Effects of process configurations for combination of rotating packed bed and packed bed on CO2 capture

Effects of process configurations for combination of rotating packed bed and packed bed on CO2 capture

Applied Energy 175 (2016) 269–276 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Effec...

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Applied Energy 175 (2016) 269–276

Contents lists available at ScienceDirect

Applied Energy journal homepage: www.elsevier.com/locate/apenergy

Effects of process configurations for combination of rotating packed bed and packed bed on CO2 capture Cheng-Hsiu Yu, Ming-Tsz Chen, Hao Chen, Chung-Sung Tan ⇑ Department of Chemical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 8 Process configurations consisting of

RPB and PB were proposed and assessed.  Two RPBs in series is the most appropriate configuration to capture CO2.  Two RPBs in series increased rich loading and thus reduced regeneration energy.  CO2 capture amount instead of CO2 capture efficiency is suggested.  Absorbent formulation is proved to be important for CO2 capture.

a r t i c l e

i n f o

Article history: Received 23 January 2016 Received in revised form 4 May 2016 Accepted 5 May 2016

Keywords: CO2 capture Rotating packed bed Packed bed Process configurations Diethylenetriamine Piperazine

a b s t r a c t The effects of different process configurations, including the operation of a single rotating packed bed (RPB), a single packed bed (PB), and RPB + RPB, RPB + PB, and PB + RPB in series or in parallel, on the CO2 rich loading, amount of treated gas, amount of captured CO2 and regeneration energy using ‘‘11 m” monoethanolamine (MEA) as the model absorbent were studied. When the same volume of absorber was used to achieve the same CO2 capture efficiency, an RPB was identified to be superior to a PB, and RPB + RPB in series showed the greatest performance on the amount of treated gas and regeneration energy among the discussed configurations. Compared with the operation of a single RPB, the amount of treated gas of RPB + RPB in series with the same volume of the single RPB increased by 20.6% due to an increase of mass transfer driving force, whereas the regeneration energy decreased by 9.5% due to an increase of rich loading. Although the CO2 capture efficiency decreased with increasing gas flow rate, the total amount of captured CO2 was found to increase. The treated gas amount could further be increased 80–140% compared with ‘‘11 m” MEA when the ‘‘4 m” diethylenetriamine (DETA) + ‘‘4 m” piperazine (PZ) was used, suggesting this was a superior absorbent for CO2 capture, and thus, the development of absorbent is as important as the development of process. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction Chemical absorption will probably be the most applicable technology for CO2 capture from the gas emissions of coal-fired power ⇑ Corresponding author. E-mail address: [email protected] (C.-S. Tan). http://dx.doi.org/10.1016/j.apenergy.2016.05.044 0306-2619/Ó 2016 Elsevier Ltd. All rights reserved.

plants before 2030 [1–3]. Although this technology has been developed for many years, there are still concerns, such as large volume of equipment and high regeneration energy [4,5]. A rotating packed bed (RPB) possesses some unique characteristics such as less barge and ship-mounted units required because of its small volume and short retention time that manipulated heat-sensitive materials in less decomposition. It is therefore regarded as a highly

