Investigation and Modelling of a Precipitation Absorber Using Concentrated Potassium Carbonate Solvents For Carbon Dioxide Capture

INVESTIGATION AND MODELLING OF A PRECIPITATION ABSORBER USING CONCENTRATED POTASSIUM CARBONATE SOLVENTS FOR CARBON DIOXIDE CAPTURE
Yue Wu, Kathryn Mumford, Geoff Stevens

As anthropogenic carbon dioxide (CO2) emissions are increasing, global warming has been drawing increased attention and concern across the world. This is particularly the case for countries and industries reliant on coal-fired power. One way to capture CO2 from the flue gas from coal-fired power plants is to use solvent absorption systems. In this project, a precipitating CO2 capture process using concentrated potassium carbonate (K2CO3) solvents is systematically investigated under post-combustion process conditions (approximately 1 bar and 20-60 °C) from three aspects: (1) thermodynamic properties of the solvent system; (2) precipitating kinetics; (3) process model (absorber) development.

Due to the strong electrolytes present in the concentrated K2CO3 solvent system, an electrolyte non-random two liquid (ENRTL) thermodynamic model is regressed through the Data Regression System (DRS) in Aspen Plus®. The model is successfully validated with experimental data, and used to predict the thermodynamic properties of the solvent system, such as CO2 partial pressure, precipitate solubility, CO2 reaction kinetics and CO2 diffusivity etc.

The precipitation kinetics of the concentrated K2CO3 solvent system including primary nucleation, secondary nucleation and crystal growth is comprehensively studied in an unseeded batch cooling crystalliser using a focused beam reflectance measurement (FBRM®) probe and OptimaxTM workstation 1001. The supersaturation of the precipitates, a primary driving force for precipitation kinetics, is evaluated from the regressed ENRTL model.

A process model using the concentrated K2CO3 solvent system, in the form of an equilibrium-based absorber and a rate-based absorber, is developed in Aspen Custom Modeller by integrating the regressed ENRTL thermodynamic model. The use of Aspen Custom Modeller is able to provide a flexible and convenient platform for the process model. The process model can be further improved via the introduction of promoters or can be transformed as a dynamic column to monitor the absorption performance in Aspen Custom Modeller.