Feasibility of carbon dioxide absorption by NaOH solution in a rotating packed bed with blade packings

Feasibility of carbon dioxide absorption by NaOH solution in a rotating packed bed with blade packings

International Journal of Greenhouse Gas Control 42 (2015) 117–123 Contents lists available at ScienceDirect International Journal of Greenhouse Gas ...

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International Journal of Greenhouse Gas Control 42 (2015) 117–123

Contents lists available at ScienceDirect

International Journal of Greenhouse Gas Control journal homepage: www.elsevier.com/locate/ijggc

Feasibility of carbon dioxide absorption by NaOH solution in a rotating packed bed with blade packings Chia-Chang Lin ∗ , Ching-Rong Chu Department of Chemical and Materials Engineering, Chang Gung University, Taoyuan, Taiwan, ROC

a r t i c l e

i n f o

Article history: Received 5 January 2015 Received in revised form 10 July 2015 Accepted 31 July 2015 Keywords: Rotating packed bed Blade packings Absorption Mass transfer Carbon dioxide

a b s t r a c t The rotating packed bed (RPB) with blade packings was applied to absorb carbon dioxide (CO2 ) from gas streams by NaOH solution. The RPB with blade packings had an inner radius of 1.6 cm, an outer radius of 10.8 cm, and an axial height of 3.0 cm. Rotational speeds ranged from 600 to 1800 rpm, providing 25–225 equiv. gravitational force. The removal efficiency of CO2 was determined at various values of operating parameters, including the rotational speed, gas flow rate, liquid flow rate, NaOH concentration, and CO2 concentration. Experimental results demonstrated that the removal efficiency of CO2 increased with the rotational speed, liquid flow rate and NaOH concentration; however, decreased with the gas flow rate and CO2 concentration. The removal efficiency of CO2 was about 90% at a rotating speed of 1800 rpm, a gas flow rate of 9 L/min, a liquid flow rate of 0.5 L/min, an NaOH concentration of 1.0 mol/L, and a CO2 concentration of 1 vol%. Accordingly, the RPB with blade packings has great potential in the removal of CO2 from the exhaust gases. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction Carbon dioxide (CO2 ), as a greenhouse gas, is the main contributor to the observed global warming and climate change (Ye et al., 2012, 2013). Accordingly, it is imperative to remove huge amounts of CO2 from the exhaust gases in many industrial processes such as coal gasification, synthesis-gas production, natural-gas processing, oil refining, and hydrogen manufacturing. Though the absorption of CO2 using various absorbents and diverse contactors has been developed for removing CO2 from the exhaust gases from these industrial processes (Ye et al., 2012, 2013; Rodriguez-Flores et al., 2013; Li et al., 2014; Khana et al., 2015; Ganapathy et al., 2014; Freeman et al., 2010; Yang et al., 2015; Bandyopadhyay and Biswas, 2012; Ganapathy et al., 2013), the cost is still high for the treatment of the exhaust gases from power generation plants owing to the fact that a huge volume of the exhaust gas is needed to be treated and low mass transfer exists in the traditional gas–liquid contactors such as packed columns, spray columns, and bubble columns. Ramshaw and Mallinson (1981) were the first to exploit a centrifugal force as an external force to improve the efficiency of gas–liquid separation. Accordingly, they developed the rotating packed bed (RPB) for distillation and absorption. This unique technology is referred to as “Higee” (an acronym for high gravity). When

∗ Corresponding author. Tel.: +886 3 2118800x5760; fax: +886 3 2118800x5702. E-mail address: [email protected] (C.-C. Lin). http://dx.doi.org/10.1016/j.ijggc.2015.07.035 1750-5836/© 2015 Elsevier Ltd. All rights reserved.

