Page 155 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

132 Biomass Gasification, Pyrolysis and Torrefaction

Cold air
Cooled
Torrefield torrefied
Raw Dry
biomass biomass
biomass biomass
Cooler
Dryer Torrefier
Flue gass Warm air

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
Torrefaction reactor 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.