Malaya, Kuala Lumpur, Malaysia b Department of Chemical Engineering, University of Malaya, Kuala Lumpur, Malaysia

Transcription

1 This article was downloaded by: [University of Malaya] On: 08 July 2014, At: 19:31 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Separation Science and Technology Publication details, including instructions for authors and subscription information: Accurate Modeling of Evaporation and Enthalpy of Vapor Phase in CO 2 Absorption by Amine Based Solution Harith Rashid a, Nurul Hasan a & M. Iskandar M. Nor b a Nanotechnology & Catalysis Research Centre (NANOCAT, IPS Building, University of Malaya, Kuala Lumpur, Malaysia b Department of Chemical Engineering, University of Malaya, Kuala Lumpur, Malaysia Accepted author version posted online: 07 Mar 2014.Published online: 03 Jun To cite this article: Harith Rashid, Nurul Hasan & M. Iskandar M. Nor (2014 Accurate Modeling of Evaporation and Enthalpy of Vapor Phase in CO 2 Absorption by Amine Based Solution, Separation Science and Technology, 49:9, , DOI: / To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at

2 Separation Science and Technology, 49: , 2014 Copyright Taylor & Francis Group, LLC ISSN: print / online DOI: / Accurate Modeling of Evaporation and Enthalpy of Vapor Phase in CO 2 Absorption by Amine Based Solution Harith Rashid, 1 Nurul Hasan, 1 and M. Iskandar M. Nor 2 1 Nanotechnology & Catalysis Research Centre (NANOCAT, IPS Building, University of Malaya, Kuala Lumpur, Malaysia 2 Department of Chemical Engineering, University of Malaya, Kuala Lumpur, Malaysia The effect of enthalpy of liquid and vapor phases for the CO 2 absorption process in mono-ethanolamine (MEA solution is one of the important factors involved in CO 2 absorption processes. This phenomenon is more prominent at the bottom of the column for countercurrent operations resulting in corrosion, erosion, and loss in amine, mostly at high enthalpy of liquid. The absorption column temperature increases during the CO 2 absorption process, due to exothermic absorption of CO 2 in amine solution. This rise in temperature increases water evaporation. These water vapors condense back to the liquid phase when they come in direct contact with cold amine solution coming from the top of the column. The Kent-Eisenberg vapor-liquid equilibrium model used is accurate with less than 3% error. A loss of MEA and water in the vapor phase is studied in this research. It is revealed that only mole% MEA and 3 mole% water leave the absorption column with flue gases at 298 K. This loss in amine solution is quite low and acceptable for industrial processes. Keywords CO 2 absorption; MEA; packed column; enthalpy; corrosion INTRODUCTION Numerous pilot plant CO 2 absorption processes are employing post-combustion capture systems and are studied for experimental purposes by many researchers. These processes are studied for full-scale deployment of CO 2 absorption processes on a commercial scale (1-5. However, they require a high capital cost to produce the pilot-scale equipment and high operating cost of electricity and chemicals (6. Modeling and simulation of different chemical processes requires considerably less investment and can give good results to validate experimental data as shown in many papers (7-11.MEAisusedas an amine in this research because of it high reaction rates with CO 2 at ambient conditions ( High reaction rate for MEA is accompanied by other operation problems associated Received 31 August 2013; accepted 08 January Address correspondence to Nurul Hasan, Nanotechnology & Catalysis Research Centre (NANOCAT, IPS Building, University of Malaya, Kuala Lumpur, Malaysia. nurulhasan@ asme.org 1326 with the use of MEA as amine solution such as corrosion, foaming, and degradation of amine solution (17, 18. Other amine solutions such as DEA, AMP, PZ, and MDEA are also used in CO 2 absorption processes, even though they have low reaction rate for CO 2 absorption because of their lesser tendency toward corrosion ( Still, MEA remains the main focus for CO 2 absorption processes. However, different amines are added into MEA solution to reduce negative aspects with little effect on absorption capacity ( Similarly, different inhibitors are also reported in the literature which can be used to reduce corrosion and degradation issues associated with MEA ( Amine solution with a very low concentration is considered in this study since higher concentrations create corrosion problems in the absorption column (25. The absorption column is a packed column, where sour gas comes in direct contact with lean amine solution counter currently. Amine solution enters the column from the top and flue gas enters from the bottom of the column. Gas liquid interaction takes place in the packed column containing structured packing. Sulzer DX is used as packing because of its high surface area and is used by many researchers for gas-liquid absorption processes ( Temperature and maximum CO 2 absorption is reported to occur at the lower section of the column and depends on many factors such as liquid to gas ratio (G/L, diameter, and height of the column (15, Much less work is focused on simulation and modeling of liquid and gas phase