Solids motion and flow structures in fluidised beds are of significant importance to combustion, pyrolysis or gasification of solid fuels, especially considering that low density, coarse biomass particles need to be well-mixed in the bulk bed of mostly sand. PEPT (Positron Emission Particle Tracking) determined that the solids flow structure and the bubble patterns in a fluidized bed vary significantly with the size and density of materials being added to the bed, such as biomass particles. Three flow structures have been found for different size of bed material: a large size (>700μm) gives rise to a single large circulation cell within the whole bed, and particles move upwards at one side of the bed to the splash zone, and then return to the bed bottom along the opposite side of the bed, thus initiating a directed circulation pattern with good control of biomass mixing. In the range of 250-450 μm, mixing is mostly determined by wall solids moving inwards and travelling upwards in the centre of the bed to the splash zone, and then return to the bottom of the bed in an outer annulus. For smaller bed particles, not commonly used in biomass processes, the mixing mode is even more complex, with 3 distinct zones of motion determined. The bubbling pattern also varies with the particle size. The bubble size and velocity decrease with decreasing particle size. These patterns define the different modes of solid-gas contact and solid mixing, and delineate an optimum operating zone for thermal biomass treatment.
Salman AD, Hounslow MJ. Fluidized Bed Applications. Chem Eng Sci. 2007; 62(1-2): 1.
He Y, Lu H, Sun Q, Yang L, Zhao Y, Gidaspow D, Bouillard J. Hydrodynamics of gas–solid flow around immersed tubes in bubbling fluidized beds. Powder Technol. 2004;145;88–105.
Bokkers GA, van Sint Annaland M, Kuipers JAM. Mixing and segregation in a bidisperse gas–solid fluidised bed: a numerical and experimental study. Powder Technol. 2004; 140:176– 186.
Ding Y, Wang Z, Wen D, Ghadiri M, Fan X, Parker D. Solids behaviour in a gas–solid two-phase mixture flowing through a packed particle bed. Chem Eng Sci. 2005; 60: 5231-5239.
Ding YL, Wang Z, Wen D, Ghadiri M, Fan X, Parker D. Solids behaviour in a dilute gas–solid two-phase mixture flowing through monolith channels. Chem Eng Sci. 2006; 61:1561-1570.
Harris AT, Davidson JF, Thorpe RB. The prediction of particle cluster properties in the near wall region of a vertical riser. Powder Technol. 2002; 127:128-143.
Werther J. Measurement techniques in fluidized beds. Powder Technol. 1999; 102:15-36.
Chen RC, Fan LS. Particle image velocimetry for characterizing the flow structure in three-dimensional gas–liquid–solid fluidized beds. Chem. Eng. Sci. 1992; 47: 3615–3622.
Berkelmann KG, Renz U. Gas and solid flow in the freeboard of a fluidized bed combustor. Powder Technol. 1991; 68:271–280.
Ibsen CH, Helland E, Hjertager BH, Solberg T, Tadrist L, Occelli R. Comparison of multifluid and discrete particle modelling in numerical predictions of gas particle flow in circulating fluidised beds. Powder Technol. 2004; 149:29-41.
Burschka AC. Wandnahe Partikelbewegung und Wärmeübergang in Gas-Feststoffwirbelschichten, Dr.-Ing. thesis, University Erlangen-Nürnberg, 1993.
Takeuchi H, Hirama T. Flow visualization in the riser of a circulating fluidized bed, in: P. Basu, M. Horio, M. Hasatani (Eds.), Circulating Fluidized Bed Technology III, Pergamon, Oxford, 1991:177–182.
Li H, Xia Y, Tung Y, Kwauk M. Micro-visualization of two-phase structure in a fast fluidized bed, in: P. Basu, M. Horio, M. Hasatani (Eds.), Circulating Fluidized Bed Technology III, Pergamon, Oxford, 1991.
Hartholt GP, Hoffmann AC, Janssen LPBM. Visual observation of individual particles in fluidized beds, First Int. Particle Technology Forum, preprints, Denver, USA, 1994.
Parker D.J, Forster RN, Fowles P, Takhar PS. Positron emission particle tracking using the new Birmingham positron camera. Nucl Instr and Meth A. 2002; 477:540-545.
Parker DJ, Dijkstra AE, Martin TW, Seville JPK. Positron emission particle tracking studies of spherical particle motion in rotating drums. Chem Eng Sci.1997; 52:2011-2022.
Geldart, D., Baeyens, J., The design of distributors for gas-fluidised beds. Powder Technology.1985; 42 (1):7–78.
Fan X, Parker DJ, Yang Z, Seville JPK, Baeyens J. The Effect of Bed Materials on the Solid/bubble Motion in A Fluidised Bed, Chemical Engineering Science. 2008: 63:943-950.
Baeyens J, Geldart D, An investigation into slugging fluidized beds, Chemical Engineering Science. 1974; 29: 255–265.
Fan X, Yang Z, Parker DJ, Prediction of Bubble Behaviour in Fluidised Beds Based on Solid Motion and Flow Structure, Chemical Engineering Journal. 2008; 140: 358-369.
Fan X, Parker DJ, Smith MD. Labelling a single particle for positron emission particle tracking using direct activation and ion-exchange techniques. Nucl Instr and Meth A. 2006; 562:345-350.
Fan X, Parker DJ, Smith MD. Enhancing 18F uptake in a single particle for positron emission particle tracking through modification of solid surface chemistry. Nucl Instr and Meth A. 2006; 558:542-546.
Mostoufi N, Chaouki J. Flow structure of the solids in gas–solid fluidized beds. Chem Eng Sci. 2004; 59:4217 – 4227.
Howaed JR. Fluidized bed technology: Principle and applications. Adam Higer, Bristol and New York, 1989, 8-12.
Baeyens J, Geldart D, An investigation into slugging fluidized beds, Chemical Engineering Science. 1974: 29: 255–265.
Lim CN, Gilbertson MA, Harrison AJL, Bubble distribution and behaviour in bubbling fluidised beds, Chemical Engineering Science. 2007; 62: 56–69.
How to cite this article
Yang, Z. and Fan, X. (2010). 'Impact of Flow Structure on Solid-gas Contacting in Bubbling Fluidisation for Biomass Gasification and Combustion'. SET Proceedings, 9, pp. 1-8. https://doi.org/10.65582/set.2010.129
