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Modification of effective surface area correlation for structured packed absorption column at elevated pressures
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 22085–22092
www.materialstoday.com/proceedings
The 3rd International Conference on Green Chemical Engineering Technology (3rd GCET_2017): Materials Science
Modification of effective surface area correlation for structured packed absorption column at elevated pressures L.S. Tana*, A.M. Shariffb, K.K Laub, T. Tsujia a
Department of Chemical Process Engineering, Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, 54100 Kuala Lumpur, Malaysia. b Chemical Engineering Department, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia.
Abstract Correlation for effective surface area is one of the important input for modeling of gas absorption in countercurrent packed column. Although the correlation previously developed by other researchers was able to provide quite decent prediction of carbon dioxide (CO2) absorption system, improvement still need to be done especially for high pressure condition whereby consideration for the decrease of effective surface area due to severe vapour backmixing situation needs to be taken into account. In this work, pressure dependent correction correlation was developed by incorporating the ratio of liquid to gas densities. The correlation developed in this study was found to successfully improve the prediction trend of the CO2 concentration profile along the column. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 3rd International Conference on Green Chemical Engineering and Technology (3rd GCET): Materials Science, 07-08 November 2017. Keywords: Absorption; structured packed column; elevated pressure; effective surface area.
* Corresponding author. Tel.: +60322031311; fax: +60322031266. E-mail address: [email protected] 2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 3rd International Conference on Green Chemical Engineering and Technology (3rd GCET): Materials Science, 07-08 November 2017.
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Tan et.al. / Materials Today: Proceedings 5 (2018) 22085–22092
Nomenclature ⁄
effective surface area liquid to gas densities ratio
1. Introduction Packing is commonly inserted into absorption tower to create longer gas-liquid contact time during absorption process. In recent years, there are increasing findings that structured packing in an absorber can provide a much higher overall mass-transfer coefficient than random packing [1-3]. Generally, the volumetric mass transfer coefficient increased with increase of surface area [4]. However, surface area of packing should not be the only judging criteria for higher mass transfer coefficient estimation as there are also other influencing factors such as pattern of packing arrangement, corrugation angle and crimp height in the case for structured packing [5, 6]. In addition, the effective surface area, , during the continuous countercurrent absorption process is very critical. The quality of liquid distribution or maldistribution across the cross-section of the column design due to the hydrodynamic factors could affect the of packing [7]. As such, correlation for estimation of needs to take into account the relevant factors in order to have more accurate prediction of absorption in packed column. Rocha et al. [8, 9] developed correlation for based on geometric parameters, physical properties of liquid and contact angle in their SRP II model. Gualito et al. [10] attempted to further improve the correlation in SRP II model, supposingly meant for high pressure condition, by considering the impact of superficial gas velocity. Billet and Schultes [11, 12] developed another model for prediction of countercurrent absorption performance by assuming liquid flow pattern to be different at different operating region i.e. pre-loading and loading region. The correlation developed by Tsai et al. [13] was a function of packing surface area, liquid surface tension and liquid flow rate. The impact of liquid viscosity, gas flow rate and flow channel configuration was neglected by the authors. Our previously developed mathematical modelling for prediction of rich carbon dioxide (CO2) absorption in Flexipac 1Y structured packed column yielded decent prediction of absorption performance in the study [14]. The correlations used in the work was based on correlations developed by Rocha et al. [9] and Tsai et al. [13]. However, improvement could still be done to correct the correlation. This is especially relevant for 5 MPa condition whereby consideration for the decrease of ae due to possible vapour backmixing situation [10, 15] needs to be taken into account. Hence, a corrected term was developed in this study based on the SRP II model combined with ae from Tsai et al. [13] as these combination provided the highest coefficient of determination, R2, for predicted value. The developed pressure dependent correction correlation would be validated with experimental results for confirmation of predicted trend against actual data. 2. Model development In our previous study [14], it was observed that the prediction trend for 1 MPa fitted well with the experimental data. For other pressure condition, i.e. 0.1 MPa, 3 MPa and 5 MPa, the predicted trend was similar, but there was noticeable deviation from experimental data. As such, correction coefficient was generated for the three pressure condition with aim to increase the R2 of the fitting for measured values of CO2 concentration in gas phase versus predicted values. The correction coefficient was obtained by adjusting the coefficient to fit the experimental trend using Matlab 2013a software. The correction coefficient was assumed to be pressure dependent, hence, identified as ( ). According to Wang et al. [16], the influence of pressure and operating load could be effectively reflected by incorporating the ratio of liquid to gas densities ( ⁄ ). As such, ( ) could be transformed to a function of the ratio and identified as ( ⁄ ). The workflow of how the correction correlation for for elevated pressure condition was obtained is summarized in Fig. 1.