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effective mass transfer device and thus has been applied in many industrial applications, including absorption of VOCs [6], H2S [7] and CO2 [8–12]. Many studies have revealed that RPB can be applied to CO2 capture from the gas emissions of fossil fuel power plants and steelmaking processes, and it is also observed that CO2 capture efficiency and mass transfer rate possessed by an RPB is higher than that of a conventional packed bed (PB), resulting in a smaller volume required compared with PB [8,13–26]. Moreover, RPB has been successfully applied to treat gases containing ppm levels of CO2 to improve zinc/air battery life and indoor air quality [27,28]. In addition to CO2 capture, RPB can also be applied to absorbent regeneration, and it can achieve the same regeneration efficiency with an regeneration energy at least 25% lower than that in a PB [29]. In a post-combustion CO2 capture process (PCC), absorber and stripper account for 55% and 17% of the total capital cost, respectively [30]. Wang et al. [2] pointed out that the capital cost of an intensified PCC could be reduced to 1/6 of that of a conventional PCC with the same capacity, the capital cost of an RPB should be reduced because RPB is classified as an intensified PCC. It is therefore expected to reduce capital cost and enhance mass transfer rate by using an RPB instead of a PB. To date, alkanolamines have been widely used for CO2 capture [31]. Nevertheless, there exists two barriers in PCC using alkanolamines as the absorbents, one is high capital cost and the other is high energy penalty in absorbent regeneration; in a consequence, to select appropriate absorbents is essential [2]. For CO2 capture in an RPB, an aqueous solution containing diethylenetriamine (DETA) was suggested because of its fast reaction rate with CO2 to compensate the short contact time between gas and liquid [14]. Piperazine (PZ) is also an effective absorbent for CO2 capture because it rapidly forms carbamate with CO2 [32–35], and an aqueous solution containing DETA + PZ had been proven as an effective absorbent for CO2 capture [14]. Moreover, the regeneration energy of 20 wt% DETA + 10 wt% PZ was 25% lower than that of 30 wt% MEA [29], and the concentration of absorbent is allowed to increase in an RPB, thereby further reducing regeneration energy [36,37]. It is known that the energy required for solvent regeneration constitutes up to 70% of the total operating cost in a CO2 capture plant [38]. Many attempts have been proposed to reduce regeneration energy. Ehlers et al. evaluated the effects of split flow process and vapor recompression process on regeneration energy [36]. For the split flow process in which the CO2-rich absorbent drained out from the bottom of the absorber was split into two streams, the regeneration energy was found to be able to save 2–8% compared with a process without split flow, depending on inlet CO2 concentration. For the vapor recompression process in which the CO2-lean absorbent drained out from the stripper entered a flash followed by passing through a heat exchanger and an absorber, 0.3–1.3% regeneration energy could be saved as compared with the conventional process. Freguia and Rochelle found that when an absorber was equipped with intercooling system, more CO2 could be absorbed because of the increasing solubility of CO2 in absorbent [39]. This led to an increase of the cyclic capacity of absorbent; as a result, 3.8% regeneration energy could be saved. When an RPB is used to capture CO2, various types of contact device inside an absorber have been proposed to increase rich loading and consequently reduce regeneration energy in the stripper [40–42]. Though the mass transfer rate can be indeed enhanced and the subsequent energy required to regenerate absorbent can be reduced due to an increase of rich loading in the above mentioned attempts, auxiliary facility and special mechanic design are required. In this study, the effect of different process configurations consisting of various combinations of commonly used RPB and PB, i.e. no special inner devices in RPB and PB, on the CO2 rich loading, amount of treated gas, amount of captured CO2 and regeneration

