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 both the specifications set by the standard EN 16900–2017 for use of FPBO in industrial boilers and REACH requirements. Commercial used wood Class C was used for fast pyrolysis. The dominant material groups in the feedstock were (virgin) wood (58%) and chemically treated wood (41%). The contents of heavy metals and plastics were low. The pyrolysis experiments were carried out in a bench scale bubbling fluidized bed reactor (1 kg/h). Organic liquid yields were lower (42 − 47%) than with sawdust (64%) but at the same level with those from stored forest residues (46%). The lower organic liquid yield was partly caused by the ash in the feedstock. The liquid product had a high water mass fraction, which resulted in a spontaneous phase separation. The phases were mixed together, and a part of water was evaporated at 40 °C to obtain a single phase product with a water mass fraction of 21%. The liquid product was a homogenous fluid, which in most cases met the demands of the EN standard and the specifications for REACH. Thermodynamic equilibrium calculation suggests that fluidized bed combustion of the pyrolysis char may increase the risk of corrosion and ash melting problems. The recycled wood case is self-sufficient in terms of heat and energy input to the process and will produce excess electricity and district heating for export.