Three-Dimensional Modelling on the Hydrodynamics of a Circulating Fluidised Bed

Abstract

The rapid depletion of oil and the environmental impact of combustion has motivated the search for clean combustion technologies. Fluidised bed combustion (FBC) technology works by suspending a fuel over a fast air inlet whilst sustaining the required temperatures. Using biomass or a mixture of coal/biomass as the fuel, FBC provides a low-carbon combustion technology whilst operating at low temperatures. Understanding the hydrodynamic processes in fluidised beds is essential as the flow behaviours causing heat distributions and mixing determine the combustion processes. The inlet velocities and different particle sizes influence the flow behaviour significantly, particularly on the transition from bubbling to fast fluidising regimes. Computational modelling has shown great advancement in its predictive capability and reliability over recent years. Whilst 3D modelling is preferred over 2D modelling, the majority of studies use 2D models for multiphase models due to computational cost consideration. In this paper, two-fluid modelling (TFM) is used to model a 3D circulating fluidised bed (CFB) initially focussing on fluid catalytic cracker (FCC) particles. The transition from bubbling to fast fluidisation over a range of velocities is explored, whilst the effects on the bubble diameter, particle distributions and bed expansion for different particle properties including particle sizes are compared. Drag models are also compared to study the effects of particle clustering at the meso-scale.

Study of wall-to-bed heat transfer in a bubbling fluidised bed using the kinetic theory of granular flow

“…The isothermal hydrodynamics of fluidised bed reactors has attracted a number of researchers for decades to understand the complex interactions between gas and particles [1][2][3][4][5][6][7].…”

“…For hydrodynamic [3][4][5]7,11] and heat transfer models [8][9][10], the Eulerian-Eulerian two-fluid model (TFM) is the most frequently applied method of modelling. The model assumes the gas-solid phases as continuous and fully interpenetrating within each control volume.…”

The influence of multiple tubes on the tube-to-bed heat transfer in a fluidised bed

“…The greatly increased computer performance and capabilities nowadays allow non-linear thermal-fluid dynamics in complex geometries under realistic conditions to be investigated in a non-invasive manner. Numerous studies on the isothermal hydrodynamics of fluidised bed reactors have been carried out to understand the complex interactions between gas and particles (Berruti et al, 1995;Ge and Li, 2003;Samuelsberg and Hjertager, 1995;Benyahia et al, 2000;Almuttahar and Taghipour, 2008;Goldschmidt et al, 2001;Armstrong et al, 2009Armstrong et al, , 2010a. Computational modelling of heattransfer in bubbling fluidised beds has also been performed (Kuipers et al, 1992;Renz, 1999, 2000;Patil et al, 2006;Armstrong et al, 2010b,c).…”