Mass-Transfer Characteristics of the CO2 Absorption Process in a

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Study on the Mass-Transfer Characteristics of CO2 Absorption Process in a Rotating Packed Bed Miaopeng Sheng, Baochang Sun, Fuming Zhang, Guang-wen Chu, Lili Zhang, Chenguang Liu, Jianfeng Chen, and Haikui Zou Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00074 • Publication Date (Web): 14 Apr 2016 Downloaded from http://pubs.acs.org on April 27, 2016

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Energy & Fuels

Study on the Mass-Transfer Characteristics of CO2

1

2

Absorption Process in a Rotating Packed Bed

3

Miaopeng Sheng,a Baochang Sun,a,b,* Fuming Zhang, c Guangwen Chu,a,b Lili Zhang,a,b

4

Chenguang Liu,a Jianfeng Chen,a,b Haikui Zou,a,b,*

5

a

6

Beijing University of Chemical Technology, Beijing 100029, PR China

7

b

8

Technology, Beijing, 100029, PR China

9

c

Research Center of the Ministry of Education for High Gravity Engineering and Technology,

State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical

SINOPEC Catalyst Co., Ltd. Beijing AUDA Division, Beijing, 101111, PR China

ACS Paragon Plus Environment

1

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ABSTRACT

2

This article presents systematic investigations on the mass-transfer characteristics, including

3

the overall gas-phase volumetric mass-transfer coefficient (KGa) and the height of mass-transfer

4

unit (HTU), of CO2 absorption process into a mixture of diethylenetriamine (DETA) and

5

piperazine (PZ) solution in a rotating packed bed (RPB). The effects of operating conditions

6

including PZ concentration, rotation speed, liquid volumetric flow rate, gas volumetric flow rate,

7

gas treatment capacity of packing, inlet CO2 mole fraction, temperature, CO2 loading of lean

8

solution and distributor specification on KGa and HTU in the RPB were systematically studied.

9

Also, a comparison of CO2 absorption performance between the packed column with Dixon rings

10

packing and the RPB is presented. Results indicate that both KGa and HTU were significantly

11

affected by rotation speed, liquid volumetric flow rate, gas volumetric flow rate, temperature and

12

lean CO2 loading while PZ concentration, inlet CO2 mole fraction and liquid distributor had

13

minimal effect on KGa and HTU. It was noted that RPB exhibit better mass-transfer performance

14

compared to a packed column with Dixon rings packing.

15

16

KEYWORDS：： Rotating packing bed; CO2 absorption; Overall gas-phase volumetric mass-

17

transfer coefficient; Height of mass-transfer unit; Diethylenetriamine; Piperazine.

18


2

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Energy & Fuels

1. Introduction

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CO2 is considered as a major type greenhouse gas (GHG) because of its massive emission

3

into the environment from various sources. 1 When the global warming which is majorly as a

4

result of CO2 emission reaches above 2 oC, it becomes necessary to carry out immediate

5

significant and sustained global mitigation.2 At present, the terminal treatment technology is

6

widely acknowledged as an effective means for controlling CO2 emission, and consequently

7

numerous studies on various capture technologies of CO2 such as absorption, 3, 4 adsorption5 and

8

membrane separation6 have been reported. Particularly, chemical absorption of CO2 by amine-

9

based absorbents has been extensively investigated

10 11

4, 7, 8

, and is touted as one of the preferred

methods for CO2 capture 9, 10. Bishnoi and Rochelle

11

studied the absorption of CO2 into aqueous piperazine in a wetted

12

wall column, and found that the second-order rate constant of CO2 and PZ is an order of

13

magnitude higher than that of MEA. Freeman et al.12 investigated the absorption of CO2 into a

14

concentrated aqueous PZ solution, and found that CO2 absorption rate of 8 M PZ is 1.5-3 times

15

higher than that of 7 M MEA. However, owing to the low solubility of PZ in water,