Tan et al. / Materials Today: Proceedings 5 (2018) 22085–22092
Fig. 1. Process workflow to generate correction correlation for
22087
.
3. Results and Discussions 3.1. Development of pressure dependent correction correlation In order to obtain prediction trend that could fit the experimental trend at 0.1 MPa condition better as shown in Fig. 2, the correction factor (CF) for was set at 1.64. This is equal to ap which is the maximum surface area that the system could logically achieve. Meanwhile, the correction coefficient which would enable the model to fit the experimental data better for pressure condition of 3 MPa and 5 MPa was found to be 0.95 and 0.78, respectively, as shown in Fig. 3 and Fig. 4. The value of ( ) for different pressure conditions is shown in Table 1.
Fig. 2. The predicted CO2 concentration profile in absorption column at pressure condition of 0.1 MPa after correction factor of 1.64 to ae.
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Tan et.al. / Materials Today: Proceedings 5 (2018) 22085–22092
Fig. 3. The predicted CO2 concentration profile in absorption column at pressure condition of 3 MPa after correction factor of 0.95 to ae.
Fig. 4. The predicted CO2 concentration profile in absorption column at pressure condition of 5 MPa after correction factor of 0.78 to ae. Table 1. Correction coefficient for Pressure (MPa)
at different pressure conditions. ( )
0.1
1.64
1
1.00
3
0.95
5
0.78
The dependence of the correction coefficient for on the density ratio of liquid to gas could either be in natural logarithm (ln) or power function as shown in Fig. 5 and Fig. 6 respectively. The correction correlation in natural logarithm (ln) and power function are as follows: ,
0.2045
0.2173
(1)
Tan et al. / Materials Today: Proceedings 5 (2018) 22085–22092
,
0.5023
.
22089
(2)
Based on Fig. 5 and Fig. 6, it is observed that the R2 for the correction coefficient for in natural logarithm (ln) function was slightly lower than R2 for correction factor in power function. However, in order to decide on the suitability of the correction correlation, the proposed correlation was validated back with the experimental results in this study.
Fig. 5. The dependence of the correction coefficient for
on the density ratio of liquid to gas in natural logarithm (ln) function.
Fig. 6. The dependence of the correction coefficient for
on the density ratio of liquid to gas in power function.
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Tan et.al. / Materials Today: Proceedings 5 (2018) 22085–22092
3.2. Model Validation Fig. 7 and Fig. 8 show the predicted results after incorporating proposed correlation in natural logarithm (ln) and power function, respectively, into our previously developed mathematical model [14]. Generally, both Eq. 1 and 2 managed to correct the prediction trend for 0.1 MPa pressure condition closer to the experimental results. However, at 1 MPa pressure condition, the concentration of CO2 at the top of the column was over-predicted for the corrected model version. The previous uncorrected version had managed to correctly predict the CO2 concentration on top of the column. As such, the higher surface area for pressure condition of 1 MPa after correction caused the CO2 absorption process to be deemed to perform even better, hence, the over-prediction. Meanwhile, the prediction trend for 3 MPa and 5 MPa was successfully corrected to almost able to fit the experimental data if compared to the uncorrected version as earlier. This shows that at high pressure condition, in the actual packed column was indeed reduced. This was probably due to severe vapour backmixing effect as earlier explained.
Fig. 7. The predicted CO2 concentration profile in absorption column at different pressure conditions after correction to ae using Eq. 1.
