indirectly fired.
Dried wood feed will be transferred to the torrefaction reactor via airlock hoppers.
Heating takes place outside this reactor meaning the biomass being processed within this reactor is not in contact with combustion gases.
Since products of combustion are completely isolated from the product being processed, two heat transfer mechanisms take place. Heat transfer is by conduction between the solids and the wetted portion of the hot shell. In most applications the shell is heated to fairly high temperatures, so radiation between shell and solids also prevails.
Also, as these units are heated from the outside, the materials of construction must be capable of withstanding higher temperatures.
A gas collection system, will aid in the isolation of volatiles and the transfer of combustible gases to the burner.
To aid in efficient heat transfer, a screw will be incorporated into the reactor. This will cause mechanical movement of the dried wood chips through the torrefaction chamber.
After the torrefaction process, torrefied biomass will then be sent to the pyrolysis reactor, designed in the main design.
An illustration of the concept design of the torrefaction reactor is shown below:
69 Cool Exhaust
Hot Exhaust
Moist Wood Chips Drier Wood
Chips
Combustion gases indirectly heating wood chips
Burner
Airlock
Gas Collection System VOC, CO, H2
Steam
Hopper Hopper
Heat Exchange
Mechanically moving wood chips through torrefaction chamber
Kwaku Asiamah.
2011-02-02.
Department of Chemical & Biological
Engineering.
Drawing not to scale
FIGURE 3.10 (a): Concept design of torrefaction reactor.
Concept from [Lipinsky ES, Arcate JR, Reed TB (2002)].
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