16

practical application entirely as an absorbent is limited, and therefore it can be used as a

17

promoter. 13 Hartono et al.14 measured the kinetics of CO2 absorption by DETA solution in a

18

string of discs contactor, and found that DETA has a significantly faster kinetics than AEEA,

19

EDA and MEA, but lower than PZ. Fu et al.15 studied the absorption of CO2 into aqueous MEA

20

and DETA solution in a randomly packed column, and found that the overall gas-phase

21

volumetric mass-transfer coefficient (KGa) of DETA is higher than that of MEA. Nonetheless,

22

the previous studies on the absorption processes of CO2 into amine-based absorbents were

23

carried out in packed columns

15-17

11

its

which simply operated under the local gravity. As a result


3

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1

they exhibit low gas-liquid mass-transfer efficiency, thus necessitating large equipment size and

2

huge dosage of absorbents, leading to higher investment cost. Therefore, there is a need for a

3

small sized efficient gas-liquid contactor with higher mass-transfer efficiency for CO2 capture.

4

A rotating packed bed (RPB), also called Higee apparatus, has been widely acknowledged

5

as an efficient process-intensification technology. 18 In the RPB, liquid going through the packing

6

is spread or split into very fine liquid elements including droplets, threads and films under high

7

shear field created by the rotating packing, which results in excellent mass-transfer performance

8

19, 20

9

bromination

As a result, RPBs have been applied to distillation 26

and reactive crystallization

27

21

, polymerization

22

, absorption

23-25

,

. Moreover, studies on the absorption of CO2 into

10

amine-based absorbents have been conducted in RPBs.28-30 For instance, Cheng et al.29 reported

11

CO2 removal efficiency of up to 90% using MEA or DETA mixed with PZ as the absorbent in

12

the RPB. Yu et al.30 has also demonstrated that the RPB exhibited high CO2 removal efficiency

13

using a mixture of DETA/PZ solution as the absorbent, and concluded that the technology is

14

feasible for industrial application for CO2 capture. However, these studies only presented the

15

effects of some operating conditions on the removal efficiency of CO2 in the RPB 29, 30, and thus

16

cannot meet the need of RPBs’ scale-up. Consequently, further systematical investigation on the

17

effects of process parameters on the mass-transfer characteristics of this technique is needed in

18

order to make it industrially feasible.

19

This study systematically investigated the effects of various operating conditions on the

20

mass-transfer characteristics including KGa and height of mass-transfer unit (HTU) in an RPB

21

using the CO2-DETA/PZ absorption system. The effects of different operating conditions

22

including PZ concentration, rotation speed (N), liquid volumetric flow rate (L), gas volumetric

23

flow rate (G), gas treatment capacity of packing (τ), temperature (T), inlet CO2 mole fraction


4

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Energy & Fuels

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(yin), lean CO2 loading (α) and distributor specification on KGa and HTU were explored. A

2

comparison of CO2 absorption performance between a packed column and the RPB is also

3

presented. The study aims to provide basic data that is necessary for optimal design of the RPB

4

and the CO2 absorption process.

5 6

2. Mass Transfer in Rotating Packed Bed

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KGa is an important parameter which can be used to characterize the mass-transfer

8

performance of an equipment, and has been explored by many researchers in several mass-

9

transfer systems. 15-17, 28-30 According to the two-film theory, the absorption rate of CO2 ( N CO2 a )

10

into solution under a steady operating condition can be written as: 16 * N CO2 a = K G a ⋅ P( yCO2 − yCO ) 2

11

* CO2

12

where P is total pressure; yCO2 and y

13

in the gas phase, respectively.

14 15

are mole fraction and equilibrium mole fraction of CO2

Considering a ring micro-size element of packing with an axial height of H and radial thickness of dr in the RPB, the mass balance can be given as:

17

 yCO2 N CO2 a ⋅ 2π rH ⋅ dr = GI d   1 − yCO  2 where GI is the inert gas molar flow rate.

