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Analysis of pollutants in the product gas of a pilot scale downdraft gasifier fed with wood, or mixtures of wood and waste materials

Vonk G., Piriou B., Wolbert D., Cammarano C., Vaitilingom G.. 2019. Biomass and Bioenergy, 125 : p. 139-150.

DOI: 10.1016/j.biombioe.2019.04.018

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.

Mots-clés : gazéification; polluant; Émission de polluant; gazéification du bois

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