A STUDY OF OXYGEN SEPARATION FROM AIR BY PRESSURE SWING ADSORPTION (PSA)

The 2nd Regional . Conf. for Eng. Sci. /College. of Eng. / Al-Nahrain University /1-2/12/2010

203

A STUDY OF OXYGEN SEPARATION FROM AIR BYPRESSURE SWING ADSORPTION (PSA)

ABSTRACTTwo small scale columns pressure swing adsorption unit (50 mm diameter, and 570 mm bed

length) has been constructed to study the separation of oxygen from air using commercial 13Xzeolite. The effect of adsorption pressure (2, 3, and 4 bar), adsorption time (10, 20, and 30 s), andpurge flow rate (1 to 6 liter/min) on the product oxygen purity were studied. For the case of 2-column, 4-step operation, the result show that a product of about 70% oxygen purity was obtained,whereas a product of about 80% oxygen purity was obtained for 6-step operation. No significanteffect on product oxygen purity was noticed throughout the adsorption pressure range studied, forboth cycle operations. This is confirmed by single bed characteristic results. The effect of theadsorption time and the purge flowrate on the product oxygen purity show some optimum values for4-step operation. Single bed characteristic result confirms the range of the adsorption time and thepurge flowrate. Similar trend results were noticed with 2-column, 6-step operation, with air initialpressurizing, for the effect of purge flowrate at constant adsorption time (30 s). The product oxygenpurity for 6-Steps operation, with pure oxygen initial pressurizing, presents a plateau (of 82% purity)for purge flowrate from 1 to 1.5 liter/min then decreases when increasing the purge flowrate above1.5 liter/min. Single column characteristics, using initial intermediate oxygen pressurizing indicatedhigher product oxygen purity expected (>90%) than that obtained in the 2-column, 6-step operation.

)50570 (

13X .

)234 ()102030()1 -6/ (

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70 %80 % .

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)30(.

82 %11,5/

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)82 ( %90.%

Z.A. Abdel-Rahman,Asst.Prof., Tikrit Univ,

[email protected],

A. J. Ali,Asst. Prof., Sohar Univ /Oman,

[email protected],

H.S. Auob, Ass.Lecturer, Tikrit Univ,

[email protected]

mailto:zaid572000:@yahoo.co.uk

mailto:ajali:@soharuni.edu.om


204

1. INTRODUCTIONAt the present time, there are three

different technologies for oxygen productionfrom air:

1. The cryogenic technology based onseparation by low-temperaturedistillation.

2. The membrane technology.3. The adsorption technologyThe latter two technologies have been

performed at ambient temperature. A moreand more popular air separation process iscurrently pressure swing adsorption (PSA) onzeolites, which was proposed by Skarstrom[1]

in the middle of the 20th century and is basedon periodic change of modes of selectiveadsorption of gases at increased pressure andtheir desorption with a decrease in pressure.According to foreign information sources,more than 20% of world oxygen productionis by pressure swing adsorption.[1,2]

The first (PSA) unit composed of twobeds and using a zeolite, was patented bySkarstrom in 1960. Four steps were used inthis unit, as follows:[1,3]

1. Pressurization step, the bed pressure isincreased with feed.

2. Producing step, high pressure feedthrough one end with raffinatewithdrawal through the other. Raffinatemeans rich in the component with thelowest adsorption affinity

3. Depressurization or blow down step,pressure is decreased opening one bedend, and the resulting flow iscountercurrent to the feed.

4. Purging step, desorption at the loweroperating pressure, which is performedby purging the bed with the raffinateproduct, flows countercurrent to the feed.