liquid flows through the RPB, it is rapidly accelerated to an extent that is determined by the rotational speed, so the RPB is less likely to flood than is a conventional packed bed. Accordingly, an RPB can be operated at high gas or liquid flow rates. Also, packings with a large specific area and a high voidage can be used. Since the centrifugal acceleration is high, thinner films and smaller droplets can be formed. The mass transfer would be 10–100 times greater than that in a conventional packed bed, so the required equipment is physically smaller, and the capital and operating costs are consequently lower (Ramshaw, 1983). The RPB has been widely used for various gas–liquid processes, including distillation (Lin et al., 2002), VOCs absorption (Chen and Liu, 2002), CO2 absorption (Lin et al., 2003), O3 absorption (Lin et al., 2009a), ozonation (Lin and Liu, 2003), reactive precipitation (Chen et al., 2000), and stripping (Lin and Liu, 2006). Over the last few years, our group successfully used the RPB with blade packings to absorb volatile organic compounds (VOCs) (Lin and Jian, 2007; Lin and Chien, 2008; Lin et al., 2009b, 2010; Hsu and Lin, 2011, 2012; Lin and Lin, 2012), as presented in Fig. 1. According to the results of these efforts, the RPB with blade packings has superior operating characteristics, including a low pressure drop and a high mass transfer (Lin and Jian, 2007). We have presented more results concerning the RPB with blade packings for removing VOCs by absorption (Lin and Jian, 2007; Lin and Chien, 2008; Lin et al., 2009b, 2010; Hsu and Lin, 2011, 2012; Lin and Lin, 2012). The RPB with blade packings could effectively process gas streams that contained VOCs, with a high mass transfer

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efficiency. Recently, we used the RPB with blade packings to remove VOCs from binary mixtures by absorption (Hsu and Lin, 2011, 2012). However, the removal of CO2 in the RPB with blade packings has not yet been reported. Accordingly, to develop an alternative gas–liquid contactor for removing CO2 from the exhaust gases, the objective of this investigation is to elucidate the removal of CO2 from gas streams by combining chemical absorption with the RPB with blade packings. The NaOH solution is adopted as a model absorbent in this investigation. The results in this investigation could provide further insight into the feasibility of applying the RPB with blade packings to the removal of CO2 from gas streams. 2. Experimental The RPB with blade packings (as shown in Fig. 1) had an inner radius of 1.6 cm, an outer radius of 10.8 cm, and an axial height of 3.0 cm. Accordingly, the depth (radial height) of the RPB was 9.2 cm. The packings were made up of twelve blades arranged within the RPB spaced 30◦ apart where gas and liquid were contacted countercurrently. Each blade was covered with a stainless steel wire mesh having a configuration of interconnected filaments with a mean diameter of 0.22 mm and an average mesh diameter of 3 mm. The packings had a specific surface area of 65 m2 /m3 and a voidage of 0.994. In general operation, the RPB can be rotated from 600 to 1800 rpm, which provided 25–225 times gravitational force based on the arithmetic mean radius. Fig. 2 shows the experimental setup for CO2 absorption. During normal operation, the CO2 N2 stream traveled inward from the outer side of the rotor owing to the pressure drop. At the same time, the prepared NaOH solution was introduced from the tank into the inner side of the rotor through a distributor. The distributor consisted of a tube in which holes were drilled. Liquid left the distributor at a relatively high velocity and, then, entered the inner side of the rotor. The velocity of the liquid exiting from the

distributor must be sufficiently high to pass the gap between the distributor and the inner side of the rotor. Otherwise, entrainment may occur in the discharged gas stream and the liquid maldistribution would subsequently occur within the rotor. The NaOH solution moved radially within the rotor owing to the centrifugal force and, then, exited the rotor from the outer side. Both the CO2 N2 stream and the NaOH solution were in contact with the countercurrentflow mode within the rotor, in which CO2 in the CO2 N2 stream reacted with NaOH in the liquid stream. The exiting CO2 N2 stream, containing low CO2 concentration, finally left the top of the rotor, and, then, was discharged from the top of the RPB, while the CO2 rich NaOH solution was expelled from the bottom of the RPB. The CO2 concentration in inlet CO2 N2 stream was varied at 1, 4, 7, and 10 vol% and the NaOH concentration in inlet liquid stream was set at 0.2, 0.5, 0.7, and 1.0 mol/L. During operation, the gas flow rate (axial direction) was varied at the range of 9–66 L/min and the liquid flow rate (radial direction) was varied at the range of 0.2–0.5 L/min. The CO2 concentrations in inlet and outlet CO2 N2 streams were measured by an infrared (IR) CO2 analyzer (Polytron, Dräger). The removal efficiency of CO2 in the RPB with blade pakcings is defined as E (%) =

