ARS | Publication request: Thermogravimetric characterization of irrigated bermudagrass as a combustion feedstock

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2010
Publication Date: April 27, 2010
Repository URL: http://hdl.handle.net/10113/41459
Citation: Cantrell, K.B., Hunt, P.G., Ro, K.S., Stone, K.C., Vanotti, M.B., Burns, J.C. 2010. Thermogravimetric characterization of irrigated bermudagrass as a combustion feedstock. Transactions of the American Society of Agricultural and Biological Engineers. 53(2):413-420.

Interpretive Summary: Varying production practices of bioenergy crops may influence their combustion behavior such as total mass lost, the energy required to begin combustion, and associated temperatures. These behaviors can be quickly assessed with a technique called thermogravimetric analysis (TGA). This analysis monitors the weight loss and corresponding temperatures to develop a degradation profile. In this work, we applied the TGA technique to identify differences in the combustion behavior of bermudagrass hay grown under varied irrigation and fertilizer schemes. The TGA profiles for each treatment scheme were almost identical and indicated three distinct combustion weight loss steps— dehydration, active combustion, and char combustion. During active combustion, there was less mass loss for bermudagrass irrigated with commercial fertilizer than with treated swine wastewater. Comparing commercial fertilized hay to treated swine wastewater irrigated hay, higher temperatures and more energy were required to begin the char combustion stage for treated swine wastewater irrigated hay. Bermudagrass hay irrigated with wider spacings for subsurface drip irrigation provided greater amounts of energy per mass of dry material. Overall, TGA functioned well for detecting microscale differences among irrigation treatments, thus suggesting minimal effect of production practices such as fertilizer source on the combustion characteristics of bermudagrass.

Technical Abstract: The bioenergy production industry can benefit from a greater understanding of potential differences among the various feedstock materials and production influences on thermochemical conversion processes such as combustion. The thermal degradation of biomass during combustion can quickly be assessed using thermogravimetric analysis (TGA) to provide a thermal profile for global characterization of reaction kinetics and temperatures associated with both the devolatilization and char combustion, as well as total volatile matter lost. In this work, the TGA technique was applied to understand combustion of Coastal bermudagrass [Cynodon dactylon (L.) Pers.] hay produced under a control treatment of commercial N fertilizer without irrigation along with eight different sub-surface drip irrigation (SDI) treatments. These eight treatments consisted of commercial nitrogen fertilizer or advanced-treated swine wastewater effluent each irrigated at two (75 and 100% of estimated evapotranspiration) irrigation rates and two lateral spacings (0.6 and 1.2 m). While thermogravimetric (weight loss) profiles of the treatments were almost identical and indicated three distinct combustion weight loss steps, some variations among the treatments were noted in the differential thermal analysis profiles. When compared to commercially fertilized bermudagrass, Coastal bermudagrass irrigated with advanced-treated swine wastewater had both greater mass loss associated with active combustion and a higher transition temperature leading to char combustion (364.9 vs. 372.5°C). This higher temperature requirement for char combustion of the hay irrigated with effluent was a direct result of a greater activation energy value required to initiate char combustion (97.9 kJ per mol for commercial vs. 105.1 kJ per mol for effluent). Consequently, char combustion required greater activation energy than the first active combustion stage. Among the SDI spacing treatments, Coastal bermudagrass irrigated using the wider SDI spacing provided greater amounts of energy per mass of dry material (11.16 vs. 12.06 kJ per gram solid converted). Overall, the TGA functioned well for discerning microscale differences among the irrigation treatments indicating minimal effects of production practices on the combustion characteristics of bermudagrass.