Torrefaction of agricultural residues: Effect of temperature and residence time on the process products properties

摘要

Up to now, a few studies on the potential utilisation of the products of agricultural residues torrefaction have been performed. The composition and toxic compounds content determine their further application. Consequently, the torrefaction products characterisation, aimed at their potential utilisation, were performed. Wheat-barley straw pellets and wheat-rye chaff were used within the study. The impact of the torrefaction temperature (280-320 °C) on polycyclic aromatic hydrocarbons (PAH) content and the torgas composition was investigated. The impact of the torrefaction time (30-75 min) on the condensable volatiles (condensables) composition and their toxicity have been studied as well. The torrefaction process was performed in a batch-scale reactor. The PAH contents were measured using HPLC, the torgas content was measured on-line using gas analyser and, afterwards, GC-FID. The condensables composition and the main compounds quantification were determined using GC/MS. Three toxicity tests — for saltwater bacteria (Microtox® bioassay), freshwater crustacean (Daphtoxkit F magna®) and vascular plants (Lemnasp. Growth Inhibition Test) were performed for the condensables. PAH content in the biochar, regardless of the torrefaction temperature, allows their use in agriculture. The produced torgas shall be co-combusted with full-caloric fuel because of its low calorific value. The toxic compounds (furans and phenols) have been identified in the condensables samples and, regardless of the process time, the condensables were classified as highly toxic. Due to that, they can be used either as pesticides or as, for example, anaerobic digestion substrate after their prior detoxification.