The comparison between the measured and predicted CO2 concentration using the proposed correlations is shown in Fig. 9 and Fig. 10. Both the correction factors from Eq. 1 and Eq. 2 had successfully increased the R2 between the predicted and measured values of CO2 concentration in gas phase from 0.9802 in our previous study [14] to 0.9948 and 0.9935 respectively. The R2 value for both Eq. 1 and Eq. 2 was very close, indicating that both equations can be used as correction correlation for ae in order to predict CO2 concentration for Flexipac 1Y system at up to 5 MPa pressure condition. However, since Eq. 1 has slightly high R2 value out of the two, it is proposed to be used as pressure dependent correction correlation for ae in the modeling of absorption process.
Tan et al. / Materials Today: Proceedings 5 (2018) 22085–22092
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Fig. 8. The predicted CO2 concentration profile in absorption column at different pressure conditions after correction to ae using Eq. 2.
Fig. 9. Comparison between measured values of CO2 concentration in gas phase versus predicted values after correction to ae using Eq. 1.
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Tan et.al. / Materials Today: Proceedings 5 (2018) 22085–22092
Fig. 10. Comparison between measured values of CO2 concentration in gas phase versus predicted values after correction to ae using Eq. 2.
4. Conclusion The pressure dependent correlation developed in this study for correction of effective surface area at elevated pressure was found to successfully improve the prediction trend of the CO2 concentration profile along the column in our study. The R2 of the predicted versus measured CO2 concentration graph was improved from 0.98 to more than 0.99. Acknowledgements The authors would like to thank Universiti Teknologi Malaysia for providing financial support (Potential Academic Staff grant- Ref No. PY/2017/01041, Q.K130000.2743.03K07). References [1] J.T. Yeh, H.W. Pennline, K.P. Resnik, Energy & Fuels, 15 (2001) 274-278. [2] A. Aboudheir, D. deMontigny, P. Tontiwachwuthikul, A. Chakma, SPE Gas Technology Symposium, Calgary, Alberta, Canada, 1998. [3] A. Aroonwilas, A. Veawab, P. Tontiwachwuthikul, Ind. Eng. Chem. Res., 38 (1999) 2044-2050. [4] N. Kolev, S. Nakov, L. Ljutzkanov, D. Kolev, Chem. Eng. Process., 45 (2006) 429-436. [5] A. Aroonwilas, A. Chakma, P. Tontiwachwuthikul, A. Veawab, Chem. Eng. Sci., 58 (2003) 4037-4053. [6] H.N. Abdul Halim, A. M. Shariff, L.S. Tan, M.A. Bustam, Ind. Eng. Chem. Res., 54 (2015) 1675-1680. [7] J.L. Bravo, J.A. Rocha, J.R. Fair, Hydrocarbon Process., 64 (1985) 91-95. [8] J.A. Rocha, J.L. Bravo, J.R. Fair, Ind. Eng. Chem. Res., 32 (1993) 641-651. [9] J.A. Rocha, J.L. Bravo, J.R. Fair, Ind. Eng. Chem. Res., 35 (1996) 1660-1667. [10] J.J. Gualito, F.J. Cerino, J.C. Cardenas, J.A. Rocha, Ind. Eng. Chem. Res., 36 (1997) 1747-1757. [11] R. Billet, M. Schultes, Chem. Eng. Tech., 16 (1993) 1-9. [12] R. Billet, M. Schultes, Chem. Eng. Res. Design, 77 (1999) 498-504. [13] R.E. Tsai, A.F. Seibert, R.B. Eldridge, G.T. Rochelle, AIChE Journal, 57 (2011) 1173-1184. [14] L.S. Tan, A.M. Shariff, W.H. Tay, K.K. Lau, H.N.A. Halim, J. Nat. Gas Sci. Eng., 28 (2016) 737-745. [15] G.Q. Wang, X.G. Yuan, K.T. Yu, Ind. Eng. Chem. Res., 44 (2005) 8715-8729. [16] G.Q. Wang, X.G. Yuan, K.T. Yu, Chem. Eng. Process., 45 (2006) 691-697.
