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ScienceDirect Energy Procedia 63 (2014) 1308 – 1313

GHGT-12

Experiment and Modeling Studies on Absorption of CO2 by Dilute Ammonia in Rotating Packed Bed Jia-Lin Kanga, Zhen-Jie Luoa, Jia-Lin Liua, Kai Sunb, David Shan-Hill Wonga*, ShiShang Janga**, Chung-Sung Tana,ġJui-Fu Shenc a Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan, ROC b Department of Automation, Qilu University of Technology, Shandong, P.R. China c New Materials Research & Development Department, China Steel Corporation, Kaohsiung, Taiwan, ROC

Abstract This study presented experimental data of packed bed and rotating packed bed adsorption of carbon dioxide by dilute aqueous ammonia solutions. The heights of transfer units of packed bed were found to be 0.35 to 1.96 m; while the heights of a transfer unit of the rotating packed bed were in the range 0.08 to 0.40 m. Predictive models of the two processes were developed (model details and implications discussed elsewhere) based on the same set of thermodynamic and kinetic data for carbon dioxide into dilute aqueous ammonia solutions and existing mass transfer correlations for packed bed and rotating packed bed. The average absolute deviations between model predictions and experiments were found to be 9.4% for rotating packed bed data and 12% pack bed data. © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

© 2013 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of GHGT.

Peer-review under responsibility of the Organizing Committee of GHGT-12

Keywords: rotating packed bed, packed bed, ammonia, carbon dioxide;

1.

INTRODUCTION

The post-combustion capture of carbon dioxide (CO2) with chemical absorption is one of the near commercial techniques to capture CO2 from existing coal fire power plants. While various types of alkanol-amines were

*

Corresponding author. Tel.: +886-3-571-5131 ext. 33641; fax: +886-3-571-5408. E-mail address: [email protected] ** Corresponding author. Tel.: +886-3-571-5131 ext. 33631; fax: +886-3-571-5408. E-mail address: [email protected]

1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of GHGT-12 doi:10.1016/j.egypro.2014.11.139

Jia-Lin Kang et al. / Energy Procedia 63 (2014) 1308 – 1313

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used[1], ammonia was also considered as a possible candidate. One of the major advantages of using ammonia as the absorbent is that ammonia is a well-known chemical with established material safety and toxicology data. Bai and Yeh first demonstrated the feasibility of using ammonia scrubbing for CO2 removal [2]. Various version of the ammonia process was developed and tested e worldwide (e.g. chilled ammonia process (CAP) [3, 4]), ECO2 process by Powerspan [5], Munmorah pilot plant by Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO) and Delta Electricity [6, 7], and POSCO pilot plant by Korea’s Research Institute of Industrial Science and Technology [8]. One of the major challenges of carbon dioxide capture by chemical absorption is that due to the large volume of gas must be handled and mass transfer limitation, traditional absorber such as packed bed can be exceptionally huge and expensive. For example a study by Zhang and Guo estimated that to capture 1.8 million tons CO2 per year approximately for a 500 MW coal-fired power plant, a packed bed (PB) absorber 40 m in diameter and 72 m in height was required [9]. Jilvero et al. presented an absorption model which has must faster kinetics [10]. The size of an absorber which can capture 1.3 million tons of CO2 per year was still found to be 12 m in diameter and 20 m in height. The rotating packed bed (RPB) was proposed by Ramshaw and Mallinson to relax the mass-transfer limitation and intensify the process [11]. The RPB utilizes centrifugal force to increase mass-transfer efficiency. The high rotator speed causes the liquid to disperse into droplets, which increases the gas-liquid interfacial area. Thus, RPB could effectively reduce the volume requirements of the equipment. A number of studies have investigated the feasibility of using RPB for CO2 capture using various amine solutions.[12-15] There have been several studies presented aimed at modelling the characteristics of the RPB in CO2 capture by alkanomines [16-19]. Sun et al. presented results absorption of CO2 and ammonia into water in a RPB [18]. However there seems to be no systematic investigation of CO2 capture by aqueous ammonia by RPB. The purpose of this paper was to conduct laboratory scale experiments to demonstrate the effectiveness of RPB in of CO2 capture by using dilute aqueous ammonia. The experiments results were compared with packed bed experiments carried out and prediction models developed in our laboratory. Nomenclature ‫ܣ‬ cross-sectional area of absorber, m2 ܽ௣ surface area of packing, m2/m3 ܽ௖ centrifugal acceleration, m/s2 ‫ܥ‬௚ molar concentrations of component i in the gas phase, mol/m3 ‫ܩ‬ superficial mass velocity of gas phase, kg/m2s ݃ gravity acceleration, m/s2 ‫ܮ‬ superficial mass velocity of liquid phase, kg/m2s ܸ volume of packing m3 ‫ݕ‬஼ைమǡ௜ CO2 mole fraction of the inlet gas, mol/mol ‫ݕ‬௢ǡ஼ைమ CO2 mole fraction of the outlet gas, mol/mol Greek letters ߩ௚ density of gas phase, kg/m3 ߩ௟ density of liquid phase, kg/m3 ߤ Ratio of liquid viscosity to that of water 2.

