• Energy Research
• 12. Responsible consumption close

The need to mitigate climate change and the progressive fossil fuel exhaustion have engendered a great interest for renewable fuels. This boosted the demand for wood fuel in all industrialized Countries creating a considerable business opportunity for the different stakeholders of the forestry sector. To increase the efficiency of the entire wood fuel supply chain, it is necessary to reduce the cost of harvesting, processing and transportation. One possible way to cut the handling costs is the densification of the chips. This paper reports the results of a study conducted on the densification process of chips, with particular focus on the demand of energy required by the process and on the density achieved. The investigation has been carried out on chips from hybrid poplar (PC) chestnut (CC), and a mixture of spruce and eastern white pine (MC) at different pressures (20, 30, 50, 80 and 110 MPa). The study pointed out that average values for density ranges between 546-898, 559-1082 and 543-913 kg m-3 for PC, CC and MC respectively. Specific energy demand ranges between 22.5-58.1, 18.8-43.3 and 19.4-50.2 kJ kg-1 for PC, CC and MC respectively.

The excessive amount of pig slurry spread on soil has contributed to nitrate water pollution both in surface and in ground waters, especially in areas classified as vulnerable zones to nitrate in accordance with European Regulation (91/676/CEE). Several techniques have been developed to manage livestock slurries as cheaply and conveniently as possible and to reduce potential risks of environmental pollution. Among these techniques, solid-liquid separation of slurry is a common practice in Italy. The liquid fraction can be used for irrigation and the solid fraction, after aerobic stabilization, produces an organic compost rich in humic substances. However, compost derived from swine solid fraction is a low density material (bulk density less than 500 kg􀀀m–3). This makes it costly to transport composted swine solid fraction from production sites to areas where it could be effectively utilized for value-added applications such as in soil fertilization. Densification is one possible way to enhance the storage and transportation of the compost. This study therefore investigates the effect of pressure (20- 110 MPa) and pressure application time (5-120 s) on the compaction characteristics of compost derived from swine solid fraction. Two different types of material have been used: composted swine solid fraction derived from mechanical separation and compost obtained by mixing the first material with wood chips. Results obtained showed that both the pressure applied and the pressure application time significantly affect the density of the compacted samples; while the specific compression energy is significantly affected only by the pressure. Best predictor equations were developed to predict compact density and the specific compression energy required by the densification process. The specific compression energy values based on the results from this study (6-32 kJ􀀀kg–1) were significantly lower than the specific energy required to manufacture pellets from biomass feedstock (typically 19-90 kJ􀀀kg–1).