a study of oxygen separation from air by psa process

8/16/2019 A Study of Oxygen Separation From Air By PSA process

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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 BY

PRESSURE 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), and

purge 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 significant

effect on product oxygen purity was noticed throughout the adsorption pressure range studied, for both cycle operations. This is confirmed by single bed characteristic results. The effect of the

adsorption time and the purge flowrate on the product oxygen purity show some optimum values for 4-step operation. Single bed characteristic result confirms the range of the adsorption time and the

purge flowrate. Similar trend results were noticed with 2-column, 6-step operation, with air initial

pressurizing, for the effect of purge flowrate at constant adsorption time (30 s). The product oxygen purity 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 above

1.5 liter/min. Single column characteristics, using initial intermediate oxygen pressurizing indicated higher product oxygen purity expected (>90%) than that obtained in the 2-column, 6-step operation.

) 50 570 (

13X.

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

.

70 % 80% .

. .

.

.

)30 (.

82% 11,5 /

)1,5 / (.

) 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.ukmailto:ajali:@soharuni.edu.ommailto:ajali:@soharuni.edu.ommailto:zaid572000:@yahoo.co.uk


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1. INTRODUCTION

At the present time, there are threedifferent technologies for oxygen production

from air:

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

2. The membrane technology.3. The adsorption technology

The latter two technologies have been performed at ambient temperature. A more

and more popular air separation process iscurrently pressure swing adsorption (PSA) on

zeolites, which was proposed by Skarstrom[1]

in the middle of the 20th century and is based

on periodic change of modes of selectiveadsorption of gases at increased pressure and

their 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 two beds and using a zeolite, was patented by

Skarstrom 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 feed through one end with raffinate

withdrawal through the other. Raffinatemeans rich in the component with the

lowest adsorption affinity3. Depressurization or blow down step,

pressure is decreased opening one bed end, and the resulting flow is

countercurrent to the feed.4. Purging step, desorption at the lower

operating pressure, which is performed by purging the bed with the raffinate

product, flows countercurrent to the feed.A very important improvement was the

introduction of the pressure equalizationstage, prior to the blow down step where two

beds are connected through one end while theother remaining ends are kept closed. The

product recovery is increased because less

feed gas is necessary to re-pressurize thecolumns.

[1,4,5]

Oxygen production (purity below 95%)

from air, using nitrogen selective zeolites of type A (5A) or type X (13X-NaX, LiX, or LiLSX), by means of pressure swing

adsorption (PSA) processes has noticeablyincreased in the past decades. However, the

concentration of the product is limited to 95%oxygen, because of the presence of argon in

air, since these adsorbents present similar adsorption 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 have been implemented for many commercial

applications, where the difference lies in theselection and sequence of the elementary

steps, and in the way in which these steps arecarried out.[3]

The main objects of present work 1. To construct a small scale Pressure Swing

Adsorption (PSA) unit for oxygenseparation from air, using two bed

columns which are packed withcommercial zeolite 13X.

2. To study the effects of operating parameters, such as pressure, cycle time,

purge and product flow rate on the performance of PSA unit, using two

columns 4-steps traditional Skarstromcyclic operation to adjust the process

variables ranges. The Performance ischaracterized by O2 purity, Recovery and

Productivity.3. To study the effects of operating

parameters, such as pressure, cycle time,Purge and product flow rate on the

performance of PSA unit, using twocolumns 6-steps equalization modification

cyclic operation. The Performance is


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characterized by O2 purity, Recovery and

Productivity.4. To investigate the characteristic of single

column operation and checking the

activity of the zeolite.

2. PRESSURE SWING ADSORPTION

Adsorption processes are often identified by their method of regeneration. Temperature

swing adsorption (TSA) and pressure swingadsorption (PSA) are the most frequently

applied process cycles for gas separation.[6]

A pressure swing adsorption (PSA) cycle

is one in which desorption takes place at a pressure much lower than adsorption. Its

principle application is for bulk separationswhere contaminants are presented at high

concentration. The PSA cycles arecharacterized by high residual loadings and

low operating loading. Fig.1 shows theoperating loading (q 1-q 2) that derives from

the 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 be

short, seconds to minutes, for reasonablysized beds. Fortunately, packed beds of

adsorbent respond rapidly to changes in pressure.