EXPERIMENT

Fig. 1 is the RPB equipment used in this study. The details of the experimental setup and the operating procedure can be found in a previous work [19]. In the study, a 3 wt% diluted ammonia solution was used as an absorbent. The absorbent was fed into central axis of the RPB and centrifuged outward.

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Fig. 1 Experimental apparatus for CO2 capture in a rotating packed bed.

The PB results were carried out in an absorber with a 2.54 cm inner diameter with 4 removable packing sections with a height of 30 cm. Details of the experiment setup, operating procedure and results were reported [20]. Table 1 summarized the design and operating conditions of packed bed and rotating packed bed. Table 1 Design and operating conditions of packed bed and rotating packed bed PB RPB Diameter (m) 0.0254 0.125 (OD); 0.025 (ID) Packing height (m) 0.3-1.2 0.023 Packing volume (m3)  Pressure (atm) 1 1 27 24 Temperature (Ԩ) Inlet NH3 conc. (wt %) 3 3 Inlet CO2 fraction (mol%) 15-50% 30% lean loading (mol/mol) 0 0 ܽ௣ (m2/m3) 800 887.6 porosity 0.65 0.96 Rotating speed(rpm) --400-1600 Gas flow rate(l/min) 2–4 10 – 25 Liquid flow rate (l/min) 0.1 0.05 – 0.25 Packing type Plastic Raschig Rings Stainless Wire Mesh

The efficiency of CO2 capture can be represented by %removal rate. ܴ ൌ ൤ͳ െ

௬಴ೀమ ǡ೚ ௬಴ೀమǡ೔ ൫ଵି௬಴ೀమǡ೚ ൯

൨ ൈ ͳͲͲΨ

(1)

However, since the volumes of the absorbers are different in the two experiments, the height transfer unit (HTU) was calculated to compare capture performance of the PB and the RPB: ௏ ‫ ܷܶܪ‬ൌ (2) ೤಴ೀ ǡ೔ మ ቇ ೤಴ೀ ǡ೚ మ

஺௟௡ቆ

For RPB, A is obtained by logarithmic mean of the areas of the inner and outer rings. A smaller value of the HTU represents better mass transfer efficiencies. In addition to the difference in HTU, the reserve capacities i.e. flooding percentage of PB and packed bed may also be different. Flooding gas capacity factor is calculated by a correlation presented from Lockett [20], which is shown in below: ଶ

‫ۍ‬ଵǤହ଻௔షబǤమఱቀೌ೎ቁబǤమమ ఓషబǤబయ‫ې‬ ೛ ೒ ‫ۑ‬ ‫ܥ‬௚ ൌ ‫ێ‬ ‫ ێ‬ଵାଵǤଷ଴ହඨቆ ಽ ൬ഐ೒൰బǤఱቇ ‫ۑ‬ ಸ ഐ೗ ‫ۏ‬ ‫ے‬

(3)

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A model of packed bed for CO2 capture by mono-ethanol-amine solutions was developed by Kvamsdal and Rochelle [21]. Such a model was modified by Kang et al. [16], to describe absorption of CO2 by mono-ethanolamine (MEA) solutions. By replacing the physical chemistry properties package of MEA absorption using the electrolyte NRTL for ammonia-CO2-water system developed by Que and Chen [17], and the kinetics of reaction [9, 17], RPB and PB models of our systems were obtained. 3.

