Modeling and scale analysis of gaseous fuel reactors in chemical looping combustion systems

Abstract

This work investigates the up-scaling to commercial scale of chemical looping combustion (CLC); a next-generation technology for carbon capture and storage. Focus lies on the bottom bed, which is considered to be the critical region in up-scaling due to its large solids inventory combined with relatively inefficient gas-solids contact. Two CLC reactors of vastly different size (bench and utility scale) are studied in order to discern the difference in effects related to up-scaling. A 1-dimensional model is used in order to simulate the units studied. The model considers kinetics dependent on the degree of oxidation of the oxygen carrier and a population distribution of the oxygen carriers, whose mixing accounts for both convective and dispersive transport. The model is validated against bench scale data and applied to evaluate the performance of a 1000 MWth CLC fuel reactor using either syngas or methane as fuel. Using the model, sensitivity analyses are carried out to depict the effect on the fuel conversion of several parameters such as solids circulation, oxygen carrier reactivity, bed height and maximum bubble size allowed. It is shown that mass transfer of gas from bubbles to the emulsion phase represents a strongly limiting factor for fuel conversion in the bottom bed of utility scale fuel reactors