Ci − Co × 100 Ci

(1)

where E is the removal efficiency of CO2 , and Ci and Co are the concentrations of CO2 in inlet and outlet CO2 N2 streams, respectively. The E values were measured at various values of the operation variables, including rotational speed (ω), gas flow rate (QG ), liquid flow rate  (QL ), NaOH concentration (CMEA ), and CO2 concentration CCO2 to evaluate the performance of the RPB with blade packings in absorbing CO2 using the NaOH absorbent. All experiments were conducted at an average temperature of 25 ◦ C with atmospheric pressure. During CO2 absorption, the CO2 concentration in outlet CO2 N2 stream were observed to drop rapidly and then reached a steady value within 10–15 min. The reproducibility tests under all of the operating conditions were carried out in this investigation. The CO2 concentration in outlet CO2 N2 stream was observed to be reproduced with a deviation of less than 5%. 3. Results and discussion 3.1. Effect of rotational speed

Fig. 1. RPB with blade packings.

Drain

CO2 Analyzer Flowmeter Blade Packings CO2 Analyzer

Motor NaOH

Pump

Flowmeter CO2+N2 Fig. 2. Experimental setup for CO2 absorption.

Fig. 3 summarizes the E values as a function of the rotational speed from 600 to 1800 rpm at a CO2 concentration of 1 vol% and an NaOH concentration of 1.0 mol/L. As expected, increasing the rotational speed enhanced the E values for a given gas flow rate and liquid flow rate. For example, the E values for rotational speeds of 600, 1000, 1400, and 1800 rpm were 73, 81, 88, and 90%, respectively, at a gas flow rate of 9 L/min and a liquid flow rate of 0.5 L/min. This result could be explained by the fact that the centrifugal acceleration could provide thinner liquid films and/or tiny droplets; a thinner boundary layer for mass transfer would be induced, thus leading to a higher gas–liquid mass transfer according to penetration theory. Similar trends were found in the absorption of CO2 by the NaOH solution in the cross-flow RPB with structured packings (Lin and Chen, 2007) and the absorption of CO2 by the MEA solution in the cross-flow RPB with structured packings (Lin and Chen, 2011). As shown in Fig. 3(a), at a low liquid flow of 0.2 L/min, E varied ωx with the x values of 0.26 and 0.29 for the gas flow rate of 9 and 66 L/min, respectively. This observation implied that the effect of the rotational speed at a low gas flow rate was close to that at a high gas flow rate. This characteristic was not found at a high liquid flow rate of 0.5 L/min, as shown in Fig. 3(b), indicating that the x value

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(a)

100

(a)

QG : 9 L/min

119

100

ω : 1800 rpm

QG : 66 L/min

ω : 600 rpm

75

50

E (%)

E (%)

75

50

25

25 0 400

800

1200

1600

2000

0

Rotational Speed (rpm) (b)

100

0

QG : 9 L/min

20

40

60

80

Gas Flow Rate (L/min)

QG : 66 L/min

(b)

75

100

ω : 1800 rpm

75

50

E (%)

E (%)

ω : 600 rpm

25

0 400

800

1200

1600

2000

50

25

Rotational Speed (rpm) Fig. 3. Effect of rotational speed on removal efficiency of CO2 (a) QL : 0.2 L/min (b) QL : 0.5 L/min.

varied from 0.20 to 0.45 as the gas flow rate was increased from 9 to 66 L/min. This feature suggested that an increase of the E values by the rotational speed was more pronounced at a high gas flow rate. Accordingly, the rotational speed offered a largest effect on the E values at a liquid flow of 0.5 L/min and a gas flow of 66 L/min.

0 0

20

40

60

80

Gas Flow Rate (L/min) Fig. 4. Effect of gas flow rate on removal efficiency of CO2 (a) QL : 0.2 L/min (b) QL : 0.5 L/min.

