Emissions of polycyclic aromatic hydrocarbons during biomass combustion in a drop tube furnace

The objective of this work is to investigate experimentally the formation of polycyclic aromatic hydrocarbons (PAH) during the combustion of biomass in a drop tube furnace (DTF). A number of biomass fuels, including furniture residues, grape pomace, kiwi residues, olive residues, wheat straw, rice husk and platanus residues were used in this work, with the tests performed at three temperatures (900, 1000 and 1100 °C). The solid fuels feed rate was 23 g/h and the total air flow rate was 4 L/min, ensuring a residence time in the DTF of around 2 s. In order to collect the PAH in the effluent gas, a narrow tube containing XAD-2 resin was connected to the flue gas duct of the DTF. A quartz fiber filter was placed just before it to collect the particulate matter, including soot, present in the flue gas. The analysis and quantification of the PAH combined Soxhlet extraction and gas chromatograph-mass spectrometer. Flue gas concentrations of O2, CO2, CO, hydrocarbons and NOx were measured to gather information regarding the combustion conditions. The results showed two distinct features for the variation of the total PAH emissions: one decreasing with temperature and other with a maximum at 1000 °C. Grape pomace, kiwi residues and platanus residues presented the lowest PAHs emission (20.8-54.2 mg PAH/kg fuel). A direct relation between the total amount of PAHs and the toxic equivalency value was found.