18

Combining eqs (1) and (2) gives the following equation:

16

19 20

(1)

  

 yCO2 * K G a ⋅ P( yCO2 − yCO ) ⋅ 2π rH ⋅ dr = GI d  2  1 − yCO  2 Thus, the KGa can be derived from eq (3) as:

(2)

  

(3)


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   Because of the fast reaction rate between CO2 and aqueous amine solution11, KG a =

 yCO2 GI 1 d  2 * π PH (rout − rin2 ) ∫ ( yCO2 − yCO )  1 − yCO2 2

(4) 12, 14

the

3

* absorbed CO2 in the solution is consumed immediately in the process. Therefore, yCO can be 2

4

assumed to be zero. Then, eq (4) can be rewritten as:

KG a =

5

  yCO2 ,in yin (1 − yCO2 ,out ) yCO2 ,out GI × ln + −   2 π PH (rout − rin2 )  yCO2 ,out (1 − yCO2 ,in )  1 − yCO2 ,in 1 − yCO2 ,out

    

(5)

6

It should be noted that the calculated KGa represents the average KGa of the packing

7

because KGa decreases along the radius of the packing.25 The number of mass-transfer units

8

(NTU) can be derived as:

10

 yCO2 ,in yCO2 ,out  (6) + −  yCO2 ,out (1 − yCO2 ,in )  1 − yCO2 ,in 1 − yCO2 ,out  Because the packing in RPB is packed hollow-annularly, gas stream and liquid stream

11

contact countercurrently along the radial direction of the packing, which is different from that of

12

a packed column. Thus, the HTU can be expressed as:

9

13 14

NTU = ln

yin (1 − yCO2 ,out )

rout − rin (7) NTU Additionally, the CO2 removal efficiency (η) can be calculated by the following equations: HTU =



η = 1 −

15



yout (1 − yin )   × 100% yin (1 − yout ) 

(8)

16 17

3. Experimental Section

18

3.1. Materials

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DETA (purity ≥ 98.0%) and PZ (purity ≥ 99.0%) were purchased from Tianjin Fuchen

20

Chemical Reagents Factory and Tianjin Guangfu Chemical Research Institute, respectively. CO2


6

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Energy & Fuels

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(purity ≥99.9%) was purchased from Beijing Ruyuanruquan Technology Co. Ltd, while air was

2

supplied through an oil free air compressor (TYW-1, Suzhou Tongyi Electrical and Mechanical

3

Co. Ltd). All the chemicals were used without further purification.

4 5

3.2. Experimental Procedure

6

Figure 1 shows a schematic diagram of the experimental setup for CO2 absorption. The

7

absorption solution comprising a mixture of DETA and PZ was pumped into the RPB through a

8

liquid inlet and a liquid distributor. It then sprayed radially onto the inner edge of the packing

9

and flowed through the packing under the action of centrifugal force. Meanwhile, the mixed gas

10

stream of CO2 and air was introduced into the RPB through a gas inlet and flowed inward

11

through the packing where it contacted counter-currently with liquid stream. CO2 was absorbed

12

into the solution and reacted with DETA and PZ, and finally both liquid and gas stream exited

13

the RPB from the liquid outlet and gas outlet respectively.

14

The specifications of the RPB used in this work are given in Table 1. The operation

15

conditions were: L of 5.4-14.8 L h-1, G of 1.1-3.8 m3 h-1, N of 400-1400 rpm, temperature of

16

303-333 K and normal atmospheric pressure. The total concentration of DETA and PZ in the

17

absorption solution was 30 wt% while the inlet CO2 mole fraction (yin) of the mixed gas stream

18

was 10-20 %. In all of the experimental runs, the chemical absorption process quickly reached a

19

steady state within a few minutes, and all the data were obtained after reaching a steady state for

20

several minutes. The inlet and outlet CO2 mole fractions in the mixed gas stream were measured

