Solid
biofuels are currently used in increasing volumes to replace
fossil equivalents. Next to the traditional wood-derived fuels, the
advancement of biomass upgrading technologies like steam explosion
(SE), followed by pelleting, further broadens the variety of materials
on the market. This thermochemical and mechanical upgrading improves
greatly the general properties of such fuels (homogeneity, energy
density, water resistance, biological decomposition, grindability,
pneumatic transport, etc.) and at the same time offers the possibility
for co-production of green chemicals/biorefinery processing. However,
these alternative SE-material pellets have different properties from
the fossil counterparts with regard to dust formation, dielectric,
ignitability, and explosive characteristics, hence posing an increased
risk of fire and explosion in handling, transport, and storage of
the biosolid fuels. These divergent properties need to be properly
addressed before their large implementation in the industry. To shed
more light on the variability of such material properties, several
batches of SE pellets varying in bulk density and subjected to different
handling and storage conditions were evaluated. This was done using
a number of standardized equipment and following industrial standard
measurement methodologies to compare steam-exploded material with
standard white wood pellets and reference coals. The main body of
the work focused on the explosivity of dust generated in the handling
of the pellets, studied using a Hartmann tube, coupled with a high-speed
camera to evaluate the sensitivity [minimum ignition energy (MIE)
and minimum explosive concentration (MEC)] and the severity maximum
flame front velocity (FFVmax) of explosions of the generated SE-pellet
dust. Thermogravimetric analyses (TGA) was used to measure and compare
the ignitability of dust layers of SE-pellet dust vs coal and as a
function of co-mixture. Finally, the SE-pellet self-heating behavior
was addressed using the standard “basket method” and
compared with that of a commercial coal sample. The results show that
the SE pellets produce very low levels of dust even after extensive
weathering, hence limiting the explosion potential. The MIE and MEC
of SE-pellet dusts exhibited similar values compared to those of the
parent raw biomass material; however, the FFVmax revealed lower values
when compared to that of the parent raw biomass. Also, the self-heating
propensity is very low as the pellets are basically immune to biological
degradation, while the spontaneous ignition temperature is high and
in the range of nonhazardous bulk materials.