[6]

A purge usually removes the desorbed components from the bed, and the bed is

returned to adsorption condition by re- pressurization. Applications may require

additional steps. Systems with weaklyadsorbed species are especially suited to PSA

adsorption. The applications of PSA includedrying, upgrading of H2 and fuel gases, and

air separation.[6]

Adsorption time estimation for the PSA

process, assuming equilibrium driven and negligible mass transfer effects, can be

calculated from the following equation [7]

:

Qf Cf tz = q f w z / LB (1)

PSA processes rarely utilize all the

adsorbents and the beds are never completelyregenerated. The unused portion of the bed

acts as a guard and is needed to maintain the

gas- and adsorbed-phases axial distribution

[8]

Adsorption is assumed to occur at someconstant fraction of equilibrium, and by using

some given fraction of the availableadsorbent.

[9]

Assuming operation at z/LB =0.75, and :

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

q N2= q s b N2Pad y N2/1+b N2y N2Pad +bO2yO2 Pad (3)

NfN2 = NExN2 = q N2 * W (4)

tz = q f W (0.75) / (78/22) NfO2 (5)

tz = 0.21 W q f / NfO2 (6)

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

3. EXPERIMENTAL WORKThe schematic diagram of the

experimental arrangement of PSA unit used in the present work is shown in Fig.2. It

contains two galvanized steel columns. Thelength of each column (L) is 0.7 m and its

diameter (D) is 50 mm. The input and outputconnections are of 5 mm tubing, fittings and

valves.The setup is equipped with an automatic

control system for controlling the time of each cycle. A programmed timer controlled

solenoid valves were used to achieve thedesired operation.

The concentrations of the effluent flowswere analyzed by a portable calibrated

oxygen analyzer (GOX 100 Greisinger Electronic GmbH).


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Atmospheric air was used as a feed to the

PSA system, after drying with activealumina.

Fig.3 shows a single bed arrangement,

used for adsorbent and processcharacteristics. One of the before mentioned two columns was used. The work with single

column was designed to simulate the work of the two columns PSA process.

The adsorbent used in this work is zeolite13X (13XHP 8x12 mesh). The characteristics

of the adsorption bed and the adsorbent withits adsorption isotherm of N2 and O2 are

shown in Table (1).The experimental work in the present study

was 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 the

experimental work. The following operating parameters are held constant during the most

experiments with little exceptions:Pressurizing time t pres= 10 s

Depressurizing time tdeprs= 10 sEqualization time teq = 20 s

The operating parameters considered inthe present work with their ranges are as

follows;Adsorption time tads= 10, 20, and 30 s

Adsorption pressure PH= 2, 3, and 4 bar Purge flow rate Q purg= 1, 1.5, 2, 3, 4, 5, and 6

L/min

Two-Columns Operation

The experimental procedure was:

1. Preparation of the PSA system shown inFig.1, using vacuum and O2 pressurizing

and purging to ensure the zeolite activity.The bed was kept at 1 Barg pressure of

pure oxygen to prevent contaminationfrom the outside air.

2. Adjust the air feed pressure by pressureregulator.

3. Adjust the system condition with or

without initial pure O2 intermediate pressure of the first column to the desired

value, especially, for 6-steps operation.

4. Starting the control board with the setted duration process steps and the valvesoperation cycle as shown in Table(2) and

Fig.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 rotameter

and a regulating valve.6. Recording the product purity (O2 %)

measured by the analyzer with time and stop the experiment when the system

reaches a steady state after about 30minutes.

Single Column Characteristics

The experimental procedure was:1. Preparation of the PSA system shown in

Fig.2, using vacuum and O2 purging toensure the zeolite activity.

2. Adjust the air feed pressure by pressureregulator.

3. Adjust the system condition with or without initial pure O2 intermediate

pressure of the column to the desired value.

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 regulating

valve.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 of

2 and 4 bar. This result is in agreement withthat obtained by Jee et al. (2001)

[5] for high

purge-to-feed ratio.