21

by two infrared gas analyzer (GXH-3010F, Beijing Huayun Analytical Instrument Institution,

22

detection range 0-30% for inlet gas and , detection range 0-10% for outlet gas), respectively. The

23

CO2 loading of lean solution (α, mol mol-1, i.e. mol CO2 per mol amine in solution) was


7

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measured through chemical analysis with the addition of extra amount of acid solution into the

2

liquid sample and measuring the released CO2 volume, 12 and the freshly prepared solution with a

3

low initial CO2 loading of solution (α ≤ 0.04 mol mol-1) was adopted in this study.

4

For a comparison, a series of similar absorption experiments were also performed in a

5

packed column, which had a 3.9 cm inner diameter and a 70 cm packing height. The packed

6

column was filled with Ф5×5 Dixon rings packing, which was made of stainless steel and had a

7

surface area of 1700 m2 m-3. The experimental setup of the packed column was similar to that of

8

the RPB as shown in Figure 1 where the RPB was simply replaced by the packed column, while

9

all the chemicals and auxiliary equipment remained the same as those used in the RPB

10

experiment.

11 12

4. Results and Discussion

13

4.1. Effect of PZ Concentration

14

Figure 2 shows the effect of PZ concentration on KGa and HTU in the RPB. It can be seen

15

that KGa increased while HTU decreased slightly with an increase in PZ concentration. The

16

reaction rate between PZ and CO2 is higher than that between DETA and CO2 11, 14, and addition

17

of a small amount of PZ into DETA solution raises the solubility of CO2 in the solution 31.

18

Therefore, an increase in PZ concentration leads to an increase in the reaction rate between the

19

mixed solution and CO2, resulting in an increase in KGa but a reduction in HTU. Based on the

20

above discussion and considering the high cost of PZ as well as its low solubility in water, 5

21

wt%PZ+25 wt% DETA solution was adopted as the major absorption solution for further

22

investigation in this work.

23


8

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Energy & Fuels

4.2. Effect of Rotation Speed

2

Figure 3 shows the effect of rotation speed on KGa and HTU in the RPB. It is evident that

3

KGa increased while HTU decreased with an increase in rotation speed. However, rotation speed

4

beyond 800 rpm had little effect on KGa and HTU. The reason is that higher rotation speed leads

5

to smaller liquid elements including smaller liquid droplets and thinner films, resulting in a

6

larger gas-liquid contact surface. Also, higher rotation speed accelerates gas-liquid surface

7

renewal rate and hence intensifies mass-transfer process. However, an increase in rotation speed

8

can also reduce liquid retention time in the packing, and thus weakens the absorption of CO2.

9

The latter factor was more predominant at rotation speed beyond 800 rpm in this study, and

10

hence resulted in the slow increase and reduction in KGa and HTU respectively.

11 12

4.3. Effect of Liquid Volumetric Flow Rate

13

Figure 4 shows the effect of liquid volumetric flow rate on KGa and HTU. It is evident that

14

KGa increased while HTU decreased with an increase in liquid volumetric flow rate. Increasing

15

the liquid volumetric flow rate leads to an increase in liquid holdup and gas-liquid contact area in

16

the RPB, and consequently increases mass-transfer efficiency. Moreover, a higher liquid

17

volumetric flow rate provides more absorption solution per unit of gas to absorb more CO2. Both

18

of these factors lead to a higher CO2 removal efficiency and mass-transfer efficiency.

19 20 21 22


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4.4. Effect of Gas Volumetric Flow Rate

2

Figure 5 shows the effect of gas volumetric flow rate on KGa and HTU in the RPB. It is

3

clear that HTU increased while KGa increased firstly and then decreased with an increase in gas

4

volumetric flow rate.

