• Energy Research
• natural sciences close

Abstract The present work aims to investigate the influence of the main process parameters (pressure and temperature) and biomass characteristics (moisture content and particle size) on some mechanical properties (density and durability) of olive tree pruning residues pellets. By means of a lab scale pellet press, able to control process parameters, the biomass, ground with three different hammer mill screen sizes (1, 2 and 4 mm) and conditioned at different moisture contents (5, 10, 15 and 20% w.b.), was pelletized at various process temperatures (60, 90, 120 and 150 °C) and pressures (71, 106, 141 and 176 MPa). Compressed sample dimensions and mass were measured in order to calculate pellet density, while compressive strength tests were carried out to estimate the durability of the final biofuel. The relationships between the factor settings and the responses (density, compression strength and modulus of elasticity) were examined by univariate and multivariate statistical analysis. Temperature resulted the most important variable influencing pellet mechanical properties, followed by the initial moisture content and the particle size of the raw material. In particular, high process temperature, low moisture contents and reduced particle sizes allowed obtaining good quality pellets. The effect of compression force resulted scarcely relevant.

Abstract The scarcity of water, the need to reduce of pesticides, the demand for on-site production of vegetables are moving the interest from greenhouse cultivation to indoor farming. Compared to greenhouses, indoor farms allow to reduce considerably the water consumption, requiring more energy, which could be provided by renewable sources. In order to assess the convenience of such a system, accurate preliminary calculations are needed for productivity, energy requirements and costs as a function of the type of cultivation and the operating conditions. While some knowledge (e.g. production rate or cooling system performance) are available from open literature, some specific predictive methods are required. Based on the few works available in literature about indoor farming, evapotranspiration rate resulted as a critical term. An assessment of different methods based on literature data with a critical analysis of their effectiveness based on several aspects (level of fidelity of the model, complexity in the calibration and use, potential strengths and weaknesses) is proposed in this work.