The present results are also inagreement with that concluded by Yuwen etal.(2005)

[10], that medium adsorption pressure

gives optimum performance. In addition, ahigh pressure level leads to higher

compression cost and a higher energy loss inthe depressurizing step.[11]

Jain et al.(2003)[11]

stated that, for constant selectivity systems, performance

increases with increasing pressure accordingto adsorption equilibrium isotherm. The

present work system behaves as a non-constant selectivity system with increasing

pressure.

Effect of adsorption time

Figure (7) shows the effect of the

adsorption time (tads) on steady state productoxygen purity, at constant adsorption

pressure (PH =3 bar). It shows an optimumvalue at tads= 20 s.

Breakthrough occurs at highadsorption time, and constant effluent

flowrate from the column. The duration of the adsorption step is the time period needed

for breakthrough to occur. After this time, the product purity will decline, and before this

time the full bed capacity will not beemployed. Thus, the adsorption time should

be near the breakthrough time. This timedepends upon isotherm, diffusivity and

residence time of the feed in the bed [11]

.Figure (8) shows insignificant change

in the product oxygen purity with theadsorption time (tads), by adjusting the

required purge flowrate.Figure (9) shows the effect of the

dimensionless adsorption time (ads) onsteady state product oxygen purity, at

constant adsorption pressure (PH =3 Bara). Itshows an optimum range of ads= 0.2 – 0.25.

The result of the optimum range of

dimensionless adsorption time ads is lessthan obtained by Cruz et al.(2003)

[12] of ads=

1 – 1.5.

Effect of Purge Flowrate

Figure (10) shows the effect of thePurge Flowrate (Q purg) on steady state

product oxygen purity, at constant adsorption pressure (PH=3 bar). It shows some optimum

values of (Q purg= 4, 2, and 1.5 liter/min) for the three levels of adsorption times (tads=10,

20 and 30 s) respectively. This result is inagreement with that obtained by Yang and

Doong (1985)[13]

and Zahra et al.(2008) [14]

.For low purge volumes, the

regeneration of the production column isincomplete for low purge volume, thenitrogen wave front eventually breaks

through, leading to a decrease of the average product concentration.

[12]

Figure (10) also shows the maximum product oxygen purity of seventies for the

both effect of the Purge Flowrate (Q purg) and the adsorption times (tads).

There is an interrelationship betweenthe adsorption time (tads) and the purge

flowrate (Q purg), which represents about 90 %of effluent flowrate from the column.

Dimensionless adsorption time (ads)calculation account partially for this

interrelationship as shown in Fig. 9.The product flowrate range, used in

the present work, can be presented as specificflowrates (Q prod / w). Fig. 11 shows the

largest product oxygen purity of seventiescontour curve for the effect of the adsorption

times (tads) on the specific product flowrate

(Q prod /w).Fig. 12 shows the effect of the Purge

Flowrate (Q purg) on steady state product

oxygen purity for 6-Steps of PSA process,with air feed initial pressurizing. It show an

optimum value at purge flowrate Q purg= 1.5liter/min. It is an identical trend with that of


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two-columns, 4-step cycle results, except the

largest product oxygen purity of eighties with6-step cycle compared to seventies with 4-

step cycle.

Fig.13 shows the effect of the PurgeFlowrate (Q purg) on steady state productoxygen purity for 6-Steps of PSA process,

with pure oxygen initial pressurizing. The product purity presents a plateau (for about

82% purity) for purge flowrate Q purg 1 to 1.5liter/min and then decreases. It is of the same

trend noticed by Mendes et al.(2001)[15]

.The decrease in product purity with

the increasing of the purge flowrate (Q purg)above 1.5 liter/min can be attributed to that

breakthrough point which may occur at higheffluent from the column in which the purge

flowrate represents the most percentage of it(about 90%).

Fig.14 shows the effect of thedimensionless adsorption time (ads) on

steady state product oxygen purity, atconstant adsorption pressure (PH =3 bar). It

shows an optimum value of about ads= 0.25,for air feed initial pressurizing. The product

purity 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 steady

state product oxygen purity, at constantadsorption pressure (PH =3 bara). It shows an

optimum value of purg= 0.67, for air feed initial pressurizing. The product purity

presents a plateau (for a about 82% purity)for the dimensionless purge time purg 0.45 to

0.7, then decreases for pure oxygen initial pressurizing. This is the same trend as the

dimensionless adsorption time.

