Calcium looping process simulation based on an advanced thermodynamic model combined with CFD analysis Konstantinos Atsonios a,b,⇑ , Myrto Zeneli b , Aristeidis Nikolopoulos a,b , Nikos Nikolopoulos b , Panagiotis Grammelis b , Emmanuel Kakaras a,b a Laboratory of Steam Boilers and Thermal Plants, National Technical University of Athens, Heroon Polytechniou 9, 15780 Athens, Greece b Centre for Research and Technology Hellas, Athens Gr-15310, Greece highlights  A new methodology for Ca-looping process simulation in a DFB is presented.  The process model was enhanced by data provided from the CFD analysis.  More accurate results are observed than using LK-model for flow calculations.  Carbonator: the specific heat density in the bottom is 22 times higher than upper.  Calciner: the CO 2 concentration follows almost linear trend along the bubbling bed. graphical abstract article info Article history: Received 4 April 2014 Received in revised form 6 March 2015 Accepted 8 March 2015 Available online 18 March 2015 Keywords: Calcium looping CO 2 capture Process model CFD ASPEN Plus™ abstract The current study presents a new methodology for the simulation of the Calcium Looping (CaL) process based on the coupling of CFD and advanced thermodynamic models. As a first step, CFD models for the two reactors, i.e. the carbonator and the calciner, of a pilot scale Dual Fluidized Bed system are developed and validated by comparing the numerical predictions with corresponding experimental data for pres- sure distribution, carbonator capture efficiency and sorbents regeneration in the calciner. For the car- bonator modeling, the Two-Fluid-Model (TFM) approach is combined with the advanced EMMS scheme in order to provide results with high accuracy, even for the difficult to model dense bottom zone of the riser. A similar approach is adopted for the calciner; numerical results indicate that CO 2 follows an almost linear trend along the bubbling bed height, while the bubbling formations might result in a reduced efficiency for the calcination reaction due to the entrapment of CO 2 bubbles inside the emulsion phase. Numerical results related mostly to the hydrodynamics of the reactors, such as the solids dis- tribution and residence time are then used as input parameters in a kinetics-based process algorithm. Process modeling simulations reveal the importance of splitting the carbonator riser into two distinct sections, i.e. the bottom zone with dense solid phase and the upper one (freeboard) with a more dilute solid concentration. The heat balance calculation for these two regions demonstrates a big gap between the heat flux density for the bottom zone (19.26 kW/m 2 ) and the freeboard (0.46 kW/m 2 ), which should http://dx.doi.org/10.1016/j.fuel.2015.03.014 0016-2361/Ó 2015 Elsevier Ltd. All rights reserved. Abbreviations: BFB, Bubbling Fluidized Bed; CaL, Calcium Looping; CCS, carbon capture and storage; CFB, Circulating Fluidized Bed; CFD, Computational Fluid Dynamics; CGSM, Changing Grain Size Model; CSTR, continuously stirred tank reactor; CV, Control Volume; DFB, Dual Fluidized Bed; EMMS, Energy Minimization Multi-Scale; FB, Fluidized Bed; KL, Kunii & Levenspiel model; NTCM, Numerical Tools Combining Methodology; RSTOIC, stoichiometric reactor; TFM, Two Fluid Model; TGA, thermogravimetric analysis; TSI, total solids inventory; UDF, User Defined Functions; VOF, Volume of Fluid method. ⇑ Corresponding author at: 52, Egialias str., Maroussi, Athens, Greece. Tel.: +30 211 1069508; fax: +30 211 1069501. E-mail address: atsonios@certh.gr (K. Atsonios). Fuel 153 (2015) 370–381 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel