Air-blown gasification of Solid Recovered Fuels (SRFs) in lab-scale bubbling fluidized-bed: Influence of the operating conditions and of the SRF composition

This article investigates the gasification of Solid Recovered Fuels (SRFs). To better understand the influence of SRF composition on gasification efficiency and syngas quality, two industrial SRFs having different compositions were studied. A detailed SRF characterization was performed (elemental analysis; ash composition; LHV; fraction of biomass, non-biomass, and inert materials) to precisely describe the chemical complexity of such materials. The gasification tests were performed at pilot-scale in a bubbling fluidized bed using air as gasifying agent, and olivine as bed material. The separate contribution of gasification temperature (T = 750-900 degrees C) and equivalence ratio (ER = 0.21-0.35) on the gasification efficiency was investigated by sequentially varying these two parameters. Gasification tests revealed that the LHV of the syngas and the cold gas efficiency decreased by 45-50% and by 20-30%, respectively, with rising equivalence ratio. These evolutions were attributed to syngas oxidation reactions which promoted the formation of CO2. Indeed, mass balances calculation revealed that the part of carbon atoms in syngas in the form of CO2 rises from 43 to 54% for SRF1, and from 35 to 50% for SRF2. High plastic content in SRF2 was responsible for the formation of stable light hydrocarbons (CH4, C2H4 and C6H6) from the decomposition of the plastic polymer chains, and to lower amount of H-2 compared to syngas from biomass-rich SAF1. The carbon conversion decreased by 8% with rising ER from 0.21 to 0.30 for SRF2, as a result of plastics biomass interactions promoting secondary reactions and leading to char formation. For both SRFs, rising temperature significantly improved the gasification efficiency whatever the SRF composition, and decreased the CO2 concentration. These evolutions were attributed to the promotion of several reactions, such as gasification, steam and dry reforming, Boudouard reaction, and Reverse Water-Gas Shift reaction.