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.

TGA–FTIR analysis of co-combustion characteristics of paper sludge and oil-palm solid wastes

“…The Cl concentration inside the biomass solid waste is known higher that sludge. High amounts of chlorine in the fuel can lead to high emissions of gaseous HCl [22]. Fig.…”

Influence of organic and inorganic flocculants on the formation of PCDD/Fs during sewage sludge incineration

“…Previous studies have concluded that aluminum compound, such as AlCl 3 and Al 2 O 3 , was an important metal catalyst for PCDD/Fs formation (Chang and Chung 1998;Lu et al 2007). Moreover, high amount of chlorine content in the sludge would provide more chlorine source for PCDD/Fs formation (Addink et al 1998;Gullett et al 2000;Mininni 2004;Åmand and Kassman 2013). However, whether aluminum ion or chlorine is the main factor to influence the formation of PCDD/Fs needs a further study.…”

“…Some flocculants contain chlorine source, especially catalytic metals, which may affect the formation of PCDD/Fs during incineration (Gullett et al 2000;Kuzuhara et al 2003;Mininni 2004;Lu et al 2007;Åmand and Kassman 2013). However, there has been to our knowledge no study on the influence of flocculants on the formation of PCDD/Fs in sewage sludge incineration.…”

Evaluation of a flue gas cleaning system of a circulating fluidized bed incineration power plant by the analysis of pollutant emissions

“…Research on characteristics of distribution of their congeners would provide the scientific basis for both reducing the second pollution and improving the treatment technology for the air pollution control process. The formation of PCDD/Fs was related to catalyzing metals and chlorine [59], and the further reduction of acid gases and heavy metals should contribute to controlling the emission of organic pollutants in the flue gas.…”