5

It can be seen from the eqs. (5) and (6) that the value of KGa depends on GI and NTU. An

6

increase in GI leads to the increase of KGa, at the same time, higher gas volumetric flow at a

7

constant liquid volumetric flow rate leads to low CO2 removal efficiency (η), which causes a

8

decrease in NTU and subsequently a reduction in the value of KGa. Under the effects of these two

9

factors, KGa may increase with an increase in gas volumetric flow rate

29

, or decrease with an

10

increase in gas flow rate 30. In our study, when the gas volumetric flow rate was below 2.5 m3 h-1,

11

the first factor dominated the absorption process while the second factor dominated at gas

12

volumetric flow rate above 2.5 m3 h-1. Therefore, KGa firstly increased then decreased with an

13

increase in gas volumetric flow rate.

14 15

4.5. Effect of Gas Treatment Capacity of Packing

16

The processing capacity of RPB, which can be characterized by the gas treatment capacity

17

of packing (τ), is an important parameter that should be taken into account during RPB’s scale-

18

up. τ can be expressed as:

20

G (9) Vp × 106 where τ and Vp are the gas processing capacity of packing and volume of packing in the RPB,

21

respectively.

19

τ=


10

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Energy & Fuels

1

Figure 6 shows the effect of gas treatment capacity on KGa and HTU in the RPB under a

2

fixed liquid-gas ratio. It can be seen that KGa and HTU increased with an increase in gas

3

treatment capacity of packing. At a fixed liquid-gas ratio, increasing gas treatment capacity of

4

packing means increasing liquid volumetric flow rate and gas volumetric flow rate

5

simultaneously, and this leads to increased flow turbulence, resulting in decrease in mass transfer

6

resistance and consequently increase in KGa. Also, an increase in gas treatment capacity of

7

packing leads to reduction in liquid-gas contact time and CO2 removal rate and consequently

8

decrease in NTU, which finally results in an increase of HTU.

9 10

4.6. Effect of Temperature

11

Figure 7 shows the effect of temperature on KGa and HTU in the RPB. It can be seen that

12

KGa increased while HTU decreased with an increase in temperature. Although higher

13

temperature leads to lower solubility of CO2 in the solution which is unfavorable to CO2

14

absorption31, it also increases the rate of reaction between amines and CO2, thereby reducing

15

liquid-side mass transfer resistance, resulting in a higher KGa. 11, 14 In this study, the latter factor

16

dominated the absorption process, resulting in the increase of KGa, and the decrease of HTU with

17

an increase in temperature.

18 19

4.7. Effect of Inlet CO2 Mole Fraction in Gas Stream

20

Figure 8 shows the effect of inlet CO2 mole fraction on KGa and HTU in the RPB. It can be

21

seen that the inlet CO2 mole fraction has little effect on KGa and HTU. Increasing inlet CO2 mole

22

fraction increases the gas-phase mass-transfer driving force of CO2, which is beneficial to the


11

Energy & Fuels

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absorption of CO2. Meanwhile, an increase in inlet CO2 mole fraction, which means an increase

2

in CO2 partial pressure, tends to increase the solubility of CO2 in the solution. 31 The above two

3

factors favor mass-transfer process. However, an increase in inlet CO2 mole fraction also leads to

4

a reduction in amount of absorbed CO2 per molar gas and consequently a decrease in CO2

5

removal efficiency, resulting in a decrease in KGa but an increase in HTU. Under the effects of

6

all the above-mentioned factors, the inlet CO2 mole fraction has little effect on KGa and HTU.

7 8

4.8. Effect of CO2 Loading of Lean Solution

9

Figure 9 shows the effect of CO2 loading of lean solution on KGa and HTU in the RPB. It

10

can be seen that KGa decreased while HTU increased significantly with the increase of lean CO2

11

loading. CO2 loading of lean solution reflects the concentration of the remaining active amines

12

that can react with CO2, and is significant for CO2 absorption. Increasing CO2 loading of lean

13

solution leads to a reduction of liquid-phase mass-transfer driving force, and is unfavorable for

14

CO2 absorption process. Similar results have also been observed in CO2 absorption process in a

15

packed column. 15, 16

16 17

4.9. Effect of Liquid Distributor Specification

18

Liquid distributor, a stationary stainless steel tube with several holes on one side, is an

19

important stationary component of the RPB, which affects liquid distribution and liquid velocity

20

in the packing. In this study, four types of distributors were adopted to investigate the effect of

21

different distributors on η, KGa and HTU, and the results are shown in Table 2.


