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.
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.