Despite reducing transportation and handling costs, pelletizing cellulosic biomass would not be cost-effective for ethanol producers, according to a Purdue University study.

Klein Ileleji, an associate professor of agricultural and biological engineering, and Preethi Krishnakumar, a graduate research student, factored the costs and logistical requirements cellulosic ethanol producers would face using different types of biomass — corn grain, corn stover and switchgrass — in both bale and pellet forms.

Their findings, published in the current issue of the journal Applied Engineering in Agriculture, show that the denser cellulosic pellets would allow ethanol producers to save money by utilizing the same equipment used to transport and handle corn grain that flows using elevators, hoppers and conveyor belts.

"If a producer is switching from a corn ethanol plant to a cellulosic plant, they are starting with an existing grain system, and the storage and handling costs for pellets will be less since they are granular and flowable like corn grain," Ileleji said. "If you use bales, you will have to invest in capital costs for storage buildings and forklifts, and your infrastructure will have to change dramatically."

But the pellet-making process causes a nearly 50 percent loss of biomass yield. If two bales of cellulosic biomass are used to create pellets, the pellets only weigh as much as one of the original bales, Ileleji said. This is because as much as 50 percent of the original feedstock could be lost in the pelleting process.

Bales were cheaper to transport at small ethanol-production facilities, while pellets were more cost-effective at larger facilities that produce 100 million gallons per year or more. That's because as a facility's size increases, it has to bring in feedstock from a larger radius and low-density bales cost more to transport. The pellet transportation cost for large plants could be further reduced if pelleting plants were located close to growing fields.