Switch to Switchgrass
Switchgrass is another potential cellulosic ethanol feedstock that has garnered a lot of attention. University of Tennessee researchers are well on their way to discovering the most economical and beneficial methods of storing switchgrass.

Switchgrass is a warm-season perennial commonly found in prairies, pastures and along roadsides. It is considered a high-yielding, versatile, adaptable plant, which is able to thrive in many different weather conditions, and requires lower fertilizer and herbicide amounts compared with typical crops.

Several companies, including Missouri-based CleanTech Biofuels Inc., have expressed interest in the crop. The research team at UT co-led by agricultural economics professor Burton English, agricultural economist James Larson and soil scientist Don Tyler began experimenting with switchgrass in January 2008 through the Tennessee Biofuels Initiative. “Logistics is a big issue in regard to biomass,” English says. “We realize that one can transport more rectangular bales in a truck than round bales, but storage is another matter.”

The group established 720 acres of switchgrass in eastern Tennessee to perform a storage study, comparing round or rectangular bales stored on three different surfaces, covered and uncovered.

Five-by-4-feet round bales, and 4-by-8-feet rectangular switchgrass bales were stored on well-drained ground, gravel and pallets. Some bales on each of those surfaces were covered with a plastic tarp, wrapped in plastic or left uncovered.

Every 100 days starting in January 2008, the group conducted bale destruction tests to see what was happening inside of them, Burton explains. “We do this by cutting them open with a chain saw, selecting four different weathered surfaces to take samples from and sending the samples to the National Renewable Energy Laboratory in Golden, Colo., for testing,” he says. The researchers have collected samples from January, May and September, and are now preparing to collect the December samples. “We are doing this every 100 days for 500 days, even though a season is 365 days,” Burton says. “We believe there will have to be some extra storage time, just in case not enough switchgrass is produced in every given year. At this time, we think the material will be stored at farms, so this study will look at the cost of each specific method.”

Cost and Findings
According to English, the least expensive switchgrass storage method is as round bales, without a tarp and on pallets. “It costs about $4 per ton that way,” he says. “If it doesn’t have a tarp it’s going to weather about 6 inches, but we don’t know if that’s bad or good for conversion processes, because we don’t have conversion process data yet.”

The samples the group has sent to the NREL will be chemically analyzed to answer that question. Among several things that were measured, English says the bale’s ethanol content will be significant.

A round bale covered with a tarp and stored on a gravel pad will cost about $12 a ton, English says, noting that a round bale typically weighs 1,300 pounds; a square bale weighs about 1,700 pounds. “If you don’t cover that square bale and leave it open to rain, it can increase in weight by up to 3,100 pounds,” English says, adding that the square bales soak up water rather quickly, which may damage their quality. All bales that were left uncovered were waterlogged when the first samples were taken in May.

Taking cost and overall effectiveness into consideration, the UT researchers found that tarp-covered bales stored on pallets resulted in less degradation compared with those stored on a gravel pad. “A gravel pad is more expensive, and it doesn’t add quality,” he says.

In the experiment, round, tarp-covered bales showed little signs of weathering, and decreased in weight by about 37 pounds per bale. Weathering on covered rectangular bales varied and significant decomposition was observable along the bottom edge and exposed sides of most bales. The average decrease in weight was about 1,313 pounds per bale.

A 25-by-100-feet tarp costs $500 and will cover about 144 rectangular bales, or 120 round bales, according to English. Pallets cost about $6.50 each, and only one bale can be placed on a pallet. Gravel pads cost approximately 60 cents per square foot.

English says UT should begin receiving experiment results from the NREL at any time and that the study should be completed by next summer.

Feedstock Future
Determining the cost and effectiveness of feedstock storage is important to the commercial development of cellulosic ethanol production, which is why so many companies and universities are working to put the pieces of this puzzle together. For example, in August 2008, Illinois-based Archer Daniels Midland Co., Deere & Co., and Missouri-based

<-- Previous Page	1   2   3	Next Page -->
View Entire Article