Experimental Results of Mass and Energy Yield Referred to Different Torrefaction Pathways

摘要

Purpose The aim of this work is to investigate the influence of temperature and time on the final quality of torrefied biomass. In particular this study analyses the influence of different time-temperature pathways in reaching selected values of Mass Yield Ratio (M.Y.R.) by applying torrefaction treatment on samples of spruce pine. This represents an innovative approach as, making reference to the majority of the published works, M.Y.R. is not considered an independent parameter but a result of random conditions with temperatures ranging from 240 to 300 ℃ and duration arbitrary selected within few minutes to 1-2 h. For the investigated torrefied samples, energy parameters as high heating value, energy densification ratio, energy yield besides ultimate analysis are therefore determined. Method The experimental investigation is carried out on a small plant located at the Thermochemical Biomass Energy Laboratory of the University of Trento. The core of the plant is a batch reactor that can accept a load approximately of 50 g of biomass. The reactor is directly fluxed by a controlled nitrogen flow of 40 1 min~(-1) (SPT) heated by an electrical resistance at selected temperatures of 265, 280, 295, 310 ℃. A single type of biomass, spruce pine, has been utilized as highly available from local sawmill residues. The size of samples are in the range from 9.50 to 30 mm in length/width and 5.60 to 9.50 mm in thickness. For 7 samples the cited properties are determined by selecting suitable temperature-time pathways. Results This investigation details in terms of the main process parameters, temperature and time, the thermochemical changes involving the selected raw biomass when submitted to selected torrefaction treatment. As main result this study demonstrates that samples reaching the same M.Y.R. present almost the same values for the foremen-tioned properties, even if the final state of the samples refers to different torrefaction process pathways. Conclusion From the proposed experimental investigation it can be deduced that, within the selected temperatures range, the torrefaction pathway imposed to reach a selected value of M.Y.R. has no impact on the final energy parameters of the torrefied biomass. These properties seem to be dependent on the imposed value of the M.Y.R. so that it can therefore be regarded as a synthetic state parameter for this thermal process.