energy was assessed. The absorbent MEA was chosen as the model absorbent because the data bank of kinetics, mass transfer coefficient and thermodynamic properties are available. Since the same liquid absorbent but separated gas streams with the same CO2 concentration entered the absorbers in the configurations, a higher driving force in mass transfer that results in a higher CO2 rich loading is therefore expected. In a consequence, regeneration energy in the subsequent stripper is expected to reduce as well. The stirred tank in series model proposed in our previous work [14] was used to evaluate CO2 capture efficiency in an RPB and ASPEN Plus (V8.4) software was used to evaluate CO2 capture efficiency in a PB under different operation conditions. The experiments were conducted to confirm the applicability of the proposed configuration, and then a more effective absorbent containing DETA and PZ was applied in the proposed configuration to verify the advantage of absorbent replacement for CO2 capture. 2. Materials and methods 2.1. Chemicals and apparatus MEA, DETA, and PZ with a purity of 99% were purchased from Tedia, Aldrich, and Seedchem, respectively. N2 and O2 with a purity of 99.99% and CO2 with a purity of 99.5% were purchased from Boclh Industrial Gases Co. (Taiwan). All of the chemicals and gases were used as received. The inner and outer diameters and height of the packing in the RPB were 2.5, 12.5 and 2.3 cm, respectively, the total volume of the packing was of 270.9 cm3. The stainless wire mesh was used as the packing material with a surface area of 887.6 m2/m3 and a void fraction of 0.96. The details of the RPB apparatus used in this study can be found in our previous work [15,16]. Due to the geometry and flow direction in RPB and PB are not the same, the volume of RPB and PB was assumed to be the same in order to make a fair comparison, so the packing height of an RPB was assumed to be the diameter of a PB, just as done by Joel et al. [43]. The diameter and height of the PB were 2.5 and 55 cm, respectively. The total volume of the packing in the PB was 270.0 cm3, which was nearly the same as that of the RPB. The 1/4 in. Raschig ring with a surface area of 710 m2/m3 and a void fraction of 0.62 was used as the packing. 2.2. Operation A N2 gas stream containing 10 vol% CO2 flowed to PB and RPB in this study. Details of the operation of RPB can be found in our previous work [15,16]. For the operation of PB, mass flow controllers (Brooks Instruments, 5850E) were used to control the flow rates of N2 and CO2 to obtain a gas mixture with the desired CO2 concentration. The absorbent was pumped from the top of the PB and spread onto the packing. The absorbent was heated in a storage tank before entering the PB. CO2 was in contact with the absorbent counter-currently in the PB. After absorption, the CO2 concentrations of both the feed and discharged gas stream were measured by an NDIR CO2 analyzer (Drager, Polytron IR CO2). The absorbent used to study the effects of the different process configurations on CO2 capture efficiency and amount as well as regeneration energy were 40.8 wt% ‘‘11 m” MEA and the same weight concentration as ‘‘8 m” PZ. The 23.5 wt% ‘‘4 m” DETA + 19.6 wt% ‘‘4 m” PZ was used to study the effect of the absorbent replacement and was compared with 40.8 wt% MEA. 2.3. Modified stirred tank in series model and the PB simulation The stirred tank in series model was used to evaluate CO2 capture efficiency under different operation conditions in the RPB

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when high lean loading MEA (0.157–0.442 mol CO2/mol amine) was used as the absorbent. The reaction rate constant between CO2 and MEA proposed by Aboudheir [44] was applied to the model, and a detailed description of the model could be found in our previous papers [14]. The CO2 capture efficiency under different operation conditions in the PB was evaluated using ASPEN Plus software. The diameter and height of the PB were the same as those of the experimental apparatus. The empirical correlations proposed by Billet and Schultes were used for evaluation of mass transfer area and coefficient [45]. The regeneration energy was estimated when the absorbent was regenerated from rich loading to lean loading at a temperature of 120 °C and a pressure of 2 atm. The flow chart for the simulation of the 8 different process configurations is shown in Fig. 1.

  CO2 inlet conc:  CO2 outlet conc:  100% CO2 capture efficiency ¼ CO2 inlet conc: ð1Þ Amount of captured CO2 ðL=minÞ ¼ CO2 flow rate  CO2 capture efficiency ð%Þ  Regeneration energy

ð2Þ

   GJ Reboiler duty ðGJÞ ¼ ton CO2 Mass of CO2 desorbed ðton CO2 Þ ð3Þ

3. Results and discussion

2.4. Description of the process configurations

3.1. Model validation

Eight different process configurations including the operation of the single RPB (2V), single PB (2V), RPB (V) + RPB (V) in series and in parallel, PB (V) + PB (V) in series and in parallel, RPB (V) + PB (V) in series, and PB (V) + RPB (V) in series were assessed in this study. The schematic diagrams of the configurations are shown in Fig. 2. For each configuration, RPB (V) and PB (V) represent RPB and PB to possess a volume of V and the total volume of one absorber and two absorbers was the same. RPB (2V) and PB (2V) represent RPB and PB to possess a volume two times V. The liquid stream was fed to the system continuously and the gas stream with the same CO2 concentration as 10 vol% was fed to RPB or PB in parallel for all configurations consisting of two absorbers in series and in parallel. The CO2 capture efficiency, amount of captured CO2, and regeneration energy were used as indicators to evaluate the performance of the different configurations. They were calculated using the following equations.

