1.
 Recovery Effect of Evacuation and Rinse Conditions on Performance in PSA Process for CO    
  

CO

  PSA   

   

* * ^†

 

*
 

(2000 2 1 , 2000 9 18 )

Effect of Evacuation and Rinse Conditions on Performance in PSA Process for CO

Recovery

Hawung Lee, Jae-ho Choi*, Yeong-Koo Yeo*, Hyung Keun Song and Byung-Ki Na^†

Clean Technology Research Center, KIST, Seoul 136-791, Korea

*Dept. of Chem. Eng., Hanyang University, Seoul 133-791, Korea (Received 1 February 2000; accepted 18 September 2000)



& 
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Abstract−The effect of evacuation and rinse step on the process performance was studied using numerical simulation to recover heavy component in a PSA process. Rinse and evacuation steps are very important to obtain heavy component as a product. Therefore, to improve the process performance, the rinse pressure, reflux ratio and flow direction of rinse step were selected as variables, and the performance change of process according to changing variables was investigated. The effect of eva- cuation condition combined with the rinse condition was studied also. As a result, the optimum operating condition was obtained to have maximum process performance. Increasing rinse pressure conduced to increase the recovery by increasing adsorbed amount of CO₂ during the rinse step. Decreasing evacuation pressure contributed to increase the purity by increasing desorbed amount of CO₂ during the evacuation step. At this point, the optimum reflux ratio was existed at certain pressure conditions.

Key words: CO₂, PSA, Rinse, Evacuation, Simulation

†E-mail: nabk@kist.re.kr

1.  

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Fig. 1. Flow schedule of PSA process.

PR: Pressurization, AD: Adsorption, CD: Countercurrent depressur- ization, PE: Pressure equalization, RN: Rinse, EV: Evacuation

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Á[6].

Overall mass balance:

(1)

where

Mass Balance of i-component:

(2) Energy Balance:

(3)

Mass Transfer Rate:

(4)

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 P(t) pressure history" ´; PSA ¶p —¢' ¤

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 €%f[9], ¶p p0 š¢ ãx6O  Table 3 €

.

w 0 ¶ý£O PSA  ¶p
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∂z

--- ∂C_total ---∂t ρ_bulk

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i=1

∑

+ +

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i=1

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+ + +

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γ–a

( )

--- ⁄t_s ln

–

=

Table 1. Boundary conditions of each step

Step Concentration Temperature Pressure Velocity

Pressurization y_i(t, 0)=y_f,i T(t, 0)=T_feed P=P(t) u(t, L)=0

Adsorption y_i(t, 0)=y_f,i T(t, 0)=T_feed P=P_H u(t, 0)=u_feed

Blowdown P=P(t) u(t, 0)=0

Evacuation P=P(t) u(t, L)=0

Pressure equalization Depressurized y_i(t, L)=y_Eq T(t, L)=T_Eq P=P(t) u(t, 0)=0

Pressurized y_i(t, L)=y_Eq T(t, L)=T_Eq P=P(t) u(t, 0)=0

Rinse Pressurized, cocurrent y_i(t, 0)=y_product T(t, 0)=T_Ev P=P(t) u(t, L)=0

Constant pressure, cocurrent y_i(t, 0)=y_product T(t, 0)=T_Ev P=P_Rn u(t, 0)=u_OR2

Pressurized, countercurrent y_i(t, L)=y_product T(t, L)=T_Ev P=P(t) u(t, 0)=0

Constant pressure, countercurrent y_i(t, L)=y_product T(t, L)=T_Ev P=P_Rn u(t, L)=u_OR2

 38 6 2000 12

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 dJ / upwind method" -%\ J ¶p$

[6, 13-15].

4.  

4-1.
  

USG U
 Ö× ‘v &' ­‰" Ϗl
w

J ÔÕ &N 
 Öבv &' 3 *~ ‹Œ[(1)-(4)]

& ¼Ó" ]$. 7 <=Rº 1 atm, ?=Rº 0.1 atm

.  ±‰" ÒÒ ßï ¦4 ¼ÓJ Fig. 2 ÍA.

Î4 l5 v» Ry USG" '  tu ±‰

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w N' #æ —¢4 àá0. “ï

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4 ‡6ˆ‰ q ¶e* USG" V~ ë  ±‰m

¼> ¤? †Æ @ 8 6 . ²' v» *Ry USG  ßï / 7 û *Ryl q* ÅP~~Ñ ßï

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 ßï ~Æ W l CMb CO2 q* †~Æ Ç . U#   CMb CO2q* †~Æ ¦4 †

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Â. Æ 9 1.