enthalpy, which is one of the most important factors involved in CO 2 absorption processes. Corrosion and erosion of the column is most likely to occur at the point where enthalpy and temperature of the system is high. However, a lot of people have made serious efforts to model and validate CO 2 absorption processes and have shown high deviation from the experimental data. Different models presented in literature to predict the experimental behaviors are summarized in Table 1. A rise in enthalpy is reported in the lower section of the absorption column where CO 2 from the flue gas comes in direct contact with the amine solution (36, 37. This is due to massive exothermic absorption of CO 2 in MEA solution (13, 15, 38, 39. This work contributes to understanding and evaluation of enthalpy change during CO 2 capture processes. The rise in

3 EFFECT OF ENTHALPY OF LIQUID AND VAPOR PHASES FOR CO 2 ABSORPTION 1327 TABLE 1 Summary of models presented in literature along with their deviation from experimental data Amine Model used parameter Deviation MEA Rate based model Amine loading CO 2 loading 10% (3 MEA VLE model Cyclic capacity 10% (36 MEA Pro-Treat software Reboiler duty 11% (12 MEA NLP mathematical model Temperature 3% (37 MEA mathematical model CO 2 loading 28% (1 MEA Kent Eisenberg Model (HYSYS CO 2 loading 3% This work Packing Data TABLE 2 Column Internals and packing details (1 Sulzer DX Surface area (m 2 /m Void fraction Packed column data Diameter m Number of packing elements 17 Element length m enthalpy of the absorption column and evaporation of water from the amine stream (to reduce the temperature of the liquid stream in the lower section is the focus in this study. It is necessary to investigate the evaporation and condensation effect of water and the amount of water that escapes from the top of the absorption column along with the sweet gas. EXPERIMENTAL DATA AND SIMULATION DETAILS Experimental data for simulation of the CO 2 absorption process in MEA solution is taken from the experiment reported in the literature (1 and details of the packed column are presented in Table 2.TheCO 2 absorption process in MEA solution is investigated in an absorption column containing Sulzer DX as packing. Structured packing has superior absorption performance as compared to random packing (40, 41. Table 2 presents details of absorption column internals and packing specifications used in this paper. The Kent-Eisenberg vaporliquid equilibrium model available in HYSYS is used in this study (42, 43. The CO 2 absorption process is associated with evaporation of water, which occurs in non-ideal conditions. Therefore, the absorption column is simulated in non-ideal conditions. Experimental results reported in the table are used to validate the model used in this paper, and the model used validated the experimental results with high accuracy (1. Table 3 show operational conditions for the CO 2 absorption experiment used in this study. The absorption column is Operational Conditions TABLE 3 Operating conditions for the process Sour gas flow rate (kmol m 2 h Lean amine solution flow rate (m 3 m 2 h MEA concentration (kmol/m CO 2 concentration in the sour gas (mole % Temperature (K TABLE 4 CO 2 Absorption in MEA solution in a Sulzer DX Packed column Sampling point Experimental run (1 Simulation results 0.00 m (GasIn m m m m operated at low liquid and gas flow rates due to the smaller diameter of the column (0.028 m. However, the height of the column is 1 m, which increases the height to diameter ratio for the column to ensure proper gas absorption. Amine concentration in the liquid phase is in the range of kmol/m 3. Similarly CO 2 concentration in sour gas is varied in the range of mole% with the operating temperature ranging from 298 K to 310 K. A large absorption column with small diameter is used (in the experimental setup to study CO 2 absorption in MEA aqueous amine solution. A controlled mixture of CO 2 and air enters into the packed absorption column from the bottom of the column and rises in the column while the amine solution enters from the top of the column and flows downwards. All the experiments were conducted in a batch mode where amine is pumped from the lean amine tank using an electrical pump. During the

4 1328 H. RASHID, N. HASAN, AND M. I. M. NOR = v L z N R R H ( Ni i V a H u ρ L c pl ρ L c pl + ha u ρ L c pl (T G T L (5 = v G z + ha u (T G T L (6 ρ G c pg FIG. 1. Systematic diagram for CO 2 absorption process in amine solution [1]. course of CO 2 absorption, an infra-red gas analyzer is used to measure CO 2 concentration in the gas phase. Fig 1 shows the systematic diagram of the packed absorption column. The CO 2 absorption process was carried out in the absorption column, and experimental results for this run are listed in Table 4. Simulated results are obtained by solving the CO 2 absorption process using the Kent-Eisenberg model. Details of total mass balance for liquid and gas phase in CO 2 absorption process are given in Appendix A. However, the total mass balance for gas and the liquid phases is shown in Eq. (1 and Eq. (2: F L F G = v L F L z + v LS ρ L (Mi.N i (1 = v G F G z + v GS ρ G (Mi N i (2 Component balance for the components in