Standard liquid fuel for industrial boilers from used wood

The purpose of the research was to validate if the fast pyrolysis bio-oil (FPBO) from used wood would meet the specifications set by the standard EN 16900-2017 for industrial boilers. Commercial used wood Class C was used for fast pyrolysis. According to physical characterization studies, the dominant material groups were (virgin) wood (i.e. no visible coatings) (58 wt%) and chemically treated wood (41 wt%). The share of plastics was 0.7 wt%. The contents of heavy metals were not significant. No bromine was observed and the content of chlorine was ≤0.05 wt%. Prior pyrolysis studies, the sample was grinded, dried, and sieved. Plastic fraction was separated to over 0.98 mm sieve fraction. The main fraction having particle size of 0.55 − 0.98 mm containing wood was tested in one experiment and a mixture of plastic fraction (over 0.98 mm) and wood fraction (0.55 − 0.98 mm) was tested in two other experiments. The fines below 0.55 mm were removed; Pb was found only in this finest fraction. The pyrolysis experiments were carried out in a bench scale bubbling fluidized bed reactor (1 kg/h). Organic yields were lower (42 − 47 wt%) than with sawdust (62 wt%) but at the same level than those with stored forest residues (46 wt%). The side products char and gases are combusted for process energy in commercial integrated process. The liquid product had a high water content, which resulted in a spontaneous phase separation. The phases were mixed together, and a part of water was gently removed to obtain a single phase product with a water content of 21 wt%. The liquid product was a homogenous fluid, which in most cases met the demands of the EN standard and hence can be used in industrial boilers. All product met the specifications for REACH.