Advanced plant solutions for dioxin emission reduction in industrial combustion processes

Dioxins are a group of persistent chlorinated organic compounds and most of them are toxic. Major sources of dioxin emission are known to be combustion processes like waste incineration, bio-fuel incineration or, generally speaking, combustion processes where chlorine compounds may be present. De novo synthesis and pyrosynthesis are the two main mechanism for dioxin formation, both being influenced by temperature and resident time. De novo synthesis occurs at relatively low temperatures (200-400°C) for reaction on the surfaces of soot particles such as soot and fly ash containing metals that act as catalysts, while pyrosynthesis occurs at relatively high temperatures (300-600°C) in the gas phase from substances called precursors such as chlorobenzenes or chlorophenols. A number of technologies are today used to destroy or separate dioxins from flue gas. This paper shows an innovative approach for dioxin emission reduction that focuses on plant’s process parameters optimization. Starting from the combustion zone and up to the chimney, flue gas encounters different heat exchange sections at different temperature levels, depending on the specific plant processes. The fundamental parameter to be controlled to avoid dioxin formation becomes the crossing velocity of the heat exchange section (i.e. resident time). In the paper heat exchange modality (by surface or by mixture) are analyzed together with the influence on plant efficiency.