liquid and gas phase is given by the equations shown below: Equations (5 and (6 represent heat balance for liquid and gas phases. The reaction rate for the CO 2 absorption process is calculated using the correlation given below: R CO2 ( = k jk0 T n exp E N C α i i (7 RT i=1 K jk0 (m 3 /mol.s is pre-exponential function, E (J/mol is activation energy, and C (mol/m 3 is concentration. All these terms are to be specified based on the physical properties of the CO 2 absorption process. RESULTS AND DISCUSSION Simulated results for the CO 2 absorption process are shown in Fig. 2. Simulated results are in good agreement with the experimental data. A detailed mathematical model was used by David et al. (1 to simulate the CO 2 capture process but the simulated curve for his work is not in line with the experimental C i L = v L C i L z + (a u N i + R j (3 C i G = v G C i G z + (a u N i (4 C i in Eq. (3 and Eq. (4 represents the concentration of any component i. Energy balance for CO 2 absorption is discussed in detail in Appendix A. Modified energy balance equations for liquid and gas phase are shown below: FIG. 2. Validation of the model used against the experimental data for the experiment performed by David et al. [1]. Height of the column in this validation is up to 1 m whereas David et al. studied for 2.4 m high absorption column.

5 EFFECT OF ENTHALPY OF LIQUID AND VAPOR PHASES FOR CO 2 ABSORPTION 1329 result reported here. Therefore, the model used in this study is quite able to predict the experimental behavior for the CO 2 absorption process. When the gas enters into the absorption column below the packing section of the column (at 0.12 m from the base of the column, it contains a high concentration of CO 2. When gas enters into the packing section (with high CO 2 concentration, it comes in direct contact with the amine solution flowing in the opposite direction. Here, most of the CO 2 is diffused and absorbed in the amine solution. Most of the CO 2 is already transferred (absorbed into the amine solution as the gas rises in the column. Therefore, CO 2 absorption becomes slow in the upper part of the column (from 0.8 to 1 m. The sweet gas stream leaving the column has much lower amount (0.3 mole% of CO 2 as compared to the inlet gas stream (14.23 mole% of CO 2. More CO 2 separation (less than 0.1 mole% of CO 2 in the gas stream can be achieved by increasing the height of the column. Fig 3 shows the change in enthalpy of the vapor phase in the absorption column at different operating temperatures (298 K to 310 K. It is observed that there is a rise in enthalpy of the vapor phase in the lower section (0.3 m from the bottom of the column, which is due to exothermic absorption of CO 2 in amine solution (heat of absorption kj/mol of CO 2 at 313 K (44. When most of the CO 2 is absorbed in the amine solution then the enthalpy of the gas stream starts to decrease (from 9157 kj/kgmol to 8700 kj/kgmol at 298 K gradually, and water starts to condense back to the liquid phase. Evaporation of water from the liquid stream to the gas stream reduces the overall enthalpy of the system to 8700 kj/kgmol at 298 K (28, 45, 46. However, at high temperatures the enthalpy of the vapor phase is always higher than at relatively low temperatures because at high temperatures, enthalpy of the liquid and gas stream is already high. This trend shows that most of the gas is absorbed into the amine solution when it enters into the column because of the high MEA reaction rate as calculated from Eq. (7. Note that the reaction rate depends upon the amine (MEA concentration and temperature of the system. Similar trends are also reported in other publications (1, 4, 47. Increase in enthalpy (9180 kj/kgmol at 298 K of the system is due to exothermic absorption of CO 2 in amine solution (44. However, decrease in enthalpy of liquid and gas streams (from 1957 kj/kgmol to 8700 kj/kgmol in the vapor phase at 298 K is due to condensation/evaporation of water (36, 37, 48. Fig 4 shows water mole% in vapor (gas stream in the absorption column. With an increase in enthalpy of the system, water evaporation also increases because the evaporation process is temperature sensitive (6 mole% in the gas stream at 0.3 m from the bottom of the column to 0.3 mole% in the gas phase at 1.6 m from the bottom of the column. At high enthalpy (9600 kj/kgmol at 310 K, water evaporation is high (11.6 mole% water in the vapor phase and more CO 2 is transferred from the gas stream into the vapor phase (30, 49, 50. This continues until there is exothermic absorption in the amine solution (enthalpy of the vapor phase increases from 9500 kj/kgmol at 0.12 m from the bottom of the column and increases up to 9600 kj/kgmol at 0.3 m and then decreases to 9157 kj/kgmol at the top of the column at 310 K. Maximum evaporation rate for both water (6 mole% in the vapor phase and MEA (0.005 mole% in the vapor phase is achieved when most of the CO 2 is absorbed in the amine solution, and enthalpy of the system has reached its maximum value (at 0.3 m from FIG. 3. Enthalpy of vapor phase along the column for different process temperature. FIG. 4. Water mole% in vapor phase along the absorption column at different operating temperatures.

