Modeling the impact of operating variables on ash agglomeration in chemical looping combustion of solid fuels

In this work, the influence of operating conditions on the rate of agglomeration in a chemical-looping combustion (CLC) fluidized bed reactor utilizing coal as fuel is modeled. The effect of the type of oxygen carrier, the composition of coal ash, temperature, gas velocity, and the ratio of the oxygen carrier to coal ash is investigated. In order to test the impact of each variable, an agglomeration model was developed. The model uses FactSage for thermodynamic simulations and MFiX for computational fluid dynamics simulations of the fluidized bed reactor. Inputs from both of these programs are used in the agglomeration model written Mathematica program, which calculates the number of two-particle collisions between particles of different sizes. Whether or not these particles stick together is determined by the Stokes criterion. The variables which affect the bed composition are the coal ash composition, the type of oxygen carrier, and the ratio of ash to oxygen carrier. It was found that the type of oxygen carrier had a significant impact on the rate of agglomeration. The composition of coal ash had a small impact on the rate of agglomeration between multiple bituminous coals, which were high in silica, but a much larger impact when compared to low silica lignite. The temperature had a moderate impact on the rate of agglomeration, and velocity had a very low impact. The ratio of ash to oxygen carrier had a high impact on the rate of agglomeration. These factors will be useful in determining safe operating conditions for a coal-based CLC system without resulting in bed defluidization.