Heat transfer in a tapered fluidized bed of biomass particles with pulsed gas flow--颗粒学报PARTICUOLOGY

Jia, D., Bi, X., Lim, C. J., Sokhansanj, S., & Tsutsumi, A. (2019). Heat transfer in a tapered fluidized bed of biomass particles with pulsed gas flow. Particuology, 42, 2-14. https://doi.org/10.1016/j.partic.2018.01.007

Heat transfer in a tapered fluidized bed of biomass particles with pulsed gas flow

Dening Jia ^a, Xiaotao Bi ^a *, C. Jim Lim ^a, Shahab Sokhansanj ^{a b}, Atsushi Tsutsumi ^c

a Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, BC, V6T 1Z3, Canada
b Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
c Collaborative Research Center for Energy Engineering, Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan

10.1016/j.partic.2018.01.007

Volume 42, February 2019, Pages 2-14

Received 16 October 2017, Revised 6 January 2018, Accepted 16 January 2018, Available online 28 May 2018, Version of Record 21 January 2019.

E-mail: xbi@chbe.ubc.ca

Highlights

• Biomass was successfully fluidized in a tapered fluidized bed with pulsed gas flow.

• Flow pattern varied from channeling, slugging to bubbling at different flow rates.

• Weak gas pulsations led to core-annulus flow that increased lateral segregation.

• Maximum heat transfer coefficient was found around the natural frequency of pulsed fluidized bed.

• Smaller biomass particles exhibited faster heat transfer and smoother fluidization.

Abstract

Bed-to-surface heat transfer of pure biomass particles in a pulsed fluidized bed with a tapered bottom section was investigated. Three biomass species — Douglas fir, pine, and switchgrass — were studied under various operating conditions. Their heat transfer coefficients were found to be closely associated with hydrodynamics dominated by gas pulsations. A higher superficial gas velocity generally yielded better gas–solid contact and higher heat transfer rates. A moderately increasing pulsation frequency promoted convective heat transfer of particles but also reduced pulsation intensity, leading to undesired flow behaviours such as channelling and partial defluidization. The study of the pulsation duty cycle revealed that, for cohesive particles, a smaller duty cycle was preferred to generate powerful pulsations to break up inter-particle forces. Moreover, a duty cycle increase allowed higher gas throughput as long as a suitable fluidization was maintained. The addition of finer particles to a coarse fraction increased particle mobility, and subsequently heat transfer, which also explained the higher heat transfer coefficients of switchgrass as it contained more fines compared with fir and pine. Experimental results in the tapered bed were also compared with those of non-tapered geometry where a 10%–20% increase in heat transfer was observed.

Graphical abstract

Keywords

Fluidized bed; Gas pulsations; Tapered column; Heat transfer; Biomass

文章导读