Fig. 3 displays the experimental and predicted CO2 capture efficiency of MEA with different lean loadings in the RPB (V). CO2 capture efficiency was calculated by Eq. (1). A good agreement between the experimental and predicted CO2 capture efficiencies with an absolute average deviation (AAD) of 11.7% can be seen when the reaction rate constant proposed by Aboudheir [44] was applied. It is also noted here that the CO2 capture efficiency was also calculated by introducing the measured gas flow rates at the inlet and outlet of the absorber in Eq. (1), the deviation was observed to be less than 1% as the calculated using Eq. (1) without flow rate, indicating the applicability of Eq. (1) for calculation of CO2 capture efficiency. Fig. 4 shows the predicted and experimental CO2 capture efficiency in the PB (V). It is observed that when lean loading increased, CO2 capture efficiency decreased. This was mainly because the concentration of the free amine decreased when the lean loading increased [37]. In addition, the AAD

Fig. 1. Flow chart for the simulation of the 8 different process configurations.

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Fig. 2. Schematic diagram of process configurations in this study.

Fig. 3. The experimental and predicted CO2 outlet concentrations in RPB (V) using the reaction rate constants provided by Aboudheir [44].

Fig. 4. The experimental and predicted CO2 capture efficiency in PB (V).

3.2. Comparison of the process configurations between the predicted and experimental data was found to be 4.8%, confirming the agreement of the experimental results with the prediction by ASPEN Plus. The following study that considered different process configurations was based on the stirred tank in series model and ASPEN Plus software in the simulation.

The amount of treated gas for achieving a 90% CO2 capture efficiency was first used to evaluate the performance of different process configurations for the same MEA concentration, liquid flow rate, lean loading and temperature. Table 1 summarizes the oper-

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ating conditions used in the comparison of the discussed 8 process configurations. When the required CO2 capture efficiency decreased from 90% to 60%, the amount of captured CO2 and regeneration energy were used to evaluate the performance of the discussed process configurations. The amount of captured CO2 and regeneration energy were calculated using Eqs. (2) and (3). Fig. 5 shows the amount of treated gas for the 8 configurations achieving a 90% CO2 capture efficiency when ‘‘11 m” MEA was used as the absorbent. The treated gas amount of RPB (2V) was 47.8% higher than of PB (2V), and the regeneration energy of RPB (2V) was 22.7% lower than that of PB (2V). These results occurred mainly because the liquid was split into small droplets and liquid film by passing through the packing under a high gravity environment in RPB, and consequently gas–liquid contact area and mass transfer rate increased [14–16]. Table 2 indicates that when the same gas amount was treated, the CO2 capture efficiency in the PB (2V) was 81.8%, which is lower than the 90% of the RPB (2V). Furthermore, if the same treated gas amount and the same CO2 capture efficiency with the RPB (2V) were required in the PB, the volume of PB was about 1.5 times RPB, suggesting a superior mass transfer performance possessed by the RPB compared with the PB. Compared with the RPB (2V), the treated gas amount of RPB (V) + RPB (V) in series was 20.6% higher than the single RPB (2V), and the regeneration energy was 10.5% lower than that of the RPB (2V). It is also noted here that the rotation energy had been indicated as 0.3–2% of the total regeneration energy for regeneration of 30 wt% MEA aqueous solution in an RPB [29], which is believed to be due to inertia, so the mechanical energy to maintain the rotation of an RPB can be neglected. Although the volume of RPB (2V) was the same as that of RPB (V) + RPB (V) in series, there were two gas streams introduced into the latter configuration, resulting in a higher driving force of mass transfer and a higher rich loading. These situation thus led to the higher treated gas amount and lower regeneration energy. The treated gas amount of RPB (V) + RPB (V) in parallel was the highest among the studied configurations, it was approximately 35.3% higher than that of RPB (2V). However, the regeneration energy was about 25.7% higher than that in RPB (2V), resulting from the lower rich loading in the configuration RPB (V) + RPB (V) in parallel. As for the RPB (V) + PB (V) in series and PB (V) + RPB (V) in series, the treated gas amount of PB (V) + RPB (V) in series was 5% higher than that of RPB (V) + PB (V) in series. It is known that the reaction rate between CO2 and amine decreases when lean loading of absorbent increases, it is not favorable to CO2 capture. However, the absorption of CO2 into alkanolamine belongs to a liquid film control process in absorber [46], mass transfer area and resistance also play important roles. As discussed before, the rich loading in the first PB, that is the lean loading for the following RPB, was lower than the rich loading of the first RPB in RPB (V) + PB (V) in series, and mass transfer rate in an RPB is superior to that in a PB for CO2 capture, as a result, the gas treated amount of PB (V) + RPB (V) in series was higher than that of RPB (V) + PB (V) in series. Though the resident times of absorbent in PB (2V) and PB (V) + PB (V) in series were the same, Fig. 5 shows that the treated gas amount of the PB (2V) was higher than that of PB (V) + PB (V) in series, mainly because the flooding ratio of PB (2V) was 40.6% as calculated by the Aspen Plus, which was higher than the