A very important improvement was theintroduction of the pressure equalizationstage, prior to the blow down step where twobeds are connected through one end while theother remaining ends are kept closed. The

product recovery is increased because lessfeed gas is necessary to re-pressurize thecolumns.[1,4,5]

Oxygen production (purity below 95%)from air, using nitrogen selective zeolites oftype A (5A) or type X (13X-NaX, LiX, orLiLSX), by means of pressure swingadsorption (PSA) processes has noticeablyincreased in the past decades. However, theconcentration of the product is limited to 95%oxygen, because of the presence of argon inair, since these adsorbents present similaradsorption capacities for oxygen and argon.Purified oxygen is necessary for someapplication such as medical application,wastewater treatment, chemical processing,etc.[4]

Different PSA processes and designs havebeen implemented for many commercialapplications, where the difference lies in theselection and sequence of the elementarysteps, and in the way in which these steps arecarried out.[3]

The main objects of present work1. To construct a small scale Pressure Swing

Adsorption (PSA) unit for oxygenseparation from air, using two bedcolumns which are packed withcommercial zeolite 13X.

2. To study the effects of operatingparameters, such as pressure, cycle time,purge and product flow rate on theperformance of PSA unit, using twocolumns 4-steps traditional Skarstromcyclic operation to adjust the processvariables ranges. The Performance ischaracterized by O2 purity, Recovery andProductivity.

3. To study the effects of operatingparameters, such as pressure, cycle time,Purge and product flow rate on theperformance of PSA unit, using twocolumns 6-steps equalization modificationcyclic operation. The Performance is


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characterized by O2 purity, Recovery andProductivity.

4. To investigate the characteristic of singlecolumn operation and checking theactivity of the zeolite.

2. PRESSURE SWING ADSORPTIONAdsorption processes are often identified

by their method of regeneration. Temperatureswing adsorption (TSA) and pressure swingadsorption (PSA) are the most frequentlyapplied process cycles for gas separation.[6]

A pressure swing adsorption (PSA) cycleis one in which desorption takes place at apressure much lower than adsorption. Itsprinciple application is for bulk separationswhere contaminants are presented at highconcentration. The PSA cycles arecharacterized by high residual loadings andlow operating loading. Fig.1 shows theoperating loading (q1-q2) that derives fromthe partial pressure at feed conditions and thelower pressure P2 at the end of desorption.These low adsorption capacities for highconcentrations mean that cycle times must beshort, seconds to minutes, for reasonablysized beds. Fortunately, packed beds ofadsorbent respond rapidly to changes inpressure.[6]

A purge usually removes the desorbedcomponents from the bed, and the bed isreturned to adsorption condition by re-pressurization. Applications may requireadditional steps. Systems with weaklyadsorbed species are especially suited to PSAadsorption. The applications of PSA includedrying, upgrading of H2 and fuel gases, andair separation.[6]

Adsorption time estimation for the PSAprocess, assuming equilibrium driven andnegligible mass transfer effects, can becalculated from the following equation [7] :

Qf Cf tz = qf w z / LB (1)

PSA processes rarely utilize all theadsorbents and the beds are never completelyregenerated. The unused portion of the bedacts as a guard and is needed to maintain thegas- and adsorbed-phases axial distribution[8]

Adsorption is assumed to occur at someconstant fraction of equilibrium, and by usingsome given fraction of the availableadsorbent.[9]

Assuming operation at z/LB =0.75, and :

NfN2 = Qf Cf = (78/22) NfO2 (2)

qN2= qsbN2PadyN2/1+bN2yN2Pad+bO2yO2 Pad (3)

NfN2 = NExN2 = qN2 * W (4)

tz = qf W (0.75) / (78/22) NfO2 (5)

tz = 0.21 W qf / NfO2 (6)

The adsorption time is within thatgiven by Eq.(6).

3. EXPERIMENTAL WORKThe schematic diagram of the

experimental arrangement of PSA unit usedin the present work is shown in Fig.2. Itcontains two galvanized steel columns. Thelength of each column (L) is 0.7 m and itsdiameter (D) is 50 mm. The input and outputconnections are of 5 mm tubing, fittings andvalves.

The setup is equipped with an automaticcontrol system for controlling the time ofeach cycle. A programmed timer controlledsolenoid valves were used to achieve thedesired operation.

The concentrations of the effluent flowswere analyzed by a portable calibratedoxygen analyzer (GOX 100 GreisingerElectronic GmbH).


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Atmospheric air was used as a feed to thePSA system, after drying with activealumina.

