Current research on CO2 absorption using MEA

https://doi.org/10.1016/j.desal.2015.08.004

“The current research on CO₂ absorption using MEA is mainly focused on the minimization of energy consumption during solvent regeneration [30], [34]. Le Moullec et al. [26] elaborated a thorough review based on patents and research articles on the process modifications of CO₂ absorption. Three main categories of research were highlighted with the corresponding sub-categories: 1) absorption enhancement: intercooled absorber, rich solvent recycle, interheated absorber, split flow arrangement, double loop absorber, flue gas compression and expansion; 2) heat integration: rich solvent splitting, rich solvent preheating, rich solvent flashing, parallel economizer arrangement, interheated stripper, heat integrated stripper, overhead condenser bypass, vacuum operated stripper, and multieffect stripper; and, 3) heat pump: lean vapor compression, rich vapor compression, integrated heat pump, stripper overhead compression, and multipressure stripper. This study concludes with the existance of a clear lack of pilot plant scale evaluation since most studies have been performed through process modeling. In addition, the energetic performance of the capture process is increased but at the expense of increasing their complexity and cost and reducing their operability.

Indeed, the MEA-based CO₂ capture process has been modeled intensively in the literature [40], [60], describing several operation strategies and control configurations that aim at a decrease in energy consumption during solvent regeneration. The liquid residence time in the reboiler was found to be the dominant factor in the response time of the system and there is a linear relationship among the optimal solvent rate, the energy flux to the reboiler and the boiler load [60]. The inlet flue gas flowrate presents also an important role in the number of unconstrained degrees of freedom and several operation regions for the process have been identified [40]. Arce et al. [2] showed that the application of dynamic optimisation approaches, such as model predictive control focused on the reboiler, to exploit the time-varying values of wholesale electricity and CO₂ prices can lead to significant savings in the operating costs associated with post-combustion CO₂ capture processes, reducing the operating cost by an average of approximately 4.66%, and in some cases by as much as 10%. Varying the lean solvent loading, or allowing CO₂ to accumulate in the circulating solvent (in sympathy with prevailing market prices for CO₂ and energy) was found to be a key to enhance the cost-optimality of the process.

Some studies are also developing technological modifications in the conventional process in order to minimize the energy consumption. For example, Jande et al. [22] coupled the CO₂ absorption–desorption system based on MEA with capacitive deionization (CDI) to minimize the hear duty requirement of the stripper. Before the carbon-rich MEA solution is sent to stripper for regeneration, it is concentrated using a CDI cell where ionic species are adsorbed at oppositely charged electrodes during the charging cycle, and an ion free solution is sent back to the absorber. Results indicated that 10–45% of the total energy supplied to the stripper can be conserved because of the high CO₂ loading of the solution. Integration of ultrasounds have also demonstrated an increase in the physical desorption rate and the desorption can be performed at temperatures below 80 °C [14].

García-Abuín et al. [15] developed two alternative processes to the desorption step consisting in removing a reaction product (mainly the bicarbonate ion) and the simultaneous amine deprotonation. Those processes (i.e., treatment of the carbon dioxide-rich amine with calcium hydroxide or with the use of an anionic exchange resin) showed an important decrease in the energy employed for the regeneration of the investigated tertiary amines (pyrrolidine—PYR, methyldiethanolamine—MDEA, triethanolamine—TEA and triisopropanolamine—TIPA).

Another example is the integration of solar-assisted post-combustion CO₂ capture into a power plant with amine-based chemical absorption for CO₂ capture [27], [59]. Solar thermal energy has the potential to support the thermal demand for CO₂ capture and the proposed integration has shown better performance than the conventional process with the limitation of the investment cost. However, due to the global magnitude of CO₂ capture, application of solar thermal energy can be considered a good strategy but its capacity is currently not large enough to cover all the energy requirements.

Thus, the conventional process can still be optimized and improved by modifying the operating conditions or by means of the integration of other emerging technologies.

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