Fig. 5. The amount of treated gas achieving 90% CO2 capture efficiency of different process configurations.

Table 2 The treated gas amount and CO2 capture efficiency for RPB (2V) and PB (2V).

RPB (2V) PB (2V) PB (2V) PB (3V)

Amount of treated gas (L/min)

CO2 capture efficiency (%)

6.8 4.6 6.8 6.8

90.4 90.3 81.8 90.7

29.9% for PB (V) + PB (V) in series. The higher flooding ratio corresponds to an increased contact area between gas and liquid in the PB, it is therefore beneficial to CO2 capture [47]. Regarding the PB (V) + PB (V) in parallel, although the treated gas amount was higher than that of PB (V) + PB (V) in series, only slightly, the regeneration energy increased 48% due to the lower rich loading of the absorbent in the parallel configuration. The tendency is the same for the RPB (V) + RPB (V) in series and in parallel. Fig. 6 shows the dependency of CO2 capture efficiency on lean loading of the absorbent. It can be seen that when lean loading of the absorbent increased, the gas flow rate introduced into RPB must be reduced to achieve 90% CO2 capture efficiency. For PB (V), however, a 90% CO2 capture efficiency could not be achieved under the same gas flow rates in the RPB at all the studied lean loadings. Furthermore, the difference in CO2 capture efficiency between RPB and PB was more pronounced when the lean loading of absorbent increased. Fig. 5 also shows that an increase in the volume of PB was required to increase the contact time between gas and liquid to achieve the same CO2 capture efficiency as the RPB. The volume ratio of the PB over the RPB increased from 1.6 to 2.4 as the lean loading of the absorbent increased, suggesting that RPB was more effective than the PB when a high loading was present in the fed absorbent. This was also the rationale for the treated gas amount of PB (V) + RPB (V) in series being higher than that of RPB (V) + PB (V) in series. Fig. 7 shows the dependence of the amount of captured CO2 and regeneration energy on CO2 capture efficiency. The figure shows that when the required CO2 capture efficiency decreased, the

Table 1 Operating conditions used in the comparison of the 8 different process configurations. Absorber volume

Absorbent

Temperature

Liquid flow rate

Gas flow rate

Lean loading

CO2 capture efficiency

V, 2V

‘‘11 m” MEA

50 °C

50 mL/min

3–25 L/min

0.345 (mol CO2/mol amine)

60%, 70%, 80%, 90%

RPB (V) was 270.9 cm3 and PB (V) was 270.0 cm3.

