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Partic. vol. 39 pp. 25-32 (August 2018)
doi: 10.1016/j.partic.2017.10.007

Effects of liquid feed rate and impeller rotation speed on heat transfer in a mechanically fluidized reactor

Dhiraj Kankariya, Cedric Briens*, Dominic Pjontek, Stefano Tacchino

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cbriens@uwo.ca

Highlights

    • Overall heat transfer was measured in a mechanically fluidized reactor of silica sand. • Enhancing bed aeration, via higher liquid injection, improved wall-to-bed transfer. • Larger particles had higher heat transfer, opposing conventional fluidized beds. • Alternating the impeller rotation direction considerably increased heat transfer.

Abstract

A mechanically fluidized reactor (MFR) is a novel and compact reactor used for biomass pyrolysis. Endothermic biomass pyrolysis requires heat provided from the wall of the MFR. Meanwhile, mixing with a vertical stirrer helps achieve effective heat transfer from the wall to the bed. Here, the heat transfer characteristics between the wall of a 1.0-L MFR and its bed of mechanically fluidized sand particles were studied. An induction heating system was used to heat the wall, while a vertical blade stirrer was used for mixing. Heat transfer measurements were carried out using silica sand particles, having three average Sauter mean diameters: 190, 300, and 600 μm. The overall wall-to-bed heat transfer coefficients were estimated using temperature measurements taken during continuous injection of water onto the fluidized bed. The overall heat transfer coefficient for bed temperatures of 500–700 °C increased as particle size increased or superficial velocity of the vaporized liquid increased. Effect of impeller rotation speed also was investigated. Typically, the overall heat transfer coefficient increased as rotation speed increased. The wall-to-bed heat transfer coefficients obtained in this study are comparable to estimates from traditional bubbling fluidized beds, even at vapor velocities below the minimum fluidization velocity.

Graphical abstract

Keywords

Mechanical fluidization; Induction heating; Impeller rotation; Heat transfer; Particle size