Zewei Miao

An overview of lignocellulosic biomass feedstock harvest, processing and supply for biofuel production.

1Energy Biosciences Institute, University of Illinois at Urbana-Champaign, 1206 West Gregory Drive, Urbana, IL 61801-3838, USA 2Department of Agricultural & Biological Engineering, University of Illinois at Urbana-Champaign, 1304 West Pennsylvania Avenue, Urbana, IL 61801, USA *Author for correspondence: Tel.: +1 217 3332854; E-mail: grift@illinois.edu

Specific energy consumption of biomass particle production and particle physical property

Comminution energy efficiency of biomass particle production and particle physical properties are important variables that directly influence feedstock supply-conversion chain from the on-farm production to the biorefinery. In this study, size reduction and particle physical property analysis of miscanthus (Miscanthus giganteus), switch grass (Panicum virgatum), weeping willow (Salix babylonica), and energy cane (Saccharum spp.) were conducted from the perspectives of feedstock supply and conversion, by using commercial-scale David Bradley chopping machine, bench-scale Retsch SM2000 knife and SK100 hammer mills. Results indicated that comminution energy consumptions were exponentially correlated with aperture sizes of the mill screens for biomass crops. Moisture contents significantly influenced comminution energy consumption, especially for finer size reduction. Given a specific mill screen, Retsch SK100 hammer mill was more efficient than SM2000 knife mill which mainly attributed to higher motor speed and material axial feeding. While particle size was negatively related to bulk densities of biomass chops, comminution ratio of biomass size reductions were positively proportional to energy consumptions for all of the four biomass crops. Bulk densities for 4-mm and smaller miscanthus and switchgrass chops were higher than that of bale. For willow and energy cane, grinding did not increase but reduce bulk densities. Particle size and surface area estimates from the commonly-used ANSI/ASAE Standards S424.1 and 319.4 were highly sensitive to particle size distributions. Further studies on standardization of particle size and surface area estimates are needed.

Determination of Energy Requirements for Densifying Miscanthus and switchgrass feedstock with a medium-scaled compressor

Biomass transportation is hampered by the inherent low bulk density of herbaceous materials, causing containing equipment to reach their volume limit far before their weight limit. To evaluate the purported efficiency increase, it is imperative to determine the energy requirement of the compression process. In addition, to design containers for compressed biomass transportation, mechanical parameters of the biomass, such as Poisson’s ratio, must be determined. This paper describes the measurement of these quantities for Miscanthus giganteus and switchgrass under uni-axial compression, using four particle sizes ranging from unground (about10-30 cm) to 25.4mm, 12.7mm, and 6.35mm, at three repetitions each.

Electrical capacitance as a proxy measurement of miscanthus bulk density, and the influence of moisture content and particle size

Electrical capacitance was measured during compression of miscanthus biomass.A quasi linear relationship between biomass bulk density and capacitance was found.Three distinct material behavior phases were observed during biomass compression.Moisture and particle size both were found proportional to electrical capacitance. This research aimed at measuring the electrical capacitance of miscanthus biomass as a potential proxy measure of bulk density. The experimental arrangement allowed for continuous variation of bulk density through compression, whereas moisture content was varied at two levels, being air-dried (<5%) and oven dried (14.5%), and particle size was varied by using material that passed milling screen aperture sizes of 6.35, 9.53, 12.7, and 25.4mm. A chamber was constructed containing the biomass, which was compressed using a hydraulic cylinder, causing the biomass bulk density to increase during the experiment. During the compression, the pressure applied vertically onto the biomass was inferred from the measured fluid pressure in the hydraulic cylinder. In addition, the displacement of the cylinder was measured using a linear encoder, allowing for instantaneous bulk density calculations.Two capacitors, each comprising dual parallel flat copper plates, were fitted inside the chamber, where the biomass under compression acted as the dielectric medium. The conjecture was made that the force with which the biomass is pushed against the capacitor plates would highly influence the measured capacitance value, and therefore, one capacitor was placed in a longitudinal direction to capture vertical forces, and a second in the lateral direction to capture transverse forces.The results showed a quasi-linear relationship between capacitance and bulk density. A proportional relationship was found between electrical capacitance and moisture content as well as between electrical capacitance and particle size. A comparison between vertical capacitance versus bulk density and the applied pressure versus bulk density showed that they are independent measurements. Therefore, the initial conjecture being that the force with which the biomass is pushed against the capacitance plates would have a large effect on the capacitance was deemed false; instead, the internal reorganization of biomass particles seems responsible for the variation in capacitance as observed.The results imply that electrical capacitance may serve as a proxy for the measurement of miscanthus bulk density, but since moisture content and particle size have a marked effect on the capacitance, they must be determined separately or calibrated for. Currently, to determine the instantaneous moisture content of field crops, capacitor plates are already an integral part of yield monitoring systems. However, the method as investigated, adds the potential simultaneous measurement of the instantaneous bulk density of a biomass flow.