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amount of captured CO2 for RPB (V) + RPB (V) in series and RPB (2V) increased; the amount of captured CO2 at 60% CO2 capture efficiency was increased approximately 49.0% and 46.4% for RPB (V) + RPB (V) and RPB (2V), respectively, as compared with 90% CO2 capture efficiency. Moreover, the regeneration energy decreased 20.7% and 21.7% for the RPB (V) + RPB (V) in series and the RPB (2V), respectively, resulting from the increased CO2 rich loading of the absorbent. On the other hand, the PB (2V) could not be operated when CO2 capture efficiency was decreased to 60% because that the increasing gas flow rate led to an 80.8% flooding in PB. This result indicated that the superior hydrodynamic behavior possessed by RPB allowed more gas to be introduced in it, and RPB was thus more suitable for capturing more CO2 in a limited space than PB due to the flooding problem in PB. Fig. 6. The dependency of CO2 capture efficiency on lean loading of absorbent.

Fig. 7. The dependency of CO2 capture amount and regeneration energy on CO2 capture efficiency in RPB (2V) and RPB (V) + RPB (V) in series.

3.3. Verification experiment and absorbent replacement Table 3 shows the experimental and predicted CO2 capture efficiencies for RPB (V) + RPB (V) in series for ‘‘11 m” MEA. A good agreement was found between the experimental and predicted values, suggesting the applicability of the models used for the configuration, RPB (V) + RPB (V) in series. After confirming the applicability of RPB (V) + RPB (V) in series for MEA, the absorbent was changed to 23.5 wt% DETA + 19.6 wt% PZ to observe the effect of absorbent replacement on the treated gas amount. Table 4 shows that the total treated gas amount of ‘‘4 m” DETA + ‘‘4 m” PZ was 64.6% higher than that of ‘‘11 m” MEA for RPB (V) + RPB (V) in series if a capture efficiency of nearly 90% is required. This observation indicates that DETA + PZ was superior to MEA for CO2 capture in RPB for any lean loadings of the absorbent. When the required CO2 capture efficiency is lowered to 80%, the total amount of treated gas of ‘‘4 m” DETA + ‘‘4 m” PZ was 140% higher than that of ‘‘11 m” MEA. In addition, the total CO2 capture amount with a capture efficiency of 80% was found to be 75% higher than that with a capture efficiency of 90% using ‘‘4 m” DETA + ‘‘4 m” PZ as the

Table 3 The verification experiments for RPB (V) + RPB (V) in series using 11 m MEA.a Gas flow rate (L/min)

RPB-1 RPB-2 RPB-1 RPB-2 a

(V) (V) (V) (V)

Lean loading (mol CO2/mol amine)

4.6 3.6 6.5 4.8

CO2 capture efficiency (%)

Predicted

Experimental

Predicted

Experimental

0.345 0.392 0.345 0.405

0.334 0.381 0.334 0.396

90.1 90.6 80.8 80.6

90.9 88.8 84.8 80.9

11 m MEA, T = 50 °C, liquid flow rate = 50 mL/min and rotating speed = 1600 rpm.

Table 4 The treated gas amounts of 23.5 wt% DETA + 19.6 wt% PZ and 11 m MEA.a Absorbent

Lean loading

Rich loading

Gas flow rate L/min

CO2 capture efficiency %

Amount of captured CO2 L/min

mol CO2/mol amine 40.8 wt% MEA (11 m)

RPB-1 (V) RPB-2 (V)

0.334 0.381

0.381 0.417

4.6 3.6 8.2

90.9 88.8 –

0.42 0.32 0.74

RPB-1 (V) RPB-2 (V)

0.380 0.491

0.491 0.582

7.4 6.1 13.5

90.2 89.9 –

0.67 0.55 1.22

RPB-1 (V) RPB-2 (V)

0.334 0.393

0.393 0.437

6.5 4.8 11.3

80.8 80.6

0.53 0.39 0.92

RPB-1 (V) RPB-2 (V)

0.380 0.623

0.623 0.735

18.4 8.7 27.1

80.3 80.0 –

1.46 0.68 2.14

Total amount 23.5 wt% DETA + 19.6 wt% PZ (4 m + 4 m) Total amount 40.8 wt% MEA (11 m) Total amount 23.5 wt% DETA + 19.6 wt% PZ (4 m + 4 m) Total amount a

T = 50 °C, liquid flow rate = 50 mL/min, rotating speed = 1600 rpm.