4.2 Single Column Characteristics

Fig.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 of the adsorption pressure (PH) was noticed on

the effluent oxygen purity. This result

confirms the result of the 2-column, 4-stepand 6-step PSA unit, presented in the previous 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. This

result confirms the range of the adsorptiontime (tads) and the purge flowrate (Q purg)

which represent the high percentage of effluent flowrate (Qeffluent) in the present

study for the 2-column, 4-step PSA unit.Fig.17 shows the single column

characteristics, as breakthrough curve, usinginitial intermediate pure oxygen pressurizing

at different effluent flowrates (Qeffluent), and constant adsorption pressure (PH=3 bar). The

breakthrough time is much higher than theadsorption time (tads) used in the present

study especially in the 2-column, 6-step PSAunit. This indicates that high pure product

oxygen 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) using

commercial 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 oxygen

purity was noticed of the adsorption pressure range studied between 2 and 4


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Bara, for both 4-step and 6-step cycle

operations. This result is also confirmed by single bed characteristic result.

3. The effect of the adsorption time (tads) and

the flow of purge flowrate (Q purg) on the product oxygen purity, shows someoptimum values, for 4-step cycle

operation. No effect was noticed whenthese two parameters had been adjusted

with each other because of their interrelationship.

4. The effect of the Purge Flowrate (Q purg) onthe product oxygen purity for 6-Steps of

PSA process, with air feed initial pressurizing, shows an optimum value at

purge flowrate Q purg= 1.5 liter/min. It isidentical trend with that of two-columns,

4-step cycle results.5. The product oxygen purity for 6-Steps of

PSA process, with pure oxygen initial pressurizing, presents a plateau (for a

about 82% purity) for purge flowrate Q purg1 to 1.5 liter/min then decreases when

increasing the purge flowrate above 1.5liter/min.

6. Single bed characteristics results confirmsthe range of the adsorption time (tads) and

the purge flowrate (Q purg), 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 pressurizing

indicated higher pure product oxygenexpected (>90%). than that obtained

experimentally in the 2-column, 6-stepPSA unit. The possible reason for the

lower product oxygen purity (~80%) is theincomplete regeneration of the adsorption

column.

REFRENCES

1. 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 , and L. I. Kheifets, Increasing the Efficiency of

an Air Separation Plant by Varying the

Cycle Stage Durations, Theo. Found. of Chem. Eng., Vol. 41, No. 2, pp. 143–149,2007.

3. Delgado, J. A., and Rodrigues, A. E.,Analysis of the boundary conditions for

the simulation of the pressure equalizationstep in PSA cycles, Chemical Engineering

Science 63 4452 – 4463, 2008.4. Santos J.C., Cruz P, Regala T., Magalhaes

F.D., and Mendes A., "High-PurityOxygen Production by Pressure Swing

Adsorption", Ind Eng chem 46, pp 591-599, 2007.

5. Jee, J. G., Lee J. S., and Lee C. H., "Air Separation by a Small-Scale Two-Bed

Medical 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 chemical

engineering handbook, CRC 2009.8. Ritter, J. A.; Yang, R. T., Pressure Swing

Adsorption: Experimental and TheoreticalStudy on Air Purification and Vapor

Recovery. Ind. Eng. Chem. Res., 30, 1023,1991.

9. Smith, O. J., and Westerberg, A. W., TheOptimal Design Of Pressure Swing

Adsorption 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 the

performance of a small-scale oxygenconcentration by PSA, Separation and

Purication 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 strategy

andoptimization procedure, Chemical

Engineering Science, 58, 3143 – 3158,2003.13. Yang, R., Doong, S., Gas separation by

pressure 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 from

Air ", Int. J. of chem.and Biomolecular Eng.1; 3, pp.140-144, 2008.

15. Mendes, A. M. M, Costa, C. A.V.,Rodrigues A. E., Oxygen Separation from

Air by PSA: Modeling and ExperimentalResults Part I: Isothermal Operation,

separation and purification technology, 24, pp173-188, 2001.