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C% Dô' "m Á U ‘v ' N
 URº

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 · NS%. E 8 6 .  USG*  

´½ ¾v d 8 7 (' ±‰. OJT. Ý, US G CMb r»#µ @ A CMb …" F*#G%. † q

 CMb c ­‰" *õ;, •' ­‰ CO2m N2 êy<=ï /  [C'. êy<=ï N CO2 …

m Rº  ± ;, “' CO2 ¤t , Rº

 Éd:W l  CO2* <=9 6 .  <=ìª%.

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F* ¦4 <=ï ~ 1 8 6 ; U
 š

CO₂ … !ú
 CO2…m Ü q H Æ Table 2. Characteristics of adsorption bed and operating conditions

Adsorbent Particle size [mesh]

Feed gas composition Bed diameter [mm]

Bed height [mm]

Adsorbent amount [kg]

Bed bulk density [g/cm³] Bed porosity, ε

Heat capacity of adsorbent, C_ps [J/g/K]

Heat capacity of gas, C_pg [J/g/K]

Adsorption pressure, P_H [atm]

Evacuation pressure, P_ev [atm]

Equalization pressure, P_eq [atm]

Time for adsorption [s]

Time for blowdown [s]

Time for pressure equalization [s]

Time for rinse/evacuation [s]

Activated carbon 8-12

17% CO₂, in N₂ 41.2

900 0.57 0.47 0.4 1.05 0.9942 1.5 0.1 0.55 300 20 20 360

Table 3. Langmuir parameters and heat of adsorption used in the cal- culation

Parameter CO₂ N₂

t₁^*[mmol/g]

t₂^*[mmol/g]

t₃^**[atm⁻¹] t₄^**[K]

∆H [kJ/mol]

23.944

−0.0517 2.1265×10⁻³

1588.315 24.103

7.052

−0.0106 4.2169×10⁻⁴

1680.038 16.928

*q_m=t₁+t₂T

**b=t₃ exp(t₄/T)

Fig. 2. The effect of flow directions on rinse step.

Case (1): cocurrent pressurization by product, cocurrent pressurized rinse, Case (2): cocurrent pressurization by product, countercurrent pressurized rinse, Case (3): countercurrent pressurization by product, cocurrent pressurized rinse, Case (4): countercurrent pressurization by product, countercurrent pressurized rinse(Reflux ratio=0.75).

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R 1.15
R, 1.3
R%. UR º ÉI 7 tu / “Æ NJ* êy<=ï /

* l F* 1.5
R q*  NJ 1%. Í K. ‡6ˆ ‹Œ å=*~. URº NJ‰ E¹ F*

‹v ÍA. Á Ù CMb r»## ‹Œ, Rº †

‹Œ l  CO2* <= Ç. RUSG )L  CO2

 Ù ‚POÆ 0. ¦4 ‡6ˆ ¤?ç NJ ‹v *

ì 6.

N URº F*#IW 3-%. tu vN#³ 6  { Ï 6 . Ε Î4 ' *~ ' pM [N5 6 ;  URº F* ¦§ tuê*òª
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 1.5
R“ 7" lW, ßï / w ßï ¦§ q

xH* § URºm ¼>' ‹v%. F* 1%. ÍK

% ßï O~W òª l *ÑÆ F* ‹v lJ:

.  USG <=@ ‰#æ o 14 C Ò0. ‡6ˆ ‹Œ, URº † ‹Œ* P Rºl Î /* F* ‹v Í· Ï 6 . # Q URº

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~
7° õ\d tu Š­‰" *õÆ 0. €    9dW J•U 3D €  ±5 6: . Î

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 F* ¦4 q Õ\ NJ % ‡6ˆ  

{ 8 6 . ²' Ur»¼ ¦§ tu xH ÀU ßï

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l
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Fig. 6‰ 7. Ur»¼* F*E ¦4 z{ ô. q*

Fig. 3. The effect of rinse pressure at P_EV=0.1, R=0.75.

Fig. 4. Equilibrium adsorption isotherm of CO₂, N₂ and O₂ on activated carbon at 25^oC.

Fig. 5. The performance curve of the Case (5), P_EV=0.1 atm, P_RN=1.0 atm.

 38 6 2000 12

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F* ¦4 G-%. tu F* ÀU" l9 1‰ ‡6

ˆ ‹Œ ^- Ur»¼* oB' 1. Î4 Ò ò ª 3 › õ§öKL ßï ÒÒ 7.6, 10, 15, 20 SLPM9 ‹

Œ" Í&.

URº‰ ?=Rº xH ¦§ 3 *~ ‹Œ P (5)m (6)

 ‹Œ" ¼ÓJ ?=Rº ' ¾v ϏlW, T SG

?=Rº P~ ‹Œ, l  Ù ?= P qm ‡6ˆ

†J :Æ 0. ¦4 (6) ‹Œ* (5) ‹Œl ù tu l 9. mÁ ‹v Fig. 8 (c)m (d) å=*~. Í ; e Î4 Š# ?=Rº P ‹Œ ù tu l .