12

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Energy & Fuels

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It can be seen from Table 3 that distributor A exhibits the worst performance in mass-

2

transfer and CO2 capture efficiency especially at a higher gas volumetric flow rate of 3.8 m3 h-1,

3

while there is no significant difference among the rest of distributors. A distributor with more

4

holes leads to greater uniformity of liquid distribution and hence increases gas-liquid contact

5

area. On the other hand, the distributor with smaller hole size leads to a higher liquid velocity

6

and causes more violent collision between liquid and rotating packing, and can thus reduce mass-

7

transfer resistance. Comparison of distributor A, C and D reveals that the effect of liquid

8

distribution is slightly stronger than that of liquid velocity towards the packing, especially at a

9

higher gas volumetric flow rate of 3.8 m3 h-1. Nonetheless, owing to the small size of RPB, a

10

distributor with a less holes and a higher hole-size also yielded good distribution performance in

11

this study.

12 13

4.10. Comparison with Packed column

14

Table 3 shows the comparison of mass-transfer performance of CO2 absorption process

15

between the packed column and the RPB under similar operating conditions of packing volume,

16

absorption solution, pressure, gas retention time, inlet CO2 mole fraction and temperature though

17

the values of the surface area of packing, liquid-gas ratio and gas velocity are lower in the RPB.

18

It can be seen that the η and KGa in the RPB are higher than that in the packed column. In the

19

RPB, liquid is spread or split into very fine liquid elements including droplets, threads and films

20

under the high shear field created by the rotating packing, leading to larger gas-liquid contact

21

area. The high-speed rotating packing of the RPB also greatly accelerates gas-liquid surface

22

renewal rate. All of these factors greatly enhanced the mass transfer rate of CO2 into the solution,

23

leading to the higher values of η and KGa.


13

Energy & Fuels

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5. Conclusions

2

This work systematically investigated the effects of operation conditions on the mass-

3

transfer efficiency in an RPB using the CO2-DETA/PZ absorption system. The results indicate

4

that rotation speed, liquid volumetric flow rate, gas volumetric flow rate, gas treatment capacity

5

and temperature significantly affected KGa and HTU while PZ concentration and inlet CO2 mole

6

fraction had minimal effect on KGa and HTU. It was also founded the type of liquid distributor

7

does not significantly affect KGa and HTU. The comparison experiment results reveal that RPB

8

has better CO2 removal efficiency and mass-transfer efficiency compared to the packed column

9

with the Dixon ring packing. This study provides basic data for scale-up and design of RPB for

10

the CO2 absorption process.

11 12

AUTHOR INFORMATION

13

Corresponding Author

14

*Tel.: +86 10 64443134. Fax: +86 10 64434784. E-mail: [email protected] (Baochang

15

Sun). P.O. Box 35, No. 15 Bei San Huan Dong Road, Beijing, China 100029.

16

*Tel.: +86 10 64449453. E-mail: [email protected] (Haikui Zou). P.O. Box 35, No. 15

17

Bei San Huan Dong Road, Beijing, China 100029.

18 19

ACKNOWLEDGMENT

20

This work was supported by National Key Technology R&D Program of China (No

21

2008BAE65B02) and National Natural Science Foundation of China (No. 21406009).


