CHARACTERIZATION OF A BIOMASS MILLING PILOT ... - circe

4.4 Characterization of sampling point
The extracted sample at IS.1 from mills is a
representative of full range of milled biomass particles,
however, this localization presents several problems to
achieve the isokinetic conditions and the sampling can
not be representative of this particle flow.
The obtained samples in GS.1 and IS.2 are not
representative of full range of milled particles. At GS.1
point, it is sampling the collected particles by cyclone. At
IS.2, the particles flow is from not collected in cyclone,
in other words, the very fines particles of the full milled
biomass particles. Both samples are not representative of
full range, but the feasibility of a right sampling is higher
due to, in the first place, GS.1 is a correct system to
obtain a sample in discharge, and in the second place, at
IS.2 presents less problems to achieve the isokinetic
conditions.
The possibility of three sampling point allows:
To obtain a representative sample of the whole
amount of milled biomass using two different
methods.
In the first place, to obtain a representative
sampling of full range at IS.1
In second place, to estimate a representative
sampling of full range as composition of the
obtained sample at GS.1 and IS.2:
χt
=
m
m
m = m + m
t
GS1
IS 2
m
· χ IS
GS1
IS 2
χGS1
+ ·
GS1
+ mIS
2 mGS1
+ mIS
2
where:
χ: analyzed property (granulometry, moisture
content, chemical composition or shape factor).
Note: bulk density can not calculate as
composition of both samples.
m GS1: mass flux solids at GS.1
mIS2: mass flux solids at IS.2
Validation of extracted sample at IS.1 through
the comparison his properties with the
properties of the composed sample from GS.1
and IS.2
4.3.2 Milled biomass sample analysis
Milled biomass characterization involves:
Particle size distribution:
It represents the mass percentage for each
particle size interval. It is the most important
parameter in analysis of milled product.
Shape factor.
The spherical approximation is a used
commonly in powder handling. However, the
milled biomass presents usually a cylindrical
shape. Shape factor allows to asses the final
particle shape.
Moisture content
This parameter is expressed as:
Ww
−Wd
M = 100
Ww
where M is the moisture content expressed in
percentage of wet matter, Ww is the weight of
the wet sample and Wd the weight of the dry
sample.
The difference between inlet and outlet
moisture content allows to asses the drying
2
effect during comminution. Several studies [8-
10] have observed a decrease between 10 and
30% of the initial moisture content as function
different factors.
Bulk density.
Miling is ones of solids densification process
due to bulk density increase with particle size
decrease.
Chemical composition
It is observable that the particle size shows
influence on chemical properties [21].
5 CONCLUSIONS
Several parameters have been instrumented to assess
the influence on particle residence time on grinding
chamber and on drying effect:
Pressure, temperature, humidity and mass flow
air at mill inlet and outlet.
Moisture content, temperature and feed rate of
biomass at mills inlet and outlet.
Variable speed drives have been installed in
mills to control the energy impact, in fans to
control the mill outlet pressure and in belt
conveyor to control the biomass feed rate.
Milled biomass properties characterization has been
realized to analyse the parameters influence on the final
product properties.
Three sampling methods have been studied to obtain
a representative sample of milling process:
Coning and quartering sampling can show size
segregration due to the sample is taken out
form stored milled biomass.
Two-way distributor has been installed to
obtain a representative sample in gravity
discharge. Particle flow is in motion and size
segregation is avoided.
Two isokinetic sampling points have been
analyzed where the air-particle flow conditions
are extremely different. At first point, high
solids concentration of all range of milled
particle sizes in horizontal ducts, isokinetic
sampling presents inertial effect of coarse
particle, possible asymmetry in the solids
concentration profiles as function sampling
point height from the bottom of the pipe in the
vertical plane of the cross section and finally,
erroneous solid concentration measurement in
case of anisokinetic sampling.
At second point, low air-particles concentration
of fines particles, isokinetic sampling can
realize suitable, even the concentration
measurement and representative sample can be
obtained in anisokinetic conditions.
Possibility to obtain two representative
sampling of full range of milled biomass size:
isokinetic sampling at first point and as
composition of isokinetic sample at second
point (fines particles representative) and gravity
discharge sample (coarse particles
representative).
First isokinetic sample validation in
comparison with a composition sample of
gravity discharge sample and second isokinetic
sample.