Gaseous emissions from co‐combustion of biosolids from the meat processing industry with wood

Abstract

AbstractFlotation sludge from the meat processing industry can be applied as biofuel in already existing plant‐scale boilers. This biosolid is rich in oil and grease and has higher energetic content on a dry ash‐free basis (22.74 and 27.71 MJ kg−1) than the wood‐based fuel (16.62 and 16.16 MJ kg−1). Co‐combustion trials were performed at a pilot‐scale cyclonic combustor (100 kg h−1) and at an industrial flamotubular rotatory grate‐fired system (6000 kg h−1), co‐firing pre‐dried and centrifuged flotation sludges (respectively) and wood at a mass ratio of 1:3. At a moisture content of 60.13 wt%, the lower heating value of the centrifuged sludge was 10.24% lower compared to wood, thus reducing it to at least 40 wt% would be advisable to obtain energy gains in the industrial plant when operating the co‐combustion. The emissions were evaluated and compared to emission standards, including the characterization of polycyclic aromatic hydrocarbons and polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans (given as Toxicity Equivalent Factors at O2ref = 7%), which have not yet been reported. The 16 target polycyclic aromatic hydrocarbons were identified at pilot and plant scales (0.582 ± 0.143 μg Nm−3 and 0.602 ± 0.506 μg Nm−3, respectively) being lower than the Danish reference standard (5.0 μg Nm−3). The polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans concentrations were 0.0004 ± 0.0001 ng Nm−3 at pilot scale and 0.3617 ± 0.1310 ng Nm−3 at plant scale, both below the Brazilian and American standards but differed greatly between the scales, requiring further investigation since their formation can occur due to combustion and postcombustion conditions.