Reduction of PCDD/F Formation in MSWI by a Process-Integrated SO₂ Cycle

Abstract

PCDD/F formation in MSWI predominantly takes place by de novo synthesis in the ash deposits in the boiler. Permanently high SO 2 concentrations cause sulfation of the boiler ash and the fly ash, which leads to low chloride concentrations in the ash deposits. This results in very low PCDD/F formation rates. High SO 2 levels can be established in an efficient way by a process-integrated SO 2 cycle, with only the SO 2 generated by the combustion process being used. The S-recycling process can be supported by reducing the transfer rates of CaO particles to the flue gas by a low primary air supply. No additional source of sulfur is needed. No negative effects of the S-recycling process on the separation of other pollutants like Hg could be observed. These findings indicate that the PCDD/F emission standards can already be met upstream of the flue gas cleaning system by these primary measures only. The flue gas cleaning efforts can be reduced without changing the emission standards.

A review of dioxin-related substances during municipal solid waste incineration

“…Another research found that under the atmosphere of high SO 2 concentration, chlorine decreased in fly ash from 20 to 0.3 wt.%. Meanwhile, CuCl 2 concentration in fly ash decreased, and PCDD/ Fs were reduced by 40% (Hunsinger et al, 2007). Recently, Wu et al (2012) also proved that at temperatures lower than 600°C, SO 2 firstly reacts with CuCl 2 to form CuSO 4 through a thermodynamic equilibrium calculation.…”

“…A significant number of studies have shown that sulfur is an inhibitor for the heterogeneous formation of PCDD/Fs Raghunathan and Gullett, 1996;Hunsinger et al, 2007;Hajizadeh et al, 2012). When (NH 4 ) 2 SO 4 was added to waste wood combustion at an S:Cl ratio of 6, significant reductions in the PCDD/Fs contents of the flue gas were observed (Lundin and Jansson, 2014;Lundin et al, 2013).…”

Air pollution control systems in WtE units: An overview

“…A new primary measure, which makes use of the Griffin hypothesis that a low Cl/S ratio reduces the dioxin formation (Griffin, 1986), has been developed in the late 2000s and is actually installed in few Scandinavian WtE plants (Hunsinger et al, 2007). In a plant equipped with wet scrubbing SO 2 is stripped from the effluents of the neutral scrubber and fed into the secondary air of the furnace, thus increasing the SO 2 concentration in the flue gas and lowering the Cl/S ratio permanently to a level, which reduces the dioxin concentration in the raw gas to values in the order of or even below 0.1 ng(TE)/m 3 (Andersson et al, 2010).…”

PCDD/Fs Inhibition by Sludge Decomposition Gases: Effects of Sludge Dosage, Treatment Temperature and Oxygen Content

“…The suppressants are added to the raw MSW or injected into incinerator flue gases. In addition, Hunsinger et al (2007) designed a system on recirculation of SO 2 for suppression of PCDD/F and that this avoids the continuous addition of sulphur or nitrogen compounds. However, the cost of supplying such substances is tangible, so finding cheap and effective suppressants has been a topical subject for R&D initiatives.…”