https://doi.org/10.1016/j.ijggc.2022.103597
“This study constructed an amine-based PCC model in Aspen Plus® as shown in Fig. 1. The model consists primarily of an absorber, a stripper, and a heat exchanger. In the absorber, amine solution flows down and absorbs CO2 from the countercurrent flow of combustion gas. The CO2-rich solution exiting the bottom of the absorber is sent to the top of the stripper. In the stripper, the solution is heated by the reboiler and desorbs CO2 along with some water vapor. Most of the water vapor is separated by the overhead condenser and pure gaseous CO2 is recovered. The CO2-lean solution leaving the bottom of the stripper preheats the CO2-rich solution from the absorber via a heat exchanger and returns to the top of the absorber.”
Fig. 1. Process flow diagram of the amine-based PCC simulation model in Aspen Plus®.
The absorber and the stripper were modelled with Aspen RatesepTM, a second-generation rate-based multistage separation unit operation model in Aspen Plus® Zhang et al., 2009). Table 2 summarizes the main specifications used in the RatesepTM model. Rate-based type calculations were used for both the absorber and stripper. The mass and heat transfer coefficients, interfacial area for gas-liquid contact, and the liquid hold-up were calculated by correlations listed in Table 2. With regard to chemical reactions, while chemical reactions in the stripper can be regarded as instantaneous and reach equilibrium due to high temperature (Van Wagener, 2011), some chemical reactions in the absorber must be considered as a kinetically controlled. Table 3 provides the kinetically controlled reactions and parameters added to the model. The reactions listed in Table 3 replace equilibrium chemical reactions with the same equation number. To calculate reaction rates, the power law expression of Eq. (14) was used for chemical reactions in which T0 is specified. When T0 is not specified, Eq. (15) was used instead. In Eqs. (14) and (15), rj is the reaction rate for reaction j in kmol∙m−3∙s−1, kj0 is the pre-exponential factor in m3∙kmol−1∙s−1 (molarity basis) or kmol∙m−3∙s−1(mole gamma basis), T is the system temperature in K, T0 is the reference temperature in K, Ej is the activation energy for reaction j in kJ∙kmol−1, R is the ideal gas constant in kJ∙kmol−1∙K−1, Ci is the molarity of species i in kmol∙m−3 (molarity basis) or the activity of species i (mole gamma basis), and aij is the reaction order of species i for reaction j.
Table 2. Calculation method for the absorber and the stripper.
| Empty Cell | Absorber | Stripper |
|---|---|---|
| Calculation type | Rate-based | Rate-based |
| Mass transfer coefficient method | Bravo et al. (1985) | Bravo et al. (1985) |
| Interfacial area method | Bravo et al. (1985) | Bravo et al. (1985) |
| Heat transfer coefficient method | Chilton and Colburn | Chilton and Colburn |
| Holdup correlation | Bravo et al. (1992) | Bravo et al. (1992) |
Table 3. Kinetically controlled reactions in the absorber and kinetic parameters.
| Num.*1 | Reaction | k0 | E kJ/kmol | T0 K | Ci basis | Source |
|---|---|---|---|---|---|---|
| 2f | CO2 + OH− –> HCO3− | 1.33 × 1017 | 5.547 × 104 | – | Mole gamma | (Aspen Technology, 2008a) |
| 2b | HCO3−–> CO2 + OH− | 6.63 × 1016 | 1.074 × 105 | – | Mole gamma | (Aspen Technology, 2008a) |
| 5f | PZ + CO2 + H2O –> PZCOO− + H3O+ | 5.37 × 104 | 3.36 × 104 | 298.15 | Molarity | (Bishnoi and Rochelle, 2000) |
| 5b | PZCOO− + H3O+–> PZ + CO2 + H2O | 2.490 × 109 | 7.022 × 104 | 298.15 | Molarity | *2 |
| 7f | PZCOO− + CO2 + H2O –> PZ(COO−)2 + H3O+ | 4.7 × 104 | 3.36 × 104 | 298.15 | Molarity | (Bishnoi and Rochelle, 2002) |
| 7b | PZ(COO−)2 + H3O+ –> PZCOO− + CO2 + H2O | 3.289 × 1010 | 5.1149 × 104 | 298.15 | Molarity | *3 |
| 9f | AMP + CO2 + H2O –> AMPCOO− + H3O+ | 1.94 × 1010 | 4.3 × 104 | – | Molarity | (Saha et al., 1995) |
| 9b | AMPCOO− + H3O+ –> AMP + CO2 + H2O | 6.811 × 1022 | 7.3341 × 104 | – | Molarity | *4 |
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*1 ‘f’ and ‘b’ mean forward and backward, respectively.
*2 Kinetic parameters determined from the reaction kinetics of 5f and the equilibrium constant of this reaction. The equilibrium constant of this reaction was obtained by the combination of equilibrium constants of following reactions: PZ carbamate formation (Ermatchkov et al., 2003), dissociation of water to proton and hydroxide ion (Edwards et al., 1978), dissociation of CO2 to bicarbonate ion (Edwards et al., 1978), and dissociation of water to oxonium ion and hydroxide ion (Posey and Rochelle, 1997).
*3 Kinetic parameters determined from the reaction kinetics of 7f and the equilibrium constant of this reaction. As with *2, the equilibrium constant of this reaction was obtained using the reaction equilibrium constant of PZ dicarbamate formation (Ermatchkov et al., 2003) instead of PZ carbamate formation.
*4 Kinetic parameters determined from the reaction kinetics of 9f and the equilibrium constant of this reaction. As with *2, the equilibrium constant of this reaction was obtained using the reaction equilibrium constant of AMP carbamate formation (Silkenbäumer et al., 1998) instead of PZ carbamate formation.
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