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Energy & Fuels

1

Nomenclature

2

α

CO2 loading of solution (mol mol-1)

3

G

gas volumetric flow rate (m3 h-1)

4

GI

inert gas molar flow rate (kmol h-1)

5

H

axial height of the packing (cm)

6

HTU height of mass-transfer unit (cm)

7

KGa

overall gas-phase volumetric mass-transfer coefficient (kmol m-3 h-1 kPa-1)

8

L

liquid volumetric flow rate (L h-1)

9

N

rotation speed of the PRB (r min-1)

10

N CO2 a absorption rate of CO2 into solution (kmol m-3 h-1)

11

NTU

number of mass-transfer units

12

P

total pressure (kPa)

13

PCO 2

partial pressure of CO2 (kPa)

14

rin

inner radius of the packing (cm)

15

rout

inner radius of the packing (cm)

16

T

temperature (K)

17

τ

gas treatment capacity of packing (m3 m-3 h-1)


15

Energy & Fuels

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1

Vp

volume of the packing (cm3)

2

yCO2

mole fraction of CO2 in gas phase (%)

3

* yCO 2

equilibrium mole fraction of CO2 in gas phase (%)

4

yCO2 ,in inlet mole fraction of CO2 in gas phase (%)

5

yCO2 ,out outlet mole fraction of CO2 in gas phase (%)

6

η

Page 16 of 27

CO2 removal efficiency (%)


16

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Energy & Fuels

1

REFERENCES

2

[1]. Le Quere, C.; Peters, G. P.; Andres, R. J.; Andrew, R.; Boden, T.; Ciais, P.; Friedlingstein,

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P.; Houghton, R.; Marland, G.; Moriarty, R. Earth Syst Sci. Data 2014, 6, 235-263. [2]. Peters, G. P.; Andrew, R. M.; Boden, T.; Canadell, J. G.; Ciais, P.; Le Quéré, C.; Marland, G.; Raupach, M. R.; Wilson, C. Nat. Clim. Chang. 2013, 3 (1), 4-6.

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[3]. Rochelle, G. T. Science. 2009, 325 (5948), 1652-1654.

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[4]. Mumford, K. A.; Smith, K. H.; Anderson, C. J.; Shen, S.; Tao, W.; Suryaputradinata, Y. A.;

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Qader, A.; Hooper, B.; Innocenzi, R. A.; Kentish, S. E.; Stevens, G. W. Energy Fuels. 2012,

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26(1), 138-146.

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[6]. Belaissaoui, B.; Willson, D.; Favre, E. Chem. Eng. J. 2012, 211, 122-132.

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[7]. Yildirim, Ö.; Kiss, A. A.; Hüser, N.; Leßmann, K.; Kenig, E. Y. Chem. Eng. J. 2012, 213,

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371-391. [8]. Reynolds, A. J.; Verheyen, T. V.; Adeloju, S. B.; Chaffee, A. L.; Meuleman, E. Energy Fuels. 2015, 29 (11), 7441-7455.

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[9]. Spigarelli, B. P.; Kawatra, S. K. CO2.Util. 2013, 1 (0), 69-87.

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Wang, M.; Joel, A.S.; Ramshaw, C.; Eimer, D.; Musa, N, M. Appl Energy. 2015, 158,

275-291. [11].

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[12].

Freeman, S. A.; Dugas, R.; Van Wagener, D. H.; Nguyen, T.; Rochelle, G. T. Int. J.

Greenh. Gas. Con. 2010, 4 (2), 119-124.

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[13].

Zhu, D.; Fang, M.; Lv, Z.; Wang, Z.; Luo, Z. Energy Fuels. 2011, 26(1), 147-153.

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[14].

Hartono, A.; da Silva, E. F.; Svendsen, H. F. Chem. Eng. Sci. 2009, 64(14), 3205-3213.

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Ind. Eng. Chem. Res.2012, 51 (37), 12058-12064.

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[16].

Aroonwilas, A.; Tontiwachwuthikul, P. Sep. Purif. Technol. 1997, 12 (1), 67-79.

