AUTH_PRES07 - Presentation

Hydrogen purification by Pressure Swing Adsorption

Dragan Nikolic1, Apostolos Giovanoglou2, Michael C. Georgiadis3, Eustathios S. Kikkinides1

PRES 2007, Ischia, Italy

June 2007

1 University of Western Macedonia, Department of Engineering and Management of Energy Resources, Kozani, Greece

2 Process Systems Enterprise Ltd, London, UK3 Imperial College London, Centre for Process Systems Engineering,

Department of Chemical Engineering, London, UK

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Overview1. Motivation2. Modelling framework 3. Process overview4. New PSA cycles5. Results6. Conclusions

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1. MotivationWhy H2: Increasing demand for H2, particularly in petroleum refineries and in the petrochemical processes (99.99+%).Why PSA: Since hydrogen is adsorbed much less than almost any other components, PSA has a clear advantage over almost all other possible approaches.Several ways to improve the separation quality and power requirements:

Multibed PSA configurationsMultilayered adsorbentsAdsorbent mixtureHybrid systems (such as hybrid PSA and membrane units)Specially designed multibed PSA process for the simultaneous production of pure H2 and CO2 from SMROG (Sircar and Golden, 2000; Sircar and Kratz, 1988)

Generic PSA modelling framework is being developed to support all the above features.

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SourceStrongPurge(i)

SourceFeed(i)

SourcePurge(i)

V(i)-2 V(i)-3

V(i)-5V(i)-4

V(i)-1

SinkLight(i)

SinkHeavy(i)

Adsorber (i)

(N-1) connections from the other beds

Layer (1)

Layer (n)

r

qi

Ni

2. Modelling framework

Main building block

Hierarchical model decomposition

Flowsheet model

Arbitrary number of beds(main building block can be replicated through an

input parameter)

All feasible inter-bedconnectivities

Operating procedures of the whole plant are easily generated by an

auxiliary program

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r

qi

Ni

Layer (1)

Layer (n)

2. Modelling framework (cont’d)

SourceStrongPurge(i)

SourceFeed(i)

SourcePurge(i)

V(i)-2 V(i)-3

V(i)-5V(i)-4

V(i)-1

SinkLight(i)

SinkHeavy(i)

Adsorber (i)

(N-1) connections from the other beds

Model of the main building block

All PSA steps are supported

Feed and product streams

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SourceStrongPurge(i)

SourceFeed(i)

SourcePurge(i)

V(i)-2 V(i)-3

V(i)-5V(i)-4

V(i)-1

SinkLight(i)

SinkHeavy(i)

Adsorber (i)

(N-1) connections from the other beds

r

qi

Ni

2. Modelling framework (cont’d)

Layer (1)

Layer (n)

Boundary conditions for all PSA steps

Layer inter-connections

Support for one or more adsorbent layers

Adsorption column model

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SourceStrongPurge(i)

SourceFeed(i)

SourcePurge(i)

V(i)-2 V(i)-3

V(i)-5V(i)-4

V(i)-1

SinkLight(i)

SinkHeavy(i)

Adsorber (i)

(N-1) connections from the other beds

r

qi

Ni

Layer (1)

Layer (n)

2. Modelling framework (cont’d)

Single adsorbent or adsorbent mixture

Adsorbent layer model

Single adsorbent or adsorbent mixture

( ) ( ),1 , 0, , 1, ,i i bed i

i z i compbed

uC C CN D z L i Nz t z z

∂ ∂ − ε ∂∂ ⎛ ⎞+ + = ∀ ∈ =⎜ ⎟∂ ∂ ε ∂ ∂⎝ ⎠…

( ) ( ) ( ) ( ),31 , 0, p p h wallbedg wall z

bed bed bed

c uT c T k Tq T T z Lz t R z z

∂ ρ ∂ ρ − ε ∂ ∂⎛ ⎞+ + + − = λ ∀ ∈⎜ ⎟∂ ∂ ε ε ∂ ∂⎝ ⎠

Mass and heat transfer through the particle surface is the only information

exchanged between the interstitial fluid and the adsorbent particles

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SourceStrongPurge(i)

SourceFeed(i)

SourcePurge(i)

V(i)-2 V(i)-3

V(i)-5V(i)-4

V(i)-1

SinkLight(i)

SinkHeavy(i)

Adsorber (i)

(N-1) connections from the other beds

Layer (1)

Layer (n)

2. Modelling framework (cont’d)

r

qi

Ni

Adsorbent particle model

Mass and heat flux through the particle surface

Film around the particle

Mass transfer within the particle can be described by any transport mechanism

(LEQ, LDF, SD, PD)

( )

( ) [ ]

*2

,211

0, , 0, , 1, ,

p ppi i i

p p p p e ip

p comp

C Q CR Dt t r rR

r R z L i N

⎛ ⎞∂ ∂ ∂∂ε + − ε ρ = ε ⎜ ⎟

⎝ ⎠∂ ∂ ∂ ∂

∀ ∈ ∀ ∈ = …

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2. Modelling framework (cont’d)

Input:Number of beds

Input:Sequence of steps

in one bed

Co-current pressurizationAdsorptionPressure equalization 1Pressure equalization 2BlowdownPurgePressure equalization 2Pressure equalization 1

Try to connectthe beds

Success?

