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

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 mu m. 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 degrees 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. (C) 2018 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.