3.2. Effect of gas flow rate Fig. 4 presents the effect of varying the gas flow rate from 9 to 66 L/min on the E values at a CO2 concentration of 1 vol% and an NaOH concentration of 1.0 mol/L. The gas flow rate influenced the E values; that is, the E values decreased with the gas flow rate for a given rotational speed and liquid flow rate. For example, the E values for gas flow rates of 9, 28, 47, and 66 L/min were 90, 73, 58, and 49%, respectively, at a rotational speed of 1800 rpm and a liquid flow rate of 0.5 L/min. Owing to that an increasing gas flow rate provided a larger amount of CO2 in the gas stream and a reduction in the contact time, the removal of CO2 was limited at a high gas flow rate. Similar trends were found in the absorption of CO2 by the NaOH solution in the cross-flow RPB with structured packings (Lin and Chen, 2007) and the absorption of CO2 by the MEA

solution in the cross-flow RPB with structured packings (Lin and Chen, 2011). As shown in Fig. 4(a), at a low liquid flow rate of 0.2 L/min, E was proportional to QG −y with the exponent y varying from 0.50 to 0.49 for the rotational speed from 600 to 1800 rpm. This feature implied that at a low liquid flow rate, the sensitivity of E to variations in the gas flow rate at a low rotational speed was the same as that at a high rotational speed. As the liquid flow rate was increased to 0.5 L/min, this characteristic was not found, as shown in Fig. 4(b), indicating that the y value varied from 0.43 to 0.30 when the rotational speed was increased from 600 to 1800 rpm. Additionally, for a given rotational speed, the sensitivity of the E values to variations in the gas flow rate at a low liquid flow rate was higher than that at a high liquid flow rate. Accordingly, the gas flow rate provided a

120

(a)

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100

Table 1 (QG /QL )95 under various operating conditions.

75

ω (rpm)

QG (L/min)

Logarithmic equation

(QL )95 a (L/min)

(QG /QL )95

600 600 1800 1800

9 66 9 66

E = 15 × ln(QL ) + 83 E = 10 × ln(QL ) + 36 E = 13 × ln(QL ) + 100 E = 21 × ln(QL ) + 63

2.2 365 0.7 4.6

4.1 0.2 12.9 14.3

E (%)

a

50

25 ω : 1800 rpm ω : 600 rpm

0 0.1

0.2

0.3

0.4

0.5

0.6

Liquid Flow Rate (L/min) (b)

100

E (%)

75

50

25 ω : 1800 rpm ω : 600 rpm

0 0.1

0.2

0.3

0.4

0.5

0.6

Liquid Flow Rate (L/min) Fig. 5. Effect of liquid flow rate on removal efficiency of CO2 (a) QG : 9 L/min (b) QG : 66 L/min.

largest effect on the E values at a rotational speed of 600 rpm and a liquid flow rate of 0.2 L/min. 3.3. Effect of liquid flow rate Fig. 5 indicates the effect of the liquid flow rate ranging from 0.2 to 0.5 L/min on the E values at a CO2 concentration of 1 vol% and an NaOH concentration of 1.0 mol/L. The liquid flow rate had an influence on the E values; that is, an increase in the liquid flow rate yielded an increase in the E values for a given rotational speed and gas flow rate. For example, the E values for liquid flow rates of 0.2, 0.3, 0.4, and 0.5 L/min were 29, 42, 44, and 49%, respectively, at a rotational speed of 1800 rpm and a gas flow rate of 66 L/min. This behavior was attributed to the fact that more NaOH used to absorb CO2 at a high liquid flow rate was favorable to the removal of CO2 . Similar trends were found in the absorption of CO2 by the

The liquid flow rate required to achieve E = 95.

