsorption beds at the end of its purging phase being derived by pressure equalization between the feed ends of the first and second beds, whereby the withdrawn gas from one of said adsorption beds at the end of the adsorption operation therein is in a direction countercurrent to feed flow and is introduced along with the gaseous mixture from the feed stream into the other of said adsorption beds, in a direction cocurrent with feed flow and after pressurization thereof.
12. A process according to claim 11, wherein a segregated storage adsorption bed is provided isolated from direct communication with the feed gas stream; wherein after pressure equalization of said adsorption beds from the feed ends thereof the gaseous mixture from the feed gas stream is adsorbed in one of said adsorption beds to release product gas from an outlet of said one of said adsorption beds and the pressures of the other of said adsorption beds and said segregated storage adsorption bed are equalized by withdrawing low purity gas from said other of the adsorption beds in a direction cocurrent with feed flow and introducing said low purity gas into one end of said segregated storage adsorption bed; wherein thereafter said other of the adsorption beds is purged by diverting product gas from the outlet of the said one of the adsorption beds into said other adsorption bed in a direction countercurrent to feed flow, before the pressure of said segregated storage adsorption bed is equalized with that of said other adsorption bed by withdrawing gas from said one end of said segregated storage adsorption bed and introducing the withdrawn gas into said other adsorption bed in a direction countercurrent to feed flow.
13. A process according to claim 12, wherein after the last pressure equalization step set out in claim 12, all the steps of claim 12 are consecutively repeated beginning with pressure equalization of said beds from the feed ends thereof, reversing the functions of one of said at least two adsorption beds and the other of said at least two adsorption beds.
14. A process according to claim 12, further including withdrawing product gas from the other end of said segregated storage adsorption bed.
15. A process according to claim 13 or 14, wherein said process steps are controlled in a manner such that said process is continued for a predetermined number of identical cycles.
16. A process according to claim 13 or 14, wherein said process steps are controlled in a manner such that the process is terminated only at an optimum point in the process cycle.
17. A process according to any one of claims 11, 12 or 13, wherein the gaseous mixture is air and the product gas is high purity oxygen.
18. A process according to claim 13 or 14, wherein said process steps are controlled in a manner such that the process is terminated only at an optimum point in the process cycle, said optimum point being at an instant when the pressures in the said at least two adsorption beds are equalized.
19. A process according to any one of claims 11, 12 or 13, wherein during said selective adsorption the flow into the feed end of one of the at least two adsorption beds and the flow of gas withdrawn from the other end of the said one of at least two adsorption beds are controlled such that the said one of at least two adsorption beds undergoes a decrease in pressure during said adsorption.
20. A pressure swing process for fractionating at least one component from a gaseous mixture by selective adsorption in each of at least two adsorption beds by sequentially passing the gaseous mixture from a feed stream through a first adsorption bed until the first bed is about saturated and the purity of the product gas is reduced while simultaneously depressurizing, purging and then repressurizing a second adsorption bed and then passing the gaseous mixture from the feed stream through the second adsorption bed until the second bed is about saturated while simultaneously depressurizing, purging and then repressurizing the first adsorption bed; withdrawing product gas from the feed end of one of the said at least two adsorption beds in a direction countercurrent to feed flow when said one bed is at the end of the adsorption operation therein and introducing it together with the gaseous mixture to the feed end of another of said at least two adsorption beds to repressurize said another bed before adsorption therein and to equalize the pressures in said adsorption beds from the feed ends thereof; withdrawing reduced purity product gas from said one of the said at least two adsorption beds in a direction cocurrent with feed flow as the pressure in said one bed decreases at the end of the adsorption operation therein and prior to purging of the said one bed; introducing the withdrawn reduced purity product gas to only one end of a storage adsorption bed which is segregated from the feed stream but is able to be communicated with an outlet end of each of said at least two adsorption beds, said withdrawn reduced purity product gas being the sole gas introduced into said segregated storage adsorption bed; then withdrawing gas from said one end of the segregated storage adsorption bed and passing said withdrawn gas into said one adsorption bed in a direction countercurrent to feed flow after purging of the said one bed and when the said one bed is at a relatively low pressure, the feed end of said one adsorption bed being closed during such passage, whereby said gas starts repressurizing said one adsorption bed; and withdrawing product gas from the other end of said segregated storage adsorption bed and recovering it directly without further treatment.
