Abstract
In a chemical looping combustor (CLC) system, the solid circulation rate (SCR) is a key parameter that determines the design, operating conditions and the overall efficiency of the system. In the present work, the gas-solid flow of a CLC cold flow model (10 kWth) has been simulated by the computational fluid dynamics-discrete element method (CFD-DEM). The results showed that the SCR at different locations of the system fluctuates with time with different amplitude, and the variation of SCR is periodically stable. The turbulent gas-solid flow regime in the air reactor was found to be the main mechanism driving the fluctuation of SCR and determined the fluctuation frequency and amplitude. The SCR increased with the flow rates of air/fuel reactors and loop seals, and the total solid inventory. Changes in operating conditions directly induced the change in the mass of solids that were entrained into the riser from the air reactor and how fast the solids were transported therein. A correlation was subsequently proposed to describe the SCR as a function of solid hold-up and gas flow velocity in the riser. The particle residence time decreased in a power law as the SCR increased. Reasonable agreements were obtained between simulations and experiments in terms of solid distribution, gas-solid flow patterns, pressure drop profiles and SCR. (c) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.