Fig.3 shows a single bed arrangement,used for adsorbent and processcharacteristics. One of the before mentionedtwo columns was used. The work with singlecolumn was designed to simulate the work ofthe two columns PSA process.

The adsorbent used in this work is zeolite13X (13XHP 8x12 mesh). The characteristicsof the adsorption bed and the adsorbent withits adsorption isotherm of N2 and O2 areshown in Table (1).The experimental work in the present studywas divided into two directions:1. Two-Column, 4-Steps and 6-Steps PSA

operation2. Single Column Characteristics

The limitation of the experimental set-uparrangement was tasted before performing theexperimental work. The following operatingparameters are held constant during the mostexperiments with little exceptions:Pressurizing time tpres= 10 sDepressurizing time tdeprs= 10 sEqualization time teq= 20 s

The operating parameters considered inthe present work with their ranges are asfollows;Adsorption time tads= 10, 20, and 30 sAdsorption pressure PH= 2, 3, and 4 barPurge flow rate Qpurg= 1, 1.5, 2, 3, 4, 5, and 6L/min

Two-Columns OperationThe experimental procedure was:

1. Preparation of the PSA system shown inFig.1, using vacuum and O2 pressurizingand purging to ensure the zeolite activity.The bed was kept at 1 Barg pressure ofpure oxygen to prevent contaminationfrom the outside air.

2. Adjust the air feed pressure by pressureregulator.

3. Adjust the system condition with orwithout initial pure O2 intermediatepressure of the first column to the desiredvalue, especially, for 6-steps operation.

4. Starting the control board with the settedduration process steps and the valvesoperation cycle as shown in Table(2) andFig.4 for 4-steps operation and Table(3)and Fig.5 for 6-steps operation.

5. Adjust the flow rates of purge and productto the desired values, using a gas rotameterand a regulating valve.

6. Recording the product purity (O2 %)measured by the analyzer with time andstop the experiment when the systemreaches a steady state after about 30minutes.

Single Column CharacteristicsThe experimental procedure was:

1. Preparation of the PSA system shown inFig.2, using vacuum and O2 purging toensure the zeolite activity.

2. Adjust the air feed pressure by pressureregulator.

3. Adjust the system condition with orwithout initial pure O2 intermediatepressure of the column to the desiredvalue.

4. Open the air feed valve.5. Open the output valve and adjust the

flow rate product to the desired value,using a gas rotameter and a regulatingvalve.

6. Recording the product purity (O2 %)measured by the analyzer with time.

4. RESULTS AND DISCUSSION

Two Columns Operation.14

Effect of Adsorption PressureFigure (6) shows the effect of the

adsorption pressure (PH) on steady productoxygen purity. No significant change was


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noticed between the pressure ratios studied of2 and 4 bar. This result is in agreement withthat obtained by Jee et al. (2001)[5] for highpurge-to-feed ratio.

The present results are also inagreement with that concluded by Yuwen etal.(2005)[10], that medium adsorption pressuregives optimum performance. In addition, ahigh pressure level leads to highercompression cost and a higher energy loss inthe depressurizing step.[11]

Jain et al.(2003)[11] stated that, forconstant selectivity systems, performanceincreases with increasing pressure accordingto adsorption equilibrium isotherm. Thepresent work system behaves as a non-constant selectivity system with increasingpressure.

Effect of adsorption timeFigure (7) shows the effect of the

adsorption time (tads) on steady state productoxygen purity, at constant adsorptionpressure (PH =3 bar). It shows an optimumvalue at tads= 20 s.

Breakthrough occurs at highadsorption time, and constant effluentflowrate from the column. The duration ofthe adsorption step is the time period neededfor breakthrough to occur. After this time, theproduct purity will decline, and before thistime the full bed capacity will not beemployed. Thus, the adsorption time shouldbe near the breakthrough time. This timedepends upon isotherm, diffusivity andresidence time of the feed in the bed[11].

Figure (8) shows insignificant changein the product oxygen purity with theadsorption time (tads), by adjusting therequired purge flowrate.

