Research Papers: Energy From Biomass

Effects of Reactor Design on the Torrefaction of Biomass

[+] Author and Article Information
Animesh Dutta

Mechanical Engineering Department,
Dalhousie University,
P.O. Box 1000,
Halifax, NovaScotia, B3J 3X4, Canada

1Greenfield Research Incorporated, P.O. Box 25018, Halifax, Nova Scotia, B3M 4H4, Canada.

2University of Guelph, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada.

Contributed by the Advanced Energy Systems Division of ASME for publication in the Journal of Energy Resources Technology. Manuscript received May 30, 2011; final manuscript received August 21, 2012; published online October 19, 2012. Assoc. Editor: Gunnar Tamm.

J. Energy Resour. Technol 134(4), 041801 (Oct 19, 2012) (11 pages) doi:10.1115/1.4007484 History: Received May 30, 2011; Revised August 21, 2012

Torrefied biomass is a green alternative to coal, and thus the interest in the torrefaction process is rising fast. Different manufacturers are offering different patented designs of torrefier with data on varying operating and process conditions each claiming their superiority over others. The choice of torrefaction technology has become exceptionally difficult because of a near absence of a comparative assessment of different types of reactors on a common base. This work attempts to fill this important knowledge gap in torrefaction technology by reviewing available types of reactors, and comparing their torrefaction performance common basis and examining the commercial implication of reactor choice. After reviewing available patent and technologies offered, torrefiers are classified broadly under two generic groups: indirectly heated and directly heated. Four generic types of reactors, convective heating, fluidized bed, rotating drum and microwave reactor were studied in this research. Convective and fluidized beds have direct heating, rotating reactors has indirect heating while microwave involves a volumetric heating (a subgroup of direct heating) mechanism. A standard sample of biomass (25 mm diameter × 64 mm long poplar wood) was torrefied in each of these types of reactors under identical conditions. The mass yield, energy density and energy yield of the wood after torrefaction were measured and compared. Rotating drum achieved lowest mass yield but highest energy density. The difference between two direct heating, convective heating and fluidized beds was small. Microwave provided only localized torrefaction in this series of tests. Indirectly heated reactors might be suitable for a plant near the biomass source while directly heated plant would give better value at the user end.

Copyright © 2012 by ASME
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Fig. 1

Torrefaction reactor types

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Fig. 2

A schematic of the quartz wool type convective reactor

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Fig. 3

Schematic of the fluidized bed reactor used for torrefaction

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Fig. 4

Schematic of rotating drum arrangements. (a) Shows the arrangement of rotating drum inside the reactor and (b) shows the cross section of the drum.

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Fig. 5

Schematic diagram of microwave torrefaction

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Fig. 6

Mass yield of 25.4 mm diameter poplar cylinder torrefied at 250 °C for 60 min

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Fig. 7

Relative mass yield on different reactor types with respect to convective bed (legend refer to Table 3)

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Fig. 8

Effect of reactor type on energy yield of 25 mm diameter × 64 mm poplar cylinder (legends refer to Table 3)

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Fig. 9

Microwave torrefaction of a 25 mm diameter poplar wood (5.4% moisture) at 280 °C, (a) for 5 min, mass yield obtained 94% and (b) for 10 min, mass yield obtained 91.9%. The figure shows photograph the exterior of the cylinder after torrefaction and after splitting.

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Fig. 10

Mass and energy yield of individual 25 mm diameter cylinders torrefied at 280 °C in different reactors. Peak core temperatures of each samples are also plotted.



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