NaOH solution in the cross-flow RPB with structured packings (Lin and Chen, 2007) and the absorption of CO2 by the MEA solution in the cross-flow RPB with structured packings (Lin and Chen, 2011). As shown in Fig. 5(a), at a low gas flow rate of 9 L/min, E correlated QL z with the exponent z varying from 0.23 to 0.15 for the rotational speed from 600 to 1800 rpm. This suggested that at a low gas flow rate, the sensitivity of E to the variation in the liquid flow at a low rotational speed was higher than that at a high rotational speed. As the gas flow rate was increased to 66 L/min, this phenomenon was opposite, as shown in Fig. 5(b), implying that the z value varied from 0.39 to 0.55 when the rotational speed was increased from 600 to 1800 rpm. Additionally, for a given rotational speed, the dependence of the E values on the liquid flow rate at a high gas flow rate was higher than that at a low gas flow rate. Accordingly, the liquid flow rate provided a largest effect on the E values at a rotational speed of 1800 rpm and a gas flow rate of 66 L/min. The results in Fig. 5 can be fitted with the logarithmic equations indicated in Table 1. According to these equations, the liquid flow rates required to achieve a CO2 removal of 95% were obtained under various operating conditions, and the corresponding QG /QL ratio was represented by (QG /QL )95 . As listed in Table 1, (QG /QL )95 increased with the rotational speed for the same gas flow rate. Additionally, (QG /QL )95 decreased with the gas flow rate at a low rotational speed. However, as the rotational speed was increased to 1800 rpm, (QG /QL )95 at a low gas rate was close to that at a high gas flow. This result verified further that a high rotational speed could improve the gas–liquid mass transfer for CO2 absorption. However, it was known that the energy consumption would be increased with an increasing rotational speed. Accordingly, the optimum between the rotational speed and the removal efficiency should be determined for industrial-scale applications. 3.4. Effect of NaOH concentration Fig. 6 displays the E values as a function of the NaOH concentration from 0.2 to 1.0 mol/L at a rotational speed of 1800 rpm and a CO2 concentration of 1 vol%. At a given gas flow rate and liquid flow rate, the E values increased with an increasing NaOH concentration. For example, the E values for NaOH concentrations of 0.2, 0.5, 0.7, and 1.0 mol/L were 59, 72, 74, and 78%, respectively, at a gas flow rate of 9 L/min and a liquid flow rate of 0.2 L/min. This characteristic was caused by the fact that increasing NaOH concentration could give higher amounts of hydroxide ions per unit volume for reacting with more CO2 at a given gas flow rate and liquid flow rate. Similar trends were found in the absorption of CO2 by the NaOH solution in the cross-flow RPB with structured packings (Lin and Chen, 2007) and the absorption of CO2 by the MEA solution in the cross-flow RPB with structured packings (Lin and Chen, 2011). As shown in Fig. 6(a), at a low gas flow rate of 9 L/min, the E values were proportional to the NaOH concentration raised to the w power. The w values decreased from 0.17 to 0.07 as the liquid flow rate was increased from 0.2 to 0.5 L/min. This result suggested that an enhancement of the E values by the NaOH concentration was more pronounced at a low liquid flow rate. This finding was not obvious at a high gas flow rate of 66 L/min, as shown in Fig. 6(b),

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(a)

100

(a)

100

75

E (%)

E (%)

75

50

25

50

25 QL : 0.5 L/min

QL : 0.5 L/min

QL : 0.2 L/min

0 0.0

0.3

0.6

0.9

QL : 0.2 L/min

0

1.2

0

(b) 100

6

9

12

100

75

E (%)

75

E (%)

3

CO2 Concentration (vol%)

NaOH Concentration (mol/L) (b)

121

50

50

25

25

QL : 0.5 L/min

QL : 0.5 L/min QL : 0.2 L/min

0

QL : 0.2 L/min

0 0

0.0

0.3

0.6

0.9

3

6

9

12

1.2

NaOH Concentration (mol/L) Fig. 6. Effect of NaOH concentration on removal efficiency of CO2 (a) QG : 9 L/min (b) QG : 66 L/min.

showing that the w values decreased from 0.24 to 0.21 with the increase in the liquid flow rate from 0.2 to 0.5 L/min. Additionally, for a given liquid flow rate, the dependence of the E values on the NaOH concentration at a high gas flow rate was higher than that at a low gas flow rate. Accordingly, the NaOH concentration offered a largest effect on the E values at a gas flow rate of 66 L/min and a liquid flow rate of 0.2 L/min. 3.5. Effect of CO2 concentration Fig. 7 shows the effect of the CO2 concentration from 1 to 10 vol% on the E values at a rotational speed of 1800 rpm and an NaOH concentration of 1.0 mol/L. At a given gas flow rate and liquid flow rate, the E values decreased with an increasing CO2 concentration. For example, the E values for CO2 concentrations of 1, 4, 7, and 10 vol% were 49, 45, 38, and 30%, respectively, at a gas flow rate

CO2 Concentration (vol%) Fig. 7. Effect of CO2 concentration on removal efficiency of CO2 (a) QG : 9 L/min (b) QG : 66 L/min.

