Oklahoma State University

Solid Biofuels

Solid Biofuels


Switchgrass has been identified as a promising pelleting feedstock as it facilitates higher throughput rates and requires less energy for crop drying than wood. Although switchgrass is a higher cost feedstock to procure than wood residues, it could become an economical biofuel. The overall energy balance of switchgrass pellets is 14.6:1, which includes energy for switchgrass production, transportation to the conversion facility, preprocessing, pelleting, and marketing. A growing number of pellet stove and boiler suppliers developing advanced combustion appliances can burn grass pellets. An opportunity exists to develop a decentralized local industry. Individuals or groups of farmers can establish their own pelleting or briquetting factories. In some locations existing alfalfa or wood pellet plants can be utilized.

Energy associated with switchgrass pellet production.

Process (GJ/ton) Energy
Switchgrass establishment 0.028
Switchgrass fertilization and application 0.460
Switchgrass harvesting 0.231
Switchgrass transportation 0.072
Pellet mill construction 0.043
Pellet mill operation 0.244
Management, sales, billing and delivery of pellets 0.193
Total energy input 1.271
Total energy output 18.5
Energy ouput/Input ration 14.6



Pelleting grasses is not difficult, provided the following conditions are met: the material needs to be ground to pass through screens of 5/64 inch or smaller; it needs to be treated with high temperature steam of at least 200° F; and an appropriate sized pellet die needs to be utilized, typically with a thickness of 2 1/4 inch to produce 1/4 inch pellets. Harvesting switchgrass for pelleting involves mowing in winter and harvesting and pelting in spring. This allows time to leach the excess potassium and chlorine from the biomass, thereby reducing the particulates emission.

Switchgrass pellets and coal co-fi ring in power plants is gaining popularity due to the low-cost and technologically simple method for reducing CO2 emissions. Recent estimates show that co-fi ring 189 million dry tons of switchgrass with coal in the existing U.S. coalfi red electricity generation fl eet, can mitigate approximately 256 million dry tons of carbon dioxide per year, representing a 9 percent reduction in 2005 electricity sector carbon dioxide emissions. The savings in greenhouse gas emissions are considerable because pellets have much lower emissions than coal, liquid natural gas, and natural gas, offering net offsets of 86 percent to 91 percent.

Switchgrass pellets.

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