• Energy Research

Air gasification of Solid Recovered Fuels (SRF) from wood, tire, plastics and sewage sludge has been performed in a pilot fixed bed reactor. As wastes contain pollutants precursors, it is of great interest regarding technical and environmental aspects to study their behavior in air gasification. Five fuels have been studied: Poplar, SRF wood, and three different mixtures of SRF wood and 20% of either tire (mix A), or plastics (mix B) or sewage sludge (mix C). After confirming their capacity of substituting raw wood in order to produce synthetic gas (syngas), emissions analyses have been performed on syngas, condensable matter and remaining char. A focus on sulfur, nitrogen and heavy metals brought to light differences and similarities between different SRF and raw wood. Proceedings of the 26th European Biomass Conference and Exhibition, 14-17 May 2018, Copenhagen, Denmark, pp. 478-485

Small scale gasification of Solid Recovered Fuels (SRF) in downdraft reactors could be an alternative to large scale waste-to-energy schemes. In this perspective, the assessment of the pollutant emissions at pilot scale is necessary. This work compares pollutant emissions from wood and SRF air gasification in a downdraft fixed bed gasifier. Five fuels have been studied: Poplar wood, SRF wood, and three different mixtures containing mass fractions of 80% SRF wood with 20% of either tire, plastic waste or sewage sludge. Air gasification was performed in a pilot scale reactor in fed-batch mode using a fuel mass ranging from 5 to 8 kg and an air inlet flow of 170–180 L min−1 (at 0 °C and 101 325 Pa). Depending on the fuel, Equivalence Ratios (ER) ranged from 0.22 to 0.29 and gasification temperatures from 690 to 850 °C. Emissions analyses were performed on product gas, condensable species and remaining chars, with a particular focus on sulfur, nitrogen and heavy metals. Regarding sulfur, wood and SRF wood led to low H2S contents (6–8 μmol mol−1), when SRF mixes led to higher concentrations (44–96 μmol mol−1) in addition to of up to 11 heavier sulfur compounds. Regarding nitrogen, SRF produced higher ammonia concentrations (2.1–7.6 mmol mol−1) than Wood (619 μmol mol−1), as a result of initial nitrogen mass fractions17 to 27 times higher in the SRF mixes. Heavy metals analyzed in remaining solids after gasification showed low recovery rates (< 0.4%), and tend to accumulate in fine particles, as a result of their volatility.