Figure (9) shows the effect of thedimensionless adsorption time ( ads) onsteady state product oxygen purity, atconstant adsorption pressure (PH =3 Bara). Itshows an optimum range of ads= 0.2 – 0.25.

The result of the optimum range ofdimensionless adsorption time ads is lessthan obtained by Cruz et al.(2003)[12] of ads=1 – 1.5.

Effect of Purge FlowrateFigure (10) shows the effect of the

Purge Flowrate (Qpurg) on steady stateproduct oxygen purity, at constant adsorptionpressure (PH=3 bar). It shows some optimumvalues of (Qpurg= 4, 2, and 1.5 liter/min) forthe three levels of adsorption times (tads=10,20 and 30 s) respectively. This result is inagreement with that obtained by Yang andDoong (1985)[13] and Zahra et al.(2008) [14].

For low purge volumes, theregeneration of the production column isincomplete for low purge volume, thenitrogen wave front eventually breaksthrough, leading to a decrease of the averageproduct concentration.[12]

Figure (10) also shows the maximumproduct oxygen purity of seventies for theboth effect of the Purge Flowrate (Qpurg) andthe adsorption times (tads).

There is an interrelationship betweenthe adsorption time (tads) and the purgeflowrate (Qpurg), which represents about 90 %of effluent flowrate from the column.

Dimensionless adsorption time ( ads)calculation account partially for thisinterrelationship as shown in Fig. 9.

The product flowrate range, used inthe present work, can be presented as specificflowrates (Qprod / w). Fig. 11 shows thelargest product oxygen purity of seventiescontour curve for the effect of the adsorptiontimes (tads) on the specific product flowrate(Qprod/w).

Fig. 12 shows the effect of the PurgeFlowrate (Qpurg) on steady state productoxygen purity for 6-Steps of PSA process,with air feed initial pressurizing. It show anoptimum value at purge flowrate Qpurg= 1.5liter/min. It is an identical trend with that of


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two-columns, 4-step cycle results, except thelargest product oxygen purity of eighties with6-step cycle compared to seventies with 4-step cycle.

Fig.13 shows the effect of the PurgeFlowrate (Qpurg) on steady state productoxygen purity for 6-Steps of PSA process,with pure oxygen initial pressurizing. Theproduct purity presents a plateau (for about82% purity) for purge flowrate Qpurg 1 to 1.5liter/min and then decreases. It is of the sametrend noticed by Mendes et al.(2001)[15].

The decrease in product purity withthe increasing of the purge flowrate (Qpurg)above 1.5 liter/min can be attributed to thatbreakthrough point which may occur at higheffluent from the column in which the purgeflowrate represents the most percentage of it(about 90%).

Fig.14 shows the effect of thedimensionless adsorption time ( ads) onsteady state product oxygen purity, atconstant adsorption pressure (PH =3 bar). Itshows an optimum value of about ads= 0.25,for air feed initial pressurizing. The productpurity presents a plateau (for a about 82%purity) for the dimensionless purge time adsof 0.15 to 0.25, which then decreases for pureoxygen initial pressurizing.

Fig.15 shows the effect of thedimensionless purge time ( purg) on steadystate product oxygen purity, at constantadsorption pressure (PH =3 bara). It shows anoptimum value of purg= 0.67, for air feedinitial pressurizing. The product puritypresents a plateau (for a about 82% purity)for the dimensionless purge time purg 0.45 to0.7, then decreases for pure oxygen initialpressurizing. This is the same trend as thedimensionless adsorption time.

4.2 Single Column CharacteristicsFig.16 shows the single column

characteristics, as breakthrough curve, usingair feed pressurizing at different adsorption

pressures and constant effluent flowrate(Qeffluent=1 liter/min). No significant effect ofthe adsorption pressure (PH) was noticed onthe effluent oxygen purity. This resultconfirms the result of the 2-column, 4-stepand 6-step PSA unit, presented in theprevious section.

