Torrefaction - Biomass Gasification, Pyrolysis and Torrefaction - page 132

Cold air

Cooled
torrefied
biomass

Torrefield
biomass

Raw
biomass

Dry
biomass

Cooler

Dryer Torrefier

Warm air

Flue gass

Oil burner

FIGURE 4.10 Schematic of a torrefaction system.

W' g ,T go

W f ,T o

W v W vl W g

Pre-drying

Evaporation X.W' g ,T go

Post-drying

Torrefaction

W air ,T' o

W t ,T t

Oil burner W oil ,T” o

W g ,T gi

FIGURE 4.11 A directly heated integrated torrefaction unit.

an example of a simple torrefaction plant where an oil burner provides the
energy required for the process. For further simplification, we assume that
the volatiles released during torrefaction are not utilized to reduce the oil
consumption.

Design Input
Figure 4.10 shows a schematic of a generic torrefaction unit, while
Figure 4.11 shows an integrated single shaft moving bed reactor that is
directly heated by hot oxygen-free flue gas. The heating medium, hot flue
gas, moves up through the biomass while heating it through gas

particle
convection. Fresh biomass drops from the top of the vertical reactor and des-
cends slowly through the reactor while undergoing different phases of the
process ( Figure 4.11 ). Biomass and the heating medium are thus in counter-
current mode.