of 66 L/min and a liquid flow rate of 0.5 L/min. This finding was explained by the fact that more CO2 was needed to be removed at high CO2 concentrations for a given NaOH concentration. Similar trend was found in the absorption of CO2 by the MEA solution in the cross-flow RPB with structured packings (Lin and Chen, 2011). As shown in Fig. 7(a), at a low gas flow rate of 9 L/min, the E values were proportional to the CO2 concentration to the −0.02 power at the liquid flow rate of 0.5 L/min. This power would vary to −0.08 at the liquid flow rate of 0.2 L/min. This feature implied that a reduction of the E values by the CO2 concentration was more evident at a low liquid flow rate. This observation was more obvious at a high gas flow rate of 66 L/min, as shown in Fig. 7(b), revealing that this power varied from −0.18 to −0.32 with the decrease in the liquid flow rate from 0.5 to 0.2 L/min. Additionally, for a given liquid flow rate, the sensitivity of the E values to variations in the CO2 concentration at a high gas flow rate was much higher than that

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Table 2 Comparison of RPB with structured packings and blade packings. Lin et al. (2003)

Present study

Operating conditions Pressure (atm) Temperature (K)

1 300

1 298

Gas phase CO2 concentration (vol%) Gas flow rate (L/min) Gas velocity (m/h)

1 4.4 38

1 9 62

Liquid phase NaOH concentration (mol/L) Liquid flow rate (L/min) Liquid velocity (m/h)

0.2 0.042 0.4

0.2 0.2 1.3

RPB Packing type Inner radius (cm) Outer radius (cm) Axial length (cm) Specific surface area (m2 /m3 ) Voidage (−) Rotational speed (rpm)

Structured packings 3.8 8.0 2.0 803 0.96 1735

Blade packings 10.8 1.6 3.0 65 0.994 1800

KG a (1/s)

0.38

0.13

KG (cm/s) (based on specific surface area) 0.05

0.20

3.6. Comparison with RPB with structured packings To compare the CO2 absorption performance of the RPB with blade packings with the RPB with structured packings, the mass transfer coefficient is considered a simple but representative design parameter. For CO2 absorption process, the experimental overall volumetric gas-phase mass transfer coefficients (KG a) of the RPB can be evaluated by the following equation (Lin et al., 2003):



QG 2

 Ro − Ri

2



Zb

ln

C  i

Co

Acknowledgements The authors would like to thank the Ministry of Science and Technology of the Republic of China, Taiwan, for financially supporting this research under contract no. MOST 102-2221-E182-001-MY3. References

at a low gas flow rate. Accordingly, the CO2 concentration gave a largest effect on the E values at a liquid flow rate of 0.2 L/min and a gas flow rate of 66 L/min.

KG a =

removal efficiency, E values. As expected, increasing the rotational speed increased the E values. The E values appeared to increase with an increasing liquid flow rate and an increasing NaOH concentration but decrease with an increasing gas flow rate and an increasing CO2 concentration. Additionally, a high gas flow rate provided a decrease in (QG /QL )95 at a low rotational speed; however, as the rotational speed was high, (QG /QL )95 was slightly affected by the gas flow rate. Also, the rotational speed always provided an increase in (QG /QL )95 for a given gas flow, indicating that the RPB with blade packings could decrease the dosage of the NaOH solution by increasing the rotational speed. The comparison of KG a between the RPB with blade packings and the RPB with structured packings indicated that the RPB with blade packings is an alternative gas–liquid contactor for the CO2 removal from gas streams.

(2)

where QG is the volumetric flow rate of gas, Zb is the axial length of the RPB, Ri and Ro are the inner and outer radii of the RPB, respectively. Ci and Co are the concentrations of CO2 in the inlet and outlet CO2 N2 streams, respectively. The estimated KG a value in the RPB with blade packings was compared to the reported KG a value in the RPB with structure packings when the NaOH solution was used as the absorbent. As shown in Table 2, the KG a value in the RPB with blade packings was much lower than that in the RPB with structured packings. With the assumption that the effective surface area is equal to the specific surface area, the KG value in the RPB with blade packings was much higher than that in the RPB with structured packings. This result is attributable to the fact the specific surface area in the RPB with blade packings was much lower than in the RPB with structured packings. Accordingly, a higher KG a value of the RPB with blade packings could be obtained as the specific surface area would be increased to 803 m2 /m3 by adding the number of blades. Accordingly, the RPB with blade packings shows its applicability in removing CO2 from gas streams. 4. Conclusions This investigation has examined the performance of the RPB with blade packings in the absorption of CO2 from gas streams by NaOH solution. The results were considered in relation with the

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