Example:

No

Yes

Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7 Step 8Bed 1 CoCP Ads EQD1 EQD2 Blow Purge EQR2 EQR1Bed 2 EQR1 CoCP Ads EQD1 EQD2 Blow Purge EQR2Bed 3 EQR2 EQR1 CoCP Ads EQD1 EQD2 Blow PurgeBed 4 Purge EQR2 EQR1 CoCP Ads EQD1 EQD2 BlowBed 5 Blow Purge EQR2 EQR1 CoCP Ads EQD1 EQD2Bed 6 EQD2 Blow Purge EQR2 EQR1 CoCP Ads EQD1Bed 7 EQD1 EQD2 Blow Purge EQR2 EQR1 CoCP AdsBed 8 Ads EQD1 EQD2 Blow Purge EQR2 EQR1 CoCP

Input:Number of A and B beds

Input:Sequence of steps

in A and B group of beds

AdsorptionCo-current rinseBlowdownEvacuationPressure equalizationCounter-current pressurization

Try to connectthe beds

Success?

A group:

No

Yes

AdsorptionPressure equalizationBlowdownPurgeCounter-current pressurization

B group:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Bed-1 A A R R B B B B B B E E E E ER1 P+Bed-2 E E E P+ A A R R B B B B B B E EBed-3 B B E E E E ER1 P+ A A R R B B B BBed-4 B B B B B B E E E E ER1 P+ A A R RBed-5 A A E B B B P P A A ED1 B B P P P+Bed-6 B P P P+ A A ED1 B B P P P+ A A ED1 B

Original algorithm Modified algorithm

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3. Process overviewTwo types of beds (called type A and B)Each type contains different adsorbent and undergoes different cycle steps

A – activated carbonB – zeolite 5A

The most distinguishing features:Co-current CO2 rinse at feed pressure in type AUse of different regeneration methods

Type A: (depressurization and evacuation)Type B: (depressurization and purge)

Pressure equalization between A-B and B-B beds to ensure mass conservation of the interstitial fluid.

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3. Process overview (cont’d)Series of steps in type A beds(*,**):

High pressure adsorption (to type B bed)Co-current purge (rinse) by CO2

Counter-current blowdown (to atmospheric P)Counter-current evacuation (to sub-atmospheric P)Pressure equalization (repressurization)Counter-current pressurization (by H2)

Series of steps in type B beds(*,**):High pressure adsorption (from type A bed)Pressure equalization (depressurization; B-A or/and B-B)Counter-current blowdown (to atmospheric P)Counter-current purge (by H2)Counter-current pressurization (by H2)

* Sircar, S., Kratz, W.C., 1988, Simultaneous production of hydrogen and carbon dioxide from steam methane reformer off-gas by pressure swing adsorption, Separation Science and Technology, 23, 2397

** Sircar, S., Golden, T.C. 2000, Purification of hydrogen by pressure swing adsorption, Separation Science and Technology, 35, 667

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4. New PSA cyclesBased on the industrial plant (6+3 beds), three new PSA cycle configurations have been developed by using the program for automatic generation

1 2 3 4 5 6 7 8 9 10 B-1 A A R R B B B E E P+

B-2 B B E E P+ A A R R B

B-3 A A B P P+ A A B P P+

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 B-1 A A R R B B B B B B E E E E ER1 P+ B-2 E E E P+ A A R R B B B B B B E E

B-3 B B E E E E ER1 P+ A A R R B B B B

B-4 B B B B B B E E E E ER1 P+ A A R R

B-5 A A E B B B P P A A ED1 B B P P P+

B-6 B P P P+ A A ED1 B B P P P+ A A ED1 B

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 B-1 A A R R B B B B B B E E E E P+ P+

B-2 E E P+ P+ A A R R B B B B B B E E

B-3 B B E E E E P+ P+ A A R R B B B B

B-4 B B B B B B E E E E P+ P+ A A R R

B-5 A A ER1 B P P ER1 P+ A A ED1 B P P ER1 P+

B-6 P P ER1 P+ A A ED1 B P P ER1 P+ A A ED1 B

(2+1)

(4+2)a

(4+2)b

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5. ResultsHigh H2/CO2 purity & recovery comparable to the original processGood quality tertiary product (suitable for a fuel gas)Lower capital cost

94.0087.10Recovery, %

99.4099.99+Recovery, %(6+3)

86.20986.038Purity, %

99.93899.991Recovery, %(4+2)b

85.73185.560Purity, %

99.94099.997Purity, %(4+2)a

85.66482.289Recovery, %

99.94899.992Purity, %(2+1)

CO2H2

Products

N beds

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6. ConclusionsA previously developed generic PSA modelling framework for PSA flowsheet generation is successfully employed in the process of simultaneous H2 and CO2 production from SMROG under high product purity and recovery requirements.In order to improve the separation performance, new complex PSA cycle configurations have been designed and simulated.In the proposed configurations two different types of beds have been employed, which contain different adsorbents and undergo different steps during the process cycle.Comparable primary and secondary product purities, recoveries and power requirements with the conventional PSA cycles are obtained.Capital costs are lower due to the lower number of beds.The proposed PSA cycle configurations exhibit comparable separation performance with the conventional cycles at a lower capital cost

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AcknowledgementsFinancial support from PRISM EU RTN (Contract number MRTN-CT-2004-512233)