RESULTS AND DISCUSSION

Table 2 shows the summary of experiments results (a complete list is given in the appendix). Although the absolute percentage removal are smaller in the RPB; the HTUs of the packed bed were 0.35 to 1.96 m, while the HTUs of the rotating packed bed were 0.08 to 0.40 m. The HTUs of the rotating packed bed are significantly smaller than those of the packed bed. Furthermore the flooding capacities of RPB experiments are also much smaller than that of the packed bed experiments. All these indicated that substantial reduction in volume and cross-sectional area can be achieved using RPB. Table 2: The summary of experiments of the packed bed and the rotating packed bed PB RPB

QG (l/min)

QL(ml/min)

Volume(cm3)

Rotating speed(RPM)

Removal%

HTU(m)

2-4 10-25

100 50-250

152~608 271

--400-1300

20-97 14-54

0.35-1.96 0.08-0.40

% Flooding 44.5-76.6 11.1-77.1

Fig. 2 showed the effect of rotating speed on removal at inlet gas flow of 20 ml/min and inlet liquid flow of 0.1 l/min. As the figure shown, CO2 removal increases as rotating speed increase but improvement is limited when rotating speed is above 1000 rpm. Fig. 3 is an agreement of experimental and model predictions of CO2 removal percentage of the PB and RPB. AAD% is 12% for PB and 9.4% for RPB.

50

experiment simulation

experiment (%)

40

30

20

10

AAD%=17.3% 0

400

600

800

1000

1200

1400

Rotating speed (RPM)

Fig. 2 Effect of rotating speed on CO2 removal

1600

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Jia-Lin Kang et al. / Energy Procedia 63 (2014) 1308 – 1313 100

+30%

Gas flow rate=4 l/min Gas flow rate=2 l/min Gas flow rate=6 l/min

80

sim. CO2 removal efficiency (%)

sim. CO2 removal efficiency (%)

100

-30%

60

40

20

Various Gas flowrate Various Liquid flowrate Various Rotating speed

80

+30%

-30%

60

40

20

AAD% = 12% 0

AAD% = 9.4% 0

0

20

40

60

exp. CO2 removal efficiency (%)

(a) PB

80

100

0

20

40

60

80

100

exp. CO2 removal efficiency (%)

(b) RPB

Fig. 3 Agreement of experimental and simulation CO2 removal efficiency

4.

CONCLUSIONS

In this work, experimental investigations of CO2 capture by dilute ammonia using a rotating packed bed absorber were presented. The HTU of the RPB were found to be much smaller than those of the PB at conditions of much further away from flooding limits. The experimental results can be adequately predicted by models developed. Substantial process intensification effect can be expected when RPB technology was applied to CO2 capture by dilute ammonia. The reduction in equipment size and general implications to process design and economics for large scale capture can be discussed using these models in the future. ACKNOWLEDGEMENTS The authors wish to express their thanks to the financial support from ROC National Science Council (grant number NSC 1032623-E-007-006-17), Ministry of Education, Taiwan, ROC (grant number 103-N-202-1E-1) and National Tsing Hua University at Hsinchu, Taiwan, ROC. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