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absorbent, revealing that CO2 capture amount instead of CO2 capture efficiency can be used to evaluate the performance of a CO2 capture process.

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efficiency as one of the targets to be achieved in CO2 capture processes.

Acknowledgments 3.4. Perspective and prospective of applying RPB for CO2 capture As reported in the literatures, RPB used for CO2 capture possess many advantages including high mass transfer area and coefficient, less volume required, reduction of flooding tendency, dealing with absorbent with high viscosity, self-cleaning capability and so on [4,14,40,48]. In this study, the advantages of an RPB without special interior design was identified to be superior to a commonly used PB. However, to apply chemical absorption for CO2 capture, regeneration energy is also needed to be concerned. The proposed process configuration RPB + RPB in series is observed not only to increase the amount of treated gas but also to reduce regeneration energy resulted from an increase in rich loading, this process configuration is therefore suggested. But it is obvious to see no more advantages exist if more RPB is introduced into the proposed configuration because of the reduction of mass transfer driving force with the following RPB. In order to capture more CO2 and to reduce regeneration energy from the proposed configuration RPB + RPB in series, some scenarios but not all are therefore suggested as follows: (1) to explore new absorbent or mixed absorbents with high CO2 absorption capacity, fast reaction rate with CO2, high vapor pressure, less corrosion, high resistance to oxidation and so on; (2) to use the packings which can be easily placed in an RPB for enhancement of mass transfer areas, (3) to use a more effective stripper such as the use of an RPB instead of a packed bed to regenerate absorbent to reduce regeneration energy and to decrease lean loading, (4) to develop a heat integrated process including absorber and stripper to fully and effectively utilize energy including waste heat at CO2 emission sources.

4. Conclusions The effects of different process configurations on the amount of treated gas, amount of captured CO2 and regeneration energy were assessed using monoethanolamine (MEA) as the absorbent because of the existence of all the thermodynamic and kinetics information of MEA. The modified stirred tank in series model demonstrated its applicability for predicting CO2 capture efficiency in a rotating packed bed (RPB). With the same volume, RPB was verified to be superior to packed bed (PB) regarding CO2 capture efficiency and regeneration energy. Among the discussed configurations, the configuration RPB (V) + RPB (V) in series showed its attractive performance on the amount of treated gas and regeneration energy when the same volume of absorber was applied. The amount of treated gas could increase 20.6% due to an increase of mass transfer driving force resulted from two separate entering gas streams to the two RPBs, and the regeneration energy could decrease 9.5% due to an increase of rich loading for RPB (V) + RPB (V) in series compared with RPB (2V) when a CO2 capture efficiency of 90% is desired to achieve. The proposed absorbent, ‘‘4 m” diethylenetriamine (DETA) + ‘‘4 m” piperazine (PZ), was verified to be more effective than MEA in the configuration RPB (V) + RPB (V) in series experimentally. The treated gas amount could increase 64–140% compared with ‘‘11 m” MEA, suggesting that the development of the absorbent was as important as the development of the process. Although CO2 capture efficiency decreased with increasing gas flow rate, the total CO2 capture amount could be increased, a 75% increase was observed when a capture efficiency of the absorbent ‘‘4 m” DETA + ‘‘4 m” PZ was reduced from 90% to 80%, revealing the appropriate use of CO2 capture amount rather than CO2 capture

The authors would like to acknowledge the financial support of the Ministry of Science and Technology, Republic of China (Grant number MOST103-2622-E-007-025) and the Chang Chun Petrochemical Company.

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