Environmental Engineering Reference
In-Depth Information
Biomass
Rotating drum reactor
Screw conveyor reactor
Gases
Torrefied
biomass
Moving bed reactor
Multiple hearth reactor
Torbed reactor
FIGURE 12.4
Reactor configurations for torrefaction.
process. The biomass can be heated directly or indirectly with steam or flue gas. The
temperature and residence time can be controlled by varying the temperature of the
heat supplying medium and the rotational velocity, length, and angle of the drum.
Some residence time distribution generally is unavoidable, which may lead to a dis-
tribution in product quality. The tumbling of the relatively brittle torrefying material
results in a relatively large fraction of fines. Rotary drum reactors have a limited scal-
ability, necessitating a modular approach for higher capacities. Companies applying
this type of reactor include TSI (United States), Torr-Coal (the Netherlands), and
Andritz (Austria).
A
screw conveyor reactor
typically uses indirect heating of the biomass via the
outer reactor wall and possibly via a hollow screw, which limits the heat transfer rates
and makes scale-up difficult. Varying the screw speed can effectively control the res-
idence time of the biomass due to the (near) plug flow of the solids. The first com-
mercial torrefaction plant, operated in the 1980s by Pechiney in France, used a
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