Page 144 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 4 Torrefaction 121

Solution
a. Volume energy density:
Raw wood:
The volumetric density of energy of raw wood, EV f , that contains 35%
moisture would be
MJ kg
EV f 5 12:92 3 300 5 3876 MJ=m 3
kg m 3
Pelletized wood:

Density of pelletized raw wood 5 650 kg=m 3
Since the energy content did not change during pelletization, the volume
energy density of the pellet is
MJ kg
EV f 5 12:92 3 650 5 8398 MJ=m 3
kg m 3
So, we note a large increase in volumetric energy density through
pelletization.
b. Energy density:
Moisture content of wood pellets is 7%.
Pelletization affects moisture content but not the energy density on dry basis.
It does not affect the energy content. So, the mass energy density of
pelletized wood is the same as the feed wood as-received:
HHV p;d 5 HHV f;d

HHV p;ar 12:92
5 HHV f;d 5 5 19:87 MJ=kg
ð1 2 0:07Þ ð1 2 0:35Þ
HHV p;ar 5 19:87 3 0:93 5 18:48 MJ=kg
But through pelletization, biomass mass density, ρ p , has increased to
3
650 kg/m . So, the volume density of energy of pelletized wood, EV p ,
will be:
3
EV p 5 HHV p 3 ρ 5 HHV r ðwtÞ 3 650 5 18:48 3 650 MJ=m 5 12:01 GJ=m 3
p
Torrefied wood:
Density of the torrefied wood reduced by 39%5ð1 0:39Þ33005183:5kg=m 3
Hence, volumetric energy density of torrefied product, EV t ,is
calculated as:
EV t 5 24:59 3 183:5 5 4512 MJ=m 3
Torrefied pellet:
When the wood is torrefied, its mass density of energy increases to
24.59 MJ/kg. Since the problem neglects any change in mass density