Torrefaction is a thermochemical pre-treatment process for upgrading the properties of biomass to resemble those of fossil fuels such as coal. Biomass properties of particular interest are chemical composition, physical property and combustion characteristics. In this work, torrefaction of beech wood and miscanthus (sinensis) was carried out to study the influence of torrefaction temperature (240-300 °C) and residence time (15-150 min) on the aforementioned properties of the biomass. Results of the study revealed that torrefaction temperature has a significant influence on mass and energy yields, whereas the influence of the residence time becomes more apparent for the higher torrefaction temperatures (>280 °C). Torrefied miscanthus resulted in higher energy densification compared to beech wood for a residence time of 30 min. A significant improvement in grindability of the torrefied beech wood was obtained even for lightly torrefied beech wood (at 280 °C and 15 min of residence time). Observation from the combustion study showed that the ignition temperature is slightly affected by the torrefaction temperature. As a whole, the torrefaction temperature determines the characteristics of the torrefied fuel compared to other process parameters like residence time. Furthermore, with optimal process conditions, torrefaction produces a solid fuel with OPEN ACCESSEnergies 2015, 8 3904 combustion reactivity and porosity comparable to raw biomass, whereas grindability and heating value are comparable to low quality coal.

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Droplet microfluidics is widespread in many chemical and biological applications where each droplet can be considered as a single, independent reactor unaffected by the presence of channel walls. This compartmentalization is facilitated by the addition of surfactants to increase the emulsion stability. However, the presence of surfactants is expected to strongly affect the dynamics and shape of flowing droplets. We report a systematic experimental study of the curvature of the front and the rear menisci of confined droplets flowing in a circular channel, with and without surfactants. In detail, the role played by surfactants on the droplet shape is investigated by dispersing them either in the droplet or in the continuous phases. The curvatures are evaluated by varying droplet speed, interfacial tension, and surfactant concentration. The curvature of the droplet front is found to scale with the capillary number (Ca) regardless of the presence or absence of surfactants. Differently, the curvature of the rear meniscus strongly depends on the surfactant concentration and whether surfactants are dispersed in the droplet or continuous phases. The surfactant accumulation at concentrations higher than the critical micelle concentration leads to an unexpected increase in the curvature in the former case and to droplet breakup in the latter.