The convection heat transfer coefficient in a Circulating Fluidized Bed (CFB)

Circulating Fluidized Beds are increasingly used in gas–solid and gas–catalytic reactions. A recent development involves their use in physical gas–solid processes such as drying, VOC adsorption or solar energy capture and storage. The heat transfer from the wall of the CFB to the flowing gas–solid suspension is the major design parameter, and was studied for different powders at different operating conditions as determined by the gas velocity and solids circulation flux. Measured values of the heat transfer coefficients are discussed, and compared with empirical predictions of Molodtsof–Muzyka, and Gorliz–Grace. Whereas Gorliz–Grace predicts heat transfer coefficients correctly within a narrow range of operating conditions only, the Molodtsof–Muzyka approach can be simplified into a linear relationship.

Graphical abstractExperimental results for selected powders, expressed as heat transfer coefficient, hm, versus G for different velocity ranges (given in m/s with each of the symbols): Powder 1(■ < 10 ⊞ 16–18 □ 18–20), Powder 2( 10–12 14–16 16–18 18–20), Powder 4( 14–16 16–18).•Heat transfer between a CFB-riser wall and bed is an important design factor.•Experimental heat transfer coefficients are discussed, and compared with empirical predictions.Figure optionsDownload full-size imageDownload as PowerPoint slideFigure optionsDownload full-size imageDownload as PowerPoint slideFigure optionsDownload full-size imageDownload as PowerPoint slideFigure optionsDownload full-size imageDownload as PowerPoint slideFigure optionsDownload full-size imageDownload as PowerPoint slideFigure optionsDownload full-size imageDownload as PowerPoint slideFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights•Circulating Fluidized Beds are increasingly used in gas–solid or gas–catalytic systems.•Heat transfer between riser wall and bed is an important design factor.•Measured values of the heat transfer coefficients are discussed, and compared with empirical predictions.