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

Abstract

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.