Comparative analysis of wood and solid recovered fuels gasification in a downdraft fixed bed reactor

This study aims to qualify air gasification performances of Solid Recovered Fuels (SRF) in a downdraft fixed bed gasifier. Five fuels have been studied: Wood, SRF wood, and three different mixtures of SRF wood and 20 %w of either SRF tire (mix A), SRF plastics (mix B) or SRF sewage sludge (mix C). The tests were carried out in a pilot scale reactor in a batch-fed mode using a fuel mass ranging from 5 to 8 kg, and an air inlet flow of 170-180 L/min, which led to an Equivalence Ratio (ER) ranging between 0.20 and 0.29. Considering Poplar wood as a reference, we observed a similar syngas quality for SRF wood, but SRF mixes led to a slight decrease of H₂ and CO contents along with an increase of CO₂, CH₄, C₂H₄ and C₂H₆ contents. However syngas Low Heating Value (LHV) remained close and ranged between 4.9 and 5.4 MJ/m³ which led to a Cold Gas Efficiency (CGE) ranging from 38 to 52%. Wood and SRF wood had a similar condensate content (159-202 g/m³), but adding 20 %w of non-woody fuel led to an increased condensate content up to 369 g/m³ for mix A and 411 g/m³ for mix C. Tar analyses confirmed the similarity of Wood, SRF wood and mix C in air gasification, but highlighted large increases in aromatics and Polycyclic Aromatic Hydrocarbon (PAH) contents when adding 20 %w of tire. This study confirms the ability of downdraft gasifier to handle non-woody fuels, with an upper limit of 20%w share in a wood-based fuel.