6 1330 H. RASHID, N. HASAN, AND M. I. M. NOR FIG. 5. Water mole% in vapor phase for different MEA concentration in amine solution and CO 2 mole% in flue gas (T= 310 K. the bottom of the column. After this point, there is a decrease in enthalpy of the liquid and gas phases (from 9600 kj/kgmol to 9157 kj/kgmol and the water evaporation process becomes slow. Water mole% in the gas phase decreases as the gas moves up in the column and interacts with the amine solution flowing down from the top of the column. However, there is a considerable amount of water vapor in the gas phase (6 mole% at 310 K when it leaves the absorption column, which shows a continuous evaporation process going on throughout the absorption column. At high temperature (310 K, loss in MEA concentration in liquid ( mole% in the vapor phase at 310 K is also high and is reported due to evaporation of MEA (49. Fig 5 shows water mole% in the vapor phase for different MEA concentrations in amine solution and CO 2 concentrations in the flue gas stream along the height of the column. From Fig. 5, there is a significant effect of MEA concentration on water vapors mole% in the sweet gas leaving the absorption column for the top of the column. With an increase in MEA concentration (from 1.5 to 3.5 kgmol/m 3 in amine solution, there is a decrease in water evaporation (from 3.09 mole% to 2.97 mole% water in the vapor phase. This is because the viscosity of the amine solution increases with increases in MEA concentration (16, 36, 37, 51. Increase of 31.4% in viscosity is reported for increasing the concentration of MEA in amine aqueous solution from 20 wt% to 30 wt% (51. However, there is a little change in water mole% in the sweet gas leaving from the top of the column, for different CO 2 concentrations in flue gas. For CO 2 concentrations in flue gas, there is an increase in enthalpy of the absorption column, but the enthalpy of the column will rapidly decrease (from 9600 to 9100 kj/kgmol at 310 K and water vapor will condense from the gas stream into the amine solution (from 11.6 to 6.5 mole% water in the vapor phase. FIG. 6. MEA mole% in vapor phase at different operating temperature. With the increase in operating temperature of the absorption column (from 298 to 310 K, the MEA evaporation process will also increase due to the low flash point of MEA (31. Fig 6 shows MEA mole% in the vapor phase for different operating temperatures. Evaporation of MEA (from 0 mole% as the amine solution enters the column from the top to mole% at 310 K from the liquid phase to the gas phase occurs due to the low flash point of MEA and high gas flow rate (31. Still, the reduction in MEA mole% is very low (almost at operating temperature of 298 K and below at the highest temperature (310 K. As the enthalpy of the absorption column rises more MEA vaporizes from the amine solution. However, MEA mole% in the vapor phase decreases with a decrease in temperature (due to incoming cold amine solution in the upper section of the column and most of the MEA condenses back to the liquid phase and a much lower amount of MEA leaves the absorption column along the gas stream (sweet gas. CONCLUSIONS This paper focuses on the behavior of vapor phase enthalpy along the height of the column for different operating temperatures. The Kent-Eisenberg vapor-liquid equilibrium model used in this paper is the most efficient model as it can validate the experimental data with less than 3% error. The finding of this research reveals that maximum CO 2 absorption into the amine solution occurs at the lower section of the column. Modeling the CO 2 absorption process in amine solution is quite complex and different process parameters are adjusted to predict this process accurately. This model can be used for simulating different industrial and pilot scale problems. Enthalpy of the system rises to a maximum value (up to 9600 kj/kgmol at 310 K which occurs at 0.30 m from the bottom of the column

