(521d) Effects of Fuel Properties on Natural Downward Smoldering of Piled Biomass Powder: Experimental Investigation

Effects
of fuel properties on natural downward smoldering of piled biomass powder:
experimental investigation

Fang
He, Zhenqiang Gao, Bin Luo, Zhihe Li, Weiming Yi

Shandong University
of Technology, Zibo, Shandong, 255049 P.R. China

Abstract: In order to obtain data for modeling
validation of one-dimensional smoldering and combustion of biomass, effects of
fuel type, moisture content, and particle size on natural downward smoldering
of biomass powder have been investigated experimentally. A cylindrical reactor
(inner size Φ26 cm × 22 cm) was built and powders of corn stalk,
pine trunk, pyrolysis char and activated char from corn stalk were prepared.

Fig. 1? Schematic of the experimental
set-up for the natural downward smoldering

Smoldering
characteristics of the four materials, different moisture contents (between 0%
and 30%, wet basis, corn stalk powder) and different particle sizes (between 20
and 100 mesh, dry corn stalk powder) were examined. Results showed that: 1) The
maximum temperature in the fuel bed is only slightly affected by fuel type and
particle size. It increases gradually for original biomass and decreases slowly
for chars with the development of the process. 2）Propagation
velocity of the char oxidation front is dominated by carbon density and ash
content. And it is almost not affected by moisture content and particle size.
3) There is always a drying front in the fuel bed during smoldering of
hydrocarbons even if the original material is dry. Propagation velocity of the
drying front is affected by moisture content significantly, decreases from more
than 10 to 3 times of char oxidation velocity with the increase of moisture
content from 0 to 20%. 4) Cracks inside the fuel bed of are dominated by fuel
type and particle size.

Typical results:

Fig. 2 ? Effects of the fuel type on
the temperature of smoldering

Temperature
histories of smoldering of the four fuels are presented in Fig. 2. Maximum
temperatures from thermocouples are between 450 and 750 ℃, varies with their
depths.

Fig. 3 ? Effects of moisture content
on propagation and mass loss rate of smoldering

The
time it takes for the thermocouples to reach the given temperatures（101
℃ for drying and the maximum for char
oxidation) at moisture content between 0 and 30 % is presented in Fig. 3. It
shows that the drying time increases significantly with the increasing moisture
content. However, there is no obvious regularity between the char oxidation time
and the moisture content.

Highlight:

1.
Natural downward smoldering of four materials, different moisture contents, and
different particle sizes were investigated.

2.
Propagation velocity of the char oxidation front differs significantly from
that of the drying front.

3.
Carbon density and ash content of fuel dominate propagation velocity of the
char oxidation front.

4.
Fuel bed of finer material is apt to have bigger cracks.

Keywords: fuel type, moisture content, particle
size, biomass, smoldering