NOMENCLATURE

A bed cross-section area, m2

bO2 Langmuir adsorption isotherm constant

of O2 , bar -1

b N2 Langmuir adsorption isotherm constant

of N2 , bar -1

Cf solute feed concentration, mol/l

d bed diameter, mmd p adsorbent diameter, mm

LB bed length, m NfN2 feed mole flowrate of N2, mol/s

NfO2 feed mole flowrate of O2, mol/s NExN2 exhaust mole flowrate of N2, mol/s

PH, P1 adsorption high pressure ,bar PL, P2 desorption low pressure, bar

Peq equalization pressure, bar Q purg purge flow rate, l/min

Q prod product flow rate, l/minQeffluent effluent flow rate, l/min

Qf air feed flow rate, l/minq N2 adsorbent capacity of N2 , mol/kg

q O2 adsorbent capacity of O2 , mol/kg

q s maximum adsorbent capacity of N2 or

O2 in Langmuir adsorption isotherm, mol/kgtz time of the front at position z, s

tads adsorption time, s

tdepress depressurization time, steq equalization time, st press pressurization time, s

uH interstitial velocity during adsorptionstep, m/s

uL interstitial velocity during purging step,m/s

W adsorbent weight, kgyi mole fraction in gas phase of

component (i)z axial co-ordinate,or distance traveled by

the front, m

Greek Symbols

ads dimensionless adsorption time

(ads = tads/ B) purg dimensionless purging time

(ads = t purg/ 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 Filter

PR Pressure Regulator CT Cold Trap

PG Pressure GaugeV1 to V5 Solenoid Valves

OA Oxygen Analyzer OF Oxygen flowmeter

Table 1 Details of PSA Columns and Adsorbent

Adsorbers

Column LengthColumn diameter

Adsorbent Type

ShapeParticle diameter Particle density

Bulk densityBed porosity

LD

d p pB

0.7 m50 mm

13X zeolite

Sphere1.7-2.6 mm1070 kg/m

3

670 kg/m3

0.4


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Adsorbent weight

Adsorbent bed lengthLangmuir isotherm

parameters[4]

Oxygen -Adsorption heat of O2

Nitrogen -

-Adsorption heat of N2

w

LB

q sO2 bO2HO2q sN2

b N2H N2

0.75 kg

0.57 m

3.091 mole/kg

0.0367 bar -1

12.8 kJ/mole3.091 mole/kg

0.1006 bar -1

17 kJ/mole

Table 2 Experimental 4-steps solenoid valves

operation. (tads=10,20,30 s)

Table 3 Experimental 6-steps solenoid valves

operation.(tads= 30 s)

Fig.1 Pressure-swing cycle[6]

Fig.2 Experimental setup of two-columns

PSA process

(D= 50 mm, L=700 mm, 750 gm

zeolite(Zeo), 150 gm alumina(Alo))

Step Column 1 Column 2

1 Pressurizing

(t prs=10 s)

(V1)open

(V3)close

Depressurizing

(tdepr s=10 s)

(V2)close

(V4)open

2 Producing

(tads)

(V1)open

(V3)close

Purging

(t pur =tads)

(V2)close

(V4)open

3 Depressurizing(tdeprs=10 s)

(V1)close(V3)open

Pressurizing(t prs=10 s)

(V2)open(V4)close

4 Purging

(t pur =tads)

(V1)close

(V3)open

Producing

(tads)

(V2)open

(V4)close

Step Column 1 Column 2

1 Pressurizing(t prs=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

(t pur =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

(t prs=10 s)

(V2)open

(V4)close

5 Purging

(t pur =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-step

process

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

process

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) on

product oxygen purity for 2-column, 4-step

cycle , (Qpurg=2 l/min).

Fig.8 Effect of adsorption time (tads) on

product oxygen purity, for 4-step cycle, byadjusting the purge flowrate (Qpurg).

Fig.9 Effect of the dimensionless

adsorption 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 oxygen

purity.

Fig.12 The effect of the purge flowrate

(Qpurg) on product oxygen purity for 6-

Steps cycle, with air feed initial

pressurizing


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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 dimensionless

adsorption time (ads) on product oxygenpurity for 2-column, 6-step cycle.

Fig.15 Effect of the dimensionless purge

time (purg) on product oxygen purity for

2-column, 6-step cycle

Fig.16 Single column characteristics, using

air feed pressurizing at different

adsorption pressures and Qeffluent=1

liter/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 psa process

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