7 EFFECT OF ENTHALPY OF LIQUID AND VAPOR PHASES FOR CO 2 ABSORPTION 1331 due to exothermic absorption of CO 2 into the amine solution. Enthalpy of the system starts to decrease gradually after this point (0.30 m as the gas rises further above in the column. The rise in enthalpy of the liquid stream also increases water and MEA evaporation. 6 mole% water and mole% MEA are present in the vapor phase at the highest overall enthalpy of the vapor phase 9600 KJ/kgmol at 298 K. Most of these vapors condense back to the liquid phase, thereby reducing loss in amine solution concentration. NOMENCLATURE a e effective mass-transfer area (m 2 /m 3 a u interfacial mass-transfer area (m 2 /m 3 C i molar concentration (mol/m 3 c p specific heat capacity (J/mol.K D i diffusivity of component i (m 2 /s E activation energy (J/mol ε hold-up (m 3 /m 3 R H reaction heat (J/mol V H vaporization/condensation heat (J/kmol F volumetric flow rate (m 3 /s h heat transfer coefficient (J/m 3 Ks K jk0 pre-exponential function (m 3 /mols k heat transfer coefficient (J/m 2 Ks M molecular weight (g/mol N interfacial molar flux (mol/m 2 s Re Reynolds number R j reaction rate of reaction j (mol/m 3 s s column s cross sectional area (m 2 S Source of heat in the system (J/m 3 s T temperature (K t time (s u velocity in x direction (m/s v velocity in y direction (m/s w velocity in z direction (m/s z axial column coordinates ρ density (kg/m 3 μ efficiency Subscript/Superscript vector G gas phase L liquid phase i CO 2, MEA and H 2 O j no. of stages in absorption column c heat transfer by convection v heat transfer by vaporization r heat of reaction FUNDING NH is thankful to the University of Malaya, Malaysia, for financial support through UMRG Grant Nos. RU and RP017A-13AET. REFERENCES 1. demontigny, D.; Paitoon Tontiwachwuthikul, A.A. (2006 Modelling the Performance of a CO2 Absorber Containing Structured Packing. Ind. Eng. Chem. Res., 45: Liu, K.T.Y.;Yuan, X.G.; Liu, C.J.; Guo, Q.C. (2006 Simulations of chemical absorption in pilot-scale and industrial-scale packed columns by computational mass transfer. Chemical Engineering Science, 261: Simon, L.L.; Graeme Puxty, Y.E.; Artanto, Y.; Hungerbuhler, K. (2011 Rate based modeling and validation of a carbon-dioxide pilot plant absorbtion column operating on monoethanolamine. Chemical Engineering Research and Design, 89: Henriques de Brito, M.; Menendez Bangerter, A.; Bomio, P.; Laso, M. (1994 Effective mass-transfer area in a pilot plant column equipped with structured packings and with ceramic rings. Ind. Eng. Chem. Res., 33(3: Idem, R.; Paitoon Tontiwachwuthikul, M.W.; Chakma, A.; Veawab, A.; Aroonwilas, A.; Gelowitz, D. (2006 Pilot plant studies of the co2 capture performance of aqueous mea and mixed MEA/MDEA solvents at the University of Regina CO2 capture technology development plant and the boundary dam CO2 capture demonstration plant. Ind. Eng. Chem. Res., : p Schumann-Olsenb, A.T. (2011 Obtaining optimum operation of CO2 absorption plants. Energy Procedia, 4: Muhammad, A., Rahmanian, N.; Pendyala, R. (2013 Flow Analysis of melted urea in a perforated rotating bucket. Applied Mechanics and Materials, 372: Muhammad, A.; Rahmanian, N.; Pendyala, R. (2013 Analysis of fluid flow of urea in a perforated rotating bucket single orifice case. Journal of Applied Sciences, 14(12: Yousaf, M. (2012 Ab initio study of optoelectronic properties of spinel Znal2o4 beyond Gga and Lda. International Journal of Modern Physics B, 26(32: Masood Yousaf, M.A.S.; Ahmad Radzi, M. I.; Rahnamaye Aliabad, H.A.; Sahar, M.R. (2013 An insight into the structural, electronic and transport characteristics of XIn2S4 (X = Zn, Hg thiospinels using a highly accurate all-electron FP-LAPW+Lo method. Chinese Physics Letter, 30(7: Yousaf, M.; Ahmed, M.A.S.R.; Alsardia, M.M.; Ahmad Radzi, M. I.; Shaari, A. (2012 An improved study of electronic band structure and optical parameters of X-phosphides (X=B, Al, Ga, In by modified Becke Johnson potential. Communications in Theoretical Physics, 58(5: Cousins, L.T.W., Feron, P.H.M. (2011 Preliminary analysis of process flow sheet modifications for energy efficient CO2 capture from flue gases using chemical absorption. Chemical Engineering Research and Design, 89: van Nierop, E.A.; Kurt, S.H.; House, Z.; Aziz, M.J. (2011 Effect of absorption enthalpy on temperature-swing CO2 separation process