Various types of feedstocks such as straws and cotton gin waste are characterized by their low bulk density and relatively low energy content as well as irregular particle sizes and shapes. These factors impact the production of bioenergy from these fluffy feedstocks. The goal of this research is to improve the physical and thermochemical characteristics of biomass via torrefaction process. Torrefaction involves the heating of biomass to moderate temperature of 200 to 3008C in an inert atmosphere. Thus, the properties of the biomass undergo chemical and physical changes under torrefaction process.Several batches of wheat straw, rice straw, and cotton gin waste were torrefied at 2608C for 0, 15, 30, 45, and 60 min using a batch torrefaction system located at the bioenergy lab, Stuttgart, AR. Another set of experiments took place in which wheat straw was used as the feedstock. The effects of torrefaction temperature (200, 260, and 3158C) and residence time (60, 120, and 180 min) on the physical and thermochemical characteristics of wheat straw were studied. During 1 hour torrefaction at 2608C, moisture content was reduced by 70.5%, 49.4%, and 48.6% for wheat straw, rice straw, and cotton gin waste, respectively. Insignificant reduction (<1.9%) of the volatile solids was observed under the same torrefaction conditions. The heating value increased by 15.3%, 16.9%, and 6.3% for wheat straw, rice straw, and cotton gin waste, respectively. Rice straw showed the highest weight loss of 30.7% under the same torrefaction conditions.The second set of experiment showed that the torrefaction temperature have stronger effect compared with residence time. The highest heating value (22.75 MJ/kg) and the highest weight loss (54%) of wheat straw were observed at torrefaction temperature of 3158C and 3-h residence time. Also, improvement of size reduction was visually observed, which has the favorable properties for application for gasification and/or pyrolysis.

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 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. OPEN ACCESSEnergies 2014, 7 549

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Background and objectives High moisture content (MC) rough rice was dried using an industrial microwave (MW) operated at a frequency of 915 MHz, and the impacts of the drying on the rice physicochemical properties were investigated. The treatments were performed at MW power levels 5, 10, and 15 kW, treatment durations 4, 6, and 8 min and for rice at initial MC of 24% (w.b.) and bed thicknesses 5, 10, and 15 cm. Near infrared spectroscopy and a rapid visco‐analyzer were used to assess the milled rice protein content, surface lipid content (SLC), total color difference (TCD), and rice peak and final viscosities. Findings The effect of increasing MW specific energy was statistically significant for all of the responses studied. Increasing MW specific energy resulted in an increase in measured rice SLC, protein content, and final and peak viscosities. Responses increased to a maximum then decreased at specific energies over 800 kJ/kg‐grain. The opposite profile was true for TCD. The TCD decreased as a result of increasing MW specific energy to a trough at 533.33 kJ/kg‐grain then increased at specific energies over 600 kJ/kg‐grain. The effect of varying rice bed thicknesses was not statistically significant. Conclusions It is vital to select appropriate MW specific energy to maintain the rice physicochemical properties. Significance and novelty Using MW heating with a frequency at 915 MHz provides new avenues to scale up the MW heating technology for rice drying; this may allow rapid, one‐pass rice drying while maintaining important quality characteristics.

Background and objectives The 915 MHz industrial microwave has a great penetration depth relative to the 2.45 GHz microwave and holds the potential to achieve one‐pass drying of deeper rice beds within a short drying duration. The objective of this research is to determine the effect of microwave specific energy on the quality, functional, and physicochemical properties of different rice cultivars. Two rice cultivars were used: a medium grain cultivar (Titan) and a long grain hybrid cultivar (XL753) from two different locations (Burdette and Carlisle). Rice samples at harvest moisture content of 20% wet basis were dried using the 915 MHz industrial microwave at specific energies ranging from 360 to 720 kJ per kg of initial wet grain mass (kJ.[kg‐grain]‐1). Rice physicochemical and functional properties were analyzed. Findings Results indicate that specific energy had a significant effect (p‐value < 0.0001) on moisture removal and head rice yield. On average, increasing specific energy (drying duration 3–4 min, power 4–6 kW) resulted in increased moisture points removed from 2.5% to 7.3% and 3.7% to 7.5% for long grain hybrids and medium grain cultivars, respectively, while head rice yield decreased. Setback and final viscosities increased while peak viscosity decreased with increasing specific energies. Kernel surface lipid and protein content slightly decreased with increasing specific energies, although specific energy did not have a significant effect on these responses. Resistant starch content decreased with increasing specific energy for hybrid rice. Water and oil absorption capacities varied at different specific energies. The most desirable specific energy for moisture removal that maintains rice quality characteristics (relative to control samples) was 525 kJ.[kg‐grain]‐1. Conclusions The 915 MHz industrial microwave has the potential to achieve one‐pass drying of rice. A study of the best specific energy for drying different cultivars of rice using this technology is essential to meet the diverse industrial needs for rice drying. Significance and novelty This study provides science‐based information on the properties of different rice cultivars dried using the 915 MHz microwave and selection of desirable microwave parameters for rice drying. The technology has a great potential to transform the rice drying industry by decreasing rice drying duration, improving milling yield, and energy efficiency.