Carbonation kinetics of fly-ash-modified calcium-based sorbents for CO2 capture

Calcium looping technology is one of the most promising technologies for CO2 capture. Nevertheless, one of the major problems for this technology is the rapid decay in CO2 capture performance of calcium-based sorbents during the calcination/carbonation cycles. It is essential to improve the sorbents' CO2 capture capacity and maintain their long-term performance during the cycles, especially in a cost-effective and environmentally benign method for further development of the technology. Calcium-based sorbents modified with fly ash present great potential for enhancing CO2 capture capacity. Carbonation kinetics of the modified sorbents, an important factor for CO2 capture system design, is critical for exploring its application. The carbonation rate of the modified sorbents has been investigated and the main parameters such as activation energy and pre-exponential factor have been calculated. Logistic and Avrami fractional kinetics models show better fitting regression, as indicated with a high regression coefficient R-2 of 0.987-0.999. The models well describe the CO2 carbonation kinetics behavior of the modified sorbents, since they have considered the multi-step reaction mechanisms including film diffusion, intra-particle diffusion, and the interaction with active sites, and have an acceptable average relative error between calculated and experimental data, for example 0.618-6.39% and 4.24-5.39% for the modified sorbents at chemical-controlled reaction and diffusion-controlled reaction, respectively. Activation energy and pre-exponential factor at chemical-controlled reaction are E-1 = 15.019kJ/mol, k(01) = 5.940mol/(m(2)s) and E-2 = 12.252 kJ/mol, k(02) = 3.195mol/(m(2)s) for modified sorbents CaO/FA Hyd (50%AC) and CaO/PFA(cal)Hyd, respectively. (c) 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.