 *h; ' *~ ' › ?=Rº  URº F*

 ‹Œl q X  ¾v â p€. #Q, Fig.

8 lW (a)m (b) Î (c)m (d)" ¼Ó5 7 (a)m (c), (b)m (d)

‹Œl q NJ l ÕE 8 6 .  ?=Rº

PÀW ¼Ó- P r»¼ † q Ctb c 6 {

 lJ: 1. •' p€, ?=Rº PL ‹Œ ?=ï

F* ¦4  ‡6ï RP Ç. Á Ur»¼4 U#

ßV  r»ï ƒ* RP Æ <%.F Í  N%. 8 6 .

3W URº F*, ?=Rº ' ‹Œm ¼Ó\ 7, w m 3&. q F*l ‡6ˆ F** ŒU p€ Ï 6 . Á ?=Rº  URº xH" ]^lW, Fig. 8

(a)m (c), Î (b)m (d)" ¼Ó8 7, ‡6ˆ Õ\ F*

N 8 6 . , URº †J:W 3-%. ‡6ˆ

F*' p€ lJ: . •' N U Rº †JŸ

%.F <=  CO2 Ù F*Æ P ‰#æ _~Ç.

 “PE ±‰. 8 6 . URº 1.5
R9 ‹Œ ‡6ˆ

 C Dô' "m Á ^-  *~Æ ; Fig. 8 (c)m (d)

 r»¼ F* P` #›È~ ‡6ˆ F*" 3Æ

<=@ ‰  #› 2 aƒ
‡6ˆ ÅP~ N

ÍAÆ 0. Ý r»¼* P ¾Š r»¼ F* ¦4 … ô,\ F* ‡6ˆ *Ñ\ F* 1. 7 ^&

 oBf  ^& 2 r»¼ q F*   P~ 3&. ‡6ˆ ô,' " ÍAÆ 0. r»¼* P

¾Š ‡6ˆ F* ß URº † ‹Œ, U#

CO₂ <=ï F*. cP~ ‡6ˆ F* ­‰* r»¼ F*

' ‡6ˆ '  ­‰l
7°%., U#æ <=

@ *\ ‰  #›È~ q F*m E¹ æ ‡6ˆ

F** Í  1[16].

²' URº † ‹Œ* P ‹Œl r»¼ F* ¦§

p€ Ï 6 . Ý, NR U ßï xH ¦§ q

xH* b òª
ó
"  Ï 6 . Ε URº

1.5
R9 ‹Œ òª
ó
* *Ñ ßï F* ¦4 q

 xHï /A Ï 6 . ßï ¦§ q NJ /

~ N € ¤Ì P URº † ‹Œ V ßï ‚J ¤Ì 1 ‡6ˆ W ß' ‘vk ´'

. " cX Ϗl
ñÆ ÍA
wJ ?=Rº 0.05
R“

‹Œ, ßï 7.6 SLPM9 ‹Œm 20 SLPM9 ‹Œ" ¼ÓJ qm

‡6ˆ Fig. 9 ÍA. Î4 8 6  "m Á UR º † ‹Œ r»¼ ¦§ ‡6ˆ ^&› Í Æ 

;  N r»¼ ´ <=@  H#IÆ P õ\d tu

Fig. 6. The effect of reflux ratio on the purity in the Case (5), P_EV=0.1 atm, P_RN=1.0 atm.

Fig. 7. The effect of reflux ratio on the recovery in the Case (5), P_EV= 0.1 atm, P_RN=1.0 atm.

" *õÆ 0. •' N ßï P ‹Œ*  ‹Œl

 €\ Í ; ßï / ‹Œ* ‡6ˆ W de ßE

 Ï 6 .

C Dô' "m Á ?=Rº m URº F* '

­‰ b-%. . § ­‰  [CÆ 0. Ý, ƒ

 ?=ï F*  U# Ub Ù  C
 ­‰

 2ƒ <=ï F*  U# <=ï  C

 ­‰. •' ß* ?=Rº $ 7l URº

F*#I ‹Œ* r»¼ F* ¦§ q xHï O~ ! 9  1.

±‰-%., URº F* ?=Rº  ¶e r»¼" 

#³ 6  ­‰" *õÆ ; qW ?=Rº PÀ  1, 3&. ‡6ˆ W URº † 1 l ­‰

-k Ï 6 .
f-%.  e *~" ¶e -5 6  Fig. 8. Comparison of the performance curves at different rinse and evacuation conditions.

