title: Decreased PCDD/F formation when co-firing a waste fuel and biomass in a CFB boiler by addition of sulphates or municipal sewage sludge.
abstract: Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are formed during waste incineration and in waste-to-energy boilers. Incomplete combustion, too short residence times at low combustion temperatures (<700 °C), incineration of electronic waste and plastic waste containing chlorine are all factors influencing the formation of PCDD/Fs in boilers. The impact of chlorine and catalysing metals (such as copper and iron) in the fuel on PCDD/F formation was studied in a 12 MW(th) circulating fluidised bed (CFB) boiler. The PCDD/F concentrations in the raw gas after the convection pass of the boiler and in the fly ashes were compared. The fuel types were a so-called clean biomass with low content of chlorine, biomass with enhanced content of chlorine from supply of PVC, and solid recovered fuel (SRF) which is a waste fuel containing higher concentrations of both chlorine, and catalysing metals. The PCDD/F formation increased for the biomass with enhanced chlorine content and it was significantly reduced in the raw gas as well as in the fly ashes by injection of ammonium sulphate. A link, the alkali chloride track, is demonstrated between the level of alkali chlorides in the gas phase, the chlorine content in the deposits in the convection pass and finally the PCDD/F formation. The formation of PCDD/Fs was also significantly reduced during co-combustion of SRF with municipal sewage sludge (MSS) compared to when SRF was fired without MSS as additional fuel.
authors.affiliation: Chalmers University of Technology, Department of Energy and Environment, Gothenburg, Sweden.
authors.forename: Lars-Erik
authors.initials: LE
authors.lastname: Åmand
authors.forename: Håkan
authors.initials: H
authors.lastname: Kassman
mesh_terms: D001572:Benzofurans / Q000737:chemistry*; D018533:Biomass; D002384:Catalysis; D002713:Chlorine / Q000737:chemistry; D060729:Coal Ash / Q000032:analysis / Q000737:chemistry; D003300:Copper / Q000737:chemistry; D000072338:Dibenzofurans, Polychlorinated; D004867:Equipment Design; D017745:Incineration / Q000295:instrumentation / Q000379:methods*; D007501:Iron / Q000737:chemistry; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives* / Q000737:chemistry; D012722:Sewage; D013431:Sulfates
chemical_list: D001572:Benzofurans; D060729:Coal Ash; D000072338:Dibenzofurans, Polychlorinated; D000072317:Polychlorinated Dibenzodioxins; D012722:Sewage; D013431:Sulfates; D002713:Chlorine; D003300:Copper; D007501:Iron
keywords: Alkali chlorides; Ammonium sulphate; Co-combustion; Dioxins; Municipal sewage sludge; PCDD/Fs