Conference Dates

May 22-27, 2016


The proper selection of the oxygen carrier and the correct design of the fuel reactor represent the main criticalities for the success of the chemical looping combustion (CLC) process for solid fuels. In a previous work (1) a two-stage fuel reactor (t-FR), consisting of two bubbling beds in series (bottom bed and top bed) (Fig. 1), has been proposed in order to overcome the limitations of a single-stage fuel reactor (poor char conversion, slip of unburnt volatiles, extensive elutriation of char fines). A mathematical model has been developed with the aim of assessing the performances of the two-stage fuel reactor varying operating conditions in comparison with a benchmark case consisting of a single-stage fuel reactor equipped with and without carbon stripper. The t-FR showed the best performances in terms of combustion efficiency, volatile matter and char conversion, carbon-to-CO2 conversion efficiency and loss of elutriated carbon for all the operating conditions investigated.

In the present work a further enhancement of the model has been developed in order to study the hydrodynamics of the proposed multiple interconnected fluidized beds (MIFB) system for the CLC of solid fuels. The modelled system consists of the two-stage fuel reactor, a riser (Air Reactor) and non-mechanical valves for the regulation of the solid circulation between the two reactors. The different parts are considered as separate blocks mutually interconnected (Fig. 1). The operation of the system has been simulated by considering chemical looping combustion of a bituminous coal with an oxygen carrier consisting of CuO supported on zirconia. The numerical simulation has been addressed to evaluate (at steady state) the solid circulation rate, the temperature and oxidation degree of solids and concentrations profiles of gaseous species at the exit of both air and fuel reactors, with the utilization of proper constitutive equations for each block. Specific attention has been paid to the fluid dynamic behaviour of the t-FR. Results of the CLC-MIFB system with the t-FR are presented and the effects on the feasibility of the process of a variation in operating conditions are commented.

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