Experimental and kinetic investigations of double-effect oxygen carriers for chemical looping gasification

With the increasing demands on syngas quality during chemical looping gasification, investigations on oxygen carriers are becoming more and more significant. A new double-effect oxygen carrier is proposed to further promote the gasification process and capture the main by-product (CO2), which will improve the gasification rate and the quality of the syngas. Three kinds of Cu-Mn composite oxygen carriers modified by CaO with different content were prepared by mechanical mixing. The phase composition and surface morphology of the double-effect oxygen carriers before and after reactions were analyzed, which demonstrated the stability of reactions. Based on thermodynamic experiments, the double-effect oxygen carriers reacted in specific atmospheres to release O-2, adsorb CO2, desorb CO2 and absorb O-2. By changing the heating rate, reaction temperature and mass ratio of substances in the double-effect oxygen carrier, it can be concluded that increasing the heating rate can accelerate the reaction to some extent. The optimal temperature range for the double-effect oxygen carrier to release O-2 and adsorb CO2 is 700-800 degrees C. To obtain pure CO2, the optimal temperature range for O-2 absorption is 700-850 degrees C and for CO2 desorption is 850-950 degrees C. The addition of CaO can improve the O-2 release velocity and O-2 absorption velocity of the active phase of the double-effect oxygen carrier. The kinetic models of the O-2 release, CO2 adsorption, CO2 desorption and O-2 absorption reactions were established by the iso-conversional method. The O-2 release reaction conforms to the one-dimensional diffusion model; the CO2 adsorption reaction conforms to the chemical reaction model (n = 3); the CO2 desorption reaction conforms to the one-dimensional diffusion model; and the O-2 absorption reaction conforms to the spherical three-dimensional diffusion model.

Automated summary

With the increasing demands on syngas quality, investigations on oxygen carriers, such as the proposed double-effect oxygen carrier in this study, have become more significant. The experiments and kinetic models demonstrate the stability and effectiveness of the oxygen carrier in enhancing gasification rate and capturing CO2.