Suppressing the formation of chlorinated aromatics by inhibitor sodium thiocyanate in solid waste incineration process

• Published in: The Science of the total environment Vol. 798; p. 149154
• Main Authors: Ren, Meihui, Zhang, Haijun, Fan, Yun, Zhou, Hongquan, Cao, Rong, Gao, Yuan, Chen, Jiping
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-12-2021
• Subjects: Chlorinated aromatics; Dioxins; Emission reduction; Solid waste incineration; Suppression; Dioxins; Emission reduction; Chlorinated aromatics; Solid waste incineration; Suppression
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2021.149154

Suppressing the formation of chlorinated aromatics (Cl-aromatics) by chemical inhibitors is an important measure to reduce dioxin emission from the solid waste incineration plants. In this study, we first investigated the reduction effect of a novel inhibitor sodium thiocyanate (NaSCN) on the emission of dioxins in 2 full-scale solid waste incineration systems. Injection of NaSCN solution into the higher temperature flue gas resulted in about 60% reduction in the concentration of total tetra- to octa-chlorinated dibenzo-p-dioxins and dibenzofurans in stack flue gas. The suppression effect was further verified by a laboratory study on the chlorination of naphthalene over model fly ashes with or without NaSCN addition. By characterizing the reaction products between NaSCN and key catalysts Cu and Fe chlorides, two main suppression mechanisms were proposed: (i) reduction of highly active cupric chloride (CuCl2) and ferric chloride (FeCl3) to less active cuprous chloride (CuCl) and ferrous chloride (FeCl2), (ii) sulfidation of Cu chlorides. The laboratory study indicated that the unreacted NaSCN in the combustion flue gas could be mainly decomposed into Na2S, C3N4, Na2S2O3, NaS2, Na2SO4, CO2, SO2, NO2 and COS. These decomposition products are low toxic or can be effectively removed by the air pollution control devices.
NaSCN suppressed the formation of chlorinated aromatics in combustion flue gas mainly through inducing the reduction of highly active Cu (II) and Fe (III) chlorides.
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•NaSCN had a higher ability to reduce the emission of dioxins than thiourea.•NaSCN strongly suppress aromatic chlorination mediated by CuCl2 and FeCl3.•Reduction of Cu (II) and Fe (III) chlorides was a primary suppression mechanism.•The application feasibility of NaSCN was evaluated.