ScienceDirect Materials Today: Proceedings 5 (2018) 22085–22092
www.materialstoday.com/proceedings
The 3rd International Conference on Green Chemical Engineering Technology (3rd GCET_2017): Materials Science
Modification of effective surface area correlation for structured packed absorption column at elevated pressures L.S. Tana*, A.M. Shariffb, K.K Laub, T. Tsujia a
Department of Chemical Process Engineering, Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, 54100 Kuala Lumpur, Malaysia. b Chemical Engineering Department, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia.
Abstract Correlation for effective surface area is one of the important input for modeling of gas absorption in countercurrent packed column. Although the correlation previously developed by other researchers was able to provide quite decent prediction of carbon dioxide (CO2) absorption system, improvement still need to be done especially for high pressure condition whereby consideration for the decrease of effective surface area due to severe vapour backmixing situation needs to be taken into account. In this work, pressure dependent correction correlation was developed by incorporating the ratio of liquid to gas densities. The correlation developed in this study was found to successfully improve the prediction trend of the CO2 concentration profile along the column. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 3rd International Conference on Green Chemical Engineering and Technology (3rd GCET): Materials Science, 07-08 November 2017. Keywords: Absorption; structured packed column; elevated pressure; effective surface area.
* Corresponding author. Tel.: +60322031311; fax: +60322031266. E-mail address: [email protected] 2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 3rd International Conference on Green Chemical Engineering and Technology (3rd GCET): Materials Science, 07-08 November 2017.
22086
Tan et.al. / Materials Today: Proceedings 5 (2018) 22085–22092
Nomenclature ⁄
effective surface area liquid to gas densities ratio
1. Introduction Packing is commonly inserted into absorption tower to create longer gas-liquid contact time during absorption process. In recent years, there are increasing findings that structured packing in an absorber can provide a much higher overall mass-transfer coefficient than random packing [1-3]. Generally, the volumetric mass transfer coefficient increased with increase of surface area [4]. However, surface area of packing should not be the only judging criteria for higher mass transfer coefficient estimation as there are also other influencing factors such as pattern of packing arrangement, corrugation angle and crimp height in the case for structured packing [5, 6]. In addition, the effective surface area, , during the continuous countercurrent absorption process is very critical. The quality of liquid distribution or maldistribution across the cross-section of the column design due to the hydrodynamic factors could affect the of packing [7]. As such, correlation for estimation of needs to take into account the relevant factors in order to have more accurate prediction of absorption in packed column. Rocha et al. [8, 9] developed correlation for based on geometric parameters, physical properties of liquid and contact angle in their SRP II model. Gualito et al. [10] attempted to further improve the correlation in SRP II model, supposingly meant for high pressure condition, by considering the impact of superficial gas velocity. Billet and Schultes [11, 12] developed another model for prediction of countercurrent absorption performance by assuming liquid flow pattern to be different at different operating region i.e. pre-loading and loading region. The correlation developed by Tsai et al. [13] was a function of packing surface area, liquid surface tension and liquid flow rate. The impact of liquid viscosity, gas flow rate and flow channel configuration was neglected by the authors. Our previously developed mathematical modelling for prediction of rich carbon dioxide (CO2) absorption in Flexipac 1Y structured packed column yielded decent prediction of absorption performance in the study [14]. The correlations used in the work was based on correlations developed by Rocha et al. [9] and Tsai et al. [13]. However, improvement could still be done to correct the correlation. This is especially relevant for 5 MPa condition whereby consideration for the decrease of ae due to possible vapour backmixing situation [10, 15] needs to be taken into account. Hence, a corrected term was developed in this study based on the SRP II model combined with ae from Tsai et al. [13] as these combination provided the highest coefficient of determination, R2, for predicted value. The developed pressure dependent correction correlation would be validated with experimental results for confirmation of predicted trend against actual data. 2. Model development In our previous study [14], it was observed that the prediction trend for 1 MPa fitted well with the experimental data. For other pressure condition, i.e. 0.1 MPa, 3 MPa and 5 MPa, the predicted trend was similar, but there was noticeable deviation from experimental data. As such, correction coefficient was generated for the three pressure condition with aim to increase the R2 of the fitting for measured values of CO2 concentration in gas phase versus predicted values. The correction coefficient was obtained by adjusting the coefficient to fit the experimental trend using Matlab 2013a software. The correction coefficient was assumed to be pressure dependent, hence, identified as ( ). According to Wang et al. [16], the influence of pressure and operating load could be effectively reflected by incorporating the ratio of liquid to gas densities ( ⁄ ). As such, ( ) could be transformed to a function of the ratio and identified as ( ⁄ ). The workflow of how the correction correlation for for elevated pressure condition was obtained is summarized in Fig. 1.
