Fuel property changes of switchgrass during one-year of outdoor storage

Abstract

Like all biomass, both quantitative and qualitative changes in switchgrass may occur during outdoor storage. Evaluating the effects of long-term storage on the qualitative properties of energy crops provides an understanding of maintaining fuel quality. Two upland varieties of switchgrass, Cave-In-Rock and Trailblazer, were harvested, baled and stored outdoors under a protective tarp. Core samples from each variety were taken monthly for one year; on-site moisture was recorded and fuel analyses (proximate, ultimate and mineral/ash) were evaluated every three months during the storage period to determine storage and variety effects. In addition to fuel analyses, fuel quality parameters of fouling and slagging indices, T250, silica value and alkali% as Na2O were determined for the first and final months of storage. Average on-site moisture for the Cave-In-Rock and Trailblazer varieties were 12.4 and 12%, respectively for the whole year. Trends in fuel analysis only showed decreasing ash and increasing oxygen for both varieties over the storage period. Storage time significantly influenced carbon content; the energy value was also significantly different for both varieties as values varied from 17.7 to 18.4 MJ/kg for both varieties. Significant differences between varieties were observed for ash, volatiles, carbon, nitrogen and oxygen contents. The fuel quality parameters show that the Cave-In-Rock variety maintains a higher melting point and reduced heat transfer in addition to a less and more stable susceptibility to boiler fouling. However, the Trailblazer variety had favorable silica values and percentage of alkali as Na2O compared to the Cave-In-Rock variety.