In addition, Fig.16 shows that theeffluent oxygen purity remains constant(except for the starting period due to the timelag of oxygen analyzer) at about 60 seconds.Then the effluent oxygen purity decreases byincreasing the time above 60 seconds. Thisresult confirms the range of the adsorptiontime (tads) and the purge flowrate (Qpurg)which represent the high percentage ofeffluent flowrate (Qeffluent) in the presentstudy for the 2-column, 4-step PSA unit.

Fig.17 shows the single columncharacteristics, as breakthrough curve, usinginitial intermediate pure oxygen pressurizingat different effluent flowrates (Qeffluent), andconstant adsorption pressure (PH=3 bar). Thebreakthrough time is much higher than theadsorption time (tads) used in the presentstudy especially in the 2-column, 6-step PSAunit. This indicates that high pure productoxygen is expected (>90%). The possiblereason for the lower product oxygen purity(80%) is the incomplete regeneration of theadsorption column.

5. CONCLUSIONSThe following conclusions can be drawn

from the present work:1. The results of air separation for 2-column

pressure swing adsorption (PSA) usingcommercial 13X zeolite shows amaximum of 70% oxygen purity for 4-stepcycle operation and a maximum of 80%oxygen purity for 6-step cycle operation.

2. No significant effect on product oxygenpurity was noticed of the adsorptionpressure range studied between 2 and 4


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Bara, for both 4-step and 6-step cycleoperations. This result is also confirmedby single bed characteristic result.

3. The effect of the adsorption time (tads) andthe flow of purge flowrate (Qpurg) on theproduct oxygen purity, shows someoptimum values, for 4-step cycleoperation. No effect was noticed whenthese two parameters had been adjustedwith each other because of theirinterrelationship.

4. The effect of the Purge Flowrate (Qpurg) onthe product oxygen purity for 6-Steps ofPSA process, with air feed initialpressurizing, shows an optimum value atpurge flowrate Qpurg= 1.5 liter/min. It isidentical trend with that of two-columns,4-step cycle results.

5. The product oxygen purity for 6-Steps ofPSA process, with pure oxygen initialpressurizing, presents a plateau (for aabout 82% purity) for purge flowrate Qpurg1 to 1.5 liter/min then decreases whenincreasing the purge flowrate above 1.5liter/min.

6. Single bed characteristics results confirmsthe range of the adsorption time (tads) andthe purge flowrate (Qpurg), which representof the high percentage of effluent flowrate(Qeffluent), in the present study for the 2-column, 4-step PSA unit.

7. Single column characteristics, using initialintermediate pure oxygen pressurizingindicated higher pure product oxygenexpected (>90%). than that obtainedexperimentally in the 2-column, 6-stepPSA unit. The possible reason for thelower product oxygen purity (~80%) is theincomplete regeneration of the adsorptioncolumn.

REFRENCES1. Ruthven, D. M.; Farooq, S.; Knaebel, K.

S., Pressure Swing Adsorption. VCHPublishers: New York, 1994.

2. Bel’nov, V. K., N. M. Voskresenskii, D.M. Predtechenskaya, M. S. Safonov , andL. I. Kheifets, Increasing the Efficiency ofan Air Separation Plant by Varying theCycle Stage Durations, Theo. Found. ofChem. Eng., Vol. 41, No. 2, pp. 143–149,2007.

3. Delgado, J. A., and Rodrigues, A. E.,Analysis of the boundary conditions forthe simulation of the pressure equalizationstep in PSA cycles, Chemical EngineeringScience 63 4452 – 4463, 2008.

4. Santos J.C., Cruz P, Regala T., MagalhaesF.D., and Mendes A., "High-PurityOxygen Production by Pressure SwingAdsorption", Ind Eng chem 46, pp 591-599, 2007.

5. Jee, J. G., Lee J. S., and Lee C. H., "AirSeparation by a Small-Scale Two-BedMedical O2 Pressure Swing Adsorption",Ind .Eng Chem.Res.40, 3647-3658, 2001.

6. Kirk-Othmer, Encyclopedia of ChemicalTechnology, volume 1,4th edition, John-Wiley & Sons (1991-1998).

7. Albright, L.F.), Albright’s chemicalengineering handbook, CRC 2009.

8. Ritter, J. A.; Yang, R. T., Pressure SwingAdsorption: Experimental and TheoreticalStudy on Air Purification and VaporRecovery. Ind. Eng. Chem. Res., 30, 1023,1991.

