MATHEMATICAL MODELLING AND SIMULATION OF CO2 CAPTURE USING POTASSIUM GLYCINATE IN AN ABSORPTION COLUMN
As global industrialization accelerates, the demand for materials and energy, mostly derived from fossil fuels continues to rise. Despite advances in renewable technologies, emission scenarios indicate that a rapid shift away from fossil fuels is unlikely in the near future. Such a shift could disrupt the global economy and industrial infrastructure. Therefore, advanced CO2 capture technologies, particularly post combustion capture using amine solvents, are crucial, as they allow emissions to be controlled directly at the source. These technologies integrate smoothly with existing systems, enabling industries to remain productive while reducing their environmental impact.
To this end, a mathematical model for CO2 absorption into potassium glycinate (KGly), a non-toxic amino acid salt solution (AASs) as the absorption solvent has been developed. The study simulates four key point-source industrial CO2 generating processes – Power Generation, Natural Gas Treatment, Cement Production, and Iron and Steel Manufacturing, along with their associated subprocesses and auxiliary systems. This approach was employed to gather real-world qualitative emission data, which was subsequently used as input for modeling the absorption process.
The model was developed using a combination of empirical data obtained from an absorption performance study of KGly under varying conditions, including temperatures of 40, 50, 60, and 70 ºC, CO2 mole percentages of 5%, 10%, 15%, 20%, 30%, and 40%, and an operating pressure between 1bar (Sam, 2023). A preliminary simulation using MEA concentrations ranging from 2M to 6M was conducted to design an optimal absorber tower metrics for testing the new solvent, KGly. The study revealed that, under identical temperature and pressure conditions, the concentration of KGly played a major role in determining its physical absorptive capacity, unlike MEA. This effect was attributed to specific physicochemical properties of KGly, such as density and viscosity. Further analysis showed that at 60ºC, despite being closer to desorption conditions due to the operating pressure, the impact of KGly’s density and viscosity decreases to a level comparable to the ambient state of the benchmark solvent, MEA. Hence suggesting that, from a physical standpoint, the mass transfer resistance posed by both solvents is generally equivalent when considering the influence of temperature on certain flow properties as the turbulent dynamic viscosity, share rate, interfacial renewal and disintegration of stagnant zones. Therefore, the key factor that distinguishes KGly in terms of performance is its chemical reactivity.
For this reason, the zwitterionic mechanism proposed by Caplow in 1968 for AASs, and later reinforced by Crooks and Donnellan in 1989, was adopted. This mechanism, combined with an empirically derived rate model and the mathematical framework for the transport of concentrated species in a two-phase counter flow profile based on the k-epsilon turbulent model, was used to resolve the mass transfer with reaction effects under varying flue gas CO2 concentrations and optimal KGly performance conditions of 60ºC and 6M; the highest solvent concentration under which precipitation wasn’t observed. This study found that KGly’s absorption potential was limited at lower CO2 concentrations, with the lowest absorption performance observed at 5% mole CO2 composition. Its performance improved gradually until reaching 20%, after which the absorption rate plateaued up to 40% mole CO2, indicating that further CO2 concentration increase did not significantly impact the reaction kinetics. The plateau at 0.0068 kg/m³·s between 10% and 20% CO2 indicates that the reaction reaches a steady state, achieving its maximum rate under the given conditions.