Researchers in three states work on densification

By Kris Bevill | April 28, 2011

In order for ag residues and energy crops to be profitably converted to biofuels, it is expected that biorefineries will need to acquire all of their feedstocks from within close proximities to the plants. Another method of acquisition could be via regional biomass processing centers that would pre-treat and densify the feedstocks to make it easier to transport the material to production facilities. An ongoing collaborative research project being conducted in South Dakota, Michigan and North Dakota is focusing on how these regional centers could achieve this goal.

“The overarching goal of this project is to develop and validate the performance of an integrated biomass pretreatment and densification process that will reduce the logistical hurdles facing second-generation biofuels,” said Kasiviswanathan Muthukumarappan, a professor at South Dakota State University’s agricultural and biosystems engineering department.

The project begins with samples of switchgrass, cordgrass and corn stover collected by SDSU researchers. The biomass is milled at SDSU to specified sizes and is then shipped to Michigan State University, where professor Bruce Dale sends them through the university’s ammonia fiber expansion pre-treatment process, known as AFEX processing. From there, the biomass samples are sent to Fargo, N.D., where they are compacted using a device developed by engineers at Federal Machine Co. The resulting densified paks, as they are called, are then returned to SDSU where researchers analyze the physical and chemical characteristics of the samples.

So far, the long-distance collaboration has achieved promising results. “We found that in terms of compacting these AFEX-treated biomass samples, we don’t have to go to lower particle sizes, we can use the larger sizes,” Muthukumarappan said. “What it means is that it’s going to require less energy in pre-processing these biomasses.” Less energy translates to lower operating costs for producers, which in turn results in improved profitability ratios.

Biomass pieces up to 12 millimeters in size (nearly a half-inch) have been shown to work successfully using the researchers’ process. Muthukumarappan said they have not yet discovered what the size limit will be. “However, I know that we can compact alfalfa that has been run through a hay grinder producing 50 millimeter-long pieces,” he added.

Ultimately, researchers hope to prove that by using the AFEX pretreatment process in combination with the novel compaction process, biomass feedstocks will not only retain their original composition, but will also be 10 times more dense than their baled counterparts and will not require further pretreatment once they arrive at the production facility. The two-year study, which is scheduled to end next June, will also address flowability of the material and whether it will produce the same amount of biofuel as uncompacted biomass. Most of the funding for the $1.1 million research project is being provided by the North Central Sun Grant Center. The remaining $400,000 is being contributed as a cost-share match by the various partners involved in the project.