21. A process according to claim 20, wherein the repetition of pressurizing, adsorbing, depressurizing and purging is controlled to continue until an instant in the repetition, optimum for shut-down.
22. A process according to claim 21, wherein said optimum point is decided on the basis of both an optimum point during the cycle and the completion of a minimun number of complete cycles from start-up.
23. A process according to claim 22, wherein said minimum number of cycles is 2.
24. A process according to claim 21, 22 or 23, wherein said continuation of the repetition terminates at an optimum point in the process, and said optimun point is at an instant when the pressures in the said at least two adsorption beds are equalized.
25. A process according to claim 11, wherein during adsorption on each of said first and second adsorption beds the feed gas mixture is flowed into the inlet of one of the respective first or second adsorption bed and product gas is flowed out of the outlet of said respective first or second adsorption bed along an outlet conduit system in an unrestricted manner in a flow direction away from the respective first or second adsorption 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 first or second adsorption bed is restricted.
26. A process according to claim 25, wherein said purging gas flow is restricted using means for simultaneously and automatically restricting flow towards the respective first or second adsorption bed but allowing unrestricted flow in a direction away from the respective first or second adsorption bed and towards said main product outlet conduit.
27. A process according to claim 26. wherein said means for simultaneously and automatically restricting flow comprises (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.
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.
28. A system for fractionating at least one component from a gaseous mixture by pressure swing adsorption, including 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; means for connecting said gas inlets of said adsorption beds to each other and to a feed gas stream; a product outlet; means for coupling said gas outlets of said adsorption beds to said product outlet; and a system control unit for controlling system operation including sequentially passing the gaseous mixture from a feed stream through said first adsorption bed until said bed is sub-stantially saturated while simultaneously purging and then pressurizing said additional adsorption bed and then passing the gaseous mixture from the feed stream through said additional adsorption bed until said bed is substantially saturated while simultaneously purging and then pressurizing said first Adsorption bed; said system control unit being operatively associated with a gas flow path connected at one end to said gas outlet of said first adsorption bed and connected at the opposite end to said gas outlet of said additional adsorption bed; said gas flow path including: (a) a first flow control valve, between said gas outlet of said first adsorption bed and said additional adsorption bed, allowing unrestricted gas flow in a direction from said outlet of said first bed toward said additional adsorption bed but controlled flow in a dir-ection towards said gas outlet of said first bed; and (b) a second flow control valve, between said gas outlet of said additional adsorption bed and said first adsorption bed, allowing unrestricted gas flow in a direction from said outlet of said additional bed toward said first adsorption bed but controlled flow in a direction to said gas outlet of said additional bed.
29. A system according to claim 28, and further including an isolation valve in said gas flow path between said gas outlets of said adsorption beds.
30. A system according to claim 28 or 29, wherein said product outlet is connected to said gas flow path between said first and second flow control valves.
31. A system according to claim 28, further including an output conduit for coupling said gas outlets of said adsorption beds to said product outlet;
a reservoir; a first reservoir conduit connected to said output conduit and to said reservoir, and including means for allowing gas flow only in one direction from said output conduit to said reservoir; and a second reservoir conduit connected to said reservoir and to said output conduit and including a valve for controlling flow of product gas from said reservoir to said output conduit.
a reservoir; a first reservoir conduit connected to said output conduit and to said reservoir, and including means for allowing gas flow only in one direction from said output conduit to said reservoir; and a second reservoir conduit connected to said reservoir and to said output conduit and including a valve for controlling flow of product gas from said reservoir to said output conduit.