performance. Energy Procedia, 4: Mores, P.; Sergio Mussati, N.S. (2011 Post-combustion CO2 capture process: Equilibrium stage mathematical model of the chemical absorption of CO2 into monoethanolamine (MEA aqueous solution. Chemical Engineering Research and Design, 89: Rochelle, H.M.K.A.G.T. (2008 Effects of the temperature bulge in CO2 absorption from flue gas by aqueous monoethanolamine. Ind. Eng. Chem. Res., 47: Tan, L.S. (2012 Removal of high concentration CO2 from natural gas at elevated pressure via absorption process in packed column. Journal of Natural Gas Chemistry, 21(1: Lawal, A.O.A.R.O.I. (2006 Kinetics of the oxidative degradation of CO2 loaded and concentrated aqueous MEA-MDEA blends during CO2 absorption from flue gas streams. Ind. Eng. Chem. Res., 45: Thu Nguyena, M.H.; Rochelle, G. (2011 Volatility of aqueous amines in CO2 capture. Energy Procedia, 4: Nattawan Kladkaew, R.I.; Tontiwachwuthikul, P.; Saiwan, C. (2009 Corrosion behavior of carbon steel in the monoethanolamine-h2o-co2- O2-SO2 system: Products, reaction pathways, and kinetics. Ind. Eng. Chem. Res., 48:

8 1332 H. RASHID, N. HASAN, AND M. I. M. NOR 20. Zoghia, A.T.; Saeed Zarrinpashneh, F.F. (2012 Experimental investigation on the effect of addition of amine activators to aqueous solutions of N-methyldiethanolamine on the rate of carbon dioxide absorption. International Journal of Greenhouse Gas Control, 7: Graeme Puxty, R.R. (2012 Modeling CO2 Mass Transfer in Amine Mixtures: PZ-AMP and PZ-MDEA. American Chemical Society, 45: Mohamed Edali, A.A.; Idem, R. (2009 Kinetics of carbon dioxide absorption into mixed aqueous solutions of MDEA and MEA using a laminar jet apparatus and a numerically solved 2D absorption rate/ kinetics model. International Journal of Greenhouse Gas Control, 3: Schäffer, K.B.A.; Scheffknecht, G. (2012 Comparative study on differently concentrated aqueous solutions of MEA and TETA for CO2 capture from flue gases. Fuel, 101: Zhu, D.;M.F.; Lv, Z.; Wang, Z.; Luo, Z.; (2012 Selection of blended solvents for CO2 absorption from coal-fired flue gas. Part 1: Monoethanolamine (MEA-based solvents. Energy Fuels, 26: Immanuel Raj Soosaiprakasam, A.V. (2009 Corrosion inhibition performance of copper carbonate in MEA-CO2 capture unit. Energy Procedia 1; pp In-Young Lee, J.H.L.; Kim, J.-H (2011 Effect of corrosion inhabitor on oxidation of MEA in carbon dioxide capture. Journal of Chemical Engineering of Japan, 44: Kladkaew, N. (2011 Studies on corrosion and corrosion inhibitors for amine based solvents for CO2 absorption from power plant flue gases containing CO2, O2 and SO2. Energy Procedia, 4: Ana-Maria Cormos, J.G. (2012 Assessment of mass transfer and hydraulic aspects of CO2 absorption in packed columns. International Journal of Greenhouse Gas Control, 6: ZareNezhad, B. H. N. (2009 An extractive distillation technique for producing CO2 enriched injection gas in enhanced oil recovery (EOR fields. Energy Conversion and Management, 50(6: Harith Rashid, N.H. (2012 Temperature profile and temperature peak analysis in absorption column for CO2 absorption/desorption process at different operating conditions. Green Chemistry. 31. Jozsef Gaspar, A.M.C. (2012 Dynamic modeling and absorption capacity assessment of CO2 capture process. International Journal of Greenhouse Gas Control, 8: p Švandová, J.M.Z.; Jelemenský, L. (2008 Impact of mass transfer coefficient correlations on prediction of reactive distillation column behaviour. Chemical Engineering Journal, 140(1 3: Al-Baghli, N.A. (2001 A rate-based model for the design of gas absorbers for the removal of CO2 and H2S using aqueous solutions of MEA and DEA. Fluid Phase Equilibria, 185(1 2: Krishna, R.W. (1997 The Maxwell-Stefan approach to mass transfer. Chem. Eng. Sci., 52: Yokoyama, T. (2004 Japanese R&D on Large-Scale CO2 Capture. ECI Conference on Separations Technology VI: New Perspectives on Very Large-Scale Operations, Fraser Island, Australia. 