Mathematical modeling and simulation of the performance of potassium glycinate in CO2 absorption in a packed-bed absorption column

Abstract

The aim of this research undertaking was to develop a mathematical model representation for the capture of CO2 using potassium glycinate as the absorption solvent. To this end, the study was subdivided into three major parts each designed to generate the requisite data for the subsequent stage. The three major parts of the study included the development of industrial process simulation to ascertain the emission data and characteristics of flue gas emanating from different industrial processes. The main processes under study were, Power Generation with particular emphasis on the Combined Cycle Gas Turbine setup, Natural Gas Pre-treatment, where the simulations were developed for gas dehydration, chilling and Natural Gas Liquid (NGL) recovery, and the Acid Gas Removal (AGR) Modules, Cement Manufacturing with emphasis on the Pyroprocessing stage and finally Iron and Steel Production, where simulations were built for such production stages as the Raw material Sintering, Pelletization, Coke Production, Pig Iron Production, and the Basic Oxygen Furnace setup. The emission data from each of these process industries were collected and used for the sizing of an absorption tower which then became the basis for the hydrodynamic solution. The Absorber model developed in Aspen Hysys based on the flowrates and CO2 partial pressures in each flue gas stream served as the template to generating a Computer Aided Design (CAD) version of the column as a flow channel facilitating the process of resolving the hydrodynamic solution. In the second section of the study, the hydrodynamic solution of the absorption model was solved based on the physicochemical properties of potassium glycinate particularly density and viscosity at 6M and 60 ºC after a thorough assessment of the flow behaviour dynamics of the solvent was performed and the results was contrasted with MEA which is the bench mark solvent in CO2 post combustion capture. The final phase of the study investigated the mass transfer with reaction aspect of the interaction of CO2 and potassium glycinate at varying CO2 concentrations to understand its impact on capture processes. The solution; based on a stated rate expression; −𝑟𝐶𝑂2 = 7.5 × 10−1 𝑒(−6.7×102 𝑇)𝐶𝑠 0.11 𝐶 𝐶𝑂2 1.14 reveal that the reaction rate of CO2 increases from 0.0022 kg/m³·s at 5% CO2 to 0.0027 kg/m³·s at 10% CO2, stabilizes at 0.0026 kg/m³·s at 15% CO2, and remains constant at 0.0027 kg/m³·s from 20% CO2 onwards. In contrast, potassium glycinate's reaction rate increases from 0.0058 kg/m³·s at 5% CO2 to 0.0068 kg/m³·s at 10% CO2, remains steady at 0.0068 kg/m³·s up to 20% CO2, and slightly rises to 0.0069 kg/m³·s at 30% and 40% CO2. The initial rise in CO2 reaction rates suggests enhanced efficiency with increasing CO2 concentration, while the plateau indicates a saturation point. Potassium glycinate shows improved absorption capacity and reaction efficiency up to a steady state, with minimal gains at higher concentrations. These trends imply that potassium glycinate remains effective across a broad range of CO2 concentrations, crucial for optimizing CO2 capture systems.