(647d) A Carbonate Absorption Process With Crystallization-Enabled High Pressure Stripping for Post-Combustion CO2 Capture: A Kinetic Study and Process Development for Bicarbonate Crystallization

A novel carbonate absorption process with high pressure stripping is currently being developed for post-combustion CO₂ capture at the University of Illinois. The process employs an aqueous solution of carbonate, such as K₂CO₃, as a solvent. Bicarbonate in the CO₂-rich absorber effluent is crystallized by cooling the solution from about 70 °C to 30-35 °C in a crystallizer. The resulting bicarbonate slurry is used for CO₂ stripping at a pressure of at least 10 bars. A preliminary techno-economic analysis indicates that the process has an overall energy penalty 30 – 40% lower than that of the bench mark monoethanolamine process, primarily due to lower stripping heat and CO₂ compression work requirements.

The phase transition of bicarbonate during cooling of the CO₂-rich solution is a key feature of the process. A kinetic study of bicarbonate crystallization has been carried out using a laboratory-scale mixed-suspension, mixed-product-removal (MSMPR) reactor. Parametric tests with respect to agitation rate, mean residence time, temperature, and super-saturation level were performed to evaluate their effects on kinetic rates such as crystal nucleation and growth rates. The results were fit to Mydlarz and Jones (1993) model. Empirical regression formulae were then developed to correlate kinetic rates and crystal dimension with process operating conditions. Based on model predictions, mass and energy balance calculations were conducted to predict the performance of a new design configuration employing multiple continuous stirred tank reactors (CSTR) for crystallizing bicarbonate in the proposed CO₂ capture process. This presentation will provide a summary of the kinetic study of KHCO₃ crystallization and its implications for the related process design.