36. Aroonwilas, A. (2008 Performance of spray column for CO2 capture application. Ind. Eng. Chem. Res., 47: Jeffery Kuntz, A.A. (2009 Mass-transfer efficiency of a spray column for CO2 capture by MEA. Energy Procedia, 1(1: Billet, R.; Schultes, M. (1999 Prediction of mass transfer columns with dumped and arranged packings: Updated summary of the calculation method of Billet and Schultes. Chem. Eng. Res. Des., 77(6: Penny, D.E.; Ritter, T.J. (1983 Kinetic study of the reaction between carbon dioxide and primary amines. Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases, 79(9: Aroonwilas, A. (1997 High efficiency structured packing for CO2 separation using 2-amino-2-methyl-1-propanol (AMP. Separation and Purification Technology, 12: Aroonwilas, A.; Veawab, A.; Tontiwachwuthikul, P. (1999 Behavior of the mass-transfer coefficient of structured packings in CO2 absorbers with chemical reactions. Industrial & Engineering Chemistry Research, 38(5: Kent, R.; Eisenberg, B. (1976 Better data for amine treating. Hydrocarbon Process, 55(2: Haji-Sulaiman, M.Z. (1998 Analysis of equilibrium data of CO2 in aqueous solutions of diethanolamine (DEA, methyldiethanolamine (MDEA and their mixtures using the modified Kent Eisenberg model. Trans IChemE. 76(Part A. 44. Svendsen, I.K. (2007 Heat of absorption of carbon dioxide (CO2 in monoethanolamine (MEA and 2-(Aminoethylethanolamine (AEEA solutions. Ind. Eng. Chem. Res., 46: Chechet Biliyoka, A.L.; Wanga, M.; Seibertc, F. (2012 Dynamic modelling, validation and analysis of post-combustion chemical absorption CO2 capture plant. International Journal of Greenhouse Gas Control, 9: Rashid, H.; Hasan, N.; Iskandar, M.; Nor, M. (2014 Temperature peak analysis and its effect on absorption column for CO2 capture process at different operating conditions. Chemical Product and Process Modeling. DOI: /cppm Onda, K.T.; Okumoto, Y. (1968 Mass Transfer coefficients between gas and liquid phases in packed columns. J. Chem. Eng. Jpn, 1(1: Khan, F.M.; Mahmud, T. (2011 Modelling reactive absorption of CO2 in packed columns for post-combustion carbon capture applications. chemical engineering research and design. 89: Abu-Zahra, M.R.M. (2007 CO2 capture from power plants: Part I. A parametric study of the technical performance based on monoethanolamine. International Journal of Greenhouse Gas Control, 1(1: Desideri, U.; Paolucci, A. (1999 Performance modelling of a carbon dioxide removal system for power plants. Energy Conversion and Management, 40(18: Amundsen, T.G.; Eimer, D.A. (2009 Density and viscosity of monoethanolamine + water + carbon dioxide from (25 to 80 C. J. Chem. Eng. Data, 54: Patricia Mores, A.; Sergio Mussati, N.S.A. (2012 CO2 capture using monoethanolamine (MEA aqueous solution: Modeling and optimization of the solvent regeneration and CO2 desorption process. Energy Procedia, 45: APPENDIX A Mass Transfer Area Equation (8 represents the correlation for calculating the mass transfer area in the column (52. a e a u = 0.456Re 0.3 L (8 where a e (m 2 /m 3 and a u (m 2 /m 3 are effective mass-transfer area and interfacial area of the packing used, respectively. Re is the Reynolds number of liquid. This expression is used to calculate the interfacial area. The Heat Balance Equation in the Liquid Phase is given as: ρ L c p,l = ( x x ρ Lc p,l u x,l T L + ( y y ρ Lc p,l v y,l T L + z ( z ρ Lc p,l w z,l T L + S This is a three-dimensional energy transfer equation, which is used for heat balance of different process. ρ L is the density of liquid, c p,l is the specific heat of the liquid phase, u x,l (9

9 EFFECT OF ENTHALPY OF LIQUID AND VAPOR PHASES FOR CO 2 ABSORPTION 1333 is the velocity in x-direction, v y,l is the velocity of liquid in y-direction, and w z,l is the velocity of liquid in z-direction and T L is temperature of the liquid phase. The unit for the left hand side of the above equation is calculated out to be W/m 3. Therefore, to make the units consistent, all the terms in 9 should have the same units including the source term S. the source term includes S c,l, for heat transfer through convection in the liquid phase, S r,l, heat of reaction, and S v,l, for heat of vaporization or condensation. Therefore, the modified form of Eq. (9 becomes: ρ L c p,l = ( x x ρ Lc p,l u x,l T L + ( y y ρ Lc p,l v y,l T L + ( z z ρ Lc p,l w z,l T L + S c,l + S r,l + S v,l (10 It is important to note that the unit of all the