Handling and transporting biomass can be
improved by drying, pre-processing, or densifying the material. The unit has 16 publications dating from 1985
through 2003 that analyze drying, storing, transporting and roll
splitting.
Small diameter trees are a potential source
for woody biomass. Problems associated
with harvesting this material arise from the high moisture content and handling
of the small multiple stems.
Additionally, some of this smaller woody biomass is located within power
line right-of-ways and other smaller tracts which are not suitable for
conventional chipping systems. Beginning
in 1985, the unit began investigating a roll crusher/splitter machine which
could crush small diameter biomass and allow it to air dry prior to some type
of baling or modulating, much like the process for conditioning hay.
In early 1984, the Forest Engineering
Research Institute of Canada (FERIC) developed a trailer-mounted roll splitter/crusher. The Tennessee Valley Authority (TVA) worked
with FERIC to evaluate the feasibility of roll crushing of biomass. Based on these results, TVA entered into a
cooperative agreement with the Forest Operations Research Unit to evaluate the
horsepower requirements of the trailer-mounted machine’s crushing process and
improve the design for mounting the unit on a mobile harvester (Barnett
and Sirois 1985). This process of splitting and crushing small
diameter biomass (less than 7 inches) accomplished a significant amount of
drying after 7 days (Ashmore
1986, Barnett
and others 1986, Barnett
and Sirois 1985,
and Sirois
and Ashmore 1986), based on
species and size. Further testing of
four different continuous-flow roll surface designs were evaluated (Ashmore
and others 1987a and Sirois
and Ashmore 1986) to determine
their ability to crush and/or feed rates.
Additionally, hydraulic pressures and flow rates were analyzed to
determine horsepower requirements for crushing and splitting based on seven
different diameter classes of four southern tree species.
Curtin
and others (1987b) provides an
overview of the above-mentioned studies and incorporates the results of the
baling studies (Curtin
1987a, Stokes
and others 1987a
and Woodfin
and Stokes 1987b).
Lower moisture content increases the value
of wood as a fuel. The benefits of
transpirational drying would be reduced transportation cost due to lower weight
and higher net BTU output during energy conversion. Therefore, in 1985, studies were implemented
to assess the transpirational drying of biomass (Stokes
and others 1987b). Moisture content, weather data, d.b.h. class,
species, and days since felling were some of the variables analyzed in three
separate studies documented in this publication. Equations were developed by species as
predictors for weight reduction. Then,
in 1986, more testing was implemented to compare summer drying to winter drying
(Sirois
and others 1991) under field
drying conditions. The study showed that
roll crushing/splitting of small diameter whole trees for extended drying in
field conditions resulted in conditional drying benefits. Crushing can accelerate the drying rate of
small cut trees. However, if heavy
rainfall occurs after the first few weeks of drying, the crushed stems would
absorb the moisture more readily than the uncrushed stems. Winter drying resulted in a larger moisture
loss than summer drying. However, all
trees lost about 80% of their original moisture, regardless of season. In 1993 and 1995, two papers (McDonald
and others 1995 and Stokes
and others 1993b) reviewed
available literature addressing the costs and economics of biomass transport
and drying techniques. Biomass bolts,
chips, and chunked wood were dried, compacted, and vibrated (McDonald
and others 1995) to analyze
methods for increasing the bulk density of transported biomass.
McDonald
and Twaddle (2000) document a
survey of mills to gather information regarding mill chip pile management. Data is reported on chip pile inventory
methods, pile sizes, inventory requirements, and quality losses.
Sometimes, the extraction of small-diameter
material for niche markets may not suit conventional forest products’
transportations systems. Rummer
and Klepac (2003) investigated the
development, use, and cost of a roll-off wood rack for transporting 100-inch
bolts to a small-volume shavings factory.
A 2004 cooperative study with the Montana Community Development
Corporation, Smurfit Stone Corporation, and others, examined the use of
roll-off containers for transporting slash (Rawlings
and others 2004). Several options were described for
incorporating roll-off containers in active logging operations, or at landings
where slash had been piled. These
containers can be loaded with slash, or with wood chips from a grinding
operation. The results indicate that the
roll on/off container system is not cost competitive with a regular highway
chip van unless access presents a problem for the chip van. Based on data from this study, a trucking
residue simulator was developed. A
spreadsheet was developed using the production and cost data from this study to
compare bin transport options with conventional hauling. It is available on the Forest
Operations Research Unit website.