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Sema, T.; Naami, A.; Fu, K.; Edali, M.; Liu, H.; Shi, H.; Liang, Z.; Idem, R.;

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Tontiwachwuthikul, P. Chem. Eng. J.2012, 209, 501-512.

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2012, 52(0), 55-62. [22].

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Sun, B.; Zou, H.; Chu, G.; Shao, L.; Zeng, Z.; Chen, J. Ind. Eng. Chem. Res. 2012, 51(33),

10949-10954.


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2014, 48(12), 6844-6849. [26].

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503-508. [27].

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2011, 168(2), 731-736. [28].

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2823-2833.

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Page 20 of 27

Tabular material:

Tables 1-3

Table 1. Specifications of the RPB used in this work item

units

packing type

value stainless wire mesh

surface area per unit volume of 2 -3 m m 650 the packing inner radius of the packing, rin

cm

2.5

outer radius of the packing, rout cm

7.5

axial height of the packing, H

cm

5.3

packing volume, Vp

cm3

833

voidage of packing

m3 m-3 0.95


20

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Energy & Fuels

Table 2. The Effect of liquid distributor specification on η, KGa and HTU* Liquid distributor η specification (%)

KGa

HTU

(kmol m-3 h-1 kPa-1)

(cm)

G=2.0 m3 h-1 A: 2×Ф 1.0 mm

87.61

1.92

2.29

B: 2×Ф 1.5 mm

89.88

2.11

2.09

C: 3×Ф 1.0 mm

90.17

2.14

2.07

D: 3×Ф 1.5 mm

89.55

2.08

2.12 G=3.8 m3 h-1

A: 2×Ф 1.0 mm

61.91

1.71

4.84

B: 2×Ф 1.5 mm

73.42

2.33

3.55

C: 3×Ф 1.0 mm

76.17

2.52

3.29

D: 3×Ф 1.5 mm

74.03

2.37

3.49

*operation conditions: L=11 L h-1, yin=10 %, T=313 K, N=1000 r min-1


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Page 22 of 27

Table 3. Comparison of CO2 absorption performance between packed column and the RPB Packed column

RPB

Packing type

Ф5×5 Dixon ring stainless wire mesh

Packing diameter (cm)

3.9

5.0 (ID), 15.0 (OD)

Packing height (cm)

70

5.3 (axial height)

Packing volume (cm3)

836

833

Packing surface area (m2 m-3)

1700

650

5 wt% PZ +

5 wt% PZ +

25 wt% DETA

25 wt% DETA

Pressure (kPa)

102

103

Temperature (K)

303-333

303-333

Inlet CO2 mole Fraction (%)

10-14

10-16

Gas volumetric flow rate (m3 h-1)

0.8-1.9

1.1-2.0

Gas retention time (s)

1.4-3.3

1.4-2.6

Liquid-gas ratio (L m-3)

5.8-13.8

2.9-10.0

CO2 loading of Solution (mol mol -1)

≤ 0.04

0.03-0.73

η (%)

65.1-84.0

71.2-95.0

KGa (kmol m-3 h-1 kPa-1)

0.52-0.86

0.91-2.59

Absorption solution


22

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Energy & Fuels

Figures1-9

Figure 1. Experimental setup for the absorption of CO2 in the RPB

Figure 2. Effect of PZ concentration on KGa and HTU


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Page 24 of 27

Figure 3. Effect of rotation speed on KGa and HTU

Figure 4. Effect of liquid volumetric flow rate on KGa and HTU


24

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Energy & Fuels

Figure 5. Effect of gas volumetric flow rate on KGa and HTU

Figure 6. Effect of gas treatment capacity on KGa and HTU


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Figure 7. Effect of temperature on KGa and HTU

Figure 8. Effect of inlet CO2 mole fraction on KGa and HTU


26

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Energy & Fuels

Figure 9. Effect of CO2 loading of lean solution on KGa and HTU


27

Mass-Transfer Characteristics of the CO2 Absorption Process in a

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