Investigation of gas-solids flow characteristics in a pressurised circulating fluidised bed by experiment and simulation

Abstract

Pressurised circulating fluidised bed (PCFB) is a new technology for coal/biomass combustion and gasification. To design, optimise and scale-up of PCFBs, it is necessary to understand the complex gas-solids flow characteristics. In this research, electrical capacitance tomography (ECT) technique, pressure measurement, and computational particle fluid dynamic (CPFD) simulation were combined for the first time to investigate the hydrodynamic behaviour of a pilot-scale PCFB test rig. The custom single- and dual-plane ECT sensors in the riser bottom and cyclone dipleg, provided the real-time cross-sectional particle distribution and circulation flux in a non-intrusive way. Pressure measurements in low and high frequency, revealed the full-loop pressure distribution and local flow regime respectively. In addition, CPFD simulations based on Wen-Yu/Ergun and EMMS (energy-minimization multi-scale) drag model, were performed and evaluated by the experiments. The results demonstrate that (i) gas-solids flow in the PCFB riser shows the non-uniform distribution both axially and radially; (ii) EMMS based simulation predicts flow behaviour in agreement with the experiments, while Wen-Yu/Ergun model significantly over-estimates the particle dispersion and circulation flux; (iii) the elevated operating pressure enhances the gas-solids mixing, by demonstrating the more uniform particles axial distribution and development of radial “core-annular” structure towards the riser bottom and (iv) the elevated operating pressure improves the particle circulation flux, with the improvement limited by the saturated carrying capacity of the PCFB test rig.