Tan et al. / Materials Today: Proceedings 5 (2018) 22085–22092
Fig. 1. Process workflow to generate correction correlation for
22087
.
3. Results and Discussions 3.1. Development of pressure dependent correction correlation In order to obtain prediction trend that could fit the experimental trend at 0.1 MPa condition better as shown in Fig. 2, the correction factor (CF) for was set at 1.64. This is equal to ap which is the maximum surface area that the system could logically achieve. Meanwhile, the correction coefficient which would enable the model to fit the experimental data better for pressure condition of 3 MPa and 5 MPa was found to be 0.95 and 0.78, respectively, as shown in Fig. 3 and Fig. 4. The value of ( ) for different pressure conditions is shown in Table 1.
Fig. 2. The predicted CO2 concentration profile in absorption column at pressure condition of 0.1 MPa after correction factor of 1.64 to ae.
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Tan et.al. / Materials Today: Proceedings 5 (2018) 22085–22092
Fig. 3. The predicted CO2 concentration profile in absorption column at pressure condition of 3 MPa after correction factor of 0.95 to ae.
Fig. 4. The predicted CO2 concentration profile in absorption column at pressure condition of 5 MPa after correction factor of 0.78 to ae. Table 1. Correction coefficient for Pressure (MPa)
at different pressure conditions. ( )
0.1
1.64
1
1.00
3
0.95
5
0.78
The dependence of the correction coefficient for on the density ratio of liquid to gas could either be in natural logarithm (ln) or power function as shown in Fig. 5 and Fig. 6 respectively. The correction correlation in natural logarithm (ln) and power function are as follows: ,
0.2045
0.2173
(1)
Tan et al. / Materials Today: Proceedings 5 (2018) 22085–22092
,
0.5023
.
22089
(2)
Based on Fig. 5 and Fig. 6, it is observed that the R2 for the correction coefficient for in natural logarithm (ln) function was slightly lower than R2 for correction factor in power function. However, in order to decide on the suitability of the correction correlation, the proposed correlation was validated back with the experimental results in this study.
Fig. 5. The dependence of the correction coefficient for
on the density ratio of liquid to gas in natural logarithm (ln) function.
Fig. 6. The dependence of the correction coefficient for
on the density ratio of liquid to gas in power function.
22090
Tan et.al. / Materials Today: Proceedings 5 (2018) 22085–22092
3.2. Model Validation Fig. 7 and Fig. 8 show the predicted results after incorporating proposed correlation in natural logarithm (ln) and power function, respectively, into our previously developed mathematical model [14]. Generally, both Eq. 1 and 2 managed to correct the prediction trend for 0.1 MPa pressure condition closer to the experimental results. However, at 1 MPa pressure condition, the concentration of CO2 at the top of the column was over-predicted for the corrected model version. The previous uncorrected version had managed to correctly predict the CO2 concentration on top of the column. As such, the higher surface area for pressure condition of 1 MPa after correction caused the CO2 absorption process to be deemed to perform even better, hence, the over-prediction. Meanwhile, the prediction trend for 3 MPa and 5 MPa was successfully corrected to almost able to fit the experimental data if compared to the uncorrected version as earlier. This shows that at high pressure condition, in the actual packed column was indeed reduced. This was probably due to severe vapour backmixing effect as earlier explained.
Fig. 7. The predicted CO2 concentration profile in absorption column at different pressure conditions after correction to ae using Eq. 1.
