Promotrice : Prof. Diane Thomas
Co-promoteur : Prof. Guy De Weireld
Nowadays, it is obvious that the reduction of carbon capture emissions is necessary to mitigate climate change. To this extent, this Ph.D. thesis focuses on carbon capture technologies using amine mixtures with an energy gain compared to reference process and being economically viable at the same time. The solvent investigated in this work is a mixture of a tertiary amine, N,NDiethylethanolamine (DEEA) and a diamine, N-Methyl-1,3-propanediamine (MAPA). In addition to the interesting absorption properties characterizing this mixture, the CO2 loaded solution of this blend can split into two liquid phases, one lean and one rich in CO2. Consequently, the two phases are separated based on differences in density and only the CO2-rich phase is sent to the regeneration column. Hence, significantly less energy is needed thanks to the reduction of the amount of the regenerated solution and to the high CO2 content of the loaded amine solution.
First, an overview about novel solvents used for CO2 capture was performed highlighting DEEA-MAPA mixture as a promising solvent. In addition to the demixing behavior, DEEA and MAPA blends are characterized with a high absorption rate, provided by the diamine (MAPA), and a high CO2 absorption capacity from the tertiary amine (DEEA). Moreover, reasonable amount of experimental data was available for the process modelling. Then, a complete modeling of the absorption-regeneration process using DEEA-MAPA mixture was developed. The methodology was based on determining the model’s parameters for the two subsystems first (DEEA-based and MAPA-based systems) and then for the global system DEEA-MAPA-H2O-CO2. Electrolyte NRTL thermodynamic model has been successfully developed. Density and viscosity models were also presented together with the reactions occurring in the system and their corresponding characteristics.
The developed model was validated trough experimental tests using UMONS micro-pilot unit and literature data from NTNU-SINTEF pilot campaign. After the modeling validation, a process simulation at industrial scale (with a flue gas from cement industry) was performed for 5M MEA reference case and for 5M DEEA-2M MAPA demixing mixture. With the stripper operating at 4 bar, an optimization of the process highlighted a regeneration energy gain of more than 40% compared to 5M MEA reference process.
Finally, a techno-economic assessment of the global process was performed through CAPEX and OPEX evaluations. The resulting global cost of CO2 capture using DEEA-MAPA demixing mixture was shown to be lower than the cost relative to MEA solvent with an estimated gain of 35%. This techno-economic evaluation showed a real interest and financial benefits related to the use of DEEA-MAPA demixing mixture.