32. A system according to claim 31, further including an output conduit valve in said output conduit between said second reservoir conduit and said adsorption beds, and control means operatively connected to said valve for controlling flow of product gas from said reservoir to said output conduit and to said output conduit valve for opening said valve for controlling flow of product gas from said reservoir to said output conduit in response to closure of said output conduit valve for supplying product gas from said reservoir to said product outlet.
33. A system according to claim 31 or 32, and further including a third reservoir conduit connected at one end to said reservoir and coupled at the other end to said adsorption beds, said third reservoir conduit including means for controlling flow of product gas from said reservoir directly to said adsorption beds for oper-ations such as purging and repressurization.
34. A system for fractionating at least one component from a gaseous mixture by pressure swing adsorption, including 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; means for connecting said gas inlets of said adsorption beds to each other and to a feed gas stream: a product outlet; means for coupling said gas outlets of said adsorption beds to said product outlet; and a system control unit for controlling system operation including sequentially passing the gaseous mixture from a feed stream through said first adsorption bed until said bed is sub-stantially saturated while simultaneously purging and then pressurizing said additional adsorption bed and then passing the gaseous mixture from the feed stream through said additional adsorption bed until said bed is substantially saturated while simultaneously purging and then pressurizing said first adsorption bed.
35. A system according to claim 34, further comprising additional control means operatively connected to said system control unit for causing said system control unit to maintain operation of said system for a predetermined number of cycles.
36. A system according to claim 35, wherein said additional control means is constructed to cause said system control unit to maintain operation of said system for two complete cycles.
37. A system according to claim 35, wherein the combination of said additional control means causes said system control unit to terminate operation of said system only at an optimum point in the cycle of operation.
38. A system according to claim 37, wherein said optimum point in the cycle is when the pressures in said adsorption beds are substantially equal.
39. A system according to claim 34, further comprising an output conduit for coupling said gas outlets of said adsorption beds to said product outlet;
a reservoir; a first reservoir conduit connected to said output conduit and to said reservoir, and including means for allowing gas flow only in one direction from said output conduit to said reservoir; and a second reservoir conduit connected to said reservoir and to said output conduit and including a valve for controlling flow of product gas from said reservoir to said output conduit.
a reservoir; a first reservoir conduit connected to said output conduit and to said reservoir, and including means for allowing gas flow only in one direction from said output conduit to said reservoir; and a second reservoir conduit connected to said reservoir and to said output conduit and including a valve for controlling flow of product gas from said reservoir to said output conduit.
40. A system according to claim 39, further including an output conduit valve in said output conduit between said second reservoir conduit and said adsorption beds, and control means operatively connected to (1) said valve for controlling flow of product gas from said reservoir to the output conduit and (2) to said output conduit valve for opening said valve in the second reservoir conduit in response to closure of said output conduit valve for supplying product gas from said reservoir to said product outlet.
41. A system according to claim 39 or 40 and further including a third reservoir conduit connected at one end to said reservoir and coupled at the other end to said adsorption beds, said third reservoir conduit including means for controlling flow of product gas from said reservoir directly to said adsorption beds for oper-ations such as purging and repressurization.
42. In a pressure swing process for fractionating at least one component from a gaseous mixture by selective ad-sorption in each of at least two adsorption zones by sequen-tially passing the gaseous mixture from a feed stream through a first adsorption zone until the zone is about saturated while simultaneously purging and then pressurizing 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 then pressurizing the first adsorption zone, the improvement comprising withdrawing gas from one of said adsorption zones 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 the feed stream into the other of said adsorption zones in a direction cocurrent with feed flow to equalize the pressures in said adsorption zones from the feed ends thereof.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000378989A CA1143301A (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 |
| CA000378989A CA1143301A (en) | 1976-11-26 | 1981-06-03 | Pressure swing adsorption process and system for gas separation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1143301A true CA1143301A (en) | 1983-03-22 |
Family
ID=27165395
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000378989A Expired CA1143301A (en) | 1976-11-26 | 1981-06-03 | Pressure swing adsorption process and system for gas separation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1143301A (en) |
-
1981
- 1981-06-03 CA CA000378989A patent/CA1143301A/en not_active Expired
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| MKEX | Expiry |