Environmental Engineering Reference
In-Depth Information
2.2 Laboratory Oven and Grindability Tests
In order to obtain higher amount of samples for determining the fuel properties and
study grindability, 5 g of samples were torre
ed in a laboratory oven. The samples
were prepared by heating at a constant rate of 20
°
C/min from room temperature till
the optimum torrefaction temperature. The samples were then torre
ed at the given
torrefaction temperature for a constant time period. Three torrefaction mediums
were used for preparing the samples: nitrogen, carbon dioxide, and argon.
Both raw and torre
ed samples were shipped to a third party commercial
evaluation laboratory for fuel property analysis. After large-scale torrefaction using
the laboratory oven, torre
ed and raw biomass samples were tested for grindability.
The grindability tests consisted of sieve analysis (size distribution analysis) and
sample grinding using a Sweco model DM1 grinding mill. All samples were ground
for 20 min so that the amount of energy used in grinding the samples was held
constant.
2.3 Torrefaction Model
For a biomass material composed of hemicellulose, cellulose, and lignin repre-
sented in a carbon-normalized form, mole balance can be represented as
CH
m
O
n
!
n
hemi
CH
hh
O
oh
þ
n
cell
CH
hcell
O
ocell
þ
n
lig
CH
hl
O
ol
where m and n stand for the number of hydrogen and oxygen atoms, respectively, in
the carbon-normalized fuel. From the atom balance; known percentage composition
of hemicellulose, cellulose, and lignin; and H/C and O/C ratios for hemicellulose
and cellulose, one can determine H/C and O/C for lignin. The heating value of the
biomass can be represented in terms of
the composition of
the individual
components.
HV
biomass
¼
Y
hemi
HV
hemi
þ
Y
cell
HV
cell
þ
Y
Lig
ð
Þ
HV
Lig
1
where Y represents the mass fraction of different biomass components. The con-
version of each of the biomass component (f
k
) and the overall conversion (F) can be
given as
m
k
m
k
;
Char
m
k
;
o
m
k
;
Char
¼
Y
k
Y
k
;
Char
Y
k
;
o
Y
k
;
Char
¼
mass of
k
that remains to be devolatilized
Max mass of k that could be devolatilized
f
k
¼
k
¼
hemicellulose, cellulose and lignin
:
ð
2
Þ
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