Abstract
Switchgrass is a high yielding, low-input intensive, native perennial grass that has been promoted as a major second-generation bioenergy crop. Raw switchgrass is not a readily acceptable feedstock in existing power plants that were built to accommodate coal and peat. The objective of this research was to elucidate some of the characteristics of switchgrass biochar produced via carbonization and to explore its potential use as a solid fuel. Samples were carbonized in a batch reactor under reactor temperatures of 300, 350 and 400 °C for 1, 2 and 3 h residence times. Biochar mass yield and volatile solids decreased from 82.6% to 35.2% and from 72.1% to 43.9%, respectively, by increasing carbonization temperatures from 300 °C to 400 °C and residence times from 1 h to 3 h. Conversely, biochar heating value (HV) and fixed carbon content increased from 17.6 MJ kg−1 to 21.9 MJ kg−1 and from 22.5% to 44.9%, respectively, under the same conditions. A biomass discoloration index (BDI) was created to quantify changes in biochar colors as affected by the two tested parameters. The maximum BDI of 77% was achieved at a carbonization temperature of 400 °C and a residence time of 3 h. The use of this index could be expanded to quantify biochar characteristics as affected by thermochemical treatments. Carbonized biochar could be considered a high quality solid fuel based on its energy content.
Highlights
Switchgrass (Panicum virgatum L.) is a North American native grass that has been promoted as a model bioenergy crop because of its high-yield potential, low input requirements on marginal soils, and potential for soil carbon sequestration [1]
The objective of this research was to study the physical, chemical, and thermochemical characteristics of switchgrass biochar produced under different carbonization temperatures and residence times in a batch system and explore its potential use as a solid biofuel
The mass yield reduction is attributed to the thermal effect which results in the loss of moisture, followed by the depolymarization of the switchgrass secondary cell wall constituents, i.e., hemicellulose, cellulose and lignin
Summary
Switchgrass (Panicum virgatum L.) is a North American native grass that has been promoted as a model bioenergy crop because of its high-yield potential, low input requirements on marginal soils, and potential for soil carbon sequestration [1]. Switchgrass has a gross calorific value between MJ kg−1 and MJ kg−1 [4,5], an energy content comparable to that of hardwoods (19–21 MJ kg−1) [6]. Several barriers faced the utilization of switchgrass as the sole source of fuel in combustors including the high moisture and ash contents in biomass, which cause ignition and combustion problems. The low melting point of the ash, which causes fouling and slagging problems [7]. A multitude of studies has investigated switchgrass conversion, thermochemical conversion to liquid or solid biofuels and bioenergy
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