(a) P_EV=0.1 atm, P_RN=1.0 atm; (b) P_EV=0.05 atm, P_RN=1.0 atm; (c) P_EV=0.1 atm, P_RN=1.5 atm; (d) P_EV=0.05 atm, P_RN=1.5 atm. : reflux ratio=0.6; :

reflux ratio=0.65;: reflux ratio=0.7; : reflux ratio=0.75;
: reflux ratio=0.8; : reflux ratio=0.85; : reflux ratio=0.9.

Fig. 9. The effect of feed flow rate on the purity and recovery at P_EV=0.05 atm.

(a) feed flow rate: 7.6 SLPM; (b) feed flow rate: 20 SLPM

 38 6 2000 12

W *é ù ¤Ð , Ε 7 ¤¥ r»¼" † 1

 tu vN i ~ ë p€ Ï 6 . r»¼  ¤Ì ¤¥ ¦4 ^-› oBÆ Ctb q g ‡ 6ˆ š ! ö ªÞJ ^- ¤¥ ªü 5 1.

+ () U Rº 1
R 1.5
R%. †J: 7m

?=Rº 0.1
R 0.05
R%. PÀ 7,
o NRUS G"  c 6 | ‡6ˆl ^& U ) N ‡6ˆ NJ

 c 6 ;,  ‰ r»¼ ¦§ ^- ‡6ˆ o B' p€ 95 6 . 6½-%. lW, 7.6 SLPM ß ï ‹Œ NRU > 0.1
R ?=Rº 0.9 r»¼" 

J c 6  q" c
w, ?=Rº 0.05
R%. P ÀP : 7 r»¼" 0.8. PL 6  ­‰" c 6 

%f 7 ‡6ˆ e ) F*$. 3&. URº 1.5

R%. † ‹Œ r»¼" Š# 0.8. PL 6 %f 7

 ‡6ˆ 2.5)* F*$.  e *~ ‹Œ" ¶e -' ‹

Œ r»¼" 0.75. PL 6 %f ‡6ˆ 3)È~ F*$

. + () ' S¶ é½" 5 7, *é ù ¤Ì ¤

¥ 0.05
R ?=Rº‰ 1.5
R URº 0.75  r»

¼" J P ßï%. ¤Ì 1 ‹-%. *é Œ6E

 95 6 .

5.  

`<=a9 CO2" Ctb. c
w' PSA  ^- ¤Ì¤

¥ ¨
w 2ü  3D € ‚, ¶p"  ^-¤

¥ ¨
w' ¸-%.,  tu vN#I; —6-9 SG9 U > T SG ¤¥ ¦§ ¾v s$. &N  Zt  <=. ', RºQHm USG*  E0 qr %.

F USG > T SG ¤¥O xH#µ*W tu xH"

¼Ó$. USG Rº F* U# <=ï F*#µ Ctb ‡6ˆ F*#h p€ 95 6 %f 7 r

»¼ F* ‰› È~ ô,' q NJ%. ÍK. ?=

Rº  ?=ï F*#µ r»# ßï F*#I ­‰"

*õf  ô,' q vN%. ÍK. ¦4  e *~

‹Œ ¶e USG r»¼" ‚“ 6  ­‰. /f 7

^- tu c r»¼* oBE 9$. ¦4 " i

¤ÐJ <=@ ‰› A ¤Ì œPTW *é ^-

¤Ì¤¥ c 6 { Ï 6 .

 

+ ()‰ 'j º()! ~! k 6] %f  p lmW.



b_i : Langmuir parameter [atm⁻¹]

C_i : gas concentration of component i [mol/cm³] C_total : total gas phase concentration [mol/cm³] C_ps : heat capacity of adsorbent [J/g/K]

C_pg : specific heat of gas mixture [J/g/K]

∆H_i : heat of adsorption of component i [KJ/mol]

k_i : overall mass transfer(LDF) rate coefficient of component i [s⁻¹] L : bed height [cm]

q_i : amount adsorped of component i on the solid phase [mol/g]

q*_i : amount adsorped of component I in equilibrium with gas phase [mol/g]

q_m : langmuir parameter [mol/g]

t : time [s]

t₁ : Langmuir parameter [mol/g]

t₂ : Langmuir parameter [mol/g]

t₃ : Langmuir parameter [atm⁻¹] t₄ : Langmuir parameter [K]

T : temperature [K]

T_o : feed temperature [K]

u : interstitial gas velocity [cm/s]

u_feed : interstitial velocity of feed gas [cm/s]

u_OR : interstitial velocity of rinse gas [cm/s]

y_EQ,i : mole fraction of component i fed in pressurized equalization step y_{f, i} : mole fraction of component i in gas mixture

y_Product,i: mole fraction of component i fed in rinse step ρ_g : density of gas mixture [g/cm³]

ρ_bulk : bulk density [g/cm³] ε : bed porosity [-]



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