9. Smith, O. J., and Westerberg, A. W., TheOptimal Design Of Pressure SwingAdsorption Systems, Che. Eng. Sci. Vol.46. No. 12, pp. 2967-2976, 1991.

10. Yuwen, Z., Yuyuan, W., Jianying, G.,Jilin, Z., The experimental study on theperformance of a small-scale oxygenconcentration by PSA, Separation andPuri cation Technology 42, 23–127, 2005.

11. Jain, S., Moharir, P. L. and Wozny, G.,Heuristic Design of pressure SwingAdsorption : A Preliminary Study,Separation and Purification Technology,33, 25-43, 2003.


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12. Cruz, P., Santos, J. C., Magalh˜aes, F. D.and Mendes, A., Cyclic adsorptionseparation processes:analysis strategyandoptimization procedure, ChemicalEngineering Science, 58, 3143 – 3158,2003.

13. Yang, R., Doong, S., Gas separation bypressure swing adsorption, a porediffusion model for bulk separation,AIChE J., 31, 1829, 1985.

14. Zahra, M., T. Jafar, and M. Masoud,"Study of a Four-bed Pressure SwingAdsorption for oxygen Separation fromAir ", Int. J. of chem.and BiomolecularEng.1; 3, pp.140-144, 2008.

15. Mendes, A. M. M, Costa, C. A.V.,Rodrigues A. E., Oxygen Separation fromAir by PSA: Modeling and ExperimentalResults Part I: Isothermal Operation,separation and purification technology, 24,pp173-188, 2001.

NOMENCLATUREA bed cross-section area, m2

bO2 Langmuir adsorption isotherm constantof O2 , bar-1

bN2 Langmuir adsorption isotherm constantof N2 , bar-1

Cf solute feed concentration, mol/ld bed diameter, mmdp adsorbent diameter, mmLB bed length, mNfN2 feed mole flowrate of N2, mol/sNfO2 feed mole flowrate of O2, mol/sNExN2 exhaust mole flowrate of N2, mol/sPH, P1 adsorption high pressure ,barPL, P2 desorption low pressure, barPeq equalization pressure, barQpurg purge flow rate, l/minQprod product flow rate, l/minQeffluent effluent flow rate, l/minQf air feed flow rate, l/minqN2 adsorbent capacity of N2 , mol/kgqO2 adsorbent capacity of O2 , mol/kg

qs maximum adsorbent capacity of N2 orO2 in Langmuir adsorption isotherm, mol/kgtz time of the front at position z, stads adsorption time, stdepress depressurization time, steq equalization time, stpress pressurization time, suH interstitial velocity during adsorptionstep, m/s uL interstitial velocity during purging step,m/sW adsorbent weight, kgyi mole fraction in gas phase ofcomponent (i)z axial co-ordinate,or distance traveled bythe front, m

Greek Symbolsads dimensionless adsorption time

( ads = tads/ B)purg dimensionless purging time

( ads = tpurg/ Bp)B bed time constant of adsorption step

( B =LB/uH) , sBp bed time constant of purging step

( Bp =LB/uL) , s

AbbreviationsDR Dryer F FilterPR Pressure RegulatorCT Cold TrapPG Pressure GaugeV1 to V5 Solenoid ValvesOA Oxygen AnalyzerOF Oxygen flowmeter

Table 1 Details of PSA Columns and Adsorbent

AdsorbersColumn LengthColumn diameterAdsorbent TypeShapeParticle diameterParticle densityBulk densityBed porosity

LD

dp

p

B

0.7 m50 mm

13X zeoliteSphere

1.7-2.6 mm1070 kg/m3

670 kg/m3

0.4


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Adsorbent weightAdsorbent bed lengthLangmuir isothermparameters[4]

