Reaction kinetics for flowsheet modeling of chemical looping combustion in fluidized bed reactors

Start Page
1025
End Page
1032
Citation
12th International Conference on Fluidized Bed Technology, CFB 2017: 1025-1032 (2017-05)
Contribution to Conference
12th International Conference on Fluidized Bed Technology, CFB 2017  
Scopus ID
2-s2.0-85052335076
Chemical Looping Combustion (CLC) is an alternative combustion process for the separation of carbon dioxide during the conversion of fuels. The process itself may be carried out in a system of interconnected fluidized bed reactors with a solid oxygen carrying material is circulated between them. CLC reaction kinetics differ sharply from regular air-fired combustion in terms of gas concentrations inside the two reactors and that the oxygen is transported between those reactors by a solid oxygen carrier. Further, they are strongly dependent on the hydrodynamics inside the fluidized bed reactors. For a predictive simulation of CLC, reaction kinetics of the oxygen carrier's reduction and oxidation, as well the conversion of solid fuels has to be known. To keep complexity low, overall reactions schemes are mostly used to describe chemical reactions. Various research groups measured the reactivity of the oxygen carrier with TGA, neglecting the effects of fluidization on the chemical conversion. In this work, the lab scale bubbling bed facility (diameter = 53mm) at Hamburg University of Technology was used for experiments on the behavior of copper oxide carriers on the basis of Al2O3. The conversion behavior was modeled with solid reaction models proposed in the literature and checked which one fits best to the experimental data from the plant. Additionally, the solid fuel lignite was investigated with regard to the conversion behavior under CLC conditions inside the lab scale fluidized bed. The oxygen carrier's gas-phase reactions are hard to capture with the typical Arrhenius type reaction rates inside the fluidized bed reactor. It is shown that several competing reactions take place, which does not lead to steadily increasing reaction rates with higher temperatures. Devolatilization of lignite is fast compared to its gasification. The gasification of lignite could be tracked over a broad temperature and particle size spectrum and modeled with particle reaction models and Arrhenius type reaction rates.