terms in Eq. (10 should be equal to W/m 3. For 1D analysis, Eq. (10 can be reduced to the following form: ρ L c p,l = z ( z ρ Lc p,l u z,l T L + S c,l + S r,l + S v,l (11 According to law, heat transfer by convection is given as: S c,l = ha u (T G T L (12 where h (W/m 2.K is the heat transfer coefficient, a u (m 2 /m 3 is interfacial area, and T G and T L represent the temperature for the liquid and the gas phase, respectively. However, the heat of reaction for CO 2 absorption in aqueous amine solution is generalized with the standard expression for exothermic heat of reaction as: S r,l = (N R R H (13 where the minus sign in Eq. (13 represents exothermic reaction between CO 2 and MEA. N R (mol/m 3.s is the number of reactants, reacting per second and R H is the heat of reaction in J/mol. Similarly, the expression for heat of vaporization or condensation for all the components is given below: S v,l = a u (N v H (14 where a u (m 2 /m 3 represents interfacial area between liquid and gas as vaporization and condensation takes place on the interface, N (mol/m 2 s is molar flux and v,i H(J/mol represent heat of vaporization or condensation. However, there are three components such as CO 2,MEA,andH 2 O. So, Eq. (14 is modified as a sum of all the components as: S v,l = a u ( Ni v,i H (15 Heat of vaporization for all the components is summarized in Eq.(15.Now,Eq.(11 can be modified by adding all the terms for heat transfer and also neglecting K L for the liquid phase as it value is very less in this case. Therefore, the heat balance for the liquid phase can be modified dividing both sides with ρ L c p,l to separate the temperature and the new form of the equation is given as: = u z,l z + ha ( u NR R H (T G T L ρ L c p,l ρ L c p,l a u. ( (16 N i v,i H ρ L c p,l Equation (16 is the expression for heat balance in the liquid phase. Heat Balance in Gas Phase: Heat balance in gas phase is obtained by changing Eq. (10 as: ρ G c p,g = ( k G x x ρ Gc p,g u x,g T G + ( k G y y ρ Gc p,g v y,g T G + ( k G z z ρ Gc p,g w z,g T G + S c,g + S r,g + S v,g (17 For the gas phase, there is no vaporization so, S v,l =0 and it is also assumed that there is no reaction taking place in the gas phase, S r,l =0. Similarly, K G for gas phase is very low so, it is also neglected in heat balance expression for gas phase. Equation (17 is modified by these assumptions into Eq. (18 as: ρ G c p,g = ρ G c p,g u z,g z + S c,g (18 Now, heat transfer by convection in gas phase is given as: S c,g = ha u (T L T G (19 Equation (18 is modified by adding the term for convective heat transfer from Eq. (19 and dividing both sides of the

10 1334 H. RASHID, N. HASAN, AND M. I. M. NOR equation with ρ L c p,l to get the equation with temperature term as: = u z,g z + ha u (T L T G (20 ρ G c p,g Equation (20 is heat balance equation for gas phase in CO 2 absorption process. Stage Efficiency of Absorber For a vapor-liquid separation process, considering that both liquid and gas streams are interacting at the interface (52. Murphree s plate efficiency for component i on stage j of the column is given as: η M = y i,j y i,j+1 y i,j y i,j+1 (21 Equation (21 represents Murphree s plate efficiency for equilibrium stage. However, for non-equilibrium stage, gas flow rate F G is introduced into the correlation for Murphree s plate efficiency. So, Eq. (21 is modified in a new form as shown below: η j = F G,jy i,j F G,j+1 y i,j+1 F G.j y i,j F G,j+1 y i,j+1 (22 where y i,j in Eq. (22 represents the composition of molecular concentration of different components leaving the stage j at equilibrium. Liquid Loading Packing Factor for Gas and Liquid Liquid loading gas factor for liquid and gas streams represented as Gf z and Lf z (kg/m 2 s is calculated by using Eqs. (23 and (24 as shown below: ( Gf z = 986 (Fpd G ( ρ G z 0.5 ( ρ G z (23 ( ( ( μ Lf z = L L 0.1 z (24 ρ Fpd 1000 where G` and L` are gas and liquid mass velocity (kg/m 2 s, ρ G and ρ G (kg/m 3 are mass density for gas and liquid streams, and μ L is the viscosity of the liquid (kg/ms (52. Pressure Drop on Each Stage The total pressure drop for each stage along the column is calculated using Eq. (25 (52. P = z P z d z (25