Numerical Tools for a BFB Calciner Reactor: CFD and Thermodynamic Models

Calcium Looping (CaL) process has emerged over the past few years as a CO2 post-combustion capture technology. Based on the reaction between a Ca-based sorbent and CO2, an apparatus consisting of two interconnected fluidized bed reactors is utilized. Within the first reactor (carbonator) CO2 is captured by CaO sorbents in the form of CaCO3, while in the second reactor (calciner) CaCO3 is regenerated to form fresh CaO. Several CFD and thermodynamic models have been developed so far individually, mainly for the carbonator unit, in order to interpret the physical mechanisms taking place. The present work focuses on the presentation of a CFD model aiming at the successful simulation of the calciner unit. The applied CFD model covers the calcination reaction kinetics and drag force modeling; two reaction rates, based on Labiano and Marti nez theory, respectively, and two drag models, an homogeneous and an EMMS based model, are used and compared. The main objective of the CFD model is its validation against available experimental data, i.e. the calciner efficiency and CO2 mole fraction leaving the calciner, as derived by the University of Stuttgart for the case of a lab-scale bubbling reactor. As a further step, the CFD model results are used as an input in a coupled thermodynamic modeling approach, and a parametric investigation for the optimization of parameters, such as temperature and bed inventory, governing the operation of the whole cycle is performed. The developed model is expected to be a helpful tool for the scale–up of the calciner.

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