Computational Fluid Dynamics (CFD) and thermodynamic modeling can play a very significant role in the design optimization and scale -up of CFB reactors that are used for combustion, gasification, carbonation / calcination and other technological applications. In this frame the present study examines the Calcium Looping (CaL) process as a post combustionCO2 capture technology both by means of CFD and thermodynamic calculations. Regarding the CFD calculations, most of the important latest features that should be taken into consideration, when a circulating fluidized bed (CFB) is simulated via TFM, are presented. These include a) the full-loop simulation of the CFB carbonator including its returning system, b) the application of the advanced EMMS scheme for the calculation of the drag coefficient acting on the inert particles by the gas medium, since conventional drag schemes (such as Gidaspow’s) are considered of low accuracy and c) the Pitman -Schaeffer -Gray –Stiles yield criterion for the formulation of the stress tensor of granulates inside the recirculation system. As a reference case a scaled modelof USTUTT’s (Universitaet Stuttgart “USTUTT”, Germany) carbonator is used and the numerical results are compared with corresponding experimental data as far as the pressure distribution along the full-loop and the re –circulation flux from the Loop-Seal are concerned. On the other hand, thermodynamic tools are used for simulation of the total energy system, where the present CO2 capture technology is coupled with an existing power plant, estimating the impact of CO2 separation and compression on the net efficiency. On grounds of the lack of knowledge about the effectiveness of the CaL technology on lignite fired plants, the application of CaL process to the 330 MWe lignite fired power plant of Meliti (Florina, Greece) is investigated. The strong difference in moisture content between coal and lignite addresses us to some considerable changes at the CO2 capture block and its integration with the secondary steam cycle, in comparison to the corresponding studies that assume coal as fuel. Air Separation and CO2 purification units are as well simulated in detail. This study demonstrates the coupling of concepts such as a) lignite pre –drying, b) heat exchange between solid circulating streams and c) fine tuning of CO2 recirculation are capable for optimizing the CaL process in terms of CO2 capture and net efficiency for the case of lignite fired plants. Except for the development of sophisticated process and CFD models, the efficient coupling of these two technologies is investigated.
Keywords: CaL, EMMS, process simulation