THERMOCHEMICAL CONVERSION: AN INTRODUCTION TO FAST PYROLYSIS - Biomass as a Sustainable Energy Source for the Future - page 370

O

HO

O

OH

O

HO
HO

O

Mass transfer
(main direction)

OH

OH

Vapors
Aerosols
Gases

5-20 μ m

Heat transfer
(main direction)

FIGURE 11.8 Schematic of the multilevel character of biomass pyrolysis (softwood is
shown) ranging from a single cavity (cells) to a wood particle. (Source: Reproduced from
Kersten and Garcia-Perez. Copyright (2013) with permission from Elsevier.)

TABLE 11.3 Bi, Py, and Py 0 classification scheme from
Pyle and Zaror (1984)

Py 0 Model Bi Py

I <1 0 - 10 >10

II <1 >1 >1

<10 -3 III >50 <<1

5 mm, the pyrolysis time might be estimated by calculating the time required to reach

95% of the temperature of the environment at the center of the particle by using
averaged properties. The prediction of product yields is under all circumstances
affected by the implemented reaction path scheme and kinetic data.
To estimate whether the rate of pyrolysis of a pyrolyzing particle is:

￿ Not hindered at all by heat transfer limitations (I)

￿ Controlled by external heat transfer (II)

￿ Controlled by internal heat transfer (III)

Biot (Bi), Py, and Py 0 numbers can be used with the classification scheme shown in
Table 11.3.
The dimensionless numbers are defined as

Bi = h R
λ

ð Biot number Þ ð Eq : 11 : 2 Þ