Study On Formation Mechanism And Emission Characteristics Of Poly-Chlorinated Dibenzo-p-Dioxins And Polychlorinated Dibenzofrans In Combustion Process

Incineration technology is one of the main municipal solid waste (MSW) disposal measures introduced in the world. Formation mechanism and controlling technology of dioxins in MSW incineration is one of the very active fields in modern environmental research.First, the physical and chemical characteristics, origin and risk of dioxins is presented in the paper. And information of dioxins formation and control in MSW incineration is introduced systematically. The method of the dioxin sampling, disposal and analysis based on HRGC/LRMS in MSW incineration is built.Dynamic properties of MSW organic compounds (PCP, paper, PVC) and release properties of pyrolysis gas are studied using DTG-FTIR equipment. The influence of heat temperature, combustion atmosphere and sulfur on dioxins' precursor formation is discussed. The results indicate that: heat temperature and reaction atmosphere effect dioxins formation obviously; adding sulfur in PCP heat process accelerates PCP de-chlorine reaction, then creates more low-chlorine phenols and dioxins. The formation mechanism of dioxins in coal combustion is consistent with that in MSW incineration, whereas few dioxins are formed in coal combustion. Co-firing coal with MSW can restrain formation of dioxins availably.Computing model of dioxin formation in MSW fluidized bed incinerator based on 0-D fluidized bed incinerator temperature field model has been put forward. The calculating result of dioxins emission of 150t/d coal and MSW fluidized bed incinerator is close to analysis results. Dioxins re-generation model in zone after combustion is established on the foundations of high temperature homologous model, low temperature catalytic models (Langmuir- Hinshelwood model and Eley- Rideal model) and de novo synthesis. Some conclusions have been drawn by the academic analysis. On the conditions of good combustion in boiler, temperature higher than 800癈, resident time more than 2s, the decomposition efficiency of dioxins which is put into incinerator with fuel can reach to 99%. Many factors, such as flue gas temperature, temperature cooling rate, precursor concentration, oxygen, fly ash concentration and carbon content in fly ash, have impact on dioxins re-generation in flue gas. In the temperature range of 300癈~400癈, dioxins produce easily. Controlling flue gas temperature cooling rate may be an effective measure to reducing dioxin. Higher dioxins' reduce efficiency of air pollution controlling device (APCD) is acquired if it operates in lower temperature.The financial support from the National Nature Science Fund of China (N59836210, N 1986 259878047) and the National Basic Fund (Gl999022211) are gratefully acknowledged.