Mathematical modeling of a two-stage fuel reactor for chemical looping combustion with oxygen uncoupling of solid fuels

The success of a Chemical Looping Combustion (CLC) process for solid fossil fuel combustion is critically affected by the performance of the oxygen carrier and by proper design and operation of the fuel reactor.In this study, a novel configuration of the fuel reactor for chemical looping combustion with oxygen uncoupling of solid fossil fuels is proposed. The configuration is based on a two-stage reactor with the aim of overcoming the main drawbacks of the single-stage design: limited conversion, slip of unburnt volatiles, extensive elutriation of char fines. The two stages of the configuration operate in series and accomplish different tasks. The bottom bed is mainly devoted to conversion of the char, taking advantage of the full oxidative power of the oxygen carrier coming from the air reactor. The top reactor exploits the residual oxidative power of the oxygen carrier to oxidize volatile matter and gasification products as well as the unconverted char issuing from the bottom bed.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. Two options were considered in the benchmark, depending on whether the single stage fuel reactor is or is not equipped with a carbon stripper at the exhaust. The operation of the fuel reactor has been simulated by considering chemical looping combustion of a bituminous coal with an oxygen carrier consisting of CuO supported on zirconia.