Oxygen -Adsorption heat of O2Nitrogen -

-Adsorption heat of N2

wLB

qsO2

bO2HO2

qsN2

bN2HN2

0.75 kg0.57 m

3.091 mole/kg0.0367 bar-1

12.8 kJ/mole3.091 mole/kg0.1006 bar-1

17 kJ/mole

Table 2 Experimental 4-steps solenoid valvesoperation. (tads=10,20,30 s)

Table 3 Experimental 6-steps solenoid valvesoperation.(tads= 30 s)

Fig.1 Pressure-swing cycle[6]

Fig.2 Experimental setup of two-columnsPSA process

(D= 50 mm, L=700 mm, 750 gmzeolite(Zeo), 150 gm alumina(Alo))

Step Column 1 Column 2

1 Pressurizing(tprs=10 s)

(V1)open(V3)close

Depressurizing(tdeprs=10 s)

(V2)close(V4)open

2 Producing(tads)

(V1)open(V3)close

Purging(tpur=tads)

(V2)close(V4)open

3 Depressurizing(tdeprs=10 s)

(V1)close(V3)open

Pressurizing(tprs=10 s)

(V2)open(V4)close

4 Purging (tpur=tads)

(V1)close(V3)open

Producing(tads)

(V2)open(V4)close

Step Column 1 Column 2

1 Pressurizing(tprs=10 s)

(V1)open(V3)close(V5)close

Depressurizing(tdeprs=10 s)

(V2)close(V4)open

2 Producing(tads= 30 s)

(V1)open(V3)close(V5)close

Purging(tpur=tads=30 s)

(V2)close(V4)open

3 Equalization(teq=20 s)

(V1)open(V3)close(V5)open

Equalization(teq=20 s)

(V2)close(V4)close

4 Depressurizing(tdeprs=10 s)

(V1)close(V3)open

(V5)closed

Pressurizing(tprs=10 s)

(V2)open(V4)close

5 Purging(tpur=tads=30 s)

(V1)close(V3)open

(V5)closed

Producing(tads= 30 s)

(V2)open(V4)close

6 Equalization(teq=20 s)

(V1)close(V3)close(V5)open

Equalization(teq=20 s)

(V2)open(V4)close


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Fig.3 Experimental setup of single column(D= 50 mm, L=700 mm, 750 gm zeolite,150 gm alumina)

Fig.4 PSA system of 2-column 4-stepprocess

Fig.5 PSA system of 2-column 6-stepprocess

Fig.6 The effect of the adsorption pressure(PH) on product oxygen purity for 2-

column, 4-step operation.


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Fig.7 Effect of the adsorption time (tads) onproduct oxygen purity for 2-column, 4-step

cycle , (Qpurg=2 l/min).

Fig.8 Effect of adsorption time (tads) onproduct oxygen purity, for 4-step cycle, by

adjusting the purge flowrate (Qpurg).

Fig.9 Effect of the dimensionlessadsorption time ( ads) on product oxygen

purity for 2-column, 4-step operation.

Fig.10 The effect of the Purge Flow rate(Qpurg) on product oxygen purity, for 2-

column, 4-step cycle

Fig.11 The effect of the adsorption times(tads) on specific product Flowrate

(Qpurg/w) at maximum product oxygenpurity.

Fig.12 The effect of the purge flowrate(Qpurg) on product oxygen purity for 6-

Steps cycle, with air feed initialpressurizing


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Fig.13 The effect of the purge flowrate(Qpurg) on product oxygen purity for 6-Steps cycle, with O2 initial pressurizing

Fig.14 Effect of the dimensionlessadsorption time ( ads) on product oxygen

purity for 2-column, 6-step cycle.

Fig.15 Effect of the dimensionless purgetime ( purg) on product oxygen purity for

2-column, 6-step cycle

Fig.16 Single column characteristics, usingair feed pressurizing at different

adsorption pressures and Qeffluent=1liter/min

Fig.17 Single column characteristics, usinginitial pure oxygen pressurizing at

different Qeffluent, and PH=3 bar.

A STUDY OF OXYGEN SEPARATION FROM AIR BY PRESSURE SWING ADSORPTION (PSA)

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