C. H. Yu, C. H. Huang, and C. S. Tan, "A review of CO2 capture by absorption and adsorption," Aerosol Air Qual. Res, vol. 12, pp. 745-769, 2012. H. Bai and A. C. Yeh, "Removal of CO2 greenhouse gas by ammonia scrubbing," Industrial & Engineering Chemistry Research, vol. 36, pp. 2490-2493, 1997. E. Gal, "Ultra Cleaning of Combustion Gas Including the Removal of Co2," ed: Google Patents, 2008. V. Telikapalli, F. Kozak, J. Francois, B. Sherrick, J. Black, D. Muraskin, et al., "CCS with the Alstom chilled ammonia process development program–Field pilot results," Energy Procedia, vol. 4, pp. 273-281, 2011. C. R. McLarnon and J. L. Duncan, "Testing of Ammonia Based CO2 Capture with Multi-Pollutant Control Technology," Energy Procedia, vol. 1, pp. 1027-1034, 2009. H. Yu, S. Morgan, A. Allport, A. Cottrell, T. Do, J. McGregor, et al., "Results from trialling aqueous NH3 based post-combustion capture in a pilot plant at Munmorah power station: Absorption," Chemical Engineering Research and Design, vol. 89, pp. 1204-1215, 2011. H. Yu, G. Qi, S. Wang, S. Morgan, A. Allport, A. Cottrell, et al., "Results from trialling aqueous ammonia-based post-combustion capture in a pilot plant at Munmorah Power Station: Gas purity and solid precipitation in the stripper," International Journal of Greenhouse Gas Control, vol. 10, pp. 15-25, 2012. C. H. Rhee, J. Y. Kim, K. Han, C. K. Ahn, and H. D. Chun, "Process analysis for ammonia-based CO< sub> 2 capture in ironmaking industry," Energy Procedia, vol. 4, pp. 1486-1493, 2011. M. Zhang and Y. Guo, "Process simulations of large-scale CO2 capture in coal-fired power plants using aqueous ammonia solution," International Journal of Greenhouse Gas Control, vol. 16, pp. 61-71, 2013. H. Jilvero, F. Normann, K. Andersson, and F. Johnsson, "The Rate of CO2 Absorption in Ammonia ί Implications on Absorber Design," Industrial & Engineering Chemistry Research, vol. 53, pp. 6750-6758, 2014. C. Ramshaw and R. H. Mallinson, "Mass transfer process," ed: Google Patents, 1981.

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Appendix: Data Run

Absorber

Volume (cm3)

QG (l/min)

QL (l/min)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

PB PB PB PB PB PB PB PB PB PB PB PB PB PB PB PB PB PB PB PB RPB RPB RPB RPB RPB RPB RPB RPB RPB RPB RPB RPB RPB RPB

152 304 456 608 152 304 456 608 152 304 456 608 152 304 456 608 152 304 456 608 271 271 271 271 271 271 271 271 271 271 271 271 271 271

4 4 4 4 4 4 4 4 2 2 2 2 4 4 4 4 6 6 6 6 15 15 15 15 15 10 15 20 25 20 20 20 20 20

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.05 0.1 0.15 0.2 0.25 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

Rotating speed (RPM) 1000 1000 1000 1000 1000 1000 1000 1000 1000 400 700 1000 1300 1600

‫ݕ‬஼ைమǡ௜

‫ݕ‬஼ைమǡ௢

% Removal

HTU (cm)

% Flooding

0.5 0.5 0.5 0.5 0.25 0.25 0.25 0.25 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30

0.398 0.341 0.278 0.271 0.178 0.135 0.102 0.085 0.077 0.036 0.012 0.005 0.097 0.072 0.048 0.036 0.120 0.094 0.072 0.054 0.2534 0.2066 0.1721 0.1517 0.1380 0.1585 0.2190 0.2424 0.2537 0.2577 0.2477 0.2424 0.2397 0.2386

20.4 31.8 44.4 45.8 28.8 46.0 59.2 66.0 48.7 76.0 92.0 96.7 35.3 52.0 68.0 76.0 20.0 37.3 52.0 64.0 15.5 31.1 42.6 49.4 54.0 47.2 27.0 19.2 15.4 14.1 17.4 19.2 20.1 20.5

131.5 156.8 153.3 195.9 88.3 97.4 100.4 111.2 45.0 42.0 35.6 35.3 68.8 81.7 79.0 84.1 134.4 128.4 122.6 117.5 35.8 16.2 10.9 8.9 7.8 9.5 19.2 28.3 36.0 39.7 31.5 28.3 26.9 26.4

64.3 64.4 64.6 64.9 62.6 62.6 62.6 62.5 44.9 44.8 44.6 44.5 61.9 62.0 62.0 61.9 76.3 76.4 76.5 76.6 11.5 15.0 18.8 23.3 28.8 10.0 12.6 15.6 18.4 77.1 32.4 20.0 14.3 11.1