The comparison between the measured and predicted CO2 concentration using the proposed correlations is shown in Fig. 9 and Fig. 10. Both the correction factors from Eq. 1 and Eq. 2 had successfully increased the R2 between the predicted and measured values of CO2 concentration in gas phase from 0.9802 in our previous study [14] to 0.9948 and 0.9935 respectively. The R2 value for both Eq. 1 and Eq. 2 was very close, indicating that both equations can be used as correction correlation for ae in order to predict CO2 concentration for Flexipac 1Y system at up to 5 MPa pressure condition. However, since Eq. 1 has slightly high R2 value out of the two, it is proposed to be used as pressure dependent correction correlation for ae in the modeling of absorption process.
Tan et al. / Materials Today: Proceedings 5 (2018) 22085–22092
22091
Fig. 8. The predicted CO2 concentration profile in absorption column at different pressure conditions after correction to ae using Eq. 2.
Fig. 9. Comparison between measured values of CO2 concentration in gas phase versus predicted values after correction to ae using Eq. 1.
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Tan et.al. / Materials Today: Proceedings 5 (2018) 22085–22092
Fig. 10. Comparison between measured values of CO2 concentration in gas phase versus predicted values after correction to ae using Eq. 2.
4. Conclusion The pressure dependent correlation developed in this study for correction of effective surface area at elevated pressure was found to successfully improve the prediction trend of the CO2 concentration profile along the column in our study. The R2 of the predicted versus measured CO2 concentration graph was improved from 0.98 to more than 0.99. Acknowledgements The authors would like to thank Universiti Teknologi Malaysia for providing financial support (Potential Academic Staff grant- Ref No. PY/2017/01041, Q.K130000.2743.03K07). References [1] J.T. Yeh, H.W. Pennline, K.P. Resnik, Energy & Fuels, 15 (2001) 274-278. [2] A. Aboudheir, D. deMontigny, P. Tontiwachwuthikul, A. Chakma, SPE Gas Technology Symposium, Calgary, Alberta, Canada, 1998. [3] A. Aroonwilas, A. Veawab, P. Tontiwachwuthikul, Ind. Eng. Chem. Res., 38 (1999) 2044-2050. [4] N. Kolev, S. Nakov, L. Ljutzkanov, D. Kolev, Chem. Eng. Process., 45 (2006) 429-436. [5] A. Aroonwilas, A. Chakma, P. Tontiwachwuthikul, A. Veawab, Chem. Eng. Sci., 58 (2003) 4037-4053. [6] H.N. Abdul Halim, A. M. Shariff, L.S. Tan, M.A. Bustam, Ind. Eng. Chem. Res., 54 (2015) 1675-1680. [7] J.L. Bravo, J.A. Rocha, J.R. Fair, Hydrocarbon Process., 64 (1985) 91-95. [8] J.A. Rocha, J.L. Bravo, J.R. Fair, Ind. Eng. Chem. Res., 32 (1993) 641-651. [9] J.A. Rocha, J.L. Bravo, J.R. Fair, Ind. Eng. Chem. Res., 35 (1996) 1660-1667. [10] J.J. Gualito, F.J. Cerino, J.C. Cardenas, J.A. Rocha, Ind. Eng. Chem. Res., 36 (1997) 1747-1757. [11] R. Billet, M. Schultes, Chem. Eng. Tech., 16 (1993) 1-9. [12] R. Billet, M. Schultes, Chem. Eng. Res. Design, 77 (1999) 498-504. [13] R.E. Tsai, A.F. Seibert, R.B. Eldridge, G.T. Rochelle, AIChE Journal, 57 (2011) 1173-1184. [14] L.S. Tan, A.M. Shariff, W.H. Tay, K.K. Lau, H.N.A. Halim, J. Nat. Gas Sci. Eng., 28 (2016) 737-745. [15] G.Q. Wang, X.G. Yuan, K.T. Yu, Ind. Eng. Chem. Res., 44 (2005) 8715-8729. [16] G.Q. Wang, X.G. Yuan, K.T. Yu, Chem. Eng. Process., 45 (2006) 691-697.